Abstract:Soil crust,which is an important factor affecting wind erosion,is widely distributed in arid and semi-arid regions.In this paper, taking the surface soils around the eastern mining area of the Junggar Basin as the object, wind tunnel test combined with soil wind erosion sensor were used to study the changes of soil wind erosion, sand flow structure and soil particle release under different soil crust and wind speed conditions by controlling soil crust cover rate and crust distribution. The results showed that:(1) Wind erosion increased significantly with the increase of wind speed and decreased significantly with the increase of soil crust cover rates.The wind erosion amount of uniform distribution was lower than that of centralized distribution. (2) The height of wind-sand flow increased with the increase of wind speed, and the collection at the height of 0~3 cm accounted for about 80% of the total. The wind speed of 14 m/s could make the soil saltation occur, and the soil skinning rate of 50% could effectively inhibit the saltation phenomenon of soil particles. (3) The number and energy of particle collision increased with the increase of wind speed and decreased with the increase of crust cover rates. The wind speed of the first particle collision increased with the increase of the crust cover rates; the number and energy of particle collision increased to the maximum value in the period when the wind speed continued to increase, and began to decrease after the wind speed was stable. It dropped to the stable value around 120 s, and then no obvious fluctuation occurred, and no particle collision occurred during the period when the wind speed was decreasing.

Abstract:In order to find out the difference of soil rill erodibility (K_r value) under different near-surface hydrological conditions in different spatial parts of gullies with different active degrees in dry-hot valleys of China, different active gullies were selected in Yuanmou County of Yunnan Province, and soil samples of different spatial parts (upstream catchment area, gully wall and gully bed) were collected, and the "V" type rill simulation scour device was used to carry out drainage scour experiment under three hydrological conditions (drainage, saturation and seepage), the flow rates were set as 150, 300, 450, 600, 750 and 900 mL/min. The results showed that: (1) In gully development area of dry-hot valley, the content of soil sand was significantly higher than that of silt and clay, accounting for more than 50%, and the content of soil organic matter (SOM) and total nitrogen (TN) was relatively low. (2) There were significant differences in mechanical composition and organic matter content among gullies with different active degrees, as the gully stability increased, the soil sand content gradually decreased, while the content of silt, clay, SOM and TN increased. (3) Under different near-surface hydrological conditions, as the gully stability increased, the soil rill erodibility (K_r value, s/m) of gully decreased, which followed the order of K_r (active type) > K_r (semi-stable type) > K_r (stable type). In addition, an obvious difference in soil critical shear force (τ_c, Pa) appeared in gullies with different activity degrees, while no obvious change tendency could be found. (4) Significant differences in K_r values could be found in the different parts of gully, which followed the order of K_r (upstream catchment area) < K_r (gully wall) < K_r (gully bed). (5) With the change of near-surface hydrological conditions from drainage state to saturation and seepage state, values of K_r in the different spatial parts of gully increased significantly. In conclusion, gully activity (vegetation restoration condition), near-surface hydrological condition, soil particle size fraction and content of SOM could obviously affected soil erodibility in the gully developed areas of dry-hot valley.

Abstract:To study the effect of soil translocation by different upslope tillage intensities on water erosion, we took the slope runoff plot in the Dry-hot Valley of Jinsha River as the research object. A series of scouring experiments were conducted in three runoff plots (2 m×10 m) with three slope gradients (5°, 10°, 15°) and a fixed flow discharge of 0.6 m²/h. Three soil depths (0.05 m, 0.10 m, 0.20 m) were set on the downslope positions of the 10° slope representing the soil loss by continuous tillage for 80, 69 and 46 years respectively. Runoff and sediment were collected at the outlet of runoff plot to examine the effect of different tillage intensities and gradients on runoff rate, runoff amount, detachment rate and total sediment yield. The main results showed that: (1) The more intensive tillage was, the more easily runoff in the 10° slope. The runoff rate, runoff amount, detachment rate and sediment yield increased with the increasing tillage intensities: 46 years < 69 years < 80 years, suggesting that soil translocation caused by long-term upslope tillage accelerated water erosion. (2) The runoff started time after the initiation of the scouring decreased with the increasing slope gradients on the 69 years slopes. In the experimented slope range, the runoff rate, runoff amount, detachment rate and sediment yield were as follow: 5° < 10° < 15°, showing that the increase of slopes further promoted water erosion. (3) A positively exponential correlation was found between runoff rates and detachment rates. The increase of tillage intensities enhanced the exponential growth, but the increase of slope gradients weakened the exponential relationship of water and sediment. These results provide references for revealing the affecting mechanism of long-term upslope tillage intensity and slope gradient on water erosion in the dry-hot valley region.

Abstract:Rice-wheat rotation is a typical intensive cropping system for food production with application of huge amounts of chemical fertilizers in the Tai Lake Basin and the control of nitrogen and phosphorus runoff losses is widely concerned. In this paper, the effects of two different fertilization modes including farmer practice (FP) and optimized control fertilization (CM)on crop yield and partial productivity of nitrogen and phosphorus fertilizers were investigated with a large-area field comparison experiment. Meanwhile, the characteristics of nitrogen and phosphorus forms in runoff water and the differences of nitrogen and phosphorus runoff losses were explored.The results showed that rice or wheat above-ground total biomass, grain yield, nutrient (nitrogen, phosphorus and potassium) contents and accumulation in plant ground parts of CM mode were not significantly (P>0.05) different from those of FP mode. The rice or wheat grain partial productivity of nitrogen fertilizer of CM mode was significantly (P<0.05) greater than that of FP mode, the same results was found for phosphate fertilizer. The concentrations of all nitrogen and phosphorus forms in runoff water of CM mode during rice and wheat growth seasons were lower than those of FP mode, even significantly (P<0.05). In the rice or wheat growth season and the whole rotation period, the cumulative losses of total nitrogen or total phosphorus of CM mode were significantly (P<0.05) less than that of FP mode. Optimized control fertilization mode could not only maintain the grain yield of rice and wheat, but also significantly reduce the runoff losses of nitrogen and phosphorus in the rice-wheat rotation system, which could be promoted and utilized in actual agricultural production.

Abstract:In order to study the production flow and nitrogen and phosphorus migration of forestland in the upstream of water source, the artificial simulated secondary rainfall test method was adopted to select Pinus densiflora forest and barren grassland in the upstream of Tai’an City Huangqian reservoir in the mountain area of south central in Shandong province as the research objects to study the characteristics of surface runoff and subsurface runoff and nitrogen and phosphorus loss. The results indicate that:(1)Under the condition of secondary rainfall, the surface runoff of Pinus densiflora forest is less than that of barren grassland. The subsurface runoff of barren grassland is less than that of Pinus densiflora forest. Soil infiltration of Pinus densiflora forest and barren grassland is proportion to vegetation coverage. The characteristics of surface runoff are small in the early stage, with the progress of rainfall, the runoff of Pinus densiflora forest and barren grassland is increasing and beconing stable, the subsurface runoff is later than the surface runoff, and the runoff is relatively stable.(2)Under the condition of secondary rainfall, the total nitrogen (TN) loss of surface runoff presented a higher output concentration in the initial stage. With the progress of rainfall, the output concentration decreased and gradually tended to be stable. TN loss is proportional to the loss concentration. The loss of TN in surface runoff and subsurface runoff in Pinus densiflora forest is lower than that in barren grassland. The TN loss of surface runoff in Pinus densiflora forest is less than that in barren grassland. The interflow presents a relatively stable state. The TN loss in the interflow of Pinus densiflora forest is less than that in barren grassland.(3)Under the condition of secondary rainfall, the total phosphorus (TP) output concentration of surface runoff in Pinus densiflora forest is positively proportional to the loss. The amount of surface runoff and subsurface runoff TP loss in Pinus densiflora forest is lower than that in barren grassland. The total amount of surface runoff TP loss in Pinus densiflora forest was lower than that in barren grassland, and the total amount of interflow TP loss in Pinus densiflora forest is lower than that in barren grassland.(4)The total loss of TN and TP in Pinus densiflora forest and barren grassland is less than that in the secondary rainfall. The total loss of TN is 1.11 times of the previous rainfall. The total loss of TP was 1.15 times of the previous rainfall. At the same time, the loss of TN and TP in Pinus densiflora forest is less than that in the barren grassland. Therefore, compared with the barren grassland, Pinus densiflora forest has a better role in regulating the loss of nitrogen and phosphorus.

Abstract:The method of artificial rainfall simulation was applied to study the effects of different slope gradients (5°, 8°, 15° and 25°) and rainfall intensities (1.0, 1.5, 2.0 and 2.5 mm/min) on the characteristics of soil erosion on the weathered granite slope land of South China. The results showed that both the runoff volume and runoff rate increased with the increasing rainfall intensity, but decreased with the increasing slope gradient. The runoff infiltration rate was significantly positively related to slope gradient (r=0.660, p<0.01)and exhibited three different stages with rainfall duration, including the initial all-infiltrated stage, rapid decreasing stage and the relatively stable stage. However, the effect of rainfall intensity on runoff yield was more obvious than that of slope gradient. There was a significantly positive correlation between the average sediment concentration and slope gradient(r=0.694, p<0.01). The relationship between rainfall intensity and average sediment concentration depended on the conditions of slope gradient. The soil erosion rate, which overall was positively related to slope gradient and rainfall intensity(r>0.580, p<0.05), showed a trend of increasing first and then decreasing with the prolongation of rainfall duration. The soil erosion rate and runoff rate showed a positive linear correlation (R²>0.861) on the steep slopes and a power function relationship (R²>0.966) on the gentle slopes. A revised typical soil loss equation model was used to predict the erosion rate, and it was found that the change trend of the simulated values was close to the actual measured values, which indicated that the revised model had certain applicability in the study area. These results could provide data support for the study of soil erosion rate in the weathered granite area, and had important significances for further understanding of soil erosion process.

Abstract:The sloping farmland in the Loess Plateau accounts for 75% of the total cultivated land area in the region, resulting in serious soil erosion. It is of great significance for agricultural production and ecological environment construction to control the soil erosion of sloping farmland. Soybean is an important crop on sloping farmland in the Loess Plateau. However, at present,the ability of soybean to regulate runoff and sediment in this area needs further study. Taking the sloping farmland with soybean as the research object, and the ability of soybean to regulate runoff and sediment under different slopes and rainfall intensities were studied. The experimental design included five growth stages of soybean (seedling stage, initial flowering stage, full flowering stage, pod-forming stage and granulation stage), five slope gradients (3°, 5°, 10°, 15° and 20°), and two rainfall intensities(40 and 80 mm/h). The effect of soybean on regulating runoff and sediment was divided into two parts, which were reducing runoff and reducing sediment yield. Comprehensive comparative analysis was carried out using six indicators, which were runoff time, initial rainfall loss, runoff, sediment yield, reduced flow benefit (RRB) and sediment reduction benefit (SRB). The results showed that soybe an played an important role in regulating runoff and sediment. Compared with bare land, the runoff of the slope decreased by 10.75%~64.94% and the sediment yield decreased by 15.38%~84.24% from the seedling stage to the granulation stage. The RRB and SRB of soybean showed an overall increasing trend from the whole growth period, and they were inversely proportional to the slope. Similarly, with the increasing of rainfall intensity, the RRB and SRB of soybean decreased slightly and the difference was not significant, and the SRB value was always greater than RRB value, so it was found that soybean was more effective in reducing sediment than in reducing runoff. In summary, planting soybean on sloping farmland in the Loess Plateau had a positive effect on control soil erosion of sloping farmland, and the interception effect on sediment was stronger than the interception of runoff.

Abstract:In this paper, the characteristics of runoff and sediment yield of two-dimensional plane and three-dimensional cone-shaped slopes under different gravel contents were studied through the indoor simulated rainfall test.The results showed that: (1) The slope velocity and runoff rate per unit area showed a trend of "rapid increase, slow increase and stable fluctuation" with the runoff time. (2) The average flow velocity and average runoff rate per unit area decreased with the increase of gravel contents.When the gravel content was the same, the velocity and runoff rate of two-dimensional plane slope were larger than those of three-dimensional cone slope. (3) The denudation rate of two-dimensional plane slope presented a change process of "stable, decreasing and stable fluctuation" with the runoff time. The denudation rate of three-dimensional cone-shaped slope presented a process of "augmented, stable fluctuation". (4)The amount of erosion per unit area increased first and then decreased with the increase of gravel contents. With the same gravel content, the erosion amount of two-dimensional plane slope was larger than that of three-dimensional cone slope.

Abstract:In order to clarify the influence of gravel content on runoff and sediment yield characteristics of lime-soil engineering deposit slope in Karst area, the runoff characteristics and erosion characteristics of lime-soil slope with meta-soil (30%) and meta-gravel (70%) under incremental rainfall (0.5, 1.0, 2.0, 2.5 and 3.0 mm/min) were studied by indoor simulated rainfall test method. The results showed that: (1) With the increasing of rainfall intensity, the runoff rate of each slope showed a stable growth fluctuation trend, and the runoff rate of soil slope was less than that of two kinds of gravel slope, and the runoff yield of partial soil and partial stone slope was 0.49 times and 0.37 times higher than that of soil slope. (2) Under the rainfall intensity of 1.0~3.0 mm/min, runoff rate of each slope fluctuated in the range of 0.16~5.4 g/(m²·s), which showed a trend of steady-fluctuation increase. The change range of erosion rate of partial soil slope and partial stone slope was 0.16~5.4 g/(m²·s) and 0.06~0.74 g/(m²·s), respectively. The former had a large range of variation and strong fluctuation, while the latter had a small and stable range. With the increasing of gravel content, the erosion amount of each slope increased first and then decreased. The erosion amount of partial soil slope was 2.5 times higher than that of soil slope, while the erosion rate of partial stone slope was 0.9 times lower than that of soil slope.(3) The erosion rate of soil, partial soil and partial stone slope was positively correlated with the runoff rate, which was power function, linear function and linear function, respectively. The results could provide a scientific basis for soil and water control of abandoned slag field in Karst area of Northwest Guangxi.

Abstract:The integrated stereo measurement of the sky and earth with UAV as the main body provides favorable conditions for the accurate and rapid measurement of the earth’s surface.When the UAV takes an orthophoto, the steep slope affects the shooting angle, which may affect the accuracy of the three-dimensional measurement of the surface.In this study,three typical farmland gullies,which were active gully (BG),stable gully (MG) and ephemeral gully (SG), were chosen to investigate the effect gully bank slope gradients on SfM-DSM error. The surface DSM (digital surface model) was obtained by using three-dimensional laser scanning (TLS) and structure from motion (SfM) methods. The elevation error of slope to the DSM of SfM was analyzed based on the DSM of TLS. The results show that: (1) The elevation error increased exponentially with the slope of gully wall, and the fitting degree was good (P value was less than 0.000 1, R² was greater than 0.80). The inflection point appeared near 60°, when the slope was less than 60°, the variation range of elevation error was 0~10 cm, and when the slope was more than 60°, the elevation error increased sharply to 10~60 cm. (2)The more active the gully was, the larger the slope ratio was, and the higher the proportion of elevation error was concentrated in the range of larger slope. For the developing gully of BG, about 75% of the elevation error was concentrated between 15° and 75°.For the stable gully of MG, about 66% of the elevation error was concentrated between 0 and 60°. For the ephemeral gully of SG, about 54% of the elevation error was concentrated between 0 and 40°.

Abstract:Corn stem flow is the amount of water flowing along the stalk to the root after intercepted by the corn canopy during rainfall. It is an important component of surface runoff on the slope and has an important effect on the soil erosion process at the root of the plant. In this paper, artificial rainfall simulation method was used to study the effect of corn stem flow on soil erosion in sloping field. The test soil trough was 0.40 m long, 0.23 m wide, and 0.14 m deep. A PVC pipe with a diameter of 2 cm was used to simulate the corn stalk at the maturity stage and the height was 1.2 m. The simulated stem flow was 5, 10 and 15 g/s, with the same rainfall under the conditions, the stalk-free sloping land was used as a control measure. The rainfall intensity was 60, 90, 120 mm/h, the rainfall lasted 108 minutes, and the slope was 10°. The results showed that: (1) Compared with the control measures, the stem flow has the effect of accelerating sloping surface runoff. (2) The surface runoff and sediment yield under simulated stem flow were higher than the control, compared with no stem flow slope, under three rainfall intensities, the contribution rate of runoff from the three stems was 14.90%~43.10%, and the contribution rate of sand production was between 12.47% and 26.75%. (3) The stem flow formed a small surface around the stem, and the currents caused the soil erosion process to change from surface erosion to gully erosion, thereby increased the slope soil erosion amout. Therefore, the soil erosion of stem flow should be considered in the calculation and evaluation of soil erosion on slope farmland.

Abstract:Sloping ridge-tillage is one of the most common ridge-tillage methods in Chinese Mollisol region. However, there are few studies related to the effects of sloping ridge-tillage on hillslope soil erosion. Thus, the indoor simulated rainfall experiments were conducted under 50 and 100 mm/h rainfall intensities with a typical slope of 5 degree (transforming from longitudinal ridge-tillage to contourridge-tillage) to analyze the differences in hillslope soil erosion between sloping ridge-tillage and longitudinal ridge-tillage system in Chinese Mollisol region. The results showed that: (1) Under 50 and 100 mm/h rainfall intensities, the erosion rates in sloping ridge-tillage before ridge failure were only 0.46% and 0.35% of the longitudinal ridge-tillage, respectively. However, during the 45-minute rainfall, once the ridge was failed, the erosion rates in sloping ridge-tillage were 1.24 and 1.03 times higher than that in longitudinal ridge-tillage under 50 and 100 mm/h rainfall intensities, respectively. (2) Both runoff and erosion rates suddenly changed with the rainfall time after ridge failure in sloping ridge-tillage system. Before ridge failure in sloping ridge-tillage system, both runoff and erosion rates were lower than those in longitudinal ridge-tillage under 50 and 100 mm/h rainfall intensities. The average runoff rate in sloping ridge-tillage were only 8.42% and 3.75% of that in longitudinal ridge-tillage under the two rainfall intensities, respectively; and the average erosion rates in the former were 0.46% and 0.35% of those in the latter,respectively.After ridge failure in sloping ridge-tillage system, the average runoff rate were 1.33 and 1.47 times higher than those in longitudinal ridge system, the average erosion rates in the former were 2.03 and 1.62 times higher than those in the later under 50 and 100 mm/h rainfall intensities, respectively.(3) Under the two rainfall intensities, there was a extremely significant linear relationship between runoff and erosion amount in sloping ridge-tillage (P<0.01), while the correlation was not significant after ridge failure (P>0.05). There was a extremely significant linear relationship between runoff and erosion amount in longitudinal ridge-tillage. (4) Under the two rainfall intensities, more than 90% of runoff and sediment generated after ridge failure in sloping ridge-tillage system. Therefore, the key approach for controlling soil erosion in sloping gridge-tillage is to improve the ridge stability and to prevent the ridge failure.

Abstract:Serious soil erosion exists in the Three Gorges Reservoir area. The comprehensive control of soil and water conservation is the key measure for decreasing the sediment which flow into the Three Gorges Reservoir and improving the comprehensive benefit of the Three Gorges project.Effective identification of the small watershed (priority watershed) with serious soil erosion is the basis for improving the efficiency of fund utilization and scientific decision-making. In this study, Hechuan district in Chongqing was selected as a test area. The regional soil erosion was assessed. The priority watershed was then identified by soil loss area method, landuse-soil loss area method, and slope-soil loss area method. The parameters including the average soil loss area percentage, the percentage of different landuse and average slope degree were used to assess the priority watershed. The results showed that the average soil loss area percentage of priority watershed from slope-soil loss area method was close to those from soil loss area method. However, the priority watersheds with high slope gradient, greater area percentage of crop land, orchard land and mining land were also identified in the slope-soil loss area method. It indicates that the slope-soil loss area method was the best method for identifying priority watershed. The results could serve as the comprehensive soil and water conservation of small watersheds.

Abstract:Artificial shrub-grass composite vegetation is the main vegetation type of restoration and reconstruction in the Loess Plateau, which plays an important role in soil and water conservation in this region.As a case study in the Anding district of Dingxiin Gansu Province, the water and soil conservation function of the artificial shrub-grassland ecosystem was quantitatively evaluated based on InVEST model,and the results would provide decision support for ecological restoration and sustainable utilization of water and soil resources in the hilly region of the Loess Plateau.The assessment results were as follows (1) the water conservation amount per unit area of artificial shrub-grassland was 369.25 m³/hm², which was 90.5% of grassland, 134% of forest and 110% of cultivated land. The total water conservation amount of Anding district was 3 970.99×10⁴m³, and artificial shrub- grassland accounted for 29.9% of the total water conservation in this area. (2) Nitrogen retention per unit area of shrub-grass land was 2.4 kg/hm², the purification rate was 72.21%, and the phosphorus retention of artificial shrub-grassland was 0.12 kg/hm², the purification rate was 71.07%. (3) The amount of soil conservation per unit area of artificial shrub-grassland was 308.76 t/hm², which were 1.88 times,1.44 times and 6.01 times higher than that of grassland, forestand cultivated land, respectively.The total soil conservation amount was 3 310.21×10⁴ t of Anding district, and artificial shrub-grassland accounted for 54.82% of the total soil conservation. The results showed that the water conservation capacity of artificial shrub-grassland was just lower than that of grassland,but higher than that of other land types,but the soil conservation capacity was the strongest in the six land types. Therefore, artificial shrub-grassland had better soil and water conservation function, which was the suitable vegetation type and land use mode in hilly region of the Loess Plateau.

Abstract:The rapid development of urban scale is the key factor that causes urban soil erosion. Taking Xi’an as the research area, the soil erosion area of each district and county was calculated and the intensity grade was divided, the spatial distribution characteristics of soil erosion were analyzed and predicted, and the areas requiring key supervision were identified. The results showed that the annual average amount of soil erosion in Xi’an was 2.784 9 million tons, the annual average soil erosion modulus was 176.74 t/(km²·a), the total area of micro-erosion and light erosion was 99.76%, and the area above moderate erosion was only 0.24%. Under the future scenario, the soil erosion modulus in Xi’an are mainly distributed in 0 to 200 t/(km²·a), of which the soil erosion area of the built-up area and the development area is 65.37 and 302.19 km² respectively;The spatial control and key areas of soil erosion are mainly distributed in Gaoling District, Huyi District, Chang’an District, and Lintong District. With the improvement of urban construction and development, the area of Xi’an key management and control area is also changing.

Abstract:Based on the measured runoff and sediment data of six hydrologic stations (Pingshan, Zhutuo, Cuntan, Yichang, Hankou and Datong) situated at Yangtze River’s main stream, this study analyzed the inter- and intra- annual variation trends of runoff and sediment during 2001-2018 and their causes using statistical methods including linear regression, Mann-Kendall test, Sen’s estimation and accumulative anomaly. The results showed that since 2000, the annual sediment discharge of each hydrologic station significantly declined compared with that before 2000, with the decreasing amplitude higher than 56%, while annual runoff decreased insignificantly with the decreasing amplitude lower than 8%. The variability of sediment discharge was higher than that of runoff. For the Yangtze River basin, from 2001 to 2018, the average monthly runoff and sediment discharge was 718×10⁸ m³ and 1 247×10⁴ t, respectively, and mainly distributed between June and September. The trend analysis indicated that annual precipitation and runoff had no remarkable changes, however, annual sediment discharge showed a significantly decreasing trend. The change-points for Pingshan, Zhutuo and Cuntan station were in 2010 and 2012, and those for Yichang, Hankou, and Datong station were in 2005. Monthly runoff for Pingshan station had no obvious trends; for Datong station, runoff only increased significantly in January, that of the other four stations increased significantly between January and April. Monthly sediment discharge from June to October for the six stations showed significant decreasing trends. In this study, human activities such as water conservancy construction and soil and water conservation were the primary causes of sediment reduction in the Yangtze River basin.

Abstract:As a main component of terrestrial ecosystem, vegetation has a profound impact on ecological structure and function. The study of spatiotemporal variation of vegetation and its relationship with climatic factors are beneficial to understand pattern, process and function of ecosystem, and provide important references for ecological protection and construction.Based on MODIS13Q1 NDVI data set during 2000-2016, combined with the precipitation and average temperature data of 14 meteorological stations in and around basin, this paper used the trend analysis method, mutation test, IDW spatial interpolation method, partial correlation analysis and R/S analysis method, analyzed NDVI temporal and spatial dynamic characteristics and the relationship with climate factors for a total of 17 years in Qinghai Lake Basin.The results showed that:(1) NDVI in Qinghai Lake Basin generally showed an upward trend, with significant and extremely significant improvement areas accounting for 40.18% of the total area during 2000 to 2016. (2) NDVI was positively correlated with the annual precipitation and average temperature, but was not significantly correlated in most areas. The correlation between NDVI and annual precipitation was higher than annual average temperature. (3) The future evolution of NDVI in the basin was mostly random, accounting for 65.07%, and the area from improvement to degradation accounted for 26.73%, mostly distributed in the permafrost area in the county of Tianjun located in watersheds upstream. The climate in Qinghai Lake Basin is developing towards warm and humid,in addition, the implementation of ecological construction project, NDVI in the basin overall has been improved from 2000 to 2016. Due to the typicality and particularity of the Tibet Plateau, the future trend of vegetation still has randomness and heterogeneity.

Abstract:Studying on the impacts of climate change and anthropogenic activities on runoff at the watershed scale is the basis for watershed management planning and achieving sustainable management of river basins.Xinshui river watershed, a typical watershed in the Loess Plateau, was selected as the study area. The M-K test method was used to analyze the trends of annual evapotranspiration, precipitation and runoff from 1958 to 2015. The double mass curve method was carried out to identify the abrupt point. Ecological hydrological analysis method and water balance principle were conducted to quantify the respective contribution of climate change and human activities on annual runoff. The annual runoff showed a significant decrease trend (Z=-5.84, p<0.000 1), however,nonsignificant trends were detected for precipitation (Z=-0.72, p=0.31) and potential evapotranspiration (Z=-0.5, p= 0.88). The muttionpoints of annual runoff were 1974 and 2000, respectively. Compared with the baseline period, the runoff reduction from 1975 to 2000 was mainly attributed to climate change. The contribution rate of climate change to runoff reduction was 73.14%, whereas the contribution rate of land use change was 26.86%. Contrarily, the runoff reduction from 2001 to 2015 was mainly ascribed to land use change. The contribution rate of land use change for runoff reduction was 103.81%,which indicated that land use change has become the main driving factor for the runoff variation in the Xinshui river watershed. It is necessary to develop land use plans rationally for realizing the coordinated development of water and soil resources in the Xinshui River Basin for river basin management in the future.

Abstract:Accurately predicting farmland surface runoff is the basis of controlling agricultural non-point source pollution. According to the motion characteristics of rainfall and surface runoff, coupled with the Green-Ampt model, the apparent function of cumulative infiltration, the Kinematic wave model and the steady-state sediment yield model, an approximate semi-analytical model for slope runoff and sediment yield under rainfall conditions was established. The model approximated the Kinematic wave equation through linear expression of the relationship between the infiltration rate and the water depth. By setting the simulated rainfall test under five different rain intensities between 30~90 mm/h, the model parameters were derived and the model accuracy was verified, and the sensitivity of the model parameters were analyzed. The results showed that: (1) The calculated value of runoff and sediment model was in good agreement with the measured value, and the model was more suitable for simulating the runoff and sediment yield process under 60 mm/h rainfall intensity, and the Manning's roughness coefficient distributed between 0.000 26~0.000 29 min/cm^1/3, and the relationship between the infiltration rate parameter c and the rain intensities could be described by an exponential function c=9×10^-4p^-0.644. The parameters a and b in the sediment yield model distributed between 0.13~0.15 and 0.10~0.12, respectively. Due to the accidental factors of sediment yield, the model simulation accuracy of the sediment yield process was lower than that of the runoff process. When the value of c was 0~0.05, the value of Dif changed little, it indicated that the soil surface runoff was not sensitive to c. In the process of runoff sediment yield, the value of Dif varied with the change of parameters a and b. Overall, runoff sediment yield was more sensitive to the runoff erosion coefficient parameter a than the parameter raindrop erosion coefficient b.

Abstract:Herbal buffer zone can effectively intercept pollutants such as sediment, total nitrogen, total phosphorus and other pollutants on slope, which is one of the main measures to prevent and control agricultural non-point source pollution. The surface runoff was simulated by artificial water distribution, and the effects of different runoff on interception capacity of herbaceous buffer zone were studied. The results showed that the herbal buffer had a certain reduction effect on pollutants. The herbal buffer had the best effect on sediment reduction and the worst effect on total phosphorus reduction. White clover had a stronger ability to reduce pollutants than ryegrass. Runoff had a greater impact on the reduction rate of total nitrogen and total phosphorus in herbal buffer zone, but a little impact on sediment reduction rate. When the flow rate increased from 0.08 L/s to 0.24 L/s, the reduction rate of total nitrogen and total phosphorus in herbal buffer zone decreased to 9% and 6%, while the sediment reduction rate was 34%. With the increasing of discharge scouring time, the concentration of total nitrogen, total phosphorus and sediment in the outflow decreased and gradually reached a stable level. When the flow rate increased to 0.24 L/s, the concentration range of total nitrogen and total phosphorus were 11.5~24.7 and 1.6~2.3 mg/L, respectively. There was no significant difference in sediment concentration under different flow rates. In this study, the removal of total nitrogen and total phosphorus by herbal buffer zone was greatly affected by the flow rate, and the buffer zone had no removal effect on total nitrogen and total phosphorus at large flow rate, but the removal of sediment by buffer zone was less affected by the flow.

Abstract:To study the effects of land use and agricultural management on non-point source nitrogen pollution in the watershed,Dan River watershed which is an important water source in the middle route of South-to-North Water Diversion project was selected as study area in this research, SWAT model was applied to simulate the nitrate nitrogen and ammonia nitrogen loads in the watershed, and quantify the contribution of land-use change and fertilization and irrigation measures on the nitrogen pollution loads of the river. The results indicated that:(1) The nitrogen pollution changed in different seasons, the most serious nitrogen pollution was from July to September, with the output of nitrate nitrogen and ammonia nitrogen loads of 734.32, 735.36 t, respectively (total accounting for more than 50% of the nitrate nitrogen and ammonia nitrogen load); (2) The nitrate nitrogen and ammonia nitrogen loads had large spatial difference, and the pollution increased from the upstream to the downstream. The sub-watershed with high nitrogen pollution load were mainly distributed in Danfeng and Shangnan counties; (3) The situational analysis indicated that when the farmland with slope greater than 15° and 25° in the basin was converted to forest, the nitrate nitrogen and ammonia nitrogen load in the basin decreased by 59.83% and 45.89%, respectively, and the ammonia load decreased by 48.91% and 35.78%, respectively. Both of fertilizer application and irrigation decreased by 20%, nitrate nitrogen load would decrease by 3.63% and 13.26%, and ammonia nitrogen load would decrease by 0.12% and 15.65%, respectively; (4) Cultivated land is the main source of nitrogen pollution in river basin, reducing the amount of fertilizer,irrigation and vegetation restoration in sloping cropland is the key to control non-point source nitrogen pollution in the watershed.

Abstract:Agricultural plastic film residual (PFR) increase quickly with the development of mulching cultivation, and have a strong impact on soil water movement. In order to study the influence of PFR on water flow movement mechanism, the experiment was carried out in water saving experiment station of Jiuzhuang, Hetao irrigation area. There were six treatments, including three PFR amounts(0, 300,600 kg/hm²) and two water infiltration amounts (20, 80 mm). The influence of different PFR amounts on soil physical properties was studied, the effects of different PFR amounts and different infiltration amounts on soil water flow was analyzed based on dye tracing method, and the preferential flow characteristics for each treatments were evaluated. The results showed that soil bulk density, saturated water conductivity, and initial soil moisture content showed a decreasing trend with the increase of PFR amount, while an increasing trend for soil porosity. The random distribution of residual film in soil lead to higher variation coefficient of each physical parameter of PFR treatment. The development degree of soil preferential flow increased with the increase of PFR amount and infiltration amount. The maximum dyeing depth (M_DSD) and the coefficient of variation of soil staining profile (Cv) of 300, 600 kg/hm² PFR treatment increased with the increase of PFR amount.Compared with 20 mm infiltration, the M_DSD and Cv for PFR treatment at 80 mm infiltration increased by 47.23% and 27.34%, respectively. In addition, the characteristic index of preferential flow of different treatments was significantly different. Five characteristic preferential flow indexes (dyeing area, uniform flow depth, preferential flow ratio, length index, and coefficient of variation) revealed that the preferential flow of 300, 600 kg/hm² PFR treatment was higher than that of 0 kg/hm² treatment. It can be seen that the increase of residual film amount and infiltration amount will increase the occurrence probability and strength of soil preferential flow.

Abstract:By measuring the saturated hydraulic conductivity, mechanical composition, bulk density, non-capillary porosity, capillary porosity, total porosity, organic carbon content and other soil properties of Karst shallow fissure soil (0—10, 10—20, 20—30, 30—50, 50—70, 70—100 cm), the permeability characteristics and influencing factors of various soil layers in Karst shallow fissures were studied. The results showed that: (1) Soil properties in Karst shallow fissures showed an increase or decrease trend with the change of soil depth, in which the bulk density, clay content and capillary porosity increased with the change of soil depth, while the change trends of the saturated hydraulic conductivity, organic carbon and non-capillary porosity with the depth of the soil layer were opposite. (2) The variation coefficient of soil saturated hydraulic conductivity was higher than that in non-Karst area, and it showed an volatility growth trend with the change of soil layer. At the same time, the trend of decreasing with the depth of soil layer could be simulated by logarithmic function (R²=0.946 2). (3) Pearson correlation analysis showed that the saturated hydraulic conductivity of the soil in the fissures was significantly related to the clay content and silt content in the mechanical composition (P<0.05), but was not related to the sand content (P>0.05), and was significantly related to other soil properties (P<0.01), and the non-capillary porosity had the highest correlation (P=0.898). Non-capillary pore of shallow fissured soil was the main factor affected its permeability, and deep fissured soil had more capillary pore which was good at storing water needed by plants. Therefore, in Karst areas which is lack of land resources, it will be the research focus in the future to make full and rational use of water distribution in deep soil of fissures. The results of this study could provide scientific basis for water transport, rocky desertification control and vegetation restoration in Karst areas.

Abstract:There are enormous differences in natural geographical environment and soil physciochemical properties in different regions of the water erosion zone in China, which may cause differences in soil detachment capacity (D_c). However,little research has paid attention to the spatial distribution of D_c and its influencing factors at large scale (such as the water erosion region). In this study, 36 sampling sites were selected in the water erosion zone according to the soil types and soil texture. D_c was measured by disturbing soils (representing freshly tilled sloping farmland) and the influencing factors were analyzed. The results showed that D_c of Aqui-Sandic Primosols was the largest, while that of Argi-Udic Ferrosols was the smallest, and D_c exhibited a strong spatial variation in the water erosion zone. The northwest Loess Plateau and the South Hilly Area had the largest D_c. The soil texture with moderate content of clay and sand had the largest D_c. There was no significant difference between shear stress and stream power in simulating D_c. D_c had a significant negative correlation with silt content, particle size parameter, cation exchange capacity and soil organic matter, and a significant positive correlation with sand content, median soil grain size, geometric mean particle diameter, and exchangeable sodium percentage. D_c in water erosion area could be well simulated by shear stress, silt content, cation exchange capacity and soil organic matter (R²=0.71, NSE=0.71).

Abstract:Soil shearing strength can not only evaluate the sensitivity of soil erosion, but also is an important parameter to reflect the tillage performance of cultivated-layer. There are some differences in soil shearing strength indexes under different shearing modes. In this paper, the soil of purple soil sloping farmland was taken as the research object, the laboratory triaxial and direct shearing test method were used to study the bulk density and water content on remolded purple soil. The effect on shearing strength of the cultivated-layer soil was analyzed, and the differences between the two test methods were analyzed. The results showed that: (1) The soil cohesion (c) of the purple soil sloping farmland increased with the increasing of the bulk densities(ρ_d) and decreased with the increasing of water contents (w). The maximum cohesive forces of the triaxial and direct shearing tests were 32.33 and 21.78 kPa respectively, both of which occurred under bulk density of 1.4 g/cm³ and water content of 10%. The internal friction angle (φ) of the cultivated-layer increased with the increasing of the bulk densities and decreased with the increasing of the water contents. The maximum internal friction angles of the triaxial and direct shearing tests were 22.67° and 29.11° respectively, under bulk density of 1.4 g/cm³ and water content of 10%. (2) Under the same confining pressure, the maximum principal stress difference of the cultivated-layer soil increased with the increasing of the bulk densities, and decreased with the increasing of water contents. Under the same bulk density and water content, the maximum principal stress difference of the cultivated-layer soil increased with the confining pressure. (3) The interaction of soil bulk density and water content in the cultivated-layer had a significant effect on cohesion and internal friction angle(P<0.05). The optimum soil bulk density—water content condition for the shear strength of the soil in sloping farmland was 1.4 g/cm³—10%.(4) Different shearing modes affected the shearing strength index of the soil. The soil cohesion of the cultivated-layer was greater or closer to the direct shearing test under the triaxial test conditions, while the soil internal friction angle was significantly lower than the direct shearing test result. This was mainly related to the difference between the two shearing test principles.

Abstract:Aiming at the instability of the collapsing gully wall under the influence of dry-wet cycling, we studied the change rule of the tensile strength of the collapsing soil under the different dry and wet cycles in Tongcheng area of Hubei Province through the indoor uniaxial tensile test. The results showed that the tensile strength of the collapsing soil gradually decreased with the increasing of the number of dry-wet cycles, and finally tended to be stable, and the attenuation of tensile strength of different layers of soil mainly concentrated on the first three dry-wet cycles.The attenuation ratio of tensile strength of topsoil, laterite, transition layer and sandy soil layer reached 90%, 82%, 83% and 90%, respectively, and the tensile strength of different layers of soil followed the order of transition layer > laterite layer > topsoil layer > sandy layer. By considering the influence of the depth of different layers and the number of dry-wet cycles, the prediction model of tensile strength attenuation was established, and the prediction value of tensile strength model had a high correlation with the measured value (R²=0.97). The model had guiding significance for the study of the attenuation mechanism of tensile strength of different layers of soil.

Abstract:Surface soil water content can sensitively reflect the changes of rainfall, temperature, erosion and other environmental factors. It can provide reference for agricultural production and evaluation of soil environmental effect to clarify the temporal and spatial variation characteristics of surface soil water content. In this study, the surface soil water content of 0-5 cm soil was continuously monitored from November 2016 to April 2018 on the eroded slopes with different soil organic carbon levels in the loess hilly region. And based on the precipitation data, the variation characteristics of surface soil water content in the sedimentary area, erosion area and control area of erosion slope with different soil organic carbon levels were analyzed. The results showed that: (1) The variation of surface soil water content was significant among different seasons, with the largest variation in summer. The maximum daily variation was 14.3% in summer, and the maximum daily variations in spring, autumn and winter were all less than 8.0%. In other words, summer was the sensitive period of soil water change.(2) The influence of soil organic carbon level, slope area and soil temperature on the variation of surface soil water content varied with seasons. (3) Soil erosion intensified the variation of surface soil water content on the slope, and the variation degree followed the order: sedimentary area > erosion area > control (non-erosion) area. With the increasing of soil organic carbon level, the difference of variation of surface soil water content before and after erosion in erosion area and that in sedimentary area increased from 0.85% to 9.81%.(4) The spatial-temporal heterogeneity of the surface soil water content on eroded slope showed a non-linear trend with the increasing of soil organic carbon level.

Abstract:The spatio temporal variation characteristics of groundwater depth and the inflow of river and its ecological effect were studied based on the monitoring of hydrological and ecological parameters in the main stream area of Tarim River in recent 20 years.The results showed that the annual variation of ground water depth in the upper and middle reaches of the main Tarim River was 0.42~0.92 m in the dry season from March to April, and 1.06~3.67 m in the flood season from July to September. After nearly 20 years of ecological water conveyance, the groundwater depth in the downstream section had increased by 3.75 m during 2009-2017. The depth of groundwater varied significantly with the amount of water conveyance. Generally, it reached the peak value within one month after the water conveyanced. After that, it gradually decreased until the next water conveyance. After 2009, the ecological water transport has obvious effect on the vegetation restoration of downstream, and the average value of NDVI in the downstream increased from 0.05 to 0.15. This study systematically analyzed the comprehensive response of regional ecological environment to groundwater since the ecological transport of the main stream of Tarim River, which could provide theoretical basis for regional water resource management and further quantification of water transport benefits.

Abstract:In order toclarify the water-saving and fertilizer-conserving effects of a new environmental sustained-release water-retaining agent,γ-polyglutamic acid (γ-PGA),four kinds of γ-PGA gradients (0, 0.1%, 0.2% and 0.4%) were applied at the same nitrogen application rate (2 g/kg), and no γ-PGA was taken as control.The effects of γ-PGA application rate on soil nitrogen transport characteristics were studied by one-dimensional soil column infiltration experiment in laboratory. The results showed that: (1) Under the condition of constant head infiltration, the cumulative infiltration amount, infiltration rate and the distance of wetting front migration all decreased with the increasing of γ-PGA application amount.Compared with the control group,the cumulative infiltration amount, infiltration rate, and distance of wet front migration in the experimental group with 0.4% γ - PGA application decreased by 27.64%, 73.45% and 31.58%, respectively. (2) According to Philip formula simulation results, the permeability S decreased with the increasing of γ-PGA application, showing a negative correlation; in the results of Kostiakov formula simulation, empirical coefficient K decreased with the increasing of γ-PGA application, showing a negative correlation,and empirical index a increased with the increasing of γ-PGA application, showing a positive correlation.(3) With the increasing of γ-PGA application, the water content of surface soil (0-15 cm) increased gradually,while that of the deep soil (below 15cm) was the opposite.At the same time, the greater the γ-PGA application amount, the greater the content of nitrate nitrogen and ammonium nitrogen in each soil layer in the same period. On the fourth day after stopping the water supply, the average nitrate nitrogen content of the experimental group added with 0.1%, 0.2% and 0.4% γ-PGA, respectively, increased by 29.55%, 42.49% and 59.50% compared with thecontrol group,and the average ammonium nitrogen content increased by 43.97%, 123.40% and 156.74%.In conclusion, applying γ-PGA to soil could effectively slow down water infiltration, gather more water in shallow soil layer, reduce fertilizer leaching rate,increase water and fertilizer utilization,reduce frequency and cost of irrigation, and achieve the purpose of improving soil structure and increasing crop yield.

Abstract:To determine the effects of nitrogen reduction combined with film mulching measures on the yield composition and the utilization efficiency of water and fertilizer of winter wheat in the Loess Plateau, and to provide theoretical basis for reducing the application of nitrogen fertilizer and increasing the yield of winter wheat in dry land, in 2013-2018, experiment was conducted in winter wheat growing region of dry highland in Southern Shanxi. In the experiment, four treatment were set up, which were farmer pattern, monitoring fertilization, monitoring fertilization plus ridge mulching-furrow planting and monitoring fertilization plus whole field filming with soil covering and hole-seeding. The yield components, soil moisture and the utilization efficiency of nitrogen, phosphorus and potassium fertilizer were analyzed under the condition of reducing nitrogen and mulching for five consecutive years. The results showed that: (1) Compared with farmer pattern, total nitrogen application in the monitoring fertilization treatments decreased by 46.9%, and under the condition of balanced application of phosphorus and potassium fertilizer, the average annual grain yield, biological yield and panicle number per hectare of winter wheat increased by 4.4%, 4.0% and 4.3%, respectively, the nitrogen harvest index and the partial productivity of nitrogen fertilizer increased by 4.3% and 120.3%, respectively. At the same time, the uptake of phosphorus and potassium by above ground part of winter wheat was promoted. (2) On the basis of monitoring fertilization, plastic film mulching planting increased water use efficiency and water consumption in growth period by 13.8%~23.9% and 7.1%~10.1%, respectively. At the same time, the harvest index of nitrogen fertilizer increased by 1.7%~3.5%, the partial productivity increased by 21.7%~41.4%, the physiological efficiency reduced by 8.7%~16.8%, and the partial productivity of phosphorus fertilizer and potassium fertilizer increased by 22.4%~39.2% and 19.3%~37.1%, respectively. Good water and fertilizer regulation effect of plastic film mulching planting increased the grain yield, the biological yield, the hectares ears and the 1000-grain weight by 21.0%, 39.2%, 18.2% and 4.7% in the treatment of ridge mulching-furrow planting, respectively, and by 23.5%, 40.3%, 27.6% and 7.0% in the treatment of whole field filming with soil covering and hole-seeding, respectively. Therefore, in order to increase wheat yield and fertilizer efficiency, the combination of the nitrogen reduction and control fertilization technology and the ground film covering measures can be applied in the planting area of the Loess Plateau.

Abstract:One-year-old peach potted seedlings were used as test materials. The base fertilizer was urea 3 g (of which ¹⁵N was labeled 0.4 g) and potassium dihydrogen phosphate 3 g. The CK was set as control. The treatment T1, T2, and T3 were added with 10, 80 and 150 mg γ-polyglutamic acid (γ-PGA) to investigate the effects of different concentrations of γ-PGA on peach seedlings growth and nitrogen uptake and utilization. The results showed that the activity of soil urease and catalase as well as the content of soil alkali-hydrolyzed nitrogen could be significantly increased by applying medium and high levels of γ-PGA. Application of medium and high amount of γ-PGA could promote root growth of peach seedlings, especially the growth of fine roots. Compared with the control group, the total root length, the number of branches, the number of root tips, the number of crossings, and the total root surface area increased by 51.95%, 40.53%, 30.72%, 35.21% and 45.23%, respectively. The net photosynthetic rate, the chlorophyll SPAD value, and the dry matter accumulation of plants could be significantly increased by applying medium and high γ-PGA. The activity of root system, the nitrate reductase, the rice straw transaminase, and the rice third transaminase were significantly increased by applying medium and high γ-PGA. Compared with the control group, the nitrogen uptake efficiency and nitrogen residual rate were increased by 27.80% and 27.07%, the nitrogen residual rate was increased by 14.00% and 19.04%, and the nitrogen loss rate was decreased by 16.43% and 19.49%, respectively. It can be seen that applying γ-PGA can improve soil physical and chemical properties in peach root area, improve nitrogen uptake efficiency and soil nitrogen residual rate, reduce nitrogen loss rate, and promote the growth of peach seedlings.

Abstract:The objective of this study was to reveal the effect of different vegetation patterns on the soil water characteristic and its temporal stability in opencast coal mine dump. Three vegetation patterns including Astrgalus adsurgens grassland, alfalfa grassland and seabuckthorn shrubland were selected, and grassland in original landform was used as control. The results showed that the average soil water content under three kinds of artificial vegetation increased by 50.7%~62.3%, compared with the grassland in original landform. The soil water deficit in the deep layer (120—260 and 120—220 cm) was observed in astrgalus adsurgens grassland and alfalfa, while higher soil water content was observed in 20-80 cm. In seabuckthorn shrubland, soil water deficit was observed in the shallow layer (20—80 cm), while higher water content was detected in the deep layer (100—280 cm). These results showed that the soil reconfiguration can improve the soil moisture condition in the reclamation of the waste site, and the selection of alfalfa and sea-buckthorn is more conducive to the alleviation of soil moisture deficiency in vegetation reconstruction.

Abstract:Based on the randomized block test with different amount of chicken manure and pig manure application (0, 15, 30, 45 and 60 t/hm²), the characteristics of accumulation and migration of Cu and Zn in soil profile, the changes in yield, quality, and the content of Cu and Zn in different organs of pepper (roots, stems, leaves, and fruits) were studied. The results showed that the content of Cu and Zn was significantly increased in the tillage layer (0-20 cm) after chicken and pig manure application. Compared to CK, the increase of Cu content reached 22.60%~66.59% and 36.13%~95.00% respectively, and the increase of Zn content reached 10.49%~39.27% and 11.18%~51.94% respectively. The increase of soil Cu and Zn content in the tillage layer (0-20 cm) after application of pig manure was greater than that of chicken manure. The content of Cu and Zn in chicken and pig manure were mainly accumulated in the soil tillage layer (0-20 cm). The highest content of Cu and Zn was 36.95 mg/kg and 137.24 mg/kg, which did not exceed the national safety level. The migration of Cu and Zn to deeper soil was significantly after 60 t/hm² chicken and pig manure application. The downward migration of Cu and Zn in chicken manure was smaller than pig manure treatment. The single fruit weight and yield of pepper significantly increased after chicken and pig manure application, and reached the highest at the 30 t/hm² application, the yield increased 24.98% and 29.04% compared to CK. The Vc content, the soluble sugar content, and the soluble protein content significantly increased, but the nitrate content significantly decreased after high amount of chicken and pig manure (60 t/hm²) application. Application of 15 t/hm² chicken manure and 60 t/hm² pig manure significantly increased Cu content in pepper fruits, but the Cu content did not exceed 20 mg/kg, which was a safe level for eating. The application of chicken and pig manure had no significant effect on the content of Zn in the fruits (from 16.35 to 20.87 mg/kg). It can be concluded that rational application of chicken and pig manure can improve soil properties, increase crop yield and quality in a short term. Although chicken and pig manure application can cause the accumulation of Cu and Zn in the tillage layer (0-20 cm), it has not caused soil pollution of Cu and Zn, and affect the safety of pepper fruits, while further monitoring is necessary if long-term application.

Abstract:Field experiment was set up in Nong’an County, Jilin Province from 2017 to 2019. Field double factor split design was employed, with two straw treatments in main plots, which were straw returning J (12 000 kg/hm²) and no straw returning (W), and the sub-plots were magnesium fertilizer M3 (10 kg/hm²), no magnesium fertilizer M0, and the treatments included JM3 (straw + magnesium fertilizer), JM0 (straw + no magnesium fertilizer), WM3 (no straw + magnesium fertilizer) and WM0 (no magnesium fertilizer + no straw). The results showed that during the growth period of maize, the content of exchangeable magnesium in the soil gradually decreased. At the mature stage, the content of soil exchangeable magnesium in JM3 treatment was 6.59%, 8.47% and 14.09% higher than that in WM3, JM0 and WM0 treatment, respectively. The application of magnesium fertilizer could promote the magnesium absorption in maize plants, and straw returning to the field combined with magnesium fertilizer application could further increase the uptake of magnesium in maize. The average magnesium accumulation in the WM3 treatment was 12.30% higher than that in WM0 treatment. The magnesium accumulation in JM3 treatment was 9.79%, 15.99% and 23.28% higher than that in WM3, JM0 and WM0 treatments, respectively. The accumulation of dry matter in maize increased continuously during the growth period. Applying magnesium fertilizer could improve the production of dry matter and the yield of spring maize. At the maturity growth stage, the dry matter accumulation and yield of maize in WM3 treatment was 5.30% and 4.38% higher than that in WM0 treatment. The dry matter accumulation and yield of maize in JM3 treatment was 11.50% and 5.52% greater than that in WM0 treatment. In conclusion, the application of magnesium fertilizer could significantly improve the content of exchange able magnesium in soil, promote the absorption of magnesium nutrients in spring maize plants, increase the dry matter accumulation and spring maize yield. Straw returning to the field with applying magnesium fertilizer could not only improve the content of soil exchangeable magnesium, maintain the continuous and effective supply of soil magnesium in the whole growth period of maize, but also further promote the absorption of magnesium nutrients by spring maize plants, increase the dry matter accumulation and yield of spring maize.

Abstract:Field experiment was conducted to investigate the dynamic changes of soil pH, organic matter and cadmium (Cd) content in soil and Cd accumulation in rice organs at different growth stages under applying different amounts of organic fertilizer and lime. The results showed that Cd content in different organs of rice at the maturity stage followed the order of root > stem > leaf > husk > brown rice. The application of lime could increase the soil pH. At the tillering stage, the soil pH significantly increased by 1.35 and 1.84 units under the treatment of low amount lime and high amount lime, respectively.The application of organic fertilizer could increase the organic matter content. Compared with the control, the content of organic matter increased by 6.60 g/kg at tillering stage and 2.72 g/kg at maturity stage in the treatment of high amount of organic fertilizer.The filling stage was an important period for the absorption and accumulation of Cd in rice. The application of lime and organic fertilizer could reduce the available Cd content in the soil during the filling stage.Compared with the control group, the content of available Cd in soil treated with high amount organic fertilizer and lime significantly decreased by 52.05% and 46.87%, respectively. Both organic fertilizer and lime could significantly reduce the Cd content of brown rice, and the effect of reducing Cd followed the order of high amount of organic fertilizer > high amount of lime > low amount of organic fertilizer > low amount of lime, the effect of high amount organic fertilizer treatment was the best, Cd content of brown rice decreased by 68.20%.

Abstract:The pretreatment (PT) of straw can accelerate the decomposition of the straw. In order to explore the influence of straw returning to the field after different pretreatment on soil nutrients leaching and the amount of COD, the straw was pretreated with white rot fungus, ball mushroom and urea, respectively. The amount of nitrogen, phosphorus and COD leaching out of the soil after straw returning to the field with applying organic fertilizer were studied by the method of indoor artificial soil column simulation. The structure and composition of straw before and after pretreatment were analyzed by scanning electron microscopy (SEM), Fourier infrared spectrum (FTIR), X-ray polycrystal line diffraction (XRD). And the best pretreatment method was determined by comparing the changes of total nitrogen, nitrate nitrogen, ammonium nitrogen, phosphorus, soluble phosphorus and COD of different treatments during the leaching process. The results showed that different methods of straw pretreatment made the straw surface structure changed in different degrees, the intermolecular hydrogen bond aggregation force was weakened, and some carbohydrates were decomposed. Compared with the blank control group (CK), the application of organic fertilizer significantly increased the content of nutrients and COD in the doused solution (p<0.05). In the treatments of involving organic fertilizer, compared with SF1(just organic fertilizer), the leaching amount of total nitrogen in SF2 (pretreated by white-rot fungi and returning, fertilization), SF3 (pretreated by urea and returning, fertilization), SF4 (no pretreatment, returning, fertilization) and SF5 (pretreated by ball cap mushroom, and returning fertilization) decreased by 16.61%, 20.42%, 13.84% and 33.22%, respectively, and the leaching amount of NH₄⁺-N decreased by 4.90%, 22.77%, 18.3% and 38.39%, respectively. Among them, the effect of white-rot fungi on the cumulative leaching loss of total nitrogen and ammonium nitrogen was more significant (p<0.05). There was no significant difference in the leaching loss of NO₃^--N, total phosphorus and dissolved phosphorus among different treatments. Until the end of leaching, the cumulative leaching loss of COD followed the order of SF1 > SF4 > SF3 > SF2 > SF5 > CK. The cumulative leaching loss of COD in SF5 was lower than that in other treatments, which indicated that the straw returning pretreated by the ball cap mushroom could effectively reduce the cumulative leaching loss of COD. In general, the straw pretreated by ball cap mushroom and returning had a positive effect on reducing the leaching loss of soil nitrogen and COD content in the leaching solution.

Abstract:The aim was to investigate the effects of different wheat cultivars on water use efficiency,water use in deep soil, and wheat yield. The experiment was conducted at Changwu experimental station during 2017—2019. A two-factor experiment was conducted, one factor was cultivar (A: "Changhan 58", B: "Changhang 1"), and another factor was sowing rate (10: 150 kg/hm² of sowing rate, 12: 180 kg/hm² of sowing rate). The effects of different factors on soil water consumption, water use efficiency, and yield at different wheat growth stages were analyzed.The results showed that the average consumption of soil storage water in different test years of "Changhang 1"was significantly higher than that of "Changhan 58". In addition,the number of grain number per panicle, harvest index,yield, and water use efficiency of "Changhang 1" were also remarkably higher than those of "Changhan 58".It was showing that compared with "Changhan 58", "Changhang 1" increased theconsumption of soil water, which may contribute to increase the grain number per panicle and the wheat harvest index, and ultimately lead to higher yield and water use efficiency.

Abstract:In order to explore the effective measures that could make rational fertilization and improve nutrient utilization of rice, 8 field experiments were conducted in the Yellow River irrigation region of Ningxia from 2016 to 2018 to evaluated the effect of side deep fertilization technology based on nutrient expert system(NE-SD) on rice yield and nutrient use efficiency. The results showed that, compared to the farmer practice fertilization (FP) treatment, the nutrient expert system (NE) treatment significantly reduced N and P application rate 24.85% and 24.78%, but increased K rate 90.71%, and increased the rice yield 4.71%. Compared to the FP treatment, the nutrient accumulation of nitrogen, phosphorus, and potassium increased 2.24%, 4.40% and 15.09%, respectively; the nutrient utilization efficiency of nitrogen, phosphorus, and potassium increased 9.84, 8.78 and 1.99, respectively; the fertilizer agronomic efficiency of nitrogen, phosphorus and potassium increased 4.73, 7.69 and 1.54 kg/kg, respectively. The side deep fertilization technology based on nutrient expert system could deepen the 4R nutrient management principle and had better application effect. Compared to the FP treatment, the rice yield of the NE-SD treatment increased 7.53%. Compared to the FP treatment, the nutrient accumulation of nitrogen, phosphorus, and potassium increased 3.92%, 7.87% and 18.74%, respectively; the nutrient utilization efficiency of nitrogen, phosphorus, and potassium increased 11.09, 11.32 and 5.82, respectively; the fertilizer agronomic efficiency of nitrogen, phosphorus, and potassium increased 5.87, 11.31 and 3.54 kg/kg, respectively. Therefore, on the basis of reducing fertilizer rate, two fertilization methods of the nutrient expert system and the side deep fertilization technology based on nutrient expert system could increase rice yield and nutrient accumulation, improve nutrient utilization efficiency, and reduce soil nitrogen and phosphorus surplus in Yellow River irrigation region of Ningxia.

Abstract:The present research evaluated the effects of the frequency of freeze-thaw cycles (FTC) (0, 3, and 9 times) and initial soil water content (WC) (40%, 60%, and 80% field capacity) on soil aggregate distribution and four aggregate associated available trace elements (Cu, Fe, Mn, Zn) in a typical Chinese pine forest soil in the Wangmaogou watershed. The results showed that FTC significantly increased the proportion of aggregates < 0.25 mm (P<0.01), decreased the proportion of aggregates >2 mm (P<0.01), thus significantly decreased the mean weight diameter (MWD) (P<0.01). Increased soil WC significantly decreased the proportion of aggregates <0.25 mm, increased the proportion of aggregates 0.25~2 mm and >2 mm, thus increased MWD. The increased effects of soil WC on MWD were much larger than the disruptive effects under FTC conditions. FTC significantly decreased the total amount of available Cu and Fe, and increased the total amount of Mn and Zn in < 0.25 mm aggregates. The total amount of the four available trace elements in>2 mm aggregates were significantly increased after FTC. Increased soil WC decreased the available trace elements content in <0.25 mm aggregates and increased in the >2 mm aggregates. The increased soil WC could offset the disruptive effects of FTC on soil aggregation, and FTC and the increase soil WC synergistically improved the available tract elements contents in >2 mm aggregate fractions.

Abstract:Soil aggregate is the basic unit of soil structure and the microscopic description of soil hydraulic erosion is the fracture process of soil aggregate. According to the research data, plant roots have the ability to change the mechanical and hydrological characteristics of soil and promote the formation and stability of soil aggregates. Therefore, this paper makes a systematic review of the relevant research results at domestic and abroad in the past 20 years, analyzed the mechanism of plant roots on the formation of soil aggregates, and put forward the existing problems and research trends from the perspectives of the physical, biological and electrochemical studies on soil aggregates by roots. It is of great significance to deeply understand the effect of plant roots on formation and stability of soil aggregates, and to develop the soil erosion process model of root-soil interaction.

Abstract:The quantity and quality of soil aggregates directly affect soil properties and soil organic carbon (SOC) sequestration. This study investigated effects of various fertilization regimes and fertilization ages on the distribution and stability of dry aggregates and water-stable aggregates, aiming at providing a scientific basis for improving agricultural production and soil quality in long-term reclaimed areas, Shanxi Province, China. Surface soil samples of 0-20 cm horizons under different fertilization regimes were collected from 6-years and 11-years reclaimed areas, respectively. There are 4 different fertilization treatments (no fertilizer (CK), chemical fertilizer with nitrogen, phosphorus, and potassium (NPK), organic manure alone (M), and chemical fertilizer combined with manure (MNPK)). All samples were separated into four aggregate-size fractions (>2, 0.25~2, 0.053~0.25 and <0.053 mm) by dry sieving and wet sieving methods. The >0.25 mm aggregate content (R_0.25), mean weight diameter (MWD), proportion of aggregate destruction (PAD) and unstable soil aggregate index (E_LT) were used to indicate the stability of aggregates. The SOC content in the bulk soil was determined. The fertilization age had a more significant effect on the distribution and stability of soil aggregates than the fertilization regime. Under the dry sieving condition, the distribution of 0.053~0.25 mm and <0.053 mm fractions in each treatment was reduced significantly at both fertilization ages, with a decrease of 68.39%~87.37%, 69.63%~78.32% (6-years) and 90.01%~93.68%, 78.29%~83.93% (11-years); under the wet sieving condition, the distribution of >2 mm fraction increased significantly by 473.35%~645.16%, but the distribution of 0.053~0.25 mm fraction was significantly decreased by 43.67%~57.54% after 11-years reclamation. The stability of soil aggregates was also gradually enhanced with the increase of fertilization ages, showing that the distribution of DR_0.25, WR_0.25 and MWD had an increasing trend, but the PAD and E_LT had a decreasing trend. SOC content showed an extremely significant positive correlation with the DR_0.25, WR_0.25 and MWD_water-stable, but an extremely significant negative correlation with PAD and E_LT. It was concluded that the SOC content in the study area increased significantly after 11 years of consecutive fertilization, resulting in a more and more stable soil structure. It was conducive to improve stability of aggregates in this reclaimed area.

Abstract:The purpose of this study was to investigate the effects of sprinkler irrigation uniformity coefficient (CU) on soil moisture, crop yield and water use efficiency, and to explore the suitable tillage patterns under sprinkler irrigation conditions. Field experiments, which included rotary tillage (RT), subsoiling (ST) and conventional tillage (CT), were conducted during the winter wheat growing season in 2018-2019 with three plots of 18 m×18 m. Each plot was subdivided into 9 subplots of 6 m×6 m. The results showed that the average CU of sprinkler irrigation varied between 63.91%~76.83%, while the CU of soil moisture varied between 84.20%~89.83%, which were 14.48%~31.75% higher than the former. The CU of winter wheat yield were 9.99%~23.79% higher than the average CU of sprinkler irrigation, 2.11%~7.85% lower than the cumulative irrigation CU, and 0.82%~6.04% different from the averaged values of soil moisture CU. Compared with RT treatment, the yield of winter wheat in ST and CT treatments increased by 9.38% and 13.22%, respectively, and the water use efficiency increased by 10.61% and 12.88%, respectively. That was, compared with the sprinkler irrigation CU, the CU of winter wheat yield were more affected by those of the cumulative irrigation CU and the averaged values of soil moisture CU. ST and CT treatments were the suitable farming method under the sprinkler irrigation condition.

Abstract:In order to reveal the hydrological process of the forest canopy and provide a reference for the scientific management of forest hydrological ecosystem, precipitation, throughfall, and canopy information were collected from typical Cinnamomum Camphora woods during April 2018 to March 2019 in Changsha to study the spatial variability of throughfall and the characteristic of stable isotopes in throughfall. The results showed that the total throughfall under the canopy was 340.1 mm, accounting for 71.2% of the total precipitation outside the forest; comprehensively affected by the canopy structure including the distance from tree trunk and the leaf area index. The throughfall presented great spatial variability and stable temporal variability.The correlation analysis showed that the coefficient of spatial variability decreased with the increase of precipitation, reflecting the important influence of precipitation characteristics on the spatial variation of throughfall.Compared with the amount of throughfall, the stable isotopic compositions in throughfall were hardly affected by canopy structure and atmospheric conditions,not obvious in spatial variation, and not stable in temporal variation. In most precipitation events,stable isotopes in throughfall were richer than those in precipitation, and there was no significant discrepancy between the mean values of them, indicating that throughfall underwent weak evaporation in its formation process. The deviation between the stable isotopes and d in throughfall and those in precipitation suggested that the canopy had the selective penetrating effect.

Abstract:In order to explore the optimal integrated management system of water and fertilizer under drip irrigation in a fruit-crop intercropping system in the loess area of Shanxi Province,a one-year experiment was carried out in the typical apple (Malus pumila)-soybean (Glycine max) intercropping system, and two factors of irrigation and fertilization were set up to analyze the influence of different water and fertilizer control measures on soil water content distribution, photosynthetic characteristics of apple and soybean, soybean growth and yield, and water use of intercropping system. In the experiment, irrigation was conducted in four key water demand periods of soybean. Fertilizer was applied with irrigation water, and different upper limit of irrigation and fertilization level were set each time. The four levels of maximum irrigation were 60% (W1), 70% (W2), 80% (W3) and 90% (W3) of field capacity (Fc), and the three different nitrogen fertilization levels were pure nitrogen 59.40 kg/hm²(F1),92.00 kg/hm²(F2) and 124.32 kg/hm²(F3). In addition, the rain-fed crop (neither irrigation nor fertilization during the whole growth period, only basal fertilizer was applied before sowing) was taken as the control (CK).The results indicated that the soil water content for each water and fertilizer treatment had significant differences in both horizontal and vertical directions. The influence of irrigation amount on soil water content was more significant than that of fertilization amount and interaction of water and fertilizer.The diurnal variation characteristics of net photosynthetic rate (P_n) and transpiration rate (T_r) for apple and soybean were similar, both of which were unimodal curves and the maximum values were obtained in W3F2.The plant height, stem diameter and leaf area index (LAI) of each water and fertilizer treatment for soybean increased by 1.3%~32.3%, 2.8%~33.9% and 3.4%~125.9%,compared with CK, respectively. Moreover, all the maximum value of growth indexes appeared in W3F2. The soybean yield and water use efficiency (WUE) for intercropping system were also optimal in W3F2, which increased by 10.9%~99.3% and 8.0%~70.0%,compared with other treatments, respectively. The irrigation upper limit of 80% Fc could be set from sowing to emergence stage, from seedling to branching stage, from flowering to pod and blast stage. Meanwhile, 92.00 kg/hm² nitrogen fertilizer could be applied at seedling to branching stage,at pod and drum stage of soybean, respectively. This water and fertilizer management under drip irrigation could make the apple-soybean intercropping system obtain higher crop yield and water use efficiency, which could provide reference for integrated management of water and fertilizer under drip irrigation for the intercropping system in this area.

Abstract:In this study, the 3-year young lateral cyperusorientalis in Beijing area was selected as the object of study. A greenhouse potted experiment was used to set five different soil water content levels, and ¹⁵N isotope natural abundance method was used to study the physiological activities, biomass allocation and nitrogen absorption and distribution of lateral cyperusorientalis seedlings under different water conditions. Results showed that: (1) Under water stress(D1), the individual net photosynthetic rate, transpiration rate and respiratory rate, were low, and increased by 4.86 times, 3.74 times, 7.29 times after relieving drought stress. The leaf water content and leaf area increased by 24.37% and 23.69%, respectively. After that, when the soil water content exceeded the normal value, with the further increase of soil water content, all indexes decreased slightly. (2) Under water stress, biomass distribution and nitrogen distribution were inhibited. With the increase of water content, biomass distribution was shown as the aboveground part > underground part. The nitrogen distribution rate was shown as follows: root > leaf > stem. The nitrogen in root and leaf were transferred to the stem with the increase of soil water content. (3) When the soil water content reached the 70% to 80% of field water capacity, the growth and development of platycladusorientalis seedlings showed the best.

Abstract:The effects of water deficit (WD) on the growth, water consumption, yield, water use efficiency, and quality of Isatis tinctoriaunder-mulche drip irrigation were studied by a field experiment. In 2018, the I.tinctoria water control experiment was carried out at the Yimin Irrigation Experimental Station in Minle County, Gansu Province. The seedling stage and the fleshy root growth period were fully flooded, and different gradients (mild, moderate and severe) WD treatment were carried out in the vegetative growth period and the fleshy root growth stage , and various growth indicators, yield, water use efficiency and quality were determined. The results showed that: (1)In the period of vegetative stage and fleshy root growth, the moderate and severe water deficit significantly reduced the plant height, leaf number, main root length, and main root diameter, and the declines increased with the raising WD level, While the mild WD treatment showed no significant difference compared with control group. (2)The water consumption of I. tinctoria in the period of vegetative and the fleshy root growth decreased gradually with the increasing of WD regulation, which was significantly lower than the control group (P<0.05). The order of water consumption intensity change was that: the vegetative and the fleshy root growth (about 3.0 mm/d) > the fleshy root maturity (about 1.5 mm/d) > the seedling (about 1.0 mm/d). (3)In the vegetative period, the mild WD treatment (V₁G₀) had the highest yield and water use efficiency, reaching 8 475.38 kg/hm² and 23.33 kg/(hm²·mm), respectively, and the treatment of V₁G₁ followed, and yield and water use efficiency of the remaining treatments decreased significantly (P<0.05). (4) In the vegetative stage and the fleshy root growth stage, mild and moderate continuous WD was beneficial to the indigo, indirubin, (R, S)-goitrin, and the polysaccharide content was significantly different from the control group (P<0.05). The indicators of severe WD treatment were the lowest. Therefore, comprehensive analysis of I. tinctoria yield, water use efficiency and quality,the optimal water-control treatment is the continuous slight WD in the vegetative growth period and the fleshy root growth period(V₁G₁), That is to say, the relative water content of the soil during this period is 65%~75%, which can be used as the optimal irrigation strategy for the planting of I. inctoria in the cool irrigation area of Hexi.

Abstract:The purpose of this study is to analyze the effect of biochar compounded with flocculated yellow river sediment on the water and salt transport and hydraulic characteristic parameters of saline soil through the laboratory tests with ring-knife. Firstly, biochar and flocculated Yellow River sediment were mixed into soil improver at the mass ratio of 4∶6, and then the soil improver was mixed into saline soil as the proportion of 0, 1%, 2%, 3%, 6%,and 10%. The results showed that: (1) Soil porosity and water content increased with the increase of soil improver.The soil porosity and water content under the 10% level are average increased 12% than the control treatment. (2) The saturated hydraulic conductivity of soil reaches the maximum at 3% addition, which is 68.9% higher than that control. (3) The additional amount of soil improver is inversely proportional to the rate of water diffusion, so that the soil pH value is higher, and then have the small effect of salt leaching.It was found that the decrease of soil salt was more obvious when the content of 3% was added. The amount of salt reduction above 17 cm reaches 30%~50%, but the increase in soil pH is only about 4%. The Boltzmann parameter λ increased by 31.5%, and the water diffusion rate was faster. All things considered, applying 3% soil improver can effectively increase soil porosity, soil water content, saturated hydraulic conductivity, water diffusivity, and reduce the soil salinity on the surface.

Abstract:The heavy saline alkali soil in Hetao irrigation area has the characteristics of poor structure and low water conductivity, and the fresh water resources in this area are in short supply. In order to improve the infiltration performance of soil water and reasonably develop and utilize the brackish water resources, a sand hole can be set under the dripper and the brackish water can be used for irrigation. In order to find out the influence of different salinity and brackish water drip irrigation on the distribution of water and salt in soil under the sand hole planting, this study adopted the indoor simulation test of 50 cm×50 cm two-dimensional soil tank, and set four different salinity treatments of distilled water (0 g/L), 2.0, 3.0 and 4.0 g/L, the experimental duration was 100 hours. The results showed that the soil water content was higher in the saline alkali soil with the depth of 5 cm and at the distance of 15~20 cm from both sides of the dripper and 25 cm below the dripper. The soil water content of the sandy soil increased with the increase of water salinity. The soil water content of the saline alkali soil increased first and then decreased with the increase of the salinity. When using 3.0 g/L water drip irrigation, the water content of the saline alkali soil was the largest (coefficient of variation was 7.64%). Therefore, using 3.0 g/L water irrigation could effectively improve the soil moisture content under sand hole planting; after 100 hours of infiltration, the salt was mainly concentrated at 25~30 cm below the dripper. In the sand hole structure test, when the salinity of irrigation water was 4.0 g/L, the average conductivity of soil was the largest (coefficient of variation was 50.59%). The effect of salt leaching in horizontal direction was better than that in vertical direction, and the lower salinity of irrigation water gave the more significant leaching effect.The desalination rate of distilled water treatment was 13.99%, and the salt accumulation rates were 7.93%, 14.57% and 30.05% for irrigation the salinity of 2.0, 3.0 and 4.0 g/L, respectively. The desalination radius decreased with the increase of the salinity, and the difference between the salt accumulation of 3.0 g/L and 2.0 g/L was not significant (P=0.460 > 0.05), which two were significantly different from that of 4.0 g/L (P=0.024 < 0.05). Combined with the spatial distribution law of soil water and salt, 3.0 g/L brackish water could be used to improve the soil water content of saline alkali soil, control the salt accumulation in sand holes, and improve the soil water conservation of root layer.

Abstract:In order to reveal the effect of vegetation degradation on soil carbon(SOC)mineralization in wetland,four intensities of vegetation degradation of Gahai wetland (non-degraded (UD), slightly degraded (LD), moderately degraded (MD), and heavily degraded (HD)) were selected for the research objects on the eastern Qinghai-Tibet Plateau.Soil samples (0-40 cm) were collected from three depths (0-10, 10-20 and 20-40 cm). SOC mineralization was determined by the laboratory incubation method.The first-order kinetic equation were applied to analyze the response of soil semi-mineralization decomposition time (T_1/2) and organic carbon mineralization potential (C₀) to vegetation degradation.The result showed that: (1) SOC mineralization rate displayed similar trends during the four vegetation degradation stages: during the early incubation period(0~4 day), SOC mineralization rate was high and decreased fast, and then the rate decreased slowly and tend to stabilize during the middle and late periods(4~41 day).The order of SOC mineralization rate in different vegetation degradation stages was UD > LD > MD > HD at all temperatures. (2) During the whole incubation period,the SOC mineralization rate in different vegetation degradation stages decreased with increasing soil depth. The SOC mineralization rate in different vegetation degradation stages were 1.14~16.23 mg/ (g·d),significantly higher than those in 10-20 cm layer (1.05~2.85 mg/(g·d)) and 20-40 cm layer (0.94~1.26 mg/(g·d)). (3) The order of average cumulative amount of SOC mineralization with four vegetation stages at different temperatures was 5 ℃ (34.54 mg/g) > 15 ℃ (46.67 mg/g) > 25 ℃ (58.28 mg/g) > 35 ℃ (86.46 mg/g).(4) The C₀ value of first-order kinetic equation decreased with increasing degradation degree, while the C₀/SOC decreased with increasing temperature. Therefore, vegetation degradation in the alpine wetland significantly decreased the SOC mineralization rate and climate warming significantly increased the cumulative amount of SOC mineralization.

Abstract:The decomposition and organic carbon release characteristics of litters of Abies georgei var. smithii and Picea likiangensis var. linzhiensis in two typical dark coniferous forests in southeastern Tibet were studied by combining the method of litter decomposition bag and laboratory analysis, the relationship between organic carbon release rate and soil organic carbon and its components in two subalpine dark coniferous forests was analyzed, the results showed that the decomposition of litters in the two original dark coniferous forests in southeastern Tibet showed the characteristics of fast decomposition in rainy season (April to September), slow decomposition in dry season (October to march), fast decomposition in early stage (march to September) and slow decomposition in late stage (October to February). The decomposition rate of fir (PLLF) was higher than that of spruce (AGSF). Olson exponential decay model could well model the decomposition of litter in two dark coniferous forests. The half-decomposition time of litter in fir (PLLF) and spruce (AGSF) were 2.11 and 2.52 years. The 95% of decomposition time were 8.96 and 10.84 years. The organic carbon content in the litters of the two dark coniferous forests showed a trend of first rising, then falling, and then steadily declining, while the release rate of organic carbon in the litters showed a pattern of first brief enrichment and then release. The contents of total organic carbon (TOC) and its active components (MBC, POC and LOC) in the soil of the two dark coniferous forests were obviously surficial (p<0.01), and the contents of TOC, MBC, POC and LOC in the same soil layer were significantly positively correlated with each other (p<0.01). There was a significant positive correlation between the release rate of organic carbon in the decomposition process of litters of the two dark coniferous forests and the contents of TOC, MBC, POC and LOC in the topsoil (0-10 cm), TOC and MBC in the soil layer of 10—20 cm and MBC in the soil layer of 20—40 cm (p<0.05).

Abstract:In this experiment, soil mixed with sand and composted straw (SSJ) and soil mixed with sand andbiochar (SSS) were used as the replacement media for urban green space to explore their changes in physical and chemical properties after adding PAM with concentration of 0~1.5%.The suitable dosage of PAM was expected to be found to provide theoretical and technical support for soil refilling in urban green space. The results showed that adding PAM could reduce the bulk density of the media, and increase the saturated hydraulic conductivity and saturated water content. The change trend of bulk density and saturated hydraulic conductivity with the increasing of PAM could be described by a quadratic curve. However, when the PAM dosage was 1.5%, the saturated hydraulic conductivity showed a tendency to decrease compared with the PAM dosage of 1.0%. Whereas the bulk density showed an upward trend. The application of PAM could reduce COD desorption quantity of the media.With the increasing of PAM dosage, the nitrogen and phosphorus desorption of SSJ media showed an increase trend, while the nitrogen and phosphorus desorption of SSS media decreased first and then increased. On the whole, the SSS media was superior to the SSJ media when the PAM concentration was 0~1.5%. When the dosage of PAM was 1.0%, it could improve the water retention and water conductivity capacity of media to the greatest extent, and reduce COD desorption.

Abstract:Freeze-thaw is an important physical factor affecting soil structure in alpine regions. Taking alpine meadow in Qinghai Lake basin as the research object, the influence of freeze-thaw cycle on the structure characteristics of soil macropores in the frost mounds and the inter space of frost mounds were studied through collecting undisturbed soil columns, simulating freeze-thaw cycle, conducting CT scanning and image interpretation. The results showed that with the increase of the freeze-thaw cycles, the soil macroporosity in the frost mounds and the inter space of frost mounds presented a trend of "decrease-increase-decrease", and the decrease of soil macroporosity by freeze-thaw cycles was mainly formed in the first freeze-thaw cycle. The variation trends of the average equivalent diameter, average volume, average branch length, branch density and node density of macropores were basically the same as that of macroporosity. The effect of freeze-thaw cycle on the soil macropores in the frozen mound was significantly greater than that in the inter space of frost mounds. There were two peaks of the soil macroporosity along the depth in frost mounds, and the size and position of the peak value changed. Soil pore structure was more sensitive at a depth of 30—80 mm in the frost mounds than other depths of the felt layer.