Abstract:To reveal effects of the half-ridge less tillage measure on soil erosion characteristics at sloping farmlands of the Chinese black soil region, the artificial simulated rainfall experiments were carried out on 5° and 7° slopes with 75 mm/h and 100 mm/h rainfall intensities. The cross ridge treatments included all looseness (the soil bulk density was 1.00 g/cm³), upper looseness+lower compaction (the soil bulk densities was 1.00 and 1.20 g/cm³, respectively), upper compaction+ lower looseness (the soil bulk densities was 1.20 and 1.00 g/cm³, respectively) and all compaction (the soil bulk density was 1.20 g/cm³). The results showed that the half-ridge less tillage measuredelayed the overflow time of crossridge, and obviously regulated soil erosion. The soil erosion amounts decreased in the order of all looseness>upper looseness+lower compaction>all compaction>upper compaction+lower looseness. Except for the 5° slope with 75 mm/h rainfall intensity, compared with the all looseness treatment, the total runoff amounts of the upper compaction+lower looseness and all compaction treatments decreased by 16.1% to 19.4% and 6.6% to 11.4%, respectively, the soil erosion amounts decreased by 25.0% to 52.5% and 17.9% to 31.6%, respectively. Furthermore, the changes of both runoff rate and soil erosion rate of the upper compaction+ lower looseness and all compaction treatments with rainfall duration were relatively stable. Therefore, the half-ridge less tillage measure not only controlled the total runoff and soil erosion amounts but also regulated the runoff and soil erosion processes. In conclusion, the half-ridge less tillage measure should be selected scientifically according to the specific rainfall characteristics and topographic slope gradients of farmlands in the black soil region.

Abstract:In order to explore the effects of tree root distribution pattern on slope soil erosion in karst area under rainfall conditions, using artificial rainfall simulation methods, soil erosion characteristics of three types of tree root distribution were studied. And the three tree root distribution patterns were partial bare surface in the direction of root transverse slope (Horizontal), partial bare surface of root along slope (Oblique) and unexposed surface of root vertical slope (Vertical). The rainfall intensity was 75 mm/h, the rainfall duration was 90 min, and the slope was 25°. The results showed that:(1) During rainfall, roots of trees growing horizontally and vertically both affected soil infiltration. The generation time of mid-soil flow and underground runoff followed the order of Oblique>Horizontal>Vertica. The initial runoff generation time of surface runoff on Oblique slope was slightly earlier than that on Horizontal and Vertical slope, but the difference was not significant (p>0.05). (2) The total amount of surface runoff on Horizontal, Oblique and Vertical slopes followed the order of Oblique>Vertical>Horizontal. The flow velocity rate of the mid-soil flow and underground runoff increased slowly in the process of rainfall and decreased sharply after rainfall stopped. (3) The surface sediment reduction benefits of three types of forest root distribution patterns followed the order of Horizontal>Vertical>Oblique. In conclusion, the confluence effect of Oblique slope promoted the increasing of surface runoff and sediment yield, while the Vertical slope increased soil rainfall infiltration and reduced erosion, and the Horizontal slope had the most obvious effect on the retention of runoff and sediment on the slope. The results could provide a reference for understanding soil erosion mechanism and soil erosion control measures of karst rocky desertification slope land.

Abstract:This paper aims to investigate the effect of different sections of unstable slope on soil anti-erodibility and deepen the understanding of the action mechanism of landslide on slope soil structure. Totally five sample plots (including Dadi shady slope, Xiaojianfeng sunny slope, Duozhao gully sunny slope, Chajing gully sunny slope and Daaozi gully shady slope) in three climate regions (including temperate humid mountain ridge region, subtropical and warm temperate sub-humid region, subtropical dry-hot valley region) were selected as a research area in the Jiangjia gully watershed, Dongchuan district, Kunming, Yunnan Province. We analyzed the physical and chemical properties of soil samples and used principal component analysis (PCA) to study the soil erosion resistance of unstable slopes in the study plots. The results showed that:(1) The soil water-holding capacity, porosity structure, organicmatter content, hydrolyzed nitrogen, available potassium, the proportion of particle size ≥ 0.25 mm, mean weight diameter of soil aggregate in the stable area were significantly larger than those in the accumulation area. The above indicators showed the trend of stable area> unstable area>accumulation area, while the soil bulk density, available phosphorus, total phosphorus, and the proportion of particle size<0.25 mm in the stable area were significantly smaller than those in the accumulation area. (2) The comprehensive index of soil anti-erodibility (F) of the 5 sample plots ranged as:stable area (2.401)>unstable area (0.017)>accumulation area (-2.417), and the difference among 3 slope sections was significant (p<0.05). The indexes of soil anti-scourability followed the rule as stable area (45.873 L/(s·g))>unstable area (33.245 L/(s·g))>accumulation area (15.723 L/(s·g)). There were significant differences between the stable zone and theaccumulation zone (p<0.05). There was a significantly positive relationship between the comprehensive index of soil anti-erodibility and the indexes of soil anti-scourability. (3) The soil water-holding capacity, porosity, organic matter content, nitrogen and potassium content, the proportion of particle size ≥ 0.25 mm and mean weight diameter in the study area were significantly positively correlated with the comprehensive scores of soil anti-erodibility, while the soil bulk density, available phosphorus content, and particle size <0.25mm were significantly negatively correlated with the comprehensive scores of soil anti-erodibility. This study clarifies the corresponding mechanism of soil erosion resistance in debris flow basin on landslide induced unstable slope, promotes the understanding of the impact of disasters on soil structure, and has reference value for comprehensive measures to improve soil erosion resistance on unstable slope.

Abstract:In order to deeply explore the influence of slope vegetation distribution on the process of sediment and runoff yield, and quantitatively analyze the relationship between vegetation distribution and sediment and runoff yield on slope, through artificial rainfall test, under the condition of 15° slope, the sediment and runoff yield process were observed under the conditions of different vegetation coverages (40% and 60%), different rainfall intensities (30, 60 and 90 mm/h) and different vegetation distribution positions (relative distance 0, 0.2, 0.4, 0.6, 0.8 and 1.0). The effects of soil and water conservation under different vegetation distribution conditions was analyzed, and the optimal vegetation allocation for controlling soil and water loss under different vegetation coverages was proposed. The results showed that:(1) Under a certain slope and rainfall intensity, the runoff and sediment yield increased rapidly at first and then tended to be stable under different vegetation distribution conditions. (2) In this study, the average runoff and sediment yield firstly decreased and then increased with the increasing of the relative distance. The average runoff yield of the slope with the relative distance of 0.2 was the minimum under different experimental conditions. (3) The random forest algorithm showed that rainfall intensity and vegetation coverage had important impact on runoff yield, and rainfall intensity and vegetation relative distance had important impact on sediment yield. (4) When the vegetation coverage was 40%, the optimal vegetation relative positions were 0 to 0.36 and 0 to 0.31, respectively, with the main objective of reducing runoff and sediment. When the vegetation coverage was 60%, the optimal relative vegetation positions were 0 to 0.43 and 0 to 0.22, respectively, with the main goal of reducing runoff and sediment. This study showed that slope vegetation distribution had an important impact on sediment yield and runoff. Under the same vegetation coverage, the smaller the relative distance of the grass belt was, the better the effect of reducing runoff and sediment. The research results could provide theoretical basis and data support for optimal allocation of vegetation in the process of ecological restoration.

Abstract:To reveal the slope erosion mechanism of coarse texture soil in China, we conducted the indoor rainfall simulation experiments with the four coarse texture soils (sieved soils of TCA, GXA, CTA, WHA from the counties of Tongcheng, Ganxian, Changting and Wuhua, China) to discussed the slope erosion process and sediment particle composition of coarse texture soil. The results showed:(1) The changes of surface runoff characteristics of the soils were significant. The surface runoff increased with the extension of rainfall time, and then decreased and tended to be stable. (2) The erosion characteristics of the soils were different, and the soil erosion rate decreased in the order of WHA>TCA>GXA>CTA. (3) The percentage of grain distribution in erosion sediment of the soils decreased in the order of Clay>Silt>Sand>Gravel. The enrichment ratio of different soils showed obvious difference. (4) There was a significant correlation between water flow power and soil erosion rate, and the relationship between them could be accurately described by power function. The model was more reliable after introducing the soil clay and gravel contents in the expression(D_r=0.001ω^1.163C_l^-4.069, R²=0.82; D_r=0.003ω^1.149G_r^-1.934, R²=0.84). The accuracy of predicting soil erosion rate was improved with a wider range of application and more realistic value in practice.

Abstract:The effect of single-particle droplet splash on sediment incipient motion was investigated through indoor simulated rainfall test. Four surface slopes (0, 15°, 25°, 35°), four particle sizes of uniform sand (0.098-0.104 mm, 0.104-0.5 mm, 0.5-0.78 mm, 1-1.4 mm) and droplets with equivalent diameter of 4.5 mm were designed in the test. The designed water-elastic water balloons made of super absorbent resin were used as the control group. The results showed that the changes of particle diameter and slope had a significant effect on particle's initiation, and the splasher droplets were of great significance to droplet splash erosion. With the increase of particle diameter, the sediment incipient motion gradually changed from the joint action of droplet impact and sub droplet splash to the transfer of droplet impact kinetic energy, supplemented by splash carrying. When the particle diameter was the same, the increase of slope led to the non-equilibrium of splashed sand particles, and the amount and displacement of particle splashing under the slope increased with the increase of slope. The greater the slope, the greater the gap between the splash erosion depth of the particles below and above, resulting in the loss of support of the particles above, overall instability and collapse, and micro landslide. When the particle size was the same, the width depth ratio of the water-bomb splash pit was significantly smaller than that of the droplet splash pit with the same diameter, and the amount of droplet splash was much larger than the number of particles started under the direct impact of the water bomb. The drag of sub droplets affected the particle's initiation significantly.

Abstract:Soil erosion is one of the global environmental problems restricting the survival and development of human beings. With the development of economy, human activities induce the aggravation of soil erosion and bring about eco-environmental problems in the short time. Therefore, taking Hubei Province as the research area, the CSLE model is used to calculate the soil erosion modulus from 1990 to 2015, and the GIS spatial analysis method is revealed the spatiotemporal characteristics of soil erosion in multiple periods. The results show that Hubei Province mainly has slight erosion, followed by mild erosion, and other grade erosion such as moderate erosion occupies a small area. The areas of mild erosion, moderate erosion, strong erosion,extremely strong erosion and severe erosion decreased by 11 267.0, 497.6, 176.9, 307.7, 313.7 km² respectively in 25 years, with decreases of 27.39%, 13.85%, 11.79%, 24.88% and 56.04% respectively. The total erosion area first decreased, then increased, and finally continued to decrease. Among them, the area of intense erosion and extremely intense erosion decreased significantly. The changes of erosion intensity in different periods show spatial heterogeneity. Soil erosion was mainly improved in 1990-1995, 2000-2005 and 2010-2015, such as Enshi and Xianning in 1990-1995, Enshi and Shiyan in 1995-2000, Shennongjia forest area, Yichang City and the periphery of Zigui County in 2000-2005, Huanggang and Huangshi City in 2005-2010, Shennongjia forest area and Yichang City in 2010-2015; Their soil erosion conditions are gradually improving, and the improvement of dry land and bare land is the most obvious. Soil erosion was intensified in 1995-2000 and 2005-2010, and the intensification of soil erosion was concentrated in Shennongjia area (1990-2000), Shiyan City (2000-2005), Zhuxi County (2005-2010) Enshi City, Xuanen County and Hefeng County (2010-2015), among which forest land and dry land were the most obvious. The main change areas of soil erosion are as follows:in the past 25 years, the area of mild and above grade erosion in thearea with slope less than 8° has increased year by year, which is closely related to the fact that the negative surface disturbance caused by human activities (production and construction projects, agricultural production of sloping farmland, land use type conversion caused by other human activities) is mainly concentrated in the region with relatively flat topography. The area with a slope of 8° to 35° with mild or above grade erosion has beensignificantly reduced, which is mainly manifested in the remarkable results achieved in the implementation of returning farmland to forests and comprehensive control of soil erosion and water loss.

Abstract:In this paper, taking the common engineering accumulation with structure in field investigation as the research background, two test materials including structural engineering accumulation and control group were designed (the control group is engineering accumulation without structures, which will be referred to as structure and accumulation for short in the later paper). Using the method of indoor rainfall simulation, the effects of rainfall intensity and rainfall field on slope runoff erosion of structure and accumulation were studied. The results show that:(1) the initial production duration decreases with the increase of rainfall intensity and rainfall field times, and the structure can delay the initial production duration, which is related to the soil characteristics and underlying surface characteristics of the structure; (2) The average runoff rate and average velocity increase with the increase of rainfall intensity and rainfall times. The average velocity and average runoff rate of the accumulation are 1.11~1.22 and1.11~1.37 times that of the structure, respectively. The time for the rapid increase and stabilization of the velocity and runoff rate of the structure is earlier and shorter than that of the accumulation; (3) The contribution rate of rainfall intensity to erosion rate, velocity and runoff rate is large, and the rainfall times is negatively correlated with erosion rate. Under all conditions, the erosion rate of structure is greater than that of accumulation, and the erosion rate and total erosion amount are 1.03~2.15 and 1.36~2.63 times of accumulation; (4) Runoff power can better describe the erosion dynamic process of structure and accumulation. The critical runoff shear force and runoff power of structure erosion are less than those of accumulation.

Abstract:In order to effectively prevent soil erosion in the watershed and maintain ecological security, based on the daily precipitation data from 1982 to 2019 in Jiuqushui watershed, the inter-annual variation rules of erosivity of moderate rain, heavy rain, rainstorm and annual rainfall were analyzed by using wavelet analysis and cross wavelet transform, the influences of Sunspots, El Niño-Southern Oscillation (ENSO), Arctic Oscillation (AO) and Pacific Decadal Oscillation (PDO) on them were discussed. The results indicated that:(1) The inter-annual variation trend of moderate rain erosivity, heavy rain erosivity, rainstorm erosivity and annual rainfall erosivity was not significant (p>0.05), and the coefficient of variation (C_V) was 0.24, 0.31, 0.64 and 0.26, respectively, which were all moderate variations. (2) The periodic variation of rainfall erosivity in different magnitudes was obviously different, the annual rainfall erosivity and rainstorm erosivity had a 15 to 23 years cycle and a 19-year main cycle, which were more closely related. (3) The annual rainfall erosivity and rainstorm erosivity had significant resonance periods of 9 to 11, 10 to 11, 10 to 11 and 9 to 10 years with Sunspot, ENSO, AO and PDO, respectively. The impact of Sunspot, ENSO and PDO on rainstorm erosivity was greater than that of moderate rain erosivity and heavy rain erosivity. And the impact of AO on heavy rain erosivity was greater than that of moderate rain erosivity and rainstorm erosivity. The research results could provide scientific basis for soil erosion prediction and prevention in southern Jiangxi and even China.

Abstract:In order to study the sources, export characteristics and influencing factors of nitrate-N, the SWAT model was implemented to simulate the runoff and nitrate-N loads in the Meixi River and Daning River basins in the Three Gorges Reservoir Area (TGRA). Then, the hydrological processes and sources of nitrate-N in the basins were analyzed. Based on the random forest model, the effects of different influencing factors (i.e., climate, land use, soil type and topography) on runoff and nitrate-N loads were also quantified. The results showed that:(1) The nitrate-N load varied significantly among different land use types, and the annual load intensity followed the order of orchard (20.41 kg/hm²)>dryland (12.51 kg/hm²)>paddy field (10.31 kg/hm²)>construction land (7.09 kg/hm²)>forestland (0.62 kg/hm²)>grassland (0.46 kg/hm²). Dryland was found to be the main source of nitrate-N export in the Meixi River (80%) and Daning River basins (67%).(2) The base flow coefficient in the Meixi River and Daning River basins was 67% and 62%, respectively, and base flow was the main transport pathway of nitrate-N, contributing 68% and 60% of nitrate-N export in the two basins, respectively. (3) Runoff distribution and nitrate-N export had obvious seasonal variation, the base flow contributed above 70% to both runoff and nitrate-N in these two basins in the dry season, and surface runoff contributed 36% and 42% to nitrate-N export in the two basins in the rainy season, respectively. (4) Rainfall was the main factor affected total runoff, and soil type was the main factor affected surface runoff and base flow. Land use was the main factor affected nitrate-N in different runoff pathways,followed by soil type, and the sum of their relative importance was over 70%. In conclusion, environmental land use conflicts were the root cause of nitrate-N loss, and source control was still a key of non-point source pollution prevention and control in the TGRA. In addition to surface runoff control, it was urgent to incorporate dry land and orchard base flow pathway control strategies.

Abstract:In order to explore the influence of slope shape on the development of ephemeral gully, 225 ephemeral gullies were obtained by visual interpretation based on the photography of unmanned aerial vehicle in the Langerzigou in Jingbian County, Shaanxi Province. The number and length of ephemeral gullies, the distance from the gully head to the watershed and the gully density were calculated. The original slope DEM was obtained by interpolating the elevation points on the ephemeral gully watershed, and the DEM was used to extract the terrain curvature to describe the hillslope shape, and then analyze the relationship between the slope shape and the ephemeral gully index. The results showed that:(1) The DEM after the elevation point interpolation on the ephemeral gully watershed was used to synthesize the ephemeral gully, which could well describe the original slope topographic features before the development of ephemeral gully. (2) From the point of view of single slope shape, the gully density of the transverse concave slope was the highest, and the number of ephemeral gullies, the average distance from the gully head to the watershed of the longitudinal concave slope were the largest. The average length of the ephemeral gully and the number of the longitudinal convex slope were the largest. From the point of view of the combined slope shape, the average length of the ephemeral gully and the average distance from the gully head to the watershed on the biconvex slope and the concave slope were larger than those on the biconvex slope and the concave-convex slope. The ephemeral gully length of double concave slope was significantly different from that of double convex slope and convex-concave slope (p<0.05). The ephemeral gully length of concave-convex slope was significantly different from that of double convex slope and convex concave slope (p<0.05).There was a significant difference in the distance from the gully head to the watershed between the concave-convex slope and the convex-concave slope (p<0.1). (3) The terrain curvature distribution characteristics of ephemeral gully development on different slope are obviously different.

Abstract:In order to explore the soil water infiltration characteristics of typical parent rocks with different developmental degrees, a disc infiltration meter was used to determine the infiltration process of three kinds of purple sandstone with different development degrees, which were Entisol (S1), Cambisols (S2) and Alfisol (S3), to explore the influencing factors of the infiltration process, and three common models were used to simulate the infiltration process to analyze and compare the suitability of these models. The results showed that:(1) There were significant differences in soil physicochemical properties among different development degrees. Compared with the Entisol, the soil bulk density of the Cambisols and Alfisol increased by 10.71% and 19.50%, the total soil porosity decreased by 8.79% and 18.69%, the aeration porosity decreased by 67.40% and 8.16%, and the soil clay content increased by 10.01% and 38.36%, the sand content decreased by 8.09% and 48.29%, and the soil organic matter increased by 2.88% and 8.68%, respectively. (2) The initial infiltration rate, average infiltration rate and saturated hydraulic conductivity of soils followed the order of Entisol>Cambisols>Alfisol, and the average infiltration rate and saturated hydraulic conductivity of Cambisols and Alfisol were 0.99, 0.58 and 0.89, 0.83 times higher than those of the Entisol, respectively. (3) Differences in soil physical and chemical properties of different soil development levels had a significant impact on soil water infiltration. Soil infiltration rate was positively correlated with total porosity, capillary porosity, aeration porosity and sand content, while negatively correlated with bulk density, clay content and organic matter. (4) The Horton model had a better fitting effect on the purple sandstone soil water infiltration process with different development degrees (R²=0.942), followed by the Kostiakov model (R²=0.858), and the Philip model had a poor fitting effect (R²=0.832). By observing and simulating the process of soil water infiltration of different development levels, the research results could provide a useful reference for the study of the soil water migration law in the watershed.

Abstract:Vegetation restoration can significantly affect soil infiltration process. On this basis, two typical abandoned grasslands, Bothriochloa ischcemum (Linn.) Keng and Artemisia vestita Wall. ex Bess, from theLoess Plateau were studied under six planted densities of 5, 10, 15, 20, 25, and 30 plants/m², and an artificial simulated rainfall experiment was adopted to determine the effect of vegetation characteristics on the soil infiltration process. The result showed that:(1) The increasing of planting density could significantly delay runoff. The initial runoff time ranged from 0.76 s to 5.74 s for Bothriochloa ischcemum (Linn.) Keng grassland and ranged from 0.87 s to 2.08 s for Artemisia vestita Wall. ex Bess grassland under six densities. The initial runoff time increased with vegetation cover, root mass density and organic matter as power functions (R² ≥ 0.18,p<0.05). (2) For Bothriochloa ischcemum (Linn.) Keng grassland, the average infiltration rate, stable infiltration rate and infiltration amount ranged from 0.47 to 0.82 mm/min,0.46 to 0.82mm/min and 7.12 to 11.84 mm respectively; for Artemisia vestita Wall. ex Bess grassland, the infiltration parameters above mentioned ranged from 0.38 to 0.67 mm/min,0.35 to 0.60 mm/min and 5.70 to 10.07 mm respectively. When the planting density was 20 plants/m², the soil infiltration parameters were the maximum.The average infiltration rate, stable infiltration rate, infiltration amount and infiltration coefficient K increased with soil organic matter as power functions (R² ≥ 0.26, p<0.01), and the attenuation coefficient α decreased with the increase of biological crust coverage (p>0.05). (3) The initial runoff time, average infiltration rate, stable infiltration rate, infiltration amount and infiltration coefficient K of Bothriochloa ischcemum (Linn.) Keng grassland were all higher than those of Artemisia vestita Wall. ex Bess grassland, while the attenuation coefficient α was lower than that of the attenuation coefficient. It showed that the Bothriochloaischcemum (Linn.) Keng grassland had high soil infiltration capacity. In general, infiltration amount (A) would be simulated by root mass density (RMD) and soil organic matter (SOC) (A=2.77×RMD^0.149SOC^0.614,R²=0.663, NSE=0.653). The purpose of this study was to provide data sources and theoretical basis for the eco-hydrological process and vegetation construction of the abandoned grassland on the Loess Plateau.

Abstract:In order to explore the initial sign and development stage of Benggang in granite red soil area in South China, field investigations were conducted in two typical Benggang areas in Tongcheng, Hubei and Cenxi, Guangxi to investigated the development process of Benggang. The results showed that there was a special niche shaped ephemeral gully developed from a rill in both survey areas, named niche-like ephemeral gully (NEG). The morphology of the NEG had the following characteristics:a distinct rill in the upstream, steep banks, a narrow upper bank and a wide, deep gully bed. The NEG was formed on slopes without plant cover where sandy soil layers were exposed, with a small contribute area and a slope steeper than 30°. The NEG was a special morphological ephemeral gully, its definition, morphology, erosion forces were different from the ephemeral gully, permanent gully, Amphitheater shaped canyons and so on. The NEG was the process of gully erosion changed from being dominated by hydraulic erosion to being highly coupled by hydraulic and gravity erosion. The NEG is the launching marker for the Benggang. The formation of the NEG is related to the soil configuration of granitic red soil with upper red clay and lower sandy soil layers. Taking the emergence of NEG as a sign, the development stage of Benggang is re-classified into the early preparation stage, initial launching stage, middle development stage and late maturation stage. The characteristics of the NEG and the management effect of the study area show that the terrace is not suitable for the area with a thin red soil layer. The discovery of the NEG will promote the study of the early development of Benggang and provide a new theoretical basis for the prevention and management of the Benggang.

Abstract:In order to explore the changes in soil shear strength during soil wind erosion, typical ploughed farmland on the disturbed and undisturbed surfaces of the Bashang Plateau in Hebei Province was used as theresearch object. The changes of soil shear strength before and after wind erosion events and wind erosion seasons were measured by in-situ direct test, and the relationship between soil shear strength and particle size of soil dry aggregate was also analyzed in conjunction with laboratory experiments. The results showed that the shear strength of undisturbed and disturbed surface soil was positively related to the normal stress acting on the soil surface, and the soil shear strength increased with the increasing of the normal stress. The change of shear strength was closely related to the occurrence of the wind erosion events, and a significant increase in shear strength occurred after the wind erosion event in both cases, except for the surface soil after the wind erosion event on April 27 and 28, 2021, which was influenced by the water content. The change of shear strength throughout the wind erosion season also showed a trend of firstincreasing, then decreasing and finally slightly increasing. In the process of wind erosion, the surface of disturbed farmland was more sensitive and its shear strength changed more sharply than that of undisturbed farmland surface. The soil shear strength increased with the increasing of mean weight diameter (MWD) of soil dry aggregate. In order to reduce the damage of wind erosion in Bashang plateau, conservation tillage measures should be reasonably applied, the interference to farmland surface should be reduced during the wind erosion season.

Abstract:In order to explore the soil erosion control effect of different vegetation patterns on the slope surface of engineering accumulation, the high and steep slopes (32°, 20 m×1 m) with different patterns (bare slope, top slope, middle slope, bottom slope and strip slope) in the loess region were simulated with three water discharge rates of 10, 20 and 30 L/min. The runoff rate, sediment yield rate, flow and sediment reduction benefit were selected to analyze the erosion control effect of vegetation patterns on the slopes of engineering accumulation. The results showed that the average runoff rates of strip, slope top, slope middle and slope bottom were 57.33%,61.17%, 41.62%, 24.78% lower than that of bare slope, and the average sediment yield rates were 74.99%, 61.10%, 55.01%, 46.43% lower than that of bare slope. The linear relationship between runoff rate and sediment yield rate (R² was 0.57 to 0.80, p<0.01) was weaker than that of bare slope (R²=0.71, p<0.01). In different vegetation patterns, the flow reduction benefits of strip pattern and slope top pattern were 65.97% and 60.52%, respectively, and the sediment reduction benefits were 71.44% and 57.22%, respectively. The erosion control effects of strip pattern and slope top pattern were much higher than other patterns. The linear correlation between sediment yield and runoff power (R² was 0.61 to 0.83, p<0.01) was higher than that of runoff shear force (R² was 0.29 to 0.76, p<0.01). Runoff power could better reflect the mechanism of soil erosion on the slope of accumulation.

Abstract:In this paper, the undisturbed roots-soil composites of Iris tectorum Maxim., the dominant species from the source area of Lanniqing landslide, Zhaotong, were taken as the research objects, and the shear characteristics of the composites were studied in depth by direct shear tests, and compared with the experimental results of remolded composites with the same water content in lab. The results showed that the samples with no roots as a whole had the characteristics of strain softening, while the composites had the characteristics of strain hardening. The shear strength of composites was higher than that of samples with no roots, which increased with the increase of roots contents, so that the roots strengthening effect was obvious; however, the undisturbed composites did not exist the optimal root content similar to that of the remolded composites. The c value of composites has no obvious change rule, while the φ value increased gradually, and both increase rates also have the same trend. The sections of failure composites showed that the ability of roots to consolidate soil was optimal when they were the taproots and they were vertical through shear plane, and the vertical pressure was high. The diameter of lateral roots without taproot was smaller, and the inclined distribution in the composites, especially along with shear direction, would affect roots reinforcing effect. The failure mode of samples with no roots was the overall shear failure with incomplete horizontal failure surface, while the failure mode of composites was that the roots were pulled out of sample instead of being sheared or pulled out, and obvious relative displacement occurred between roots and soil. The results could provide a theoretical basis for the selection of slope protection vegetation in order to enhance the shear strength of composites.

Abstract:In order to explore the evolution of soil and water conservation benefits of vegetation at different growth stages during the implementation of grass planting measures on granite red soil erosion and degraded slopes, this study set up three different grass planting patterns, including strip type (D1), random type (D2), patch type (D3), and an eroded degraded bare slope (CK) as the control to conduct experiments. The characteristics of slope soil erosion during the whole vegetation growth process were monitored under natural rainfall conditions. The results showed that:(1) The growth of vegetation could significantly improve the soil and water conservation ability of slope. With the advancement of vegetation growth stage, the runoff and sediment yield of slope decreased obviously.The runoff reduction benefit could reach from 20.74% to 79.03%, and sediment reduction benefit could reach from 97.42% to 99.40%. Under different rainfall types, with the growth of vegetation, the increasing and changing laws of the benefits of runoff and sediment reduction on the slope were different. (2) Vegetation growth could gradually weaken the influence of rainfall factors on slope sediment yield, so that the difference in slope sediment reduction rate between different rainfall patterns gradually decreased, and sediment reduction finally stabilized at a high level. The difference of runoff reduction rate on the slope between different rain types was large in each vegetation growth period. There was a logarithmic function relationship between runoff reduction rate, sediment reduction rate and vegetation growth time, with correlation coefficients greater than 0.491 and 0.792, respectively. Vegetation growth indicators (tiller number, coverage, plant height) were significantly or extremely significantly negatively correlated with the runoff and sediment yield of slope. (3) From the perspective of the entire vegetation growth process, the order of 3 grass planting pattern for soil and water conservation benefits was D1>D3>D2. In the early stage of vegetation growth, the distribution pattern of high plant density was stronger than that of low plant density, and the difference of each pattern was small in the later stage. The results provide scientific basis and technical support for vegetation restoration in seriously eroded degraded areas of the red soil region of south China.

Abstract:The upper reaches of the Yellow River span arid, semi-arid, sub-humid and humid/semi-humid climate zones. Soil conservation service (SCS) of the region is an important guarantee for preventing soil erosion and promoting high-quality development in the Yellow River Basin. We used the Revised Universal Soil Loss Equation, Geographically Weighted Regression model, trend line method and the factor influence degree defined in this paper, in combination with remote sensing and precipitation data, to identify the change regions of SCS in the upper reaches of Yellow River from 2001 to 2015, to analyzed spatial-temporal variation characteristics of SCS and then identified their influencing factors and quantified its influence degree. The results showed that:(1) The declining area of SCS was mainly located in arid and semi-arid climate region of the northeast parts of the study area, which was mostly concentrated along the Yellow River from Jishi Gorge to Hekou Village. The ascending area of SCS was mainly located in the semi-arid, humid and semi-humid climate region of the west and south of the study area, which was concentrated in mountains and plateaus. (2) Precipitation was the dominant factor affecting SCS in the declining subareas, while vegetation coverage and precipitation was the dominant factors affecting SCS in the significantly and slightly ascending subareas, respectively. (3) Facing the uncertainty in precipitation in the future, improving vegetation coverage was the fundamental strategy to improve SCS, and the suggestions of soil and water conservation measures were also put forwarded according to the influence intensity of dominant factors. Thisstudy could provide a scientific basis for coping with future climate change, formulating zoning and classification strategies and measures and improving soil conservation services.

Abstract:It is vital to evaluate and predict regional water resource variation and its influencing factors for sustainable development of arid and semi-arid areas. Based on four global climate models of CMIP5 and CLM 4.5, the temporal and spatial characteristics of evapotranspiration and water availability were studied in Inner Mongolia under two Representative Concentration Pathways (RCPs) from 2020 to 2099. The results showed that under RCP 6.0 and RCP 8.5 scenarios, the future evapotranspiration in Inner Mongolia would increase at a rate of 0.37 mm/a and 0.69 mm/a, respectively (p<0.05), decreasing form east to west. Water availability in Inner Mongolia did not show a significantly trend under the two scenarios (p>0.05), but there were significant spatial differences.From a spatial perspective, water availability in most areas showed an increasing trend and increased by more than 10 mm/a in the southern semi-arid and semi-humid regions of temperate zone by 2090s; however, the area with reduced water availability accounted for 46.32% of the entire territory under the RCP 8.5 scenario, especially in the arid, semi-arid and semi-humid areas. There were great regional differences influencing of driving factors in evapotranspiration. Precipitation was the main influencingfactor of evapotranspiration changes in arid and semi-arid area. The changes in semi humid area were jointly affected by precipitation and temperature. The changes in humid area were dominated by temperature and in the higher heating scenario, the effect further increased with temperature increased. At the same time, vegetation was also an important factor affecting evapotranspiration with less than climate factor.

Abstract:MODIS-EVI, climate factors and meteorological drought index SPEI were used as the indicators to characterize the spatio-temporal changes of vegetation and climate, Theil-sen Median trend analysis, Mann-Kendall significance test, Hurst index analysis and residual analysis were used to explore the response of vegetation growth to climate change and human activities in Guizhou Province from 2001 to 2020. The results showed that:(1) The regional area ratio of vegetation increase in Guizhou Province from 2001 to 2020 was 84.97%, and the main improvement areas were mainly in the north and southwest of Guizhou Province. In terms of the future spatial change trend, vegetation was mainly in reverse continuous increasing, accounting for 69.23% of the total area of Guizhou Province. (2) There was a positive correlation between vegetation and precipitation and a negative correlation between vegetation and temperature in Guizhou Province, but the correlation was weak. While the positive correlation between regional vegetation growth and SPEI was greater than the negative correlation. (3) In the northern, western and southwestern regions of Guizhou Province, EVI and human activities showed positive improvement, while in Guiyang, Zunyi and its surrounding areas, EVI and human economic activities showed inhibitory effect. On the whole, there was a positive correlation between human economic activities and vegetation EVI in the study area. The conclusion could provide objective scientific theoretical support for the study of vegetation ecological protection and its suitability with climate change and human activities in Guizhou Province.

Abstract:Jiaozishan National Nature Reserve preserves the most complete vegetation and habitat of the central Yunnan Plateau, and is one of the hot spots with climate sensitivity. Univariate linear regression, Pettitt mutation test and Spearman correlation and other methods were used to analyze the change characteristics of climate elements and the extreme climate index from 1961 to 2019 in this area, as well as the temporal and spatial change trend characteristics of NDVI and its response to extreme climate index from 1999 to 2016. The aim was to study the climate change characteristics and the dynamic response of vegetation in Jiaozi Mountain, providing a reference for climate risk management in the reserve. The results showed that:(1) Global warming led to a significant change in the climate elements (average temperature, sunshine hours, wind speed and foggy day) from 1961 to 2019. The vertical temperature zones changed dynamically, and the baseband changed from a south subtropical zone to a north tropical zone in 2017-2019. (2) On the whole, the change rate and abrupt change point of the extreme temperature index from 1961 to 2019 were more significant than those of the extreme precipitation index. (3) From 1999 to 2016, the growth rate of NDVI decreased with the increasing of altitude. Taking the altitude of 2 736 m and 3 236 m as the boundary, the change rate of NDVI growth rate showed the trend of "high-low-high". (4) The correlation of NDVI_mean, NDVI_max and NDVI_min to extreme temperature index was stronger than that to extreme precipitation index, and NDVI_mean, NDVI_max, NDVI_min were most sensitive to warm index, precipitation intensity index and extreme precipitation day index. (5) If (extreme) climate change exceeds the vegetation tolerance threshold, vegetation growth might be inhibited. In view of the uncertainty of future climate change, it is necessary to further identify the impact of extreme climate change on NDVI in the reserve and strengthen the early warning, monitoring and control of extreme climate risk in the reserve.

Abstract:Using the daily measured precipitation data of 171 meteorological stations in the Yangtze River Delta from 1961 to 2018, this study evaluated the detection ability of ERA5 reanalysis precipitation data for rainy days, analyzed the accuracy of ERA5 precipitation simulation and the ability of ERA5 to describe extreme precipitation indices. Assessment results showed that ERA5 reanalysis precipitation data could reproduce the precipitation process, with high probability of detection (POD), small equitable threat score (ETS) and low false alarm ratio (FAR). The detection performance in the south of the study area was better than that in the north. The percent of false alarm occurrences for rainy days of ERA5 was about 17.68%, mainly occupied by light rain. ERA5 overestimated the regional multi-year average precipitation by about 15.75%, and the root mean square error (RMSE) was small. The error was also large when the precipitation was large. And the error in the south region was slight higher than that in the north region. ERA5 had a good linear correlation on monthly,seasonal and annual scales. ERA5 showed a trend of overestimation and then underestimation over time for six extreme precipitation indicators such as PRCPTOT, RX5d, R95P, R99P, R20 and R25. And the intensity indices over estimated much higher in the south than those in the north, while the occurrence indices had opposite trend. The three indices RX1d, SDII and CDD had been underestimated, and there was a significantly large underestimation in the north than that in the south. While ERA5 had a continuously overestimation for CWD and R10 with no significant difference between the north and the south.

Abstract:The objective of this study was to explore the effect of different film hole diameters on the characteristics of multi-point interference infiltration wetting body, a testing program of laboratory experiment with four different film hole diameters was designed, the changes in the characteristics of the wetting body with time under different film hole diameters were measured. The results showed that at the same time, the larger the film hole diameters, the greater the horizontal and vertical wetting front transport distance. The power function model was suitable for characterizing the relationship between the horizontal and vertical wetting front transport distance on the free infiltration surface and the time of infiltration. As the diameter of the film hole increased, the transport parameters gradually increased and the transport indexes gradually decreased. The relationship between the horizontal and vertical wetting front transport distance and the infiltration time were logarithmic function model on the intersection profile. As the diameter of the film hole increased, the soil moisture content around the film hole was close to the saturated, and the soil moisture content at the same locationincreased, and the time of unidirectional and multidirectional interference to occur gradually decreased. The irrigation uniformity coefficient in the wetting body of muddy water with film hole irrigation was greater than 90%, and the irrigation uniformity was very high.

Abstract:There are few studies on the spatial heterogeneity law and response mechanism of soil water under the synergistic effect of topography, vegetation and other elements at the regional watershed scale. Taking the typical small watershed restored by artificial forest in Datong, Qinghai Province as the research object, three slope aspects (shady slope, semi-shady slope and sunny slope) were selected, and the sample points were laid out in three transect belts, which were in a radial pattern. Statistical analysis, principal componentanalysis and redundancy analysis methods were used to study the soil moisture spatial variation characteristics in 0-20 cm, 20-40 cm, 40-60 cm, 60-80 cm and 80-100 cm layers at the beginning and the end of the growing season, as well as the effects of environmental factors (altitude, vegetation height, vegetation canopy, aboveground biomass, herb richness, herb cover and dry weight of litter). The results showed that the average and maximum water content at the end of the growing season were both greater than those at the beginning of the growing season, and the maximum and average values of volumetric water content in each slope aspect followed the order of shady slope>semi-shady slope>sunny slope, and each soil layer showed a moderate variation (10%sunny slope>shady slope at the initial stage, and at the final stage the order was sunny slope>semi-shady slope>shady slope. The water sampling point interval should be from 36.50 to 448.90 m at the initial stage and 18.30 to 552.40 m at the final stage. The redundancy analysis results showed that altitude was the main controlling factor affecting soil moisture heterogeneity in the alpine region of Qinghai, with an explanation rate of 35.3% (p<0.01), followed by the herb richness, with an explanation rate of 26.1% (p<0.01).Vegetation height and vegetation crown width also had significant effects. The research's results could provide data and theoretical reference for the study of the eco-hydrological process and the subsequent vegetation restorationin small watershed of returning farmland to forest in the loess alpine region of Qinghai.

Abstract:In order to explore the soil moisture distribution characteristics and growth conditions of Hippophae rhamnoides under different site conditions, the plot experiment was adopted, and two slope directions (shade slope and sunny slope) and three slope positions (slope top, middle and bottom) were set up. The results showed that:(1) Seasonal variation of soil moisture could be divided into consumption period (May-June), rapid supplement period (June-July) and regression period (July-September). Natural precipitation had great influence on soil moisture content. (2) The vertical distribution of soil moisture in each sample plot was soil moisture significantly changed layer (Cv>0.2), soil moisture sub-change layer (0.2>Cv>0.1) and soil moisture relatively stable layer (Cv<0.1). (3) Different site conditions had significant influence on soil moisture and plant growth. The soil moisture of shady slope was significantly higher than that of sunny slope, and the soil moisture decreased from slope top to the bottom. The growth index and survival rate of H. rhamnoides followed the order of shady slope>sunny slope), bottom>middle>top. The results could provide reference and theoretical basis for the afforestation of H. rhamnoides in the front mountainous zone of Manas County.

Abstract:Grassland desertification is one of the most serious ecological and environmental problems in Qinghai-Tibet Plateau. To investigate the characteristics of vegetation and soil under different restoration measures in alpine desertification grassland, desertification grassland (DG), artificial herbage grassland (AG), artificial shrub grassland (AS) and natural grassland (NG) were selected to study the changes of vegetation community and soil characteristics and their relationship, and to evaluate the restoration effect of different artificial vegetation restoration measures on alpine desertification grassland after 22-year restoration. The results showed that:(1) AG and AS increased the aboveground biomass of desertification grassland to 109.21 and 1 293.21 g/m², respectively. However, the aboveground biomass of herbs under AG and AS were significantly lower than that of NG, and the species richness of AG was significantly lower than that of AS by 31.48% (p<0.05). (2) Compared with the 0-10 cm surface soil of DG, the soil porosity, water content, total carbon and total nitrogen contents of AG significantly increased by 7.94%, 67.95%, 22.09% and 257.14%, respectively. And these indexes of AS significantly increased by 6.41%, 43.00%, 17.18% and 242.86%, respectively. However, the content of soil carbon and nitrogen in the two restoration measures were significantly lower than that of NG (p<0.05). (3) The total accumulation of soil organic carbon mineralization in AS andAG was significantly higher than that in DG by 133.39% and 116.96%, respectively, but both were significantly lower than that in NG, and there was no significant difference between the two restoration measures (p>0.05). Therefore, artificial vegetation restoration measures significantly promoted vegetation and soil restoration in desertification grassland, but shrub restoration was more conducive to improve the species richness of vegetation communities, while herb restoration was more conducive to increase soil moisture of desertification grasslands.

Abstract:In order to explore variation characteristics of frequency coupling between streamflow and sediment in the period 1 of base(1960-1979),period 2 of comprehensive harness of soil and water conservation (1980-1999) and period 3 of the Grain for Green project (2000-2019) in the Loess Plateau, the study based on measured daily data of streamflow and sediment from 1960 to 2019 at Liujiahe hydrological station in the upper reaches of the Beiluo River Basin in the Loess hilly and gully region, and copula function were used for frequency statistics and simulation of streamflow and sediment.The results indicated that:(1) The Gumbel-Houggard Copula function could well simulate the joint probability distribution of streamflow and sediment. (2) Streamflow and sediment transport decreased significantly in each return period in 5 to 100 years. The asynchronous probability of both rich and poor enhanced at each design frequency from period 1 to period 3. (3) The impact of soil erosion control and ecological environment construction on the ecohydrological process of the Loess Plateau was mainly reflected in greatly reducing the probability of extreme runoff and sediment events in the return period of more than 20 years. Great improvement in the ecological environment of the Loess Plateau has already demonstrated the ecological functions on a regional scale in reducing streamflow and sediment and adjusting the probability of extreme runoff and sediment events.

Abstract:Biochemical fulvic acid (BFA) has shown favorable application value in improving soil structure, promoting crop growth and improving fertilizer efficiency. In order to explore the effect of BFA addition on the water-salt migration law of saline-alkali soil, and reveal the salt leaching efficiency mechanism of BFA, this research based on one-dimensional vertical soil column infiltration experiment, to investigate the water-salt migration characteristics, the parameters of the infiltration model, and the composition of soil exchangeable base ions of saline alkali soil under different BFA application amounts (0, 1, 2, 4 and 8 g/kg). The results showed that the application of BFA under infiltration conditions could reduce the soil water infiltration rate, prolong infiltration time and improve soil water retention performance. The Kostiakov model, Philip model and algebraic model could all describe the soil infiltration process well. The empirical coefficient K, the absorption rate S and the comprehensive shape coefficient α in the models all showed a trend of decreasing and then increasing with the increasing of BFA application amount. Compared with the control, the application of BFA could improve the soil water holding efficiency and relative desalinization rate. Under the condition of 2 g/kg BFA addition, the average volume water content, average water holding efficiency and relative desalinization rate in 0-20 cm soil layer increased by 3.38%, 10.65% and 36.32%, respectively. In addition, compared with the control, the total exchangeable base (TEB) of soil increased after adding BFA, and the concentration of Ca²⁺ in TEB increased, while the concentration of Na⁺ decreased. Therefore, BFA application could significantly affect soil water infiltration and water and salt transport characteristics, improve the distribution of soil water and salt, and had favorable effect on water retention and desalination of saline soil. Moreover, studies have found that BFA application could significantly increase soil TEB, significantly improve soil exchangeable base ion composition and improve soil quality.

Abstract:In order to reveal the law of soil water and nitrogen transport and transformation under different fertilization timing (the whole process, the first 1/2 and the last 1/2 infiltration water fertilization), we analyzed the migration and transformation law of soil water and nitrogen distribution and redistribution under different fertilization timing, and compared their effects on soil nitrogen content quantitatively based on the one-dimensional vertical fertilizer solution (urea) infiltration experiment of sandy loam and clay soil. The results showed that fertilization timing hadlittle effect on the cumulative infiltration of soil and the distribution of water in moist body, but it had a significant effect on the transport and transformation of different forms of nitrogen in the process of distribution and redistribution. At the end of infiltration in sandy loam and clay loam, during the whole processand fertilization of the last 1/2 infiltration water, the content of urea nitrogen, ammonium nitrogen (NH₄⁺-N) and nitrate nitrogen (NO₃^--N) decreased with the increasing of soil depth. When the first half of the infiltration water was fertilized, the content of urea nitrogen and NO₃^--N accumulated at the edge of the wet body, andNH₄⁺-N increased first and then decreased, mainly distributed in 5-25 cm soil layer. In the redistribution stage, urea nitrogen in sandy loam and clay loam was basically hydrolyzed after 3 and 5 days of redistribution during the whole process and the last 1/2 infiltration water fertilization, respectively. At the same time, NH₄⁺-N content reached the peak, and NO₃^--N content did not decline within 10 days of redistribution. When the first half of the infiltration water was fertilized, the hydrolysis of urea nitrogen was basically completed after 10 days of redistribution, the content of NH₄⁺-N reached the peak after 5-10 days of redistribution, and the content of NO₃^--N increased first and then decreased. Under the condition of the last 1/2 infiltration water and the whole process of fertilization, when sandy loam and clay loam were distributed for another 10 days, the content of NH₄⁺-N and NO₃^--N in the 0-40 cm soil layer both were greater than those of the first 1/2 infiltration water, indicating that its potential nitrogen utilization efficiency was high. Therefore, it was recommended that the rational fertilization time of border (ditch) irrigation was the last half of the infiltration water or the whole process of fertilization. The results of this research could provide theoretical basis and technical support for the design and management of farmland border (ditch) irrigation and fertilization system.

Abstract:In order to explore the response of foliar water use efficiency (WUE) of typical artificial ecological forest(Robinia pseudoacacia) and artificial economic forest (Apple) to environmental factors and the difference in different climate zones in the Loess Plateau, leaf samples from 22 samples were taken as research subject in the Loess Plateau. The stable carbon isotope technique was used, which could reflect the long-term WUE of plants.We measured the δ¹³C value of mature leaves of plants, analyzed its response to annual precipitation, temperature, solar radiation, relative humidity and water vapor pressure, and examined the difference between artificial ecological forest and economic forest in different climate zones. The results showed that:(1) The foliar WUE of apple was significantlyhigher than that of Robinia pseudoacacia, the values were 4.29 mmol CO₂/mol H₂O and 3.83 mmol CO₂/mol H₂O respectively. (2) The foliar WUE of the same plant in semi-arid area was higher than that in semi-humid area in climate regionalization. The foliar WUE of apple in semi-arid area was 12.5% higher than that in semi-humid area. The foliar WUE of Robiniapseudoacacia in semi-arid area was 6.4% higher than that in semi-humid area. (3) The foliar WUE of apple and Robinia pseudoacacia had the same response to environmental factors, and the response of foliar WUE to average water vapor pressure was more sensitive than other factors. The results expand the study of WUE and provide theoretical guidance for the improvement of WUE in the Loess Plateau.

Abstract:In order to explore the water consumption characteristics, root physiological characteristics and yield response to anthesis stage drought of different drought-tolerant wheat varieties, taking drought-tolerant variety "Xinchun 6" (XC 6) and drought-intolerant variety "Xinchun 22" (XC 22) as the experimental materials, conventional irrigation (CK), mild drought (T1) and moderate drought (T2) at anthesis stage were set up under soil column cultivation and field conditions to investigate the effects of drought stress on water consumption characteristics, root physiological characteristics of different soil layers and yield of drip irrigation wheat field. The results showed that after anthesis stage drought, the water consumption and water consumption intensity of the two wheat varieties in the whole growth period were CK>T1>T2, and the water consumption modelcoefficient reached the maximum at the jointing-booting stage. After rehydration with T1 treatment, the bleeding fluid, root activity, hydraulic conductivity (Lpr), the avtivity of catalase (CAT), peroxidase (POD) and superoxide dismutase (SOD) and soluble protein (SP) content significantly increased, which promoted the increase of shoot mass and 1 000 grain weight, and improved yield and water use efficiency. Compared with XC 22, bleeding fluid, Lpr, root activity, SOD, POD, SP content, shoot quality and yield of XC 6 all significantly increased. In T1 treatment, the bleeding fluid and Lpr of XC 6 were 5.4% to 25.1%, 2.2% to 15.7%higher than those of XC 22, respectively, and the SOD (6.9% to 20.0%, 2.6% to 24.7% and 3.6% to 31.1%), POD (4.1% to 19.1%, 3.9% to 25.2% and 3.7% to 21.6%), CAT (7.8% to 15.2%, 8.3% to 13.3% and 10.8% to 13.3%) activities and SP content(4.5% to 20.4%, 0.8% to 29.4% and 1.3% to 7.9%) in 0-20, 20-40 and 40-60 cm soil layers were significantly higherthan those of XC 22, respectively. Root mass, shoot mass and yield had a quadratic parabola relationship with water consumption, and there was a significant positive correlation with bleeding fluid, Lpr, MDA and CAT activities. The interaction between water treatment and varieties had significant effects on Lpr, POD, CAT and SP content. Therefore, mild anthesis stage drought of drought-tolerant variety could reduce water consumption, improve root SP content and antioxidant enzyme activity, so as to enhance root activity, improve shoot mass, and improve yield and water use efficiency.

Abstract:Heterogeneous soil landscapes are common under interaction of natural processes and human activities, and in turn, under combined impacts of land use and land cover in the hilly areas of South China. Variation of soil quality across these soil landscapes impacts development of agro-industries in rural area. In this study, 4 types of soil-landscapes including forest land under conservation on hill slope, orchard, dry crop land and paddy field in the basin, were selected in a small watershed of Zhishan Village, Jingqiao Town, Lishui District in suburb Nanjing. Topsoil samples were collected in autumn to analyze basic physico-chemical properties, soil aggregate size distribution and microbial phospholipid fatty acids as well as extracellular enzyme activities. Concerned for soil fertility, the variation of key parameters of soil organic carbon, aggregation and biological activity were explored across these soil landscapes. The relationship between soil landscape and topsoil quality was explored by soil quality evaluation method. The results showed that, compared with the conserved forestland soil-landscape, the soil organic matter (SOM) declined by 50.93% to 69.63%, the mean weight diameter of soil aggregates reduced by 41.34% to 68.71%, the total phospholipid fatty acids reduced by 19.20% to 42.04%, while normalized enzyme activity dropped by 22.48% to 63.27% in the topsoil of the agricultural soil-land scapes. Accordingly, compared with forest land, the ecosystem functions and service of topsoil under the agricultural soil-landscapes had been significantly weakened. However, paddy fields had higher SOM content and microbial activity. Regression analysis showed that, SOM content was the strongest driver for topsoil quality change within the watershed. Theevaluation of soil quality based on total data set and minimum data set and the evaluation of soil functional quality based on the concept of soil health show that, the overall topsoil quality was in an order of forest land>paddy field>upland>orchard. Further, the evaluation system based on the concept of soil health can comprehensively reflect the changes of soil quality and the significance of ecosystem function among different soil-landscapes.

Abstract:The formation of organic-mineral complex in soil can protect organic matter and make it difficult to be decomposed. This study aimed to investigate the dynamic effects of long-term application of different livestock manures on the organic-mineral complex status of phaeozem and the distribution of organic carbon. The phaeozem under a long-term locality experiment started in 2010 at the teaching experimental field of Jilin Agricultural University was used as the research object. Four treatments were set up in the experiment, namely, application of chicken manure, cow manure, pig manure and the control. Soil samples were selected in 2010, 2012, 2015, 2018 and 2020 to determine the content of heavy fraction organic carbon, the degree of organic-mineral complexation, the content of different components of organic-mineral complex. And the distribution of organic carbon in the organic-mineral complex were also determined. The results showed that:At the beginning of the experiment, the effect of exogenous organic matter on soil complex condition was not significant, but with the extension of time and the long-term application of livestock manure, moreorganic-mineral complexes were formed, and the accumulation of organic matter was significantly enhanced, with the best effect observed in chicken manure treatment. The amount of heavy fraction organic carbon and quantity of organic-mineral complexation under treatment with chicken manure increased by 12.0% and 10.0%, respectively, compared with the control in 2020. After the application of livestock manure, the content of each component gum dispersion complex was also higher than that of the control, however, the content of G₁ complex showed a decreasing trend. Long-term application of organic materials increased the distribution of organic carbon in each organic mineral complex. The application of livestock manure could improve the soil complex condition and increase the complex and its carbon content, of which chicken manure was the most effective.

Abstract:As an important carbon reservoir in the Loess Plateau, the stability of soil organic carbon in the deep layer of silt dam greatly affects soil carbon storage capacity and carbon emission. In this study, the soil organic carbon content and its components of the silt dam profile in loess hilly-gully region were investigated to study the variation characteristics and influencing factors of soil organic carbon content and its stability under different utilization years and different deposition depths. Results demonstrated that:(1) Soil organic carbon (SOC) content in the deep layer of the dam was lower than that in the surface layer of the sloping farmland, and there was no obvious organic carbon enrichment phenomenon. The SOC content of dam land increased with the increasing of utilization years. (2) The contents of SOC, EOC, MBC and DOC in the dam land with different utilization years showed obvious surface aggregation phenomenon. The content of MBC, DOC and EOC was higher in 0-60 cm soil layer. (3) Compared with the shallow soil, the SOC in the deep layer of the dam had higher stability, long-term tillage in dam would reduce the stability of SOC in deep soil. (4) The dominant factors affected SOC stability in shallow and deep soils were different. The stability of shallow SOC was mainly affected by soil depth, organic carbon content and clay content, which could explain 50.4%, 19.6% and 11.8% of the variation, respectively. The stability of deep SOC was mainly affected by organic carbon content, soil water content and utilization years, which could explain 38.9%, 33.9% and 11.8% of the variation, respectively.

Abstract:Based on the field experiment, the effects of irrigation water salinity and irrigation amount on soil water and salt distribution and spring maize yield were explored. Taking spring maize in Hetao Irrigation District as the research object, two irrigation waters (1.1, 5.0 g/L) and three irrigation amounts (210, 255, 300 mm) were set up for field experiments. The results showed that at maturity, the average water content and soil conductivity of 0-100 cm soil layer under 5 g/L brackish water irrigation were significantly higher than those under groundwater irrigation. In groundwater irrigation, with the increase of irrigation amounts, the decreasing trend of soil average water content in growth period decreased, and the leaching effect of soil salt was more obvious. In brackish water irrigation, when the amount of irrigation was small, the surface accumulation of soil salt appeared. With the increase of irrigation amounts, the salt content of surface soil decreased, and more salt accumulated in the deep soil. After irrigation, the surface soil water content changed obviously and there was a phenomenon of salt return, and the horizontal movement of soil water and the accumulation of deepsoil salt were more obvious in brackish water irrigation. In groundwater and brackish water irrigation, the increase of irrigation could significantly improve the yield of maize, but there was no significant difference between 255 mm and 300 mm treatments. Compared with groundwater irrigation, brackish water irrigation significantly reduced the yield of spring maize. In conclusion, under the conditions of groundwater and brackish water irrigation, 255 mm irrigation water could not only be suitable for the growth of spring maize, but also ensure the yield. It could be used as a better irrigation quota and meet the requirements of ensuring crop production and saving fresh water resources in the irrigation area.

Abstract:In this study, Kenli District and Wudi County, representative regions of the Yellow River Delta, were selected to classify the soil surface water and salt data obtained from field survey and indoor analysis according to seasons, vegetation types and the distance from Bohai Sea. Classical statistical analysis, coupling degree model, buffer zone analysis, origin three-dimensional relationship analysis and other methods were used. The spatial-temporal characteristics of water and salt in soil surface (0-15 cm) and its coupling relationship were analyzed. The results showed that the soil water and salt content was higher in the study area, and the salt content was mainly moderate salinization. The water and salt contents of soil surface in Kenli District was higher than those of Wudi. The order of soil water contents in different seasons was summer>spring>autumn>winter, and the order of soil salt contents was spring>autumn>winter>summer. The relationship of coupling degree was spring>autumn>winter>summer. The order of soil water contents of different vegetation types was waste grassland>bare land>cultivated land>forest land, the order of soil salt contents was bare land>waste grassland>cultivated land>forest land, and the order of coupling degree was bare land>waste grassland>cultivated land>forest land. From offshore to inland, soil surface water content, salt content and coupling degree of water and salt in the study area gradually decreased. The changing trend in Wudi County was gentle, while the salt content in Kenli District increased from 40 to 50 km to the sea, and the water content increased significantly from 30 to 40 km to the sea, and the coupling degree of surface water and salt also increased. These results provide a theoretical basis for the rational planning and utilization of soil resources in the coastal area of the Yellow River Delta.

Abstract:Through a three-year field experiment, the effects of nitrogen reduction and straw returning on the yield of spring maize, soil nitrate nitrogen and ammonia oxidizing microorganisms in dryland of the southern Loess Plateau were studied. The study set up fivetreatments, including no fertilizer (CK), traditional nitrogen application (N250), traditional nitrogen application combined with straw return to field (N250+S), nitrogen reduction 20% (N200), and nitrogen reduction 20% combined with straw return (N200+S). The results showed that:(1) Nitrogen reduction by 20% and straw returning to the field for 3 consecutive years can increase maize yield and control soil nitrate leaching.Compared with N250 treatment, N200 treatment increases maize yield by 5.9%, and N200+S treatment increases maize yield compared with N200 treatment 7.4%, compared with N250 treatment, N250+S treatment increased maize yield by 9.1%; In the 0-300 cm soil layer, compared with N250, N200 reduced nitrate nitrogen residue by 51.3%. And the N200+S reduced nitrate nitrogen residue by 18.0% compared with N200. The residual nitrate nitrogen in N250+S was reduced by 41.2% compared with N250. (2) Nitrogen reduction and straw returning reduced soil nitrification potential. Compared with N250, N200 reduced soil nitrification potential by 8.8%, and N250+S reduced it by 14.2%.The soil nitrification potential in N200+S was reduced by 20.4% compared with N200. (3) Returning straw to thefield significantly increased soil microbial biomass carbon and nitrogen (SMBC, SMBN). Compared with N250, the SMBC and SMBN in N250+S were increased by 17.5% and 24.0%, respectively. Compared with N200, SMBC and SMBN in N200+S were increased by 18.4% and 31.3% respectively. (4) Nitrogen application and straw returning had little effect on ammonia oxidizing archaea (AOA), but increased the abundance of ammonia oxidizing bacteria (AOB). (5) The abundance of ammonia oxidizing bacteria (AOB) was extremely significantly positively correlated with nitrate nitrogen, ammonium nitrogen, SMBC, SMBN and nitrification potential, while ammonia oxidizing archaea (AOA) was abundant. There was no obvious correlation between degree and impact factor.These results could provide a scientific basis for nitrogen fertilizer management and agricultural sustainable development in the spring maize planting area of the Loess Plateau.

Abstract:In order to reveal the impact of water and fertilizer interactions of shallow-buried drip irrigation on the water use efficiency (WUE) of spring maize, a field experiment on the effects of different water and fertilizers combinations on WUE of spring maize under shallow-buried drip irrigation was carried out in 2017-2020 by using quadratic regression orthogonal test design, with irrigation amount (W), nitrogen application rate (N) and potassium application rate (K) as independent variables and WUE as dependent variables. The results showed that under the action of single factor, WUE increased first and then decreased with increasing of water and fertilizer consumption, and the degree of influence followed the order of W>N>K. When the two factors interact, the influence of WN, WK and NK on WUE showed a convex trend, and there was a maximum value, and the degree of influence was WN>NK>WK. When the three factors of W, N and K interacted together, WUE increased first and then decreased with the increasing of the coding level of W, N and K. The treatments of middle-water-fertilizer could get higher WUE compared with the treatments of low-water-fertilizer and high-water-fertilizer. By the model optimization, it was concluded that higher WUE (≥ 25.00 kg/(hm²·mm)) could be obtained under the conditions of irrigation rate of 43.25 to 58.87 mm, nitrogen application rate of 229.93 to382.97 kg/hm² and potassium application rate of 104.94 to 148.49 kg/hm². This study provided a scientific basis for optimizing the management of water and fertilizer under shallow-buried drip irrigation and obtaining high-efficiency use of water for spring maize in the experimental area.

Abstract:In order to clarify the optimal film mulching type and nitrogen application system in arid areas, a two-year film mulching farmland fertilization experiment was conducted at Muleitan Water-saving Experimental Station in the Hetao Irrigation District, Inner Mongolia. Three mulching treatments were set at high nitrogen level (conventional nitrogen application 336 kg/hm²), including plastic film (PFM3), biodegradable film (BFM3) and no film mulching (NFM3); at the same time, three nitrogen levels were set up under biodegradable film mulching, including medium nitrogen (BFM2:276 kg/hm²), low nitrogen (BFM1:216 kg/hm²) and no nitrogen (BFM0:0 kg/hm²), making up to a total of six treatments. The DNDC model was calibrated and verified by the observed values of two-year yield, nitrogen uptake and leaching, and the film type and fertilization system were optimized based on the improved TOPSIS method. The results showed that the DNDC model was sensitive to crop growth and nitrogen migration under different film mulching and nitrogen regulations. The simulated EF and R² of yield, nitrogen uptake and leaching were greater than 0.83, NRMSE were less than 20%, which could predict and evaluate crop productivity and resource utilization. With the increase of nitrogen application amount, the nitrogen leaching of each mulching treatment increased linearly. When nitrogen application amount increased to 106 kg/hm², nitrogen use efficiency reached the peak; when the nitrogen application amount increased to 256 kg/hm², the yield of mulching treatments did not change significantly. At the same time, the net income of BFM reached the maximum, but the cost of biodegradable film was high, which resulted in a net income of 6.84% lower than PFM and 3.17% higher than NFM. There was no significant difference in nitrogen leaching, use efficiency and yield between biodegradable film mulching and plastic film mulching, which were significantly higher than no film mulching, and the average increase from 8.22% to 26.69%. The improved TOPSIS method was used to comprehensively evaluate the yield, nitrogen leaching, use efficiency, residual film amount, and net income. The results showed that the application of 231 to 256 kg/hm² nitrogen fertilizer was the most reasonable fertilization system under biodegradable film mulching in arid areas.

Abstract:The croplands in arid regions are characterized by saline-sodic soils, low content of soil organic carbon (SOC), and large proportions of soil inorganic carbon (SIC). Both SOC and SIC are influenced by agricultural management. However, it remains unclear that how the stock and stability of SOC and SIC at different soil depths vary after long-term fertilizations. We investigated the vertical patterns of soil carbon (C) change and SOC stability in six fertilization treatments (e.g., CK, NPK, N2P2K, NPKS, NPKS2, and NPKM) in the Fukang Station for Desert Ecological Research, Chinese Academy Sciences. The results showed that:(1) The contents and stocks of SOC in the tilled layer (0-20 cm) increased after 31-year fertilizations, especially in the treatment of chemical fertilizer combined with straw returning, which could be due to high plant C inputs. (2) In addition, the thermal stability of SOC decreased in all the fertilization treatments, suggesting that increased SOC after long-termfertilizations might be vulnerable to environmental changes and would promote the transformation of soil nutrients. (3) The contents and stocks of SIC decreased in different fertilization treatments, and the decreases in SIC reduced along soil profiles, resulting in the increment of SIC to the depth of 60 cm, which might be caused by irrigation. (4) Despite the increases in SOC after the long-term fertilizations, the decreases in SIC led to the loss of soil total C, demonstrating that the changes in SIC determine the net changes in soil C in the arid regions. Overall, the results of this study suggest to estimate accurately the changes in soil C in the arid regions, we need to understand changes in both SOC and SIC and their stabilities at different soil depths.

Abstract:In order to scientifically evaluate the carbon sequestration capacity of the Grain for Green Project in China, the detailed afforestation data of the first phase of Grain for Green Project were collected. Combined with the growth curve of plantation volume (biomass) of Chinese tree species, the characteristics of soil organic carbon change before and after Grain for Green Project and the relevant parameters of carbon storage calculation of the main tree species, the carbon sequestration capacity and its changes of the Grain for Green Project from 1999 to 2050 were estimated. The results showed that the project's total carbon storage was 355.87 Tg when the project completed in 2010. When the project was implementing, the total carbon sequestration (trees and soil) of the former period was larger than that of the latter period, and the mean annual carbon sequestration was 29.66 Tg. The potential increment of carbon sink for the project increased. It is expected the potential increment of carbon sink of China's project are 1 234.04 Tg in 2050. Therefore, China's Grain for Green Project has produced huge carbon sink benefits.

Abstract:To understand the seasonal variation of plant organs-litter-soil stoichiometry in Pinus tabulaeformis plantation in Loess Hilly region, the field investigation and laboratory experiments were used by means of spatio-temporal substitution method in Zhifanggou Watershed, Ansai District, Yan'an City, Shaanxi Province, China. The ecological stoichiometry characteristics of carbon (C), nitrogen (N) and phosphorus (P) in different organs-litter-soil of Pinus tabulaeformis from April to October were analyzed. The results showed that:(1) From April to October, the contents of C and P in leaves increased gradually, and reached the highest in October. The contents of N and N:P in leaves and branches decreased first and then increased, and reached the lowest in August. While the contents ofC:N and C:P in branches and C:P and N:P in fine roots increased first and then decreased, and reached the highest in August. Soil C and N contents, C:P and N:P increased first and then decreased, and reached the highest value in August. Litter N content, C:P and N:P all showed a trend of decreasing first and then increasing, and reached the lowest in June, while P content had no significant change. (2) Except for N:P>14 in leaves from April to June and fine roots from April to August, N:P<14 in other organs from April to October, the growth of Pinus tabulaeflorus in this region was mainly restricted by N. (3) There were significant positive correlations between C and N contents and C:N of leaf and litter, and there were significant positive correlations between C:N, C:P and N:P (p<0.05). There was a significant negative correlation between leaf N:P and soil C:N (p<0.01), but no significant correlation between other stoichiometric characteristics. There was a significant positive correlation between litter C content and soil P content (p<0.05). The results make the study of ecological stoichiometry of plantation more systematic and provide reference for vegetation growth in loess hilly region.

Abstract:Studying the dynamic changes of soil enzyme activities and its stoichiometric characteristics at the micro-scale altitude and aspect of alpine meadows has important ecological significance for exploring the nutrient cycling process of grassland ecosystems. The alpine meadows in eastern Qilian Mountain was taken as the research object, and the changes of soil enzyme activities and its stoichiometric characteristics in seven altitudes and two aspects of alpine meadows, and their relationships with soil physical and chemical factors were analyzed. The results showed that the interactive effects of altitude and aspect had significant effects on soil LAP, BG, PPO, POD, lnBG/ln(NAG+LAP), lnBG/lnAP and ln(NAG+LAP)/lnAP. The LAP, AP, BG, POD, lnBG/ln(NAG+LAP) and lnBG/ln(NAG+LAP) first increased and then decreased with the increasing altitudes, while NAG and PPO decreased with the increasing altitudes. At the same altitude, The AP, BG, POD and PPO in the sunny aspect were lower than those in the shady aspect, and NAG in the sunny aspect were higher than that in the shady aspect, and LAP in sunny aspect under 3 800 m were lower than that in the shady aspect, and lnBG/ln(NAG+LAP) in sunny aspect except 3 000 and 4 000 m were higher than that in the shady aspect, and lnBG/lnAP in sunny aspect under 3 000 to 4 000 m and ln(NAG+LAP)/lnAP in sunny aspect under 3 000 to 3 600 m were lower than that in the shady aspect. Correlation analysis found that, soil enzyme activity and its stoichiometric characteristics were regulated by soil C, N, P resources and soil moisture conditions to varying degrees, and soil moisture and SOC were the main factors affecting soil enzymes activities. In conclusion, soil enzymes activities and their stoichiometric characteristics were different in micro-scale elevations and slope directions, and were affected by soil C, N, P resources and soil moisture conditions, especially soil water content and SOC.

Abstract:In order to clarify the treatment effect of Microbial Induced Calcium Carbonate Precipitation (MICP) in the heavy metal tailings in highly wind erosion areas in arid and semi-arid region, this paper used Bacillus (Lysinibacillus fusiformis) as the research object, which was the carbonate-mineralizing bacteria-spindle lysine bacillus screened in the habitat soil of the study area. We added the bacillus fermented liquid and the cementing solution mixed by 1mol/L urea and calcium chloride in the tailings slag to carry out indoor simulation experiments. And we compared the varieties of basic physical and chemical properties (heavy metal element content, pH, electrical conductivity and enzyme activity) in tailing slag with different size which were from slope top (fine particles:K1<5 mm), slope middle (middle particles:5 mm15 mm) before and after MICP treatment. And according to the method of two factor analysis of variance and correlation comparative analysis, we revealed the effect of MICP remediation technology based on habitat microorganisms on the regulation of regional tailing slag pollutants and determined the dosage of bacterial agent in MICP technology for the remediation of tailing slag with different particle sizes. The results showed that the MICP treatment had a significant effect on the basic physical and chemical properties such as heavy metal content, pH, electrical conductivity and enzyme activity in tailings slag. Under the MICP treatment, the arsenic (As) content of small particles (K1<5 mm) reduced by 21%, the mercury (Hg) of medium particles (5 mm15 mm) decreased by 22%. The pH in K1 and K3 reduced by 5% and K2 reduced by 4%. The total potassium (K) and urease in K1 significantly increased by 33% (p<0.05), the total carbon in K2 increased obviously by 39% (p<0.05), and the sucrase in K3 increased by 7% (p<0.05). The amount of microbial carbon and nitrogen significantly increased in K1, K2 and K3 (p<0.05). At the same time, Ni-Pb, As-Cu, electrical conductivity and Pb were significantly positively correlated (p<0.01) under MICPtreatment and pH-Pb was extremely significantly negatively correlated (p<0.01). And after MICP treatment, the correlations among total nitrogen, total potassium, total phosphorus, the contents of organic matter, heavy metal elements were enhanced.In summary, the MICP remediation technology based on habitat microorganisms could reduce the content of heavy metal elements amount in tailings slag, adjust the nutrient status of tailings slag soil, so as to regulate the quality of contaminated soil, and reduce the risk of environmental pollution caused by mineral resources development. At the same time, this study further determined the application dosage of bacterial agent for different particle tailings restoration to reach the remediation level, which has the better application value in the treatment and remediation of polluted soil.

Abstract:In order to explore the regulatory effects of indole-3-acetic acid (IAA) and kinetin (KT) on the physiological response and cadmium (Cd) tolerance of Helianthus tuberosus L. under Cd stress, taking H. tuberosus of Yulin and Chengdu as research objects, five treatment groups were set up, which were CK (no Cd), T1(Cd_{300 mg/kg}), T2(Cd_{300 mg/kg}+IAA_{4 mg/L}), T3(Cd_{300 mg/kg}+KT_{8 mg/L}) and T4(Cd_{300 mg/kg}+IAA_{4 mg/L}+ KT_{8 mg/L}), respectively, to study the effects of IAA and KT on the growth, antioxidant system, ChlorophyⅡ fluorescence properties and Cd accumulation ability of H. tuberosus seedlings under Cd stress. The results showed that the plant height elongation, leaf area, root elongation and dry weight of plants in the T1 group all decreased compared with CK. Spraying hormone could effectively increase chlorophyⅡ content, and the maximum increase was 162.87% in the T4 group of Yulin H. tuberosus. The proline (Pro) content of each group increased with the treatment time, the maximum increase of H. tuberosu T4 group in two places was 223.94% and 112.73%, respectively, while the decrease of MDA in T4 group was greater than that in T2 and T3.The antioxidant enzyme activity of T1 group was generally lower than that of other groups, and the gap in enzyme activities between groups was gradually widening with the plant growth. The increase ofthe three protective enzyme activities in T4 group was ideal. Hormone spraying significantly improved the root vigor of H. tuberosus (p<0.05), and the H. tuberosus T4 group in two places increased by 39.00% and 9.10%, respectively. In the treatment group of T4, the number of bubbles in the pith of H. tuberosus stem was much larger than that of T1 to T3, and the black area of plants from the two producing areas increased by 142.59% and 700.00%, respectively. Single or combined spraying of plant hormones could promote absorption of Cd in the root, stem and leaf organs of H. tuberosus, the content of Cd in root was the highest, followed by the stem. The Cd enrichment coefficient of each organ was all greater than 2, and transport coefficient was greater than 1. The Cd content of H. tuberosus T4 group was greater than T1 to T3.In summary, 4 mg/L IAA and 8 mg/L KT could help H. tuberosuseffectively respond to the Cd stress environment and strengthen its accumulation capacity by increasing the antioxidant enzyme activity and Pro content, so as to maintain the dynamic balance of reactive oxygen species (ROS) production and removal, reduce membrane lipid peroxidation, and improve root vitality. The results could provide theoretical guidance for the cultivation of H. tuberosus in Cd-polluted areas and phytore mediation of soil Cd pollution.