Abstract:Soil detachment capacity is the maximum soil detachment rate when sediment concentration of overland flow is zero. It is the foundation of the determination of rill erodibility and soil critical shear stress, and wide application of the process-based soil erosion models. A detailed analysis indicated that runoff plot could not be used to measure soil detachment capacity by overland flow. The potential effects on soil detachment capacity and their mechanisms were fully discussed in the aspects of the type and size of hydraulic flume, representation of soil sampling, length of soil sample, disturbance of soil sample, initial soil moisture, and duration of flowing water scouring. The uncertainties in soil detachment capacity measurement were systematically analyzed. This paper is helpful to understand the dynamic mechanism of soil erosion processes, and to choose the rational methods and experimental procedures to measure soil detachment capacity by overland flow.

Abstract:Soil nitrogen loss caused by slope runoff is one of the important source of agricultural non-point source pollution. In order to investigate the effects of slope length (2 m, 3 m, 4 m, 5 m) and rainfall intensity (0.65 mm/min, 0.69 mm/min, 0.83 mm/min, 0.85 mm/min, 1.01 mm/min, 1.20 mm/min, 1.37 mm/min, 1.54 mm/min, 1.68 mm/min, 1.80 mm/min) on runoff producing processes and nitrogen loss, an artificial simulated rainfall experiment was conducted. The results showed that: (1) Under the condition of rainfall, the changing trends of different forms nitrogen concentration in runoff were high in early stage, then reduced with increasing time, and slowed down at 20 min, and gradually became stable for the final rainfall, and in the end they tended to coincide; (2) Under the same slope length, the loss content of different forms nitrogen increased with increasing rainfall intensity, showing a significant positive correlation. In each rainfall events, the loss of different forms of nitrogen was always the maximal when the slope length was 5 m, and the minimal when the slope length was 2 m; (3) There were very significant correlations between runoff volume and total loss of TN and NO3-—N, but the influence on NH4+—N was weak; (4) The correlation between total loss of TN, NO3-—N and slope length, rainfall intensity, runoff volume were very significant, and the significance of the correlation followed the order of runoff volume＞rainfall intensity＞slope length. However, the total loss of NH4+-N was significant correlated with rainfall intensity only; (5) The influence of slope length, rainfall intensity or runoff volume to the total loss of different forms nitrogen in the runoff could be described as linear correlation equations, and the significance level was in order of TN>NO3-—N>NH4+—N.

Abstract:In this study, the impedance controlling effects of deep loosening building block on losses of different forms of phosphorus (P) on black soil sloping farmland were studied. The results show that: Deep loosening building block could Intercept runoff and sediment, and reduce soil and water loss on sloping farmland. Compared with CK, deep loosening building block processing reduced the total P concentration, dissolvable total P concentration, and particulate P concentration in farmland runoff by 58.19%, 64.19% and 55.02%, respectively; it could reduce the cumulative loss of total P concentration, dissolvable total P concentration, and particulate P concentration by up to 89.32%, 90.74% and 88.48%, respectively. Relatively speaking, the effects of deep loosening building block on reducing dissolvable total P concentration in runoff was better, particulate P was the predominant form of phosphorus lost in the runoff of black soil sloping farmland. Deep loosening building block measures had certain controlling effects on reducing the losses of different form of phosphorus in the runoff of sloping farmland.

Abstract:Based on the data of individual rainfall, runoff and sediment yield of five runoff plots from 1984 to 2015 in Suining Soil and Water Conservation Experimental Station, 68 rain processes were classified into four rainfall patterns. The effects of rainfall patterns on runoff and sediment yield of sloping farmland were analyzed for different slopes. Then the results showed that there were highly significant correlations between runoff depths and rainfall intensities of different periods (p＜0.01). With the slope gradient increasing, the period of rainfall intensity for the greatest correlation coefficient became shorter. The amount of sediment was significantly correlated with the average rainfall intensity during each individual rainfall, and the correlation coefficient was maximum. The fitting curve between runoff depth, the amount of sediment, and rainfall intensity was an increasing function of convex and concave shape, of which interval was between 0.79 and 0.88, and 0.90 and 0.97, respectively. It was indicated that the correlation between sediment yield and rainfall intensity was more affinitive than that between runoff depth and rainfall intensity. With the slope gradient increasing, runoff and soil erosion became greater. At the same slope gradient, the yields of sediment and runoff of rainfall IV (short duration, heavy rainfall) was the biggest, followed by rainfall Ⅲ (moderate duration, moderate intensity), rainfall II (long duration, moderate intensity), and rainfall I (long duration, light intensity). Furthermore, the difference between rainfall IV and rainfall I was significant (p＜0.05). When the slope gradient was about 15°, the effects of rainfall pattern were the most obvious. Overall, runoff and sediment yield increased with increasing slope gradient. Rainfall IV was the main pattern of rainfall causing soil erosion. In the future, we should take some measures of soil and water conservation to reduce soil erosion caused by rainfall IV on sloping farmland.

Abstract:This paper studied the influence of corn straw cover on the processes of runoff and sediment yield in the sloping farmland of a Karst area by indoor simulated rainfall experiments. The treatments were divided into two rain intensities (63 mm/h and 100 mm/h), and five levels of straw cover (0, 20%, 50%, 80% and 100%). The results showed that under the moderate rainfall intensity (63 mm/h), corn straw mulching reduced surface runoff coefficient and surface runoff rate, but increased subsurface runoff coefficient and surface runoff rate. When the straw mulching percentage was greater than 50%, straw cover reduced the amount of soil loss. Under high rainfall intensity (100 mm/h), subsurface runoff was the main component of total runoff on the bare slope, when the bare slope was covered with corn straw, subsurface runoff coefficient and runoff rate were decreased, and the amount of soil loss increased with the increase of surface runoff amount and rate.

Abstract:In order to study the influence of rainfall factors on runoff and erosion of fly ash (CFA), and reveal the law of runoff and sediment yield of CFA，runoff generation and erosion (RGE) characteristics of CFA were studied under natural rainfall conditions during the rainy season. This study was carried out by means of located observation methods to analysis natural rainfall events in experimental plots. The results showed that: (1) During the observation period，the total rainfall was 1 160.0 mm, while the erosive rainfall was 720.7 mm. The total rainfall and erosive rainfall in July were the most, being 409.6 mm and 217.1 mm, respectively. Heavy rains of erosive rainfall was 280.1 mm; (2) RGE in July was the greatest, being 0.72, 1.06, 0.67 m3, and 0.30, 0.90, 0.21 kg, respectively. RGE of rainstorm were biggest, respectively was 0.62, 1.02, 0.73 m3 and 0.16, 0.57, 0.15 kg. RGSE of the rainfall more than 50 mm were the biggest, being 0.79, 0.98, 0.53 m3, and 0.17, 0.72, 0.15 kg, respectively, RGE of the Rainfall intensity stronger than 40 mm/h were the biggest, being 0.82,1.06,0.76 m3, and 0.21,0.87, 0.19 kg, respectively; (3)Rainfall, I30, rainfall erosion force were associated with a significant yield in RGE. Rainfall capacity played a vital role in the runoff, rainfall erosion played a vital role in the sediment yield, while the relationship between RGE and rainfall duration was not significant. The relationships between RGE and rainfall capacity, and I30 implied by the equation were polynomial. The relationship between runoff and rainfall duration was linear, but there was no significant relationship between sediment yield and rainfall duration. RGE increased with the accumulation of rainfall characteristics, with erosive rainfall and rainfall erosion having particularly evident impact on RGE. The results are beneficial to the prevention and control of CFA loss in the storage yard, and can provide a reference for the ecological restoration of the CFA storage yard.

Abstract:In order to reveal the process of soil erosion and the characteristics of nitrogen loss on bare slopes under different rainfall intensity, by using artificial rainfall simulation device, we simulated rainfall of three intensities (1 mm/min，1.5 mm/min，and 2 mm/min) and set two processing method (bare land, slope covered with yarn net) to find out the characteristics of surface runoff and nitrogen loss under different rainfall intensity. The results were as follows：（1）Runoff intensity, runoff sediment concentration, and soil erosion rate were positively correlated with rainfall intensity, while soil infiltration rate and rainfall intensity was negatively correlated.（2）Cumulative runoff and sediment yield in the bare ground showed a linear correlation, while in the yarn net covered treatment they showed a power function relation.（3）Nitrogen loss decreased with the duration of rainfall, the amount of nitrogen loss increased with the increase of rainfall intensity, nitrate-nitrogen loss accounted for a higher proportion of total nitrogen than ammonium-nitrogen.（4）Soil erosion and nitrogen loss could be effectively controlled by covering the slope with yarn net，runoff and nitrate nitrogen loss decreased by 60.21% and 56.74% under the 1 mm/min rainfall intensity, respectively; the amount of total nitrogen and ammonium nitrogen loss could be reduced by more than 59% under the 1 mm/min and 1.5 mm/min rainfall intensity; the amount of eroded sediment was decreased by more than 79% under all three rainfall intensities. The results showed that the yarn net coverage could effectively control the amount of soil erosion and nitrogen loss on the care slope of in the engineering construction area, and this research can provide a reference for the prevention and control measures of soil and water loss in engineering construction area.

Abstract:By the simulated rainfall experiments, we identified the effects of different vertical structures on runoff and sediment production processes in the community of Artemisia capillaries. The results showed that the reduction effects of runoff and sediment yield of the multi-layer vertical structure (Artemisia capillaries + Setaria viridis (L.) Beauv + biological crusts) and double-layer vertical structure (Artemisia capillaries + biological crusts) were significantly greater than those of the single-layer vertical structure (Artemisia capillaris) under the same condition of vegetation coverage. Compared with the single-layer vertical structure, the other two structures could reduce soil erosion significantly. In additional, runoff was reduced by 22.6% and 40.5% over the double-layer vertical structure and multi-layer vertical structure, respectively, and the sediment yield was reduced by 73.5% and 86.6%, respectively. The cumulative sediment yield could be expressed as a power function of the cumulative production flow (R2＞0.98), showing that the cumulative sediment yield increased with the augment of the runoff production, and the degree of the enhancement decreased when the community structure became more complex. The results also showed that plant roots could improve soil structure by increasing rainfall infiltration and reducing overland runoff, which was the key factor influencing the runoff and sediment yield processes. All results indicated that the ability of community to prevent soil erosion could be improved with complicated vertical structure and components. In conclusion, in order to provide the theory basis for grassland vegetation restoration and structural configuration optimization for the Loess Plateau, we have to study further the vertical structure of grassland community and reveal the mechanisms of the soil and water conservation.

Abstract:To analysis suspended sediment sources in a typical collapsing hill watershed in the granitic region, a collapsing hill watershed in the Longmen town, Anxi County, was selected as the research object, 85 soil samples from four kinds of sediment source (erosive woodland, tea plantations, cultivated land, and the erosive area of collapsing hill area) were collected, in the meantime, erosion suspended sediment in the sampler in the channel was also collected. 34 kinds of fingerprint factor of the samples were analyzed, the best combination of fingerprint factors was screened, and the migration regularities of the sediment derived from different source were figured out. The results showed that there were significant differences in the same fingerprint factors of suspended sediments derived from different sources. By using the Kruskal-Wallis test and multivariate discriminant, the combination of Ca, Li, Sn, K and Ba was screened as the best combination of fingerprint factor, of which the cumulative contribution rate was more than 90%. The relative contribution of suspended sediment was approximately 33% by tea plantations, 27% by cultivated land, and 20% by erosive woodland and collapsing hills. The goodness-of-fit test value of this Hybrid model was 0.89. Further analysis showed that the influence of rainfall on collapsing erosion was the biggest. Suspended sediment yields of collapsing erosion and tea plantations per unit area were obviously higher than those of other sediment sources, indicating that the prevention and control measures should be focused on the collapsing erosion and tea plantations in this study area.

Abstract:In order to systematically investigate the effects of vegetation types and spatial patterns on hydrodynamics of overland flow, this study was conducted to explore variations of hydrodynamic elements such as depth, velocity, flow regime and roughness through conducting a series of laboratory flume simulation experiments on smooth and vegetated beds under conditions of emerged flow, seven flow discharges, two vegetation types (flexible vegetation, rigid vegetation) and three vegetation spatial patterns at a gentle slope gradient of 1.4%. The results showed that: (1) In comparison with bare plot, mean flow depth increased by 1.4 to 2.8 times than bare plot and mean velocity was reduced by 31% to 65% with vegetation cover, while the combination of flexible vegetation and a banded pattern retarded overland flow best. (2) Flow index m indicated that the flow with rigid vegetation and checkerboard pattern had the roughest turbulence and index k, suggesting that the combination of rigid vegetation and the pattern of a single long strip parallel to slope direction exerted the most efficient influence on flow characteristics. (3) The flow regime was mainly transition state and was majorly controlled by the discharge. With the cover of vegetation, the flow pattern changed from supercritical flow to subcritical flow and was mainly influenced by vegetation patterns. (4) Mean friction coefficient (f) of the whole slope for vegetation treatment was 2.9 to 20.9 times higher than that of bare slope, demonstrating that f increased more efficiently under subcritical flow. Emerged flexible vegetation with a banded pattern or a checkerboard pattern performed in a more efficient way than other vegetation distributions. While f alone slope distance under the banded pattern fluctuated, but the parameter kept stable with the checkerboard pattern under a better hydrodynamic condition.

Abstract:Based on the water infiltration experiments of sandy loam and clay loam soil, we determined the coefficients of entropy equations (E-Horton, E-Kostiakov, E-Philip, E-Green-Ampt) and general equations (Horton, Kostiakov, Philip, Green-Ampt). Infiltration rates were calculated from these equations, and compared with the data obtained by experimental observations. The results showed that E-Horton, E-Kostiakov, and E-Philip equations were suitable to fit soil water infiltration rates, and that E-Green-Ampt equation over-estimated soil water infiltration rates in sandy loam soil. However, these entropy equations were not suitable to fit infiltration rates in clay loam soil. Compared with the general equations, the entropy equations were more suitable to study infiltration rates in sandy loam soil. Since the entropy equations do not need any calibration parameters, they are feasible to reflect the physical meaning of the parameters and provide a theoretical basis for the optimization of irrigation.

Abstract:In order to evaluate the influence of vegetation restoration on soil properties of the abandoned land, in the paper we adopt the spatio-temporal substitution method, and took the abandoned land at different stages in Loess Hilly Region as the research object. By combing with laboratory experiments and physiochemical analysis, soil infiltration and anti–scouribility were studied through the point-source infiltration method and undisturbed soil erosion experiment. The results indicate that: at the same abandoned stage, initial infiltration rates(IIRs), stable infiltration rates(SIRs), average infiltration rates(AIRs), and anti–scouribility (AS) decrease with the increasing soil depth. As the abandoned stage extended, the initial infiltration rates(IIRs), stable infiltration rates(SIRs), average infiltration rates(AIRs) and anti–scouribility (AS) in surface layer increased significantly after the first pre abandonment, then gradually stabilized. The differences in abandonment phase was significantly greater than that between the soil layer. In the Loess Hilly Region, the Kostiakov model could effectively characterize the initial infiltration rate, and the correlation coefficient was 0.999 1. The Fang Zhengsan model parameters |1 and K could simultaneously characterize the initial infiltration rate and stable infiltration rate, the correlation coefficients was 0.869 4 and 0.998 1, respectively. Its initial infiltration rate was not as good as that of the correlation of the Kostiakov model. The process of soil infiltration could be well described by combining Kostiakov model and Fang Zhengsan model.

Abstract:Freeze-thaw cycle is one of the significant characteristics of soil thawing process in the area of seasonal freeze-thaw. In order to reveal the influence of freeze-thaw cycles on soil physical properties and soil anti-scouribility, aeolian sandy soil collected in a sloping farmland in Inner Mongolia was taken as the research object. Two factors of freeze-thaw cycles (0 to 10) and soil water content (6%, 9% and 12%) were controlled to simulate field freeze-thaw cycles and the runoff scouring process. The influence of freeze-thaw cycle on soil water content, bulk density, porosity, and soil anti-scouribility were analyzed quantitatively. The results show that: (1) Soil moisture content increased with the increasing number of freeze-thaw cycles, and was increased by 0.51% to 0.87%. The increasing extent for the soil with high water content was greater than for the soil with lower water content. (2) With the increasing number of freeze-thaw cycles, soil bulk density and porosity were increased and decreased slowly, respectively, with the extent of change decreasing gradually, and finally reached a basically stable state, under which soil bulk density was 0.05±0.01 g/cm3 lower than the soil not subjected to freeze-thaw; (3) When the soil had the same numbers of freeze-thaw cycles, soil bulk density of the soil with high water content (12%) was greater than that of the soil with low water content (6%), but the porosity and soil anti-scouribility showed the opposite trend; (4) The numbers of freeze-thaw cycle had a significant effect on soil anti-scouribility. Soil anti-scouribility significantly decreased with the increasing number of freeze-thaw cycles. However, after sixth freeze-thaw cycles, the change of water content, bulk density, porosity, and soil anti-scouribility gradually decreased. The results can provide a reference for studying the mechanism of soil erosion in the seasonal freez-thaw area.

Abstract:By combining indoor pot experiment and scouring of undisturbed soil, three treatments were set up, i. e. bare land(CK), low planting density Lolium perenne L.(H1), and high planting density Lolium perenne L.(H2), to study the changes of soil physiochemical properties and root system at different growth stages. Soil anti-scourability of the growing grass and its relationship with influencing factors in loessial soil area were analyzed. The results showed that：(1) Soil bulk density, organic matter content, and water stable aggregate of CK fluctuated at four growth stages, but the range of changes were small. Soil bulk density decreased, organic matter content, water-stable aggregate, root surface area density (RSAD), and root weight density (RWD) showed an increasing trend with the extension of the growth cycle of H1 and H2. The RSAD of H1 and H2 treatments decreased with increasing root diameter at four growth stages. (2) Soil anti-scourability index (ASI) of CK and H2 were not significantly different at four growth stages. The ASI of H1 showed an increasing trend with the extension of growth time, and the effect of H1 treatment on ASI was the most significant at the16th weeks. (3) ASI had a diminishing power function relationship with soil bulk density. ASI had an increasing power function relationship with organic matter content, and water-stable aggregate. ASI had an increasing exponential function relationship with RSAD, and RWD. (4) There was no significant different between ASI and bulk density, water-stable aggregate, and 1.0 mm to 2.0 mm, 2.0 mm to 5.0 mm, and ＞5 mm diameter class RSAD. There was a significantly positive correlation between ASI and organic matter content, RSAD, and RWD (p＜0.05). There was a highly significantly positive correlation between ASI and ＜1 mm diameter class RSAD (p＜0.01).

Abstract:The aims of this study were to analyze the correlation between rocky desertification at different slopes and water and soil loss quantitatively, and provide the scientific theoretical basis for the ecological environment management and restoration in the county area. Takeing Panxian County of Guizhou Province as the research area, with the support of RS and GIS technology, based on ALOS remote sensing images, lithology and 1∶50 000 topographic maps, using Remote sensing interpretation method, Surface analysis and Map Algebra principle, the index factors of rocky desertification and water and soil loss were extracted. Through ArcGIS spatial analysis and correlation analysis model, analysis of the correlation between rocky desertification at different slopes and water and soil loss in Panxian County. The results showed that: Panxian County had a rocky desertification area of 1 008.45 km2, accounting for 24.9% of the total area, the degree of rocky desertification was mainly mild, moderate and strong, accounting for 45.47%, 29.67% and 20.29% of the total area of rocky desertification, respectively. Water and soil loss area of 521.05 km2, accounting for 12.85% of the total area, the degree of water and soil loss was maily mild and moderate, and 67.75% and 17.36% of the area of water and soil loss, respectively. Rocky desertification and water and soil loss occurred in the place where the slopes were 5 and 35 degrees, accounting for 85.08% and 82.45% of the area of rocky desertification and water and soil loss, respectively. When the slopes were less than 8 degrees, there was a negative correlation between rocky desertification and grade of water and soil loss, and between water and soil loss and grade of rocky desertification. When the slopes were between 8 and 35 degrees, the area of rocky desertification and water and soil loss decreased first, then increased, and later decreased again. When the slopes were greater than 35 degrees, rocky desertification and water and soil loss grade were negatively correlated under strong erosion, but the correlation became positive when the erosion went beyond strong erosion. Water and soil loss and rocky desertification grade were positively correlated under mild rocky desertification, but they were negatively correlated when the rocky desertification went beyond mild rocky desertification.

Abstract:In order to reveal the relationship between sediment deposition and precipitation and reconstruct the depositional environment of redeposit loess, the natural dam on the Loess Plateau in northern Shaanxi was chosen as the object of the study. By sampling soil cores at different sites repeatedly and sample measurement, we classified natural dam types and established the erosive sediment model of the standard natural dam in Huangtuwa by means of contrast analysis of 60-year’s rainfall data, grain size, and mathematical modeling, etc. The results are as follows: (1) Soil erosion in Huangtuwa could be better reflected when the erosive rainfall standard was set at 9.2 mm. (2) Based on the rainfall data, 88.1% of the annual precipitation in Huangtuwa occurred when the average daily maximum rainfall was less than 52.7 mm, therefore, the area of “non- natural” could be determined using the sediment area resulted from a rainfall less than 52.7 mm. (3) A suitable model for Huangtuwa was established by simulating the capacity curve and setting the elevation point of the vacant capacity at 1 058.03 m, and amending the individual rainfall watershed erosion sediment transport model of Chabagou based on the fractal dimension of Huangtuwa. (4) By contrast analysis of the sediment particle size cycle law of different profiles in combination with data calculated by the model, it could be determined that the “natural dam” was closed to the dam , the “non-natural dam” was between the dam and gully, while the “non-dam” was between the gully bed and the gully head.

Abstract:In order to study the erosion caused by spring snowmelt of slope farmland in Northeast China and the affecting factors, in-situ observation was carried out on a sloping farmland in small watershed in Jixing, Jilin province. The changes of runoff and sediment yield during snowmelt were analyzed, the effects of factors such as snowmelt runoff and soil thawing depth on snowmelt erosion were investigated, and process and change rules snowmelt erosion of sloping farmland were explored. The results showed that, under the meteorological conditions of the average temperature of 0 to 3.8 ℃, spring snowmelt erosion was relatively concentrated, runoff and sediment yield increased first and then decreased. Snowmelt runoff and soil thawing depth were important factors affecting snowmelt erosion. In the early stage, runoff from melting snow increased dramatically, and accounted for 59.15% of the total snow melting period, soil was frozen at the same time. In the middle stage, snowmelt tended to stabilize, surface soil began to thaw, runoff decreased and sediment yield continued to increase, the amount of erosion reached the maximum and accounted for 41.74% of the total erosion. At the end, there was no snow on the slope, and the depth of soil thawing increased, runoff decreased and sediment concentration reached the maximum (8.00 kg/m3). Spring snowmelt erosion of sloping farmland was affected by the topographic changes of ridge area and catchment basin, runoff and sediment yield showed a strong regularity. When their peak frequency was consistent, runoff sediment showed an “8”cycle lag relation, but showed a compound cycle lag relationship when their peak frequency was inconsistent.

Abstract:Soil hydraulic properties are important factors affecting hydrologic process on soil surface and efficiency of irrigation and drainage. The aim of this study was to explore the differences in soil hydraulic properties in South China. The pressure membrane method, the constant head seepage method, one-dimensional horizontal soil column were used to measure the hydrodynamic parameters of five typical soils (clay fluvo-aquic soil, sandy fluvo-aquic soil, red soil, paddy soil, and purple soil) in South China. The differences in soil hydraulic characteristics and the reasons for the differences were compared and analyzed. The results were as follows: Soil texture and clay content were the major factors affecting soil hydraulic characteristics. Because of the clay fluvo-aquic soil and sandy fluvo-aquic soil were well graded soil, while red soil, purple soil, and paddy soil were poorly graded soil, the saturated hydraulic conductivity followed the order of clay fluvo-aquic soil＞sandy fluvo-aquic soil＞red soil＞purple soil＞paddy soil, being 1.75×10-3 cm/min, 3.15×10-3 cm/min, 4.77×10-3 cm/min, 11.02×10-3 cm/min, 11.87×10-3 cm/min, respectively. The water holding capacity of sandy fluvo-aquic soil, red soil, and purple soil were higher than that of the paddy soil and sandy fluvo-aquic soil. The available water content followed the order of sandy fluvo-aquic soil＞clay fluvo-aquic soil＞paddy soil＞purple soil＞red soil, the effective water pore volume accounted for 48%, 29%, 27%, 18% and 17% of the total pore volume, respectively. Under the unsaturated condition, the water movement speed of sandy fluvo-aquic soil and red soil were much higher than that of the clay fluvo-aquic soil, which was 6.8 times of that of the clay fluvo-aquic soil. Soil texture, particle size, clay and organic matter content were the factors contributing to the differences in the hydraulic properties of typical soils in South China，and soil texture and particle size distribution were the main influential factors.

Abstract:In order to reveal the effects of freezing and thawing on soil water erosion, and to study the temporal and spatial evolution processes of hydrodynamic erosion parameters on freeze-thaw slopes during the spring thaw period, two slopes (10° and 15°), four flow rates (4.5 L/min, 6.5 L/min, 8.5 L/min, and 10.5 L/min), and four original thaw depths (2 cm, 5 cm, 10 cm, and 15 cm) had been taken into consideration in this experiment under the circumstances of scouring slopes in the field. Hydrodynamic erosion parameters (the Reynolds number, Froude number, flow velocity, flow shear stress, stream power, and unit stream power) were systematically analyzed under the conditions of different original thaw depths, flow rate and slopes. The results showed that hydrodynamic erosion parameters, including the Reynolds number, flow velocity, flow shear stress, and stream power, were increased with the increasing flow rate. The flow shear stress, stream power, and unit stream power increased with the increasing of gradient. The flow shear stress and stream power were increased with the deepening of original thaw depth. The Reynolds number, Froude number, flow velocity, and the unit stream power changed less obviously with the original thaw depth. However, when the original thaw depth was 5cm, hydrodynamic erosion parameters changed the most dramatically with time. The power function prediction equation was established, including the Reynolds number (R2=0.728), the flow shear stress (R2=0.644), the stream power (R2=0.721), flow velocity (R2=0.533), and the unit stream power (R2=0.553).

Abstract:To explore the changes of pore and unfrozen water contents in saline soils during the freezing-thawing process, the pore and unfrozen water contents in different saline soils and NaCl saturated soil samples were determined using nuclear magnetic resonance spectrometer (NMR) to detect, the effects of soils texture on unfrozen water content in freezing process were studied, and the hysteresis during the freezing-thawing process was analyzed. Eight treatments were designed, i. e. two types of soils (mild saline silt loam and moderate saline loam) and four types of solutions (distilled water, 0.2% NaCl, 0.6% NaCl and 1.0% NaCl ). The findings were as follows: (1) macropores showed a faster decrease in unfrozen water content than micropores during the process of salinized soil freezing, with the thawing dissolved first in micropores in salinized soil. (2) For both the light and moderate salinized soils, unfrozen water content was the maximum when the soil were treated with 1.0% NaCl solution. (3) As could be seen from the comparison of unfrozen water content between different soils during the freezing-thawing process, the loam had higher unfrozen water content than in the silt loam. According to the experimental results, water content reduction started in macropores, while water content increase started in micropores during freezing-thawing process. The higher the concentration of NaCl solution was, the larger the unfrozen water content was, and the lower the freezing temperature was. Unfrozen water content changed to varying degree in different soils, and the unfrozen water content in the loam was obviously higher than that in the silt loam; saline soil frozen and thawed relatively slowly, and in the areas where freezing and thawing lagged behind obviously, the temperature range tended to decrease with the rising concentration.

Abstract:Drip irrigation under plastic mulch can effectively improve conditions of soil water and heat conditions, and increase crop yield. Moreover, change range of soil water, heat and crop yield as well as water supply from groundwater are maily effected by irrigation amount. To explore the effect of irrigation on soil and water consumption to groundwater recharge ratio of cotton in the growth period, four treatments with different irrigation amount（3 000 m3/hm2, 3 750 m3/hm2, 4 500 m3/hm2, 5 250 m3/hm2）were conducted and the effects of irrigation amount on soil temperature and water supply from groundwater were investigated during growth period of cotton by the balance plots. The results showed that, at a given irrigation amount, the shallow soil was more easily affected by the atmospheric temperature; under the same meteorological conditions, soil temperature and effective accumulated temperature at the same layer decreased with increase irrigation amount, when the irrigation amount was increased by 75%, effective accumulated temperature decreased by 11.3%, while the temperature changes were relatively small; the greater the irrigation amount, the greater the water consumption of cotton and the amount of water in the groundwater supply. When the irrigation water was increased from 3 000 m3/hm2 to 5 250 m3/hm2, the water consumption of cotton increased by 146.3%, groundwater recharge rate increased by 540%, the water supply in the sensitive period of cotton increased by 152.93 mm, and the amount of groundwater recharge in the water sensitive period was the greatest, but daily groundwater recharge increased with the increase of cotton growth period, and the water use efficiency of each treatment was not significantly different. Furthermore, it was found that at the conditions of higher soil temperature in summer (flowering and boll opening stage) and the lower irrigation amount, the amount of water supply from groundwater in the night was greater than or close to that in the daytime. The results of this study will provide an effective basis for using of agricultural water resources rationally and efficiently and optimizing the irrigation system of drip irrigation under plastic mulch.

Abstract:The objectives of this study were to quantify the characteristics of water transport and conservation in different locations (the inner field, paddy bund, and irrigation canal) in the paddy inner field-bund transition zones, and to identify the dominant pathways for water flow in these zones. Two typical transition zones in a more than 100-year paddy field were investigated by soil sample analysis and dye tracing field experiment in the Jianghan Plain, Hubei Province. Saturated hydraulic conductivity (Ks) decreased with increasing soil depth for each site, and was characterized by higher standard deviation in the upper soil layers. The highest Ks was observed in the paddy bunds, followed by the irrigation canal, and the lowest in the inner field, indicating that the water preferred to flow through the paddy bunds. In addition, significant differences in soil water retention curves (SWRC) were observed, the highest soil water-holding capacity was identified in the inner field, followed by the irrigation canal, and the lowest in the paddy bunds. The macroporosity calculated based on the SWRCs revealed that there were more macropores in the bunds than in the inner field, which resulted in more preferential flow paths. Corresponding to the macropore distributions, the larger stained area ratio (SAR) of the lower soil layers was also observed in the paddy bunds than in the inner field. Different soil Ks and water capacity between the inner field and paddy bund could be mainly attributed to the enhanced macroporosity in the bunds, which was mainly resulted from soil animal activation and root penetration. Except for the vertical water infiltration in the inner field, two other water flow paths in the paddy inner filed-bunds transition zone were identified: (i) water flowed laterally into the paddy bund and percolated vertically into the deep soil layers quickly through the macropores; (ii) water transported laterally into the irrigation canal firstly, then percolated vertically into the deep soil layers. In conclusion, water losses from the paddy bunds should be considered seriously in the water and solute transport researches in the paddy field in the Jianghan Plain.

Abstract:In order to investigate the temporal and spatial variation of soil moisture in the dry-hot valley, a study was carried out in the demonstration area of soil and water conservation at the old town village of Yuanmou, taking the Leucaena leucocephala plantation, Twig grassland and sloping land as the research object, by combining classical statistics and geostatistics analysis methods, the spatial and temporal variability of soil moisture on sloping lands of three land use types were studied. The results showed that: Soil water content in Yuanmou in the dry-hot valley was low (which was 7.56% and 12.80% in the dry and rainy season of forest land; 8.05% and 12.66% of grassland, and 19.37% and 22.95% in the farmland, respectively), soil moisture in the rainy season was significantly higher than that in the dry season, and followed the order of sloping farmland＞grassland＞forest land in both the dry and rainy seasons, and showed moderate variation (between 0.14 to 0.72); the autocorrelation coefficients of soil water content in different layers of soil of different land use types were all showed a positive to negative transformation trend, but the inflection point was different. The autocorrelation coefficients in the rainy season were higher than those in the dry season; the best fitting model for the forestland and grassland of soil moisture in the dry and rainy season were the same for different land use patterns (both the forest and grassland were spherical models during the rainy and dry season, and the farmland was the exponential model in the dry and rainy season), and all showed moderate or strong spatial correlation(between 0.05 to 0.39), which was greater in the dry season than in the rainy season. The spatial distribution patterns of soil moisture in different layers of soil of the same land type were similar in the dry season and rainy season, but the distribution patterns in the same layer of soil of different land use patterns were different.

Abstract:Artificial rainfall experiments were carried out to investigate the distribution characteristics of nitrogen and phosphorus in runoff system of urban backfill soils of different slope gradients. The results showed that soil slope had a significant effect on hydraulic distribution. Specifically, when the slope was 4°, the proportion of surface runoff, side-percolation flow, and down-percolation flow was 72.5%, 25.3%, and 2.3%, respectively. However, the surface runoff was prominent when the slope reaches 8°. Furthermore, for the slope of 4°, the percentage of total nitrogen in the surface runoff, side-percolation flow, and down-percolation flow was 69.7%, 26.1%, and 4.2%, respectively. Meanwhile, the proportion of total phosphorus was 77.6%, 22%, and 0.4%, respectively. The proportion of nutrients in surface runoff increased slightly with increasing slop gradient. Therefore, in the design of backfill soil, smoothing the surface would be beneficial to improve soil water infiltration, reduce surface runoff, and decrease nitrogen and phosphorus pollution of urban backfill soil.

Abstract:Based on the data of runoff and sediment discharge measured from 1951 to 2014 in Dongting Lake, evolution characteristics of water and sediment were analyzed by Mann-Kendall test, sliding t-test and ordinal clustering analysis. The relationship between precipitation, runoff, and sediment was analyzed by regression curve fitting and normalization curve, so that the driving factors influencing the variation of water and sediment in Dongting Lake could be figured out. The main results were as follows: (1) There were differences in the mutation year of runoff and sediment into and out the lake. The mutation year was 1971 for runoff into and out of the lake, 1985 for sediment into the lake, and 1970 for sediment out of the lake, respectively. (2) The runoff in Dongting Lake was attenuated by the stage, with the change being the most obvious during 1972 to 1977. (3)The sediment into the lake was characterized by the stage attenuation, and the average annual sediment decreased by 75.34% from 2004 to 2014. (4) The runoff into and out the lake was mainly affected by precipitation change during 1951 to 1971 and 1978 to 1985, and by human activities such as beach natural bending cutting, Gezhouba hydro-power stations, Wuqiangxi reservoir and the Three Gorges Project during 1972 to 1977 and 1986to 2014. (5) The amount of runoff had a certain impact on the amount of sediment into the lake during 1951 to 1971. The main factor affecting the reduction of sediment was the water conservancy project during 1972 to 2014. In summary, the dominant driving factors were different at different stages of the processes of water and sediment in Dongting Lake Basin. The runoff into the lake were mainly driven by water conservancy projects during 1972 to 1977 and 2004 to 2014. The runoff out of the lake were mainly driven by water conservancy projects during 1976 to 1985 and 2004 to 2014.The runoff into and out of the lake were mainly driven by precipitation change in the other two other stages.

Abstract:Through integrated analysis of the chroma parameters, magnetic susceptibility, grain size and Rb/Sr ratio on the Tuojiawan loess-paleosol profile in Yunxi County, the correlation between the features of chroma parameters and palaeoclimate change in the upper reaches of Hanjiang River was revealed. The results showed that: a* was strongly correlated with the content of iron oxide, and the average value of a* was significantly different between loess and paleosol layers, and followed the order of S0(6.34)＞MS(5.52)＞Lt(5.18)＞L0(4.98)＞L1(4.82)＞T1-al2(3.66). L* was negatively with the content of iron oxide and the organic matter, with iron oxide having a agreater effect on L*, which reached the peak in the lows layers. h* was the lowest (68.64°) in the palwosol layers, but was high in the loess layers. In contrast, a*/b* was high in the paleosol layers (0.39), but was low in the loess layers. In Manlan Loess, there were two weak paleosol layers, i.e. L1-S2 and L1-S1, which showed higher a* and a*/b*, but lower of L*and h* than Manlan Loess. h*, a*/b*, L* and a* could be used as good indicators of climate change. A high a* and a*/b*, or a low L* and h* indicated that the climate was warm and wet, and the pedogenesis was strong. In conclusion, h*, a*/b*, L* and a* together recorded climate evolution since the late Pleistocene: the climate was cold and dry during the late Pleistocene, but a short warm and wet period happened in the glacial period (27.3-21.6 ka B.P.), Then the climate gradually became warm and humid during the early-mid Holocene. However, cold and dry climate appeared again since the late Holocene in the region.

Abstract:Under the control of drying-wetting cycle, taking the effects of initial dry density, wetting frequency and the number of drying, formation and evolution of crack of Yunnan laterite was studied by the combination of indoor experiment and image processing in this paper. The initial dry density was set at 1.20, 1.30, 1.40, 1.50 g/cm3, the change of crack was observed under drying-wetting cycles and expansion rate test method, characteristic parameters of cracks were extracted by Matlab image processing technology. The results show that the laterite samples were easier to crack when the initial dry density was higher under drying-wetting cycles; the laterite samples did not crack all the time when dry density of was smaller (1.20 g/cm3); the laterite samples cracked during the third wetting when the dry density increased to 1.30 or 1.40 g/cm3, the laterite samples crack in the second wetting when the dry density reached 1.50 g/cm3; The effect of the wetting process on the development of the laterite cracks was significantly greater than that of the drying process. The expansion rate of laterite samples increased with the time of immersion. The expansion was stable at dry density of 1.20, 1.30, 1.40 g/cm3 for about 8 min and about 36 min at dry density of 1.50 g/cm3. The number, length, area and width of cracks of laterite samples increased with the number of wetting and drying cycles. The number, length and area of cracks increased with the increase of dry density, and the crack width reached a peak at a dry density of about 1.30 g/cm3. The key factor of the laterite cracking caused by drying-wetting cycle was the inhomogeneous expansion of the laterite samples during the process of wetting, the laterite cracks were expanding cracks. The development process included cracks gestation period (0 to 2 times), cracks formation and development period (2 to 6 times) and cracks stabilization period (6 to 8 times), the result of these three stages finally affected the developmental trend of laterite cracks.

Abstract:The aim of this paper was to study the effect of phosphobacterias on phosphorus in a reclaimed soil. The tricalcium phosphate-solubilizing ability of individual phosphobacteria and their combinations was tested using laboratory shake-flask culture. The culture broth of Rahnella sp (W2) + Fluorescent pseudomonas1 (W3) + Fluorescent pseudomonas2 (W4) produced the highest available P content, 609.1 mg/L. Therefor, W2+W3+W4 was selected as the optimal combination of phosphobacterias. The effects of the optimal combination of phosphobacterias on soil nutrients, enzyme activities, P desorption properties, and maize yield were investigated by carrying out a field experiment in a reclaimed soil in a coal-mining subsidence area. The results showed that phosphobacteria increased soil nutrient contents and improved soil enzyme activities. Soil available P and K contents, as well as phosphatase, invertase, and urease activities, were increased 2.8, 25.43, 7.41, 4.21, and 7.15 mg/kg, respectively, by phosphobacteria compared to the medium control. The greatest reduction in the maximum P adsorption capacity (114 mg/kg) and adsorption constant (0.021) of soil was found with phosphobacterias compared to the blank control (p＜0.05). The mean P desorption rate of soil with phosphobacteria was 14.7, significantly higher than those in other treatments. The highest maize yield was also obtained with phosphobacteria, which was 8 036 kg/hm2 and significantly differed from those on other treatments. In conclusion, the application of phosphobacteria could improve soil P desorption properties, facilitate rapid improvement of soil fertility, and contribute to crop yield in reclaimed soil.

Abstract:Two kinds of paddy soil with different organic carbon contents were selected to evaluate the effects of ultraviolet radiation (UV-B，280 to 315 nm) on soil total carbon (TC), dissolved organic carbon (DOC), and alkali-extracted phenolics (AEP), and to characterize the responses of soils of different thicknesses (0.95 mm, 1.89 mm, 2.84 mm) to UV-B radiation by simulating incubation experiment. The results demonstrated that, compared with dark treatment, UV-B radiation significantly decreased soil TC by 3.11% and 6.18%, but increased DOC concentration by 16.05% and 9.89% for the two soils with low (A) or high (B) organic carbon content at the end of experiment. After 96 h UV-B radiation, compared to the soil of 1.89 mm and 2.84 mm thickness, UV-B radiation had more significant effects on soil TC, DOC and AEP in the thinnest soil (0.95 mm), TC was reduced by 19.11% and 14.35%, but DOC concentration was increased by 18.66% and 18.92%, and AEP concentration was increased by 23.52% and 22.70% in the thinnest treatments (0.95 mm) for soil A and B, respectively, but there was no significant difference observed between the soils of 1.89 mm and 2.84 mm thickness. It was concluded that UV-B radiation had significant effects on the stability of soil carbon pool, and the completely bare surface should be reduced as much as possible to protect the stability of the soil carbon pool.

Abstract:A study was conducted in Minqin Oasis of wuwei city in North-West China to understand the trend of soil organic carbon fractions and its influencing factors after several years of alfalfa planting in the Minqin Oasis. Three treatments were conducted, including 3 years (A3), 14 years (A14) and 22 years (A22) continuous cropping of alfalfa. Content of total organic carbon (TOC), heavy fraction organic carbon (HFOC), light fraction organic carbon (LFOC), particulate organic carbon (POC), and microbial biomass carbon (MBC) in the soil were determined through field survey sampling and indoor laboratory analysis. The results showed that soil bulk density and electrical conductivity of 22 years alfalfa soil decreased by 13.9% and 95.4%, respectively, compared with that of cotton soil. Compared with the cotton soil (CK), the TOC, LFOC, HFOC, and MBC of 3 years, 14 years and 22 years alfalfa soil was significantly increased by 175.0%, 1 416.0%, 47.8%, and 216.0%, respectively. Vertical profile of cotton soil showed that content of LFOC, POC, MBC decreased with the increase of soil depth. Stepwise regression analysis showed that there was a significant positive correlation between LFOC and TOC (p＜0.05). Alfalfa planting age, soil layer and their interaction had a significant impact on POC/TOC (p＜0.01), and an extremely significant effect on TOC, LFOC, HFOC, POC, MBC, LFOC/TOC, HFOC/TOC, and MBC/TOC (P＜0.001). Alfalfa planting could improve soil quality and reduce soil bulk density and salinity. The study revealed that continuous planting for 14 years is the most reasonable planting time for Alfalfa. Meanwhile, Alfalfa planting is beneficial to the accumulation of organic carbon fractions in the 0—60 cm soil layer, especially to the increase of TOC, LFOC, and MBC.

Abstract:In order to elucidate the distribution characteristics of the soil organic carbon density and the spatial distribution pattern of soil organic carbon storage in a small Karst watershed, used the combination of the field sampling, the laboratory determination and the Geo-statistics analysis, using the combination of field sampling, laboratory determination, and Geo-statistics analysis, 2 755 profiles which were investigated in detail and 23 536 soil samples were selected, the spatial heterogeneity and distribution characteristics of soil organic carbon density and soil organic carbon storage in a small Karst watershed were studied quantitatively. The results showed that the content of the soil organic carbon and the average of the soil organic carbon density in the surface layer (0—20 cm) of the watershed was 25.07 g/kg and 5.23 kg/m2, respectively; the content of the soil organic carbon and soil organic carbon density in the profile (0—100 cm) in the watershed was 20.71 g/kg and 10.21 kg/m2, respectively; the content of the soil organic carbon and the soil organic carbon density in two layers showed medium intensity variations. Soil organic carbon storage was 1.48×108 kg in the first 10 cm soil layer, 2.65×108 kg in the first 20 cm soil layer, 3.43×108 kg in the first 30 cm soil layer, and 5.39×108 kg in the 0—100 cm soil layer. The Nugget C0 of organic carbon storage in each layers increased with the increase of soil depth, being the maximum in the 0—100 cm soil layer. The organic carbon storages of four different soil layers were low in the middle, higher in the surrounding border, and the lowest in the south. Elevation, slope, bare rock and gravel content were the main factors affecting the spatial heterogeneity of soil organic carbon storage in the watershed.

Abstract:In order to study the effects of biochar addition on soil organic carbon (SOC) mineralization and carbon pool in upland red soil, a field experiment was conducted r amend the soil with biochar at different rates, i.e. 0 t/hm2 (C0), 2.5 t/hm2 (C1), 5 t/hm2 (C2), 10 t/hm2 (C3), 20 t/hm2 (C4), 30 t/hm2 (C5) and 40 t/hm2 (C6). The components of soil organic carbon (SOC) and cumulative carbon mineralization were measured on the basis of the three pool theory of SOC, in combination with a laboratory soil incubation experiment. The results showed that：(1) The SOC content was higher in the C4, C5, and C6 treatments than in the C0 treatment, with the C5 treatment significantly increasing SOC content by 14.66%. Compared with the C0 treatment, the C2, C3, C4, C5, and C6 treatments increased active SOC content significantly. The increase rate of active SOC content in the C6 treatment (25%) was the highest. The C3, C4, C5, and C6 treatments significantly increased the inert SOC contents, i.e. by 18.92%, 40.09%, 53.60% and 49.55%, respectively, compared with C0 treatment. The inert SOC content in the C1, C2, C3, C4 and C6 treatments were significantly decreased, i.e. by 1.96%, 6.54%, 8.82%, 9.31% and 12.91%, respectively, compared with the C0 treatment. (2) The SOC cumulative mineralization rate was lower in the biochar addition treatments than in the C0 treatment, being reduced by 25.93% in the C6 treatment. Furthermore, the SOC cumulative mineralization decreased as the biochar application rate was increased. (3) The contents of SOC, active SOC, and inert SOC were significantly positively correlated with biochar application rate. There was a significant negative correlation between slow SOC content and biochar application rate. This study can provide a scientific basis for improving soil fertility and reducing the emission of greenhouse gas in the upland red soil.

Abstract:This paper examined the effects of biochar, polyacrylamide, and maize straw on the soil aggregate structure and distribution characteristic of organic carbon on sloping farmland in the purple hilly area, in order to provide the best choice for the protection of sloping farmland in the purple hilly area. Taking sloping farmland under different conservation practices, including CK (no-conservation practice), BC (biochar addition alone), PAM (application of polyacrylamide on the soil surface), and SM (maize straw addition ) in purple hilly area as the research objects, the composition of soil aggregates and the content of organic carbon were determined by soil physiochemical analysis. The result showed that: (1) Soil aggregates in the studied area were mainly of the size of＞5 mm and 5 mm to 2 mm, which accounted for 58.18% to 40.12% and 30.34% to 24.46%, respectively. Compared with the CK, the three conservation practices were all effective in increasing the content of large soil aggregates, among which SM was most effective. Mean weight diameter (MWD) of soil aggregates under different conservation practices decreased with increasing soil depth, and followed the order of SM＞PAM＞BC＞CK, while the soil aggregate fractal dimension showed the opposite trend. (2) Organic carbon content of soil aggregates varied greatly with aggregate size, being the highest at 0.5 mm to 0.25 mm. Within the 0—30 cm soil depth, the average content of organic carbon in soil aggregates was in the order of SM＞PAM＞BC＞CK, and decreased with increasing soil depth. (3) The contribution rate of soil aggregates to organic carbon content was the greatest when they were the size of ＞5 mm (53.64% to 27.92%) and 5 mm to 2 mm(30.92% to 11.80%), which accounted for 27.92% and 25.35% for average contribution, respectively. Aggregates in the size of ＞2 mm could be taken as the characteristic aggregates for organic carbon sequestration in soils in the purple hilly area. (4) The density of soil organic carbon in the studied area was in the order of SM＞PAM＞BC＞CK. The density of soil organic carbon and the difference among the three conservation practices decreased with increasing soil depth in the same treatment. The three conservation practices were effective in improving soil structure and increasing soil organic carbon content, among which the effect of SM was the best, showing that SM is a relatively ideal method for protection of sloping farmland in the studied area.

Abstract:In this study, PAM, humic acid, chitosan and aluminum sulfate were used as soil cementing materials to research the processes and effects on the formation of large aggregates from ＜0.25 mm aggregates in the loessial soil. The results showed that: (1) Based on the analyses of soil particle size distribution, soil cementing materials used in this study were all beneficial for formation of ＞2 mm aggregates, especially for ＞5 mm aggregates. (2) All of these four cementing materials could effectively increase the mean weight diameter and mean geometric diameter of the loessial soil, and the enhance the stability of aggregates, which increased with the increasing application rate of the cementing material. (3) Different soil cementing materials had different ability to improve soil structure, and showed the order of PAM≈humic acid＞chitosan＞aluminum sulfate. The findings obtained from this work will provide theoretical supports for application soil cementing materials to improve soil structure scientifically．

Abstract:This paper studied the dynamics of soil aggregation in responses to organic materials and their incorporation methods through a laboratory cultivating experiments. Five treatments were involved: no addition as a control (CK), mixing straw (M-Str), straw mulching (Str), biochar (BC) and swine manure (SM). The results show that the M-Str and SM treatments significantly increased soil organic carbon (SOC), hot water extractable carbon (HWC), tensile strength (TS) and mean weight diameter (MWD) of aggregate stability (p＜0.05), whereas the Str treatment did not enhance SOC and MWD (p＞0.05). Compared to the CK treatment, the BC treatment did not improve MWD although it increased SOC significantly (p＜0.05). The aggregate stability in the M-Str and SM treatments was linearly related to soil respiration (CO2) (p＞0.05). Our results demonstrate that organic materials and their incorporation methods played a critical role in soil aggregation stability.

Abstract:In order to study the changes in the composition of humic substance and elemental composition of humic acid in the rhizosphere soil of different crops, a two-year field experiment in Jilin Agriculture University experimental field was carried out. Three crops (corn, soybean and cabbage) were selected in the experiment with chemical fertilizer, leaves combined with chemical fertilizer, and poultry manure combined with chemical fertilizer. The water-soluble substance (WSS), humic acid (HA), fulvic acid (FA), and humic material (HM) were extracted by the modified method of humic substance composition. The organic carbon contents of soil humic components were measured by the method of K2Cr2O7 thermal oxidation, the optical properties of HA and FA were measured by a spectrophotometer, and the structural changes of humic acid were indicated from the ratio of E4/E6 and elemental composition. The results showed that the contents of total organic carbon and humic components followed the order of cabbage＞corn＞soybean. Compared with the CK, the application of organic materials significantly increased the organic carbon contents of TOC, WSS, HA in rhizosphere soil of different crops by 5% to 8%, 34% to 55%, 8% to 20%, respectively. Organic materials had no significant effect on carbon contents of FA. Compared with leaves and poultry manure, the application of maize straw significantly increased total organic carbon, application of different types of organic materials did not show a remarkable difference in organic carbon contents of WSS, the order of carbon contents of humic material were: maize straw＞leaves＞poultry manure＞CK. The effect of organic materials on the PQ values (the radio of HA/(HA+FA)) varied with different crops. The maize straw and poultry manure treatments had similar effects on PQ values in the rhizosphere soil of corn and soybean, and the poultry manure significantly increased PQ values in rhizosphere soil of cabbage. The application of organic materials resulted in a significant increase of the E4/E6 value in fulvic acid, while a little bit decreased E4/E6 of humic acid. Organic materials enhanced condensation degree, complicated the structure of HA, and increased the contents of nitrogen-containing groups of HA, with the effect of maize straw being the most significant. In general, organic materials showed better fertilization effect on soil than chemical fertilizer. The effect of poultry manure on the rhizosphere soil of cabbage was the most significant, maize straw and poultry manure treatments had similar effects on the rhizosphere soil of corn and soybean.

Abstract:The effects of four different kinds of super absorbent polymers (SAP) on clay soil aggregates and nutrient accumulation by maize were studied through pot experiments. The results showed that the effects of SAP on water-retaining capacity appeared in the middle to late stage of maize growth. Compared with the treatment of no absorbent application (T1), the water contents of soil were increased by 21.45%- to 65.09% at harvest time. Five soil aggregate characteristic parameters were calculated, and their correlation with soil particle size composition were analyzed. The amount of water-stable macro-aggregates (R0.25) of the soil treated with Poly (acrylate sodium) (WT1), and organic fertilizer and SAP compound (OSC) notably was increased by 72.40% and 58.00%, respectively, compared with the control (T1). Mean weight diameter (MWD) and geometric mean diameter (GMD) of the soil treated with the two above-mentioned SAP was significantly increased, i. e. by 45.91% and 67.89%, and by 57.34% and 64.11%, respectively, while the soil unstable aggregate index (ELT) was decreased by 18.51 and 14.83%. In addition, the application of SAP could reduce fractal dimension (D) by 0.65% to 2.64%. Correlation analysis showed that soil particles size distribution was extremely significantly correlated with GMD (p＜0.01), which could be the best quantitative index of soil texture. Acrylamide/ potassium acrylate copolymer (AS) and OSC promoted the uptake and utilization of nitrogen nutrient by maize, and the nitrogen content of grain significantly increased, i .e. by 10.37% to 15.67%. The application of OSC could improve soil structure and nutrient absorption more efficiently. This research provides academic and instructive bases for developing soil amendments.

Abstract:In order to understand the influence of reclamation on the soil physical and chemical properties of alpine-cold grassland in northwest Sichuan, the method of replacing the time with the space was applied, and the vegetable lands in the alpine grassland which had been reclaimed for three and ten years were chosen as the research objects. In addition, the uncultivated natural grassland was taken as the control group to study the changing characteristics of the physical and chemical properties of 0—60 cm soil layers of different land reclamation years. The results showed that the artificial cultivation led to significant reduction in soil nutrient content, soil physical and chemical properties of natural alpine meadow, and the soil quality further decreased with the increase of reclamation years. After ten years of reclamation, soil bulk density and sand content in the 0—60 cm soil layer were increased by 21.1% and 8.0%, respectively; soil moisture, organic matter, total nitrogen, available nitrogen, and clay contents were decreased by 38.4%, 44.1%, 39%, 47.1%, and 19.2% respectively. Soil physical and chemical properties, and soil carbon and nitrogen contents were decreased most significantly in the surface layer (0—20 cm). With increasing soil depth, soil physical and chemical properties were weakened. The losses of soil carbon and nitrogen in the 0—20 cm soil layer occurred in the first three years of reclamation, while soil carbon and nitrogen in deeper layers (20—40 cm, and 40—60 cm) were not significantly lost in first three years of the reclamation. Losses of soil carbon and nitrogen mainly occurred in the first three to ten years of reclamation.

Abstract:In this study, a field experiment was performed by using split-plot to investigate the effects of supplemental irrigation and nitrogen fertilizer application on winter wheat yield, nitrogen absorption and distribution. Based on measured soil moisture content in 0—40 cm soil layers at the jointing stage of wheat, three irrigation levels were designed in main plots, which could make the moisture content of target soil reach 60%（W1）, 70%（W2）, and 80%（W3）. In the sub-plots, three nitrogen levels were designed, 0 kg/hm2 (N0), 195 kg/hm2 (N195), and 255 kg/hm2 (N255). The results were as follows: (1) Supplemental irrigation and nitrogen application had significant effects on plant height and leaf area of winter wheat. For the same irrigation treatments, plant height and leaf area of followed the order of N255＞N195＞N0（p＜0.05），under the same nitrogen application treatments, plant height and leaf area in W2（569.4 m3/hm2） and W3（873.45 m3/hm2） were significantly higher than that in W1（265.2 m3/hm2）（p＜0.05）, but the differences between W2 and W3 were not significant（p＞0.05）, indicating that excessive nitrogen application and irrigation had no significant influence on the plant height and leaf area of winter wheat. (2) Under the same nitrogen application treatments, the threshold response to wheat yield was observed under different ratios of N application and irrigation, the highest yield (8 500 kg/hm2) was reached under the N195 and W2 (569.4 m3/hm2). (3) During the maturity stage of winter wheat, under W2 and W3, nitrogen accumulation under N255 was significantly lower than that under N195（p＜0.05）; especially for N255, nitrogen application had no significant influence on nitrogen accumulation, indicating that appropriate irrigation and nitrogen application could increase’s ability to absorb nitrogen. (4) Though wheat nitrogen absorption increased with t increasing amount of water irrigation, nitrogen distribution proportion in the grain was reduced. Considering the growth status of winter wheat and nitrogen risk status, a N level of 195 kg/hm2 and an irrigation rate of 70% field capacity (569.4 m3/hm2) is suitable for water and fertilizer application in this region.

Abstract:Water resource deficiency is one of major problems in wheat (Triticum aestivum L.) production in the North Plain. Irrigation plays an important role in achieving high grain yield and quality. In this study, to determine the effects of different applications of inorganic and organic nitrogen fertilizer on water consumption characteristics, dry matter accumulation and allocation, grain yield and water use efficiency of winter wheat, a long-term field experiment was conducted using the winter wheat (Triticum aestivum L.) variety Shimai 15 under winter wheat/maize rotation in the North China Plain from 2013 to 2015. The source of organic nitrogen was cow manure, and four fertilization modes were included, i.e., single application of organic manure (M), mixed application of urea and manure (U+M), single application of urea (U), and no N fertilizer application (CK). The results showed that types of fertilizer and fertilization way obviously influenced water consumption characteristics and water use efficiency of winter wheat. Crop water consumption of U+M was higher, reaching 548.46 mm to 556.72 mm and showed no significant difference from that of U in two growing seasons. In all growth stages, the water consumption, water consumption model coefficient of U+M was the highest in the stage of flowering to maturity, the water consumption that allocated to the flowering to maturity accounted for 33.55% to 42.38% of the total water consumption. The mixed application of urea and manure increased the consumption of soil water, especially the deep water storage. Soil water storage consumption of U treatment was the highest, but that of U+M treatment was distributed more in the grouting phase. Leaching of the U+M treatment was the lowest, which was 66.79%, 52.45% and 37.61% lower than those of other treatments. U+M treatment had the highest dry matter accumulation in two growing seasons, which was 11.9% and 22.3% higher than those in the U and M treatments, respectively. The grain dry matter accumulation and grain dry matter distribution ratio in the U+M treatment were significant higher than those in other treatments. The yield of U+M, U, and M treatments increased by 65.96%, 49.44%, and 46.59% compared with CK, respectively. The grain yield water use efficiency and dry matter water use efficiency of U+M treatment were significantly higher thanthose in other treatments in the two growing seasons. In conclusion, application of chemical fertilizer and organic manure is a reasonable way of fertilization under wheat/maize rotation system in the Huanghuaihai area, it can significantly increase grain yield and dry matter accumulation, improve water consumption characteristics of winter wheat, increase crop water consumption, significantly reduce water leaching loss, increased water supply during the grain filling stage, and increase the water use efficiency of winter wheat.

Abstract:In order to explore the effective measures that could make rational utilization of livestock manure and improve nitrogen utilization of maize, a three-year field experiment was conducted to evaluate the effects of combined applications of manure and chemical fertilizers on maize yield and nitrogen utilization in irrigation silting soils. The results showed that, compared to the no nitrogen fertilizer (CK), pH of soil treated with combined manure and chemical fertilizer decreased by 0.59 to 0.86, soil bulk density decreased by 8.05% to 10.74%. Soil organic matter of combined application of organic manure and chemical fertilizer (N1M1, N2M2) was increased by 0.86 g/kg and 0.44 g/kg per year, respectively; total nitrogen concentration was increased by 0.09 g/kg and 0.06 g/kg per year, respectively; the concentration of alkali-hydrolyzable nitrogen was increased by 4.74 mg/kg and 3.68 mg/kg per year; plant-available phosphorus concentration was increased by 6.62 mg/kg and 5.35 mg/kg per year; plant-available potassium concentration was increased by 8.46 mg/kg and 6.66 mg/kg per year. Compared to that in the conventional chemical nitrogen treatment (N1), maize yield was increased by 12.38% and 13.43% in the third year by the N1M1 and N2M2 treatment, respectively; the NUE was increased by 10.98% and 16.20%; the AEN was increased by 4.65 kg/kg and 10.50 kg/kg; the PFPN was increased by 4.65 kg/kg and 21.02 kg/kg, respectively. Therefore, soil pH value and bulk density were all decreased in lowered chemical nitrogen combined with manure as compared to the conventional chemical nitrogen, soil organic matter and nutrient concentration were all significantly increased. Combined application of organic manure and chemical fertilizer had a positive effect on maize yield and nitrogen utilization. Applying chemical nitrogen at 168 kg/hm2 + manure nitrogen at 72 kg/hm2 could maintain maize yield and alleviate environmental pollution in irrigation silting soils of Ningxia.

Abstract:In order to explore the ways of water-holding, yield-increasing and high-efficiency cultivation technology of dryland wheat, a field experiment was carried out at the Wenxi Experimental Base of Shanxi Agricultural University during 2011 to 2014. Taking the summer mulching with water-permeable plastic film and non-mulching as the main plots, and sowing patterns, i.e. inter-mulching drilling（FM） and conventional drilling (CD）as sub-plots, the effects of interannual mulching in different precipitation years on soil water movement, plant nitrogen accumulation and utilization, and nitrogen efficiency in dryland wheat field were studied. The results showed that the soil water content in the first 3 m soil layer before sowing could be improved by summer mulching, and the effect of water conservation could last to the booting stage, with FM having better effects. Summer mulching increased N accumulation of plants at different growth stages, the effect was significant in humid years, in which N accumulation was increased by 27 kg/hm2 to 31 kg/hm2, and the FM under summer mulching could increase N accumulation significantly, i.e. by 2 kg/hm2 to 8 kg/hm2 in dry years. Summer mulching could promote N mobilization in leaves and spikes in humid years, promote N mobilization in stems + sheaths in normal years and dry years, and increase N mobilization and their contributions to grain before anthesis, especially dry years. Summer mulching could also promote N mobilization in stems + sheaths in normal years and in leaves in dry years, increase N mobilization and their contributions to grain after anthesis by using FM. Nitrogen use efficiency and nitrogen production efficiency were improved by summer mulching, and nitrogen absorption efficiency was better under FM in dry years; nitrogen absorption efficiency was increased by FM, and summer mulching had greater impact on nitrogen production efficiency in dry years. The results also showed that after summer mulching, the yield of N accumulation per unit after anthesis was significantly higher in humid and normal year, an 1 kg/hm2 increase of N accumulation could increase yield by 176 kg/hm2 to 224 kg/hm2. The yield of N accumulation per unit before anthesis was larger in dry years, with the yield being increased by 142 kg/hm2 to 185 kg/hm2. Compared with the CD, the yield of N mobilization per unit before anthesis and N accumulation per unit after anthesis were higher than those under FM in humid and normal years, the yield of N mobilization per unit after anthesis was higher under summer mulching condition with FM in dry years, an 1 kg/hm2 increase of N accumulation could increase the yield by 234 kg/hm2. In conslusion, interannual mulching is beneficial to nitrogen absorption and mobilization by plants, and high yield and high efficiency of dryland wheat.

Abstract:To clarify the effective mechanism of applying biogas residue on the yield, the benefit and soil fertility of maize for two consecutive years, we conducted a field experiment in Hailin farm, Hailin City, Heilongjiang Province. From May 2013 to October 2014, treatments of the single biogas residues, the mixtures of biogas residues and chemical fertilizers, full dose of chemical fertilizers were applied to the test field of maize. The results showed that both applications of the biogas residues and the mixtures of biogas residues and chemical fertilizers for two consecutive years could increase the yield of maize. More specifically, the application of biogas residues at 45 000 kilogram per hectare increased the yield of maize the most significantly. However, the full dose of chemical fertilizer application at 600 kilogram per hectare slightly decreased the yield of maize. The application of biogas residue at one ton could substitute 135.25 kilogram carbamide, 180.18 kilogram diammonium phosphate, and 107.09 kilogram potassium sulfate. As a result, it generated a direct economic benefit of 956.72 yuan. Application of biogas residues achieved significant more economic benefits compared with the control. Application of the mixtures of biogas residues at 7 500 kilogram per hectare and chemical fertilizers at 450 kilogram per hectare exhibited the highest economic benefits, and its average economic benefit was 18 066.2 yuan per hectare. The pH values could be increased by 0.02 to 0.28 units and the organic matter could be increased by 0.14 g/kg to 2.84 g/kg in the surface layer of soil after the single application of biogas residue, and the mixed application of biogas residues and chemical fertilizers. Nutrient contents of the surface layer of soil were also increased to some degrss. Therefore, the reasonable application of biogas residues in the practical production may replace the application of chemical fertilizers to realize the efficient and economic utilization of the biogas residue in the cold high-latitude area of the northeast China.

Abstract:In order to explore the effective measures that could improve the stable supply nitrogen in orchard soil, six-year-old ‘Yanfu3’/SH6/Malus hupehensis Rehd. and 15N isotope labelling technique were used to explore the effects of FSA (furrow applicator fertilizer), FS+BC(half applicator and half bag-controlled release fertilizer), BCRF(bag-controlled release fertilizer) on soil mineral nitrogen and 15N-urea absorption, utilization and loss of Fuji apple. The main results were as follows: Soil mineral nitrogen content provided by BCRF treatment stably throughout the growing season, soil mineral nitrogen content provided by FSA treatment increased rapidly in the short term, and then decreased sharply. At the fruit maturity stage, nitrogen content in the plant of the BCRF treatment (121.64 g) was higher than that in the FSA treatment (79.01 g), and slightly higher than that in the FS+BC treatment (95.92 g). Ndff in different organs was significantly affected by different fertilizer treatments, and the Ndff of fruits was the highest. Ndff in different organs was the highest in the BCRF treatment, followed by the FS+BC treatment, and the lowest in the FSA treatment. The BCRF treatment increased N use efficiency significantly, which was 1.82 and 1.32 times as high as of the FSA treatment and FS+BC treatment. 15N loss rate in the BCRF treatment was 36.23%, which was obviously lower than that in the FSA treatment (57.44%) and FS+BC treatment (51.16%). 15N residue in soil of BCRF treatment mainly concentrated in the upper soil layer (0—40 cm), deep soil leaching and losses decreased. The results suggested that the BCRF treatment was beneficial to ensure a stable supply of soil nitrogen, improved nitrogen use efficiency and reduced nitrogen loss.

Abstract:A pot experiment under the conditions of awning was conducted to clarify the coupling effects of different irrigation and potassium supply on the change of soil organic matter, total nutrient （total nitrogen, total phosphorus, and total potassium）and available nutrients （available nitrogen, available phosphorus, and available potassium）, and accumulation of nutrient by peanut (Arachis hypogaea Linn.), by using the random block design with two factors and four levels for each factor, i.e. W1—35% field capacity, W2—50% field capacity, W3—65% field capacity, W4—80% field capacity, and K0—K2O 0 g/kg soil, K1—K2O 0.15 g/kg soil, K2—K2O 0.30 g/kg soil, K3—K2O 0.45 g/kg soil. Peanut variety ‘Huayu 25’ was the tested materials. The results showed that the absorption of available nitrogen was promoted as the potassium fertilizer amount was increased. Soil available phosphorus in W1K1 and W2K1 treatments increased with the decreasing of soil total phosphorus under water stress. It showed that a small amount of potassium fertilizer helped to the release of phosphorus for the dryland. The fertilizer K1(135 kg/hm2) treatment could promote the increasing of soil available potassium and soil nutrient balance, the concentration of available potassium in K1 was 0.43 to 0.59 times more than that in the initial soil, and increased with the increasing potassium fertilizer amount. The accumulation of nutrients (N, P and K) by peanut showed a rising trend with increasing irrigation amount when the potassium fertilizer amount was the same. N uptake increased firstly and then decreased with increasing irrigation amount, but only under the condition of water stress. Except the adequate moisture treatment (W4), the accumulation of P by peanut increased firstly and then decreased with increasing K application in other water treatment. No matter how the water supply was changed, K accumulation showed a parabolic pattern with the increase of potassium supply, and all the maximal values appeared in the mild potassium (K2) treatment. The correlation between peanut nutrient accumulation and total biomass yield, and pod yield were significant or extremely significant, there was also a significant positive correlation between total biomass and pod yield. Based on the comprehensive consideration of sustainable soil nutrient supply, the accumulation of nutrient by peanut and the formation of yield, it was recommended to maintained the moisture at 65% FC, and to control the amount of potassium fertilizer (K2O) at 135 kg/hm2 to 270 kg/hm2.

Abstract:The contents and vertical distribution of phosphorus fractions were analysed comparatively for core sediment samples taken from north sampling site for Core AB1 and south sampling site for Core AB2 of Aobao Lake in Lianhuan Lake using the SMT sequential extraction method. With the dating approach, the evolution characteristics and polluted history of phosphorus and the risk of phosphorus release in lake sediments were discussed. The results showed that the contents and vertical distribution of phosphorus fractions in Core AB1 and Core AB2 varied and the contents of phosphorus fractions in Core AB1 were higher than those in Core AB2, with fluctuations significantly with the depth. During the mid—1940s and 1981, the contents of phosphorus fractions and OM in Core AB1 showed large fluctuations; the contents of Ca-P, IP, and TP in Core AB2 first increased and then decreased, while the contents of Fe/Al-P, OP, and OM relatively constant. During 1981 to 2009, the contents of Ca-P, IP, and OM changed less and the contents of Fe/Al-P, OP, and TP showed relatively large fluctuation in Core AB1; the contents of Ca-P, Fe/Al-P, and TP first increased and then decreased to different degrees and the contents of IP, OP, and OM tended to increase in Core AB2. The sources of phosphorus in core sediments of Aobao Lake were mainly from industrial wastewater, sewage, and the loss of pesticides and fertilizers. The content of phosphorus in the north of lake was higher than that in the south, which was closely related with human activity. There were several villages in the northern part of Aobao Lake but none in the southern part. By using single single factor standard index method, the assessment of ecological risk of phosphorus in surface sediments showed that the content of total phosphorus in the northern part of lake exceeded the standard and showed a certain safety risk. Meanwhile, active phosphorus (Fe/Al-P and OP) in the upper part of sediment showed a greater increase than that at the bottom of Core AB1, and active phosphorus (Fe/Al-P and OP) were the dominant fractions of the increasing phosphorus sedimentation in Core AB1. It was indicated that phosphorus in the sediment in Aobao Lake would release more easily to the overlying water, and the effect on the eutrophication of lake water should be given attention.

Abstract:Roots are important for the nutrition absorption of Flue-cured tobacco. In this study, by changing the amount of biochar in the soil, the effects of biochar on root system development, leaf photosynthetic characteristics, and physiological parameters of the coordinated growth of the aboveground and underground of flue-cured tabacco were investigated. A field experiment was carried out in 2015 and 2016, and there was six treatments, i.e. CK, T1, T2, T3, T4, and T5. Compared with the conventional fertilization, the nitrogen fertilizer application rate of each treatment was decreased by 40%. In the key growth period of flue-cured tobacco, root system growth characteristics and leaf photosynthetic characteristics were determined. The results showed that biochar application at 2 400 kg/hm2 increased root vigor by 177.8%, total root area by 91.35%, the total root tip number by 100.9%, leaf area by 73.29%, chlorophyll relative value by 57.68%, net photosynthetic rate by 77.32%, and leaf area coefficient by 23.48%, respectively. Biochar could effectively promote the growth and development of the root of flue-cured tobacco, optimize root physiological parameters, and improve leaf photosynthetic physiological and leaf development parameters through the improvement of root development, with the improvement effects of biochar ranching a peak in T4.

Abstract:In order to improve the production of Trichosanthes kirilowii in the red soil and provide theoretical support for the cultivation of acid soils. Mainly in compare the difference of aluminum tolerance in between two places of origin, and determine the best relief concentration. Two kinds of Trichosanthes kirilowii Maxim., Baoding Trichosanthes kirilowii and Puyang Trichosanthes kirilowiiis selected as the experiment materials. Six different concentrations of Al3 + and abscisic acid were set up. To study the interaction of Al3+ and ABA on the root length, chlorophyll fluorescence characteristics, root activity, MDA content, antioxidant enzyme activity and antioxidant content of two species of the plant. The results show: (1) Baoding Trichosanthes kirilowii and Pu Yang Trichosanthes kirilowii under the effect of aluminum stress and exogenous abscisic acid, each index reflects similar trend, but varying degrees of each index and sensitivity revealed some differences, Baoding Trichosanthes kirilowii has stronger resistance ability of aluminum. (2)Aluminum threat forced two varieties of Trichosanthes kirilowii root length, root activity, Fv/Fm, Fm, ETR, SOD, POD, CAT and ASA, GSH content are decreased, and F0, MDA and DAsA rise. (3) After exogenous abscisic acid is added, two varieties of Trichosanthes kirilowii root length, root activity, chlorophyll fluorescence parameters except F0, anti-oxidase and ascorbate glutathione cycle system (ASA and GSH) show the trend of first increased and then decreased, MDA was decreased continuously, F0 and DAsA presented by the descending and ascending trend. 5 mg/L of exogenous abscisic acid make root length, root activity, Fv/Fm, Fm, ETR, SOD, POD, CAT and ASA, GSH rose to a peak, MDA decreased, F0 and DAsA down to the valley. (4)Through membership function and the analysis of the aluminum resistance coefficient, two varieties of Trichosanthes kirilowii can get the same result, the ability of Al tolerance: 5 mg/L＞7.5 mg/L＞2.5 mg/L＞0 mg/L＞10 mg/L. So the ability of aluminum resistance Baoding Trichosanthes kirilowii is stronger than Puyang Trichosanthes kirilowii, low concentration of exogenous abscisic acid can alleviate the stress of aluminum, but when the exogenous abscisic acid concentration is too high, unable to protect the plant from aluminum stress influence function, namely “promoting at the low concentration and high concentration inhibit”, 5 mg/L ABA can effectively relieve Al stress, So we should select aluminum resistant Trichosanthes kirilowii to plant, supplemented with appropriate concentration of exogenous ABA.

Abstract:In recent years, with the increase of irrigation area and the decrease of water quota from the Yellow River, several agro-ecological issues, such as water scarcity and soil salinization, are becoming more and more severe. It is important to maintain a farmland ecological environment and soil health. In order to explore soil salinity movement of mulched drip irrigation under different plastic film mulch modes in arid areas, a two-year consecutive experiment was carried out in Shuguang experimental station located in Hetao Irrigation Area. We designed two treatments, including flat tillage with full film mulching (PQ) and flat tillage with half film mulching (PB). Soil moisture and salinity was checked by 5TE sensor. The results indicated that soil salinity was redistributed after drip irrigation. The main desalination area was formed under dripper around 30 cm under the dripper, and salt accumulated towards the outer side of humid area. Soil salinity of the partial film mulching treatment was likely to build up on the surface of the un-filmed soil by evaporation. However, full film mulching treatment could effectively decrease soil salt due to the effects of soil moisture. Under mulched drip irrigation, salt content of different horizontal position from drip irrigation zone showed the same trends of electrical conductivity curve variation, and the variation decreased with the increasing soil depth. Soil electrical conductivity of the surface layer followed the order of 50 cm＞20 cm＞0 cm with the distance from the dripper, and soil conductivity value fluctuated greatly in the soil without film mulching. During the whole growing stages, different film mulching treatment all played a certain desalting effect on the 0—70 cm soil layer, the desalination capacity of partial film mulching treatment was much less than the that of the full film mulching treatment. Soil salt content (SA) of the half film mulching treatment in the two growing seasons was 4.71 mg/hm2 and 9.24 mg/hm2, respectively, and SA of the full film mulching treatment was 12.22 mg/hm2 and 21.55 mg/hm2, respectively. Full film mulching treatment efficiently restrained soil water evaporation, resulted in decreased upward movement of soil salt, and created suitable environment for the growth of crops. The results will provide a theoretical basis for water and salt management under mulched drip irrigation in Hetao irrigaiton district.

Abstract:In order to explore the temporal and spatial variations of soil salinity under human cultivation and natural conditions in the Yellow River Delta, to realize the efficient development of the reserve land resources and ensure the ecological and environmental safety, in this study, spatial transformation was used to deduce the time succession. A sampling zone was set from Lijin County Beisong town to the Yellow River Estuary in a protected area（118°10′50″E to 119°09′02″E，37°26′37″N to 37°49′36″N）along the Yellow River to reveal the temporal and spatial characteristics of soil salinity in the farmland of typical crops (wheat, cotton, rice) and under natural conditions. 28 main sampling areas were randomly selected and 140 samples were collected, with every 20 cm as a soil layer, and the salt content of 0—100 cm soil layer was determined. in samples. The results showed that the average soil salinity in 0—20 cm soil layer was 3.58 g/kg in the sampling belt, which was significantly (P＜0.05) higher than that in the 60—100 cm and soil layer, and these soils were of moderate salinity. The salinity distribution showed a strong spatial variability（CV=131%） in the 0—60 cm soil layer, but with the increase of soil depth, the coefficient of variation decreased continuously. The spatial distribution characteristics of soil salinity profile reflected the temporal effect of cultivation and natural conditions. Inverted salinity profiles were mainly distributed in the coastal zone, which accounted for 83.3% of the alluvial area formed after the year of 1972, and the main vegetation types were low-yield cotton crops and natural vegetation, which accounted for 45.5% and 85.7%, respectively. The average salinity profiles were mainly distributed in the middle and inland regions of the sampling area, which both accounted for 40.0% in regions formed before 1855 and during 1855 to 1972, respectively, and the main vegetation types were rice, wheat and intertidal zone. The normal salinity profile types were mainly distributed in the inland regions of sampling zone (which accounted for 31.3% of the area formed before 1855), and the main vegetation types were farming field, with cotton, wheat, and rice fields being distributed equally. Random factors such as, cultivation management and vegetation were the main factors that caused the variation in soil salinity in 0—80 cm soil layer, with the increase of soil depth, the effects of these random factors weakened, but the effects of structural factors such as drainage and groundwater level became stronger. Based on the spatial evolution characteristics of soil salinity, a map of crop distribution was made to provide a support for the development and utilization of saline soil in the Yellow River Delta. In conclusion, the study revealed the time-spatial revolution characteristics of soil salinity in the Yellow River Delta under different land cultivation and natural conditions, i.e. from coastal to inland, the soil salinity profile changed from inverted salinity profile to normal salinity profile. Cultivation can reduce soil salinization so some degree, but cultivation and soil salinization are reciprocal causations and can promote the development of each other.

Abstract:To clarify the continuous and environmental effects of the amelioration of heavy soda saline soil using desulfurized gypsum, an outdoor pot experiment was conducted to study the growth situation of forage maize, physicochemical properties of the soil, and contents of heavy metals in plants when the soda saline soil was treated with different rates of desulfurized gypsum (0 t/hm2, 15 t/hm2, 22.5 t/hm2, 30 t/hm2). The results showed that the remediation effect of 15 t/hm2 desulfurized gypsum was the best. It could significantly improve seedling emergence rate, plant height, stem diameter, and seedling biomass of forage maize, which was increased by 20.6%, 16.8%, 8.1% and 10.1% compared to the control, respectively. The pH, EC, and the content of Na+ in the soil were decreased, but the contents of Ca2+ and SO42- in the soil were increased. As the amount of desulfurization gypsum was increased, the effect of desulfurization gypsum became more obvious. The content of As, Hg, and Ni in the soil and forage maize roots increased with increasing amount of desulfurization gypsum. According to the second grade of national environmental quality for the soils (GB 15618—1995), the contents of heavy metals (As, Hg, Cd, and Ni) in the tested soil were all complied with the Environment Quality Standard. The contents of heavy metals in the forage maize shoots were not significantly correlated with the application rate of desulfurization gypsum, and the heavy metals contents in each treatment did not exceed the standard limits according to Hygienical standards for feeds (GB 13078—2001). The heavy metal contents in stems were less than those in shoot, and the accumulation rate of heavy metals was in the order of Cd＞Hg＞As＞Ni. It can be concluded that the continuous effects of desulfurization gypsum to ameliorate the soda saline soil were good, and did not show adverse impact on the environment.

Abstract:The author made a simulated leaching soil columns experiment in outdoors, including intermittent leaching and continuous leaching, the purpose was to analyze the improvement effect of saline soil under the combination of different irrigation amount and different irrigation frequency. The results indicated: (1) Under the same irrigation amount, the percolate electric conductivity of intermittent leaching higher than continuous leaching, leaching efficiency of intermittent leaching was higher than continuous leaching from beginning to end. (2) Under the different irrigation amount, the percolate volume of amplified along with the irrigation amount growth, the greater irrigation amount, the better leaching efficiency. (3) The change trend of soil pH value was drop than before after leaching, and it was same of the change trend of soil salt; the greater irrigation amount was, the better the efficiency of alkali removes. In this experiment, leaching efficiency of 15 L points three times is optimal, leaching efficiency was 11.58 g/L, 15 L of the surface soil pH values decreased from 8.42 to 8.07. The results can provide reference for the improvement of saline alkali land in arid area and the establishment of water saving irrigation system of maintaing farmland water and salt balance.

Abstract:The aim of this study was to explore the chemical characteristics of surface water and groundwater, and the contribution of various salts to the main ions. Karst small watershed was taken as the research scale, field monitoring and sampling, and laboratory experiments for surface water and groundwater chemistry in Shuanghe Cave area was carried out. SPSS statistical software was used to analyze the principal components of water samples. The results were as follows: (1) Ca2+ and Mg2+ were the predominant cations of groundwater and surface water in Shuanghe Cave, and the predominant anions were HCO3- and SO42-. The water chemistry could be classified as Ca2+?Mg2+—HCO3- type, but Gypsum Cave was Ca2+?Mg2+—SO42- type. The contents of most ions varied with different sampling points, seasons and types of water; (2) Gibbs and triangular diagrams analyses revealed that the water compositions in the watershed were significantly impacted by rock weathering process. The main anions were derived from carbonate dissolution and evaporation, weathered rock or rock salt. Evaporation salt dissolution was the main controlling mechanism of cation, and the effect of silicate weathering and erosion also affected regional ion change; (3) The principal component analysis showed that the degree of influence on the regional composition of ion chemistry followed the order of carbonates＞evaporites＞silicates. Among them, the influence of H2CO3 weathering carbonate rock was obvious, but in certain underground river, water chemistry was mainly affected by H2SO4 weathering carbonate rock. In addition, agricultural and domestic activities also showed some impacts on water characteristics. The results of this study have a great significance for the protection, development, and utilization of water resources in Shuanghe Cave and for karst carbon cycle research.

Abstract:Using comparative analysis and substituting temporal serial with spatial serial data , we analyzed data collected from abandoned farmland with eight different vegetation restoration periods (1 to 35 years). The responses of plant community and soil stoichiometry to different fertilization treatments were studied. The results were as follows: (1) Compared with the no fertilization treatment, the aboveground biomass was increased by 77.1% and 142% by the + N and + N + P treatment, respectively. The response of aboveground biomass to the + N + P treatment was more significant than to the + N treatments. Compared with no fertilization treatments, leaf N and P concentration was increased by 13.6% and 0.6%, while the N/P ratio was reduced by 3.8% by the + N treatment. Leaf N and P concentration was increased by 15.6% and 8.7%, while the N/P ratio was reduced by 15.2% by the + N+ P treatment. The responses of leaf N and P concentration, and N/P ratio to the + N+ P treatment were all more significant than to the + N treatment. Compared with the no fertilization treatment, soil N and P content was increased by 27.7% and 36.2%, respectively, and N/P ratio was reduced by 9.1% by the + N treatment. Soil N and P content was increased by 16.6% and 25%, respectively, and N/P ration was reduced by 9.1% by the + N+ P treatment. The response of soil N and P content to the +N treatment were more significant than to the + N+ P treatment. In conclusion, a proper fertilization mode is beneficial to the utilization and distribution of soil nutrients.

Abstract:In order to clarify the effects of different ages of Robinia pseudoacacia forest on soil nutrient and ecological stoichiometric characteristics, we selected four kinds of artificial Robinia pseudoacacia forests of different ages (10 years, 15 years, 25 years and 40 years) located in Yan’an, Shaanxi province to investigate the distribution patterns of soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP) and total potassium (TK) in 0—200 cm soil layer, and analyzed the ecological stoichiometric characteristics. Three sample sites were set up in each selected Robinia pseudoacacia forest and three sampling points were set randomly. Soil samples were collected to analyze soil C, N, P, K and stoichiometry. The results showed that: (1) SOC，soil TN and TK increased with the growth of Robinia pseudoacacia forest on the whole, and the change of soil TP with the growth of Robinia pseudoacacia was not obvious. There were significant positive correlations among SOC, soil TN and TP. (2) The spatial distribution of SOC and soil TN were quite consistent, showing the same trend of declining first then tending to be relatively stable with soil depth, and they were higher in the surface layers than in the subsurface layers. TP was lower than SOC and TN in spatial variability．The content of TK was higher than that of SOC, TN and TP, and it did not change much with soil depth. The 15 years occurred the minimum value. (3) Soil C∶N ratio, C∶P ratio, N∶P ratio, C∶N∶P ration all decreased first and then deceased with the growth of Robinia pseudoacacia forest. (4) Soil C∶N didn’t change much, as soil C∶P, N∶P showed the same trend with SOC and TN with soil depth.