Abstract:Water and soil erosion due to destruction of forest vegetation by the intense human activities and frequent rainstorm in mountainous and hilly area of southern China has attracted extensive attention. Forest vegetation restoration is an effective measure to control water and soil erosion because of the changes in reaction interfaces in forests, such as canopy structure, floor cover and soil characteristics, and thus affecting the rainfall erosion processes. Therefore, this study makes a systematic review of the relevant research results at domestic and abroad. From the research perspectives of vegetation canopy structure (canopy and understory vegetation), floor cover (litter and biological soil crust) and soil properties (root system, microorganism and aggregate) to reduce rainfall erosivity and enhance soil erosion resistance, this study analyzed the processes and underlying mechanisms of forest vegetation restoration on water and soil erosion, and put forward the existing problems and research trends. It is very important to deeply understand the regulation mechanisms of forest vegetation restoration on water and soil erosion and improve the soil and water conservation benefits of forest in mountainous and hilly area in southern China.

Abstract:Bedrock exposure is a common phenomenon in karst area, which forms "rocky desertification" similar to desertscape. And the occurrence and development of rocky desertification affect the mechanism and results of regional soil erosion. Therefore, it is necessary to study the quantitative relationship between rocky desertification factors (D) and soil and water loss in order to revise soil loss equations. On the basis of reviewing domestic and abroad literatures, this paper summarized the research status of the impact of rock exposure on soil erosion on slope. The results showed that the research conclusions were relatively discrete, and the viewpoints fell mainly into two categories. One was that the soil and water loss tended to decline in a linear, quadratic function and exponential trend with the increases of rock exposure rates, and the exponential attenuation was the main way; the other was that the effect of rock exposure on soil and water loss on slope was complex, which was related to slope gradient, soil type, rainfall stage and range of rock exposure rate. Under the certain conditions, with the increases of rock exposure rates, soil erosion would be intensified. For the research status of D-factor in karst areas in China, we think that there are two main problems:One is that there are few quantitative observation experiments between D-factor and soil and water loss, which limits the application of RUSLE and other commonly used soil loss equations in karst areas; the other is that field positioning observation is an important means to study soil erosion factors, but the construction of natural rock exposure runoff plot in karst areas is very difficult. The results can provide a reference for the quantitative study of D-factor and the correction of soil loss equation in karst areas of China.

Abstract:Taking three typical vegetation communities (Bothriochloa ischaemum, Artemisia gmelinii and Periploca sepium) in the loess hilly region as research objects, and the abandoned land for one year as the control (CK), the characteristics of soil preferential flow under different vegetation community patch patterns were analyzed based on in-situ dye-tracer and laboratory experiment methods, and the effects of plant roots and soil physicochemical properties on preferential flow were explored. The results showed that vegetation restoration improved the development of preferential flow in comparison with the CK. For each vegetation patch, the highest dye coverage (45.62%), maximum staining depth (30.30 cm), preferential flow proportion (39.76%) and the length index (475.90%) were found in A. gmelinii vegetation patch, followed by P. sepium and B. ischaemum. For the same vegetation community, the development degree of preferential flow was higher in vegetation patches than that in bare patches, except for the B. ischaemum community. Furthermore, the structural equation model indicated that the dyeing area ratio of preferential flow was directly affected by soil total porosity, aggregate stability, root mass density and soil organic matter content, and which could explain 70% of the total variance. Therefore, the natural vegetation restoration could affect soil properties through roots development, thereby improving the development degree of soil preferential flow and soil infiltration capacity.

Abstract:Soil erosion has always been one of the hot issues that China has paid attention to when developing regional ecological environment management. With the support of RS and GIS technology, this study analyzed the characteristics of soil erosion intensity under different land uses, altitudes and slope conditions in the Sunshui River Basin of Liangshan Prefecture based on the RUSLE model, and quantitatively evaluated the spatial characteristics of soil erosion. The results showed that:(1) The average soil erosion modulus of the Sunshui River Basin was 1 954.32 t/(km²·a), and the areas with severe soil erosion were mainly concentrated along the mainstream of the Sunshui River and its tributaries. (2) Moreover, the slope farmland and middle-cover grassland were the main types of eroded land use in the watershed. Soil erosion in the 2 000~3 000 m altitude zone of the basin was more serious, with an average soil erosion modulus exceeding 2 000 t/(km²·a). (3) Furthermore, the soil erosion modulus increased with the increases of slope, and 15°~25° was the most severely eroded zone in this watershed. We expect that these research results could serve the water and soil conservation and management work of the Sunshui River Basin in Liangshan Prefecture, and provide certain theoretical support for the realization of rural revitalization.

Abstract:In order to clarify the effect of grass cover in water level fluctuating zone (WLFZ) on agricultural non-point source pollution control in the Three Gorges Reservoir (TGR), the field scouring experiment was conducted to analyze the interception rate of nitrogen and phosphorus in surface runoff and the spatial change of nitrogen and phosphorus content in soil before and after scouring, and the effects of the typical grass cover on the transport of nitrogen and phosphorus pollutants in WLFZ were studied. The results showed that:(1) Grass buffer zone intercepted pollutants with a good overall efficiency, and interception rate for nitrate nitrogen was the highest, ranging from 93.5%~99.3%. The interception rate was directly proportional to the width of grass buffer zone and inversely proportional to the scouring intensity. (2) The maximum change rates of TN, TP, NO₃^--N and NH₄⁺-N before and after scouring were 2.30, 1.96, 5.01 and 4.75, respectively, which all appeared in the lower slope position of the plot. With the increasing of grass buffer zone width and the decreasing of scouring intensity, the change rate of pollutant content increased. (3) The variation rates of nitrogen and phosphorus pollutants in 0-10 cm soil layer were larger, and the variation range was 0.91~5.01. The change rates of TN, TP and NH₄⁺-N in 10-30 cm soil layer were generally close to 1, while the change rate of NO₃^--N in this soil layer was still large. (4) RDA analysis results showed that the most important factor affecting the change rate of pollutants content was the soil depth, followed by the slope position, the width of the grass buffer zone, and the scouring intensity. In conclusion, the grass buffer of the WLFZ could effectively intercept pollutants and promote their migration to the soil interior. In the process of restoration of herbaceous plants of the WLFZ and the prevention and control of non-point source pollution in the TGR, attention should be paid to increasing the coverage width of grass buffer, reducing the influence of high-intensity rainfall and runoff, promoting the pollutants to be intercepted on the up-slope and migrating to the soil, thus reducing the risk of pollutants being released into the overlying water. It could provide a theoretical basis for the restoration of herbaceous vegetation in the WLFZ and the prevention and control of agricultural non-point source pollution in the TGR.

Abstract:Taking bare Pisha Sandstone slope as the research object, based on the field runoff plot scouring test and three-dimensional laser scanning technology, the evolution of rill micro morphology and erosion sediment yield mechanism on Pisha Sandstone slope were studied under combined erosion with three kinds of flow (60, 100 and 200 L/h) and four slopes (5°, 10°, 20° and 30°). The results showed that the rill developed first at the bottom of the slope and then extended upward with the increasing of scouring flow and slope gradient. The occurrence time of rill decreased with the increasing of slope gradient. The rill shape was "wide and shallow type" on the slope less than 10°, the maximum width to depth ratio was 0.038. While the rill shape was "deep and narrow type" on the slop more than 20°, the minimum width to depth ratio was 0.038. With the increasing of erosion intensity and slope gradient, the ratio of rill width to depth became smaller, while the number, density, complexity and fragmentation of rill increased. Slope gradient and scouring intensity affected the change of slope sediment yield together. With the increasing of slope gradient and scouring intensity, the sediment yield increased first and then decreased. There was a significant negative correlation between ratio of rill width to depth and slope sediment yield (-0.935, P<0.01), and a significant positive correlation between rill density, rill fragmentation and sediment yield (0.888, 0.944, P < 0.01).

Abstract:This research was based on the ecological problems of granite red soil in South China, such as the coarse texture, poor physical properties, serious soil erosion and so on. In order to reveal the effects of SAP application on slope erosion of granite red soil, a simulated rainstorm experimentwas conducted. SAP was applied with three methods:layering (K1), furrowing (K2), mixing (K3) application. The results showed that:(1) Under the application of SAP, the initial runoff production time of granite red soil slope was 1.09~1.61 times longer than that of the control. The orders of infiltration rate and the water contents were K2 > K3 > K1 > CT and K3 > K1 > K2 > CT respectively. (2) The order of flow reduction rate was K3 > K2 > K1, and the sediment reduction rate was shown as follow K2 > K3 > K1. Compared with the control slope, the cumulative runoff and sediment yield in mixing treatments decreased by 59% and 66%. The mixing treatments achieved the better benefits of soil and water conservation in this research. (3) Under the different treatments, the cumulative runoff and sediment yield formed a power function model on the granite slope of red soil, and the correlation coefficients were all greater than 0.990. The findings provided theoretical basis and practical references for the study on the granite slope of red soil.

Abstract:Landslide is the common geological disaster in loess hilly and gully areas, and rainfall is the main cause of instability of loess slopes. In order to study the stability of loess slopes under continuous rainfall conditions, an artificial rainfall device was used to carry out experimental studies on the outdoor site. The soil moisture content, density, shear zone location and crack development were measured. The FLAC3D geotechnical engineering numerical calculation software was used to analyze the slope stability. The results showed that with the increase of rainfall duration, the moisture content of the loess slope soil gradually increased, the soil strength gradually decreased, and its own weight gradually increased. The gully erosion on the slope gradually developed, the slope toe collapsed, and the tensile cracks occurred on the top of the slope. The cracks increased the infiltration of rainfall, which made the strength of soil around the crack decrease rapidly, and finally caused a landslide when the rainfall lasted 308.8 h. Rainfall infiltration and concentrated infiltration caused by cracks accelerated the reduction of soil strength and led to the landslide. The deeper and more cracks developed, the greater their damage to slope stability.

Abstract:Soil-water characteristic curve is usually used to estimate the shear strength of unsaturated soil. In consideration of the water absorption and reinforcement effect of plant roots, the shear strength of plant slope can not be directly calculated by the formula of unsaturated soil shear strength based on matrix suction.In this paper, the bare slope and vegetation slope are taken as the research objects, and the soil and water characteristic curve of the test soil is obtained by combining the tensiometer field test and indoor shear test. The results show that the plant root implantation can effectively improve the air intake value of slope soil, which is 41.10% higher than that of plain soil. Under the same water content, the matric suction of plant slope is significantly higher than that of plain soil slope, which improves the water holding capacity of slope soil.The Van Genuchten model can be used perfectly to fit the datum from the soil water characteristic curve. With the increase of water content, the shear strength parameters of the soil with root and plain soil are similar, which are both increasing first and then decreasing. But the change parameters of the soil with root are large. When the water content is 21.29%, the cohesion of the soil with root increases by 4.86 kPa, and the increase is 18.55%, while the sensitivity of the internal friction angle to the root system is not as good as the cohesion.With the increase of soil matric suction, the change trend of mechanical parameters of shear strength of vegetation slope and plain soil slope is basically the same, and the cohesion of soil increases most obviously in the range of matric suction of 60~90 kPa. However, the matric suction of vegetation slope increases the shear strength of slope soil more greatly due to the existence of plant roots, The maximum increases of cohesion and internal friction angle are 37.34% and 40.30% respectively.By establishing the relationship between the parameters of soil water characteristic curve and the shear strength of plant slope, the shear strength of plant slope under different water content or matric suction can be calculated, which provides a theoretical basis for further analysis of the stability of plant slope in engineering practice.

Abstract:In order to investigate the effect of autumn tillage on the regulation of seasonal freeze-thaw soil thermal conditions, this study compared and analyzed the effects of the five treatments:Traditional tillage (FG), no-tillage (MG), ridge-furrow (LG), tillage followed by activated carbon mulching (FH), and tillage followed by straw mulching (FJ), on soil temperature, freeze-thaw cycles and soil temperature gradients. The results showed that compared with the FG, MG, LG, FH and FJ treatments all weakened the correlation between soil temperature and air temperature, reduced the dynamic magnitude of soil temperature throughout the freeze-thaw period and the degree of diurnal variability of soil temperature at different freeze-thaw stages, and maintained the stability of the soil temperature sequence as FJ > FH > LG > MG. The FG was the first to freeze and melt, and the remaining treatments delayed the effect of soil freezing and melting rate as FJ > FH > LG > MG. And the smaller the freezing and melting rates, the more frequent the freeze-thaw alternation and the greater the number of freeze-thaw cycles. The soil temperature gradient of all treatments showed a highly significant correlation with air temperature (P < 0.01), and the degree of correlation was FG > LG > MG > FH > FJ. All treatments showed a highly significantly negative correlation with soil water storage (P < 0.01), and the degree of correlation was FJ > FH > LG > MG > FG. MG, LG, FH, and FJ treatments all enhanced the retention of soil water and heat resources, in which FJ and FH promoted the upward movement of deep soil heat, which was more conducive to improving soil water and heat conditions during seasonal freezing and thawing and maintaining soil moisture in spring sowing in the north Xinjiang.

Abstract:In order to explore the effects of different nitrogen inputs on soil erosion and soil water-stable aggregates in red soil slope farmland, four nitrogen treatments including N1(300.00 kg/hm²), N2(225.00 kg/hm²), N3(150.00 kg/hm²) and N4(75.00 kg/hm²) were designed, and the runoff and sediment yield were measured during the whole growth period of silage maize. Meanwhile, the aggregate components with particle size >2,1~2,0.5~1,0.25~0.5 and <0.25 mm were obtained by wet screening method, and the content of water-stable aggregates (WSA_>0.25), mean weight diameter (MWD), geometric mean diameter (GMD) and parting dimension (PD) were calculated. The results showed that:(1) The characteristics of runoff and sediment yield of different nitrogen inputs were closely related to rainfall intensity. The runoff and sediment yields of N1 and N2 treatments were significantly lower than those of N3 and N4 treatments under the condition of low, medium and high intensity rainfall (P<0.01), and there was no significant difference in runoff and sediment yield between N1 and N2 treatment (P>0.05). Whereas, the differences in runoff and sediment yield were not significant among different treatments under extremely high intensity rainfall (P>0.05). (2) WSA_>0.25,GMD and MWD of N2 treatment were higher than those of the other three treatments, but the PD was relatively low. Additionally, there was a very significant positive correlation among WSA_>0.25, MWD and GMD, but an extremely significant negative correlation with PD, runoff and sediment yield. (3) The soil bulk densities of N1 and N2 treatments were significantly lower than those of N3 and N4 treatments (P<0.01), but the porosity and soil water holding capacity of N1 and N2 treatments were significantly higher than those of N3 and N4 treatments (P<0.05). Therefore, reducing 25% of nitrogen input at the local fertilization level will not aggravate soil erosion, and improve the soil physical properties to maintain the productivity of red soil sloping farmland.

Abstract:Aggregate is the basic structural unit of soil, and its stability is an important index to evaluate soil quality. In this paper, the stability of soil aggregates developed from different parent materials (Limestone, Quaternary laterite, Sand shale) in the south subtropical region was determined by wet-sieving method and Le bissonnais method. The results showed that:(1) With the increase of soil depth, soil bulk density increased gradually, while porosity, organic matter and free iron oxide content decreased. The highest content of organic matter was 22.44~42.97 g/kg. The clay (40.93% and 42.51%) and silt (41.69% and 42.31%) were the main parent materials of Limestone soil and Quaternary laterite soil, while clay content of Sand shale soil was the lowest, 33.79%. (2) After wet-sieving, the contents of water stable aggregates in Limestone soil, Quaternary Red soil and Sand Shale soil were 91.58%~92.31%, 76.45%~90.80%, and 79.18%~86.67%, respectively. The stability of aggregates in soils decreased with the increase of soil depth. (3) The MWD values of soil aggregates of the three parent materials were slow-wetting treatment > pre-wetting shock treatment > rapid-wetting treatment, The 40-60 cm soil layer developed from Sand shale was most sensitive to dissipation and mechanical crushing, and its relative dissipation index RSI and relative mechanical crushing index RMI were 0.78 and 0.42, respectively. The stability of soil aggregates was positively correlated with clay, organic matter and free iron content.

Abstract:In order to study the effects of vegetation restoration on the composition and stability of soil aggregates in the water-level-fluctuation zone, dry screening and wet screening methods were used to determine the composition and distribution of soil aggregates in willow forest under different water levels and elevations in the water-level-fluctuation zone of Daqiao Reservoir, and fractal characteristics of soil aggregates were analyzed based on fractal theory. The results showed as follows:(1) The contents of non-water-stable aggregates and water-stable aggregates that greater than 0.25 mm in willow forest land in the water-fluctuation zone were 73.13%~93.69% and 47.62%~82.06%, respectively, which were higher than those of control plots without vegetation, but the difference between them was not significant. The content of macro-aggregates in water-level-fluctuation zone decreased with the increasing of water level elevation and depth of soil layer, however, there was no significant difference between different water levels and soil layers (p>0.05). (2) The fractal dimension (D) of soil water-stable aggregates in willow forest in the water-level-fluctuation zone ranged from 2.51 to 2.82, with an average of 2.67, which was lower than that of the control (2.75). The fractal dimension (D) of soil water-stable aggregates showed no significant difference between different water level elevations and different soil layers (p>0.05), and it decreased with the increasing of water level, and the D value of 0-10 cm soil layer was lower than that of 10-20 cm soil layer. (3) The average values of soil MWD and GMD of willow forest in water-level-fluctuation zone were 0.81 and 0.24 mm, respectively, which were higher than those of the control (0.71 and 0.15 mm). The stability of soil aggregates in willow forest was higher than control. The stability of soil aggregates had a certain spatial difference in the water-level fluctuation zone. Both MWD and GMD followed the order of high water level (2 016~2 019 m) > medium water level (2 010~2 013 m) > low water level (2 007 m), and the MWD and GMD in the 0-10 cm soil layer were both greater than those in the 10-20 cm soil layer. However, there was no significant difference between different water levels and different soil layers (p>0.05). In conclusion, vegetation restoration in the water-level-fluctuation zone of Daqiao Reservoir could improve soil aggregate structure to a certain extent, and the stability of soil aggregate in willow forest land in the water-level-fluctuation zone decreased with the increasing of flooding depth.

Abstract:Root system plays an important role in the formation and permeability of soil macropores. Aiming to clarify the numerical relationship between root biomass distribution and soil macropores characteristics, a naturally grown Chinese fir in JinYun mountain was selected as research object. The macropore area and root distribution characteristics on 4 dye tracing treated soil profiles in field were observed, and then a series of water penetration tests were conducted using self-designed constant head device for soil sampling in dyed and undyed zone in Lab. Results showed that:(1) The dyed area of soil was different for different soil profiles and different soil depths. The farther away from the trunk of the tree, the larger the dyed area, while the closer to the trunk, the smaller the dyed area, and the overall depth increased. The dyed area ratio of each section above all decreased. (2) The four soil profiles mainly showed a trend of decreasing root coefficient with the increasing soil depths. The root diameter mainly concentrated between 0.2~10 and 0.2~1 mm diameter. (3) The dyed area had a greater stable outflow rate than the undyed area. The outflow rate of the dyed area in the four sections was 1.97, 1.81, 1.77 and 1.70 times those of the undyed area, respectively. As the depth of the soil layer increased, the number of macropores decreased, and the radius of the macropores ranged from 0.3 to 1.7 mm; (4) The macroporosity and root biomass were positively correlated with the permeability coefficient, and the macroporosity contributed 94.5% of variation in the permeability coefficients, while root biomass contributed 87.4%.

Abstract:In order to study the soil infiltration characteristics and soil quality evaluation under different vegetation cover after returning farmland to forest in the loess region of Western Shanxi Province, the field double-ring infiltration method was developed for the determination of soil water infiltration characteristics. The soil bulk density, porosity, organic matter, and total nitrogen were studied. Correlation analysis was used to study the relationships between soil infiltration capability and the physical and chemical properties of soil. Principal component analysis was also used on the soil physical and chemical properties. The results showed that:(1) Vegetation type had a great influence on soil permeability rate, which was as follows natural secondary forest > Mixed forest of Robinia pseudoacacia and Pinus tabulaeformis > Robinia pseudoacacia forest > Pinus tabulaeformis forest > Shrub > Malus pumila > waste grassland > farmland. (2) After the conversion of farmland to forest, the soil physical and chemical properties of different types of vegetation had significant differences. With the better degree of forest restoration, the soil bulk density decreased, and the contents of porosity and organic matter increased, the soil physical and chemical properties was also gradually improved. Soil infiltration characteristics were significantly positively correlated with total porosity, non-capillary porosity, organic matter and total nitrogen content (P < 0.01), significantly negatively correlated with bulk density (P < 0.01), and significantly negatively correlated with available phosphorus (P < 0.05). With the conversion from farmland to waste grassland, shrub and arboreal forest, soil physical and chemical properties were improved and soil permeability was also gradually enhanced. (3) Soil infiltration performance and soil physical and chemical properties were used as soil evaluation indexes. The order of soil quality of different vegetation types from high to low was as follows natural secondary forest > Mixed forest of Robinia pseudoacacia and Pinus tabulaeformis > Robinia pseudoacacia forest > Pinus tabulaeformis forest> Shrub > Malus pumila > waste grassland > farmland.

Abstract:In order to explore the regulation effect of biochar on potassium leaching loss in fluvo-aquic soil and sandy soil, a soil column leaching simulation test was conducted, and water washed biochar was used as the research object, the contents of different forms of potassium, surface morphology and oxygen-containing functional groups in biochar before and after washing were compared, and then explore the regulation effects of different amounts of washed biochar on potassium leaching loss in two types of soil. The results showed that the water-soluble potassium content in biochar was decreased from 13.9 g/kg to 0.06 g/kg by water-washed treatment, but the change of pore structure and surface oxygen-containing functional groups of biochar were less affected. Moreover, the effect of water-washed biochar on water leaching loss of fluvo-aquic soil and sandy soil was influenced by its application amount, which showed a trend of low amount of water-washed biochar promoted the water leaching loss, but high amount inhibited the water leaching loss, and adding 1% water-washed biochar significantly increased the total amount of water leaching loss in the two types of soil. The effects of biochar on potassium leaching in two types of soils were different. Adding 2% and 4% washed biochar showed significant inhibition and control effect on potassium leaching in sandy soil, and compared with the treatment without biochar, the total leaching amount of potassium decreased by 21.2% and 28.3%, respectively. While adding 1% washed biochar increased the total amount of potassium leaching in fluvo-aquic soil. In addition, biochar could improve soil cation exchange capacity and exchangeable potassium content of topsoil, and the increasing extent improved with the increasing of biochar application amount, and the improvement effect was more obvious in sand soil. Therefore, for the perspective of potassium leaching, biochar was more suitable for sandy soil with low cation exchange capacity and poor fertilizer retention capacity.

Abstract:Through field sampling and laboratory analysis, the effects of land use patterns on soil structure and fertility of calcareous soil in karst area of Northwest Guangxi were investigated. Based on the long-term observation plots, we selected five common land use patterns, including mowing grassland (CD), native tree species (XT), deciduous orchard (GY), planted pasture (MC) and planted maize (YM). The stability of soil aggregates and the characteristics of organic carbon in the surface (0-10 cm) and sub-surface (10-20 cm) soil of the five land use patterns were analyzed and compared. The results showed that the content of soil mechanical stable aggregates of the five land use patterns all decreased with the decreasing of particle size, and the content of water-stable aggregates decreased first and then increased with the decreasing of particle size. In addition, the soil aggregates measured by both dry and wet sieve methods were dominated by the aggregates that bigger than 1 mm, and their ratio ranged from 67.04% to 90.11% and from 66.83% to 84.65%, respectively. The mean weight diameter (MWD) and geometric mean diameter (GMD) were employed to evaluate the stability of soil aggregates. Under the dry sieve method, MWD and GMD of both surface and subsurface soil followed the order of XT>MC≈GY≈YM>CD. Under the wet sieve method, MWD and GMD were significantly (P<0.05) different in surface soil, which were relatively higher in XT and MC, and relatively lower in CD and YM. The total soil organic carbon content was higher in surface soil than that in sub-surface soil, and it was significantly (P<0.05) higher in MC, CD and XT than those in GY and YM in surface soil, but only relatively higher in sub-surface soil in CD. The organic carbon content of soil aggregates at all levels was similar to the total soil organic carbon content under each land use patterns. In addition, the contribution rate of organic carbon of aggregates generally decreased with the decreasing of aggregated size under different land use patterns. The stability of soil aggregates and the organic carbon content were relatively higher in XT and MC. The results of this study could provide theoretical support for the adjustment of land use structure in this area.

Abstract:Soil water is the key factor of eco-environmental restoration in the water-wind erosion crisscross region of the Loess Plateau, which demonstrates a great temporal and spatial heterogeneity. In this study, the representative LaoYeManQu watershed in the water-wind erosion crisscross region was selected as the research area, and 73 sampling points were set up with a grid of 50 m×50 m. From June 2013 to October 2019, 23 in-situ observations of soil water content (SWC) in 0-5 m profile was carried out by using neutron probe, and the environmental factors of each sampling point were collected simultaneously. Combined with classical statistics, geostatistics, and random forest, the seasonal variation characteristics and controlling factors of SWC at different soil layers (5 layers in total, one layer per meter) in the watershed were investigated. The results showed that the distribution characteristics and seasonal variations of SWC for soil layers differed. For the 0-1 m soil layer, the mean SWC between summer and winter was significant different (p < 0.05); while below 1 m, the mean SWC in spring was higher than that in other seasons, but it was not significant. In the soil layers above 3 m, significant differences were found in SWC among different land uses and between loam and sandy soil for four seasons (p < 0.05). For each soil layer, the SWC between shady and sunny slopes also differed significantly in different seasons (p < 0.05). SWC in all seasons was negatively correlated with soil bulk density and sand content, and positively correlated with other measured factors. With the increasing of soil depth, the correlations between SWC and measured factors generally decreased except soil organic carbon density and clay content. The factors contributing to SWC variation were soil properties, topography, and land use in sequence. These results could provide reference for the management of deep soil water resources, soil hydrological observation and simulation, and vegetation optimization in the study area and other similar regions characterized by the water and wind erosion crisscross.

Abstract:In order to study the water conservation function and its change tendencies of Taiwania flousiana plantations, T. flousiana plantations at different ages (9, 17, 25 and 37 years old) in Nandan county of Guangxi were taken as research objects, and the water holding capacities of the canopy, undergrowth vegetation lager, litter lager and soil lager of the T. flousiana plantations were studied by the indoor soaking method and the cutting ring method. The results showed that:(1) The water holding capacity of the canopy and the vegetation layer under canopy for the different ages of T. flousiana plantations ranked 18.79~28.37 and 1.27~4.72 t/hm², respectively. The water holding capacity of the understory vegetation increased significantly with the increasing of forest age (P < 0.05). The litter amount was 2.23~10.67 t/hm², and the maximum water holding capacity was 5.95~34.15 t/hm², which increased significantly with the increasing of forest age (P < 0.05). (2) Soil non-capillary porosity and total porosity of different T. flousiana plantations were 5.60%~15.68% and 48.27%~66.85%, respectively. Soil non-capillary porosity and total porosity in 0-20 and 20-40 cm soil layers were significantly higher than those in 40-80 cm soil layers (P < 0.05), and increased with the increasing of forest age. The maximum water holding capacity and the effective water holding capacity of the soil layer (0-80 cm) were 4 196.74~4 416.47 and 540.13~648.07 t/hm², respectively. The maximum water holding capacity and the effective water holding capacity of the 0-20 and 20-40 cm soil layers increased with the increasing of forest age. (3) The total water storage capacity of 9, 17, 25 and 37 years old T. flousiana plantations were 4 222.43, 4 272.55, 4 355.29 and 4 484.32 t/hm², respectively, which increased with the increasing of forest age. In conclusion, the T. flousiana plantations could improve the soil structure and moisture condition and enhance the water conservation performance of stands.

Abstract:Soil saturated hydraulic conductivity (Ks) is an important parameter affecting soil hydrological process, which reflects soil infiltration and water holding capacity. In order to explore spatial distribution characteristics and influencing factors of Ks, we used the grid method (2 km×2 km), 27 samples of different landscape types were arranged in the desert-oasis ecotone of the middle reaches of the Heihe River. Ks was determined by Hood-IL 2700 infitrometer and soil physicochemical properties of 0-30 cm soil depth were obtained. Spatial distribution characteristics of Ks and its influencing factors were analyzed by classical statistics and geostatistics, and pedo-transfer functions were constructed. The results showed that:(1) The variation coefficient of Ks was 1.21, which belonged to strong variation. Ks had significant negative correlations with soil water content, soil organic carbon, clay and silt, while had significant positive correlations with bulk density and sand. (2) The best fitting model of semi-variable function of soil water content was exponential model, and those of bulk density and clay were spherical models. The optimum sampling distance of bulk density, water content and clay were 0.38~0.77, 1.86~3.72 and 1.41~2.83 km. The constructed pedo-transfer function was log Ks=-2.914+2.772ρ_b-0.09SW+0.068clay. Bulk density, soil water content and clay could be used as predictive variables that could simulate the spatial distribution of Ks in the desert-oasis ecotone. This study could provide data support for simulating soil water movement and simulation in desert-oasis ecotone.

Abstract:The litter and soil of the forest park in Dongguan may have good water conservation functions, but the information is lack. In order to explore the water conservation capacity of different forest litter and soil, the study for 5 types of 30-year non-commercial forests were conducted in July 2020. Drying method and experimental water soaking method were used to study the water holding capacity and physical properties of litter and soil (0-20 cm). The results showed that the thickness of the litter layer of the ecological public welfare forests varied from 1.5 to 10.5 cm, and the biomass varied from 0.32 to 5.73 t/hm². The rank of the maximum water holding capacity and effective interception power showed that Pinus elliottii-Psychotria asiatica forest>Acacia mangium-Garcinia oblongifolia forest>Machilus chekiangensis-Litsea rotundifoliaf forest>Schima superba-Camellia oleifera forest>Eucalyptus robusta-Schefflera heptaphylla forest. It was also found that the cumulative water holding capacity had a significant logarithmic relationship with the immersion time, and the water absorption rate had a significant power function relationship with the immersion time; the cumulative water loss and the water loss time have a significant three-time relationship, and the water loss rate and water loss time showed a significant reciprocal relationship. The soil water holding capacity of different types of forest stands was directly related to the size of porosity. The higher the total soil porosity and capillary porosity, soil bulk density decreaed, while soil water retention capacity increased with increasing total soil porosity and capillary porosity. This study can provide references for sustainable forest management and ecological benefit evaluation in this area.

Abstract:Ecosystem quality is essential for the region to explore new high-quality development methods with ecological priority and green development-oriented. Carrying out regional ecosystem service assessment can obtain the land space's ecological background characteristics, provide a base map of the status quo for the construction of ecosystem protection patterns, clarify the focus of ecosystem restoration, and provide guidance for the optimization of land space. This study concentrated on the Changting County of Fujian Province and attempted to explicitly elucidate its ecosystem services at the county, town, village, and system patch scales. Our methodology's distinctive contribution was that we coupled the ecological carrying capacity and gross ecological product approaches and set specific evaluation indicators based on regional ecological representativeness, regional biomass differences, and public willingness to pay and competence. The results showed that the ecosystem services grade conformed to the zoning rules, roughly appearing the low characteristics in the middle and high in the surroundings. Refinement of the scale made the distribution of results more heterogeneous, providing targeted suggestions for ecological restoration and space optimization. The ecosystem was relatively fragile in Changting County, with low ecological level townships accounting for as high as 38.89%. The influencing factors were diverse, among which soil erosion and forest coverage had a significant impact. Topography, human activities, and policy implementation affected the spatial distribution of ecological carrying capacity, and densely populated areas with flat terrain were concentrated areas with low ecological carrying capacity. Forest ecosystems value was the dominant part of the gross ecological product in Changting County. The forest ecosystem area accounted for more than 89% in the four townships with extremely high average gross ecological product level. The methodology applied in the study could help promote the application and practice of the "two mountains" theory. Our findings will provide recommendations on regional ecosystem services function improvement and spatial development.

Abstract:Discovering the response and path of natural environmental elements to extreme drought events has important scientific and practical significance for efficiently and reasonably preventing and mitigating the impact of drought on society and the natural environment. Based on the El Niño extreme drought event in 2019, this study identified a drought year (2019) and a normal year (2013) using the weather data from meteorological station. And the landsat8 images of these two years were used to invert the natural environment factors of Hani Rice Terraces region, including surface temperature (TEM), soil moisture (TVDI), vegetation coverage (NDVI), surface water body (NDWI). Furthermore, the response status, interaction of these natural environment factors and the path to the extreme drought event are revealed. The results showed that:(1) Under the extreme drought event, the Hani Rice Terraces region temperature increased by about 2℃, vegetation index decreased by about 0.04, soil moisture index increased by about 0.07, water area decreased almost 40.2%. (2) The surface temperature, soil moisture, vegetation coverage, surface water changed significantly, and a positive feedback path was formed, and it helped to accelerate the regional drought.

Abstract:Net primary productivity (NPP) of vegetation is an important part of the ecosystem carbon cycle process, and also an important part of carbon source/sink. Based on MODIS reflectance data (MOD09A1), temperature and sunshine hours data from 2001 to 2019, this study used the light energy utilization model to estimate the NPP of the terrestrial ecosystem in Jilin Province, and analyzed the spatial-temporal dynamics of NPP and their correlation with climate factors using trend analysis and spatial variability analysis. The results showed that:(1) From 2001 to 2019, the annual average and total amount of vegetation NPP in Jilin Province fluctuated and increased. The total amount of vegetation NPP within the jurisdiction showed the following:forest>farmland>grassland. (2) The distribution of NPP from 2001 to 2019 showed obvious spatial differences. NPP in most regions showed an increasing trend, and the overall variability was stable. However, the degree of spatial variability of NPP in the northwest region was relatively larger. Grassland degradation, desertification, and salinization were related to a certain extent, and vegetation restoration was obvious. (3) The correlations between vegetation NPP and annual average temperature and annual precipitation in Jilin Province had certain regional differences. Most areas of the study area had a positive correlation with temperature, and a small part of the study area had a positive correlation with precipitation.

Abstract:Clarifying the characteristics and influencing factors of specific soil enzyme activities in the process of vegetation restoration is of great significance to objectively revealing the change characteristics of microbial activity in the process of vegetation secondary succession. Based on the method of spatiotemporal interaction, this study selected five stages in the vegetation secondary succession process in the loess hilly region as the research objects, including farmland, grassland, shrubs, pioneer forests and top community stage, and discussed the change characteristics and influencing factors of specific soil enzyme activities of seven enzymes (β-1,4-glucose Glucosidase (BG), cellobio hydrolase (CBH), β-xylosidase (BX), N-acetyl-beta-D-glucosaminidase (NAG), leucine amino peptide (LAP), alaninase transaminase (ALT)) and alkaline phosphatase (AP)). The results showed that in the process of vegetation secondary succession, unit soil organic carbon (SOC), soil CBH, BX and NAG activities increased significantly at first and then decreased significantly (P < 0.05), and it reached the highest point in the pioneer forest stage; while the activities of three enzymes per unit soil microbial phospholipid fatty acid (PLFA) showed opposite trends (P < 0.05), and reached the highest level in the top community stage. Correlation analysis showed that soil CBH, BX and NAG enzyme activities per unit SOC and PLFA were significantly negatively correlated with soil pH and significantly positively correlated with soil DOC (P < 0.05); specific soil enzyme activity per unit SOC and PLFA were significantly positively correlated and negatively correlated with soil biological factors, respectively (P < 0.05). Redundancy analysis showed that the phosphorus content as well as the carbon and nitrogen content in the soil were the main driving factor for the change of specific enzyme activity per SOC and PLFA, respectively. This study provided new information for further revealing the soil nutrient cycling and quality changes during the secondary succession process.

Abstract:Global concern about the restoration and reconstruction of vegetation ecosystems has increased, thus the concepts of potential natural vegetation (PNV) and habitat suitability should be integrated into revegetation programs to achieve sustainable ecosystems. Based on high spatial resolution climate data, this study revealed the dynamic evolution of spatial pattern and habitat suitability of PNV during 2001-2020 in the Loess Plateau (LP) using a dynamic vegetation model (LPJ-GUESS), and identified the vegetation priority restoration area. The results showed that the main PNV in the LP were grassland and forest, and potential grassland was mainly distrubuted in the north and northwest regions (about 73.23% of LP area), while potential forest was mainly located in the south (about 26.16% of LP area), and very few barren ground was mainly distributed in the western high-altitude mountains. Among the potential forests, temperate deciduous broad-leaved trees, cold temperate evergreen coniferous forest and temperate evergreen coniferous trees accounted for about 22.28%, 3.88% and 0.01%, respectively. With the advance of climate change, the area of potential forest had decreased, while the area of potential grassland hand increased slightly. The habitat suitability of PNV was low in the northwest, high in the south and southeast. The potential temperate deciduous broad-leaved trees distributed in the southern plain of the LP had higher habitat suitability, while the potential grassland distributed in the northern and northeastern LP had lower habitat suitability. For each kind of PNV, the geographical space and priority restoration area occupied by its highest habitat suitability were significantly different. These reaserch results could provide a scientific basis for vegetation restoration and reconstruction in the Loess Plateau.

Abstract:In this study, the hourly transpiration rate of Cinnamomum camphora was measured from June 2019 to October 2020 using the Grainer-type thermal dissipation probes. Meteorological factors and soil water content were simultaneously monitored during the study period. To deepen the understanding of the relationship between plant physiological changes and environmental changes, and to provide a basis for improving the accuracy of transpiration predicting model, this study analyzed the relationship between the transpiration of C. camphora and the main meteorological factors at different periods during the day. The variation characteristics of time lag and the change of hysteresis correction on the predicting model of transpiration were also investigated. The results showed that the time lag between transpiration and solar radiation is counterclockwise, and that between transpiration and saturated water vapor pressure or temperature is clockwise during the growing seasons (from June to October). Based on Gauss equations, it was found that on average transpiration in the growing seasons of 2019 and 2020 lagged behind solar radiation by 0.94 hours, and advanced by 2.60 and 2.61 hours on saturated vapor pressure difference and temperature. This time-lag effect was caused by the different responses of transpiration to meteorological factors at different stages of the day. In the rising stage (7:00-11:00), transpiration was more sensitive to changes of solar radiation than that in the descending stage (17:00-21:00). On the contrary, in the rising stage, transpiration was less sensitive to variation in saturated vapor pressure and temperature than that in the descending stage. The time-lag effects between transpiration and solar radiation or saturated vapor pressure or temperature had obvious seasonal variation. There were certain differences in the hysteresis loop area between the growing seasons of 2019 and 2020, but the maximum area appeared in October and the minimum area appeared in August or September. On the hourly scale, when soil moisture was sufficient, the hysteresis added with the increase of the main daily mean meteorological factors, but under soil moisture stress, the time lag did not change significantly with the increase of the major daily mean meteorological factors. After correcting time lag, the determinants of the regression equations of transpiration and solar radiation increased by 4% and 9%, and the coefficient of determination of the regression equations of transpiration and integrated meteorological factors constructed by principal component analysis increased by 7%. Therefore, eliminating time lag could improve the accuracy of transpiration predicting model.

Abstract:In order to explore the effects of different thinning intensities on soil carbon and nitrogen fractions in Chinese fir plantation, this study was conducted in 11-year-old fir plantations in Guanzhuang state-owned forest in Sanming City, Fujian Province. Three types of thinning, including light intensive thinning (LIT), moderate interval thinning (MIT), and hight intensive thinning (HIT) were adopted. The variations of total organic carbon (SOC), total nitrogen (TN), readily oxidized organic carbon (ROC), nitrate nitrogen (NO₃-N), ammonium nitrogen (NH₄⁺-N), microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), microbial entropy carbon (qMBC) and microbial entropy nitrogen (qMBN) in the 0-10,10-20,20-40,40-60,60-80,80-100 cm soil layers of different thinning intensities were explored. The results showed that thinning reduced soil SOC and TN contents by 1.4%~36.9% and 3.1%~45.7%, respectively. Thinning increased soil MBC and NO₃-N content, while the change degrees on ROC, NH₄⁺-N and MBN showed differences in different soil layers. With the increase of thinning intensity, the values of qMBC and qMBN gradually increased. Correlation analysis showed that soil SOC was significantly positively correlated with TN, qMBC, ROC, NH₄⁺-N, MBC and MBN, respectively (P<0.01). TN was significantly positively correlated with qMBN, ROC, NH₄⁺-N MBC and MBN (P<0.01). The thinning treatment of Cunninghamia lanceolate plantation decreased SOC and TN content in soil surface layer, increased SMBC content and qMBC, qMBN value in soil, and increased SMBN content in soil surface layer (0-10 cm). The results indicate that the decrease of soil SOC and TN content caused by thinning is mainly due to the increase of active carbon and nitrogen content, which improves the decomposition rate of organic matter in soil, and finally leads to the decrease of soil SOC and TN content.

Abstract:Through the analysis of soil moisture data at 77 sites in Gansu Province from 10 to 100 cm, the purpose of this study was to reveal the differences in soil bulk density, field water capacity, and wilting pointunder different soil textures in different climate regions, and to evaluate the applicability and promotion of the observed data. The results showed that the soil bulk densities ranged from 0.89 to 1.79 g/cm³, with an average of 1.36 g/cm³. There was a significant difference between the bulk density of top soil and deep soil. The bulk densities of shallow soils in semi-humid areas and semi-arid areas were more likely to be disturbed by the external environment and human activities. The field water holding capacity in most area was increasing from northwest to southeast, with the maximum of 36%~40% in the 10-50 cm soil layer in the alpine humid area. The difference in field water holding capacity between 10 and 20 cm soil layers was small, with a correlation coefficient (0.96), which was quite different from other layers, the 50 cm soil layer was likely to be the boundary layer of soil field water holding capacity. The maximum wilting point of each soil layer appeared in the arid area of the cold temperate zone and the middle of the alpine semi-arid and semi-humid area. The field water holding capacity and the wilting point of different layers were extremely significantly correlated. Most parts of Gansu Province are mainly loam, in addition, the arid area is mainly sandy loam soil, the semi-arid area is dominated by sandy loam and clay loam, and the semi-humid area by silt loam and clay loam.

Abstract:Soil water is the main source of plant water consumption, and its change has an important effect on the whole ecosystem. Using GRACE satellite data and GLDAS-NoAH model, this study analyzed the spatial and temporal variation of soil water in the Loess Plateau from 2002 to 2020. Combined with the from 2002 to 2020 MODIS NDVI product data set of GEE platform and the precipitation data from 2000 to 2017, the correlation analysis of soil water changes was carried out for comparative analysis, and the M-K test method was used to test the change trend. The results showed that:(1) The monthly mean of equivalent water height (mm water column height) of GRACE from 2002 to 2020 was (-7.56±4.38) mm, and showing a significant decreasing trend from 2008. (2) From 2000 to 2020, soil water in the 0-10 cm soil layer showed no significant increase trend, while it showed no significant change trend in the 10-40, 40-100 and 100-200 cm soil layers, and it showed a significant decrease trend in the 200 cm soil layer from 2012 to 2020. (3) With the increasing of soil depth, the correlation between precipitation and soil water decreased significantly in the Loess Plateau from 2000 to 2017. Correlation coefficient decreased from 0.581 of 0-10 cm soil layer to 0.099 of 100-200 cm soil layer. The correlation coefficient between NDVI and soil water of the soil layer deeper than 200 cm 2002 to 2020 was -0.805, which was a significant negative correlation. The results revealed the change law of soil water in the Loess Plateau, revealed the correlation between precipitation and NDVI changes and soil water, which could provide a theoretical support for the next step of vegetation restoration in the Loess Plateau.

Abstract:It is of great significance to study the temporal and spatial dynamic characteristics of groundwater level depth and its response to land use change in arid and water-scarce areas for strengthening land use and groundwater resource management in agricultural areas. Taking the plain irrigation area of Hutubi County as the research area, based on geostatistics and GIS, the spatial and temporal distribution of groundwater depth was fitted by ordinary Kriging interpolation in 2000, 2010 and 2018. Moreover, the land use type map was generated by interpreting remote sensing data during the corresponding period. Superposition analysis was conducted on the response relationship between the change of groundwater depth in different periods and the transfer of land use types in the corresponding periods. The results showed that space variation of groundwater depth in Hutubi County was mainly due to structural natural factors such as topography and climate. The spatial correlation of groundwater depth increased year by year, while the spatial heterogeneity weakened gradually. Spatially, the groundwater depth was gradually shallow from south to north, and from 2000 to 2010, the area with the groundwater depth less than 10 m decreased by 86.61%. The substantial increase of arable land was controlled after 2010. However, due to the large base of cultivated land, the amount of extracted groundwater began to decline from the maximum value in 2014, and the groundwater began to recover in some areas. The cultivated land was the main land use type in the study area, and the proportion of agricultural water in groundwater was as high as 84.68%. Therefore, the dynamic change of groundwater depth was highly correlated with the change of cultivated land area.

Abstract:In order to reveal the different growth adaptation strategies of the root system of Populus euphratica seedlings growing in different groundwater depth and soil texture, taking P. euphratica seedlings as experimental materials, three groundwater depths of 30 (A₁), 60 (A₂) and 90 (A₃) cm were set up, and three soil textures of sand (B₁), sandy loam (B₂) and clay loam (B₃) were combined in the study. The impacts of groundwater depth and soil texture on the root growth and architecture of P. euphratica seedlings in Tarim River Basin were studied. The results showed that:(1) The increase of groundwater depth promoted the development of root morphology and root biomass accumulation of P. euphratica seedlings. The root depth, total root length, total root volume and total root surface area of P. euphratica seedlings all reached the maximum under the A₃B₂ treatment. (2) root weakening coefficient (β), R₅₀ and R₉₀ (50% and 90% of root biomass distribution depth, respectively) were proportional to groundwater depth, and the root biomass of deep soil increased with the increasing of groundwater depth. Under the condition of A₂ and A₃, the root biomass showed the trend of B₂ > B₃ > B₁. The vertical distribution of fine root biomass presented a "single peak" curve under each treatment. (3) The average root connection length increased with the deepening of groundwater depth, and reached the maximum of 14 cm under the A₃B₁ treatment. Under B₂ and B₃ conditions, with the increasing of groundwater depth, the root system of seedlings gradually changed from a forked branch structure to herring bone branching. Under the B₁ condition, the root topological parameters were larger, and the root branch structure of seedling tended to herring bone branching. These results could provide reference for the optimal allocation of water resources in the Tarim River Basin.

Abstract:In order to study the distribution characteristics of the fine roots of Populus simonii with different degradation degrees in Bashang area, this paper used soil column method to compare the distribution rules and difference of fine root parameters in horizontal and vertical directions in P. simonii stands with different degradation degrees (no degradation, moderate degradation and severe degradation), and analyzed the proportion of root parameters in different soil layers. The results showed that:(1) With the decreasing of soil moisture content, the degradation degree of P. simonii increased, the proportion of fine roots in the surface layer increased, and its proportion in the deep layer decreased. (2) In the vertical direction, the fine root biomass of P. simonii in 0-20 cm soil layer was significantly higher than that in other soil layers (P < 0.05), and the root length density, root surface area density and root volume density decreased significantly with the deepening of soil layer. In 0-20, 20-40, 40-60, 60-80 and 80-100 cm soil layers, the root surface area density and root volume density of fine roots followed the order of no degradation>moderately degradation>severely degradation. (3) In the horizontal direction away from the trunk, the root length density of fine roots increased at first and then decreased in no degeneration and moderately degeneration stands, while there was no significant difference among 0-50, 50-100 and 100-150 cm soil layers in severely degenerated P. simonii stand, and that increased significantly in 150-200 cm soli layer and reached the maximum (0.465 7 cm/cm³) (P < 0.05). The root surface area density and root volume density of fine roots all followed the order of no degradation>moderately degradation>severely degradation at four horizontal distances. The fine root biomasses of no degraded P. simonii were all the largest (19.53, 15.74, 14.17 and 14.20 g). The root volume density decreased with the increasing of horizontal distance. The results of this study could provide a scientific reference for exploring the fine root distribution pattern and degradation reasons of shelterbelts, and for guiding the vegetation restoration and reconstruction in Bashang plateau.

Abstract:Our objective was to understand the relationship between leaf stoichiometric characteristics, nutrients reabsorption efficiency and nitrogen (N) supply of Larix principis-rupprechtii. We selected 24-year-old Larix principis-rupprechtii plantation as study object, and set up a 3-level (0, 8 and 15 g/(m²·a)) field experiment of N addition for 6 years to explore the change of mature leaves, leaves litter and soil nutrients contents. The results showed that the content of C in mature leaves was significantly different among years. The N addition significantly increased the C and N contents of mature leaves in 2016-2018, and decreased the P content in 2018, resulting in an increase of 20.20% in N/P ratio under light nitrogen addition and 34.43% under heavy nitrogen addition in 2018, and a peak of 20.50 in N/P ratio under heavy N addition in 2018, which indicated that N addition could drive the P nutrient limitation of the stand growth to a certain extent. The contents and stoichiometry of C, N and P in leaves litter were significantly different between years and different N addition. The N addition significantly increased the C content, C/P and N/P of leaves litter in 2016-2018, and significantly decreased the P content in 2016-2018. NRE and NRE/PRE decreased significantly under light N addition, while PRE increased significantly under N addition in 2016-2018. Correlation analysis showed that there were significant negative correlations between NRE and leaf N contents, and between PRE and leaf P contents, with the correlation coefficients of -0.860 and -0.772 respectively. The N addition significantly increased the content of soil available N, decreased soil pH (except 2016) and available P content. The results indicated that the growth of coniferous forests in North China was limited by P in different degrees due to N addition. It was speculated that the P nutrient limitation of the forests driven by N addition might be related to the initial soil nutrient status in this region, which provided reference for forest nutrient management under global climate change.

Abstract:In order to reveal the migration and transformation of different forms of nitrogen in the wetted soil under the influence of fertilizer solution (urea) concentration, clay loam and sandy loam were selected as the different soil textures for infiltration experiments, and we quantitatively analyzed the influences of fertilizer concentration on soil cumulative infiltration and transport and transformation characteristics of different forms of nitrogen in the process of distribution and redistribution. The results showed that during the same infiltration time, the cumulative infiltration increased with the increasing of fertilizer concentration, and a linear relationship between the infiltration coefficient of Kostiakov equation and fertilizer concentration were found. The estimation equation of cumulative infiltration considering the effect of fertilizer concentration was established and verified. The simulated value was in good agreement with the measured value, and the average absolute value of relative error between them was less than 8.0%. At the end of infiltration, the contents of urea nitrogen, ammonium nitrogen (NH₄⁺-N) and nitrate nitrogen (NO₃^--N) at the same position all increased with the increasing of fertilizer concentration. NH₄⁺-N mainly distributed above 20 cm of soil wetted depth, and the contents of urea nitrogen and NO₃^--N decreased with the increasing of soil wetted depth.During the redistribution process, the contents of urea nitrogen in clay loam and sandy loam decreased with the increasing of redistribution time, and the hydrolysis of urea nitrogen in the wetted clay loam and sandy loam was basically completed at the 5^th and the 3^rd days of redistribution, respectively. The content of NH₄⁺-N increased first and then decreased, the peak value of NH₄⁺-N content clay loam appeared within the range of the 3~5 days in redistribution, while that of sandy loam appeared about around 3 days in redistribution. The content of NO₃^--N in clay loam increased first and then decreased, and its peak value appeared within the range of the 5~10 days in redistribution, while the content of NO₃^--N in sandy loam remained at a high level after 10 days. The research results could provide theoretical basis and technical support for the design and management of irrigation and fertilization system.

Abstract:The objective of the present study was to explore the suitable combined pattern of tillage practice and nitrogen(N) rate for synchronously increasing the grain yield, water use efficiency and planting benefits in dryland wheat. In the dry year 2016-2017 and wet year 2017-2018, a field experiment was carried out in the typical dryland in western Henan province. In the experiment, the two tillage practices:Subsoiling tillage (ST) and conventional ploughing (PT), were set as the main treatment, and the four N fertilizer application rates of 0, 120, 180 and 240 kg/hm², expressed as N0, N120, N180 and N240, respectively, were set as secondary treatment. The subsoiling in ST was conducted about two weeks after the harvest of previous wheat every two years, and the ploughing in PT was carried out each year around late July to early August after once heavy rainfall. We tested the soil water content, yield and its components, water use efficiency and planting profit. Compared with PT, ST significantly enhanced rainfall fallow efficiency, and increased the water storage in 0-200 cm soil depth by 6.5%~11.7%, 5.0%~8.5% and 4.7%~8.2% respectively at pre-seeding, anthesis and maturity. Therefore, ST significantly enhanced the spike numbers and numbers per spike in the wet year and the 1000-grain weight in the dry year, and thus increased the grain yield and economic return by 7.1%~17.8% and 5.5%~30.2% in the dry year, and increased the grain yield, water use efficiency, economic return by 10.2%~22.0%, 3.0%~13.0% and 16.1%~35.1% in the wet year, compared with PT. With the increase of N rates, the rainfall fallow efficiency was significantly enhanced, resulting in that the water storage at pre-seeding was recovered in PT and significantly increased in ST. N180 was the optimal treatment in PT, and the grain yield, water use efficiency and economic return in N180 was 6.5%~43.9%, 8.1%~36.1% and 12.4%~61.3% higher than those of the other N rate treatments. Under the ST, the optimal N treatment was N180 in the dry year while N240 in the wet year, and the grain yield, water use efficiency and economic return in the optimal treatment was 3.9%~67.9%, 1.0%~54.1% and 3.6%~95.8% higher than those of the other N rate treatments. Above all, subsoiling at about two weeks after the harvest of previous wheat once every two years contributed to accumulating precipitation and increasing soil water storage, and thereby improving grain yield, water use efficiency and planting profit in dryland wheat, particularly with N rate at 180 kg/hm² in the dry year, and with N rate at 240 kg/hm² in the wet year. These results can provide a theoretical basis and technical reference for improving the grain yield, efficiency and profit in dryland wheat.

Abstract:Soil organic carbon (SOC) is an important component of soil organic matter and an important index to evaluate soil fertility. The purpose of this study was to investigate the effects of soil water saving and soil moisture conservation on surface soil structure stability and organic carbon sequestration capacity in rain-fed agricultural area of the Longdong dry tableland, Northwest China. In this study, the fine root growth of 0-20 cm topsoil of apple orchards with different plastic film mulching years (2,4,6 years) was investigated. The soil physical properties and texture was classified. With microbial biomass carbon (MBC), easily oxidized organic carbon (EOC) and particulate organic carbon (POC), soluble organic carbon (DOC), and other indicators, the dynamic change of characterization of soil organic carbon were evaluated. With the help of β-1, 4-wood glycosidase (βX), β-1, 4-glycosidase enzymes (βG), cellobiose hydrolysis (CBH) enzymes activities, the soil carbon metabolism circulation features were characterized. The relationship between root growth, soil physical structure, soil carbon metabolism enzymes activities and organic carbon sequestration under different plastic film mulching years were established to investigate the response of surface soil organic carbon to physical "recessive" degradation. The results showed that:short-term film mulching (2Y) effectively improved soil water content, total porosity, capillary porosity, reduce soil bulk density, which was 112.39%, 105.65%, 104.29%, 90.08% of CK. As a result, the growth of fine roots and the active organic carbon contents were promoted. The contents of POC, DOC, MBC and EOC were 220.11%, 129.42%, 151.35% and 111.72% of those of CK, resulting in the increased total organic carbon of 137.21% compared with that of CK. Long-term film mulching (6Y) showed a "recessive" degradation of surface soil, and the deterioration of soil pore structure was dominated the growth of fine roots. The EOC and MC were decreased significantly by 46.88% and 43.54%, compared with the CK. βX, βG and CBH enzyme activities, as the dominant factors determine the variability of organic carbon storage, accounted for only 65.60%, 53.08%, 47.04% of CK. The damage of surface soil structure under long-term plastic mulching conditions led to the inhibition of root growth, which resulted in the decrease of soil carbon metabolism enzyme activity, carbon pool management index and organic carbon storage, which was not conducive to the long-term, stable and healthy development of soil quality. Short-term film mulching for 2 years was suitable for apple cultivation in the Longdong dry tableland. In order to provide theoretical basis for improving the adjustment vnechunism of soil physical structure evolution, soil fertility improvement, root grouth and drought-resistant cultivation technology of fruit trees in rainfed agricultual areas of the Loess Plateau.

Abstract:In this study, a pot experiment of wheat-maize rotation was carried out to explore the mechanism of increasing yield and enhancing effect, and the influence on soil nutrient status of alginate and controlled release urea application. Through the pot experiment with nitrogen blank (CK0) as the control, 9 treatments were set up:normal urea (N2A0), normal urea with alginic acid (N2A1), controlled-release urea (CN2A0), controlled-release urea with alginic acid (CN2A1), reducing nitrogen 30% of urea (N1A0), reducing nitrogen 30% of urea with alginic acid (N1A1), reducing nitrogen 30% of controlled-release urea (CN1A0), reducing nitrogen 30% controlled-release urea with alginic acid (CN1A1). The results showed that the wheat and maize yield of the treatment combined application of controlled-release urea with alginic acid (CN2A1) was the highest with 98.22 and 134.84 g/pot. Compared with the treatment of controlled-release urea, the maize yield of CN2A1 was significantly increased by 16.38% (P<0.05) and the N use efficiency increased by 17.79% (P<0.05). Compared with reducing nitrogen 30% of controlled-release urea (CN1A0), the yields of wheat and maize in the treatment of reducing nitrogen 30% controlled-release urea with alginic acid (CN1A1) was significantly increased by 15.92% and 26.05% (P<0.05), respectively, and the N use efficiency was significantly increased (P<0.05). In addition, the leaf transpiration rate, SPAD value and leaf area index of treatments fertilized with alginic acid were increased compared with those without alginic acid. Compared with the treatments without alginic acid, the controlled-release urea combined with alginic acid significantly increased the contents of NO₃^--N and NH₄⁺-N in the soil at the jointing stage of wheat and flaring stage of maize, and significantly increased the content of soil available potassium at the flaring stage of maize. Combined application of alginic acid and controlled-release urea significantly increased the supply intensity and capacity of soil available N and K, and promoted the growth and yield of wheat and maize.

Abstract:Taked spring corn as the research object, through magnetized water irrigation experiments, the effects of different irrigation amounts (4 200, 4 800, 5 400 m³/hm²) on the distribution characteristics of soil water and salt, dry matter accumulation, yield and growth of maize under the conditions of magnetized water irrigation were studied. The impact of characteristics, to explore the appropriate irrigation volume under the conditions of 3 500 Gs magnetized water, to provide relevant data support for promoting the efficient use of agricultural resources in the Tarim Basin. The results show that magnetized water irrigation could increase soil water content under different irrigation amounts. The soil salt leached effect of 40-60 cm soil layer was better than that of 0-20 cm soil layer. Magnetized water irrigation could promoted corn plant growth and increased yield. Each treatment of magnetized water Irrigated corn yield increased by 2.11%~19.31% compared with non-magnetized treatment; magnetized water 3 500Gs magnetization intensity irrigation 4 800 m³/hm² treatment yields the best, water use efficiency and irrigation water use efficiency reached the maximum, respectively 2.64 and 2.86 kg/m³.Therefore, compared with non-magnetized irrigation, the appropriate amount of magnetized water irrigation could improved the dry matter accumulation of corn ears,which was beneficial to increased the yield and water used efficiency of corn.

Abstract:In order to provide scientific basis for the regional management of soil nutrients, the optimization of crop fertilization and the guidance of agricultural production in Shaanxi Province, the temporal and spatial variation of soil available potassium(AK) in Shaanxi Province and its influencing factors were analyzed. A total of 705 soil samples were collected from farmland in Shaanxi Province 2016-2017 to determine the content of available potassium. Common Kriging interpolation method was used for spatial interpolation analysis, and the influencing factors were discussed. On this basis, suggestions for scientific fertilization were put forward. The results were as follows, the AK content in farmland soil of Shaanxi province ranged from 55 mg/kg to 301 mg/kg, and the AK content in three natural geomorphic areas followed the order of Guanzhong plain (GZ)>Northern Shaanxi plateau (SB)>Southern Shaanxi mountainous area(SN), and the AK content in each administrative region followed the order of Xianyang>Weinan>Xi'an>Baoji>Yan'an>Tongchuan>Ankang>Hanzhong>Yulin>Shangluo. In terms of time, compared with 1980s, the average AK content in all cities of Shaanxi Province increased in different degrees in 2017. Among the three natural geomorphic areas, GZ had the largest increase of 82%. The average AK content in Shaanxi Province was 181 mg/kg, which was at a very high level, and the AK content in GZ was mainly at the first and second levels, while the AK contents in SB and SN were mainly at the second level. Spatially, the AK content in Shaanxi Province increased first and then decreased from north to south, while the AK content in SB increased from north to south, and it was enriched in southwest Yan'an. The AK contents in the junction of Xianyang and Xi'an, the northeast of Weinan in GZ were significantly higher than those in other areas. In SN, the AK content was higher in the north than that in the south, while the AK content in the central part of Shangluo city was lower. The spatial and temporal variation of AK in farmland soil in three natural geomorphic regions of Shaanxi Province were significantly different (P<0.05), which was related to soil pH values, soil types, topography, climate and human factors. It was suggested that all regions of Shaanxi Province should implement potassium fertilizer zoning management to maintain the profit and loss balance of soil potassium.

Abstract:The purpose of this study was to explore the effect and its mechanism of long-term nitrogen application on the characteristics of endophytic fungi community in crop transport roots and absorbing roots. Based on the field long-term location fertilization experiment (1995-2019), through the high-throughput sequencing technology, the long-term 5 nitrogen fertilizer treatments (CK, N1, N2, N1P, N2P) were studied. Among them, the CK, N1, N2 nitrogen application rates were respectively:0, 55.2, 110.4 kg/hm²) on the composition and structure of endophytic fungi community in different functional roots of millet. The results showed that the number of OTUs and fungal diversity (shannon index and Chao 1 index) of absorbing roots in CK treatment were significantly higher than those of transporting roots. At the phylum level, the abundance of Ascomycota and Glomeromycota of absorbing roots was significantly higher than that of transporting roots, but the abundance of Mortierellomycota and Basidiomycota was significantly lower than that of transporting roots. At the genus level, the relative abundance of the dominant genus Mortierella and Bipolaris in absorbing roots was significantly lower than that in transporting roots, but Fusarium and Minimedusa were significantly higher than transporting roots. The number of OTUs and Chao 1 index of absorbing root and transport root of high nitrogen fertilization increased by 23.62%, 23.87%, respectively, while other fertilization was just the opposite. The Shannon index of fertilization and transporting roots increased by 7.12%~19.62%, but the absorbing roots were the opposite. The relative abundance of fertilization-absorbing root pathogenic bacteria (Bipolaris, Fusarium, Magnaporthiopsis, Microdochium) increased by 52.99%, 40.74%, 133.06%, 200.00%, respectively, and the relative abundance of pathogen-resistant bacteria (Minimedusa) in transporting roots increased 40.16%~97.11%. The carbon, nitrogen, and phosphorus contents of the millet root system increased by 2.33%~11.63%, 13.30%~94.66%, 3.89%~263.92%, respectively. The effect of combined application of nitrogen and phosphorus was particularly significant. The biomass of fertilization and transport roots increased by 106.67%~336.41%, and the biomass of absorbing roots was reduced by 35.20%~60.20%. Long-term fertilization increased the abundance of endophytic fungi in absorbing roots by increasing soil available phosphorus, total phosphorus, soluble nitrogen and root carbon content, and reducing the abundance of endophytic fungi in transporting roots by increasing root biomass, and applying phosphorus fertilizer with low nitrogen (N1P) has the greatest impact on the soil nutrient content and the development of the flora. In short, long-term nitrogen application could change root endophytic flora by affecting the soil or root chemical composition, which might lead to the changes in plant survival strategies and ultimately affect farmland ecosystems.

Abstract:In order to investigate the effects of residual film content on soil water-salt and crop growth in cotton field under drip irrigation, eight treatments of residual film contents, 150 (T1), 230 (T2), 465 (T3), 857 (T4), 1 250 (T5) and 1 640² kg/hm (T6), original soil (CK1) and no residual film control (CK2), were set in a cotton field. The effects of residual film contents on soil water-salt, soil and crop root nitrogen and yield in drip irrigated cotton field were analyzed. The results showed that with the increases of residual film contents, soil water contents decreased gradually, and the enrichment effect of soil salt increased gradually. The variation degree of soil water and salt was positively correlated with the residual film content in 0-40 cm soil layer, and the Coefficient of variation CV of soil water and salt in T5 and T6 was significantly larger, the CV of water content was 0.52 and 0.44 and salt was 0.34 and 0.31 respectively. The nitrogen contents in soil increased with the increases of residual film contents, and the total nitrogen contents in root were negatively correlated with the residual film contents. The yield of cotton decreased gradually with the increases of residual film contents. When the residual film content was more than 230 kg/hm², the decline was significantly enhanced, compared with CK2, the yield of T3, T4, T5 and T6 decreased by 14.19%, 21.69%, 29.19% and 37.29% respectively. This study could provide theoretical basis and scientific support for the sustainable development of mulched drip irrigation cotton field and the prevention and control of residual film pollution in Xinjiang.

Abstract:In order to explore the influence of the amount of soil residual plastic film on the water and nitrogen transport characteristics of the infiltration of film hole irrigation, five residual plastic film levels were set up through an indoor simulation test, which were 0, 90, 180, 360 and 720 kg/hm², respectively. The cumulative infiltration volume, the wetting front migration distance, the characteristics of the wetted body, the distribution of water and nitrogen were studied. The results showed that the residual plastic film had a negative effect on the infiltration of film hole fertilizer solution, and the cumulative infiltration of the residual plastic film soil reduced by 10.63%~30.77% compared with the without residual plastic film soil. The Kostiakov model matched well with the cumulative infiltration per unit pore area of the residual plastic film soil and the infiltration time. Concretely, the vertical wetting front migration distance of different soil residual plastic film amount did not change significantly for initial 30 min, while, the amount of residual plastic film was negatively correlated with the wetting front migration distance and the wetted body volume with time. When the infiltration was completed, the wetted body volume decreased by 18.09%~41.96%. The vertical wetting front migration distance and wetted body volume had significant power function relationship with infiltration time with R²>0.98; the soil water content with residual plastic film at the same position was lower than that without residual plastic film except for the center of the film hole, and the area with high water content of 30% decreased. The content of NO₃^--N and NH₄⁺-N in the soil at the same depth in the wetted body decreased with increasing residual plastic film, and the range was 4.20%~16.27%. The research can provide theoretical reference for the application of film hole irrigation technology in residual plastic film area.

Abstract:A pot experiment was conducted to study the effects of different levels of phosphorus (P) (0, 20, 80 mg/kg) and oxytetracycline (OTC) (0, 40, 160 mg/kg) on the biomass and root development of wheat and alfalfa seedlings. The results showed that at all OTC levels, the aboveground biomass of wheat in 20 and 80 mg/kg P treatments was greater than that when no P was added, being 22.7%~34.1%, 10.0%~30.0% and 9.1%~18.3% greater. Except for the 160 mg/kg OTC+ 80 mg/kg P treatment, root biomass of alfalfa in all treatments was less than that in the control without OTC and P, being 8.8% less. Root length and surface area of wheat decreased with increasing OTC level. Overall, P application significantly enhanced the aboveground growth of wheat, but had no significant effect on the growth of alfalfa. OTC inhibited root development of alfalfa. The results of the present study can provide a theoretical basis for evaluating the effect of soil OTC residue on seedling growth of crops and instructing proper application of P-fertilizers.

Abstract:In this study, biochar were produced from coconut shell and peanut shell, and then modified with 14% H₃PO₄ and 1.0 mol/L NaOH-30% H₂O₂, respectively. The changes of physicochemical properties of biochar before and after modification and the sorption mechanism of diethyl phthalate (DEP) were studied. The results showed that the aromatization degree and the content of oxygen-containing functional groups of modified biochar increased, the specific surface area (SA) increased except C300N (the 300℃-coconut shell biochar modified by NaOH-H₂O₂). P800N (the 800℃-peanut shell biochar modified by NaOH-H₂O₂) had the highest sorption affinity for DEP because of the largest SA (584.22 m²/g). The sorption affinity of DEP by the NaOH-H₂O₂ modified biochar was stronger because of the higher organic carbon partition coefficient K_oc (C_e=0.1S_w) value. The π-π EDA interaction played an important role in the sorption of DEP by all biochar, while the pore-filling effect regulated the sorption of DEP by the original biochar, NaOH-H₂O₂ modified biochar and H₃PO₄ modified 800℃-biochar. The water clusters formed by hydrogen bonding inhibited the sorption of DEP by the 300℃- and 500℃-biochar modified by H₃PO₄ compared with the original biochar. In addition, the hydrogen bonding was helpful to enhance the sorption affinity of low-temperature (300℃) biochar for DEP.

Abstract:The different addition proportions of foreign soil has an important impact on the improvement effect and economic cost of iron ore waste reclamation soil. From January to December in 2019, field experiments and laboratory analysis were conducted to investigate the dynamic characteristics of soil carbon emission and reveal its driving factors. In the natural remediation state, the volume ratios of iron ore waste to foreign soil were set as T1 (1:1), T2 (1:2), T3 (1:4) and T4 (0:1), respectively. The physical and chemical properties of the mixed soil were determined in April, July, October and December 2019. The results showed that the carbon emission of mixed soil of iron ore and waste rock was higher in summer and lower in winter with the rise and fall of temperature. With the increase of the proportions of foreign soil, the carbon emission of mixed soil had an increasing trend, and the difference was significant only from July to September, which was T4 (0:1) > T2 (1:2) > T3 (1:4) > T1 (1:1). On the daily scale, the maximum carbon emission appeared at 12:00-14:00 pm, and the minimum appeared at 4:00-6:00 am. When the temperature of mixed soil was low, the carbon emission appeared negative. With the increase of the proportions of foreign soil, the sensitivity coefficient Q₁₀ of carbon emission of iron ore waste rock mixed soil gradually increased (2.07~2.37), and the addition of foreign soil reduced the pH values of mixed soil to a certain extent, but increased the contents of available phosphorus, total nitrogen, organic carbon and the activities of catalase and sucrase. Comprehensive study on the effects of physical and chemical properties of mixed soil of iron ore and waste rock on carbon emission can provide a theoretical basis for the study of soil carbon emission in iron ore reclamation area.

Abstract:Near-surface vegetation coverage of erosion-degraded forestlands is low in the red soil region of South China, which leading to serious soil erosion. Inoculation of arbuscular mycorrhizal (AM) fungi can promote vegetation growth and improve soil structure and then can reduce soil erosion. The effects of AM fungi inoculation on soil carbon, nitrogen and glomalin were investigated in erosion-degraded Pinus massoniana forestland, and two treatments were set up, including shrub planting (S), and shrub planting with AM fungi (S+AMF). The results showed that nearly one year after inoculation with AM fungi, mycorrhizal colonization rate (MCR) of S+AMF treatment was significantly higher than that of S treatment on the upper slope position and the whole slope (P<0.05). The contents of SOC, TN, SMBC, EE-GRSP and T-GRSP in the lower slope were significantly higher than those in middle slope in the S+AMF treatment (P<0.05), while there was no significant difference among slope positions in the S treatment (P>0.05). There was no significant difference in AN, SMBN and pH among different slope positions in each treatment (P>0.05). Compared with S treatment, the mean contribution rates of S+AMF treatment to MCR, SOC, TN, SMBC, SMBN, EE-GRSP, T-GRSP, AN and pH were 43.83%±15.10%, 5.33%±1.57%, 14.69%±7.92%, 27.88%±4.89%, 39.25%±4.82%, 6.90%±2.56%, 12.47%±7.95%, -13.18%±6.63%, -0.71%±2.74%, respectively. The Pearson correlation and stepwise regression analysis suggested that there was a significant positive correlation between MCR, SOC, TN, SMBC, SMBN and glomalin (P<0.05). TN, SMBC and MCR explained 80.5% variation of SOC and SOC, SMBC, SMBN and MCR explained 90.4% variation of TN, while TN, SMBN, pH and MCR explained 48.9% variation of AN, indicating that inoculation with AM fungi increased mycorrhizal colonization rate of Amorpha fruticosa Linn root system, which indirectly promoted the increase of soil carbon, nitrogen and glomalin. This study was of great significance for effectively improving the soil quality and promoting vegetation restoration in erosion-degraded forestlands.

Abstract:M9T337 apple seedlings were used to study the effects of different organic materials and their combination on plant growth, nitrogen utilization and soil properties by using the ¹⁵N isotope tracer technique. There were 8 treatments:CK (chemical fertilizer), S (straw), B (biochar), F (cow dung), SB (1/2 straw + 1/2 biochar), SF (1/2 straw + 1/2 cow dung), FB (1/2 cow dung + 1/2 biochar), SFB (1/3 straw + 1/3 cow dung + 1/3 biochar). The results showed that the application of organic materials promoted the growth of apple seedlings, and SFB treatment had the best fresh weight, height, stem diameter, leaf area and root activity, which were significantly higher than CK and the treatment of single organic materials. The application of organic materials decreased soil bulk density, increased soil total porosity and soil moisture content. The soil bulk density and total porosity under the combined application of biochar were better. During the treatment period, the soil mineralized nitrogen contents, the soil enzymes activities and microbial population under the treatments with mixed organic materials were better than those under the treatments with organic materials alone. Compared with CK and the single organic materials, the combined application of organic materials significantly improved the ¹⁵N utilization rate of apple seedlings and ¹⁵N residual rate in soils, reduced the ¹⁵N loss rate and the SFB treatment had the best effect. According to the comprehensive analysis, the application of different organic materials could promote the growth of apple seedlings, improve soil properties, and improve the absorption and utilization of ¹⁵N, among which the combined application of cow dung, straw and biochar (SFB treatment) had the best effect. These findings could provide a basis for the application of organic materials in apple orchard for the soil quality improvement and fertilizer reduction and efficiency.

Abstract:Nitrogen reduction combined with biochar application is of great significance for improving land productivity, improving soil carbon sequestration and mitigating climate warming. Based on the field experiment, five nitrogen fertilizer dosage gradients (T0~T4) were set:The response of organic carbon mineralization and enzyme activity to nitrogen reduction combined with biochar application in paddy fields was revealed by using the principle of isonitrogenous fertilizer (100% N, 90% N, 80% N, 70% N, 60% N). The results showed that compared with T0 treatment, the soil total nitrogen, alkaline hydrolysable nitrogen and available phosphorus in T3 treatment (70% N +7.5 t/hm² biochar nitrogen) were significantly increased by 6.67%, 8.36% and 30.94% (P < 0.05), respectively. The content of available potassium in T4 treatment was the highest and significantly increased by 23.78% (P < 0.05). Soil organic carbon (SOC) content increased with the increase of nitrogen reduction combined with biochar application ratio. Compared with before mineralization, SOC, microbial biomass carbon (MBC) and microbial entropy (qMB) decreased by 1.39~1.75 g/kg, 24.62~67.57 mg/kg and 0.13%~0.32% (P < 0.05) after mineralization. SOC mineralization rate reached the peak value on the first day of culture, decreased rapidly in the first stage (1~6 days), decreased slowly in the second stage (6~30 days), and tended to be stable in the third stage (30~45 days). The relationship between mineralization rate and culture time was logarithmic (P < 0.01). At the end of culture, the SOC cumulative mineralization amount and cumulative mineralization rate varied from 1.39~1.75 g/kg and 6.02%~8.43%, respectively, and T3 treatment was the lowest. Compared with CK and T0 treatments, the activities of catalase, urease and sucrase in T3 treatment were the highest, and the activities of acid phosphatase in T1 treatment were the highest. The highest rice yield was found in T3 treatment (7.37 t/hm²), which was 39.58% higher than that in T0 treatment (P < 0.05). In conclusion, 30% reduction of nitrogen fertilizer combined with biochar can significantly improve soil fertility, reduce SOC mineralization, increase soil carbon sequestration, improve soil enzyme activity and rice yield.

Abstract:To clarify the interaction between super-absorbent polymers (SAPs) and soil particles, and the influences of SAPs on soil structure and soil moisture availability under alternating dry and wet conditions, the soil column simulation experiments were carried out to study the effects of SAPs with different particle sizes (> 0.85, 0.6~0.85, 0.30~0.45 mm) on soil moisture characteristics, soil aggregate distribution and soil structure stability, and the microscopic changes of the valence bonds of SAPs and soil mixtures. The results showed that, compared with the control, the SAPs' treatments significantly increased the relative soil moisture content by more than 72.9% in the first (T1) and second (T2) sampling stages (P < 0.05), except for the minimum particle size treatment in T2 stage. The particle size of SAPs and soil moisture condition would affect the SAPs' application effect on soil water supply capacity. The SAPs with the smallest particle size had the poor ability to change the continuous soil water absorption and supply, but it had the most beneficial to promote the composition of soil water-stable macro-aggregates and the stability of soil aggregates. The interactions between SAPs and soil particles were intensified during continual soil wetting and drying cycles. The mineral colloids such as Si-O-Si bond, -OH, montmorillonite and quartz in the loam soil would enter into the network structure of SAPs, and the reaction intensity might affect the formation and stability of soil water-stable macro-aggregates. It was preliminarily analyzed that more soil clay minerals would destroy the molecular structure of SAPs during the process of repeated water loss and rehydration, which resulted in the decreases of the water absorption and holding capacities of SAPs.