Abstract:In order to reveal the sorting characteristics and transportation mechanism of erosion sediment driven by runoff on the steep slope of engineering deposit, the field simulated runoff scouring test under three upper inflows of 10, 20, and 30 L/min were designed, and the particle distribution characteristics of erosion sediment on the steep slope (32°) of the engineering deposit body in Yangling were analyzed. The results showed that the clay and fine silt in the eroded sediment (before dispersion) increased significantly compared with the original soil, which was easy to produce erosion. The fuction of runoff on the fragmentation of aggregates affected the clay content of eroded sediment. The clay content was negatively correlated with the runoff power when the runoff power was less than 1.71 N/ (m·s), but it was positively correlated when runoff power was greater than 3.89 N/(m·s). In sediment, fine and coarse silt particles were mainly transported in the form of single grain, while clay and sand particles were mostly transported in the form of aggregates. In eroded sediment, clay particles were enriched and sand particles were depleted. The particle size of sediment determined its main transportation mode, sediment particles less than 0.11 mm were mainly suspension/saltation transport, and sediment particles more than 0.11 mm were mainly rolling transport. The contribution rate of rolling transport increased first and then decreased with the increasing of runoff transport capacity. The conclusion of this study was conductive to reveal the mechanism of slope water erosion process of engineering deposit body, and could provide scientific basis for improving the prediction accuracy of slope water erosion model on the steep slope of engineering accumulation.

Abstract:In order to study the variation of runoff and sediment yield and gully erosion characteristics on alien soil slopes with different slope lengths in the abandoned mining area of Wula mountain, scouring tests were conducted by designing field runoff plots with different slope lengths (2, 4, 6, 8 and 10 m) under two slope gradients (15° and 20°). The results showed that: (1) The variation range of initial runoff generation time and runoff generation stop time both increased with the increasing of slope length. The runoff rate increased rapidly at the beginning and fluctuated irregularly after reaching the initial peak value. The cumulative runoff increased with the increasing of slope length. The runoff rate and cumulative runoff were highly significant (p＜0.01) correlated with slope length and runoff generation time and their interaction, and cumulative runoff showed a power function correlation with slope length and runoff generation time under the two slope gradients. (2) The sediment rate increased rapidly at the beginning and reached the initial peak value, then decreased gradually with the increasing of scouring time, and its mean value increased with the increasing of slope length, and the total cumulative sediment yield increased with the increasing of slope length. The cumulative sediment yield was significantly correlated with slope length, runoff generation time and their interaction (p＜0.01), and the cumulative sediment yield was related to the slope length and runoff generation time as a power function under the two slope gradients. (3) The average cross-sectional area of erosion ditch from the top showed two trends of decreasing along the slope and decreasing-increasing-decreasing again. The cumulative sediment yield and the estimated gully erosion volume had a highly significant correlation(p<0.01), and their difference increased with the slope length, and their ratio tended to increase firstly and then decrease with the increasing of slope length, and the maximum value appeared at 6 m slope length. The research results could provide technical support for erosion control and erosion model establishment of alien soil slopes in mine rehabilitation.

Abstract:In order to understand the characteristics of soil and water loss and benefit of soil and water conservation on the cross ridge slope in arid valley area, field investigation and indoor artificial rainfall simulation were carried out, and the characteristics of runoff and sediment yield and benefit of runoff and sediment reduction on cross ridge slope were analyzed under four rainfall intensities (30, 60, 90 and 120 mm/h) and four slopes (10°, 15°, 20° and 25°). And the flat sloping farmland was taken as the control. The results showed that: (1) The runoff production time on the cross ridge slope was advanced with the increasing of rainfall intensity and slope gradient, and it was much less affected by slope than by rainfall intensity. Under the same conditions, the runoff production time on cross ridge slope lagged behind that of flat sloping farmland by 8.14%~55.60%. (2) With the increasing of rainfall intensity and slope gradient, both runoff yield and sediment yield on the cross ridge slope showed an increasing trend. (3) With the increasing of rainfall intensity, the relationship between slope gradient and benefit of runoff and sediment reduction on cross ridge slope changed from positive phase to negative phase, while the relationship between rainfall intensity and benefit of runoff and sediment reduction on cross ridge slope was complex without obvious change law. Rainfall intensity and slope gradient had important effect on the process of runoff and sediment yield and the benefit of runoff and sediment reduction on the cross ridge slope, and cross ridge slope could prolong the time of slope runoff formation, effectively reduce the slope sediment production rate, however there were critical conditions for the effect of runoff and sediment reduction on the cross ridge slope. The results could provide data support and theoretical basis for the regional reasonable layout of farmland cross ridge measures and the effective prevention and control of soil erosion.

Abstract:The black soil in northeastern China is suffering severe soil erosion, which is greatly impacted by slope shapes. In this paper, based on the measured runoff and sediment data derived from 15 erosive rainfalls in 2014—2015 on 9 runoff plots in the Liangshigou catchment, Keshan County, the WEPP (Water Erosion Prediction Project) was used to explore the impacts of different slope shapes on soil erosion characteristics, and meaningful results were obtained. The determination coefficient (R²) and Nash-Sutcliffe efficiency (NSE) of the overall runoff depth and sediment yield simulation results were both greater than 0.5, and the model was suitable for soil erosion simulation for the black soil region under natural rainfall conditions. For both runoff depth and sediment yield, the simulation accuracies of the WEPP model decreased with increasing slope degrees. For the simulated sediment yields from different slopes, the R² and NSE decreased from 0.60 and 0.65 on 3° slope, 0.55 and 0.61 on 5° slope, and 0.48 and 0.60 on 8° slope, respectively. The soil erosion intensities were closely related to the slope shapes. The simulated runoff depths had no obvious difference on different shaped slopes, but the simulated soil erosion intensity was the highest on the straight slope, followed by the convex slope, and the smallest sediment yield on the S-shaped slope. This study can help soil erosion control for the black soil region, northeastern China.

Abstract:To further explore the mechanism of slope protection by herbaceous plants in the loess region of northeastern Qinghai-Tibet Plateau, the Changlinggou catchment in Xining Basin was selected as the testing area. By designing two different slope shapes and selecting three herbaceous plants suitable for the local climatic conditions, and using the method of artificial rainfall simulation based on the field experimental area, the distribution and transformation of slope soil hydrological parameters (soil infiltration, soil moisture content) were analyzed first, then characteristics of soil water infiltration and its main influence factors on the slope of planting herbs were discussed. Finally, the process of soil water infiltration on the slope was simulated and evaluated. The results showed that the runoff generation time of the terraced slope planted with Elymus nutans in the area was the latest, and the maximum runoff occurred in straight bare slope, and the maximum stage cumulative runoff was 17 730 mL when the artificial rainfall time was 40~45 min. The average stable infiltration rate of the six different types of slope in the region from large to small was terraced slope planted with E. nutans (0.519 mm/min), straight slope planted with E. nutans (0.423 mm/min), straight slope planted with Elymus sibiricus (0.422 mm/min), straight slope planted with Agropyron trachycaulum (0.318) mm /min), terraced bare slope (0.321 mm/min), straight bare slope (0.192 mm/min). The increase of soil moisture content at 0—50 cm below the surface of the slope planted with E. nutans and E. sibiricus were relatively the highest, indicating that planting herbs was conducive to the internal water infiltration of slope soil. On this basis, Horton model, Kostiakov model and general empirical model were used to simulate moisture infiltration on slope. The results showed that Horton model and general empirical model were more suitable for fitting soil moisture infiltration on straight slope. While Horton model was more suitable for fitting soil moisture infiltration process on terraced slope. Pearson correlation analysis showed that soil organic matter and vegetation coverage were the main factors influencing slope infiltration characteristics in the testing area. And initial infiltration rate was significantly and positively correlated with soil organic matter content (R² was 0.986). And an extremely significant correlation between vegetation coverage and stable infiltration rate was identified (R² was 0.997). The results of this study had theoretical research value and practical guiding significance for the scientific and effective prevention and control of soil and water loss in alpine and semi-arid areas, and for the study of vegetation types and slope shape soil and water conservation capacity.

Abstract:Rainfall is one of the main driving forces of soil erosion. In order to explore the spatial-temporal variations of rainfall erosivity with different magnitudes, the 24 h rainfall data of 42 meteorological stations in Chongqing and its surrounding stations from 1960 to 2017 were selected so as to calculate the R value by the daily rainfall erosivity model. And the spatial-temporal variation of different magnitudes rainfall erosivity in different time scales were analyzed by utilizing the climate tendency rate, variation coefficient and ordinary Kriging. The results showed that: (1) The average annual R value of Chongqing was 5 751.55 (MJ·mm)/(hm²·h·a) in 58 a, and the variation coefficient of the average annual R value was 0.19, which between 0.1 and 1, belonging to a medium variation. (2) The order of contribution rate of rainfall erosivity of different magnitudes to annual R value was heavy rain (34.82%)＞rainstorm (30.53%)＞moderate rain (23.93%)＞downpour (10.53%), and the increasing trend of downpour erosivity was dominant in annual rainfall erosivity. (3) The distribution of annual R value was extremely uneven, with 54.19% concentrated in summer and only 0.91% in winter. (4) The annual and each magnitude rainfall erosivity showed a decreasing trend from east to west. This study clarifies the periods and areas with high possibility of soil erosion, protective measures are supposed to take to control soil erosion according to local conditions.

Abstract:The C factor is an important artificially controllable factor of soil erosion prediction model. It plays a vital role in reducing soil erosion and controlling water and soil loss. In this paper, the maize, a typical crop on sloping farmland of the Loess Plateau, was studied using an artificial rainfall simulation experiment. Besides, five change features of maize on near-surface conditions in different growth periods were analyzed and the C value was calculated according to the sediment yield of maize in different growth periods. The results showed that vegetation coverage, plant height and crusted thickness increased gradually with the prolongation of maize growth period and that the surface roughness decreased first and then increased with the prolongation of maize growth period. Besides, the sediment yield decreased gradually with the continuous growth of maize and sediment reduction benefit increased with the extension of maize growth period. Based on the previous C-value model calculated by vegetation coverage, the vegetation coverage was taken as the key factor and the plant height, soil crust and surface roughness as the adjusting factors to build a local C-value model. On the basis of that, a better C-value model for maize slope farmland (model R²=0.94, RMSE=0.017, MAE=0.014, NSE=0.992) was obtained. Based on the research results, a C-value calculation formula was established according to change characteristics of near-surface conditions. This helped improve the accuracy of C-value estimation and its applicability to the Loess Plateau, which could provide a scientific basis for improving the accuracy of soil erosion prediction model on the Loess Plateau.

Abstract:Based on the LPJ-GUESS model, the temporal and spatial evolution and trend of soil conservation function of vegetation change on the Loess Plateau during 2001—2100 were simulated and analyzed, in order to provide a basis for the development of vegetation management and erosion control strategies adapted to climate change on the loess Plateau. The results showed that: (1) From 2001 to 2100, the soil conservation function of the Loess Plateau showed the distribution characteristics of "high in the southeast and low in the northwest". (2) From 2001 to 2020, the soil conservation function of the western high-altitude area, and that of the eastern Wutai Mountain Area and the northwest area of the Loess Plateau increased significantly. Under the SSP119 scenario, soil conservation function of the Qilian Mountains of the western area increased significantly, while that of a small part of the central region decreased significantly. Under the SSP585 scenario, the soil conservation function of most areas in the north part increased significantly. (3) From 2001 to 2020, the soil conservation function of the central part of the Loess Plateau had a significant mutation. It had a significant mutation in central south and western China under the SSP119 scenario. Under the SSP585 scenario, the soil conservation function of most areas except the south area had significant mutations. The soil conservation function declined in western high-altitude areas caused by vegetation, therefore, the vegetation management in these areas should be strengthened, such as scientific planting of appropriate vegetation. The dynamic vegetation model could describe the dynamic change of vegetation structure under climate change and made the simulation of soil conservation function more accurate. The dynamic vegetation model such as LPJ-GUESS model could be used to carry out corresponding research in other parts of the world.

Abstract:To define the rill erosion characteristics and the law of runoff and sediment yield of loess soil in the process of rill development under runoff scouring, rill simulation test was conducted in variable slope soil troughs, and three flows (2, 4 and 8 L/min) and four slope gradients (5°, 10°, 15° and 20°) were set up. The maximum runoff sediment concentrations during rill development on the loess soil slope under different slopes and flows were measured, then its corresponding sediment transport capacity (A) was obtained. The results showed that, when the slope was constant, the sediment transport capacity increased linearly with the increasing of the flow rate, and the steeper the slope was, the more obvious the increase was. When the flow rate was low, the sediment transport capacity increased slowly with the increasing of the slope gradient. When the flow rate reached 8 L/min, the sediment transport capacity increased faster with the increasing of slope gradient, but it hardly changed after the slope increased to 15°, indicating that flow rate had more significant effect on sediment transport capacity. The trend of sediment concentration (c) with length of rill (x) conformed to mathematical formula c=A(1-e-Bx). We run a simulation by scouring the slope surface of 1 m and 2 m under all combinations of different slopes and flow rates we had set up, and the sediment concentration of runoff measured by scouring and the sediment transport capacity (A) under each combination were substituted into the formula, and attenuation coefficient (B) of sediment concentration varying with the rill length under different test conditions was calculated by method of undetermined coefficient. The results could provide theoretical and scientific basis for soil and water conservation research and practice in loess soil.

Abstract:The Cele Oasis-Desert Ecotone in Xinjiang is a typical extreme arid zone, where wind is the most important driving force of land desertification caused by the transport and accumulation of soil sand grains by wind erosion and sandstorms. Regression analysis and correlation analysis methods were used to investigate the sedimentation law and influencing factors of sand dune development of aeolian sand dunes in different shrublands, and the morphological characteristics and sediment particle size of sand dunes under different vegetations were also analyzed. The results showed that: (1) Under different vegetation cover, Tamarix chinensis was more uniformly distributed than the sand particle size of the sand pile of Alhagi sparsifolia shrubs, and the coarsest particle size of the sand material sorted by Tamarix chinensis and Alhagi sparsifolia appeared under the high and medium coverage respectively, and both the finest appeared under the low coverage. (2) In the evolution process of dunes and obstacles, all the height, length and width changed in synergy, influencing each other and giving feedback to each other. There was a significant relationship between the height and width of the obstacle and the length, width and height of the dune, and the size of the plant affected the development of the dune morphology. (3) The sand material of wind shadow and shrub dunes was mainly composed of extremely coarse silt sand, extreme fine sand and fine sand, and the sand material of the whirlpool sand dunes was mainly composed of extremely fine sand and fine sand, and the remaining granular sand particle content was very small, less than 5%. From the analysis of vegetation types, the thickness of sand material was Tamarix chinensis＞Alhagi sparsifolia＞Karelinia caspia, and from the analysis of sand dune types, the thickness of sand matter was echo dunes＞shrub dunes＞wind shadow dunes. (4) The average sorting coefficient of sand dune sand material was between 1.42 and 1.60, which belonged to the upper middle to medium sorting, the average deviation of sand as iws between 0.01 to 0.20, which belongd to symmetry, and the peak state average of sand matter was between 0.96 to 1.07, which belongd to the constant peak state. (5) The sorting coefficients and skewness values of sand dunes were significantly correlated (R²＞0.70, p＜0.01), and the average particle size of sand substances was significantly correlated with the sorting coefficient and skewness value (p＜0.01). The results are of great significance for the in-depth understanding of the particle size characteristics of sediment surface sediments and the development of dune morphology in shrubland dunes under different vegetations.

Abstract:Through indoor simulated rainfall experiment, three kinds of rainy intensity (30, 60 and 90 mm/h) and three types of slope cover (bare slope, 1 cm Masson's pine litter cover, and 1 cm Masson's pine ash cover) were set up to study the process of runoff and sediment yield of slope under different ground cover before and after forest fire, and to clarify the benefits of runoff and sediment reduction under pre-fire litter cover and post-fire ash cover. The results showed that: (1) Compared with the bare slope, the initial runoff yield time was extended by 33%~80% and 51%~200% on litter-covered slope and ash-covered slope, respectively, and the ash cover had a more obvious ability in delaying runoff generation. (2) Compared with the bare slope, the runoff reduction benefit of litter cover was stable at 12%~36% under three rain intensities, while the runoff reduction benefit of ash cover was larger than 70% under 30 mm/h and 60 mm/h rain intensities, and reduced to 7% when the rain intensity was 90 mm/h. (3) The runoff yield on the bare slope showed a trend of rapid increase at first and then stable, while on the slope covered by litter and ash exhibited "stepwise" upward trend. (4) Litter cover could reduce runoff sediment carrying capacity and total sediment yield, and the sediment reduction benefits were all over 85% under the three rain intensities, and higher than that of the ash-covered slope under the same rainfall intensity. The runoff and sediment reduction benefits of the litter cover were relatively stable under different rainfall intensities, and the runoff and sediment reduction benefit of the ash cover was significantly affected by rainfall intensity. Moreover, the sediment reduction benefits of the litter cover was superior to the ash cover under three rain intensities, indicating that the change of land cover after forest fire was one of the critical factors causing the increase of soil erosion.

Abstract:In order to reveal the effect of returning farmland on the soil infiltration characteristics of the outcrop rock-soil interface in the rocky desertification area, the arable land was taken as the control, and the fallow field, farmland return to shrubs grassland and orchard were selected as the research objects, and the soil infiltration characteristics of rock-soil interface with different shapes of straight, convex and concave were studied through the ring knife method. The results showed that: (1) The soil infiltration process and characteristics at the rock-soil interface of different types of returning farmland varied greatly. From the initial infiltration rate to the stable infiltration rate, the attenuation range was between 0.350 mm/min and 55.756 mm/min, and the soil infiltration rate varied greatly among different rock-soil interface shapes. (2) The main influencing factors of soil infiltration rate at rock-soil interface of different types of returning farmland were capillary porosity and non-capillary porosity. The initial infiltration rate, average infiltration rate and stable infiltration rate all had extremely significant negative correlation with capillary porosity (p＜0.01). The initial infiltration rate was significantly positively correlated with non-capillary porosity (p＜0.05). (3) Compared with Kostiakov model and Philip model, Horton model had the best applicability for fitting the soil infiltration process at the rock-soil interface of different types of returning farmland, and it could better simulate the soil infiltration process and predict the soil infiltration capacity. (4) According to the principal component analysis, soil infiltration capacity at the rock-soil interface followed the order of arable land (0.99)＞fallow field (0.16)＞returning farmland to shrubs and grassland (-0.43)＞returning farmland to orchard (-0.72). The returning farmland significantly reduced the soil infiltration capacity of the outcrop rock-soil interface in the rocky desertification area, especially at the convex rock-soil interface. The research results were expected to provide a scientific basis for future understanding of the water leakage at the rock-soil interface in rocky desertification areas after returning farmland.

Abstract:In order to reveal the effect of biological soil crusts on process of soil and water loss on the slope after the implementation of ecological restoration project in typical red soil region under rainstorm, simulated rainstorm experiments and indoor experiments were conducted. In this research, the soil physical properties, hydrodynamic characteristics, runoff and sediment yield processes of slopes with different biological soil crusts coverages (0, 20%, 40%, 60% and 80%) were explored. The results showed that: (1) Under different coverages of biological soil crusts, the soil cohesion of red soil slope increased by 13.26% on average, while the soil bulk density and penetration resistance decreased by 8.97% and 61.51% on average, respectively, indicating that biological soil crusts effectively enhanced soil stability and soil anti-erodibility in red soil area. (2) Compared with the control slope, biological soil crusts effectively improved the flow pattern of slope, and the values of runoff shear stress ranged from 0.08 to 0.12. The water flow power and section unit energy reduced by 12.22%~78.89% and 8.32%~53.15%, respectively, and the slope resistance coefficient increased by 1.09~1.50 times. (3) The benefits of runoff reduction and sediment reduction on the slope surface of each biological crust coverage were between 12.50% and 78.76%, 17.03% and 94.31%, respectively, in which the soil erosion intensity of the slope with high coverage (80%) was the lowest. The results provided theoretical basis and practical references for effective prevention and control of soil and water loss on slope in red soil area.

Abstract:In order to explore water hold capacity of water storage clay and improve soil water movement characteristics of the Loess Plateau, the water retention test of water storage clay and the indoor infiltration and evaporation test of soil column with water storage clay layer were carried out. Three particle size levels (20~30, 5 and 2 mm) were set for water storage clay. The thickness of water storage clay layer over the soil column was 5 cm, and the treatment without water storage clay was used as control (CK). The results showed that when the room temperature was 15 ℃, three particle sizes of water storage clay could reach saturation within 40s, and the water absorption rate was between 30%~90%. Meanwhile, the water release rate was relatively slow, so it indicated that the water retention of water storage clay was better. In terms of the infiltration of the soil column, the migration distance of wetting front was significantly promoted by water storage clay with different particle sizes, and the cumulative infiltration amount increased by 40%~60% compared with CK, and it increased with the increasing of the particle size. In terms of soil column evaporation, after continuous evaporation of seven days, soil evaporation was inhibited in varying degrees by water storage clay with different particle sizes. Moreover, the inhibition effect was the most obvious when the particle size was 5 mm, its accumulated evaporation was 67.23% lower than that of CK. The overlying water storage clay layer could reduce the loss of soil water. The soil moisture content in the 10—25 cm soil layer of the soil column covered by water storage clay with different particle sizes increased by 4~5 times compared with CK. With comprehensive consideration of soil infiltration and evaporation, the effect was the best when the particle size of water storage clay was 5 mm. This study could provide theoretical basis for constructing methods to improve the infiltration and storage capacity of slope on the Loess Plateau.

Abstract:In order to explore the seepage characteristics in loess, and clarify the influence extent of different initial conditions on preferential flow, a dye tracing experiment was carried out in the southern Loess Plateau, using brilliant blue and ionic dye and controlling the infiltration water and initial water content. According to the obtained dyeing image, the preferential flow extent was analyzed qualitatively and quantitatively. The results showed that the dyeing depth of brilliant blue in loess was limited, while the ionic dye could well trace the seepage of water after color reaction. The type of preferential flow in loess in southern Loess Plateau from small to large with depth was in order as follows: homogeneous matrix flow, heterogeneous matrix flow and fingering, macropore flow with high interaction, macropore flow with mixed interaction. The order of preferential flow indicator was test pit A (0.55)＞test pit C (0.48) ＞test pit B (0.46), and the extent of preferential flow was from high to low: test pit A, test pit C, test pit B. When other conditions were the same, more infiltration water and higher initial water content in loess would inhibit the development of preferential flow, resulting in greater depth of matrix infiltration, higher extent of matrix flow, and lower extent of preferential flow. The study can provide reference for disaster prevention and control in loess area and for proving the mechanism of groundwater pollution.

Abstract:In order to reveal the characteristics of soil preferential flow in the catchment areas of gully systems in Yuanmou Dry-hot Valley, the catchment areas of gully systems with different development degrees (active and stable phases) were selected as the research objects in Yuanmou Dry-hot Valley of the Jinsha River, using a combination of field staining tracing and statistical analysis, five preferential flow indicators were integrated from the field staining images by image processing techniques, and combined with the root characteristics, the differences of soil preferential flow were analyzed. The results showed that: (1) In the gully catchment areas at stable stage, massive clump-like staining appeared in the depth range of 0—15 cm soil layer, and then it was distributed twig-like, and the distribution of staining areas were relatively more concentrated. In the active phases, the staining showed a monolithic-clumpy-branched distribution, indicating that the staining morphological characteristics in the active phases were more differentiated. (2) The mean matrix flow depth, the average staining area ratio, the average shape coefficient of staining patch and the mean length index of preferential flow (20.53 cm, 54.25%, 24.94 and 592.46%) in the active phases gully catchment areas was 1.79, 1.62, 2.20 and 1.16 times that in the stable phases, respectively. It showed that the occurrence time of preferential flow in the catchment areas of active gully was relatively late, the development degree of preferential flow was greater and the spatial heterogeneity of priority flow was relatively strong. (3) Both root weight density and root length density decreased with the increasing of soil depth, and both of them showed a significant positive correlation with staining area ratio (p＜0.05). The root weight density and root length density of each soil layer in the active gully catchment areas were greater than those in the stable phases. The results of the study provided theoretical basis for revealing the soil preferential flow characteristics of catchment areas of Yuanmou Dry-hot Valley of the Jinsha River, and also provided references and lessons for ecological restoration and soil and water conservation in this area.

Abstract:Studying the temporal and spatial changes of rainfall erosivity (RE) and erosivity density (ED) in Chongqing is conducive to soil erosion control and soil erosion risk assessment. Using the daily rainfall data and TM remote sensing image data of 34 meteorological stations in Chongqing from 1961 to 2020, the daily rainfall erosion force model, Mann-Kendall nonparametric test, coefficient of variation, Kriging interpolation, superposition analysis and other methods were used to analyze RE and ED. The spatial and temporal analysis of soil erosion intensity in Chongqing was carried out. The results showed that: (1) Chongqing’s annual average rainfall erosivity was 5 672.32 (MJ·mm)/(hm²·h·a), the annual average erosive force density was 4.94 MJ/(hm²·h·a), and the variation trend of average rainfall erosivity and erosivity density in each season were basically the same. (2) The annual RE and ED were the largest in northeast Chongqing, the second in southeast Chongqing, and the smallest in western Chongqing. Seasonal rainfall erosivity and erosivity density were concentrated in summer, and the rainfall erosivity was the highest in northeast Chongqing, and the erosivity density was highest in eastern Chongqing. (3) The soil erosion intensity in Chongqing in 2020 was dominated by slight erosion, followed by mild, moderate, intensity, extreme intensity and severe erosion. (4) The spatial distribution of the erosion risk level of rainfall erosivity and erosivity density was similar to the spatial distribution of soil erosion intensity level, and the highest values were both in northeast and southeast Chongqing. The research results could help managers to formulate soil and water conservation measures to effectively prevent and control soil erosion in Chongqing.

Abstract:In order to clarify the blockage and control law of nitrogen and phosphorus in simulated runoff under different conditions, five vegetative buffer strips were constructed with control, Cynodon dactylon, Zoysia matrella, Festuca elata and Ophiopogon japonicus, and the blockage and control effects on nitrogen (N) and phosphorus (P) in surface flow and seepage were explored by simulating runoff with different pollutant concentrations. The results showed that compared with the control, the vegetative buffer strips significantly improved the interception ability of the soil system on runoff and pollutants such as nitrogen and phosphorus in the incoming water, and the average runoff reduction rates of the filter strips of Cynodon dactylon, Zoysia matrella, Festuca elata, Ophiopogon japonicus and the control group were 56.10%, 54.28%, 63.16%, 60.53% and 39.10% respectively under three hydraulic load intensities. The runoff reduction rates of all four plantings were significantly higher than those of the control (p＜0.05). All four plantings significantly reduced the surface infiltration ratio and improved the infiltration capacity of the soil. The increase in hydraulic load intensity reduced the removal efficiency of NH₄⁺—N and total P (TP) in the vegetated filter zone, but the reduction in the removal rate of the vegetated treatment was less than that of the control. Within a certain range, the removal rates of total N (TN), NO₃^-—N and TP in the seepage increased with the increase of N and P concentrations in the incoming water. Under a certain hydraulic load, the vegetative with low root to shoot ratio has a stronger ability to reduce runoff.

Abstract:In order to guide the rational fertilization of paddy fields and prevent non-point source pollution of paddy fields, we studied the effects of different nitrogen fertilizer reduction ratios on the nitrogen and phosphorus loss in the surface water of paddy fields under the milk vetch (Astragalus sinicus L.) -rice rotation system. In 2020, field plot experiment was conducted on Jiande, Zhejiang. Two treatments of winter idle and winter milk vetch were set up, and four nitrogen reduction ratios of 0 (CT0), 10% (CT1), 20% (CT2) and 30% (CT3) on the basis of winter planted milk vetch. There were 5 treatments in total, each treatment was repeated three times. After paddy transplanting and fertilization, surface water samples of paddy field were collected (including continuous sampling within two weeks of fertilization and sampling at intervals of 7, 14, and 28 days after two weeks), and the concentration of nitrogen and phosphorus in the field water was measured. After the rice matured, soil and plant samples were collected and soil physicochemical properties, rice growth properties and yield were determined. The total nitrogen, soluble nitrogen, ammonium nitrogen, total phosphorus and soluble phosphorus in the field surface water of each treatment reached their peaks on the first day after fertilization. The total nitrogen decreased significantly within four days after basal fertilizer application, which was 4.2%~9.1% of the maximum value, and the soluble phosphorus decreased to 4.7%~13.7% of the maximum value within five days of basal fertilizer application. During the sampling period, the average concentration of total nitrogen, soluble nitrogen, total phosphorus and soluble phosphorus in the CK was 48.87, 36.82, 0.82 and 0.64 mg/L, respectively. The average concentration of total nitrogen in CT0, CT1, CT2 and CT3 was 93.9%, 78.1%, 79.7% and 69.7% of CK, respectively. The average concentration of soluble nitrogen was 95.1%, 84.1%, 85.7% and 73.2% of CK, respectively. The average concentration of total phosphorus was 90.9%, 76.9%, 96.2 and 81.3% of CK, respectively. The average concentration of soluble phosphorus was 79.4%, 73.8%, 87.3% and 68.7% of CK, respectively. Compared with CK, CT2 and CT3 significantly increased soil available phosphorus content by 61.7% and 37.0%, respectively. Compared with winter fallow treatment, turning over and pressing milk vetch increased rice plant height by 0.7%~3.5%, effective panicle number by 7.0%~15.2% and rice yield by 0.4%~4.9%. Compared with the treatment of winter fallow, the combination of winter planting of milk vetch and different proportions of nitrogen fertilizer reduction could reduce the risk of nitrogen and phosphorus loss in paddy field surface water, of which 30% nitrogen fertilizer reduction was the best. Milk vetch combined with nitrogen reduction fertilization measures improved content of soil available phosphorus and total nitrogen and rice yield. In these treatments, milk vetch combined with 20% nitrogen reduction fertilization had the best effect. Considering the rice yield, soil fertility and risk of loss of nitrogen and phosphorus in paddy field surface water, the combination of milk vetch and 20% nitrogen fertilizer reduction was a more suitable planting method for this area.

Abstract:Ecological protection measures are effective means to control the slope erosion of completely weathered granite backfill slope. Taking the completely weathered granite backfill slope of Longling section of China-Myanmar oil and gas pipeline as the research object, through the indoor artificial simulated rainfall test, under the same slope length, four soil and water conservation measures (engineering measures, plant measures, engineering + plant measures and engineering + tillage measures) with different slopes (10°, 20°, 30° and 40°) and the same rainfall intensity (220 mm/h) were selected to analyze the change law of soil erosion on slope surface and calculate the flow yield rate and sediment yield rate to evaluate its control effect. The results showed that: (1) The protective measures set up in different slopes could reduce flow and sediment, and the best water and soil conservation measure was engineering+plant measure. (2) The slope≤10°was basically stable under the condition of bare slope, and no protective measure was required. For 10°~20° and 20°~30° slopes, the slope protection measures of grass planting (coverage rate 100%) and grass planting+slope interception and drainage measures are effective. For slopes ＞30°, biological measures must be set on the slope surface on the basis of slope consolidation measures to effectively control slope erosion. (3) The threshold of slope was not fixed. The more complex the slope protection measures were, the greater the threshold was. Under different protective measures, the slope had the greatest impact on the cumulative sediment yield.

Abstract:In order to explore the laws and differences of soil water movement between the vertical-pipe drip irrigation and the common surface drip irrigation, two types of sand infiltration and evaporation tests were carried out simultaneously outdoors. And the distribution of soil water, evaporation regularities and transport characteristics of soil wetting front were compared and analyzed. The results showed that: (1) When the irrigation volume was fixed 2 L, the volume and uniformity of irrigation water gradually decreased with the increasing drip emitter flow, while the average water content of the wetting pattern dimensions gradually increased. When the drip emitter flow was constant, the water content of the wetted body in the vertical-pipe drip irrigation was higher than that in the common surface drip irrigation, while the irrigation uniformity was lower. (2) After 7 days of evaporation, with different drip emitter flow treatments, the soil evaporation of the surface drip irrigation accounted for 32.5%, 35.0% and 40.0% of irrigation amount respectively, while the vertical-pipe drip irrigation only accounted for 22.5%, indicating that the vertical pipe drip irrigation significantly inhibited the soil evaporation. (3) When the irrigation amount was 2 L, the migration distances of wetting fronts of the common surface drip irrigation in horizontal and vertical directions decreased slightly with the increase of drip emitter discharge. In the law of the vertical downward movement of vertical surface drip irrigation was similar to the common surface drip irrigation, while the movement in the horizontal and vertical upward directions were opposite. However, with the increase of infiltration time, the transport distance ratios of wetting front in horizontal and vertical direction between common surface drip irrigation and vertical surface drip irrigation showed a decreasing trend and finally tended to be stable. (4) The wetting front migration distance empirical formula, including drip emitter flow and irrigation time, was constructed. And the reliability was verified with the prediction error statistics. That is, the mean square root errors were between 0.24 and 0.27 cm and the Nash efficiency coefficients were greater than 0.985. The research results are expected to provide references for the further researches of vertical pipe drip irrigation.

Abstract:The distribution of soil saturated hydraulic conductivity (K_s) and its influencing factors under typical vegetation types can provide a powerful reference for vegetation construction in Beijing mountainous area and deepen the understanding of soil water movement. In this study, four typical vegetation types in Beijing mountainous area were selected, and soil physical and chemical properties,root biomass and gravel volume were investigated. Based on Pearson correlation analysis, multiple stepwise regression analysis and path analysis,the distribution of soil saturated hydraulic conductivity and its influencing factors were obtained. The results showed that: (1) The soil saturated hydraulic conductivity ranged from 0.05 mm/min to 2.23 mm/min, which belonged to the height variation and decreased with the soil layer downward. The soil saturated hydraulic conductivity of the mixed forest of Platycladus Orientalis and Shrub, pure forest of Platycladus Orientalis and mixed forest of Platycladus Orientalis and Acer elegantulum were significantly different (p＜0.05). The relationship between soil saturated hydraulic conductivity and depth was in accordance with logarithmic function y=±aln x+b, R²≥0.858. (2) Correlation analysis showed that soil saturated hydraulic conductivity was significantly correlated with bulk density, total porosity, capillary porosity, root biomass and organic matter content (p＜0.01), there was significant correlation with non-capillary porosity and natural water content (p＜0.05). (3) Stepwise regression analysis showed Y=3.42X₂+0.78X₆-1.333, R²=0.862. Further path analysis showed that root biomass mainly affected soil saturated hydraulic conductivity directly, while total porosity affected soil saturated hydraulic conductivity indirectly. And as it turns out, the mixed forest of Platycladus Orientalis and shrub has the best water conductivity, and the latter vegetation construction should focus on the mixed forest of Platycladus Orientalis and shrub in order to reduce runoff and conserve water sources.

Abstract:Gully erosion leads to massive soil loss, which aggravates the migration, loss and morphological changes of organic carbon, and thus induces CO₂ emission effects. Most of the previous studies on CO₂ emission effects of eroded soil were carried out at watershed and regional scales by model estimation, but not enough attentionwas paid to the CO₂ emission effects induced by gully erosion. According to the carbon pool redistribution model, organic carbon and Cesium-137 content of soil profiles from three gullies were used to estimate the CO₂ flux induced by gully erosion on the Loess Hilly Region, and the model prediction efficiency and its influencing factors were tested. The results showed that: (1) After long-term erosion, severe erosion occurred in both erosion area and sedimentary area of gullies in the three study areas. The erosion rate in erosion area was between 30.99 and 46.44 mm/a, and that in sedimentary area was between 34.20 and 37.88 mm/a, and the soil loss rate in eroded areas were slightly higher than that in deposition areas. (2) The stronger carbon source existe in both erosion and sedimentary areas. The modeling fluxes in erosion and sedimentary area of gullies ranged from 18.41 to 28.44 g/(m²·a), and from 22.19 to 29.25 g/(m²·a), respectively. (3) Erosion site, soil bulk density, soil organic carbon content, soil erosion amount, average slope of gully, aboveground biomass and underground biomass of vegetation jointly explained the variability of prediction efficiency of the carbon pool redistribution model (R²=0.68), among which erosion site, erosion amount, organic carbon content, soil bulk density, and below-ground vegetation had strong driving effects on prediction efficiency. (4) The neglected parameter of new input organic carbon pool induced by vegetation should be introduced to correct the carbon pool redistribution model and improve the model prediction efficiency. It was clear that the carbon pool redistribution model had a higher prediction efficiency of CO₂ flux in gully erosion area compared with deposition area. In order to further improve the prediction accuracy of the model, the new organic carbon pool induced by vegetation should be considered as a calibration parameter incorporated in to the carbon pool redistribution model.

Abstract:The sediment yield caused by rill erosion is the main source of sediment yield in the water-wind erosion crisscross region of the Loess Plateau. It is of great scientific significance and practical value to make clear the characteristics of rill erosion process and its influencing factors in this region, so as to effectively prevent and control sediment entering the Yellow River and effectively maintain the safety of the watershed. In this study, the typical aeolian sandy soil on the underlying surface in the water-wind erosion crisscross region was selected as test soil, and the indoor flume scouring experiments with different flow discharges (3, 5, 7,9, 11 L/min) and different slope gradients (9°, 12°, 15°, 18°, 21°) were carried out, so as to establish equations, which could quantitatively reveal the response of rill detachment capacity to slope gradient, flow discharge and flow velocity. The results showed that: (1) The responses of detachment capacity to slope gradient and to flow discharge were both linearly and positively correlated, and the correlation were significant. The influence of flow discharge on detachment capacity was greater than that of slope gradient. In addition, detachment capacity was also affected by the superposition effect of slope gradient and flow discharge. The order of the influences on detachment capacity were: flow discharge, superposition effect of slope gradient and flow discharge, slope gradient. The relationships between detachment capacity and above three factors could also be well expressed by linearly positive correlations. (2) Flow velocity could be used as a key factor to reflect the superposition effect between slope gradient and flow discharge. There was a significant positively linear correlation between rill detachment capacity and flow velocity. Under the experimental conditions, the critical velocity was 0.607 m/s. (3) The four detachment capacity equations under the combination of slope gradient and flow discharge, under the combination of slope gradient, flow discharge and the superimposed effect of slope gradient and flow discharge, under the single flow velocity factor, and under the combination of slope gradient, flow discharge and flow velocity factor could predict and simulate the detachment capacity of aeolian sandy soil well, among which the equation considering the combination of slope gradient, flow discharge and the superimposed effect of slope gradient and flow discharge was the best. The results provide a theoretical basis for perfecting the rill erosion process model in water-wind erosion crisscross area.

Abstract:In order to better understand water use characteristics of Cinnamomum camphora, based on stable isotopes of stem water, leaf water and soil water of C. camphora during growing seasons (April-October) of 2017—2019 and corresponding environmental factors in the same period, as well as transpiration rate during the growing season of 2019—2021, we analyzed the relationship between plant water isotopes and influencing factors of C. camphor plants at daily scale, explored the variation characteristics of water absorption depth of C. camphor under different environmental conditions during the growing season. The results showed that in the sunny day, the δ¹⁸O of leaf water and transpiration rate were higher in daytime than those at night, while the δ¹⁸O value of stem water was lower in daytime than that at night. The time lag between transpiration rate and leaf water δ¹⁸O was larger on the sunny day in August than that in May, and the average time lag was 2.32 h. On the sunny day in May, the δ¹⁸O of leaf water and stem water had a quadratic function with temperature, vapor pressure difference, relative humidity and transpiration. On the sunny day in August, there was a quadratic relationship between leaf water δ¹⁸O and the above factors, but there was no obvious functional relationship between stem water δ¹⁸O and the above factors. The water absorption depth of C. camphora had obvious seasonal variation characteristics. At the beginning of the growing season (April-May), C. camphora had single water-absorbing layer, mainly used shallow soil water. It had two water-absorbing layers during the middle growing season (June-August) and the late growing season (September-October). C. camphora used middle and deep soil water in the middle of the growing season, while it used shallow and deep soil water in the late growing season. The water absorption depth and transpiration were also affected by habitat. During seasonal drought, the width of the diurnal variation curve of transpiration gradually narrowed with the duration of drought, and the water consumption of transpiration decreased correspondingly. Affected by environmental changes and its own physiological characteristics, water absorption depth of C. camphora gradually changed from shallow to deep and then shallow. However, compared with that before precipitation, transpiration of C. camphora increased after precipitation, the water absorption depth moved up, and the water absorption layer became narrow.

Abstract:Vegetation restoration affects soil water content and organic carbon, as well as water conservation and soil carbon sequestration capacity in Bashang region. To ensure the sustainability of vegetation restoration, it is critical to determine the response of soil water content and organic carbon to vegetation restoration for maintaining the ecosystem stability. In this study, the vertical distribution characteristics of soil water and organic carbon in 0—200 cm depths were studied in different vegetation types, including forestland, shrub, farmland and grassland, and the driving factors affecting their variations were also studied. The results showed that: (1) Compared with grassland, vegetation restoration resulted in deep layer soil water deficit, and the deep layer soil water deficit of forestland and shrub was -0.23±0.08 and -0.16±0.05, respectively. (2) Compared with grassland, vegetation restoration increased the soil carbon sequestration, and the soil carbon sequestration effect increased with depth. (3) The carbon-water coupling coordination degree of control grassland was significantly higher than that of other vegetation types (p＜0.05), and was always in carbon-water coordination state. The shallow layer (0—60 cm) of forestland and shrub was in a carbon-water coordination state, while the deep layer (120—200 cm) soil carbon-water coordination degree was only 0.54±0.03 and 0.57±0.04, respectively. (4) Land use was more important for deep layer (120—200 cm) soil organic carbon and soil water variations, while soil texture was a stable factor affecting their variations in the whole soil profile (0—200 cm). It is concluded that the improvement of carbon sequestration effect of vegetation restoration was at the cost of deep soil water deficit, the imbalance of carbon and water could affect the sustainability of regional ecological restoration.

Abstract:Tamarix ramosissima and Haloxylon persicum in the desert-oasis transition zone of the southwest edge of the Gurbantunggut Desert were used as research objects, and the δ¹⁸O values of plant xylem water and potential water sources were analyzed in combination with the MixSIAR model, and the water sources and utilization ratio of each water source of T. ramosissima and H. persicum in different communities were analyzed. The results showed that: (1) The δ¹⁸O values of soils in the 0—60 cm layer under T. ramosissima and H. persicum thickets varied widely, and the δ¹⁸O values tended to be stable with the increasing of soil depth, indicating that the surface soil was greatly affected by the external environment. (2) In the symbiotic communities of T. ramosissima and H. persicum, T. ramosissima mainly used soil water in the 300—500 cm soil layer throughout the growing season, and H. persicum mainly used soil water below the 60 cm soil layer in spring and autumn, and used soil water in each layer more evenly. It mainly obtained soil water in the 0—60 cm soil layer in summer, and the utilization ratio was as high as 88.0%. It showed that there was ecohydrologic niche separation of water use strategies between T. ramosissima and H. persicum, which was conducive to their rational use of limited water resources under water deficit conditions. T. ramosissima had similar water use sources in single and symbiotic communities and mainly obtained stable deep soil water, indicating that the root water absorption of T. ramosissima was insensitive to fluctuation of the external environment and had no obvious seasonal variation in water consumption. (3) The single H. persicum community made more uniform use of soil water in each layer in spring, and mainly absorbed soil water in the 300—500 cm soil layer in summer, and the utilization ratio was as high as 76.4%, while in autumn, it mainly used soil water in the 60—300 cm soil layer. Artificial H. persicum communities mainly utilized soil water in the 0—60 cm soil layer in spring and summer with contribution rates of 64.2% and 80.6%, respectively, while they mainly absorbed soil water in the 120—300 cm soil layer in autumn with a utilization rate of 93.9%. The result showed that the natural growing H. persicum had a relatively wide range of water sources, reflecting its strong adaptability to arid environments, while the artificial cultivated H. persicum was sensitive to precipitation and showed opportunistic characteristics in water use.

Abstract:To explore the soil nitrogen content and composition characteristics of sagebrush desert grassland, a paired experimental design was used to study the effect of grazing exclusion on total nitrogen, alkaline hydrolyzable nitrogen, nitrate-nitrogen, and ammonium nitrogen in different regions of the northern slope of Tianshan sagebrush desert grassland. The results showed that: (1) After grazing exclusion, the soil nitrogen density (0.59~0.79 kg/m²), soil total nitrogen (0.81~1.50 g/kg), soil alkaline hydrolyzable nitrogen (19.44~67.49 mg/kg) did not significantly changed (p＞0.05). (2) The effects of grazing exclusion on soil nitrate-nitrogen (6.41~21.26 mg/kg) and ammonium nitrogen (0.26~2.53 mg/kg) in sagebrush desert grassland were different due to regional differences. After grazing exclusion, the content of nitrate-nitrogen in the soil layer of 0—50 cm in Gongliu and Hutubi plots decreased significantly by 24.61% and 47.25% (p＜0.01) respectively, while Qitai plots increased significantly by 20.95% (p＜0.05). After grazing exclusion, the content of ammonium nitrogen in the 0—50 cm soil layer of the Manas plot increased significantly by 27.98% (p＜0.05), while that of the Gongliu, Bole, and Hutubi plots did not decrease significantly. (3) The contents of nitrate nitrogen and ammonium nitrogen in the soil of sagebrush desert grassland accounted for 0.27%~3.01% and 0.02%~0.42% of the total nitrogen, and with the increase of total soil nitrogen, the proportion of organic nitrogen increased, while the proportion of inorganic nitrogen, nitrate nitrogen, and ammonium nitrogen decreased. (4) Correlation analysis showed that soil total nitrogen, alkali-hydrolyzable nitrogen, nitrate-nitrogen, and ammonium nitrogen were positively correlated with organic carbon and total phosphorus, and negatively correlated with soil bulk density, pH, and electrical conductivity, and ammonium nitrogen was correlated with soil water content. It was positively correlated and negatively correlated with available phosphorus. Partial redundancy analysis showed that the main factors influencing soil physicochemical factors on soil nitrogen were soil organic carbon and soil water content, and the explanation rates were 32.60% and 17.90% respectively. The research results provide scientific data support for revealing the soil restoration and nutrient management of sagebrush desert grassland in the process of grazing exclusion.

Abstract:Inversion of Crop Water Stress Index (CWSI) was conducted based on the evapotranspiration (ET) and potential evapotranspiration (PET) of MODIS. Temporal and spatial variation of drought and its impact on vegetation were analyzed through a variety of statistical methods. The results showed that the annual average drought severity gradually decreased from southwest to northeast, the crops were mainly light and moderate drought, the grassland was mainly medium and heavy drought, and the desert was mainly severe drought. In addition, except coniferous forest and swamp, the drought tendency of other vegetation types was eased. The variation characteristics of annual drought showed a bimodal curve, and the severe drought occurred in 113 to 144 days. The annual variation characteristics of drought severity for each vegetation type were consistent with the change trend of the whole region, showing a bimodal curve. The impact of summer drought on vegetation growth was the strongest, and the stress effect of annual average drought intensity on vegetation growth was mainly dominated by summer drought. For different vegetation types, shrub in spring, crops in summer and autumn were more sensitive to drought. The results could provide theoretical reference for ecological early warning and ecological restoration of plant communities in Inner Mongolia.

Abstract:Soil moisture is a key factor restricting ecological restoration and reconstruction in the Loess Plateau, and exploring the increase and storage of soil moisture is an important part of land reclamation and ecosystem reconstruction on the slope of the dump. In this paper, the slope of the southern dump of ATB Opencast Coal Mine was selected as the study area through micro-topography shaping and artificial rainfall simulation experiments. For the design of level benches, the step width was 1 m, the step length was 2 m, and the spacing between each level bench was 1 m. For the design of fish-scale pits, the length was 60 cm, the width was 40 cm, and the depth was 30 cm. The horizontal and row spacing of each fish-scale pit was 1 m, and the unshaped terrain was used as the control. Dynamic monitoring of soil moisture was carried out, and descriptive statistical analysis and variance analysis were used to discuss the dynamic changes and vertical changes of soil moisture under different rainfall intensities and different micro-topography. In addition, the effects of rainfall intensity, micro-topography shaping mode and soil depth on soil moisture were studied by multivariate analysis of variance. The results showed that: (1) Under the same micro-topography, soil moisture content increased with the increase of rainfall intensities, and the variation range gradually decreased. High-intensity rainfall caused significant changes in surface soil moisture content, while low-intensity rainfall caused significant changes in deep soil moisture content. (2) Under the same rainfall intensity, different micro-topography could effectively increase soil moisture, and compared with fish-scale pits, level benches could better increase soil moisture. (3) With the increase of soil depth, the coefficient of variation of soil water content gradually decreased, and all belonged to medium variation. Under different rainfall conditions, the vertical variability of soil moisture caused by micro-topography was greater than that of the control. (4) The effects of rainfall intensity, micro-topography and soil depth on soil moisture were extremely significant, and the magnitude of the impact on soil moisture was: micro-topography＞rainfall intensity＞soil depth. These findings indicate that micro-topography shaping in open-pit coal mine dumps is beneficial to the replenishment and storage of soil moisture, and has positive significance for land remediation and ecological restoration of dumps.

Abstract:In this study, three land use types (flat field farmland, shady slope terrace and sunny slope plantation) of Jiaxinzhuang Formation in the loess region of southern Ningxia were selected. Soil water content (SMC) was observed by soil drill in the growing season of 2021. At the same time, meteorological data were monitored by an automatic weather station. The spatio-temporal variation characteristics of SMC under the influence of land use, slope position and crop species were analyzed. The results showed that the order of SMC of the three land use types was flat field farmland (16.32%)＞shady slope terrace (12.66%)＞sunny slope plantation (10.82%). With the advance of the study period, SMC decreased first and then increased. There was excellent temporal synergy between SMC and precipitation. Temperature, solar radiation and saturation vapor pressure deficit were significantly related to the SMC of sunny slope plantations. With the increase of soil depth, SMC increased in flat field farmland, decreased in shady slope terrace, first decreased and then increased in sunny slope plantation. The variation coefficient of SMC in the 0—100 cm soil layer was greater than that in the 100—200 cm soil layer. Seasonal variation of SMC were divided into a relatively stable period (April-May), regression period (June-August) and recovery period (September-October). The change of SMC in different soil layers was divided into the active layer (0—40 cm), the relatively active layer (40—140 cm) and the relatively stable layer (140—200 cm). The replenishment time of soil moisture lagged behind precipitation, and the replenishment of lower soil moisture lagged behind that of upper soil. SMC of shady slope terrace and sunny slope plantation decreased first and then increased with the decreasing of slope position, and the minimum values were at the upper and middle-down slope position, respectively. Land use, slope position, crop species and meteorological elements were all factors that affected SMC. In terms of the variation degree of SMC, the effect of each factor on SMC followed the order of meteorological＞land use＞slope position＞crop species. The results of this study were conducive to guiding the vegetation reconstruction and ecological industry development in semi-arid loess area, and determining the reasonable vegetation allocation under different site environments.

Abstract:In view of the shortage of water resources and the serious degradation and low quality of natural grassland in Hexi Corridor, the reasonable water regulation and planting patterns were explored to alleviate the contradiction between grass and livestock, improve the ecological environment and realize the sustainable development of regional grassland animal husbandry. The experiment was conducted in a 2-year field trial to study the effects of three planting patterns (O: Sainfoin (Onobrychis viciifolia) monoculture, A: Sainfoin and Bromus inermis mixture, B: Sainfoin, B. inermis and Elytrigia elongate mixture) and four types of water regulation (upper and lower limits of irrigation were based on the proportion of soil water content in field capacity (θ_FC), W0: adequate irrigation (75%~85% θ_FC), W1: slight water deficit (65%~75% θ_FC), W2: moderate water deficit (55%~65% θ_FC), W3: severe water deficit (45%~55% θ_FC)) on soil moisture characteristics, hay yield, quality and water use efficiency of artificial grass. The results showed that: (1) In the temporal dimension (from April to September), soil water content in 0—40 cm soil layer decreased firstly and then increased, and this trend of W2 and W3 was more obvious than that of W0 and W1, and more obvious for monoculture than mixed sowing. Soil water content in 40—100 cm soil layer decreased gradually. In the vertical spatial distribution, the soil water content of each treatment increased firstly and then decreased, and then tended to be stable. The soil water contents of the three planting patterns were moderate variation, and the variation coefficient of surface layer and 60—100 cm soil layer was large. (2) With the aggravation of water deficit, the herbage yield of monoculture and mixed sowing decreased gradually, and the WUE increased firstly and then decreased. There was no significant difference in forage yield between W1 and W0 (p＞0.05), and the WUE of W1 was the highest. Compared with O, the two-year average total herbage yield of A and B increased by 16.01% and 12.74%, respectively, and the two-year average WUE increased by 18.64% and 11.19%, respectively. (3) Suitable water deficit improved the herbage quality, and the herbage quality of mixed-sowing pattern was better than that of monoculture. Compared with O, the two-year average ADF, NDF and CP in planting patterns A and B decreased by 4.40% and 2.73%, 2.82% and 2.02%, and 3.53% and 7.24%, respectively. However, under W0 and W1 water treatment, there was no significant difference in CP between planting patterns O and A. Compared with O, the two-year average Ash of A and B increased by 18.50% and 16.58%, EE increased by 23.19% and 20.37%, and RFV increased by 4.87% and 3.20%, respectively. Through comprehensive evaluation of principal component analysis, it was concluded that the combination of slight water deficit and mixed sowing of Sainfoin and B. inermis was the suitable water regulation and planting pattern for artificial grassland with high yield, high quality and high efficiency in Hexi Corridor.

Abstract:Throughfall is the main component of rainfall redistribution, which affects vegetation growth and soil moisture distribution. Taking the typical tree species in the southern dump of Pingshuo mining area as the research object, the spatial distribution characteristics of throughfall of Pinus tabulaeformis, Robinia pseudoacacia, Euonymus maackii, Caragana microphylla and Elaeagnus multiflora were compared and analyzed by using geostatistical methods and time stability plots. The average throughfall percent from large to small was: Elaeagnus multiflora, Caragana microphylla, Pinus tabulaeformis, Euonymus maackii, Robinia pseudoacacia. The coefficient of variability of throughfall percent from large to small was Euonymus maackii, Elaeagnus multiflora, Caragana microphylla, Pinus tabulaeformis, Robinia pseudoacacia. The throughfall percent of Pinus tabulaeformis, Robinia pseudoacacia, Euonymus maackii, Caragana microphylla and Elaeagnus multiflora increased with the increase of rainfall, and finally reached a steady state, and the coefficient of variability of throughfall percent decreased rapidly with the increase of rainfall, and finally reached a steady state, and the logarithmic function was the best fitting effect. The still of throughfall percent decreased exponentially with the increase of rainfall, and the nugget coefficient increased with the increase of rainfall, indicating that with the increase of rainfall, the throughfall percent tended to be uniform in space, and the spatial heterogeneity caused by random factors gradually increased. Moreover, the throughfall percent of the five tree species was higher than 100% in the middle and outer parts of the plant canopy. The temporal stability of the distribution pattern of throughfall shrubs was higher than that of trees. The canopy near the base and the outer edge of the canopy showed extreme persistence of throughfall. The base near the vegetation was mostly in an extremely dry state, and the outer edge of the canopy was mostly in an extremely wet state. Considering the throughfall percent and its spatial variability, Robinia pseudoacacia was the best choice of vegetation type for reconstruction in soil erosion areas. The throughfall appeared continuously wet at the edge of the vegetation canopy, and some shrubs could be planted to intercept part of the throughfall. These research results could enhance the understanding of the ecological and hydrological process of the mining dump, and provide a theoretical basis for the selection of vegetation for the reconstruction of the mining dump.

Abstract:In this study, based on Vegetation Condition Index (VCI) of the Loess Plateau from 1983 to 2015, Standardized Precipitation Evapotranspiration Index (SPEI) and the Standardized Precipitation Index (SPI) at the scale of 1~48 months, we investigated the spatial-temporal response characteristics of vegetation to meteorological drought index at multi time-scales on the Loess Plateau through Pearson correlation coefficient method, linear regression method and Mann Kendall trend test method. The results showed that: (1) The overall vegetation condition of the Loess Plateau improved, but no significant drying or wetting trend could be detected in the study area during 1983 and 2015. (2) The change of vegetation was well positively correlated to the meteorological drought index in most areas of the Loess Plateau, indicating that the vegetation growth was largely restricted by the moisture in the study area. However, in the past few decades, such restriction effect from atmospheric moisture to the vegetation was gradually weakening. (3) The vegetation on the Loess Plateau was relatively much more sensitive to the change of water balance at a short time sale, the cultivated land and grassland were more sensitive to the SPEI of 1~4 months, while the response time-scale of forest land to SPEI was relatively scattered. Furthermore, the maximum correlation coefficient between VCI and SPEI or SPI on the Loess Plateau mainly occurred during the growing season (April to October), indicating that the water conditions had a much more significant effect on vegetation growth during growing season.

Abstract:As the dividing line between the north and the south of China, it is necessary for the Qinling Mountains to construct a complete set of evaluation and monitoring index system. Its internal driving factors and internal mechanism should be studied to promote the ecological environment protection at a new level, and also to fully grasp the driving mechanism and changes of the water conservation function. In this study, an evaluation index system of water conservation capacity in the Qinling Mountains was proposed based on geoweighted principal component analysis (GWPCA). The spatial dynamic changes of primary and secondary indicators of water conservation capacity in the Qinling Mountains in 2010 were analyzed, and their spatial distribution mechanism were revealed. Based on GWPCA, considering the water conservation effects of meteorological factors, underlying surface factors and social factors, an index system of water conservation capacity in Qinling Mountains containing 10 spatial variables was constructed. According to the results, the water conservation capacity of the Qinling Mountains could be divided into five grades: low, lower, medium, high and higher. The spatial variation rules of water conservation capacity of the Qinling Mountains were revealed, and some suggestions for ecological management were put forward. The results showed that the water conservation capacity in most areas of Qinling Mountains was at high and higher levels, accounting for 66.48% of the whole region. The water conservation capacity in some economic development regions and the central region of Qinling Mountains is at low and low levels. Extreme climate events and human activities were the main reasons for its distribution. The index system of water conservation capacity in Qinling based on this method could effectively quantify the water conservation capacity in Qinling and its spatial heterogeneity, and could clarify the main driving factors.

Abstract:This study aimed to solve the problem of excessive dependence of rice yield on pure chemical nitrogen fertilizer, the environmental problem and high efficiency utilization of chemical nitrogen fertilizer, and even the scientific application of biochar in paddy field. A field experiment was conducted from 2019 to 2021 in Sinan county, Guizhou province. Taking no fertilization as the control (CK), five treatments of chemical nitrogen fertilizer dosages: T0~T4, i.e., 100%, 90%, 80%, 70% and 60% of nitrogen fertilizer, respectively, was set up under the principle of equal total nitrogen application. The rice yield, yield components and nitrogen, phosphorus and potassium uptake and utilization were studied. The results showed that biochar application with reduced nitrogen fertilizer significantly affected the yield, yield composition, aboveground nitrogen, phosphorus and potassium accumulation, and nitrogen, phosphorus, and potassium utilization efficiency of rice. The grain yield and nitrogen, phosphorus and potassium accumulation of rice increased first and then decreased with the increase of biochar application amount and the decrease of nitrogen fertilizer. The highest actual and theoretical rice yield were found under T2, T3 and T2 respectively in 2019, 2020 and 2021, which three significantly increased by 16.04%, 17.94% and 14.73%, and 55.72%, 64.08% and 118.91%, respectively, compared with T0. The accumulation of N, P₂O₅ and K₂O, partial productivity, agronomic efficiency, apparent utilization, and harvest index of rice grains were also higher. So T2 and T3 were the relatively better treatments with reduced nitrogen fertilizer application of biochar. The regression equation of yield-biochar application and extreme value analysis showed that the applied nitrogen fertilizer decreased by 21.76%, 24.60% and 19.00%, respectively in 2019, 2020 and 2021, i.e., 32.64, 36.90 and 28.50 kg/hm².The highest rice yield (7.80, 8.57 and 8.03 t/hm², respectively) was obtained at the biochar application of 5.44, 6.15 and 4.75 t/hm², these yields were increased by 22.52%, 18.78% and 13.74%, respectively, compared with T0. Application of biochar with reduced N fertilizer significantly increased the utilization rate of N, P and K of chemical N, P and K fertilizers, but decreased the utilization rate of that of the chemical fertilizers plus biochar. Therefore, N, P and K fertilizers should be reduced simultaneously when applying biochar in Guizhou yellow soil paddy fields, the reduction percentage of which are 19.00%~24.60% and best application rate of biochar is 5.00~6.25 t/hm². This study has important guiding significance for N, P, and K fertilizer reduction and biochar application in yellow soil paddy fields in Guizhou Province.

Abstract:Taking the litter of Castanopsis carlesii foliar, a constructive species of subtropical evergreen broad-leaved forest, as the research object, compared with the forest surface environment, a field study was conducted to understand the content changes and loss characteristics of water-soluble organic carbon, nitrogen and phosphorus during the decomposition of C. carlesii foliar litter in streams and intermittent streams. The results showed that: (1) In the three habitats, the water-soluble organic carbon of litter decreased continuously in the decomposition process, but the most loss was detected in the streams with a loss property of 92.18%. In contrast, the release time of water-soluble nitrogen in streams and intermittent streams were earlier and the changes were relatively small. Compared with the forest floor and intermittent streams, the content of water-soluble phosphorus in litter decreased continuously in streams with the loss ratio of 86.75% during the whole decomposition process. (2) Compared with the forest floor, both streams and intermittent streams significantly promoted the release rates of water-soluble organic carbon, nitrogen and phosphorus in litter, indicating that the continuous water flow could promote the release of water-soluble components during litter decomposition. (3) Although the loss rate of water-soluble organic carbon, nitrogen and phosphorus in litter were jointly affected by temperature, precipitation and the content of nutrient elements in the three habitats, the continuous water flow in head water streams and the frequent alternation of dry/wet in intermittent streams promoted the release of water-soluble components in the litter. The results provide some basic data for revealing the decomposition dynamics of water-soluble components in the litter of different habitats in subtropical mountain forests.

Abstract:In order to determine the change characteristics and influencing factors of soil organic carbon (SOC) and easily oxidized organic carbon (EOC) under different vegetation types of engineering deposits, four types of sample plot of tree, shrub, grassland and bare land were set up in this study, and the soil samples were collected at the depth of 0—10, 10—20, 20—40, 40—60 and 60—80 cm. The organic carbon components and physical and chemical properties of the soil were determined by principal component analysis and correlation analysis. The results showed that: (1) There were significant differences in SOC content among different vegetation types. The mean values of SOC in tree plot, shrub plot, grassland plot and bare soil were 45.73, 41.81, 34.75 and 21.11 g/kg, respectively. Vegetation restoration significantly increased SOC content, especially in surface soil. (2) Soil carbon pool activity (ratio of active organic carbon to inactive organic carbon) of tree plot and shrub plot was significantly higher than that if grassland plot, and SOC of tree plot and shrub plot was easier to be absorbed and utilized by plants. (3) Total nitrogen (TN), total phosphorus (TP) and hydrolysis nitrogen (HN) were significantly positively correlated with SOC and EOC (p＜0.05), and played a major role in the improvement of SOC. Therefore, mixing legumes with nitrogen fixation effect was beneficial to the improvement and accumulation of SOC.

Abstract:The effects of biochar application on soil aggregates under different sieving methods were studied experimentally to provide a theoretical basis for the agricultural utilization of biochar. Four levels of biochar dosage (0, 10, 20 and 30 t/hm²) and two levels of nitrogen fertilizer dosage (0 and 150 kg/hm²) were set up in the experiment. Through two-year field positioning test, the distribution and stability of soil aggregates in 0—30 cm soil layer were measured and analyzed by dry sieving method and wet sieving method. The results showed that under the two sieving methods, the distribution trends of soil aggregates of each particle size in different treatments were basically the same. The mechanical soil aggregates obtained by the dry sieving method were mainly of ＞5 mm, 2~5 mm and 0.5~1 mm, while the water-stable aggregates obtained by the wet sieving method were mainly of 0.25~0.5 mm and ＜0.25 mm. The mean weight diameter (MWD) and geometric mean diameter (GMD) of soil aggregates in the dry sieving method were higher than those in the wet sieving method. In all treatments under wet sieving method, whether nitrogen was applied or not, both MWD and GMD increased with the increasing of biochar content. Among them, the MWD and GMD of the B0N0 treatment were the smallest, and the diameter of the soil aggregates in B3N0 (single application of biochar) was the largest, which was significantly higher than that of B0N0 by 60% (MWD) and 52% (GMD), respectively. The soil aggregate destruction rate (PAD) decreased with the increasing of biochar amount, while the soil aggregate stability rate (WASR) increased with the increasing of biochar amount. The fractal dimension (D) of each treatment in the dry sieving method was lower than that in the wet sieving method. The D value decreased continuously with the increasing of the biochar amount, and the fractal dimension of B3 biochar was the lowest, which were 2.63 (B3N0) and 2.64 (B3N1), respectively, 3.3% and 2.9% lower than that of the control. There was a significant negative correlation between the fractal dimension (D) and the content of soil aggregate larger than 0.25 mm (R_＞0.25). Under the experimental conditions, the soil aggregate stability was the best when the amount of biochar was 30 t/hm². At the same time, the wet sieving method could better simulate the field environment than the dry sieving method, and truly reflect the distribution and stability of soil aggregates.

Abstract:This research investigated the effects of drip and spray irrigation on the physical, chemical and biological properties of the soil and root growth of tea seedlings, and could provide a theoretical basis for scientific irrigation and fertilization. Three types of fertilizer application were set up, soil application (SA), spray application (FA) and drip application (DA). After 15, 30, 45 and 60 days, the soil was divided into three spatial zones according to the difference in horizontal and vertical distance from the center of the topsoil of the culture bowl, and pH, conductivity, nutrients and biological properties were observed. In the pot experiment of tea seedlings, six treatments were set up, including two nitrogen levels and three fertilization methods of soil application, spraying and dropping. The root growth and morphology of tea seedlings were observed. The results of the soil culture showed that there was no significant difference between FA and SA treatments in different spatial soil regions, while there were significant differences between DA and FA. After 60 days, in the soil region 5 cm horizontally and 0—10 cm vertically from the center point, compared with FA, the conductivity, pH, content of alkali-hydrolyzed N, available K and available P of DA increased by 35.6%, 30.7%, 40.6%, 34.3% and 74.8%, respectively, and bacterial, fungal and actinomycetes in the region of DA increased by 174.6%, 167.0% and 289.0%, respectively. The activities of urease and acid phosphatase in the soil region of DA showed opposite trend, decreased by 42.5% and 31.4%, respectively, compared with FA. The results of pot experiment showed that the overall root growth of tea trees followed the order of FA＞SA＞DA, and the root fresh weight, total root length, root volume, root tip number, branch number and cross number of tea seedlings in the FA treatment were significantly higher than those of DA, while there was no significant difference in the root promoting effect among different N levels. In summary, fertilization methods had significant effects on the spatial distribution of soil nutrients, soil biological properties and root growth of tea seedlings. Compared with SA and FA, the conductivity, nutrient content and microbial population in the micro domain at the center of the DA drip head increased significantly, and there was a significant micro domain aggregation effect, while the urease and acid phosphatase activities decreased. DA significantly inhibited the root growth of tea seedlings, while FA significantly promoted the root growth and morphological establishment of tea seedlings.

Abstract:This study aimed to study the differences of wheat yield, light energy and nitrogen use efficiency between high-yield and medium-yield wheat fields, so as to provide a theoretical basis for reducing the difference of yield and resource use efficiency and realizing high-yield and high-efficiency production of wheat. Two wheat fields with high and medium yield were selected, and their annual wheat yield was about 9 000 kg/hm² and 7 500 kg/hm² respectively. The wheat variety Yannong 1212 was used as test material to analyze the difference of light and nitrogen utilization in wheat field at different yield levels. The results showed that the nitrogen accumulation in the high-yield field was 6.65%~11.25% higher than those in the medium-yield field at jointing, flowering and maturity stages, the nitrogen transport to grain before flowering was 11.60 kg/hm² higher than that in the middle field, and the nitrogen assimilation after flowering was 21.99 kg/hm² higher than that in the middle field. From 14 to 28 days after anthesis, the activities of nitrogen metabolic enzymes in flag leaves in high-yield fields were significantly higher than those in medium-yield fields. The apparent surplus and deficit of soil nitrogen in high-yield field decreased by 48.61% compared with that in medium-yield field. The leaf area index and SPAD value of flag leaf in high-yield fields were 6.89%~34.56% and 8.45%~27.32% higher than those in mediun-yield fields at flowering and 7~28 days after flowering, respectively. At flowering stage and 7~28 days after flowering, the interception rate and amount of solar energy available radiation in high-yield fields were 3.92%~7.70% and 3.97%~7.85% higher than those in medium-yield fields. The grain yield of high-yield field was 26.71% higher than that of medium-yield field, and the light energy utilization rate and nitrogen utilization rate were 17.39% and 19.50% higher respectively. To sum up, the interception rate of effective light energy radiation in canopy and the transport of nitrogen stored in vegetative organs to grains are high in high-yield fields after wheat flowering, which improves the accumulation of nitrogen in grains at maturity, thus improving the yield, light energy utilization and nitrogen utilization, reducing the apparent nitrogen surplus and deficit in soil and reducing nitrogen loss.

Abstract:Wheat-maize double cropping system is the main cropping system in North China Plain. The aims of the present study were to delineate the responses of soil microbial biomass N (SMBN), soil microbial biomass C (SMBC) and enzymes activities to different fertilization methods of maize and limited irrigation treatments of wheat. The split plot experiment design was adopted on the field experiment. The main control was fertilization methods of maize, F1 (conventional method, 5cm depth of subsoil with sowing) and F2 (application N, P, K fertilizers to designated different soil depth with subsoiling), and the sub-control was three irrigation treatments in the growing season of wheat, W0 (no irrigation events after the overwintering stage), W1 (irrigation at the jointing stage after overwintering), and W2 (irrigation at jointing and flowering stages after overwintering). The results showed that: (1) Subsoiling fertilization in maize season was beneficial to increase the supply of N, P and K, improve soil fertility, and significantly affected the physical and chemical properties of topsoil in wheat flowering stage. In 0—20 cm and 20—40 cm soil layers, soil moisture content and nitrate nitrogen content of F2W2 treatment were significantly higher than those of other treatments. Soil water content was affected by F2 and limited irrigation of wheat, and the interaction effect was significant (p＜0.05). The effect of water treatment on nitrate nitrogen was significantly greater than that of subsoil fertilization. (2) SMBC and SMBN were not only affected by fertilization of F2, but also limited irrigation of wheat. Irrigation in wheat growing season significantly increased the contents of SMBC and SMBN in 0-20 cm soil layer, and soil water content had a significant effect, contributing 78.3%. In 20—40 cm soil layer, the content of SMBC and SMBN were significantly affected by fertilization methods in maize season and limited irrigation treatment in wheat season, and their interaction had significant effects on the content of SMBN. The soil water content had significantly effect on the SMBN, contributing 88.9%. The SMBN content of 0—20 cm under F2W2 was 94.16 mg/kg, which was significantly higher than that of other treatments(p＜0.05). The SMBN and SMBC contents of 20—40 cm under F2W2 were 57.57 mg/kg and 243.77 mg/kg, respectively, which were significantly higher than those of other treatments. SMBC and SMBN were positively correlated with organic carbon, available potassium and nitrate nitrogen, and had a significantly positive correlated with soil water content. (3) The activities of soil sucrase and catalase in 0—20 cm under W2 was the highest, following by W1 and W0, and the differences between different water treatments were significant. Under the same water management condition in wheat season, the activities of sucrase and catalase in 0—20 cm soil layer were the highest under F2, which were significantly higher than that of F1. The activities of soil sucrase, alkaline phosphatase and catalase were positively correlated with the available K and available Pin 0—20 cm soil layer, while soil sucrase, urease and catalase activities were positively correlated with soil water content in 0—40 cm soil layer. (4) The yield of wheat under F2W2 was the highest, and the differences in uptake of total N, P and K were significantly compared with other treatments. The yield and the uptake of N, P and K were significantly positively correlated with the activities of sucrase, urease and catalase, and the contents of SMBC and SMBN. Therefore, irrigation at jointing and flowering stages of wheat combined with maize fertilization with subsoiling could effectively accelerate soil nutrient activation, improve soil quality and ensure sustainable of soil production.

Abstract:In order to explore the effects of long-term interaction between controlled-release urea blended fertilizer and maize straw on soil enzyme activities and soil nutrient status in wheat season, based on 8-year experiment of positioned fertilization experiment of wheat-maize rotation in brown soil of North China Plain, the effects of controlled-release urea blended with urea (CRF) and bulk blending urea (BBF) on soil enzyme activities and soil nutrients in wheat season were compared under maize straw returning (S) and non-returning conditions. The results showed that under the condition of no straw returning, compared with BBF treatment, the CRF treatment significantly increased the neutral phosphatase activity (rejuvenation and maturity stages), sucrase activity and cellulase activity (rejuvenation and booting stages) and the content of soil organic matter, NO₃^-—N and Olsen phosphorus (Olsen—P) at maturity. At maturity, the neutral phosphatase activity and NO₃^-—N content increased by 29.6% and 34.8%, respectively. Under the condition of straw returning, activities of urease and cellulase at maturity and neutral phosphatase activity at booting stage were significantly higher in the BBF+S treatment than that in the CRF+S treatment, but there was no significant difference in soil enzyme activities between the two types of blended nitrogen fertilizers at other stages. The content of soil total nitrogen, soil organic matter, NO₃^-—N and Olsen—P at maturity was significantly higher in the CRF+S treatment than that in the BBF+S treatment. The interaction of nitrogen fertilizer types and maize straw returning had significant effects on the activities of neutral phosphatase, sucrase and cellulase in soil and the contents of total nitrogen, NO₃^-—N, NH₄⁺—N, Olsen—P and available potassium in soil. Straw returning significantly increased the activities of neutral phosphatase and sucrase and the contents of available potassium and Olsen—P compared with non-returning treatment. In summary, under the conditions of straw returning and non-returning, CRF treatment could significantly increase soil organic matter content, improve the supply intensity and supply capacity of available nitrogen and phosphorus nutrients in late stage of wheat compared with the BBF treatment, and the treatment of CRF+S showed the best performance in improving soil enzyme activity and soil nutrients. The research results could provide a theoretical basis for the optimal application of nitrogen fertilizer under straw returning.

Abstract:In order to promote the resource utilization of mushroom residues, and to reduce the application rate of chemical fertilizers and increase its use efficiency, the residues of Auriculariapolytricha, Lentinus edobes, and Agaricus bisporus were selected as organic materials in this study. Based on the nitrogen application of conventional chemical fertilizers in Chengdu Plain, a total 8 treatments were set: blank treatment (CK), conventional chemical fertilizer (CF), 25% and 50% Auriculariapolytricha residues (APR1, APR2), 25% and 50% Lentinus edobes residues (LER1, LER2), 25% and 50% Agaricus bisporus residues (ABR1, ABR2). The differences in soil fertility and soil enzymes activities of different mushroom residues and chemical fertilizers were discussed. The results showed that the mushroom residue and chemical fertilizers could effectively enhance the activities of soil sucrase and urease, increase the contents of soil organic carbon, total nitrogen, total phosphorus, available phosphorus and available potassium, promote the accumulation of nitrogen in crops, and improve the utilization rate of nitrogen fertilizer, thereby promoting crop production. However, the higher C/N ratio (C/N＞30), P₂O₅ replacement rate and K₂O replacement rate of mushroom residues resulted in a decrease in nutrient use efficiency and a significant decrease in yield. Even the positive effects of P₂O₅ and K₂O on soil and crops were not enough to compensate, which was significantly negatively correlated with crop yield. On the whole, the mushroom residues with a C/N ratio close to 30, the use of 50% or less of nitrogen fertilizer replacement rate in the rice season, and the use of 25% nitrogen fertilizer replacement rate in the wheat season are conducive to increasing crop yield.

Abstract:In order to elucidate the distribution characteristics of soil microorganisms at different altitudes, we selected Sejila mountain as a model area, a typical forest ecological area in southeastern Tibet. In this study we investigated the cultivable microorganisms and the richness of fungal community composition and relative abundances along an altitude gradient (approximately 3 400~4 600 m) in Sejila mountain. The amount of soil cultivable microorganisms in the 0—5 and 5—10 cm layer showed the following rank order: bacteria＞actinomycetes＞fungi, and the number of fungi was significantly correlated with altitude, while the number of bacteria and actinomycetes had no obvious change with altitude. The high-throughput sequencing results showed that there were 4 phyla, 18 classes, 47 orders, 74 families, and 93 genera of fungi detected. Basidiomycota and Ascomycota were predominant fungal at the phylum level, and Agaricomycetes had the highest relative abundance at the classes level. Alpha diversity analysis showed that the soil fungal abundance and diversity of the Quercus aquifolioides forest in lower altitude and the alpine grassland in the higher altitude area were higher, while the Rhododendron aganiphum and Abies georgei var. smithii forest in the middle altitude (3 900~4 110 m) was lower. The redundancy analysis found that, at the phylum and class classification level, the fungal community was mainly caused by soil organic carbon and total nitrogen contents, while the influence of altitude was relatively small. The results suggest that the distribution of microorganisms at different elevations may mainly depend on soil properties and vegetation type.

Abstract:This study aimed to analyze the variation of soil physical and hydrodynamic properties of saline soil with different salinization levels, the experimental study was carried out in Xuwei New Area of Lianyungang City, Jiangsu Province. Five kinds of soils with different salinization levels were sampled and their pH, EC_e, bulk density, total porosity, water content and saturated hydraulic conductivity were measured. The changes of physicochemical parameters and hydrodynamic properties of coastal saline soils with different salinization levels were analyzed. The results showed that: (1) The soil EC_e of 0—50 cm profile of different saline soils first decreased and then increased, but the EC_e of 40—50 cm profile was larger than that of 0—10 cm profile. The changes of soil EC_e in 0—50 cm profile of non-saline soil and extremely heavy saline soil were small, and the EC_e value of 0—50 cm section of light saline soil, medium saline soil and heavy saline soil fluctuated greatly. (2) Soil EC_e was negatively correlated with bulk density, and positively correlated with capillary porosity, non-capillary porosity, total porosity, moisture content, capillary water capacity, field water capacity and maximum water capacity. There was a very significant positive correlation between soil porosity and water holding capacity. (3) The saturated hydraulic conductivity of extremely heavy saline soil was significantly lower than that of other saline soils, and the saturated hydraulic conductivity of 0—20 cm profile was greater than that of 20—50 cm profile. The results could provide a theoretical reference for water and salt management and ecological environment construction of coastal saline soil.

Abstract:In order to explore the effects of increasing application of organic fertilizer on organic carbon and nitrogen components and microbial community in saline-alkali soil, the wheat-maize rotation sample plot in the saline-alkali reclamation area of the Yellow River Delta since 2018 was taken as the research object. The content of soil organic carbon and nitrogen components and the response of microbial community to the measures of increasing organic fertilizer under three treatments (common chemical fertilizer CN, chemical fertilizer plus pig manure organic fertilizer PCOF, and no fertilizer CK) were measured, aiming at providing a theoretical basis for the improvement of organic fertilizer and the sustainable development of agriculture in the saline-alkali land of the Yellow River Delta. The results showed that: (1) The input of fertilizer played a positive role in promoting saline-alkali soil. Compared with the application of chemical fertilizer alone, the content of basic nutrients such as nitrogen, phosphorus and potassium in soil increased significantly by 15.6%, 251.7% and 65.2% respectively (p＜0.05). Moreover, the plough layer structure has been improved. (2) Combined application of inorganic and organic fertilizers was helpful to increase the active components of soil organic carbon and nitrogen. Compared with CN, POC, DOC and MBC were significantly increased by 40.8%, 13.2% and 69.1% respectively. HTN and AAN increased significantly by 11.6% and 33.3% respectively. Compared with CK, EOC and MBC of single application of chemical fertilizer significantly increased by 32.9% and 17.5% respectively, and organic nitrogen components had no significant effect. (3) After three years of combined application of organic fertilizer, the diversity of bacterial community and the richness of fungal community were significantly higher than that of CK and CN, and the relative abundance of beneficial bacteria such as Acidobacteria, Curvularia and Ascomycetes increased. (4) RDA analysis showed that organic carbon and organic nitrogen components had a significant positive correlation with the relative abundance of beneficial bacteria in microbial community, and a significant negative correlation with the relative abundance of Oligotrophic Bacteria. In conclusion, increasing the application of organic fertilizer is an effective measure to improve the organic carbon and nitrogen components of saline-alkali soil, as well as the diversity of bacterial community and the richness of fungal community.

Abstract:In order to reveal the effect of forage grass planting on improving saline alkali land and better develop and utilize the reserve land resources, the coastal saline alkali land in the Yellow River Delta was taken as the research object, using the methods of plot experiments, field sampling and indoor tests, we investigated the dynamic changes of physical, chemical and enzymatic activities of saline soils planted three annual forage grasses (Sorghum bicolor×sudanense, Sorghum bicolor 'Dochna’, Purus frumentum) during a growing period, and comprehensively evaluated the improvement effects based on the soil quality index. The results showed that: (1) Soil water content, pH and conductivity showed a decreasing trend with the increasing of growth time, and the most significant reduction in soil pH was observed for Sorghum bicolor×sudanense and P. frumentum during the vigorous growth period, and the best reduction in pH was observed at the harvest stage of Sorghum bicolor 'Dochna’. The soil conductivities of all three forage grasses were significantly lower than that of CK, and the reduction effect on 20—40 cm soil layer was better than that on 0—20 cm soil layer, among which P. frumentum was the best. (2) Planting of different forage grasses significantly improved soil nutrient content, and the content of soil organic matter, avail nitrogen and avail phosphorus increased significantly, but had little effect on soil avail potassium content. (3) The three forage grasses had different effects on soil enzyme activities at different growth periods. During the vigorous growth period, the soil enzyme activity was the strongest, and activities of soil catalase, sucrase and urease significantly enhanced. Sorghum bicolor 'Dochna’ had the greatest effect on activities of catalase and sucrase. (4) There were differences in the contribution of different forage grasses to the improvement index of saline alkali soil. Taking soil physical and chemical properties, nutrient content and soil enzyme activity as soil evaluation indexes, the soil quality after planting different forage grasses from high to low was Sorghum bicolor 'Dochna’＞Sorghum bicolor×sudanense＞P. frumentum＞CK. The research coud provide theoretical basis and important reference for the phytoremediation technology of saline alkali land in the Yellow River Delta and the screening and introduction of salt-tolerant plants with high ecological and economic benefits at home and abroad.

Abstract:Soil in mining areas are easily to be contaminated by heavy metals, which fact is a major challenge for land resource utilization and maintenance. In the present study, the contaminated soil in copper mining area was used as the research material, and 0, 1%, 2%, 4%, and 10% (w/w) biochar were added by weight ratio to carry out an indoor potted experiment for planting Vetiveria zizanioides. The effects of biochar on soil pH and microbial activity, and the enrichment and transport of heavy metals by Vetiveria zizanioides were investigated to find out the correlations between the contents of heavy metal species, biochar and microbial activity, aiming to provide a theoretical reference for the combined remediation of heavy metal-contaminated soil in mining areas by biochar and Vetiveria zizanioides. The results showed that the addition of biochar increased soil pH, significantly increased the activities of soil FDA hydrolase, sucrase and urease, and significantly promoted soil basal respiration, but had no significant effect on soil microbial biomass carbon. The addition of biochar significantly increased the biomass of Vetiveria zizanioides, decreased the available state of Cu and Pb, while the changes of Cd species was opposite. The addition of high doses of biochar attenuated the enrichment of Cu in Vetiveria zizanioides, while the addition of biochar promoted the enrichment of Cd and Pb and attenuated the transport of Cu, Cd and Pb in Vetiveria zizanioides. So Vetiveria zizanioides could be used as a stabilized plant for Cu, Cd and Pb. Soil sucrase activity was significantly positively correlated with the contents of Cu, Cd and Pb in leaves, soil available state Cu and residual state Cu; soil basal respiration was significantly negatively correlated with the contents of Cu, Cd and Pb in leaves, available state Cu and available state Pb, while significantly positively correlated with available state Cd. In conclusion, biochar can reduce the toxic effect of heavy metals on the growth of Vetiveria zizanioides in mining soil and promote the enrichment of heavy metals by Vetiveria zizanioides, and the combination of both can improve the physicochemical properties and microbial activity of contaminated soil in copper mining areas. These findings are conducive to the remediation of heavy metal-contaminated soil and the improvement of soil quality.

Abstract:Soil enzymes activities are important indicators for ecosystem function, playing key roles in nutrient cycling. In this study, five different land use types in Min River estuary wetland, i.e. reed wetland, tidal flat, grassland, farmland and fallow, were selected to investigate the effects of land use changes and restoration on soil enzymes activities as well as their relationship with soil properties. Soil enzymes activities including β—Glucosidase, N—Acetyl—β—glucosaminidase, L—Leucine aminopeptidase and phosphatase were detected. Results showed that soil pH, NH₄⁺—N and NO₃^-—N contents were significantly higher in farmland than other land uses, while soil total carbon (C), nitrogen (N), and phosphorous (P) were significantly higher in fallow and reed wetland. Soil DOC, DON contents were significantly higher in fallow land, farmland and reed wetland than tidal flat and grassland. Soil microbial biomass carbon and nitrogen showed similar trend along different land uses with the highest in fallow land around 1 272 and 124 mg/kg, respectively. Soil enzymes activities showed similar pattern along different land uses, with the highest in fallow land, followed by reed wetland, farmland, grassland and tidal flat. Soil enzyme vector length ranged from 1.12~1.34, while all the vector angles were over 45°. Additionally, enzymatic eco-stoichiometric value was 1.00∶1.03∶1.33, indicating all the land uses were limited by phosphorus. Soil enzymes activities were significantly related with DOC, DON, microbial biomass C and N. These findings indicated that land use change from reed wetland to tidal flat significantly reduced soil nutrients, while fallow land increased soil microbial function, thereby providing alternative restoration strategy for wetland.