Abstract:To explore different compost methods of straw returning on runoff, sediment and nitrogen losses in small watershed, a slope farmland in Erlongtan watershed in central Yunnan Province was chose as research object. Nine different compost methods of corn straw returning were set up: CK and 8 treatments. Each treatment included two straw return amounts to the field (0.75,1.5 kg/m²), two straw particle sizes (1,5 cm), two straw heap retting methods with urea reactor (water or water and urea stacking). In this study, the characteristics of runoff, sediment and nitrogen losses in a flue-cured tobacco slope farmland were studied. The results showed that: (1) In the 4 rainfalls with typical runoff, the application of higher straw return amount (1.5 kg/m²) and coarse grain straw (5 cm) could effectively reduce runoff and sediment losses in the slope farmland (10.06% ~ 38.60% and 10.07% ~ 38.60%). (2) The concentrations of total nitrogen (TN) and NO₃^--N in runoff under the application of lower straw return amount (0.75 kg/m²), coarse grain straw (5 cm), and compost with no urea were lower than those with higher straw amount, fine grain straw, and compost with urea (1.96% ~ 32.79% and 3.97% ~ 40.89%). (3) The proportions of NO₃^--N/TN, NH₄⁺-N/TN and PN/TN were 63.64% ~ 86.18%, 5.31% ~ 13.86% and 5.33% ~ 25.80%, respectively, and the main form of nitrogen loss in runoff on slope farmland was NO₃^--N, dissolved nitrogen was the main nitrogen pollutant in runoff. (4) TN losses concentration of sediment with the application of lower straw return amount (0.75 kg/m²), coarse grain straw (5 cm), and compost with no urea decreased (16.87% ~ 48.15%). (5) TN losses of runoff and sediment with the application of higher straw return amount, coarse grain straw and compost with no urea could effectively reduce the risk of nitrogen loss in the slope farmland in central Yunnan province (0.32% ~ 35.05% and 54.52% ~ 77.23%). Among TN runoff and sediment loss, runoff output was the main factor, accounting for 50.09% ~ 71.67% of TN runoff. In order to reduce the nitrogen losses in this watershed, higher straw returning amount (1.5 kg/m²) and coarse grain straw (5 cm) was recommended. Small or compost with no urea also could be applied according to different growth periods of flue-cured tobacco absorption and soil nutrient conditions.

Abstract:Based on the location observation data of the wild outflow plots from 2018 to 2019, taking the corn monoculture treatment without straw mulch (M₀) as the control, this study was aimed to explore the effects of maize monocropping treatment and different straw coverage (M₁~M₅, 1 111, 2 222, 3 889, 5 556, 6 944 kg/hm²) on runoff and sediment yield characteristics of sloping farmland in the karst area of Guizhou Province. The results showed that: (1) Under different rainfall levels, straw mulching had better soil and water conservation effect, and with the increase of mulching amount, the total runoff and sediment yield decreased gradually, but there was no significant difference between M₄ and M₅ treatments (p > 0.05); (2) The runoff and sediment yield of each treatment from seedling stage to jointing stage were greater than those of the latter two stages, and the runoff and sediment yield of each mulching treatment in each stage were lower than that of the control; (3) Compared with the control, the annual average runoff depth decreased by 21.85%~50.46%, and soil erosion modulus decreased by 50.10%~85.87%; (4) As the amount of straw mulching and the amount of straw buried in the soil increased, the runoff and sand production of each treatment showed a downward trend. However, when the straw mulching amount exceeded 5 556 kg/hm² and continued to increase to 6 944 kg/hm², the soil and water conservation did not change significantly. Straw mulching was an effective way to control soil and water loss of sloping farmland in karst area, and the coverage amount of about 6 000 kg/hm² was recommended in the soil and water conservation.

Abstract:In order to explore the main sub-rainfall factors that cause soil erosion in the agricultural small watershed of the Three Gorges Reservoir area, the study selected the Shipanqiu small watershed located in the heart of the Three Gorges Reservoir area as the research area, and analyzed the distribution characteristics of erosive rainfall in 2019 and the variation law of sediment yield process in catchment A and catchment B under typical sub-rainfall, and the correlation analysis method was used to explore the main influencing factors of sediment erosion caused by sub-rainfall. The results showed that: (1) Of the 119 rainfall events for the whole year, 19 were erosive events, including 10 erosive moderate rainfall events. The erosive moderate rainfall was the most common type in erosive rainfall events. Rainstorm and above is the type that caused the largest amount of sediment in the study area. (2) In the typical moderate rain, heavy rain and rainstorm sediment yield events, the amount of sediment yield in catchment B was 5.13, 1.66 and 7.56 times that of catchment A respectively. The analysis of the sediment yield process of three typical sub-rains showed that the variation of sediment yield line in catchment B was more dramatic with the extension of rainfall duration. (3) The correlation coefficient of PI_n factors and the amount of sediment yield in the study area ranked as PI₃₀ > PI₁₀ > PI₁₅ > PI₆₀ > PI₅ > PI₉₀ > PI. Correlation analysis of various rainfall factors and the amount of sediment yield in the study area ranked as P > PI_n > I_n > I > T. There was a very significant positive correlation between the amount of sediment yield and the indicators P and PI₃₀ in catchment A and B. To sum up, when carrying out soil and water conservation work in the three Gorges reservoir area, it is necessary to strengthen the ability of monitoring and early warning response to soil and water loss in agricultural small watershed caused by rainstorm and above. P and PI₃₀ can reflect the impact of natural sub-rainfall on sediment yield in small watersheds of Three Gorges reservoir well. When estimating the rainfall erosivity of natural sub-rainfall, PI₃₀ can be used as the main reference factor. Compared with the traditional farming mode with simple structure, agroforestry-water complex ecosystem has a richer and more diverse structure, which can not only fully develop and utilize agricultural resources in small watershed, but also be more conducive to soil and water conservation, and it is also more adaptable to the changes of rainfall environment.

Abstract:Nitrogen runoff loss from paddy fields is one of the main sources of agricultural non-point source pollution. In order to reduce the risk of nitrogen runoff loss from single-crop paddy fields in the climatic zone of the middle and lower reaches of the Yangtze River, a suitable fertilization and water level control model for this region was sought and the model of the SMNRL was built. This article used the historical meteorological data from 1957 to 2019 in the Chaohu Lake area by setting the rice transplanting interval (June 6 to 25) and the water level (3, 10, 20 cm) to simulate nitrogen loss in paddy fields. The result showed that: (1) After fertilization, the nitrogen concentration in the paddy field surface decreased exponentially. Nitrogen decay time of field water was 9 days at base fertilizer stage, and 7 days at tillering and earing fertilizer stage. (2) According to the order of nitrogen runoff loss that accounts for the whole growth in each fertilization period, in the combination of LW and HW, it was the basal fertilizer stage, the tiller fertilizer stage, and the panicle fertilizer stage. The nitrogen loss of basal fertilizer, tiller fertilizer, and panicle fertilizer was respectively 72.4% to 98.4%, 1.9% to 27.6%, and 0 to 8.3% in the combination of LW, and the basal fertilizer period was the period of high nitrogen runoff loss. (3) Controlling water level was more effective than reducing planting time to reduce nitrogen runoff loss. Under the same water level, the total nitrogen runoff loss during the transplanting period were reduced by 0.4 to 4.5 kg/hm² and 32.8% to 80.3% during the whole growth period. Under the same transplanting time, the nitrogen runoff loss of the LW and MW combinations were reduced by 8.8 to 13.1 kg/hm² and 92.1% to 98.8% compared with the HW combination. (4) In the three combinations of LW, MW, and HW, June 6 to 25 was divided into the early and late stages of rice transplanting, with June 19, June 11, and June 17 as the boundaries respectively. The average nitrogen runoff loss in the early stage could be reduced by 37.0%, 25.0%, and 21.7% compared with the later stage. (5) The effective measures to reduce nitrogen runoff loss in rice fields in Chaohu Lake region were to control the water level during the fertilization period to 3 cm and choose a rice transplanting time between June 6th and June 19th.

Abstract:This study applied a field experiment to investigate the effects of different fertilizer types on nitrogen loss in a paddy field. The fertilizer types included control (CK), conventional formula fertilizer (CT), partial replacement of organic fertilizers to chemical fertilizers (BS) and carbon-based fertilizer (CB). The results showed that the BS and CB had significant effects on reducing nitrogen runoff loss in the paddy field (p < 0.05) and the total runoff loss of ammonium decreased in the following order: CT (20.08 kg/hm²), BS (15.53 kg/hm²), CB (12.68 kg/hm²), CK (0.63 kg/hm²). The estimated nitrogen leaching loss showed that BS and CB had no significant effects on reducing nitrogen leaching loss from the paddy field. The inorganic nitrogen (ammonium and nitrate) runoff loss under CT, BS and CB accounted for 5.26%~8.31% of fertilizer application, while leaching loss accounted for 0.21%~0.27%, demonstrating that runoff was the main way of inorganic nitrogen loss in the paddy field in this study. The fertilization treatments of CT, BS and CB increased rice yield by 18.3%, 28.4%, and 24.9%, respectively (p < 0.05). In summary, the application of carbon-based fertilizer and organic fertilizer could significantly reduce the nitrogen loss in the paddy field.

Abstract:The key to study the sediment deposition of the Yellow River is to clarify the sediment transport characteristics of the erosion sediment on the Pisha Sandstone slope. The physical simulation technology of water, wind and freezing-thawing composite erosion was used to study the variation characteristics of erosion sediment particles on Pisha Sandstone slope under the composited action of three groups of different erosion dynamics, which were single water erosion, freezing-thawing water erosion, and freezing-thawing wind water erosion, under the condition of 35° slope and 110 mm/h rain intensity. The results showed that the Pisha sandstone slope was dominated by overall erosion under single water erosion action, and the erosion sediment particles changed stably. Under the action of freezing-thawing water erosion, coarse particles were produced obviously, and the effect of freezing-thawing on coarse particles was prominent. The slope stability was the worst under freezing-thawing wind water erosion, and the change of erosion sediment particles was the most drastic. In the process of slope erosion under composite erosion, sediment particles with larger diameter were mainly transported. The fluctuation of erosion sediment particles with the increase of erosion dynamics changed dramatically.

Abstract:Contour ridge system is an effectively agricultural practice used throughout the world. Due to microtopography, rainwater from side slopes flows into furrows and ponds in lower areas of furrows, and thus induces seepage to occur more readily. In addition, the ponding results in that raindrop impact enhances or weakens the capacity of soil detachment and transport. Therefore, the interactive influence of raindrop impact and seepage on soil erosion process is more complicated relative to traditional slope systems. Runoff and sediment yielding process were analyzed under two soil surface hydrological conditions (free drainage, FD and seepage, SP) and two soil surface conditions (with and without raindrop impact, RI and WRI) through simulated rainfalls. Results showed that: (1) Runoff ranked in the order of SP+WRI > SP+RI > FD+RI > FD+WRI. Raindrop impact and seepage contributed -47.09% ~ 54.37% and 41.96% ~ 85.62% to the runoff, respectively. (2) Soil loss decreased in the sequence of SP+RI, SP+WRI, FD+RI, and FD+WRI. Raindrop impact and seepage made contributions of 12.92% ~ 94.94% and 25.83% ~ 97.28% to soil loss, respectively. (3) Raindrop impact showed a slightly influence on runoff process under FD condition. However, raindrop impact and seepage induced the temporal variation of runoff rate and sediment concentration more fluctuated when soil was saturated. (4) With or without raindrop impact, a power function relation was found between runoff rate and soil loss under FD condition, while exponential function could describe their relation under SP condition. These findings were helpful to understand soil erosion process within contour ridge systems, and supply guidance for soil and water comprehensive conservation for implementing contour ridge systems.

Abstract:In order to explore the temporal and spatial evolution process of energy parameters dynamic response of sand covered loess slope in spring thawing period, two soil treatments (unfrozen slope and frozen slope) and four sand cover thicknesses (0, 1, 2 and 3 cm) were used under the same discharge (1 L/min). The temporal and spatial evolution process of runoff velocity (V), stream power (W), unit stream power (P), and runoff kinetic energy (E) under different soil treatments and different thickness of sediment cover were systematically analyzed. The results showed that: (1) The runoff velocity under different treatments decreased with the extension of runoff generation time, and increased with the increase of distance from the top of slope. The average runoff velocity of unfrozen slope and frozen slope varied from 0.23 to 0.35 m/s and from 0.18 to 0.35 m/s, respectively. The temporal and spatial variation of runoff depth was opposite to that of runoff velocity. The values of unfrozen slope and frozen slope varied from 0.36 to 1.32 mm and 0.46 to 2.89 mm, respectively. (2) The variation range of stream power of unfrozen slope and frozen slope was 0.22 ~ 0.82 and 0.29 ~ 1.13 N/(m·s), respectively. The average value of unit stream power of unfrozen slope and frozen slope varied from 0.047 to 0.072 m/s and 0.037 to 0.072 m/s, respectively. The runoff kinetic energy of unfrozen slope increased with the increase of sediment thickness, and the runoff kinetic energy of frozen slope increased at first and then decreased with the extension of time. In space, the energy parameters of unfrozen slope and frozen slope could be expressed by linear function (R² > 0.71). (3) There was a significant linear relationship between runoff rate and runoff velocity and energy parameters (p <0.01). Runoff velocity and unit stream power could describe the runoff generation process of unfrozen slope and frozen slope under different sediment thickness. The results of this study can provide reference for the establishment of erosion model of sand covered loess slope in thawing period.

Abstract:In order to explore the influence of sugarcane planting on the soil erosion of lateritic red soil slope under high intensity and high frequency rainfall in southern China, we based on the in-situ observation test of runoff plot, analyzed runoff and erosion characteristics of bare slope and sugarcane land that under different planting methods (down-slope and cross-slope), and discussed the effects of sugarcane planting on slope erosion. At the same time, we obtained the main rainfall patterns that affecting the slope erosion of lateritic red soil. The results showed that: (1) The runoff amounts and sediment yields were both showed that bare slope > down-slope sugarcane planting slope > cross-slope sugarcane planting slope. The runoff amounts and sediment yields of bare slope were 1.7 ~ 5.3 times of the down-slope and cross-slope sugarcane planting slope. The runoff amount and sediment yield of down-slope sugarcane planting slope were 1.9 and 2.3 times of the cross-slope sugarcane planting slope. (2) Under different rainfall events, runoff amount and sediment yield of bare slope were higher than all sugarcane planting slopes, and the runoff amount and sediment yield of down-slope were larger than that of the cross-slope. However, the difference between the two sugarcane lands decreased with the sugarcane growth. (3) The highest frequency rainfall pattern was type A (mid duration, low rainfall intensity, low rainfall depth). However, type B (short duration, strong rainfall intensity and medium rainfall depth) was the main rainfall pattern that caused runoff and erosion in bare slope and down-slope sugarcane planting slope, the runoff and erosion accounted for 49.9%, 57.6% and 62.3%, 64.2%, respectively. Type D (long duration, extremely strong rainfall intensity and extremely great rainfall depth) was the main type that caused the soil and water loss in cross-slope sugarcane planting slope, and the runoff amount and sediment yield caused by the rain of type D accounted for 49.5% and 72.2% respectively. The results can provide a theoretical basis for clarifying the mechanism and control of soil erosion on the sugarcane land in the lateritic red soil region of southern China.

Abstract:In order to study the effects of different tillage practices on the yield of runoff and sediment in purple soil area in peanut podding stage. Field rainfall simulation experiments were carried out to study the yield of runoff and sediment in four tillage practices and one control group (longitudinal ridge, cross ridge, bunch planting, flat planting and bare land on flat slope). The sliding-rank-sum-test was used to find out the catastrophe point of runoff and sediment production process. The Mann-Kendall trend test method was used to analyze the trend of runoff and sediment yield process after the catastrophe point. The results showed that the runoff and sediment yield process was in a relatively stable state after the catastrophe point. The stable rate of runoff and sediment yield in bare land was the largest, followed by longitudinal ridge, then flat planting, bunch planting, and cross ridge was the smallest. However, the initial runoff yield time of each tillage practice was opposite to the stable rate of runoff and sediment yield. Compared to bare land on flat slope, all tillage practices showed the effects of runoff and sediment reduction. The specific performance was cross ridge > bunch planting > flat planting > longitudinal ridge.

Abstract:Based on the measured runoff and sediment data of Cuntan hydrologic station that at upper situating Yangtze River's main stream, this study analyzed the temporal trends of runoff and sediment transport as well as the variations of their relationships during 1953-2018 by statistical methods including linear regression, Mann-Kendall test, and sediment rating curve. Double mass curve was further used to analyze the driving factors of water and sediment variation. The results showed that the average annual water and sediment discharge of Cuntan station was 342.5 billion m³ and 361 million tons, respectively. The average monthly water and sediment discharge was 29.48 billion m³ and 30.13 million tons, respectively, which mainly distributed in June to October, accounting for more than 70% and 95% of the total annual runoff and sediment, respectively. The trend analysis indicated that the variation trends of annual precipitation and runoff were not obvious, however, annual sediment discharge showed a significantly decreasing trend. The monthly runoff increased significantly from January to April and the changes in other months were not significant, while the monthly sediment discharge showed a significantly decreasing trend in each month. In this study, the relationships between water and sediment could be fitted by power functios, and the fitting parameters were affected by the time scale. Statistical test detected that there was no significant difference between the measured value suspended sediment load and the estimated values by sediment rating curve. Double mass curve analysis found that human activities, such as water conservancy construction and soil and water conservation, were the main factors driving the sediment reduction in Cuntan station, accounting for 69%~93% in different decades, among which human activities had contributed more than 90% since 2000.

Abstract:In order to improve the calculation accuracy of the contribution rate of check dams and reveal the effect of check dams on the reduction of sediment discharge in watershed. Taking Dali river basin as the research object, we developed a method based on integrated GIS and soil erosion model to calculate the annual sediment deposition of check dams. The results showed that: (1) From 1954 to 2011, the sediment reduction in check dams increased in a fluctuant way year by year, and the average and cumulative capacity were 0.12×10⁸ t and 7.17×10⁸ t respectively. In the period of 1980—1989, the average sediment reduction in check dams reached up to 0.19×10⁸ t. (2) The sediment discharge of Dali river were significantly reduced in 1960-2015, and had significant mutations in both 1971 and 2002 (P<0.05). (3) Human activity was the main reason for sediment reducing in Dali river watershed, the contribution of sediment reduction in check dams were 47.42% in 1971-2001, while declined to 31.04% in 2002-2011 with the restoration of vegetation in Dali river watershed. The method we proposed was helpful for evaluating the contribution rate of sediment reduction of check dams in Dali river basin. After 2000, the contribution rate decreased in Dali river basin due to vegetation restoration in this area.

Abstract:Infiltration is critical to the redistribution of rainfall in a collapsed wall and directly affects its gravity erosion process. In this study, the experiment designed six dry-wet cycles, and through saturated infiltration experiments of four layers of soil fissures and digital image processing technology, the evolution of four layers of soil fissures under the effect of dry-wet cycles and its influence on saturated soil permeability of each soil layer were studied. The results showed that: (1) With the increasing of the wet and dry cycles, the fissures in the topsoil layer and the laterite layer developed obviously, the fissure rate gradually increased and then tended to be stable, while the transition layer and sand layer had almost no fissures. The fissures of the topsoil were almost completely developed after the third cycle, and the fissure rate reached 3.50%. The fissures were slender and broken. However, for the laterite, after the first cycle, the fissures were basically fully fixed, the fracture width would remain unchanged when it increased to a certain extent with the progress of the dry-wet cycle. (2) The soil permeability coefficient of the four layers followed the order of sandy soil layer > transition layer > laterite layer > topsoil layer. With the increasing of the number of wet and dry cycles, the permeability coefficients of the topsoil layer and the laterite layer gradually increased and then tended to be stable, the transition layer was relatively stable, and the sand layer gradually decreased and then tended to be stable. (3) There was a quadratic function relationship between the soil fissure rate and the permeability coefficient. The impact of fissure development on soil permeability increased first and then decreased. The results could provide a scientific basis for the study of the mechanism of wall collapse instability under rainfall infiltration and redistribution.

Abstract:Under natural conditions, rainfall mostly occurs intermittently, and slope soil erosion is a gradual and complex process. Through 15 indoor simulated rainfall experiments, including three rain intensities (60, 90, 120 mm/h) and five slopes (5°, 10°, 15°, 20°, 25°), the runoff and erosion process were studied under the conditions of primary and secondary rainfall. The slope erosion development process and the changes of main influencing factors under intermittent rainfall conditions were discussed. The results showed that: (1) The runoff time of the second rainfall was earlier than that of the first rainfall. The total runoff of the first rainfall was affected by rain intensity, slope, and rainfall. The slope of 15° was a turning point for the change of the total runoff. The effect of rainfall was weakened during a single rainfall, the maximum difference multiple under each rainfall intensity was reduced, and the multiple gap between the slopes was also reduced. (2) The main driving force for rill erosion in a single rainfall was the rainfall intensity. Rill erosion was more likely to occur in the case of steep slopes, and the 15° slope was of great significance to the generation of rill erosion. At this time, if rill erosion occurred, the slope erosion was mostly dominated by rill erosion, and both erosion showed a positive proportional function relationship. The amount of rill erosion caused by the secondary rainfall was related to the development of the rill during the primary rainfall. The more intense the rill development of the primary rainfall, the less the amount of rill erosion caused by the secondary rainfall. The amount of rill erosion had a linear function relationship with the total erosion amount. In general, the change in the total erosion amount was closely related to the stage of rill development. (3) Under intermittent rainfall conditions, there were differences in the influences of different rainfall intensity, slope, and rainfall on the slope soil runoff. At the same time, the change of soil runoff and erosion in the primary rainfall had an important impact on the development of secondary rainfall runoff and erosion in the later period, so that at different stages of soil erosion development, the influencing extent of rain intensity, slope, rainfall and other factors on the slope soil runoff and erosion also changed accordingly.

Abstract:Quantifying hillslope soil erosion process will provide an important basis for arrangement of sloping soil and water conservation measures. Thus, a field simulated rainfall experiment was conducted to analyze the effects of freeze-thaw, wind and water agent superposition action on sloping soil erosion in the typical thin mollic thikness region (Binxian county), middle mollic thikness region (Hailun city) and thick mollic thikness region (Keshan county). The experimental treatments included three treatments of only water erosion (I), freeze-thaw + water agent superposition action (Ⅱ) and freeze-thaw + wind + water agent superposition action (Ⅲ). The results showed that compared with the experimental treatment of water erosion only, freeze-thaw action decreased runoff depth in the Binxian, Hailun and Keshan mollic thikness regions by 29.4%, 39.3% and 32.1%, respectively; while it increased water erosion rate by 16.3%, 36.0% and 26.3%, respectively. The freeze-thaw and wind agent superposition actions decreased runoff depth in these three mollic thickness regions by 3.6%, 4.1% and 10.8%, respectively, but it increased water erosion rate by 38.5%, 102.1% and 64.1%, respectively. Under the experimental treatments, both sloping runoff depth and water erosion rates tended to increase from the thick mollic thikness region to the middle mollic thikness region and then to the thin mollic thikness region. The effects of freeze-thaw action and freeze-thaw + wind agent superposition actions on sloping water erosion rate among these three different mollic thickness regions were in orders of Hailun Mollisol > Keshan Mollisol > Binxian Mollisol. The freeze-thaw action reduced soil hardness and soil shear strength by 24.4% ~ 36.7% and 21.3% ~ 23.9%, respectively and increased soil erodibility, thus it increased sloping water erosion rate. The surface wind erosion formed the micro-morphology of wind erosion dent, which enhanced the surface flow concentration and increased flow velocity by 12.4% ~ 19.1%; then runoff depth erosivity and transport capacity were increased, thus sloping water erosion rate increased.

Abstract:Based on the monthly runoff data of Nuxia hydrological station in the Yarlung Zangbo River Basin from 1961 to 2015, the heuristic segmentation method was used to identify the year of abrupt runoff, and Mann-Kendall nonparametric test was used to analyze the long-term variation trend of runoff, and the concentration degree and concentration period were used to study the inner-annual changing patterns of runoff. The results indicated that: (1) The annual runoff showed a significant decrease trend first with the decreasing rate of 2.715 mm/year before 1992, and then an increase trend after 1992. (2) The runoff in the humid season accounted for 71.6%±4.4% of the annual runoff, which dominated the runoff dynamic change of the Yarlung Zangbo River Basin. After the turning point, the increasing of runoff in the dry season was another important reason for the increasing trend of annual runoff. (3) The annual runoff distribution in the Yarlung Zangbo River Basin presented a "smoothing phenomenon", that was, the occurrence time of the maximum runoff was delayed and the annual distribution was more uniform, which might be attributed to the restoration and improvement of vegetation coverage in the region. The results obtained in this study could lay a good foundation for further identifying the role of climate change and underlying surface in runoff change process, and provide practical suggestions and guidance for the sustainable development of regional ecological environment.

Abstract:This study aimed to quantitatively evaluate the effect of tillage erosion on runoff yield, sediment yield as well as hydraulic characteristics in the hilly croplands in the Dry-hot Valley Region by the simulated tillage and scouring experiments. Two forms of tillage erosion were adopted that one was the simulated tillage duration (10-, 20-, 30-, 35-, 40-year tillage) which caused the attenuation of soil thickness at the upper slope positions, and the other was the simulated soil flux (0, 12, 21 kg/m) which occurred in rills at the lower slope positions. Results showed that under the influence of tillage duration, both runoff yield and soil detachment rate displayed an increasing trend with the increase of tillage duration. Runoff stayed in the pattern of rapid laminar-flow for the treatment of 40-year tillage, while the slow laminar-flow for the other treatments. The drag coefficient and shear stress exhibited a decreasing and increasing trend as the tillage duration increased, respectively. Under the influence of soil flux, runoff yield rate was in a decreasing trend with the increase of soil flux while soil detachment rate was in an increasing trend. Runoff changed from the pattern of rapid laminar-flow to slow laminar-flow when the soil flux reached 21 kg/m. As the soil flux increased, drag coefficient presented an increasing trend and shear stress was in a decreasing trend. Reynolds number was the best hydrodynamic parameter which could explain the characteristics of hydraulic erosion under the influence of tillage erosion by correlation analysis. These results could provide scientific guidance for the exploration of soil erosion mechanism and treatment methods in the hilly croplands of Dry-hot Valley Region.

Abstract:To clarify the characteristics of flow-sediment movement process, changing tendency and movement state of Toudaoguai hydrologic station of the Yellow River, based on the flow and sediment data of Toudaoguai hydrological station in the Yellow River from 2006 to 2018, the flow-sediment movement process was systematically analyzed by using the cumulative anomaly, R/S range analysis, sediment coefficient and incoordination degree methods. The results showed that the inter-annual and monthly average variation of flow-sediment discharge in Toudaoguai station were well consistent, but the seasonal differences between them were significant, and the significance of sediment discharge was more prominent than runoff. Compared with other seasons, the synchronicity of variation trend of flow and sediment discharge in winter was worse. The Hurst index of seasonal revealed that the reverse persistence of the variation trend of sediment discharge, and the incongruity of flow and sediment in winter, could easily lead to erosion and deposition of the river channels. Based on sediment coefficient, which was the basis for the division of water and sediment states, the flow and sediment states were divided into three types, less water and more sediment was the characteristics of flow and sediment state in spring, summer and autumn, while in winter the state was more water and less sediment, and the flow-sediment coordination state appeared in spring of very few years. The incoordination degree of seasonal flow-sediment followed the order of summer > autumn > spring > winter. The special water and sediment inflow process, hydrological and climatic characteristics and human activities were the main factors influenced the imbalance of flow and sediment.

Abstract:Runoff yield from revegetated grasslands with different coverage of biocrust was measured by simulating rainfall in the study. Meanwhile, the relationship between biocrust coverage and CN value of SCS-CN model was analyzed. The results showed that: (1) Under a 90 mm/h rainfall intensity, the initial runoff yield time decreased against the increase of biocrust coverage, and the initial runoff time with low biocrust coverage (0~20%) was 1.64 and 2.46 times of that with medium biocrust coverage (40%~60%) and high biocrust coverage (80%~100%), respectively. (2) In the first 15 minutes of rainfall, biocrusts with high coverage promoted runoff yield compared with medium and low biocrust coverage. After 15 minutes, high biocrust coverage inhibited runoff yield compared with medium and low biocrust coverage. After 45 minutes of rainfall, runoff coefficient of each treatment tended to be stable. (3) There was a significant negative correlation between biocrust coverage and runoff depth, and runoff depth decreased in the form of logarithmic function with the increase of biocrust coverage (y=-13.87ln x+73.515,R²=0.761 4). (4) By adjusting CN value, SCS-CN model could be suitable for runoff estimation from biocrustal slope, and there was a significant negative correlation between biocrust coverage and CN value, the relational expression is that CN=-0.2672×C_BSC+79.0166,R²=0.680 0. In which, C_BSC was the percentage coverage of biocrust. In this study, the influence of biocrust on the parameters of runoff model was revealed, which was of great significance to the establishment of hydrological model considering biological crust.

Abstract:In order to study the influence of different runoff path regulation measures on the erosion characteristics of yellow soil slope in the east of Sichuan Province, three kinds of bare slope (25°, 30° and 35°, respectively) with sparse diamond grid (R1), dense diamond grid (R2) and contrast (R0) were set up. Based on the simulated rainstorm experiment, the erosion process and characteristics of slope surface under three rainfall intensities (60, 90 and 120 mm/h) were compared and analyzed. The results showed that: (1) On the slopes with the same gradient, under the rainfall intensities of 60 mm/h and 90 mm/h, the initial runoff production time followed the order of R0 < R1 < R2, when the rainfall intensity increased to 120 mm/h, the initial runoff production time was R0 < R2 < R1. (2) The runoff increased rapidly at first and then tended to be stable during the process of runoff production, the sediment yield rate decreased with the increasing of runoff time. (3) When the slope gradient was small (25°) or the rainfall intensity was small (60 mm/h), the average runoff and sediment yield rates followed the order of R0 > R1 > R2. When the slope gradient increased to 35 ° and the rainfall intensity increased to 120 mm/h, the runoff and sediment yield rates of R1 and R2 gradually approached or even slightly exceed that of R0 slope. (4) Corresponding to the process of runoff and sediment yield, under the different slope and rainfall intensity combinations, the benefit of sediment reduction was generally greater than that of runoff reduction on R1 and R2 slope, and the relationship between cumulative sediment yield and cumulative runoff could be expressed in power function. The results could provide reference for revealing the slope erosion process in the yellow soil area of East Sichuan, and provide scientific basis for the control of soil and water loss in this area.

Abstract:In order to study the regulation mechanisms of vegetation on rill erosion in a slope, the occurrence and development process of rill erosion with different grass spatial distributions were studied by artificial rainfall simulator and three-dimensional scanning technology. The results showed that the grass strip positioned at about 60% of the hillslope length from the top could fully exhibit its regulation effect on erosion by reducing the runoff and sediment by 7.4% and 62.9% respectively compared with bare slope. The grass strip showed direct sediment interception more than its water storage function. The regulation of vegetation on soil erosion was realized by regulating the rill formation, development and density in a slope, especially at the gully-slope. Moreover, vegetation not only changed the occurrence position of rill erosion, but also changed the erosion process and erosion pattern, the degree of erosion was greatly reduced with rill erosion transforming into sheet erosion. The information indicated that vegetation can regulate the erosion sedimentation processes by affecting the erosion pattern, and the results can be useful for better understanding the effect of vegetation configuration on rill erosion development morphology in a slope.

Abstract:A heavy storm occurred from 06:00 am August 10 to 06:00 am August 12, 2019, caused by Typhoon "Lichima", in Zibo, Dongying, and Weifang, Shandong Province. This storm caused severe soil erosion disaster. A survey was organized by the Water and Soil Conservation Monitoring Center of the Ministry of Water Resources to conduct a systematic and comprehensive field survey of soil and water conservation. The survey was taken in typical small watersheds just in the rainstorm center, and modern technology was utilized. The characteristics of runoff and sediment transport, soil erosion rate, disaster, and the effectiveness of soil and water conservation measures were surveyed. The methodology for soil and water conservation survey with heavy storm was primary established based on the results and processes of this survey. This survey could provide an essential information for future establishment of a legal system of heavy storm soil and water conservation survey.

Abstract:In order to systemically evaluate soil water conservation function under the different conversion patterns after implementation of "The Grain For Green" program in the hilly and gully region of the Loess Plateau. This study selected 0-200 cm soil water storage, stratification ratio of soil water content, soil moisture suction, and inter-annual change rate of soil water content as the representative indicator of storage, infiltration, maintenance and stability of soil, which is to compare soil hydrologic properties separately in different patterns. The results showed that: (1) Soil water storage (SWS) under different conversion patterns was significantly different. The maximum SWS of grassland model was about 1.6 and 1.7 times of that under shrub and arbor model; (2) The arbor forest pattern had the best permeability of surface soil water and the biggest permeability potential of deep soil water; (3) Soil water retention under different conversion patterns was significantly different. The arbor forest pattern had the best soil water retention capacity; (4) The grassland pattern had the best stability of SWC, and the stability of SWC within 0-200 cm of each model had an inflection point around 30 years. The annual change rate of SWC changed from negative to positive, and the soil layer below 120 cm was more stable.

Abstract:Studying on the effectiveness of natural rainfall on the water restoration in the dried soil was conducive to use precipitation rationally, to strengthen the management of the dried soil water, and to promote the effective restoration of the soil dry layers. By setting a large underground soil column in Mizhi test station located in northern Shaanxi, the precipitation and soil moisture content were monitored continuously from 2014 to 2019. And the effectiveness of natural rainfall for the remediation of dry soil moisture was analyzed. The results showed that: (1) From the perspective of water remediation in deep dried soil, rainfall in the semi-arid loess hilly region could be divided into three types: surface layers infiltration with rapid evaporation, shallow layers infiltration with slow evaporation and deep layers infiltration with water recharge. The type of deep layers infiltration with water recharge rainfall was effective, and others were ineffective. The precipitation of this type was usually greater than 26 mm and could effectively recharge water to the deep dried soil. From 2014 to 2019, there were only 16 times of deep layers infiltration with water recharge rainfall, and the cumulative precipitation was 791.8 mm. The precipitation frequency and effective rate were 4.64% and 35.19%, respectively. (2) On a monthly scale, the precipitation (P) showed the quadratic function changes with the monthly infiltration depth (Z) and monthly cumulative infiltration depth (Z_accumulation): Z=-0.0102P_month²+3.955P_month-6.7335(R²=0.963 9), Z_accumulation=-0.0003P_month²-0.1331P_month+191.71(R²=0.920 8). (3) On the annual scale, the precipitation from 2014 to 2019 was 187.6, 391.6, 590.8, 337.6, 342.4 and 400.0 mm in sequence. The infiltration depths caused by rainfall year by year were 160, 220, 400, 260, 260 and 120 cm, and the cumulative infiltration depths were 180, 220, 400, 700, 1 000 and 1 400 cm, respectively. The research results played a positive role in revealing the mechanism of natural precipitation restoration of dried soil, strengthening the technology of artificial water storage and soil moisture conservation in the dried layers, selecting the measures of soil moisture conservation rationally and promoting the local ecological environment construction.

Abstract:In order to clarify the quantitative relationship between the moisture vertical migration and the main influencing factors during soil freezing-thawing process, a unidirectional freezing-thawing simulation test was carried out using typical black soil in Northeast China, under the conditions of different initial moisture contents, temperature drop ranges, and groundwater levels. The results showed that: (1)The temperature changes in the samples were fast first and then slow, and the internal temperature of the samples showed a stable temperature gradient distribution with the variations of the depths. (2) The influence of initial moisture content on soil freezing was obvious. The higher the initial moisture content of soil was, the longer the duration of freezing process was, and the larger the latent heat consumed in the freezing process was, and the later the formation time of freezing front was. (3) Various temperature drop ranges caused the obvious difference of soil temperature gradients. The migration of water in the vertical direction was the largest with the temperature changes at 15 ℃, the soil entered the freezing stable stage at fastest speed, and the moisture content near the 20 cm soil layer reached the peak value after 16 hours. (4) The higher the groundwater level was, the smaller the temperature difference was, the slower the downward migration rate of the freezing front was. The water content in each layer increased significantly, and accumulated in the upper and middle layers.

Abstract:To provide basic hydrological data for sustainable management of south subtropical forest plantations, we measured rainfall, throughfall, stemflow and canopy interception in a 30-year old Pinus massoniana stand at Guangxi Youyiguan Forest Ecosystem Research Station from January to December 2018. The results showed that total annual rainfall was 1 303.6 mm, with throughfall, stemflow and canopy interception accounting for 60.9%, 0.4% and 38.7% of total rainfall, respectively. The minimum rainfall that produced throughfall and stemflow was 0.4 and 2.2 mm, respectively. Among the four rainfall factors (rainfall amount, rainfall intensity, rainfall duration, and interval time between two rainfall events), rainfall amount had the strongest effect on rainfall distribution pattern. Rainfall intensity and rainfall duration had a significant impact on throughfall, throughfall rate, stemflow, canopy interception, and canopy interception rate. Interval time between two rainfall events only had a significant impact on throughfall, stemflow, and canopy interception. Results of multiple linear regression analysis showed that the responses of the three components of rainfall partitioning to rainfall characteristics were not synchronized, with throughfall and canopy interception being more affected by rainfall characteristics than stemflow.

Abstract:In this study, five typical forest lands (Poplar Populus×Quercus liaotungensis natural secondary forest, Pinus tabulaeformis×Robinia pseudoacacia mixed forest, artificial Pinus tabulaeformis forest, artificial Robinia pseudoacacia forest, and artificial Platycladus orientalis forest) in the Caijiachuan watershed of the loess area in west Shanxi were selected as the research object. A soil moisture observation point was placed in the center of each plot, and the soil volumetric water content from January 2016 to December 2018 were determined by the TRIME-TDR soil moisture analyzer, and the soil moisture in 0-200 cm soil layer was determined stratified with every 20 cm respectively in the early, middle and late of each month. Then the annual variation and the vertical variation of soil moisture in different forest types were analyzed. The results showed that (1) annual variation of soil moisture in different forest lands in this study area could be divided into four periods, including stationary period (January-March), fluctuation period (April-June), growth period (July-September) and consumption period (October-December), and the average soil water storage of the five forest types during the year followed the order of the natural secondary forest land (338.68 mm) > artificial P. tabulaeformis forest (319.74 mm) > artificial P. orientalis forest (314.15 mm) > the mixed forest land(303.37 mm) > the R. pseudoacacia forest (292.03 mm), and the water consumption of R. pseudoacacia forest land was the highest. (2) At the end of the rainy season, the soil moisture of the five forest types in the study area was positively supplemented, and the soil water recovery capacity followed the order of natural secondary forest land > coniferous forest land > mixed forest land > R. pseudoacacia forest land. (3) The vertical change of soil moisture in the study area could be divided into two layers, including the rapid change layer of soil moisture content and the relatively stable layer of soil moisture content. As the soil layer depth increasing, the average water content of different forest profiles generally increased first and then decreased. Surface soil moisture content of different forest types followed the order of P. orientalis forest > natural secondary forest land > P. tabulaeformis forest > mixed forest land > R. pseudoacacia plantations. Replenishment depth of soil moisture followed the order of natural secondary forest land > coniferous forest land > mixed forest land > R. pseudoacacia forest land.

Abstract:Soil conservation (SC) is the primary ecological service function of the Loess Plateau, which is vital to the sustainable development of ecological economy in Loess Plateau. Therefore, it is necessary to carry out research on changes and its influencing factors of soil conservation in this area. In the context of Grain for Green Project, the spatiotemporal changes and its influencing factors of soil conservation services in Ziwuling (ZWL) from 2000 to 2017 were analyzed by using the InVEST Sediment Delivery Ratio Module, spatial autocorrelation, geographic detector and other methods. The results showed that a large amount of cultivated land in ZWL area changed into woodland and grassland from 2000 to 2017, and the soil conservation service showed an increase trend. Among them, the amount of soil conservation per unit area of woodland was the highest. The soil conservation service first increased and then decreased with altitude, and increased with the increasing of slope. The amounts of soil conservation in the west slope and east slope were the highest. The spatial autocorrelation of soil conservation variation was high in ZWL area, and the main aggregation types were high-high and low-low. The high-high concentration area located in the northeastern part of ZWL, and the low-low concentration area mainly distributed in the northwestern part. The changes of influencing factors had an interactive enhancement effect on soil conservation changes, and NDVI was the most important factor in high-high aggregation area. The low-low aggregation area was mainly affected by the changes of precipitation and land use intensity, and the insignificant area was weakly affected by each factor. The soil conservation changes of whole ZWL area were mainly affected by the changes of precipitation, GDP density, population density and NDVI.

Abstract:Soil hydraulic parameters are critical to the numerical simulation of land surface processes such as soil moisture and pollutant transport. This study aimed to explore the spatial variation characteristics and influencing factors of soil hydraulic parameters, and then simulated these parameters through indirect method in classic cultivated area. A total of 124 sampling sites were set up in the Guanzhong Plain area, and undisturbed and disturbed soil samples at the depth of 0-20 cm were collected separately at each sampling site. Soil retention curve was estimated by the van Genuchten (VG) model and the hydraulic parameters (i.e. θ_r, residual water content; θ_s, saturated water content; α and n, shape coefficients) of the VG model were calculated. Classical statistics, geostatistical and structural equation methods were used to determine the spatial variation characteristics and influencing factors of θ_r, θ_s, α and n, and the prediction model of hydraulic parameter pedo-transfer functions was established. The results showed that the variability of n and θ_s was weak and moderate, respectively; while θ_r and α had strong variability. Semi-variance functions of θ_r, θ_s, α and n could be best fitted by the spherical model, the exponential model, the exponential model and the spherical model, respectively. θ_s and n exhibited strong spatial dependence, with the range of 32.7 and 54.3 km, respectively. θ_r and α exhibited moderate spatial dependence, with the range of 52.8 and 52.8 km, respectively. Soil texture, bulk density, pH, organic matter and elevation were the main direct factors affecting soil hydraulic parameters. The pedo-transfer functions model of hydraulic parameters based on soil physical and chemical properties and elevation had good simulation effect, and could be used to simulate and predict soil hydraulic parameters of large-scale farmland ecosystem in the Guanzhong area.

Abstract:This study employed GIS and geostatistics technology to explore the spatiotemporal variations of vegetation from 2000-2018 by using the normalized vegetation index (NDVI) from MODIS images. The potential of vegetation restoration in the Loess Plateau was predicted by similar habitat method. The results showed that during 2000-2008, the area with low vegetation coverage decreased, while the area with high vegetation coverage increased in the Loess Plateau. The vegetation cover showed evident increasing rate (0.015 ~ 0.050/year) in the region between Toudaoguai and Longmen, and significant increasing (over 0.015/year) in vegetation cover were examined in the Yanhe, Qingjian and Tuwei River basin. A significant decreasing in the vegetation cover was observed in the downstream of Wei-Fen plain due to rapid urbanization. Similar habitat method indicated that the spatial difference of future vegetation restoration potential was significant, and the vegetation cover in the southeastern Loess Plateau had reached its maximum recovery potential, therefore there was no restoration space. There was still 25% ~ 50% potential for vegetation cover increasing in the cross areas of hilly gully and windy sandy areas. Due to the influence of the project of returning farmland to forest and grassland, the artificial vegetation had strong interference, and considering the limitation of the rainfall and water carrying capacity of the this region, we proposed that future vegetation restoration should focus on selecting local plant species, optimizing vegetation structure to improve ecological service functions. The results of this study could provide theoretical and methodological support for future vegetation restoration and soil and water conservation in the Loess Plateau.

Abstract:Soil fertility and nutrient use efficiency are the basis for sustainable food production. A field experiment was conducted to investigate the effects of different fertilization modes on nitrogen use efficiency of crops and available nutrient balance in soil with a rice-wheat rotation. The results showed that the rice shoot biomass of RF-OM and RF-S treatments with the reduced total nutrient inputs were significantly higher than that of LRF treatment (P < 0.05), similar to that of FP treatment. The differences of wheat straw biomass among the four fertilization treatments were not significant, the wheat grain biomass and shoot biomass of RF-OM and RF-S treatments were similar to that of LRF treatment. At rice harvesting stage, the nitrogen contents in the main shoot organs of RF-OM treatment was similar to those of LRF treatment, but the total nitrogen amount accumulated in shoots was significantly higher than that of LRF (P < 0.05). For wheat plants, the nitrogen contents and accumulation amounts in straws or grains of RF-OM and RF-S treatments were not significantly different from LRF treatment. At rice or wheat harvesting stage, the phosphorus contents and accumulation amounts in brown rice, rice husks, wheat straws and grains of RF-OM and RF-S treatments were not significantly different from FP and LRF treatments. As a result of increasing potassium doses, potassium contents and accumulation amounts in rice straws, rice husks and wheat straws were significantly higher than those of FP or LRF treatments (P < 0.05). Nitrogen agronomic efficiency, nitrogen apparent recovery and nitrogen partial factor productivity of RF-OM and RF-S treatments for rice or wheat were significantly higher than those of FP or LRF treatment (P < 0.05), the nitrogen grain production efficiency was also higher than that of FP or LRF treatment, even significantly (P < 0.05). At rice or wheat harvesting stage, soil exchangeable and slow-release potassium concentrations of RF-OM and RF-S treatments with raising potassium dosages were significantly higher than those of FP and LRF treatments. Soil alkali-hydrolyzed nitrogen concentrations at rice harvesting stage and soil available phosphorus concentrations at wheat harvesting stage of RF-OM and RF-S treatments were not significantly different from LRF treatment. After a whole rice-wheat rotation, concentrations of soil available nutrients (alkali-hydrolyzed nitrogen, available phosphorus, exchangeable potassium, slow-release potassium) of the four fertilization treatments were all higher than those of the initial soil. Organic manure used as an alternative for chemical fertilizers is able to significantly increasing crop nitrogen use efficiency, being conducive to the balance of soil available nutrients and significant increases in the concentrations of soil exchangeable potassium and slow-release potassium, which can be regarded as a suitable technique for reducing application of chemical fertilizers, stabling grain yields and increasing fertilization efficiency in rice and wheat cropping.

Abstract:In order to explore the variation characteristics of soil water storage and the potential yield improvement of dryland wheat by different tillage practices in south area of Shanxi Province. Field experiments were conducted to investigate the effect of two consecutive years tillage models (no tillage + drilling sowing, no tillage + furrow sowing, subsoiling + drilling sowing, and deep tillage + drilling sowing) on soil water storage, yield and water use efficiency of dryland wheat with Jinmai 92 as experimental material. The results showed that under no-tillage condition, furrow sowing performs more soil water storage in 100-200 cm depths compared with drilling sowing. The increasing effect of furrow sowing on wheat yield showed weak and even slightly decreased in drought years of 2018-2019. Furthermore, furrow sowing decreased water use efficiency by 3.6% and 9.3% during the two years, respectively. Subsoiling and deep tillage in fallow period increased soil water storage of 0-200 cm before sowing and regreen stage, of which deep tillage performed excellent in water contention. Besides, the increasing effect was mainly concentrated in 0-100 cm depth. During the two experimental years, deep tillage increased yield greatly by 44.6% and 147.2%. There was significant positive correlations between yield and aboveground biomass and grain numbers per spike. Subsoiling and deep tillage increased water use efficiency by 12.7%, 46.74% and 53.70%, 94.91% during the two years, respectively, and the more obvious effect was obtained in the drier year of 2018-2019. Therefore, deep tillage and subsoiling for two consecutive years in fallow period can improve the water storage capacity and the yield, water use efficiency of dryland wheat. The effect of furrow sowing on wheat yield under no tillage condition varies with different years, which needs further discussion.

Abstract:A reasonable and efficient rotation sequences were established to solve the problem of replanting obstacles caused by continuous cropping of crops via determining the level of soil nutrient immobilization and residue under annually fallowing and seasonally planting different crops. The nutrients contents of 0-20 cm black flax soil under fallowing, and planting spring wheat, potato, Mongolian astragalus and Angelica sinensis were investigated. The field trial was followed by the single-factor randomized block design in Zhanpo village, Lianfeng town, Weiyuan, Gansu in 2018 and soils were sampled by "S" shape. The results showed that the contents of organic matter, total nitrogen, available phosphorus, available potassium, total anion and anion, Mg²⁺, SO₄^2- and Cl^- in 0-20 cm soil layer respectively were increased for annually fallowing and seasonally planting Mongolian astragalus. however, the contents of organic matter, total nitrogen, available phosphorus, available potassium, total amount of ions and ions, Mg²⁺, SO₄^2- and Cl^- in 0-20 cm soil layer were decreased for annually planting Angelica sinensis. The variance analysis showed that the contents of organic matter, total nitrogen, available phosphorus, available potassium, total anion, Mg²⁺, SO₄^2- and Cl^- in 0-20 cm soil layer were significantly higher for annually fallowing and seasonally planting Mongolian astragalus than those for seasonally planting Angelica sinensis. The principal component regression analysis showed that the soil fertility composite index scores respectively were up to 0.98 and 0.56 for annually fallowing and seasonally planting Mongolian astragalus, while the soil fertility composite index score was down to 0.07 for seasonally planting Angelica sinensis. This demonstrated that annually fallowing was a simple and effective method for combination of land utilization and maintenance in black flax soil, while seasonally planting Mongolian astragalus was an effective rotation sequence to improve soil fertility in black flax soil.

Abstract:The typical black soil areas of Jilin Province were studied under corn, paddy, orchard, forests and vegetable fields. We used the indoor cultivation method to study the morphological transformation characteristics of nitrogen in black soil with different land use patterns. The application of nitrogen fertilizer increased the contents of ammonium nitrogen and nitrate nitrogen in black soil with different land use patterns. The difference of ammonium nitrogen contents was not significant, but the difference of nitrate nitrogen contents was significant. For the urea treatment, the contents of nitrate nitrogen S2 (129.82 mg/kg) and C2 (138.01 mg/kg) were significantly higher than those of G2 (111.89 mg/kg) and D2 (105.35 mg/kg). The nitrate nitrogen content of Y2 (126.92 mg/kg) was significantly higher than that of D2. The analysis of the treatment of diammonium phosphate showed: The order of the nitrate nitrogen content of each soil was C3 (160.23 mg/kg) > Y3(150.00 mg/kg) > S3(140.12 mg/kg) > G3(133.45 mg/kg) > D3(126.70 mg/kg). The nitrate nitrogen content of C3 and Y3 was significantly higher than those of G3 and D3. Moreover, soil net mineralization rate and net nitrification rate were significantly negatively correlated with soil C/N, soil microbial biomass carbon, and soil microbial biomass nitrogen. During the whole cultivation period, the order of the average NMR of Y, G, C and D soils were as follows treatment 1 > treatment 2 > treatment CK. The average NMR of S soils were in the order of treatment 2 > treatment 1 > treatment CK. The average NR of Y, G and D soils were in the order of treatment 1 > treatment 2 > CK treatment, and the average NR of S and C soils were in the order of treatment 2 > treatment 1 > treatment CK. These results showed that the physical and chemical properties of the soil had an important influence on the characteristics of nitrogen conversion in black soil.

Abstract:This study was aimed to explore the optimal water and nitrogen allocation of winter wheat and achieve the efficient utilization of nutrient and water resources. Three irrigation supply levels (low, 25 mm, W1; moderate, 40 mm, W2; high, 55 mm, W3) and five nitrogen supply levels (N0, 0 kg/hm²; N1, 80 kg/hm²; N2, 180 kg/hm², N3, 240 kg/hm², N4, 300 kg/hm²) were designed to optimize the crop irrigation and fertilization. There were 15 treatments in total. The effects of irrigation, nitrogen application and their interaction on the grain filling characteristics and water and nitrogen use efficiency were explored, meanwhile, optimal water and nitrogen supply rates were solved by modeling.The results showed that t_e (grain-filling lasting time) and t_m (the time when maximum filling rate occurred) were affected by fertilization significantly, both of which increased first and then decreased as nitrogen application rates increased. t_e and t_m at N3 level were the largest, with an average of 43.9 and 24.6 days, which were 1.7 and 3.0 days longer than that of N0. The largest t_m value was obtained at W2N3 treatment, which happened 5.0 days later than W1N0 did. GF_max (maximum grain filling rate) and AG (average grain filling rate) exerted extremely significant correlation (r=0.841^**), 1000-kernel weight was extremely positive correlated with yield (r=0.791^**), t_e (r=0.755^**) and t_m (r=0.717^**). The highest grain yield and water use efficiency were obtained at W2N3 treatment with the maximum of 8 960 kg/hm² and 2.83 kg/m³. Water and nitrogen coupling efficiently improved yield of winter wheat by optimizing grain filling process. Optimal irrigation quota of sprinkler was 26~35 mm, nitrogen application rate was 193~204 kg/hm² (basal application 40% and topdressing 60% at jointing stage) achieved the goals of water-saving and yield-increasing.

Abstract:In order to understand the effect of microtopography on vegetation restoration and soil physical properties, exploring the influence mechanism between grassland restoration and soil physical properties and to provide scientific basis for local ecological restoration. This study choose the Zaozhuanggou basin in Wuqi county as the study area, vegetation restoration and soil physical properties differentiation characteristics on the different landscape positions were studied. We chose 4 slopes and set eight sampling positions on every slope from top to bottom, a total of 128 sampling points of vegetation investigation and soil samples collected in this study. The soil was divided into three layers 0—10, 10—20 and 20—40 cm for sampling and determining soil physical properties, analyzed the correlation between vegetation distribution and soil physical properties. The results showed that the vegetation distribution and soil physical properties on different landscape positions showed the tendency of lower slope better than others above the groove line, and the bottom slope is worst. The vegetation restoration has improvement effect on soil aggregate, the improvement of soil aggregate and soil physical properties caused by vegetation restoration was mainly concentrated on the surface soil of 0—20 cm, and weak in the soil of 20—40 cm. Gradient has a significant impact on vegetation coverage, soil bulk density, porocity and saturated water capacity. But it has no significant effect on the soil aggregate and soil particle composition. The effect of vegetation restoration on improving soil particle composition is slow. If the soil particle composition is destroyed, it will be difficult to recover in the short term.

Abstract:The X-ray computed tomography (CT) technique was used to study the effects of different rape intercropping densities (CK: clean tillage; L: low-density intercropping; M: medium-density intercropping; H: high-density intercropping) on the characteristics of soil macropores in the apple orchard. The results showed that compared with the CK, rape intercropping improved the characteristics of soil macropores between rows of apple trees (0—60 cm), and the number of soil macropores, macropores' area and macro porosity in each soil layer were significantly higher (P<0.05). The effects of different intercropping densities on the macropores were different in the same soil layer, except for 10-20 cm, the improvement effect of the medium-density intercropping on soil macro porosity was significantly better than that of other treatments. Under the medium-density treatment, the number of macropores (d > 1 mm) was large, and the difference in macropores number between soil layers was small, and the rounding rate was the highest in 0-30 cm soil profile. The soil macropore characteristic parameters of medium and high-density rape intercropping were better than those of the clean tillage and low-density treatments, and that in the medium-density intercropping treatment, the distribution of macropores was more uniform and the shape was more regular, which was an appropriate intercropping density to improve soil structure for dryland apple orchards in the Loess Plateau.

Abstract:In order to study the influence of multiple factors on soil water movement characteristics of muddy water film hole fertilizer solution infiltration, indoor soil box infiltration test was carried out. Four experimental factors including initial soil moisture content, soil bulk density, sediment concentration of muddy water and fertilizer solution concentration, 3 levels for each factor, and 12 groups of experiments (9 of orthogonal experiments and 3 of validation experiments). The effects of each factor on cumulative infiltration volume per unit membrane hole area, infiltration rate and average volume water content increment of muddy water membrane hole irrigation fertilizer solution were analyzed. The empirical model and model parameters of cumulative infiltration per unit membrane pore and average volume moisture content increment of wetting body with experimental factors were deduced and verified by multiple regression. The results showed that the initial moisture content of the soil, soil bulk density and sand content and fertilizer concentration had a significant effect on the cumulative inlet of the unit membrane hole (P<0.01). The degree of influence from large to small was the sand content, soil bulk density, the initial soil moisture content, the concentration of fertilizer. The increase in the average moisture content of the wet body was almost independent of the permeation time. The initial moisture content, sand content and fertilizer concentration of the soil were significantly related to it (P<0.01), and the soil weight was significantly related to it (P<0.05), and the degree of influence from large to small was the initial moisture content of the soil, fertilizer concentration, sand content, soil bulk density. The empirical model and model coefficient established were qualified. The error between the predicted and the measured values was within ±10%, and the precision was good, which could be used to predict the soil moisture infiltration situation when the experimental factors were different.

Abstract:In order to investigate the effects of different irrigation and fertilization conditions on the growth of maize at different fertility stages in the Loop irrigation area, three irrigation levels of low water (1 800 m³/hm²), medium water (2 250 m³/hm²) and high water (2 700 m³/hm²), and three fertilization levels of low (300 kg/hm²), medium (375 kg/hm²) and high (450 kg/hm²) fertilization were investigated using maize "Jinping628" as the material, respectively. At the same time, the local irrigation and fertilization amount were used as the control group (CK). The effects of 10 treatments on soil moisture, nutrient and maize growth in the seedling stage, jointing stage, tasseling stage, filling stage and maturity stage were analyzed. Based on the results, it was found that the average soil water content tended to decrease after the pulling stage. Maize water consumption was highest during the pulling and filling stages, accounting for more than 65% of water consumption during the entire reproductive period. Soil nitrate-nitrogen accumulation was minimal during the pull-out stage, and plants absorbed large amounts of nutrients for rapid maize growth. Under high water levels, maize yield and water-use efficiency tended to increase and then decrease with irrigation and fertilization. Through multiple stepwise regression analysis, the effects of soil moisture and nutrients on maize growth in different growth stages were screened out. The results showed that soil moisture had a greater influence on maize growth than soil nutrients at tasseling, filling and maturity stages, and soil nutrients at jointing stage had a greater impact on maize growth than soil moisture. The results of the study can provide a theoretical basis for water conservation and reduction of chemical fertilizer use in the loop irrigation area, rational allocation of water resources, reduction of nitrogen surface pollution, and ensuring stable growth of maize.

Abstract:In order to identify the amelioration of uncultivated saline wasteland, transformation of phosphorus (P) fraction after different plants plantation in the Yellow River Delta, we investigated the dynamics of P fractions and availability after the uncultivated saline wasteland with reed (RU) was reclaimed by plantation of Chinese tamarisk (CT), Chinese ash (CA) and clover (C). Results showed that the phosphatase activity of 0—20 cm soil were significantly increased by 3 plants plantation compared with RU. CT plantation significantly decreased soil pH of 0—20 cm soil, while it significantly increased soil organic carbon (SOC) concentration of 0—40 cm soil and promoted the formation of large size aggregate particles of 0—20 cm soil, but it significantly increased soil salinity of 0—100 cm soil and accelerated transformation of P fractions from soluble P (Ca₂—P) or slowly soluble P (Ca₈—P and Al—P) to insoluble P (Ca₁₀—P) that reduced P availability. CA plantation could significantly decrease soil salinity of 0—100 cm soil and pH of 60—100 cm soil, while it accelerated transformation of P fractions from insoluble P (O—P) to slowly soluble P (Fe—P), but it increased ratio of small size aggregate particles of 0—20 cm soil and decreased SOC concentration of 0—40 cm soil that were beneficial to improve P availability. C plantation could significantly increase soil available P concentration of 0—20 cm soil with improved soil phosphatase activity of 0—20 cm soil which was much higher than those of other 3 plants. While it accelerated transformation of P fractions from insoluble P (O—P) or slowly soluble P (Ca₈—P and Al—P) to soluble P with accelerated formation of large size aggregate particles of 0—20 cm soil. Soil microbial nitrogen was significantly increased by plantation of CT, CA and C, but soil microbial carbon and soil microbial phosphorus were significantly decreased. No significant difference was observed on soil respiration and urase activity. In this study, Chinese ash plantation could decrease soil salinity and soil pH, while clover plantation could promote soil P availability of 0—20 cm soil. Plantation of all 3 plants had no significant beneficial effect on P availability in 20—100 cm soil. However, more research is necessary to explore the long-term dynamics of soil microorganisms community and regulation mechanism on P fraction by soil microorganisms in the saline land.

Abstract:In order to find out the spatial distribution characteristics of soil saturated hydraulic conductivity (Ks), 136 undisturbed soils were collected in Ningdong. The spatial structure characteristics of Ks were analyzed by classical and geostatistical methods. Taking terrain factors and soil properties as auxiliary variables, the regional soil Ks were predicted by the random forest method (RF), ordinary Kriging method (OK) and stepwise regression Kriging method (RK), and the accuracy of the prediction results of the three methods were evaluated. The results showed that Ks ranged from 0.05 to 7.13 mm/min, with an average value of 1.46 mm/min and a coefficient of variation of 106.86%. Ks had autocorrelation and cross-correlation with bulk density, porosity, elevation, slope, aspect, plane curvature and section curvature under different lag distance. The nugget value of soil Ks was 38, indicating that the variability of soil Ks caused by random factor was large, and the spatial heterogeneity ratio was 15.32%, showing strong spatial variability. The prediction accuracy of RF was the highest, and the absolute values of mean relative error (MRE) and root mean square error (RMSE) were both the smallest. Compared with OK and RK, the prediction accuracy of RF was improved by 5.53% and 2.49%, respectively, and the description of local details was more accurate and the simulation effect was the best. RF could accurately predict soil Ks in Ningdong, and provide data reference for understanding soil hydrological process and forest and grass vegetation construction in the study area.

Abstract:A better understanding on the effect of biochar derived from different straw types on soil infiltration and evaporation is of great significance for resource utilization of agricultural straw waste and efficient use of soil and water resources. In the present study, by using the soil column simulation investigation, biochars derived from three straw materials (oilseed rape stalk, quinoa stalk, and potato stalk) were used to explore the effect of biochar from different raw materials on soil wetting process, the cumulative infiltration amount and evaporation. The results showed that biochars derived from different feedstocks had significant effect on soil infiltration and evaporation. Biochar derived from potato stalk accelerated significantly the advancement of wetting front, while the ones derived from oilseed rape stalk, quinoa stalk slowed down the mid-late wetting process. Overall, biochar addition improved early soil infiltration rate and decreased stable infiltration rate in late period. Among the three tested biochars, the one derived from potato stalk performed the best in improving soil infiltration, with the cumulative infiltration 67.8 mm after 55 minutes, which was 41.8% higher than control treatment without biochar addition. The Kostiakov model performed best in simulating soil infiltration with biochar addition. Biochar addition had no significant effect on early soil evaporation, but increased significantly the later soil evaporation rate. After the successive evaporation of 30 days, the cumulative evaporation rates with biochar addition derived from potato stalk, oilseed rape stalk, and quinoa stalk were 5.2%, 9.2% and 10.2% respectively higher than CK. Our results suggest that biochar derived from potato stalk could improve soil infiltration ability, which provides scientific basis for choosing reasonable biochar raw materials in the eastern Qinghai Province.

Abstract:Groundwater recharge is the main source of water replenishment of surface vegetation in the arid desert areas, and the depth of groundwater is closely related to the vegetation index NDVI. In view of the shortcomings of the research on the relationship between NDVI and groundwater depth change, this paper carried out a quantitative relationship between NDVI and groundwater depth (H) based on the Jiefangzha irrigation area in the Hetao Irrigation District. Using ten landsat8 remote sensing image data from March 2016 to the end of September 2016 and 57 groundwater observation data in the same period, the spatial and temporal dynamics of NDVI and groundwater depth (H) were obtained by geostatistical analysis. On this basis, the spatial and temporal correlation between NDVI and H was established through ArcGIS, and the significance test and the degree of closeness were divided. The quantitative relationship between H and NDVI in different groundwater depth zones was further analyzed. It was concluded that there was a significant linear relationship between NDVI and H. The close degree of NDVI and H was mainly moderate and high correlation. The negative correlation area was concentrated in the shallow groundwater area, and the positive correlation area was concentrated in the deep groundwater area. In terms of space, the linear relationship with statistical significance accounted for about 40% of the total irrigation area. When H ≤ 2.5 m, the influence of different groundwater depth zones on NDVI mean value showed a negative correlation change; while when H > 2.5 m, the mean value of NDVI was larger, and the groundwater did not supply water for crop growth. Therefore, the increase of NDVI mean value had little relationship with the change of H division. Carrying out the point-to-point correlation analysis of NDVI and H in space could enhance the spatial visibility of the correlation between the two, provide theoretical support for irrigation management in irrigation districts, and contribute to the in-depth planning and implementation of water-saving and production-increasing measures.

Abstract:The application of soil saline-alkali modifier is very important for soil improvement and crop growth, the organic acid-rich modifier is widely used because of its non-toxic and harmless effect. This paper selected the "hekang" saline-alkali scavenger as a typical organic acid modifier (hereinafter referred to as OA) through the indoor one-dimensional soil column infiltration test, and set up four groups of application content gradients (0.140, 0.145, 0.150 and 0.155 g/cm²), with the treatment without OA as the control. At the same time, different OA application depth(0-10,15-20,25-30 cm) was also set to study the influence of OA on water and salt migration in saline-alkali soil. The results showed that mixed OA treatment with the increase of the applied amount, the soil infiltration capacity was decreased, as well as the steady infiltration rate. By fitting the infiltration process by Philip and Green-Amp infiltration models, the Philip model calculation parameters and fitting parameters calculated by the model parameter extrapolation relationship were in good agreement, and the relative errors were 9.82% and 2.23% respectively, which indicated that the Philip model is more suitable for the infiltration process with the application of organic acid modifier in soil. Both the absorption rate S and the steady permeability A decreased, and the saturated water conductivity K_S and the soil water suction S_f decreased. Furthermore, the addition of OA could improve the water holding performance of soil and significantly improve the desalination rate of soil. After layer application OA treatment, with the increase of layer application depth, the cumulative infiltration increased, the steady permeability decreased, and the desalination rate of soil did not increase significantly. It is hoped that the organic acid modifier could provide theoretical basis for the application of saline-alkali soil.

Abstract:In order to explore the comprehensive control measures of soil salinity in the Hetao irrigation area, taking the Jiefangzha irrigation area as an example, the effects of irrigation water salinity, the mixing ratio of saline and fresh water, the depth of drainage ditch and the level of channel lining on soil salinity in root zone were studied using the SaltMod model. The results showed that the soil salinity in the root layer increased with the increase of the irrigation water salinity, and the surface brackish water of 1.0 g/L was more suitable for irrigation in this study area; when the mixed irrigation ratio of fresh water (Yellow River water) and underground brackish water (salinity is 2.2 g/L) was 1：1, the utilization of underground brackish water was increased and the groundwater depth dropped to a relatively stable balance of about 2 m. status; when the drainage depth was between 1.5 and 2.0 m and the canal utilization coefficient reached 0.7, the root layer salinity was significantly reduced. Appropriately increasing the drainage depth and canal water utilization coefficient could effectively reduce the accumulation of soil salt induced by high-salinity irrigation water. The results of this study could provide a scientific theoretical basis for formulating reasonable comprehensive control measures for soil salinity in the Jiefangzha irrigation area of the Hetao Irrigation District.

Abstract:Withered Litters from Leymus chinensis, Stipa breviflora and Leymus chinensis + Stipa breviflora were taken as the research object. The decomposition bag method was used to measure the residual rates of different litters through a simulation experiment, and to analyze the release law of litter elements and the influence on soil properties during the decomposition process. The results showed that: (1) During the whole test period, the residual rates and mass loss rate sof different litters showed a slow-fast trend, and the decomposition rates showed Leymus chinensis + Stipa breviflora > Stipa breviflora > Leymus chinensis. The litter decomposition in the test area could be well fitted by Olson model. Decomposing 50% and 95% of different litters needed 2.79~3.15 and 12.05~13.62 years, respectively. (2) After 360 days of decomposition, the total C, N and P of different litters all showed the state of release (NAI < 100%), and the total C showed the characteristic of fluctuating release, with the release ratio ranging from 47.88% to 54.54%. Total N and P showed the characteristics of release-enrichment-release, with the release ratios of 36.34%~47.87% and 57.08%~74.71%, respectively. (3) Decomposition of different litters increased the contents of soil organic C, N and P, which increased by 1.41~1.50 g/kg, 1.27~1.40 g/kg and 0.14~0.15 g/kg respectively compared with the initial values. These research results could provide theoretical basis for the element circulation process of grassland ecosystem.

Abstract:In this study, a series of field microfield experiments were set to explore the effect of amendments on aggregates composition and organic carbon distribution in reclaimed soil. Peat, humic acid and vermiculite as amendments were added to the soil (0-20 cm) at the weight ratios of 1%, 3% and 5%. Soil aggregates composition, total organic carbon, organic carbon distribution in each fraction aggregates, soil infrared spectrum characteristics were analyzed. The results showed that soil mainly composed by > 5 mm mechanical stabilized aggregates, and the content of > 5 mm aggregates increased with the increase of the proportion of peat and humic acid application in all treatment, and the MWD in all treatments were higher than CK. The effect of 5% humic acid application was the best for improving the content of > 5 mm mechanical stabilized aggregates, and the proportion of > 5 mm mechanical stabilized aggregates reached to 60.03% in the sixth month. However, compared with CK, the proportion of > 5 mm mechanical stabilized aggregates decreased after vermiculite was used. After the application of amendments, soil mainly composed by < 0.053 mm water stabilized aggregates, but its content all decreased with the increasing amounts of amendments. Peat and humic acid could increase the content of total organic carbon and the resistance to erosion and the stability of aggregates for reclaimed soil. However, the organic carbon content decreased after vermiculite was used. For all peat, humic acid and vermiculite treatments, the content of organic carbon in > 5 mm aggregates were the highest, followed by 0.053 ~ 0.25 mm aggregates, and the content of organic carbon in < 0.053 mm aggregates were the lowest. The organic carbon contribution in > 5 mm aggregates were the highest. The organic carbon contribution rate of > 5 mm aggregates were higher than 50%. The organic carbon contribution rate of < 0.053 mm aggregates were the lowest, and accounted for 0.63% ~ 2.82% in all of peat and humic acid treatments. The soil infrared spectroscopy characteristic showed that humic acid increased the content of polysaccharides in soil. There were many hydroxyl in polysaccharides and they could form hydrogen bonds with the oxygen atoms on the crystal surface of clay minerals, which can agglomerate the soil particles.

Abstract:In order to screen the remediation technology suitable for Cd pollution of paddy soil and crops in Southwest China, a field experiment was used to compare the effects of single application of lime, biochar, combined application of lime + biochar and their different amounts on the basic physical and chemical properties of Cd contaminated paddy soil, the Cd content and its influence on the enrichment and transportation of various parts of rice. The results showed that single application of lime and biochar as well as combined application can reduce the Cd in rice and the enrichment and transport coefficients of various parts of rice in the first year of restoration test. With the increase of the applied amount, the Cd content of rice showed a decreasing trend, and the Cd enrichment coefficient of soil to rice root system first decreased and then increased. Compound application (lime (1.5 t/hm²) + Biochar) was more effective than single application of lime and biochar. Compared with the control, the Cd content of rice treated with combined application (lime (1.5 t/hm²) + Biochar) reduced by 57.14% ~ 88.57%, and the enrichment coefficient of soil to rice root system reduced by 22.06% ~ 32.96%. The application of lime could significantly increase soil pH and reduce the soil available Cd content. In the second year of the remediation agent application continuation effect test, the effect of lime in reducing soil effective Cd and rice Cd in a short period of time was better, but its long-term effect and stability were not as good as biochar. Compared with the control, the effective Cd of soil treated with single application of lime, biochar and combined application reduced by 2.97% ~ 25.19%, 13.94% ~ 23.41%, and 1.93% ~ 21.41%, respectively, and the Cd content of rice reduced by 0.72% ~ 34.87%, 12.11% ~ 49.14%, and 36.55% ~ 51.71%, respectively. Overall, under the experimental conditions, the combined application (lime (1.5 t/hm²) + biochar (3.0 t/hm²) had the best effect.

Abstract:In order to verify the effects of biochar application and water management on the availability of heavy metals in contaminated soil, a soil incubation experiment was conducted to explore the effects of biochar application on the availability of cadmium (Cd) and arsenic (As) in the heavily Cd/As contaminated farmland soil under the alternate unflood-flooded condition. The results showed that under the alternate unflood-flooded condition, the application of biochar at the rates of 2%~10% significantly reduced the concentrations of Cd in soil solution by 33.1%~62.2%, indicating biochar promoted the immobilization of Cd from porewater to soil solid phase. However, the impacts of biochar application on the concentrations of As in soil solution was not stable, which mainly depended on the water management. For the variation of extractable Cd and As, the biochar application at the rates of 6%, 8%, 10% significantly decreased the levels of DTPA—Cd and NH₄H₂PO₄—As in soil by 8.7%~16.8% and 5.1%~7.9% compared with the control (CK) (P < 0.05), respectively. This indicated that the addition of biochar could significantly reduce the concentrations of DTPA—Cd and NH₄H₂PO₄—As in the Cd/As-contaminated soil. Moreover, the soil sequential extraction experiment illustrated that the application of biochar promoted the transfer of soil Cd from the fractions of acid-soluble and oxidative to the residues, and the transfer of soil As from the fractions of specifically sorbed, and amorphous and poor-crystalline hydrous oxides of iron-aluminum or iron-manganese to the residues, which suggested that biochar inhibited the availability of Cd and As in contaminated soil significantly. Therefore, the application of biochar at the rate of 6% combined with alternate unflooded-flooded water regimes might reduce the availability of soil Cd and As in the Cd/As contaminated calcareous soil.

Abstract:Soil enzyme plays an important role in the biochemical processes of forest ecosystems, which can quickly reflect the changes of soil environment (such as nutrient content and availability). Harvest residue is an important source of forest soil nutrients, and its treatment methods will affect the nutrient content and availability of forest soil. In order to explore the effects of different harvest residue treatments on soil enzymes activities, harvest residue was managed in the following ways, i.e., residue retained (RR), residue removed (R) and residue burnt (RB) after cutting a 40-year-old mature Chinese fir forest in Sanming City, Fujian, and six soil extracellular enzymes activities in 0-10 and 10-20 cm soil layers were studied. The results showed that: (1) After 4 years of harvest residue treatment, compared with RR treatment, the contents of dissolved organic carbon (DOC), dissolved organic nitrogen (DON), inorganic nitrogen (IN) and NO₃^--N in RB and R treatments decreased significantly. Further, the decrease of NO₃^--N content under RB treatment was significantly higher than that of R treatment, decreased by 88% and 51% for 0-10 and 10-20 cm soil layers respectively; (2) Compared with RR treatment, microbial biomass phosphorus (MBP) and carbon (MBC), and six soil enzymes activities, that were acid phosphatase (AP), β-1,4-glucosidase (βG), Cellobiohydrolase (CBH), β-1,4-N-acetylglucosaminidase (NAG), Poly-phenol oxidase (PHO), and Peroxidase (PEO) of RB and R treatments decreased significantly. Also MBC and MBP contents in two soil layers under RB treatment were significantly lower than those of R treatment; (3) Redundancy analysis showed that soil enzymes activities in the 0-10 cm layer were significantly correlated with soil MBP and MBC contents, and DON, NO₃^--N and MBC were the key factors affecting soil enzyme activities in the 10-20 cm layer. Therefore, the retention of harvest residues is beneficial to the improvement of soil nutrients and enzyme activity, and it is an effective management measure for the maintenance of soil fertility and the improvement of forest productivity.

Abstract:This study monitored and analyzed the wind and sand movement indexes of potato cultivated land under high ridge cultivation technology, such as upwind wind field, upper edge of cultivated land, center of cultivated land, lower edge of cultivated land, and downwind wind flow field.Results showed that the airflow from the upwind to the downwind during the movement was influenced by the high ridge cultivation techniques. The wind speed reduction, aerodynamic roughness and friction wind speed increased first and then decreased, which reached the maximum at the lower edge of the cultivated land. The wind prevention efficiency at the 10, 30, 50, 100, 200 cm height were 34.96%, 46.59%, 38.37%, 26.68%, 18.31% respectively. The aerodynamic roughness and friction wind speed were 2.15 cm and 0.91 m/s, which were 4.56 and 1.19 times that of the upwind. From the vertical direction, high ridge cultivation technique had the most obvious weakening effect on wind speed at 30 cm height. During the sand flow from the upwind to the downwind, its total sediment discharge per unit width decreased first and then decreased, with the lowest value in the lower edge of the cultivated land, 0.02 g/(cm·min), reduced by 207.97 times than the upwind. Within the cultivated land, sand flow structure changed, the sediment rates in different layers no longer met the law of exponential decline. This study could provide some theoretical basis for the application of high ridge cultivation technique in the wind prevention and sand resistance.