Abstract:Sediment load research is of important theoretical and practical significance. In the past 60 years, with the increasing climate change and human activities, the sediment loads in many world rivers have undergone significant changes. Based on global sediment database and regional river studies, status, distribution patterns, and influencing factors of suspended sediment loads (SSL) of global rivers were reviewed. The results showed that: (1) Before the proliferation of dam construction in the latter half of the 20th century, the annual SSL of global rivers was around 2×1010 t. New data of 36 rivers indicated that most global rivers had a decreasing trend in SSL. (2) Geology and geomorphology conditions were decisive factors controlling SSL on a global scale. Meteorological and hydrological conditions and human activities had comparable contributions in controlling the difference in SSL among rivers. (3) Representative river studies in various climatic zones showed that changes in global SSL were mainly affected by human activities. In the future, the total SSL of global rivers would continue to decrease due to the impact of human activities, especially dam construction.

Abstract:The China-Pakistan Economic Corridor is the flagship project of the Belt and Road Initiative. Rainfall erosivity is an important indicator to evaluate the carrying capacity of regional resources and environment. Estimation of the overseas high spatial resolution rainfall erosivity is significant to the construction of the China-Pakistan Economic Corridor. In this paper, rainfall erosivity of Pakistan in 2010 was estimated with TRMM 3B42 data, and a spatial downscaling algorithm based on the relationships between rainfall erosivity and relevant environmental factors such as meteorology, topography, and vegetation was proposed. By applying the spatial downscaling algorithm, the spatial resolution of rainfall erosivity was improved to 1 km. The results were as follows: (1) The rainfall erosivity simulated by the spatial downscaling algorithm displayed a significant correlation with the rainfall erosivity estimated from TRMM 3B42 data (R2 = 0.94), suggesting that the simulated rainfall erosivity by spatial downscaling algorithm could reflect the spatial distribution of rainfall erosivity effectively, especially in the northern mountains and east edge of the Baluchistan Plateau. (2) The rainfall erosivity of Pakistan in 2010 varied from 0.58 to 5 929.85 (MJ·mm)/(hm2·h·a), and the average value was 524.15 (MJ·mm)/(hm2·h·a). The spatial distribution of rainfall erosivity was high in the east and low in the west, and the areas with high-value of rainfall erosivity were mainly located in the vicinity of Islamabad, Mankera, Sialkot-Lahore-Sahiwal, and Karachi.

Abstract:To explore the characteristics of soil and water loss in the Karst region, we analyzed the spatial statistic features and soil erosion characteristics of blocks. According to the First National Water Census, field surveys were carried out using blocks as the minimum survey units. A block is an area in which land use, soil and water conservation measures and coverage are identical. Soil erosion modulus was calculated using CSLE (Chinese Soil Loss Equation). The results showed that farmland and forest were dominated in the Karst region, accounting for 86.2% of the total area. Because of cracked terrain and steep slopes, the landscape showed fragmentation characteristics. The average area, slope length, slope gradient of blocks were 3.45 hm2, 45.3 m, and 21.7°, respectively. Analysis of the erosion modulus showed that 68.6% of farmland blocks had steep gradients and accounted for 65.6% of the total sediment yield. About 50% of farmland suffered severe erosion. The effects of slope gradient on soil erosion were significantly greater than that of slope length. Engineering measures reduced soil erosion by 75%. With the increase of slope gradient, the efficiency of engineering measures in reducing soil erosion decreased and became smaller than that of the forest and grassland. The most serious soil erosion occurred in southwest of Guizhou Province, and the degree of soil erosion decreased from west to east. When planning for regional soil and water conservation, the most seriously eroded area should be given the primary consideration, and reducing cultivation on steep slopes and returning farmland to forest should become the first choice.

Abstract:To study the effects of different mulching methods on soil nutrient loss and soil particle size distribution, we simulated different rainfall intensities (30 mm/h, and 60 mm/h) and different mulching methods (litter, gravel) by an artificially simulated rainfall experimental system. The results showed that: (1) Both litter cover and gravel cover could reduce soil erosion effectively. A 250 g/m2 litter cover and a 50% gravel cover could reduce soil erosion by 91%-98% and 68%-91%, respectively. (2) The concentration of organic matter, available nitrogen, and?available phosphorus did not change with the variation of coverage, but the concentration of available potassium was increased to 144%-325% of that of the control treatment. (3) The total nutrient loss decreased with the increase of coverage. A 250 g/m2 litter cover and a 50% gravel cover could reduce the nutrient loss by 64%-96% and 43%-94%, respectively. (4) The particle size of the eroded soil was significantly smaller than that of the soil before erosion, and the larger the erosion modulus, the closer the soil particle size was to the undisturbed soil.

Abstract:Based on simulated field rainfall experiment in the Beijing Mountain Area, this paper tried to analyze and evaluate the effects of the litter layer under artificial Platycladus orientalis forests on the runoff and sediment yield of the slope by comparing two kinds of treatment conditions (slope surface with litter coverage, and bare slope) under two rainfall intensities (126 mm/h, and 70 mm/h). The results showed that: (1) Compared with the bare slope, the runoff and sediment yield of the slope with litter coverage was significantly reduced by 67.0% and 90.6%, respectively. The benefit of litter layer on reducing the sediment was greater than that on reducing the water. (2) The runoff rate increased initially and then tended to be stable during the slope runoff process on the two types of slopes. Compared to the bare slope, the time for the runoff rate to be stable was shorter on the slope with litter coverage. (3) The average sediment transport rate under 70 mm/h and 126 mm/h rainfall intensity on the slope with litter coverage was 2.8 g/min and 80.8 g/min, respectively, which was significantly less than that on the bare slope with the value of 51.4 g/min and 872.7 g/min under 70 mm/h and 126 mm/h rainfall intensity, respectively. For the slope with litter coverage, sediment transport rate and sediment concentration did not significantly change with runoff duration, and the slope sediment transportation was a relatively stable process. For the bare slope, the sediment transport rate and sediment concentration increased initially and then tended to be stable under 70 mm/h rainfall intensity, while this change sharply increased initially and then decreased fluctuantly under 126 mm/h rainfall intensity. (4) There was a linear relationship between sediment and runoff yield on the slope with litter coverage, while the relationship was an exponent power function on the bare slope. Finally, this study can provide a theoretical basis for evaluating the benefit of plantation restoration in Beijing mountain area on soil and water conservation, and also improve the understanding of the process mechanism of runoff and sediment transportation on the slope of the forest.

Abstract:The paper analyzed the erosion processes of purple soil slopes using the method of artificially simulated rainfall experiment and lab analysis to study the effects of vegetation coverage on the erosion processes of purple soil slopes, and discussed the critical point problem of slope vegetation cover. The results showed that: (1) As a whole, with the increase of vegetation coverage, the runoff on purple soil slopes decreased. The was a significant negative relationship between the vegetation coverage and the runoff. However, when the vegetation coverage was less than 25%, the changes in runoff were not obvious. When the vegetation coverage reached 75%, the stable value of the runoff was low, being obviously lower than that when the vegetation coverage was 0%, 25%, and 50%. (2) Sediment yield decreased rapidly with the increase of vegetation coverage. There was a significant quadratic term correlation between the vegetation coverage and the runoff. When the vegetation coverage was below the critical value of 25%, the vegetation played an important role in decreasing sediment load. A vegetation coverage 50% was the critical coverage for soil erosion control on purple soil slope. (3) Soil microaggregates (< 0.25mm) were the main parts in eroded sediment. Basically, all levels of soil aggregates decreased with the increase of vegetation coverage. (4) Through statistical analysis, the vegetation coverage caused an extremely significant effect on runoff and sediment yield (p < 0.01). Moreover, when the vegetation coverage reached 50%, vegetation played a vital role in soil and water conservation, and reduced soil and water erosion on purple soil slopes.

Abstract:In China, agricultural non-point source pollution has become an important reason for water environmental deterioration and lake eutrophication, with the contribution of nitrogen and phosphorus to the eutrophication of surface water being more than 50%. This study was conducted to evaluate the effects of herbaceous grass filter strips established by perennial ryegrass (Lolium perenne Linn), Jingcao No.2 (Elytrigia repens (L.) Nevski) and smooth bromegrass (Bromus inermis Leyss.) on the interception of runoff, sediment, nitrogen, and phosphorus in a simulated experiment in soil boxes with runoff generators. The results showed that: (1) The runoff, nitrogen, and phosphorus loss on the plot were significantly reduced by the three types grass filter strips. The sediment loss of ryegrass filter strip was significantly less than that of Jincao No.2 and smooth bromegrass. The result of correlation analysis showed that the nitrogen, phosphorus interception rate was significantly correlated with the runoff, and sediment interception rate. (2) The loss of phosphorus in four kinds of treatments were lower than that of nitrogen, with more than 90% of nitrogen being lost in dissolved nitrogen, and phosphorus being mainly lost in particulate phosphorus. (3) Nitrogen was mainly intercepted by soil infiltration, and phosphorus was mainly intercepted by plant stem. (4) The nitrogen loss of Jingcao No.2 filter strip was less than that of ryegrass and smooth bromegrass filter strip, and the phosphorus loss of ryegrass filter strip was less than that of Jingcao No.2 and smooth bromegrass filter strip. Theredore, in order to improve the interception of nitrogen and phosphorus, ryegrass and Jingcao No.2 can be planted in a mixing way when building the herbaceous filter strips.

Abstract:Through artificially simulated rainfall experiments, we studied the regularities of the runoff and sediment yield on slopes of different gradients (5°,and 10°) under different rainfall intensities (30 mm/h, 60 mm/h, and 90 mm/h) with different coverages (60% coverage of Festuca arundinacea grassland in the first year of planting, and bare land). A quantitative study was carried out on the soil and water regulation of F. arundinacea grassland. The results showed that: (1) Festuca arundinacea grassland had a remarkable effect on extending the initial runoff time. However, such effect decreased with the increase of rainfall intensity and slope gradient. The effect on the extension the initial runoff time of grassland was not significant under rainfall intensity of 90 mm/h on the 10° slope. (2) Under different experimental conditions, there were significant differences between F. arundinacea grassland and bare land, except under rainfall intensity of 90 mm/h on the 10° slope. (3) Under different experimental conditions, the total runoff of F. arundinacea grassland was about 0.8 times as much as that of the bare land, and the total sediment yield of F. arundinacea grassland was 1/244.68-1/28.34 times as much as that of the bare land. (4) A 60% coverage of F. arundinacea grassland could effectively reduce runoff and soil erosion, but the reduction degree was different. When the rainfall intensity was 30 mm/h, 60 mm/h, and 90 mm/h, the average runoff reduction was 33.23%, 23.04%, and 13.78%, respectively. The sediment reduction could be more than 95% under different rainfall conditions. (5) Sediment-carrying capacity of F. arundinacea grassland was different from that of the bare land under the same test conditions. The amount of soil erosion in the F. arundinacea grassland was lower than that of the bare land under the same runoff conditions. (6) The relation between runoff and sediment was established for F. arundinacea grassland and bare land.

Abstract:Forest regeneration or transformation is a critical period for forest land to be prone to soil erosion. In this paper, through the analysis of single rainfall and runoff and sediment yield data of five artificial runoff plots in different transformation models of low-efficiency Pinus massoniana Lamb. forest in Yibin City, Sichuan Province, the relationship between rainfall, runoff and sediment characteristics was explored. The results showed that, with the vegetation evolution, the total runoff of I-V in 2014 decreased by -6.44%, -10.51%, 20.95%, 13.28%, and 12.73%, respectively, compared with that in the same period of 2012; the total sediment yield decreased by 58.4% , 56.38%, 77.72%, 78.16%, and 79.68%, respectively. The runoff and sediment yield increased exponentially with the increase of rainfall, but the amount of sediment yield increased more. The sediment yield of runoff plots in the second and third year was significantly lower than that in the first year, but the difference between the second and third year was not significant, and there was no significant correlation between the runoff and sediment yield. The different patterns were not the main factors leading to the aggravation of soil erosion. There were significant differences between the time of reconstruction and the runoff and sediment yield. The results showed that the restoration effect of the clear cutting plot was better at the early stage of the reconstruction, but with the growth of the forest and the formation of the forest environment, the relationship between the transformation model and the runoff and sediment yield might be different.

Abstract:In order to compare the effects of Astragalus adsurgens Pall. and Medicago sativa L. on reducing runoff and sediment, we set up three rates of flow (1 m3/h, 2 m3/h, and 3 m3/h), and five kinds of vegetation coverage (100%, 75%, 50%, 25%, and 0%). The submersible pump was used to carry out the runoff scouring experiment. The results show that: (1) The permeability coefficient of the slopes on which A. adsurgens and M. sativa were planted was larger than that of the control group, but the runoff and sediment of the slopes on which A. adsurgens and M. sativa were planted was less than that of the control group, indicating that A. adsurgens and M. sativa having effects on runoff and sediment reduction. (2) The effects of A. adsurgens on runoff and sediment reduction were better than that of M. sativa in the northern mountain area of Beijing. For example, compared with the control group, when the flow rate was 3 m3/h, the permeability coefficient of the slopes on which A. adsurgens and M. sativa were planted was increased by 5.8% and 45.3%, respectively. Total runoff of the slopes on which A. adsurgens and M. sativa were planted was less than that of the control group, being decreased by 3.7% and 11.2%, respectively. Sediment yield of the control group was 6.40 and 9.19 times the size of that of the slopes on which A. adsurgens and M. sativa were planted. The effects of A. adsurgens on slope infiltration and sediment reduction were better than those of M. sativa. (3) There was a critical phenomenon in the effect of vegetation on sediment reduction. The critical coverage of herbaceous plants for sediment reduction in this region was 50%-75%.

Abstract:The influencing factors of laterite starting on slopes under the effects of rainfall were revealed. The starting conditions of laterite starting on slopes under the effects of rainfall were established, in order to provide a reference for further study on slope erosion of laterite in Yunnan. According to the characteristics of laterite and the erosion processes and phenomena on the slope surface, the method of combining the model test and the mechanical model was adopted. The results indicated that: (1) The splash erosion and crust were the two main phenomena in the processes of erosion of laterite on slopes. (2) The cohesive force of laterite could block the starting of laterite particles on slopes. The greater the shear strength, the greater the critical shear stress of the laterite particles. Rainfall and pore water pressure could promote the starting of laterite particles on slopes. The greater the raindrop density and the final velocity , the greater the impact of rainfall. When the particle size d was larger and the ratio of raindrop diameter to water depth decreased, the effect of rainfall was smaller. (3) The formulas of the critical starting shear stress of laterite particles in the connection and loose state were established. The critical starting shear stress of laterite particles on slopes was closely related to the particle size, shear strength, rainfall characteristics, and runoff characteristics. Under the effects of rainfall, a small flow shear stress could make the laterite particles under loose state start.

Abstract:Tillage practices play a key role in soil and water loss control in agricultural lands. The objective of this study was to measure the soil and water loss from the tilled surfaces and analyze how slope gradient affects soil and water conservation benefit of tillage practices. All experiments were conducted in outdoor runoff plots with a size of 4 m length by 1 m width. The slope gradient was 5°, 10°, 15°, 20°, and 25°. The rainfall intensity was 1, 1.5, and 2 mm/min. We found that the runoff yields from contour ploughing, deep hoeing, and shallow hoeing were decreased by 38.19%, 32.25%, and 15.84%, respectively, compared with the smooth surface; the decrease level of sediment yields was more than 50% in three tillage measurements compared with the SS. It was suggested that tillage practices had a significant benefit in soil and water loss control in agricultural lands, but depended on slope gradient. On the tilled surfaces, the difference in runoff yields between small and large slope gradient was not significant; sediment yield increased sharply with increasing slope gradient when slope gradient ranged from 10° to 25°. The soil conservation benefit of contour ploughing, deep hoeing, and shallow hoeing was decreased by 3.08%, 4.74%, and 7.61% for each gradient rise in slope when the slope gradient was more than 15°. Regression analysis showed that the change in sediment yield with slope steepness and rainfall intensity for all treatments could be described by the exponential function. Therefore, the benefits of soil and water conservation of tillage practices changed with the increasing slope gradient, but to different ways and extents. The results provide a mechanistic understanding of how slope gradient affects soil and water conservation benefit of tillage practices in agricultural lands.

Abstract:In order to reveal the effects of rainfall on nitrogen export and the characteristics of nitrogen export in a Karst small catchment, this paper studied a typical small agricultural catchment in the Karst area, i.e. Houzhai catchment in Guizhou Province. This study monitored and tested concentrations of various forms of nitrogen in samples from sinkhole, surface water, and groundwater to estimate the annual flux of nitrogen during the rainy season, and investigated the effects of rainfall on nitrogen export with regional precipitation data. The results indicated that: (1) Nitrogen concentration in the Houzhai catchment was considerably higher than those in the large rivers in China: The average concentration of TDN was 6.5 mg/L in the groundwater system and 7.3 mg/L in the surface water system. (2) The main nitrogen form was NO3--N, with a small amount of NH4+-N, NO2--N, and DON export in the Houzhai small catchment. (3) The estimated flux of the TDN, NO3--N, NH4+-N, NO2—N, and DON output was 55.13, 52.12, 0.40, 0.01, and 2.61 t, respectively, in the Houzhai catchment during the rainy season. (4) The continuous precipitation over a couple of days accelerated nitrogen loss in the Karst area. The NO3--N concentration in the upstream increased after the beginning of rainfall events and decreased after the termination of precipitation. Moreover, there was an observable hysteresis between the change in NO3--N concentration with the occurrence of rainfall at the outlet of the catchment.

Abstract:The riparian zone of the Three Gorges Reservoir undergoes high-pressure water submergence and alternate wet-dry condition, leading to changes in soil mechanical properties, influencing soil erodibility and bank instability. Based on the wide distribution of purple soil in the Three Gorges Reservoir, we simulated the hydraulic effect and the process of alternate submergence and exposure, researched stress-strain and shear strength of purple soil in response to high-pressure water submergence and wet-dry cycles. It was found that water column pressure, and the frequency and magnitude of wet-dry cycles significantly drove the changes in soil mechanical properties. Compared with CK, stiffness increased, the decreasing rate of cohesion (c) became slower, but the internal fraction angle (φ) increased with increasing water column pressure. With the increasing number of wet-dry cycles, stiffness and cohension decreased, while the internal fraction angle increased. The shear strength decreased quickly with increasing amplitude of wet-dry cycles under the same confining pressure. Compared with CK, the purple soil which suffered minor amplitude of wet-dry cycles showed a significant increasing trend in the internal fraction angle and a decreasing trend in cohesion.

Abstract:The aim of this study was to explore the influence of gravel on infiltration characteristics of the colluvial deposit. The cutting ring method was used to study the changes of infiltration characteristics of the colluvial deposit that mixed with different content and size of gravel. The results were as follows: (1) The steady infiltration time of the colluvial deposit was between 9 and 10 min when the content of gravel was 0%, 10%, 20%, and 30%, but it was between 19 and 20 min when the content of gravel was 40% and 50%. (2) The initial infiltration rate, steady infiltration rate, average infiltration rate, and accumulative infiltration volume of the colluvial deposit were enhanced with the increasing gravel content. The infiltration parameters changed little at 10%, 20%, and 30% gravel content when the colluvial deposit was mixed with gravels of of 2-3 mm, 3-5 mm, and 5-10 mm size. The values of infiltration parameters decreased with increasing size of gravels when the gravel content was 40%; when the gravel content was 50%, the values of infiltration parameters of the colluvial deposit mixed with 2-3 mm gravel were the least. (3) A further comparison showed that the Kostiakov model was more suitable for simulating the infiltration process of the colluvial deposit.

Abstract:In order to analyze the infiltration characteristics and the effects of vegetation restoration of dumps, infiltration characteristics of dumps with different restoration ages were studied and evaluated by using field double-ring infiltration and principal component analysis method. The results indicated that: (1) The initial infiltration rate of two-month (P1), two-years (P2), four-years (P3) dump and mulberry land (P4) was 11.32, 9.34, 15.84, and 19.38 mm/min, respectively; the stable infiltration rate was 4.64, 3.62, 6.71, and 7.81 mm/min, respectively. The stable infiltration rate of mulberry land was 1.68, 2.16, and 1.16 times greater than that of the other three dumps, respectively. (2) The fitting effect of Kastiakov model was better than that of the common empirical infiltration model, the Philip model, and the Horton model, with the determination coefficient ranging from 0.905 to 0.956. (3) The eigenvalues of soil infiltration had significantly negative correlations with soil bulk density, and 20-5 mm and 5-2 mm gravel content, but showed significantly or very significantly positive correlations with non-capillary porosity, organic matter content, and 2-0.075 mm soil particle content. (4) Soil infiltration capacity was evaluated by principal component analysis, and was in the order of P4 (2.398) > P3 (0.792) > P1 (-1.104) > P2 (-2.089). The infiltration capacity of dump was improved with the increasing restoration ages, and was close to that of the mulberry land.

Abstract:To study the effects of herbs’ root systems on soil shear strength in a collapsing gully alluvial fan. Pennisetum sp. and Paspalum wettsteinii were chosen as the research objects. A root analysis system (WinRHIZO) was used to characterize the root systems, and the in-situ shearing test was applied to analyze soil shear strength. The results showed that: (1) Root systems could improve soil structure and water status. (2) Root systems of both herbal plants were mainly distributed in the 0-5 cm soil layer, in which root parameters of Pennisetum sp. and Paspalum wettsteinii were 3.1 to 4.39 times and 2.23 to 2.57 times as great as their average values in the whole soil profile, respectively. Root parameters of Pennisetum sp. and Paspalum wettsteinii showed a logarithmic and linear decrease with the increase of soil depth, respectively. (3) The average soil shear strength followed the order of Pennisetum sp. > Paspalum wettsteinii > bare land, being 21.04, 16.43, and 9.89 kPa, respectively. In the 0-20cm soil layer, shear strength of soil with two herbal plants were significantly greater than that of the bare land. (4) Soil shear strength had extremely significantly positive correlations with biomass density, root surface area density, and fork density (P < 0.01), and it also had a significantly positive correlation with root length density (P < 0.05). The most important factor of Pennisetum sp. to characterize soil shear strength was biomass density, while that of Paspalum wettsteinii was root length density. It is concluded that, root systems of both herbal plants could improve soil shear strength in the collapsing gully alluvial fan, and Pennisetum sp. was more effective than Paspalum wettsteinii.

Abstract:In order to correctly understand the control effect of grass cover on non-point source pollution and promote the construction of ecological orchard, a research was carried out to study the effects of cover crop (Vulpia myuros) on the accumulation and runoff loss of nitrogen. Three management modes, including grass cover on soil surface until withering (Cov), grass removed (Rem), and cleaning tillage as control (Cle). The results showed that the content of mineral nitrogen in the soil surface (0-1 cm) of the Cov treatment was 2.6 and 4.5 times as high as that of the Rem and Cle treatments when the withered grass degraded quickly (in September), respectively. At the same time, the Cov treatment increased the concentration of mineral nitrogen in the runoff by 42.6% and 20.9%, respectively. The Cov treatment decreased the rain runoff by 88.3-98.7%, and increased the rain leakage by 42.1-97.6% when compared with the Cle treatment. The results of three rainfall events showed that the runoff loss of mineral nitrogen was 90% lower than that of the clean tillage, and deep layer (25 cm) leakage was increased by 89.6%. In conclusion, planting grass and covering it on the soil surface in orchard is an advantageous management to prevent non-point source pollution by reducing nitrogen loss through runoff.

Abstract:Sediment discharge signi?cantly decreased in the Yellow River because of the effect of the ‘grain-for-green project’ (GGP). The typical watershed parsing method was applied to obtain the sediment yield and analyze the variation of the annual erosion modulus in a typical watershed in the loess hilly-gully region between 2003 and 2011. The results indicated that that sediment yield from the watershed declined dramatically, and the average erosion modulus was less than 500 t/km2?a, which was 8.3% of that before the implementation of GGP. Moreover, when excluding the data in 2003 because of the influence of the beginning of dam implement, the average erosion modulus during 2004-2011 was 144.93 t/km2?a, which was only 2.4% of that before the implementation of GGP, suggesting that there was a mild erosion in this watershed after the GGP. This study proved the significance of the effects of controlling sediment yield of the GGP, and it may help the planners and managers to make proper decisions for the control of soil erosion from watersheds under similar conditions.

Abstract:In order to know the soil infiltration characteristics of the Xilamuren grassland, a study was carried out in an enclosed grassland to investigate the soil infiltration process of six plant communities (Allium mongolicum, Convolvulus ammannii, Leymus chinensis, Koeleria asiatica, Stipa krylovii, and Stipa krylovii) using the double-ring sampling method, and the influencing factors were analyzed. The results indicated that soil infiltration rates in different plots could be divided into three stages. The first stage was from 0 to 10 minutes, in which the infiltration rate showed a sharp decreasing trend; during 10 to 30 minutes, the infiltration rate decreased slowly, and remained constant after 30 minutes. By analyzing the soil infiltration rates and infiltration amount, soil infiltration characteristics of the Koeleria asiatica community were the best, followed by those of the Leymus chinensis community, while those of the Convolvulus ammannii community was the worst. The differences in soil infiltration characteristics were caused by the differences in soil structures among communities. Correlation analysis showed that bulk density, maximum porosity, and non-capillary porosity were important factors affecting soil infiltration. Soil infiltration in the study area fitted thr Honton model very well.

Abstract:To investigate the hydrological function of different afforestation tree species in the feldspathic sandstone region, we selected Pinus tabuliformis, Platycladus orientalis, Populus cathayana, Prunus armeniaca, Hippophae rhamnoides and Caragana korshinskii from the area to analyze and compare the water-holding capacity in the litter layer and soil layer of different tree species by the soaking method and ring sampling method. Our results demonstrated that the litter accumulation variation range of the major afforestation tree species in the feldspathic sandstone region was 1.55-7.89 t/hm2, and Populus cathayana forest litter exhibited the highest maximum water holding capacity, i.e. 281.26%, followed by Pinus tabuliformis (217.14%), Platycladus orientalis (201.05%), Prunus armeniaca (202.79%), Hippophae rhamnoides (170.96%), Caragana korshinskii (158.08%), and abandoned land (143.88%). For the soil layer under the Pinus tabuliformis forest, the smallest bulk density was 1.46 g/cm3, the maximum porosity and capillary porosity was 43.55% and 36.99%, respectively, with the maximum capillary moisture capacity being 14.50 mm. For the soil under Prunus armeniaca forest, the maximum non-capillary porosity was 13.12%, and the maximum non-capillary moisture capacity was 6.86 mm. The water-holding capacity of both the litter layer of Pinus tabuliformis and the under-forest soil layer was great. Therefore, Pinus tabuliformis is more suitable for vegetation construction in the feldspathic sandstone region.

Abstract:In order to investigate the function of water conservation in lands of different using types in the dump reclamation area, using field double-ring infiltration method and indoor soil physical and chemical analysis, this paper systematically investigated soil infiltration characteristics and their influencing factors under different utilization types (arbor, shrub, farmland, and grassland) in the dump reclamation area. The results indicated that infiltration rates, stable infiltration rate, and cumulative infiltration under different utilization types in the dump reclamation area showed the following order of arbor > shrub > farmland > grassland; The goodness of fit of the infiltrating processes were different under different utilization types in the dump reclamation area, with the average value being 0.926, 0.908, and 0.905 for the G-P model, the Kastiakov model, and the Horton model, respectively. The relative error of the G-P model was 79.2%-123.69%, it was closed to the actual process of soil infiltration in the reclaimed area, and could be used as the prediction model of soil infiltration process in the reclaimed area. The initial infiltration rate under different utilization types in the dump reclamation area had significantly positive correlations with non-capillary porosity, and stable infiltration rate, while cumulative infiltration had significantly positive correlations with non-capillary porosity, gravel content, root length density, and root surface area density. Principal component analysis showed that soil infiltration capacity followed the order of arbor > shrub > farmland > grassland. The initial infiltration rate, stable infiltration rate, 14-min infiltration rate, and cumulative infiltration together accounted for 99.047% of the principal component variance, and described the soil infiltration capacity well.

Abstract:Soil water content and potential of the 0-200 cm soil profile in Robinia pseudoacacia forest land were observed continuously with a neutron moisture meter and a negative pressure meter to study the soil water characteristic curve (SWCC) and soil water potential characteristics in the Loess Hilly Region from April 1, 2015 to October 31, 2015, and the gray relational grade of soil water potential in different soil depths and months were analyzed by gray relational analysis. The results showed that: (1) Soil water characteristic curve (SWCC) at different soil depths could be well described by the Gardner power function. The fitting parameter a was in the order of the surface layer (0.103 8) > the middle layer (0.094 4) > the deep layer (0.086 0), while parameter b followed the order of the surface layer (0.284) < the middle layer (0.291) < the deep layer (0.298). (2) According to the SWCC, soil water constant of the artificial R. pseudoacacia forest land was as follows: average field capacity and wilting coefficient was 25.53% and 8.42%, respectively, and the maximum effective water range was 17.11%. Normally, when the soil water suction was 0.1 MPa, soil water supply capacity was characterized by the specific water capacity. The value was in the order of surface layer (56.73%) > middle layer (53.74%) > deep layer (50.84%) in the artificial R. pseudoacacia forest land. (3) The vertical spatial distribution of soil water potential of the artificial R. pseudoacacia showed that the water potential of the surface soil layer increased from -0.21 MPa to -0.08 MPa, the middle layer soil water potential fluctuated greatly, and the deep layer soil water potential was stable, being around -1.14 MPa. The grey relational grade analysis showed the order of R12 (0.899 8) > R23 (0.711 5) > R13 (0.702 8). The results showed that the relationship between the surface layer and the middle layer of the artificial R. pseudoacacia forest land was close, the relationship between the deep layer and the middle layer was the second, and the relationship between the surface layer and the deep layer was the worst. (4) Soil water potential of the 0-200 cm soil layers in the artificial R. pseudoacacia forest land decreased from April to June, then increased significantly from July to August, and decreased again from September to October. The grey relational grade of soil water potential in each month showed the order of R10 (0.868 9) > R05 (0.806 7) > R09 (0.780 4) > R07 (0.676 3) > R06 (0.654 8) > R08 (0.611 4). The soil water potential variation trends in May, September, and October were similar to that in April. In contrast, the soil water potential variation trends in June, July, and August were different from that in April.

Abstract:In order to study the effects of different plant cultivation patterns on soil fertility of mining abandoned lands, this paper selected eight typical plant cultivation patterns (Lolium perenne L., Melilotus suaveolens Ledeb., Astragalus adsurgens, Coronilla varia L., Amorpha fruticosa Linn., Amorpha fruticosa Linn.+ Coronilla varia L., Amorpha fruticosa Linn. + Lolium perenne L., and Melilotus suaveolens Ledeb. + Lolium perenne L.). Soil fertility of different plants and planting patterns were analyzed by soil sample collection, lab analysis and principal component analysis. The results showed that different planting patterns could improve soil water conditions, the average soil water content was 8.7% higher than that of the control. With the increase of soil depth, soil water content under different planting modes showed an increase-decrease-increase-stable development trend. The improvement effect of plants on soil water retaining was mainly reflected in the 0-40 cm soil layer. The total quality score of each nutrient in the soil was larger in the 0-10 cm soil layer than in the 10-20 cm soil layer, showing a certain aggregation effect. In the early stage of plant growth, the effects of different planting patterns in the soil of mining abandoned land followed the order of Astragalus adsurgens > Melilotus suaveolens Ledeb. > Lolium perenne L. > Melilotus suaveolens Ledeb. + Lolium perenne L. > Amorpha fruticosa Linn. + Coronilla varia L. > Amorpha fruticosa Linn. + Lolium perenne L. > Amorpha fruticosa Linn. > Coronilla varia L. Unicast planting patterns were better than mixed cropping patterns. The results can provide a reference for the study of soil moisture change, the good planting pattern, and the rapid improvement of soil fertility in the future.

Abstract:In order to quantitatively evaluate the soil characteristics and water conservation function of different forests in the alpine mountainous areas of Datong County of Qinghai Province and to provide a theoretical basis for reasonable spatial allocation of forests, immersion method, cutting ring method, fixed head method and sulfuric acid potassium dichromate method were used to determine litter properties, soil porosity, soil permeability and soil nutrient status of the 0-40 cm soil layers of five kinds of forest. The results showed that there were significant differences in soil properties and water conservation function among forest types. (1) The litter size and the maximum water holding capacity of the litter in the five forest types were in the order of Picea crassifolia-Betula platyphylla > P. crassifolia-Larix principis-rupprechtill > P. crassifolia forest > L. principis-rupprechtii forest > Betula platyphylla forest. (2) In the 0-40 cm soil layer, the average soil organic matter content was in the order of P. crassifolia –L. principis-rupprechtill > P. crassifolia-B. platyphylla > B. platyphylla forest > P. crassifolia forest > L. principis-rupprechtii forest. (3) In the 0-40 cm soil layer, soil bulk density of five kinds of forest types increased with the increment of soil depth, and followed the order of B. platyphylla forest > L. principis-rupprechtii forest > P. crassifolia-B. platyphylla > P. crassifolia forest > P. crassifolia-L. principis-rupprechtill. (4) In the 0-40 cm soil layer, total porosity of the soil under five forest types decreased with the increment of soil depth. The mean value of soil total porosity was in the order of P. crassifolia-L. principis-rupprechtill > P. crassifolia forest > P. crassifolia-B. platyphylla > L. principis-rupprechtii forest > B. platyphylla forest. (5) In the 0-40 cm soil layer, soil average infiltration rate of the five types of forests was in the order of B. platyphylla forest > P. crassifolia-B. platyphylla > P. crassifolia-L. principis-rupprechtill > L. principis-rupprechtii forest > P. crassifolia forest. (6) Based on the total water-holding capacity of litter and soil, water conservation function of the five types of forests followed the order of P. crassifolia-L. principis-rupprechtill (4 427.40 t/hm2) > P. crassifolia forest (4 365.33 t/hm2) > P. crassifolia-B. platyphylla (4 055.04 t/hm2) > L. principis-rupprechtii forest (3 729.64 t/hm2) > B. platyphylla forest (2 650.31 t/hm2).

Abstract:To evaluate the water conservation capacity of forests in the Mount Tumor Nature Reserve quantitatively, comprehensive water storage capacity method was used to investigate the canopy interception capacity (C), litter water-holding capacity (L), soil water storage capacity (S) of Picea schrenkiana forest ecosystems in the upper Tailan River, then a comprehensive evaluation of its water conservation function was made. The results showed that: ① In the four sample areas, the canopy interception capacity followed the order og the middle altitude spruce forest (29.94 mm) > higher altitude spruce forest (20.56 mm) > high altitude spruce forest (11.72 mm) > low altitude mixed?broad leaf-conifer?forest (5.84 mm), and the stem flow showed the opposite order. ② Except for the middle altitude spruce forest, the average?thickness of un-decomposed litter was thicker than that of the?intermediately decomposed layer. The high altitude spruce forest had the largest average volume of decomposed layer (79.32 t/hm2), while the middle altitude spruce forest had the largest intermediately decomposed layer (59.47 t/hm2). On the whole, the rank of the maximum water holding capacity was the middle altitude spruce forest (32.55 mm) > the high altitude spruce forest (31.05 mm) > the higher elevation spruce forest (30.78 mm) > the low altitude mixed?broad leaf-conifer?forest (12.84 mm). ③ Soil bulk density in the four sampled forests ranged from 0.73 to 1.06 g/cm3. Both the average soil porosity and water holding capacity of capillary pore in the 30-cm soil layer were in the order of the middle altitude spruce forest > the higher altitude spruce forest > the high altitude spruce forest > the low altitude mixed?broad leaf-conifer?forest. Overall, soil moisture content of natural forests increased with the increase of the altitude. The average water holding capacity of non-capillary pore in the 30-cm soil layer followed the order of the middle altitude spruce forest (37.6 mm) > the higher altitude spruce forest (30.7 mm) > the high altitude spruce forest (25.73 mm) > the low altitude mixed?broad leaf- conifer?forest (13.92 mm). ④ Comprehensive water conservation capacity of the forest ecosystems in the study area was bwteen 141.12 and 280.84 mm, with the low altitude mixed?broad leaf-conifer?forest and the middle altitude spruce forest having the smallest and largest water holding capacity, respectively. The soil layer contributed the most to water conservation, accounting for 77.75%-86.96%. Comprehensive effective water storage capacity was far less than the theoretical total capacity, but could work well in the water conservation function as well as water and soil conservation effect.

Abstract:To study the soil ecological effects of different restoration models in the karst gorge of the Karst Plateau, six typical ecological restoration models were selected as the research objects to analyze the soil physical-chemical properties, anti-erosion characteristics, infiltration properties, and the relationship between soil nutrients and the above-mentioned properties, taking an abandoned grassland as the control. Field survey, sample collection, and lab analysis were carried out. The results indicated that: (1) Compared with the abandoned grassland, the restoration models significantly improved soil physical properties such as bulk density, and total porosity, as well as anti-scouribility coefficient and anti-erodibility index (p < 0.05). Total porosity and non-capillary porosity was increased by 2.62% and 6.45% by different restoration models, respectively. Soil compactness and bulk density was decreased by 19.95% and 3.98%, respectively. The mean value of anti-scouribility coefficient of different restoration models was 1.79 times of that of the abandoned grassland, the average dry soil loss was only 45.42% of that of the abandoned grassland, and the average value of anti-erodibility index was 27.53% higher than that of the abandoned grassland. (2) Infiltration experiments showed that the average initial infiltration rate (2 min), stable infiltration rate, average infiltration rate, and total infiltration of the six restoration models was 1.6, 1.0, 1.2, and 1.3 times of that of the abandoned grassland, respectively. Comprehensive evaluation model of soil permeability based on principal component analysis (Z = 0.9689 × F1) showed that the average soil permeability score of the restoration models (0.1860) was higher than that of the abandoned grassland (-1.115 8), indicating that the permeability of the ecological restoration models was stronger than that of the abandoned grassland. (3) Correlation analysis showed that there was a highly significant correlation (p < 0.01) between available nitrogen, available phosphorus, available potassium, organic matter and total infiltration, the anti-scouribility coefficient, anti-erodibility index, respectively. Soil anti-erosion characteristics and infiltration ability had important effects on soil nutrients. In conclusion, compared with the abandoned grassland, the restoration models significantly improved soil physical properties, anti-erosion characteristics, and infiltration properties, which had a great connection with the occurrence and loss of soil nutrient.

Abstract:In view of the fact that shortage and uneven temporal and spatial distribution of rainfall in the semi-arid area of the Loess Plateau, this paper aimed to study the hydrothermal regime effect of the ridge-furrow planting mode, and reveal the mechanism of hydrothermal regulation and the enhancement of crop yield. Field experiments of open field treatment (CK) and plastic film combined with straw mulching treatment (RMFS) were conducted in 2014 and 2015 in Yangling, Shaanxi. The results showed that the plastic film combined with straw mulching cultivation had effects on the growth of summer maize, and the mulching could improve soil moisture condition. Soil temperature showed a phenomenon of ‘lowering the temperature when the temperature was high, and vice versa’. The RMFS treatment shortened the duration of crop growth and adjusted crop water consumption to improve the balance between water supply and demand. Soil water use efficiency and thermal time use efficiency was increased by 39.85% and 43.34% in the RMFS treatment in the second year, respectively. Although water consumption could not be saved and soil thermal time was not increased, soil water use efficiency and thermal time use efficiency were significantly improved. In short, ridge covered plastic mulching with furrow covered with straw mulching treatment improved crop yield by improving the hydrothermal interaction regime. Plastic film combined with straw mulching treatment is a suitable effective practice to collect rainwater harvesting.

Abstract:Water-heat-salt dynamics in sandy soil are essential to design a reasonable irrigation schedule in the Taklimakan Desert Highway Shelterbelt. In order to reveal spatial and temporal rules of the water-heat-salt dynamic changes under different plant types in the region, based on the field investigation and real-time monitoring between May and September in 2015, we discussed the correlation between air temperature and soil temperature in the shelterbelt, and also analyzed the spatial and temporal dynamics of soil water and salt under different plant types. The results showed that: (1) Soil temperature was basically consistent under different plant types, and air temperature was significantly correlated with soil temperature (p < 0.01). Meanwhile, the correlation of soil temperatures in different soil layers decreased as the soil depth increased. (2) In the soil of artificial shelterbelt, the dynamics of soil water and salt displayed an obvious periodic rule. With respect to Haloxylon ammodendron, the distribution of soil water and salt displayed a single-peak curve with the peak appeared at a depth of 30 cm, while the distribution of soil water and salt in the soil under Calligonum mongolicum showed a single-peak curve with the peak occurred at a depth of 10 cm. In the 0-200 cm soil profiles, soil moisture was divided into an active layer, a weak layer, and a stable layer in the soil under Haloxylon ammodendron, but only an active layer and a weak layer in the soil under Calligonum mongolicum. (3) The soil wetting front was a semi-ellipsoid shape after drip irrigation. The affected depth of irrigation water was 0.6 m in the soil under Haloxylon ammodendron, and 1.5 m in the soil under Calligonum mongolicum. The soil salt was concentrated in the upper layer. However, soil salinization did not exist (EC was less than 1.0 mS/cm). (4) During the growing season, soil pondage was 116.34 mm in the soil under Haloxylon ammodendron, but 100.99 mm in the soil under Calligonum mongolicum. All the soil water deficit ullage was more than 270 mm. Plant types had minor influences on soil temperature. The irrigation of Calligonum mongolicum should be properly increased to maintain the health of the shelterbelt system. Our study is beneficial to provide a suitable irrigation system and approach, which can ensure the sustainable development of the shelterbelt system in the Taklimakan Desert.

Abstract:Taking coal mining subsidence farmland with high groundwater level as the research object, the distribution of soil thermal conductivity and the influencing factors under three different reclamation modes, including regional leveling reclamation, filling reclamation, and dynamic reclamation were studied. In this research, soil profiles of three layers, i.e. 0-20 cm, 20-40 cm, and 40-60 cm, were dug in typical areas under three different reclamation modes. After collecting soil samples, soil thermal conductivity and other relevant physical indicators were acquired through experiments. The results indicated that reclamation mode, profile layer, and their interactions were the factors making the soil thermal conductivity different significantly (p < 0.01), and the contribution rate was 86.8%, 89.6%, and 71.9%, respectively. The changing trend of the soil conductivity showed a pattern of ">" with the increasing of soil depth. Reclamation could influence soil thermal conductivity significantly (p < 0.05), and increase its differentiation of distribution among soil layers. Under the same conditions of soil water content and temperature, soil silt content was the main factor affecting soil thermal conductivity when soil bulk density was between 1.205 and 1.593 g/cm3, while soil sand content was the main factor when soil bulk density was between 1.604 and 1.813 g/cm3. Thermal conductivity of reclaimed soils was lower than that of the normal soil, and its differentiation of distribution among soil layers was higher. Therefore, in order to improve thermal conductivity of reclaimed soils, soil bulk density and texture shou be taken into consideration comprehensively, and soil bulk density should be reduced.

Abstract:A field test was conducted at the Mizhi Experimental Station of Northwest A & F University from October 2014 to April 2015, to research the soil moisture movement law and temperature difference under different plastic film mulching in plant dormancy period in semiarid loess hilly region. No plastic film mulching (CK) and transparent film mulching (TF) treatments were set up at the same level of terraces at the depth of 0-400 cm to observe soil moisture movement. Three treatments, including CK, TF, and black film covering (BF) were designed at the same level at the depth of 0-50 cm (15 cm, 30 cm, 50 cm) to observe soil temperature. The results showed that soil water storage capacity of TF was 51.9% higher than that of CK at the depth of 0-400 cm in the dormancy period, and the difference was significant (p < 0.05). The maximum amplitude of soil water storage appeared at the depth of 0-20 cm, and soil water storage at the depth of 20-60 cm decreased from 54.9% to 26.3%. In typical sunny days, the maximum temperature difference between the three treatments of CK, TF, and BF was 2.25-2.7 oC, 3.45-3.5 oC, and 1.5-1.8 oC at the non-freezing stage. Whereas the difference was 1.65 oC, 2.1 oC and 1.2 oC at the freezing stage, and the effect of film insulation was not obvious when the soil was frozen. The depth of film insulation was up to 15 cm, the warming effect of BF treatment was better than that of TF. The above evidences suggested that the plastic film mulching in plant dormancy period could increase soil moisture and soil temperature, reduce soil water loss and promote water deep infiltration in the 0-20 cm soil layer. Furthermore, BF treatment might be more favorable for warming and stabilizing temperature change than TF treatment.

Abstract:The effects of different mulching pattern on soil organic carbon, carbon components, and the relationships between carbon components on the Loess Plateau were investigated by carrying out a field positioning test and laboratory analysis. Four treatments were set up, including a control without mulching treatment (CK), straw mulching at a rate of 9 000 kg/hm2 (M1), straw mulching at a rate of 4 500 kg/hm2 (M2) during winter wheat growing season, and straw mulching at a rate of 9 000 kg/hm2 (SM) during fallow summer. The main results were as follows: (1) Compared with CK, the M1, M2, and SM treatments could increase the contents of soil organic carbon, microbial biomass carbon, potential mineralized carbon, and particulate organic carbon significantly (p < 0.05) at the depth of 0-10 cm and 10-20 cm, but not significantly at the depth of 20-40 cm. The effect of M1 treatment was the best among different mulching patterns, and the effect of SM treatment was relatively weak. (2) Different straw mulching influenced the proportion of soil microbial biomass carbon, potential mineralized carbon, and particulate organic carbon in total organic carbon. The relative content of soil microbial biomass carbon, potential mineralized carbon, and particulate organic carbon was 1.96%-3.31 %, 2.83%-3.78%, and 18.13%-37.25%, respectively. (3) The content of soil organic carbon and its components decreased with the deepening of soil layer, and the deeper the soil layer was, the more slowly the change was. (4) There was a significant positive correlation between soil organic carbon and its components in different mulching treatments (p < 0.01), the correlation coefficient of particulate organic carbon, microbial biomass carbon, and potential mineralized carbon with soil organic carbon was 0.847, 0.700, and 0.614, respectively. It was suggested that microbial biomass carbon, potentially mineralized carbon, and particulate organic carbon content depended on the storage of soil organic carbon. In conclusion, straw mulching could increase the contents of soil organic carbon and its components. A rate of 9 000 kg/hm2 had a higher practical application value. The dynamic changes of particulate organic carbon and microbial biomass carbon could reflect the early changes of soil organic carbon. Particulate organic carbon and microbial biomass carbon could indicate the changes of soil fertility more sensitively.

Abstract:In order to describe the quantitative relationship between soil salinity in the profile of a saline alkali?soil and leaching water volume, the effects of leaching water volume on soil water and salt movement in a typical saline alkali?soil in Ningxia Province treated with desulfurized gypsum were studied by an indoor soil column leaching test. The results showed that applying desulfurized gypsum had a positive effect on increasing water infiltration, reducing soil pH and salinity of the 0-20 cm soil layer, and soil desalinization rate was between 84.39% and 95.41%, but large leaching water volume might aggravate soil alkalization. Under?continuous leaching condition, the maximum desalting depth lied in the 60-80 cm soil layer. In the 0-20 cm soil layer, the?desalting?ratio of Cl- and Na+ had a small variation with the increasing amount of leaching water volume. Under small leaching?water volume, the?desalting?ratio of SO42- was lower than those of Cl- and Na+. Under large leaching?water volume, the?desalting?ratios of three ions were very close. In the 20-40 cm soil layer, the?desalting?ratio of major salt ion was in a descending order of Cl- > SO42- > Na+, and it increased quickly, finally remained stable. Under small leaching?water volume, Cl-, Na+, SO42- accumulated in the 40-60 cm soil layer. Under large leaching water volume, they continued downward migration. When leaching?watervolume reached 60 cm, SO42- and Na+ accumulated in the 80-100 cm soil layer, while Cl- migrated to >100 cm soil layer.

Abstract:In this paper, the main objective was to better understand the spatial distribution characteristics of soil organic carbon (SOC) and labile organic carbon (LOC) on the sloping farmland. Soil samples were collected from different geomorphic positions at the Suining site, which was a typical purple soil hilly region. Content and storage of SOC and LOC were studied. The results showed that soil depth was only 22.3 cm in the upper position. Compared with the soil depth in the upper position, it was almost 2.01 times in the middle position and 3.30 times in the lower position. Soil bulk density in the middle and lower position was 12.12% and 2.42% lower than in the upper position, but soil porosity in the middle and lower position was 19.82% and 3383% higher than in the upper position, respectively. Storages of SOC and LOC significantly increased from the upper position to the lower position. Compared with the upper and middle positions, SOC storage in the lower position was 674.74% and 104.09% higher, LOC storage was 958.51% and 267.75% higher, respectively. Contents of SOC and LOC in different positions of the sloping farmland decreased with the increasing soil depth. The depth distribution of SOC and LOC for the middle and lower positions could be described by the formula [Y = aln(X) + b], but it did not follow this formula for the upper position. There was a significant positive correlation between SOC and LOC in the sloping farmland. Therefore, the spatial distribution pattern of SOC and LOC were affected by soil erosion in the sloping farmland.

Abstract:To comparatively investigate the stoichiometric characteristics of carbon (C), nitrogen (N), and phosphorus (P) in plant organs and soil layers of coniferous forests, we conducted plot surveys in five prefectures/cities (Tianshui, Gannan, Dingxi, Lanzhou, and Wuwei) in Gansu Province on western Loess Plateau. Contents of C, N, P, and their stoichiometric ratios in each plant organ and different depth of soil layers were analyzed, the relationships among components in the coniferous forest ecosystems were analyzed and compared across the five study areas. The results showed that C, N, and P contents in the foliage were higher than in other organs of the trees, and C content reached 511.97-538.66 g/kg. The C content in stems, branches, and roots in Wuwei was 425.04 g/kg, 400.58 g/kg, and 400.55 g/kg, respectively, being significantly lower than those in the other four areas. The differences in C:N among study areas were only significant for stems (p < 0.05). Significant differences in C:N among different organs of the conifers were found in Gannan and Lanzhou. The N:P in stems and roots of the conifers were significantly different among study areas, whereas the differences in N:P among organs were only significant in Lanzhou and Wuwei. Differences in the contents and stoichiometric characteristics of soil C, N, and P among the five survey areas were mainly detected in the 0-30 cm soil layers, while the deeper soil layers showed little difference among study areas. In addition, C, N, and P contents in stems of the conifers were significantly correlated with each other, while a significant correlation was only detected between N and P contents in leaves. Soil C and N contents in the surface layer (0-20 cm) showed a significant positive correlation.

Abstract:The effects of different rainfall intensity on spatial and temporal variation characteristics of soil moisture of different forest types were studied based on positioning and long term observation and data processing. Soil moisture of the Quercus variabilis forest land and the Pinus tabulaeformis forest land in Beijing region was monitored by the ECH2O monitoring system and the EM50 data acquisition system. The results showed that: (1) The daily soil water storage amount changed significantly with the precipitation. However, the average monthly soil water storage increased with the increasing amount of rainfall. (2) Vertically, the increase rate of soil water storage in the 0-40 cm soil layer of the Q. variabilis and P. tabulaeformis forest land decreased with the increase of the rainfall intensity, and the average increase rate of soil water storage of the Q. variabilis forest land (94.17%) was higher than that of the P. tabulaeformis forest land (84.19%), while the soil water storage rate in the 40-100 cm soil layer showed an increasing trend, and the average increase rate of soil water storage of the Pinus tabulaeformis forest land (15.81%) was greater than that of the Q. variabilis forest land (5.83%). (3) Soil water storage in the same layer was significantly different between the Q. variabilis and P. tabulaeformis forest land (p < 0.05), and it was also significantly different between different soil layers in the same forest land (p < 0.05). In terms of the spatial and temporal characteristics of soil moisture change in the Q. variabilis and P. tabulaeformi forest land, soil water storage distributions of the two forest types were different. Therefore, it worths considering mixing the two species together in afforestation. The results of this study could provide a reference and theoretical basis for the construction and management of vegetation in the mountainous areas of Beijing.

Abstract:The characteristics of mineral nitrogen loss through surface flow and interflow in different types of vegetation in a water conservation forest were analyzed in the headstream of Taizi river. To explore the limiting factors which affect nitrogen loss, redundancy analysis and partial redundancy analysis were applied to study the relationship between nitrogen loss and environmental factors, and quantitative analysis was applied among the main influential factors. The results showed that nitrate nitrogen was the main form of nitrogen loss in both the surface flow and interflow. The concentration of nitrate nitrogen was 1.5 times more than the ammonium nitrogen in the surface flow and 20.5 times in the interflow. Whether in the surface flow or interflow, ammonium and nitrate concentrations were in the order of plantation forest > hardwood forest > secondary forest. Owing to the effects of surface flow and interflow, the amount of ammonium loss was the largest in secondary forest; the amount of nitrate loss was the largest in plantation forest. Soil physical and chemical properties were the main influential factors of the concentration of nitrogen loss, with their effects accounting for 46.36% and 16.42% of the total explanation, respectively. Geomorphology-hydrology factors and vegetation types were the main influential factors of the amount of nitrogen loss, with their effects accounting for 22.85% and 15.09% of the total explanation, respectively. The mixed effects of hydrological factors, vegetation characteristics, soil physical properties, soil chemical properties on nitrogen loss characteristics also played an important role, accounting for 36.03% and 51.36% of the total explanation for the concentration and the amount of nitrogen loss, respectively.

Abstract:The distribution of soil organic carbon was studied under different soil types and land use patterns, samples were collected in Mingshan River watershed and analysed in the laboratory. The results showed as follows: (1) Organic carbon content of the three types of soil was 17.50-34.70 g/kg, and followed the order of paddy soil > yellow soil > purple soil; From the way of land use, the content of paddy soil organic carbon and active organic carbon were significantly higher than those of the dry land, tea gardens and orchards, soil active organic carbon and soil organic carbon were significantly positively correlated (R2 = 0.884 6). (2) The content of organic carbon of soil decreased gradually with the increase of soil depth. Soil organic carbon content showed the order of paddy soil > yellow soil > purple soil at the depth of 0-20 cm, and paddy soil > purple soil > yellow soil at the depth of 20-40 cm, and active organic carbon showed a similar pattern. (3) Under different land use patterns, organic carbon content in the surface soil followed the order of paddy field > dry land > tea garden, and that in the subsoils (20-40 cm) was in the order of paddy field > tea garden > dry land. Active organic carbon contents in both in the upper and the lower layers of the paddy field were significantly higher than those of the dry land, orchard and tea garden. It is proved again that active organic carbon is one of the important indicators of organic carbon. (4) Organic carbon content of soil aggregates decreased with the increase of soil depth, at the same time, the organic carbon content of soil aggregates showed a wavy changing trend with the decreasing particle size. Organic carbon content of soil aggregates was positively correlated with total soil organic carbon content. In conclusion, organic carbon contents in the soil and soil aggregates of different particle sizes were influenced by soil types and different utilization pattern, the distribution characteristics of organic carbon in the soil and soil aggregates were different.

Abstract:Based on the fact of the formation of large-scale soil dry layers in recent years, a field soil column up to 10 m was established to simulate the drying soil in jujube forests at the Mizhi experimental station, which is located in the north of Shaanxi Province. The purpose was to explore the regularities of rainfall infiltration and water migration, also to clarify the infiltration capability of dry loess. By using the CS650-CR1000 automatic system, changes of soil moisture within different depths were observed continuously under natural conditions. Meanwhile, the precipitation during the monitoring period was recorded by an automatic weather station. The results showed that both of the depths of infiltration and migration under independent rainfall mainly depended on the precipitation. The depth could reach up to 90-140 cm, 70-80 cm, and 40 cm, respectively, when influenced by heavy rain, middle rain, and light rain. With the same precipitation, it was affected by other factors such as rainfall intensity and initial soil water content. The greater the rainfall intensity and the higher the initial soil water content was, the deeper the depth was. Under intermittent rainfall conditions, several rainfall events promoted infiltration and migration interactively. Compared with independent rainfall, the intermittent rainfall could significantly increase the infiltration depth by 100-160%, and the migration depth by 91%-197% with the same precipitation. In the loess region, not all the rainfall events could influence the soil. During the observation periods, the effectiveness of the rainfall frequency and amount were 36.3%, 72.7% respectively. Under the influence of multiple rainfall events, the soil profile tended to be layered. According to the changes of soil moisture, the affected soil could be mainly divided into three levels, i.e. the sensitive layer of rainfall infiltration within 90 cm, the delayed layer of rainfall infiltration between 90 cm and 160 cm, and the migrating layer of rainfall between 160 cm and 240 cm. The results are of great theoretical and practical significance to the restoration of woodland drying soil and scientific management of soil moisture in the loess hilly region.

Abstract:The effects of plastic film mulching on soil organic carbon and nitrogen fractions were investigated in a spring maize field. Three treatments, i.e. plastic film mulching, no mulching, and bareland fallow were included and soil organic carbon (SOC), total nitrogen (STN), particulate organic carbon and nitrogen (POC, PON), potential mineralized carbon and nitrogen (PCM, PNM), and microbial biomass carbon and nitrogen (MBC, MBN) were measured at 0-40 cm soil depth. No significant differences in SOC and STN were found among treatments for all soil depths. Compared with no mulching, the contents of POC, PON, POC/SOC, and PON/STN at 0-40 cm soil depth was decreased by 29.0%, 33.3%, 29.9%, and 35.7% by plastic film mulching, respectively. The PCM content and PCM/SOC was decreased by 17.8% and 16.1%, respectively, and the MBN content and MBN/STN at 0-10 cm soil depth was increased by 10.6% and 10.5% (p < 0.05), respectively. Compared with the bareland fallow, the content of PCM and PNM at 0-40 cm soil depth was increased by 12.8% and 14.7 by no mulching, respectively, and was increased by 7.8% and 6.5% (p < 0.05) by plastic film mulching, respectively. The contents of MBC and MBN and their contributions decreased after maize planting in spite of plastic film mulching or not. In general, plastic film mulching could increase microbial biomass carbon and nitrogen at the top layers but decrease both the contents and conributions of moderate labile fractions, indicating that plastic film mulching may not be beneficial for long-term soil carbon and nitrogen sequestration in dryland maize fields.

Abstract:To explore the effects of different degrees of degradation on soil microbes and soil enzyme activities in alpine meadows, lightly degraded grassland, moderate degraded grassland and severe degraded grassland of alpine grasslands in the Qilian Mountains of the northeastern Qinghai-Tibet Plateau were chosen as the research objects. Characteristic changes of the number of soil microbes (bacteria, fungus, and actinomycetes), soil nitrogen bacteria groups (ammonifier, aerobic nitrogen fixing bacteria, anaerobic nitrogen fixing bacteria and nitrifiers, denitrifying bacteria), soil microbial biomass (soil microbial biomass carbon and soil microbial biomass nitrogen), and soil enzyme activities (sucrose, urease ,phosphatase, and catalase) were determined and analyzed in alpine meadows under different degrees of degradation. The results showed that, for the same soil layer under different degrees of degradation, the number of soil microbes, soil microbial biomass, soil nitrogen bacteria groups, and soil enzyme activities decreased with the increase of degradation degree, and each index was the lowest under severe degradation. The number of actinomycetes, ammoniated bacteria, and denitrifying bacteria in the 10-20 cm soil layer, and the number of bacteria, fungi, actinomycetes, aerobic nitrogen fixing bacteria and denitrifying bacteria in the 20-30 cm soil layer increased in the moderate degraded grassland (p < 0.05). For different soil layers under under the same degrees of degradation, the number of soil microbes, soil nitrogen bacteria groups, soil microbial biomass, and soil enzyme activities decreased with the increase of soil depth. These results provide a new method for assessing the degradation of grasslands, and thus offering important theoretical bases for the restoration of degraded alpine meadows.

Abstract:In order to improve nutrient utilization efficiency by cucumber and reduce the environmental pollution, special?slow-release fertilizers containing urease inhibitor (NBPT), hydroquinone (HQ) and nitrification inhibitor (DCD) were produced according to the nutrient requirements of cucumber. Nitrogen release characteristics of?two special?slow-release fertilizers were studied by using the "soil incubating method". Pot experiments were conducted to study the effects of slow-release fertilizers on yield, uptake and utilization rate of fertilizer and NPK by cucumber. The results showed that in three different soils, nitrogen release accumulation was in the order of ordinary compound fertilizer (OCF) > commercial slow-release fertilizer (MSRF) > cucumber special compound fertilizer NO.1 (CCF) > cucumber special slow-release fertilizer NO.2 (CSRF1) > cucumber special slow-release fertilizer (CSRF2), and nitrogen release accumulation in special slow release fertilizers (CSRF1 and CSRF2) were less than that of other fertilizer treatments. The amount of accumulated nitrogen release of different fertilizer treatments in three different soil types showed the order of alkaline soil > neutral soil > acid soil. Nitrogen accumulation amount of NH4+-N was more than that of NO3--N, possibly due to the nitrification inhibitor (DCD) could not only inhibit soil nitrification and denitrification processes, but could also inhibit soil denitrification process. The nitrification process was inhibited by nitrification inhibitors, and the nitrogen fertilizer would remain in the soil for a long time in the form of NH4+-N. Nitrogen accumulation amount of NH4+-N and NO3--N was also in the order of alkaline soil could neutral soil > acid soil. The dynamic release of different forms of nitrogen in three soils was fitted with a dynamic equation of the first order kinetic equation (r = 0.952**-0.993**). Using the first order kinetic equation, the N0 value of the maximum release rate of different forms of nitrogen was in the order of total N > NH4+-N > NO3--N, which was consistent with the changes of the accumulation and release characteristics of different forms of nitrogen in the soil. The dynamic characteristics of nitrogen release by the equation were suitable for the prediction of the release properties and release characteristics of nitrogen in the soil. Two kinds of special slow release fertilizers (CSRF1 and CSRF2) significantly increased the yield of cucumber by 59.1%, 30.3%, 33.8% (CSRF1), and 46.2%, 19.7%, 22.9% (CSRF2), compared with treatments of OCF, MSRF and CCF, respectively. Compared with common compound fertilizer, nutrient relative utilization efficiency of NPK in two kinds of special slow release fertilizer treatments was increased by 18.52%-24.20% (N), 19.27%-20.02% (P), and 28.54%-35.69% (K), respectively. Compared with traditional fertilizer, the use of two special slow-release fertilizers could effectively delay the N release in the soil, and increase the uptake of N, P, and K by cucumber plants and cucumber yield.

Abstract:Nine kinds of organic materials from three categories, including poultry excrement, natural organic material, and organic fertilizer were studied in a field trial. This research studied on the effects of different kinds of organic materials on variation characteristics in soil nutrients and biological traits following main cropping and continuous cropping. The results indicated that the application of organic materials apparently increased soil nutrient contents and improved soil biological properties. Soil pH values of the main cropping and continuous cropping were 5.70-6.00 and 5.50-5.90, respectively, with pH values being increased by the application of organic materials. Poultry excrement significantly increased available potassium content by 12.73% and 17.09% in the soil of the main cropping and continuous cropping of soybean, repectively; pig manure increased soil respiration by 11.30%. Chicken manure increased microbial biomass nitrogen in the soil of continuous cropping by 13.85%. Alkaline hydrolysis nitrogen in the soil was significantly increased, i.e. by 6.31% and 3.30%, respectively, by the application of natural organic materials for both the main cropping and continuous cropping. Available phosphorus content in the soil was increased by the application of organic fertilizer by 2.13% and 2.27%, respectively; organic matter content was increased by 1.98% and 4.20%. Chicken manure fertilizer increased soil microbial biomass carbon for the main cropping by 3.45%. All fields treated with organic materials had better soil nutrient and biological traits compared with the control, indicating that the application of organic materials can increase nutrient contents in soybean soil and improve its nutrient properties.

Abstract:In order to provide the basis for ecological construction in the area of grassland, we studied the effects of enclosure and level trench ecological restoration on soil biological characteristics in the Hilly Loess Plateau Gully steppe. Using the method of space gradient instead of time gradient, in typical steppe in the loess hilly area of Ningxia, we selected soils in areas which included the unenclosed (grazing), enclosed for 3-15 years, the level trench after 1-15 years, analyzed the change characteristics and relationship of the number of microorganisms, soil microbial biomass nitrogen and carbon, and soil enzyme activity the in 0-10 cm, 10-20 cm, 20-30 cm, and 30-40 cm soil layers. The results showed that: (1) Soil microbial community in the test area was dominated by actinomycetes, which accounted for 86.18-94.43%, and the overall order was actinomycetes > bacteria > fungi; the amount of soil microorganisms, the number of bacteria and actinomycetes, microbial biomass carbon and nitrogen, urease, protease, phosphatase, sucrase activity all showed an upward change with the increase of enclosure ages, but they all showed an up-down-up trend in level trench; on the contrary, the change of soil catalase activity had a opposite trend in both the enclosure and level trench, and the number of fungi was lower in FY6 and SP6, being 11.33 cfu/g and 4.67 cfu/g, respectively. (2) Under different treatments, in the 0-40 cm soil layer, microbial and enzyme activity in the upper soil was higher than in the underlying soil. The correlations between soil microorganism, enzyme activity and contents organic matter and main nutrients were significant (p < 0.05); (3) Within the similar recovery period, the number of soil microorganisms, microbial biomass carbon and nitrogen, and enzyme activity were generally higher in the enclosed grassland (p < 0.05). Our research showed that, compared with level trench, enclosure was more conducive to increase soil microorganisms and enzyme activities in typical steppe of the Loess Hilly Area.

Abstract:Two random block experiments were conducted to study the effects of reducing nitrogen and applying organic fertilizers on soil microbial biomass carbon and enzyme activity in the hilly area of central Sichuan basin. The treatments included different types of organic fertilizers and different application rates of nitrogen fertilizers (reducing 20% of nitrogen + without organic fertilizer N1O0, reducing 20% of nitrogen + ordinary organic fertilizer N1O1, reducing 20% of nitrogen + biological organic fertilizer N1O2, reducing 40% of nitrogen + without organic fertilizer N2O0, reducing 40% of nitrogen + ordinary organic fertilizer N2O1, reducing 40% of nitrogen + biological organic fertilizer N1O2). Two control treatments (CK0:No fertilizer; N100: Nitrogen100%) was established in order to study the effects of reducing nitrogen on increasing benefits and raising the utilization efficiency of nitrogen. The results showed that with the decrease of nitrogen fertilizer application rate (N1O0, N2O0), the activities of soil urease, invertase and catalase, and the contents of microbial biomass carbon showed decreasing trends. Compared with N100, the content of microbial biomass carbon was decreased by 25.6 and 35.08 mg/kg at the silking stage; the urease activity was decreased by 11.1% and 14.1%, and the invertase activity was decreased by 30.4% and 97.1% at the big trumpet stage. The yield was decreased by 921.98 and 1 719.62 kg/hm2, respectively. The experiment also showed that using organic fertilizers could increase the activities of soil urease, invertase and catalase, the contents of microbial biomass carbon content and grain yield. Compared with N1O0, the contents of microbial biomass carbon was increased by 38.57% and 54.45%, the activity of urease was increased by 9.73% and 14.82%, the activity of invertase was increased by 42.75% and 64.26%, and the activity of catalase was increased by 11.05% and 11.93%, and the yield was increased 2% and 6% by N1O1 and N1O2, respectively, with N1O2 increasing the yield by 4% more than N1O1. Reducing 20% of nitrogen and using organic fertilizers reduced bare top length, increased spike length, ear rows, 100-kernel weight and grain yield. The correlation between the content of soil microbial biomass carbon, the activities of soil enzyme and the yield was significant or extremely significant. Reducing 20% of nitrogen fertilizer and applying biological organic fertilizer could not only improve maize yield, biomass carbon, soil enzyme activity significantly, but also improve the condition of plant root growth to promote maize yield in the upper dome area under poor siltstone soil conditions.

Abstract:Effects of potassium fertilizer application rates on crop yield, economic benefit and soil potassium content were studied in a cotton-garlic intercropping system by a four-year located experiment. There were four treatments, CK (K2O 0 kg/hm2), K90 (K2O 90 kg/hm2), K180 (K2O 180 kg/hm2) and K270 (K2O 270 kg/hm2). The results showed that K fertilizer application significantly increased cotton yield by 18.4%-72.7%. Lint cotton yield increased with the increase of potassium application rate, but no significant difference was observed between K180 and K270. The bolls and boll weight were significantly increased compared with CK. Potassium application increased garlic bulb and bolt yield by 10.1%-64.2% and 8.7%-93.3%, respectively, compared with CK. K270 had the highest bulb yield in 2016. Soil available K content increased in the 0-20 cm soil layer with the increase of potassium application rate but no significant difference was observed among treatments in the 60-100 cm soil profiles. After four-year fertilization, water-soluble K content of K90, K180, and K270 was increased by 13.6, 20.1, and 26.1 mg/kg, respectively; non-specifically adsorbed K content was increased by 10.4, 19.6, and 53.4 mg/kg, respectively; and non-exchangeable K content was increased by 34.3, 53.9, and 140.1 mg/kg, respectively compared with CK. The overall results suggest that the appropriate potassium application rate ia K2O 180 kg/hm2 for cotton and K2O 270 kg/hm2 for garlic in the cotton-garlic intercropping area.

Abstract:Effects of different utilization models of Chinese milkvetch and rice straw on characteristics of paddy soil organic carbon fractions under chemical fertilizer reduction were studied in order to provide a reference for rational utilization of organic materials for soil fertility control. A field experiments for five consecutive years (during 2011-2015) were designed to study the responses of the contents of purple soil total organic carbon (TOC), microbial biomass carbon (MBC), dissolved organic carbon (DOC), easily-oxidized organic carbon (EOC), and light fraction organic carbon (LFOC) to different utilization models of Chinese milkvetch and rice straw in double-rice cropping field of the Dongting Lake region in Nan Country of Hunan Province. The results indicated that F100 significantly increased the content of soil TOC, MBC, DOC, EOC, and LFOC, which was 12.2%, 19.5%, 18.5%, 11.3%, and 100.9% greater than that of the unfertilized control, respectively.?Compared with F100, different utilization models of Chinese milkvetch and rice straw could be more suitable for the accumulation of TOC, MBC, DOC, EOC, and LFOC under chemical fertilizer reduction. Wherein the optimal was F80+HR+A, which was 18.3%, 47.2%, 24.1%, 20.0%, and 204.0% greater than that of the unfertilized control, respectively. Applying Chinese milkvetch alone under chemical fertilizer reduction favored the buildup of MBC, DOC, and EOC, which was 9.8%, 4.0%, and 0.6% greater than that of rice straw alone, respectively, but the LFOC was the opposite, being 34.8% lower. Sensitive index showed that the LFOC and MBC had high activity, LFOC was more labile than MBC, and they could be used to evaluate soil quality. The sensitive indices of all organic carbon fractions in F80+HR+A were significantly higher than those of F100. Correlation analysis showed that there was a significant relationship among rice yield, TOC and its labile organic carbon fractions (p < 0.01). In conclusion, there were significant differences in TOC, labile organic carbon fractions among treatments amended with Chinese milkvetch and rice straw under chemical fertilizer reduction in purple soil. Returning?rice straw could be prone to increase TOC and LFOC pool, and application of Chinese milkvetch was favorable?to?promote MBC, DOC, and EOC. The pattern of Chinese milkvetch-rice straw synergistic dispatching, especially returning high pile of straw and winter?planting?Chinese?milkvetch,?could be prone to increase TOC and labile organic carbon fractions.

Abstract:The shortage of water resources has become the main bottleneck for social and economic development in the Yellow River Delta area, thus rational exploitation and utilization of brackish water resources is an important strategy to alleviate the shortage of water resources in this area. In this paper, taking a typical area of the Yellow River Delta as an example, soil water and salt distribution characteristics and the influence of the irrigation method using fresh water and brackish water on the growth and yield of winter wheat were investigated, and some control measures of soil salt accumulation were also put forward. The results showed were as follows: (1) Brackish water irrigation increased the total salt content of the soil in the experimental plot, especially in the 0-20 cm soil layer (increment 0.9 g/kg), and the amount of salt accumulation became smaller with the increase of the depth. Plenty of rainfall in the rainy season could make the soil salinity leaching into deeper soil layer and thus avoiding excessive salt accumulation after winter wheat harvest. Salt content increment in the 0-20 cm soil layer decreased to 0.12 g/kg at the period of next winter wheat sowing. (2) Photosynthetic rate and stomatal conductance of winter wheat were not significantly decreased under the influence of brackish water irrigation, while significant difference in transpiration rate was observed. (3) There was no significant difference (p > 0.05) in the yield of winter wheat between the two irrigation methods using brackish water (9767 kg/hm2) and fresh water irrigation (10455 kg/hm2). A large amount of fresh water resources were saved, which could result in social and economic benefits. The study can provide a scientific reference for scientific and safe use of brackish water in the study area.

Abstract:In this study, stable isotope compositions of the precipitation and soil water of five different kinds of land use patterns in Wang Mao ditch small watershed on the Loess Plateau were analyzed, the aim was to understand the characteristics of stable isotopes along the soil profile, and provide a scientific basis for understanding the mechanisms of soil water movement, the identification of model parameters and the ecological protection and reconstruction. The results showed that: (1) The variation ranges of δD (or δ18O) in the precipitation was from -118.08‰ (or -16.13‰) to -14.37‰ (or 1.41‰), with a mean value of -37.36‰ (or -5.65‰). The variation range of δD (or δ18O) in soil water of five kinds of land use was from -92.36‰ (or -12.48‰) to -34.98‰ (or -5.01‰), with a mean value of -60.18‰ (or -7.81‰). (2) There were significant differences in the changes of hydrogen and oxygen isotope. Soil permeability of the five kinds of land use was as follows: grassland > terraced fields > forest land > dam land > slope cropland. Soil water evaporation fractionation in different land use patterns was as follows: terraced fields > grassland > dam land > slope cropland > forest land. (3) The woodland and grassland “preferential flow” phenomenon was obvious; the grassland “preferential flow” was the maximal, and the woodland could extend the “preferential flow” path obviously. (4) Hydrogen and oxygen isotopic values in the 160, 200 and >200 cm soil layers of the grassland, woodland, and terrace were relatively stable. The dam land and sloping farmland might affect the quality and recharge of groundwater significantly.

Abstract:Concentrations of total nitrogen (TN) and total phosphorus (TP) in submerged macrophytes, the corresponding sediments and water of the pollution admitted area, living and aquaculture area, and fringe area of Baiyangdian Lake were determined in April and September, 2015. Along with the nutrient pollution assessment in the sediment, nutrient status and distribution of TN and TP in the waterbody of Baiyangdian Lake were investigated, the accumulation abilities of TN and TP by submerged plants from natural waters were also investigated. These findings contribute to the application of submerged aquatic plants to TN and TP removal from eutrophic water. The results showed that the content range of TN and TP in the surface water was 0.77-13.65 and 0.05-1.21 mg/L, respectively. The highest concentration of TN and TP were observed in the pollution admitted area, where the water quality ranged from Class IV to inferior Class V because of the influence of the Tanghe and Fuhe River. Concentrations of TN and TP in the living and aquaculture area and the fringe area were relatively insignificant (p > 0.05). Nitrogen and phosphorus were mainly discharged by the rivers. Moreover, the content range of TN and TP in the surface sediments was (3.16±1.86) and (0.72±0.20) g/kg, respectively. The variation range of the standard index of TN and TP, and comprehensive pollution index (PI) of the sediments in Baiyangdian Lake was 3.42-9.09, 0.93-1.44,and 2.19-5.26, respectively, indicating that Baiyangdian Lake was heavily polluted, with the living and aquaculture area being more seriouly polluted than other areas. Contents of TN and TP in the sediments of the living and aquaculture area and the fringe area were relatively insignificant (p > 0.05). Among the samples of submerged macrophytes, the concentration of TN was in the order of Potamogeton crispus > Ceratophyllum demersum > Potamogeton pecinatus, while for the concentration of TP, the order was Ceratophyllum demersum > Potamogeton crispus > Potamogeton pectinatus. Significant correlations were found between the concentrations of TN and TP in the water and sediments (p < 0.05). The concentrations of TN and TP in submerged macrophytes were significantly positively related to the water but had no correlation with the sediments. In conclusion, submerged macrophytes showed strong TN and TP accumulation abilities, which are essential for developing strategies to engineer plants for phytoremediation. Accumulation of TN and TP by different submerged aquatic plants may influence the distribution of TN and TP in the waterbody, and the removal of shoots of submerged macrophytes is suggested for effective removal of TN and TP from the water system to avoid secondary pollution caused by excessive decomposition.

Abstract:The study took the primary saline alkali land in the western of Jilin Province as the research object to investigate the effects of different types and forms of organic materials (granular corn straw, normal corn straw, grass, and sheep manure) on the physical properties and features of water stable aggregates in a primary saline soil by analyzing the immersion bulk density, sedimentation coefficient, field capacity, evaporation rate and quantity, form, failure rate (PAD), water stability coefficient, mean weight soil surface, mean weight diameter (MWD), fractal dimension of soil water stable macro-aggregates and micro-aggregates in the primary saline alkali soil treated with different organic materials in the experimental field. The results showed that: (1) The main components of water stable aggregates were micro-aggregates in each treatment, with the 0.05-0.25 mm micro-aggregates being dominant. The effects of different organic materials on the contents of aggregates of different sizes were significantly different. (2) The stability of soil water-stable aggregates treated with organic materials was better than that of CK. The optimum improvement in MWD was the sheep manure treatment, in which MWD was increased by 104%. The optimum improvement in water stability coefficient and the optimum reduction in PAD was the granular corn straw treatment. (3) The morphology of water stable aggregates was improved by all organic materials, with the granular corn straw treatment showing the best improvement effect, in which the shape of aggregates was round, the surface was rough, and the size distribution was moderate. (4) There were significant differences in fractal dimension of soil aggregates between the granular corn straw treatment and other treatments, but there was no significant difference among other treatments. The fractal dimension of the granular corn straw treatment was the lowest, being 2.62% lower than that of CK. The average mass specific surface area of each organic material treatment was significantly different from that of CK, among which the normal corn straw treatment was the best, which increased the average mass specific surface area by 171.01%. (5) Compared to CK, each organic material treatment had a positive effect on the physical properties of the primary saline alkali soil. Immersion bulk density had a significant positive correlation with PAD and fractal dimension, and had a significant negative correlation with water stability coefficient and average weight diameter. The correlations for settlement coefficient were similar to those of immersion bulk density, but the correlations for field capacity were opposite. Evaporation did not show significant correlation, physical parameters and average mass specific surface area did not show significant correlation. In conclusion, organic materials could improve the primary structure of saline alkali soil, the same organic materials of different forms had different effects; in the present study, the granular corn straw treated with crushing, high temperature and pressure had better effects than other treatments and greatly shortened the improvement time.

Abstract:To explore the influence of dry-wet cycles on soil aggregate stability in Southwest China, an experiment was conducted in the Jinyun mountain in Chongqing. A typical yellow soil in cultivated land was taken as the research object. With four groups of aggregates of different particle sizes (1-2, 2-3, 3-5, and 5-7 mm) , seven dry-wet cycle processes (1, 2, 3, 5, 7, 10, and 15 times) under four antecedent moisture levels (air dried, 10%, 15%, and 20%) were simulated. The stability?features of soil aggregates after dry-wet cycles under different broken mechanisms were discussed with the Le Bissonnais method. The results showed that: (1) Fast wetting (FW) had the most serious damage on soil aggregate stability, and there was a significant difference between FW and the other two broken mechanisms (slow wetting (SW) and stirring (ST)). (2) Compared with large-size aggregates, the stability of small-size aggregates was higher. (3) The destructive effect of dry-wet cycles on aggregate stability was obvious, and the extent of the damage was different under different antecedent moisture levels. (4) The dry-wet cycle processes mainly affected the stability of aggregates by affecting the percentage of >2 mm aggregate fragmentation. These results had an important reference value for the study of soil erosion mechanisms in Southwest China.

Abstract:In order to investigate the effects of citric acid on isothermal adsorption of Zn(II) and Cd(II) under conditions of single element, coexistence of two elements, and adding citric acid into the competitive system (a form of shorthand：the first, second, and third condition) by the purple bulk soil and micro-aggregates of different particle sizes in a tea plantation. The experiment was carried out by using methods of siphon settlement and centrifugal freezing thawing. The results showed that: (1) The multilayer adsorption dominated by specific adsorption was saturated gradually with increase of the Zn2+ and Cd2+ concentration. The adsorptive amount order was <0.002 mm > 0.05-0.002 mm > bulk soil. The Zn and Cd accumulating ability of the micro-aggregates of 0.25-0.05 mm and 2-0.25mm particle sizes were relatively lower. Under different conditions, Cd was easier to accumulate than Zn. The adsorption of Zn and Cd on soil surface was spontaneous and exothermic. The fitting results of the Freundlich equations were better than those of the Langmiur equation. At the same time, there was a significant correlation between the maximum adsorption capacity and organic matter content. (2) Under a single processing mode, the holding effects of Zn and Cd were obvious. When Zn and Cd coexisted, their competitive behaviors weaken each other, with Zn having a stronger inhibitory effect on Cd. (3) Citric acid promoted the adsorption of Zn and Cd when the concentration was 0.1-1 mmol/L, but accelerated leaching when the concentration was higher than 10 mmol/L. The retention of Zn and Cd by micro-aggregates (<0.002mm) was further increased after adding citric acid at different concentrations. The results showed that citric acid could be used as a regulator to maintain the supply of Zn in the soil appropriately while weakening the migration of Cd, in order to alleviate the compound pollution in the soil in tea plantations.

Abstract:Subsurface drip irrigation (SDI), which has a wide application prospect, is one of the high-efficiency water-saving irrigation techniques. Because the emitters are buried in the soil, the hydraulic characteristics of SDI subunit pipe network are often affected by soil physical properties, and the research present on these problems are inadequate. In the paper, laboratory tests were carried out to investigate the influencing factors of hydraulic factors under subsurface drip irrigation, the treatments included work stress (60, 100, 150, 200, 250, 300, 370 kPa), soil initial moisture contents (12%, 18%), and soil bulk densities (1.25, 1.40 g/cm3). In addition, the sensitivity was also analyzed. In this study, PLASSIM emitters and Heping emitters were used. The main results were as follows: The work pressure was the main factor that affected the emitter discharge in all three soil samples, and the SDI emitter discharge was larger under higher work pressure. Soil bulk density and initial soil water content could limit the discharge, especially in the sandy soil. Significant differences in the sensitivities of emitter discharges for different soil samples were obtained. The sensitivity was larger in the sandy soil, while it was smaller in the loamy soil and smallest in the clay soil. Three kinds of sensitive indicator of the PLASSIM emitter declined with the increase of work pressure, soil initial moisture content, and soil bulk density. The results obtained in this study could provide scientific instructions on irrigation program and efficient irrigation system.

Abstract:In order to explore the changing rules of soil water and salt movement under the condition of snow cover and surface mulching during the freezing and thawing season in Shihezi irrigation areas, we conducted a field plot test during 2015-2016 and investigated the temporal and spatial dynamic rules of water and salt in the soil with three different surface coverings, i.e. straw, plastic film, activated carbon, and bare land, during the whole seasonal freezing and thawing period. The results suggested that surface coverage was more effective in the preservation of soil moisture and salt reduction than the bare land. After the frozen soil was fully thawed, the deepest soil layer in which the water content increased was 0-30 cm and 0-40 cm for the soil covered with straw and activated carbon, respectively, indicating that the two kinds of coverings were more beneficial to the maintenance of soil moisture and the efficient use of snowmelt water after the freezing and thawing process. Compared with the initial value, the increase in salt content in the 0-30 cm soil layer in the soil covered with activated carbon, straw, plastic film, and bare land was 18.08%, 20.30%, 30.91%, and 32.81%, respectively, suggesting that the inhibition effect on the upward movement of salt by activated carbon coverage was the most significant, followed by straw mulching. During the process of freezing and thawing, the variability of soil moisture and salinity showed a decreasing tendency with the increasing of soil depth.