Abstract:The particle-size characteristic of eroded sediments is important in understanding, characterizing and modeling the transport behavior of sediment and sediment-associated chemicals. The objective of this study was to provide references through summary and reorganization of relevant researches at home and abroad. This paper reviewed and evaluated the transport forms of eroded sediments, the primary particle-size composition of sediments undispersed with different size, the enrichment and selectivity of different size-class particles, and factors. Some results reached a consensus:(1) Undispersed sediment-size distribution is required for describing and modeling sediment transport and the associated movement of nutrients and contaminants. (2) This erosion selectivity, in fact, primarily results from the energy limitation of rainfall and runoff. When the energy is small, runoff is preferred to transport fine particles, and sediment is mainly enriched by fine particles. As the energy gradually increases, the sediments gradually thicken. When the energy is large enough to produce rill, the sediments size distribution tends to be close to the original soil. (3) The size distribution of sediments for the well-aggregated soils usually is much coarser than the less-aggregated one.

Abstract:The spatial variation of precipitation and erosion sediment production in loess areas of Wuding River basin in the middle reach of the Yellow River were studied by using Thiessen polygon weighted coefficient of variation method, and the correlation between the spatial variability was explored by using linear regression analysis. Based on Wuding River basin, one of the main sediment source area of the Yellow River, this paper analyzed the temporal and spatial variation of precipitation and sediment yield of the loess area in 1959-2015 before and after the soil and water conservation measures, choosing flood season precipitation (P_flood) and flood season rainfall erosivity (R_flood) for the precipitation characteristics, and specific sediment yield (SSY) for sediments production. The results showed that:(1) Before soil and water conservation measures (1959-1970), the trend of precipitation characteristics in this region was consistent with the change of SSY in time, and the two precipitation characteristics showed a significant power function correlation (P<0.01). The effects of P_flood and R_flood on erosion sediment yield were consistent. After large-scale soil and water conservation measures (1971-2015), due to the construction of a large number of silt-dam in study area, sediment yield decreased sharply, and there was no significant correlation between precipitation characteristics and SSY. (2) On the multi-year time scale (1959-2015), the spatial variability of P_flood was 8%, and the spatial variation coefficient of R_flood was 15%, and the spatial variability of P_flood was less than that of R_flood. The spatial variability of SSY between 1959-1970 was smaller than that between 1971-2015. During 1959-1970, the spatial variability of precipitation characteristics and SSY showed a significant quadratic polynomial correlation (P<0.01), and the correlation between R_flood and SSY was more significant (R²=0.76, P<0.01). There was no significant correlation between precipitation characteristics and SSY from 1971 to 2015. The results showed that the spatial variability of SSY before human activities was mainly affected by the spatial variability of R_flood, while the spatial variability of SSY as mainly affected by human activities after soil and water conservation measures.

Abstract:It is of great importance to know the soil erosion situation, spatial distribution and variation pattern and its internal driving factors in Soil and Water Loss Dynamic Monitoring Area of Sichuan Province for the warning of ecological conditions and controlling of soil erosion. In this paper, China Soil Loss Equation (CSLE) method was used for calculating the overall soil erosion situation of the monitoring area. The different soil erosion sensitivity assessments was used to identify the sensitivity factor in CSLE, GeoDetector was used to explore the spatial distribution and variation pattern and its internal driving factors in the monitoring area. The results indicated that the intensity of soil erosion in the monitoring area was mainly micro erosion, the average modulus of soil erosion was 806.08 t/(km²·a), which belonged to the mild erosion. But the soil erosion in the area was obviously different, and serious soil erosion occurred in some local area. Soil erosion sensitivity analysis showed that biological measure factor B was the most sensitive factor in CSLE. Quantitative attribution of soil erosion in different soil and water conservation zones showed that land use was the main driving force for spatial heterogeneity of soil erosion, and the interaction of the two factors could increase the ability to explain the spatial distribution of soil erosion. There was a significant difference in the extent of each factor in different soil and water conservation zones. Therefore, when using CSLE to calculate the amount of soil erosion, it was the key to improve the calculation accuracy by establishing regionalization algorithms for sensitive factors in different research areas. This study could provide a basic reference for the prevention and control of soil erosion in the monitoring area.

Abstract:In order to reveal the law of soil erosion of different canopy density Pinus massoniana forests in the red soil erosion area of southern China, the standard runoff plot observation method was adopted in different canopy density (0.2, 0.4, 0.6, and 0.8) Pinus massoniana forest in the Changting of Fujian Province. A rainfall gradient was constructed to analyze the variation of soil erosion with the rainfall level of different canopy density Pinus massoniana forests based on the 37 natural rainfall events observed in 2015. The correlation between runoff and sediment yield and rainfall factors was conducted. The results showed that:(1) The runoff and sediment yield of different canopy density Pinus massoniana forests increased gradually with the increase of rainfall grade, and the increase was more obvious under rainstorm condition. (2) Under three rainfall grades such as moderate rain, heavy rain, and rainstorm, the runoff and sediment yield of Pinus massoniana forests with the canopy density of 0.2 and 0.8 were higher than that with the canopy density of 0.4 and 0.6. The runoff and sediment yield of Pinus massoniana forests with the canopy density of 0.4 and 0.6 showed less variation with the increase of rainfall grades. (3) The runoff and sediment yield of different canopy density Pinus massoniana forests were significantly correlated with rainfall and rainfall erosivity (P<0.05) under the natural rainfall gradient. (4) The stepwise regression analysis showed that the main variables of the regression equation of the runoff of Pinus massoniana forests with different canopy density are rainfall and the maximum 30 min rain intensity, while of the sediment yield regression equation are rainfall and rainfall erosivity. In summary, the higher or lower degree of canopy pine forest is not conducive to soil and water conservation, and the most effective canopy closure degree of Changting red soil erosion is 0.6 to control the soil and water erosion of Pinus massoniana forests.

Abstract:In order to study the effects of different soils on sediments particle transport on slopes of engineering accumulation, a field scouring experiment was carried out under two kinds of disturbed soil, red and aeolian sandy soil, four flow gradients 8, 12, 16 and 20 L/min, and under the condition of 32°. The results showed that:(1) The runoff and sediment yield of the two accumulation slopes showed a "multi-peak and multi-valley" change process with time. (2) Compared with the disturbed aeolian sandy soil accumulation, the rate of sediment yield on the slope of disturbed red soil accumulation increased slowly with the increasing discharge flow rates. When the discharge flow rate was 20 L/min, the gravity factor played a leading role in the slope erosion of aeolian sandy soil accumulation. (3) The cumulative sediment yield of the two engineering accumulations was significantly correlated with the cumulative runoff, which could be described by linear function (P<0.01, R²>0.99). (4) With the increase of discharge rates, the proportion of sediment particles transported on the slope of the accumulation was close to the original soil. The main erosion sediment particles of the aeolian sandy soil were sand grains (> 60%), the proportion of transportation of red soil particles was relatively uniform(the sediment transport contents ranged from 24% to 41% for each particle size). The difference in slope erosion of different accumulations was closely related to soil texture. These results could provide theoretical basis for the prevention and control measures for soil erosion on slopes of different soil types.

Abstract:Due to the impact of upstream reservoir, control project and climate change, the Yellow River Inner Mongolia reach has the characteristics of different sources of runoff and sediment, less water and more sediment. This phenomenon leads to sediment deposits, sharply decline and morphological evolution violently. This is seriously threatening the safety and ecological environment during summer flood and ice flood period. Shizuishan and Toudaoguai hydrologic station runoff and sediment transport process were chosen to analysis water-sediment time-order character, motion state and evolution characteristics by using spectral analysis method, R/S range analysis method and Markov method from 2009 to 2016. The results showed that the sediment transport variation period was one year at Shizuishan and Toudaoguai hydrologic station, but runoff variation period was one year and six months for the two stations respectively. Runoff Hurst number was 0.576 and 0.515, and sediment transport Hurst number was 0.519 and 0.249 respectively at Shizuishan and Toudaoguai hydrologic station. The probability of abundant flow low sediment and less discharge high sand was about 50%, the sum of the limit probability of large discharge high sediment and water shortage low sediment transport was greater than 0.8. There were asynchronization and incongruity of runoff and sediment time-order characters by the effect of incoming runoff and sediment process, hydroclimatic characteristics, human activities. Runoff and sediment transport process will be gradually coordinated in the future.

Abstract:In the Loess Plateau, as the significant measure for preventing and reducing the sediment into the Yellow River, check dams are playing an essential role in sediment retention and farmland-making. In order to study the effect of check dam on the changes of soil erosion, sediment yield and sources in dam-controlled watershed, a check dam named Yuanzigou in Huangfuchuan watershed of Pisha sandstone area was selected as the research object. The soil samples were collected on the check dam profile and the surface of the slopes including land between gullies and gully region. The sediment deposition records of sediment couplets were analyzed by identifying the relationship between rainfall events and sediment couplets. The sediment sources were assessed and the changes of the sediment yield intensity were analyzed. The particle size analysis indicated that the sediment particle size distribution of the sediment profiles in the check dam mostly concentrated in the range of 0.05~2 mm sand, in which the proportion of very fine sand and fine sand was the most, followed by silt and clay. According to the corresponding relationship between rainfall events and sediment couplets, the minimum daily rainfall corresponding to erosive rainfall events in the dam-controlled watershed was 22.8 mm. And the sediment deposition process was divided into 2007-2013 and 2013-2016. In the early stage, it mainly depended on the dam body to trap sediment, and in the later stage, as more sediment is trapped the effect of erosion reduction was prominent. The results of sediment contribution analysis indicated that 71.4% of the sediment was contributed by the gully region and 28.6% by land between gullies. The erosion and sediment yield of land between gullies were not only affected by vegetation. When the daily rainfall was more than 45.4 mm, topographic factor would limit the the further occurrence of erosion.

Abstract:Taking the wind-break and sand-fixing forests in the Bashang area of northern Hebei as the research object, the effects of three artificial shrublands (Hippophae rhamnoides Linn. Caragana korshinskii and Salix pasmmophia) on wind erosion prevention were compared and analyzed by observing wind speed, surface roughness, critical sand-blown wind speed, sand transporting quantity and wind-sand flow structure. The results showed that artificial shrubland could increase the surface roughness, change the near-surface wind field and wind-sand flow structure, reduce the wind speed, reduce the sand transporting quantity, and consequently effectively control soil wind erosion. The effects of different artificial shrublands on wind erosion prevention were quite different. From the main observation indicators, roughness and critical sand-blown wind speed:Caragana korshinskii > Hippophae rhamnoides Linn. > Salix pasmmophia; sand transporting quantity:Caragana korshinskii < Hippophae rhamnoides Linn. < Salix pasmmophia; windbreak effect:Hippophae rhamnoides Linn. > Salix pasmmophia > Caragana korshinskii; sand fixation effect:Caragana korshinskii > Hippophae rhamnoides Linn. > Salix pasmmophia. The characteristics of windbreak, sand fixation and soil and water conservation of trees should be fully utilized. The biological desertification control technology and measures should be used for ecological construction in Bashang area of northern Hebei, and ultimately for controlling soil wind erosion and improving the ecological environment.

Abstract:To study the mechanism of vegetation affecting gravity erosion may provide the theoretical basis for the design of soil and water conservation on the Loess Plateau, China. This study explore the effects of vegetation on the gravity erosion using the models of loess gully sidewall with the slope degree of 70° and height of 1.5 m under a series of rainfall simulations, in which vegetational and bare lands were used, respectively. The experimental results are shown as follows:(1) The influence of the vegetation on the total amount of gravity erosion might be ignored. The average amount of gravity erosion for each event of rainfall on the vegetational sidewall was only decreased by 12% compared with that on the bare sidewall. (2) The vegetation had a positive effect on the gravity erosion after rainfalls. The ratio of the gravity erosion volume after rainfalls to the total on the planted slope was almost 12%, while the ratio on the bare slope was only 1%. (3) The vegetation on the gully sidewall had different influences on various types of gravity erosion. Compared with those on the bare land, the average amounts of the avalanche and mudslide on the vegetated slope was decreased by 72% and 69%, respectively. In the meantime, the average amount of landslide in the vegetated slope was increased by 220% compared with that on the bare slope. (4) The effects of vegetation on gravity erosion were caused by several factors. The plant roots might reinforce the soil and reduce the amount of gravity erosion, but the self-gravity of the plant and increase of the permeability on the planted slope might aggravate the gravity erosion. In addition, the soil permeability was increased by the plant roots, which could intensify the landslides. As a result, the vegetation construction was preferable for the sidewall vulnerable to mudslide. The results might be referred to analyze the mechanism of mass failure and design the control of gravity erosion.

Abstract:To reveal the soil developmental characteristics on the erosive weathered granite slopes, soil samples of a typical weathering granite slope in Zhejiang Province were studied by the methods of CT scanning technique, X-ray fluorescence spectrometer and laboratory soil physicochemical properties test based on the principles of soil genesis and water erosion. The results showed that the total developmental degree of the soil samples was weak because the varying difference between the up and bottom layers was very small and the soil level-development was not obvious. The weathering intensity displayed an order of bottom profile < middle profile < top profile, which was just opposite to that in terms of the erosion intensity. The physical weathering indexes increased significantly with soil depth while the desilication process weakened. The varying range of chemical weathering intensity was not significant in the all soil profiles and it was different from the local zonal soil development which gave priority to chemical weathering features. Physical and chemical weathering indexes had the equal effect on describing the soil developmental characteristics. Water erosion affected the soil weathering processes and hindered the soil development to typical zonal soil. The maximum weathering intensity was between the surface layer of 20-40 cm, which indicated that the soil layer of 0-40 cm was greatly affected by water erosion.

Abstract:The application of earthworm casts has significant effects on soil infiltration and aggregate composition. This study was carried out in the test area of the idle farmland of the loess area. Earthworm casts were applied in two methods:(A) earthworm casts mixed with the soil of the (0-5 cm) surface layer and (B) mulched 5 cm of soil layer after broadcast application of earthworm casts. Different levels of earthworm casts were designed to study on sediment yield and nitrate nitrogen loss with the runoff under rainfall conditions. The results showed that:(1) Both application methods effectively delayed the time of runoff occurring. The time of runoff occurring under layer application of 800 g/m² was delayed by 3.88 min compared with CK, and the delay effect was the most obvious. (2) The layer application of 800 g/m² could significantly reduce the rate of runoff increase in the early stage and delay the time of entering the stable stage. The variation of cumulative runoff with time could be well described by a power function. (3) Under the mixed application and layer application at 800 g/m², the sediment yield in the stable phase was significantly reduced by 79.61% and 86.74% than CK. The accumulated sediment yields could be well described by the power function with the time, and the initial sediment yield was significantly reduced with the increase of the amount of earthworm casts. (4) Mixed application could significantly reduce the nitrate concentration in runoff. When the amount of application was large and the application method was layer application, it could play a good role to prevent the sediment and chemical solute loss with runoff.

Abstract:In order to reveal the typical soil splash erosion characteristics of slope farmland in Low Mountain and Hilly Region of Western Liaoning Province, cinnamon soil and brown soil were selected as the research objects, and the differences of splash erosion between the two soils were studied by artificial simulated rainfall experiment. The results showed that there were great differences in splash erosion, net splash erosion and total splash erosion in different directions between cinnamon soil and brown soil. The splash erosion rate of brown soil decreased and tended to be stable with the increasing rainfall duration under different rainfall intensities; the changes of splash erosion rate of cinnamon soil with rainfall duration could be divided into four stages:slow growth stage, rapid growth stage, rapid decline stage and relative stably stage. The critical value of rainfall duration for completing migration of small particles in cinnamon soil and brown soil were 20~25 min and 10~15 min, respectively, which was consistent with the critical values of rainfall duration for splash erosion rate, net splash erosion rate and total splash erosion rate with different directions. The uphill splash erosion rate, downhill splash erosion rate, net splash erosion rate and total splash erosion rate of cinnamon soil were significantly quadratic polynomial relationship correlated with rainfall duration, while significantly logarithmic for brown soil.

Abstract:Fingerprint technique is effective in relative sediment contribution estimation. As recently developed methods, Bayesian model and analytical solutions for single factor received more and more attentions. However, compared with most often used multivariate mixing models, their performance and stability in calculating the proportion of sediment sources kept unknow. In order to make clear the contribution of topsoil and subsoil in a typical small watershed in the black soil region of Northeast China, where distributed vast farmlands experiencing serious soil erosion and a number of gullies developing very fast, these three methods were introduced to provide estimation. In this studied watershed with 27.60 km² area, totally 69 samples from the sediment sources area and 30 samples from the sedimentation area were collected. Sediment sources covered 45 topsoil samples in farmland, woodland and grassland, and 24 subsoil samples from gullies. Based on the analysis for 33 properties in these samples, the optimal composite fingerprints including P, Ce, Ga, Rb and ¹³⁷Cs were screened by non-parametric test and multiple discriminant analysis. Taken these 5 fingerprints as group I, radionuclides ¹³⁷Cs and ²¹⁰Pb_ex as group II, Walling-Collins model, the representative of multivariate mixing models, and Bayesian model were used to calculate the sediment contribution for the two potential sources, respectively. Taken each property in the optimal composite fingerprints as group III, analytical solutions for single factor were also used to provide such estimation. The results showed that the contribution ratios of sediment sources based on different fingerprint group and various methods were similar, for example, the ratio provided by group II (topsoil 47.5% and subsoil 52.5%) kept consistent with that calculated by group I (topsoil 44.6% and subsoil 55.4%), while the multivariate mixing model was adopted, the contribution estimated by group II (about half to half) was slightly different with that based on group I (topsoil 58.8% and subsoil 41.2%) in Bayesian model. However, the results provided by these two models were relative great-up to 14.2%, while taken group I as tracers. In group III, P, Ce, Ga, and ¹³⁷Cs could differentiate the sources while applying for the single factor in analytical solutions, the results that half contribution from topsoil and half from gully, were not completely same, but very closed. The differences in sediment contribution might be caused by different principles of models. There were still some spaces to make improvement for different models in order to obtain more reliable results. Attention should also be paid to the gully, as it has caused severe soil erosion and contributed about 50% sediments with less than 1% area ratio in the whole watershed. To reduce sediment derived from the watershed, it is necessary to strengthen prevention and treatment for the gullies to the future land management and soil erosion controls.

Abstract:The abandoned cropland is spreading widely all over the world. Traditional survey methods can not meet the need of timely and accurate grasp of abandoned cropland. In view of the insufficiency of optical remote sensing images, and that it is difficult to accurately identify and extract the abandoned cropland in karst rocky desertification land from the serious mixed pixels, taking Xifeng County of Guizhou Province as an example, the high-resolution image and rocky desertification grade data were used to identify and extract different rocky desertification grade cultivated land plots. The time series NDVI data of 2003-2018 obtained by calculating the Landsat data by MVC method was superimposed, and the spatial and temporal distribution of the abandoned cropland and reclamation in Xifeng County in 2003-2018 was extracted. The results showed:(1) The combination of cultivated land plot and time series NDVI could accurately identify and extract abandoned cropland. This method had a good application in the area lacking of optical data and the cloudy rainy mountain area where the cultivated land is broken. (2) In 2003-2018, the abandoned cropland in Xifeng County was randomly scattered and mainly distributed in the potential, mild and moderate rocky desertification area in the north and east. In 2008, the largest abandoned area was 2 545.6 hm² and the highest rate of abandonment was 7.7%. In the period of 2003-2018, there were 7 plots of abandoned land that lasted for a maximum of 12 years, and 8 plots accumulated for up to 15 years. (3) In 2003-2018, the reclamation rate of Xifeng County was basically consistent with the fluctuation trend of the abandonment rate, but the response to the reclamation rate was delayed by one year. There was a certain difference between the non-karst cultivated land reclamation behavior and the rocky desertification cultivated land reclamation behavior. The higher rock desertification grade negatively affected the reclamation behavior. The research results could provide an efficient and feasible idea and method for the accurate identification and extraction of abandoned cropland in karst cloudy and rainy mountainous areas, also provide the accurate and basic data for driving factor analysis, trend monitoring and risk assessment, effect assessment and policy design in abandoned cropland.

Abstract:The mining of rare earth produces a large amount of tailing, resulting in serious soil erosion, associated with water quality and geological disasters. Evaluating the effect of vegetation restoration measures on soil erosion control of rare earth tailings can provide theoretical basis for the optimization of measures. With the method of spatial sere substituting for time sere, this study took ion-type light rare earth tailings area of Xunwu County as an example to analyse the response mechanism of soil erosion to vegetation restoration measures under different repair years, using the RUSLE and its total differential formula based on GIMMS NDVI 3 g data from 1982 to 2015, DEM and field survey data. The results showed that soil erosion modulus decreased obviously at a rate of -60 t/(km²·10a), and the change point was 2008. The annual average soil erosion decreased by more than 60% before and after the implementation of vegetation restoration measures (2008). The soil erosion modulus showed the stage changes of rising, stable, rising, stable, rising and falling, and the NDVI showed the opposite changes in the corresponding period. The contribution rates of the soil and water conservation practices factor, the vegetation cover factor, the soil erodibility factor and the rainfall erodibility factor to soil erosion reduction were 33.18%, 32.19%, 19.95% and 13.19% respectively. The main influencing factors of soil erosion reduction in the rare earth mining area of Xunwu County were the soil and water conservation practices factor and the vegetation cover factor.

Abstract:Due to the poor structure and severe compaction of tailings, surface runoff is easily generated. Water has become an important limiting factor for its ecological restoration. In order to further understand the difference of hydraulic characteristics between tailings and soil, and to provide a scientific improvement for iron tailings sand, the water transport characteristics of iron tailings and soil under five compaction levels from natural bulk density to maximum compaction density (iron tailings from 1.50 g/cm³ to 1.70 g/cm³, soil from 1.30 g/cm³ to 1.50 g/cm³) were compared by indoor soil column simulation. The water infiltration capacity of natural bulk density of 1.50 g/cm³ iron tailings sand was lower than that of soil with 1.30 g/cm³ under natural bulk density. With the increase of the bulk densities, the water infiltration parameters of both tailings sand and soil decreased in the form of power function. But the infiltration capacity of iron tailings and soil presented respectively significant reduction at the level of 1.60 g/cm³ and 1.40 g/cm³. Based on the overall water parameters including water infiltration rate, wetting front distance, cumulative infiltration volume, saturated hydraulic conductivity, and water distribution in profile, the water transport capacity of soil was higher than that of iron tailings in the lower bulk density levels; however, due to the effect of bulk density on soil water transport was greater than that on iron tailings, the water transport capacity of soil was not as good as iron tailings under the higher bulk density levels. The shape of the water characteristic curve of the iron tailings sand was completely different from soil; the iron tailings sand was "convex", which was characterized by gentle change in the high suction and steep change in the low suction section, while that of soil was "concave", which was characterized by steep change in the high suction section and gentle change in the low suction section. Therefore, soil or other matrix similar to soil structure can be added to tailings to tailings sand could be added by soil or other matrix similar to soil structure to enhance its poor water holding and hydraulic conductivity, and promote ecological restoration.

Abstract:In order to study the effects of different straw application depths on soil water transport and water suction changes, the characteristics of soil water transport and distribution under different straw application depths were simulated by laboratory simulation test. Corn straw was crushed into small sections of less than 5 mm and stored in dry space. For the given application depth, straw was mixed with dry soil evenly with 1% application ratio. Five treatments were set up:no straw returning (CK), straw application depth of 15 cm (S15), straw application depth of 20 cm (S20), straw application depth of 25 cm(S25), straw application depth of 30 cm (S30). Soil water suction value was measured by micro-tensiometer(T5). The results showed that the application depth of straw had an effect on soil water infiltration characteristics. With the increase of straw application depth, the transport distance of wetting front and the cumulative water infiltration amount decreased. The influence of straw application depth on wetting front migration was obvious. At the same infiltration depth, the moisture content of soil layer containing straw increased significantly than that without straw layer. Straw application depth had an important impact on soil water suction, the changing trend of soil water suction values at different soil depth was roughly the same. Different straw application depth led to the difference of soil water suction peak and peak time under the same soil layer depth. The deeper straw application was applied, the greater the peak value of soil water suction and the longer the time to reach the peak value.

Abstract:The application of chemical amendments is an important way to improve soil and water availability of farmland. It is the basis for rational use of chemical methods to improve soil by understanding the effects of chemical amendments on soil water movement processes. In this study, the effects of different chemical amendments on soil infiltration and evaporation characteristics were studied by applying different rates of polyacrylamide (PAM) and sodium carboxymethyl cellulose (CMC). The results showed that with the increasing rates of chemical amendments applied, both amendments hindered soil water infiltration and inhibited soil surface evaporation. Considering the performance of water retention and evaporation inhibition for different amendments, the effect of applying CMC was higher than that of PAM, and the CMC application rate of 0.08% was the best. Under the same effect on water retention and evaporation inhibition, the application rate of CMC was less than that of PAM, and thus CMC had a wider application prospect. This study could provide a theoretical reference for rational use of chemical amendments for soil water retention and evaporation inhibition.

Abstract:There are many methods to measure soil permeability, however, each method shows some defects when used on the biocrustal (biological soil crusts) soil on slope lands. Line source infiltration method is a simple and rapid method for the measure of infiltration on slope land without biocrusts. In this study, the water infiltration processes of bare soil (control) and different types of biocrusts, including cyanobacteria dominated, cyanobacteria-moss mixed and moss dominated biocrust soil in the Hilly Loess Plateau region were tested by using line source infiltration method. Meanwhile, the simulated rainfalls were applied on the same plots to get the permeability of the soils. The results showed that:(1) The line source infiltration method can describe the water infiltration process quickly and completely without disturbing the biocrusts. Meanwhile, the parameters such as initial infiltration rate, average infiltration rate and stable infiltration rate were observed stably. (2) The initial infiltration rate range of different types of biocrust obtained by the line source infiltration method in the study area was 3~12 mm/min, the average infiltration rate range was 0.5~4.5 mm/min, and the stable infiltration rate range was 0.3~1.8 mm/min. With the increase of moss coverage, the initial, average and stable infiltration rates were significantly different. (3) There was a significant linear correlation between the stable infiltration rates of biocrusts soil measured by the line source infiltration method and those of the simulated rainfall (y=1.73x-1.24, R²=0.376 8, ρ =0.539^*). This study provides a simple and easy method for the determination of water infiltration rate in biological crusts soil on slope lands.

Abstract:Surface microtopography measurement is the basis of surface roughness quantification, which is of great significance to the dynamic monitoring of surface morphology and the study of soil erosion process. This research adopted the chain method, cameras and unmanned aerial vehicle (uav) method, selected the conventional artificial rainfall soil bin and field runoff plots, set up the bare land and two processing plant roots respectively, to determine the surface roughness. The results showed that:(1) The average curvature indexes determined by the chain method, cameras and uav method were 0.257, 0.219 and 0.248, respectively, with the average actual bending index deviation was less than 0.242 < 10%. Among them, the bending index measured by the chain method was relatively large as a whole (6.2%), the bending index measured by the camera method was relatively small as a whole (-9.5%), and the bending index measured by the uav method was slightly large, but the error was only 2.5%. (2) The groove of bare soil was deep, and the measured results of chain method and camera method were inconsistent with the reality. The measured results of uav method were relatively consistent with the reality, and the chain method and camera method were slightly smaller than uav method by 50.0% and 40.3% respectively. The results of the chain method with root soil groove were not consistent with the actual conditions, and the results of the camera method and the uav method were relatively consistent with the actual conditions. The chain method was 48.2% and 57.8% respectively smaller than the camera method and the uav method. (3) Limited by the topographic factors, the camera method could not determine the surface roughness of runoff plot. For bare land and rooted plots, the measured results of uav were relatively consistent with the actual situation, while the measured results of chain method were inconsistent with the ups and downs of the surface. The surface bending index measured by chain method was slightly higher than that by uav method by 28.6% and 24.8%, respectively. In general, stereoscopic photogrammetry could effectively reflect surface roughness. However, due to the limitations of shooting height and terrain factors, the measurement results of camera method might be underestimated or limited, and the measurement results of uav method were relatively stable. Due to the influence of human operation and the error of the measurement process, the error of the measurement results of the chain method was relatively large.

Abstract:In order to find out the main factors affecting the leakage of pressure infiltration channels, the constant water level static water test method was adopted to carry out the leakage test of channels. Eight infiltration heads were set up to explore the change rules of the cumulative infiltration amount and infiltration rate of channels under different water depths, and Hydrus-2D software was selected for simulation analysis. The results showed that the simulated values and measured values were basically consistent. The RMSE values of infiltration rate were 0.003 6~0.376 3 cm/h, and RMSE was 0.001 7~0.300 9 m³ for cumulative infiltration amount, the average of R² was always more than 0.9, indicating that the soil water movement equation and its related parameters were reasonable, the channel leakage evaluation was feasible. The influence of water depth, bottom width and slope coefficient were analyzed by field expansion test of Hydrus-2D model. The results showed that the change of channel water depth had a great influence on the infiltration rate, while the change of channel bottom width and slope coefficient had a small influence on the infiltration rate. The influence of channel water depth, bottom width and slope coefficient on cumulative infiltration amount was extremely significant (P<0.01), and the degree of influence on cumulative infiltration amount was:channel water depth > channel bottom width > slope coefficient. Among them, the interaction between channel bottom width and slope coefficient had no significant influence on cumulative infiltration amount (P>0.05), but the interaction between channel water depth and slope coefficient had an extremely significant correlation with cumulative infiltration amount (P<0.01), and the interaction between channel water depth and slope width had an equally significant correlation with cumulative infiltration amount (P<0.01). This study could provide a reference for exploring the rule of water infiltration, improving the technology of seepage prevention and developing a new method for calculating leakage loss.

Abstract:Bioretention facilities are one of the effective measures for rainwater management with low impact development. In order to explore the method of optimizing the configuration and parameters of biological facilities by using mathematical models, the RECARGA model was used to evaluate the hydrological regulation effect of the changes of design parameters and structure of biological detention facilities, and to quantitatively analyze the relationship between design parameters and hydrological performance, so as to determine the appropriate method of setting biological detention pools. The results showed that the soil hydraulic conductivity at the bottom of the facility was a limiting factor for the hydrological performance of the whole system, and the annual rainfall retention increased with the increase of soil hydraulic conductivity in a significant logarithmic function. There was a significant logarithmic function relationship between rainfall retention rate and facility surface area ratio. Rainwater retention had a significant power function relationship with depression zone thickness, and a good linear relationship with root layer and storage layer thickness. Considering drainage time factors, the depth of depression zone should not be greater than 15 cm. These research results could provide a theoretical basis for the scientific design of bioretention facilities structure.

Abstract:Soil aggregation and transformation play an important role in soil erosion and vice versa. The quantifiably breakdown and transformation pathways of soil aggregate have not been clarified. The limitation hampers the in-depth study of sediment separation and transport mechanism of soil erosion processes. Recently, ¹³⁷Cs, ²¹⁰Pb, ⁷Be and magnetite tracer methods have been widely applied to soil erosion research at slope and small watershed scales. However, those methods are not suitable for tracking multiple erosion processes simultaneously. Six typical agricultural soils with different texture from Loess Plateau and black soil region in China were selected in this study. Rare earth elements (REE) tracer method was applied to quantify the transformation pathways of five soil aggregate fractions (5~2, 2~1, 1~0.5, 0.5~0.25, < 0.25 mm). The adsorption and desorption capacity of REE on different aggregates were analyzed with the simulated runoff disturbance cycles. Results showed that the actual adsorption concentration of REE and soil aggregates were lower than that of the application concentration. REE adsorption concentration of soil aggregates at 2~1, 1~0.5, 0.5~0.25 and < 0.25 mm were significantly positively correlated with the clay content (P<0.05). The effect of runoff disturbance on the desorption of REE adsorbed on soil aggregates was very weak, and the desorption concentration only accounted for 0.001%~0.139% of the actual adsorption concentration of REE. The transformation pathways among the 5~2, 2~1, 1~0.5, 0.5~0.25 and < 0.25 mm soil aggregates fractions were basically the same, converting to < 0.25 mm microaggregates was the main pathway. The transformation rate of soil aggregates with high sand content to 1~0.5 and 0.5~0.25 mm fractions was generally lower, compared with soil aggregates with high content of silt and clay. The REE tracer method underestimated the labeled > 0.25 mm aggregates, which ranged from -27.96% to -11.08%. However, < 0.25 mm aggregates was overestimated by 3.65%~22.73%. Based on the REE quantification values of soil aggregates of various particle sizes, a correction relationship was established, which could reduce the calculated relative error to 0.04%~16.24%.

Abstract:Based on the agricultural flood drought data from 1950-2017 and the runoff data from 1956-2017 in Dongting Lake area, the degree and risk of agricultural flood and drought disasters and their trends in Dongting Lake area after impoundment of the Three Gorges Reservoir were analyzed by using the methods of flood and drought disaster acceptance rate, theory model of entropy information diffusion, standardized runoff index (SRI), and re-standard polar difference analysis (R/S). The results showed that:(1) After impoundment of the Three Gorges Reservoir, the rate of flood stricken decreased from 6.65% to 1.21%, the rate of flood disaster decreased from 2.97% to 0.71%, the rate of drought stricken decreased from 5.97% to 2.48%, and the rate of drought disaster decreased from 2.98% to 0.99%. (2) When the disaster rate of agricultural flood and drought disaster was more than 5%, 10%, 15%, and 20%, the probability of flood risk was 0.415, 0.192, 0.057 and 0.025, and the probability of drought risk was 0.518, 0.359, 0.037 and 0.001, respectively. The flood risk level was medium to low risk (disaster rate was more than 5%, 10%) and low risk (disaster rate was more than 15% and 20%). Drought risk level was medium risk (disaster rate was more than 5%), medium to high risk (disaster rate was more than 10%), and low risk (disaster rate was more than 15%, 20%). (3) The trend of flood and drought disasters will be a reducing trend for floods and an increasing trend for drought in studied areas.

Abstract:Taking nine typical measures for controlling rocky desertification in Huajiang karst Canyon of Guanling, Guizhou Province as test objects, including Zanthoxylum bungeanum (HJ), Hylocereus undulatus (HL), Zanthoxylum bungeanum and Hylocereus undulatus (HHL), Pennisetum hydridum (HZ), Medicago sativa (MX), Sabina chinensis (YB), Sabina chinensis and Ligustrum lucidum (YBN), Bare land (LH), and slope farmland (PD), the distribution of organic carbon, total nitrogen, and water-soluble organic carbon in soil profile under different control measures was studied. The results showed that the contents of soil organic carbon, total nitrogen, reserves and water-soluble organic carbon decreased with the increase of soil profile depth in 0-20 cm soil layers, and the phenomena of surface accumulation were obvious. The order of average soil organic carbon and total nitrogen content in 0-20 cm layer was YB > YBN > LH > HJ > MX > PD > HHL > HL > HZ, YBN > YB > LH > PD > MX > HJ > HZ > HHL, respectively. Soil organic carbon, total nitrogen reserves and water-soluble organic carbon content also showed that YB, YBN, and LH were significantly higher than the other six control measures. Soil C/N of each control measure ranged from 7.19 to 16.35. Correlation analysis showed that soil organic carbon content was significantly correlated with soil total nitrogen content, organic carbon storage and soluble organic carbon content. Soil bulk density was the key factor of soil carbon and nitrogen index, and had a good correlation. The study clarifies that in the process of controlling rocky desertification in the future, returning farmland to forest and abandoning desert land will be beneficial to the control and protection of karst ecological environment. Zanthoxylum bungeanum forest can be regarded as the priority economic vegetation type in the process of agricultural production or ecological restoration in Karst Mountainous areas.

Abstract:Rock fragments in purple soil can directly affect soil water diffusion. The past research mainly focused on the rock fragments with particle size > 2 mm, while the particle size of < 2 mm was ignored. Therefore, based on discussing the influence of the particle size > 2 mm on the water migration of purple soils, it is of great significance to clarify the influence of < 2 mm rock fragments on the moisture diffusion of purple soil containing rock fragments, thus providing theoretical basis for the construction of soil hydrodynamic model. Purple shale and mudstone in Sichuan basin and their developed soils (dark brown purple soil and red brown purple soil) were taken as research objects, three kinds of rock fragments particle sizes (0.25~2, 2~5, 5~10 mm) and four kinds of rock fragments contents (0, 30%, 50%,70%) were set. The horizontal soil column suction method was used to determine the progress of wet front of the soils containing rock fragments, the water diffusivity D(θ) and the soil moisture content θ, Fitting the relationship between D(θ), Boltzmann parameters λ and θ. The result showed that for dark brown purple soil, when the particle size of the rock fragment was 2~5 mm, with the increase of rock fragments contents, the advancing rate of soil wetting front and D(θ) both had a tendency of increasing first, then decreased and finally increased; while when the particle size of the rock fragment was 0.25~2, 5~10 mm, with the increase of rock fragments contents, the advancing rate of soil wetting front and D(θ) gradually increased. For red brown purple soil, when the size of rock fragment was 2~5, 5~10 mm, the D(θ) of 70% rock fragments content was obviously larger than that of the other three rock fragments content of soils. The D(θ) of 30% rock fragments contents and 50% rock fragments contents were not significantly different. The advancing rate of soil wetting front had a tendency of increasing first, then decreased and finally increased. While when the particle size of the rock fragments was 0.25~2 mm, with the increase of rock fragments contents, the advancing rate of soil wetting front and D(θ) gradually increased. Therefore, with the increase of rock fragments contents, the soil water migration rate showed an increasing trend as a whole, and the water migration rate of soil which was developed by mudstone was higher than that by shale.

Abstract:In order to understand the C cycle characteristics in dominant tree communities in soils developed form different lithologies in Karst area, the δ¹³C value and soil organic matter renewal of various tree species communities were measured for six woody species (cypress, Cupressus funebris; mansur shrub, Coriaria nepalensis; camphor, Cinnamomum bodinieri; birch, Betula luminifera; alder, Alnus cremastogyne and dyetree, Platycarya longipes) planted in three different lithologic soil types (dolomite, dolomite sandstone, limestone) in the karst area of Guizhou Province. Results showed that:(1) Changes of δ¹³C values in plant species in different lithologies, the δ¹³C value of cypress funebris on limestone had very significant difference with other lithologies (P<0.001), Alnus cremastogyne had significant difference in limestone and dolomite (P=0.024). There were significant or extremely significant differences among three tree species (Cinnamomum bodinieri, Cupressus funebris, Coriaria nepalensis), or with other tree species (P<0.05 or P=0.001). The δ¹³C values of each organ in tree species were leaf < branch < root. (2) Changes of δ¹³C values in plant-litter-soil system:on the three lithologies, the change law of community of each tree species was basically the same, that is, plant leaves (fresh litter) < litter decomposition layer < branch < root < upper soil < lower soil. There was a significant difference in δ¹³C values between soil layer and plant and litter (P<0.001). Compared with litter layer, the increased degree of community of Cinnamomum bodinieri and Cupressus funebris on dolomitic sandstone was larger, 11.68‰ and 11.10‰ respectively, while the increased degree of Coriaria nepalensis on dolomite and Alnus cremastogyne on limestone was smaller, by 1.07‰ and 2.73‰, respectively. (3) Renewal rate of soil organic matter:the highest was the community of Coriaria nepalensis on dolomite, 43.84%, followed by the community of Alnus cremastogyne on limestone, 34.17%, and the lowest was the community of Platycarya longipes on limestone, 1.15%. Organic carbon turnover showed that the slope K of regression equation of dolomite plant community was 3.15, followed by plant communities on limestone was 0.85. The organic carbon contents were not correlated with δ¹³C values in dolomitic sandstone. The results of the study would be of great significance to reveal the characteristics of C cycle, migration and nutrient transfer in different plant communities in lithologies of karst area.

Abstract:Rainfall is the main source of water in arid and semi-arid areas. Rainfall, rainfall duration and rainfall intensity all affect rainfall water infiltration, which in turn affects the replenishment of rainfall to different soil layers under the surface. It is important to study the dynamic response of soil moisture in different soil layers to different rainfall patterns in arid and semi-arid areas to reveal the key elements of water and soil, grassland desertification prevention and climate change responses. Through the continuous observations of the rainfall and the volumetric water content data of 5, 15, 30, 60 and 100 cm below the soil surface in the Xilin Gol League, and the changes of soil moisture in each soil layer and their response to the rainfall events were studied. The results showed that for grassland in arid and semi-arid areas, rainfall could significantly affect the soil moisture in soil layer of 5-60 cm; with the deepening of soil layer, the soil moisture increment caused by the same rainfall process showed a decreasing trend. The increase in soil moisture in 0-10 cm and 10-20cm soil layer was obvious, while if the rainfall was less than 3, 6, 20, 50 mm, water could not reach the 5, 15, 30 and 60 cm soil layers. The heavier rainfall intensity and the higher soil moisture content before rainfall were favorable for the rain water infiltration. The increase of soil moisture in 5-60 cm soil layer had significant or extremely significant linear relationship with rainfall intensity, initial soil moisture content and their interaction. But there was no significant linear relationship in 100 cm soil layer. The soil moisture increments in the 30 and 60 cm soil layers occurred only when the rain-free day interval was extremely short or the rainfall was very large.

Abstract:To reveal the water-uptake patterns of different plant species in subtropical humid area and to understand the hydrological cycle of regional forest system, the typical evergreen plant species Cinnamomum camphora, Cunninghamia lanceolate, and Camellia pitardii in Changsha were used as research objects by using stable isotope techniques and Iso-source Mixed Model for quantitative analysis of the water-uptake patterns of different plant species and their responses to precipitation. The results showed that the variations of δD in water from 0-10 cm soil layer and the δD in precipitation are basically identical, and the two kind of δD become more positive with time gradually during the observation period from September 2018 to February 2019. With the increase in depth, the influence of precipitation on δD in soil water gradually reduced and tended to be stable. During September to November, the reflection to precipitation of the three plant species became smaller. The δD in the plant stem water did not show more positive in line with the δD in precipitation. From December to the next February, the three plant species responded sensitively to precipitation. The variation of δD in plant stem water was consistent with the change of δD in precipitation. During the observation period, the water use depth of these plants changed from deep to shallow with time. In September, these plants mostly used 60-100 cm soil water, and the proportion exceeded 65%. During October to November, there were obvious differences in the water-uptake patterns of these plants. The water use of C. camphora from the four soil layers for 0-10, 10-20, 20-60 and 60-100 cm was relatively uniform, and the proportion was 28.2%, 23.5%, 22.0%, and 26.3% respectively; C. lanceolate primarily used 0-10 and 60-100 cm soil water, and the proportion was 56.4% and 22.2% respectively; C. pitardii principally absorbed 0-20 cm shallow soil water, the proportion was 67.4%. From December to February of the next year, these plants generally used 0-10 cm soil water, and the proportion was above 70%.

Abstract:To study the effects of different cultivation methods and irrigation schedules on growth, yield, and water use of winter wheat, three cultivation modes were conducted with field experiment in Shandong province:Traditional Cultivation (TC), Ridge Cultivation (RC), and High and Low Cultivation (HLC), three levels of irrigation quota (900 m³/hm², 720 m³/hm², 540 m³/hm²) were set up in RC and HLC respectively, while there was only 900 m³/hm² irrigation quota for TC. The changes in soil moisture, water consumption, and water use efficiency (WUE) of winter wheat in the three cultivation methods were studied. The results showed:the soil water content of winter wheat at different growth stages was significantly different under different cultivation methods, and the ability of storing rainfall in RC method was better than the other two methods. The cultivation methods had significant effects on the water consumption characteristics and water use efficiency of winter wheat, and there was a significant positive correlation between winter wheat yield and water consumption (R²=0.86, P<0.01). Compared with RC and TC, the wheat of HLC developed vigorously, with higher number of panicles and grains per mu. The total water consumption under HLC method was 14.16% and 19.90% higher than that of TC and RC respectively, while the yield of HLC was 22.63% and 27.37% higher than that of TC and RC respectively. Furthermore, the WUE of HLC was 7.69% and 6.87% higher than that of TC and RC. Overall, HLC cultivation can significantly improve the yield and WUE of winter wheat, and it could be an ideal water-saving and high-yield cultivation method in the study area.

Abstract:The effects of temperature change on wheat field temperature, soil moisture change, and water use efficiency were studied by simulated temperature increase and decrease method. The results showed that the average 5 cm ground temperature of the warming wheat field and the cooling wheat field in the whole growth period increased by 0.85 ^oC and decreased by 2.57 ^oC, respectively, compared with the conventional wheat field. The simulated warming effect of the warming wheat field was winter > autumn > spring, and the simulated cooling effect of the cooling wheat field was spring > autumn > winter. The average volumetric water content of 5 cm soil layer in the whole growth period of the simulated warming and cooling wheat field was 3.76% lower and 4.84% higher than that of conventional wheat field, respectively. The study of soil water change in 0-200 cm soil layer of simulated warming, cooling wheat field, and conventional wheat field showed that the water storage of simulated warming and conventional wheat field (except mature stage) was lower than that of simulated cooling wheat field at all growth stages; the water consumption in 0-200 cm soil layer during whole growth period in warming wheat field was higher than that in simulated cooling and conventional wheat field, of which the proportion of 0-100 cm water consumption to 0-200 cm in simulated warming wheat field (55.72%) and conventional wheat field (55.14%) was lower than that of simulated cooling wheat field (63.45%), while the proportion of water consumption of 100-200 cm to 0-200 cm in simulated warming wheat field (44.28%) and conventional wheat field (44.86%) was higher than that of simulated cooling wheat field (36.55%). The water use efficiency of simulated warming wheat field was lower than that of conventional wheat field and simulated cooling wheat field. This study can provide theoretical basis and technical support for the impact of climate warming on wheat production system.

Abstract:The purpose of this study was to investigate dynamic variations of soil water under the phreatic evaporation with different aperture ratios of plastic mulch. Based on column simulation laboratory indoors, HYDRUS-1D model was used to simulate variations of soil water content under different aperture ratios of plastic mulch and atmospheric evaporation capacity, and then the result was compared with the measured data.The results indicated that soil water content was affected by both aperture ratio of plastic mulch and atmospheric evaporation capacity.The soil water content decreased with the increase of the aperture ratios of plastic mulch and atmospheric evaporation capacity with the same depth of soil profile. The fluctuations of soil water content in the upper layer was more obvious than that in the lower layer. When the aperture ratio of plastic mulch and atmospheric evaporation capacity was fixed, the soil water content increased in the early evaporation period and remained stable in the later evaporation period. The evaporation was obviously inhibited by plastic mulch, but when the opening rate of mulching increases to a certain value, the effect of surface salinity on soil evaporation is greater than that of mulching. Mulching increases soil moisture content and decreases cumulative evaporation. The simulation precision of model which was checked by the measured data was well. So it is feasible with HYDRUS-1D model to simulate soil water movement under different aperture ratios of plastic mulch.

Abstract:In order to investigate the effects of sandy soil and mixed biochar on water and salt transport and tomato growth characteristics in saline-alkali soil under drip irrigation, field plot experiment was carried out with three treatments, including control (CK), sand hole (T1), and sand hole mixed with biochar (T2), analyze the effects of sand holes on soil moisture, salinity distribution and tomato growth characteristics under drip irrigation. The results showed that the distribution of soil moisture and salinity in different treatments was extremely uneven. The average water content and EC value of each treatment in the sand area were CK > T2 > T1. Soil salinity mainly migrated to the bare area between plant and plant, showing a high value area of EC, and the location of the high value area was different. In the section below drip irrigation belt, T1 and T2 all desalinated in 0-80 cm soil, CK accumulated salt in 0-40 cm soil and desalinated in 40-80 cm soil. Root volume under T2 was 3.00 times larger than that under CK, and showed trend as T2 > T1 > CK. The highest yield was 57.37 t/hm² under T2, which was 80.78% higher than that of CK. The yield of each treatment shown as T2 > T1 > CK, and sand hole had a significant effect on tomato quality. In conclusion, T2 can significantly improve soil infiltration, inhibit soil salt return, improve soil water and salt status, and promote crop growth. This study provides theoretical basis for agricultural development and utilization of saline-alkali land.

Abstract:Field experiments were conducted to study nitrogen composition of soil aggregates under straw and plastic film mulching in dryland wheat fields. Based on an 8 years mulching experiment in the Losses Plateau, the experiment set up three treatments:straw mulching (SM), plastic film mulching (PM), and no mulching (CK) during the growth period. The dry sieve method was used to determine the distribution characteristics of aggregates and the contents of total nitrogen (STN), microbial biomass nitrogen (MBN), and potential mineralizable nitrogen (PNM) in difference particle size aggregates. The results showed that:(1) Compared with no mulching, both straw mulching and plastic film mulching had no significant effects on soil total nitrogen content of difference particle size aggregates. SM increased the content of STN of the 1.00~0.25 mm particle size aggregate in the 0-10 cm soil layer compared with PM (12.88%, P<0.05). (2) Compared with CK, in the 0-10 cm soil layer, SM increased the content of MBN of the particle size classes >2.00, 2.00~1.00, and <0.25 mm by 18.67%, 24.05%, 20.08% (P<0.05), and increased the content of PNM of the particle size classes >2.00, 2.00~1.00 and < 0.25 mm by 35.13%, 30.03%, 42.88% (P<0.05). In the 10-20cm soil layer, SM increased the content of MBN of the particle size classes > 2.00 mm by 23.02% (P<0.05), and SM improved the PNM content of the particle size classes >2.00, 1.00~0.25 and < 0.25 mm by 28.59%, 31.31%, 32.48% (P<0.05). (3) Compared with CK, PM significantly increased the content of PNM of the particle size class < 0.25 mm in 0-10 cm soil layer (32.34%, P<0.05). (4) The content of nitrogen components of micro-aggregates (< 0.25 mm) was significantly higher than that of macro-aggregates (> 0.25 mm), however the contribution rate of the macro-aggregates nitrogen component was 81.88%~87.66%. SM increased the contribution rate of soil macro-aggregates to nitrogen component, so that more nitrogen was stored in macro-aggregates, and the effect of PM on the contribution rate of nitrogen in the aggregates was marginal. Overall, compared with CK and PM, SM increased the STN content and the nitrogen content of the micro-aggregates and macro-aggregates, so that more nitrogen is stored in the macro-aggregates and promote soil nitrogen turnover.

Abstract:The effects of different nitrogen application modes on the variation of nitrogen concentrations in paddy field surface water and rice yield were analyzed, through constructing six nitrogen application modes with different fertilizer types, fertilizer amounts, fertilization modes and times. The results showed that after slow-controlled fertilization and urea application, the concentration of total nitrogen and ammonuim reached peak in 1 day, and the concentration of nitrate reached peak in 2~3 days, and then gradually decreased to a stable level. Ammonium nitrogen was the main form of nitrogen in the initial stage after fertilization, and the proportaion of ammonium nitrogen in total nitrogen concentration reached 50.6%~92.8% in 1 day, while nitrate nitrogen only accounted for 3.8%~22.6%. The peak concentration of total nitrogen and ammonium nitrogen in surface water was correlated with fertilizer type, fertilizer amount and fertilization mode. Under the condition of equal nitrogen fertilization, the order of peak concentration of total nitrogen and ammonium nitrogen in surface water was as follows:Spraying urea treatment > spraying slow-release fertilizer treatment > side-deep application of slow-release fertilizer treatment. Under 48 kg/hm² N fertilization condition, the average peak concentrations of total nitrogen and ammonium nitrogen in the treatments of spraying urea, spraying slow-release fertilizer, and side-deep application of slow-release fertilizer were 38.44, 16.44, 7.55 mg/L, and 34.39, 13.00 and 3.82 mg/L, respectively. Under the same amount of nitrogen application and times of fertilization, the yields of treatments 4, 5, and 6 with side-deep slow-release fertilizer were 2.8%, 3.5%, and 2.7% higher than those of treatments 1, 2 and 3 with corresponding spraying slow-release fertilizer, respectively. Under the condition that the total amount of nitrogen fertilizer was reduced by 30%, the yield of rice of treatment 6 with side-deep application of slow-release fertilizer during base fertilizer period and two-times fertilization only decreased by 0.3% compared with that treatment 1 with spraying slow-release fertilizer during base fertilizer period and three-times fertilization. The results showed that side deep application of slow-release fertilizer could effectively reduce the peak concentration of ammonium nitrogen in surface water at the initial stage of fertilization, thus reducing the risk of ammonia volatilization and runoff loss, and would not affect rice yield under certain reduction conditions.

Abstract:A field experiment was carried out in Fifteen-year-old ‘Gala’/M. hupehensis Rehd. trees with ¹⁵N and ¹³C labeled tracers, to understand the characteristics of absorption, utilization, distribution, loss of carbon and nitrogen nutrition and fruit yield and quality under different nitrogen application methods (ON, TN and IN represented traditional one-time nitrogen, topdressing nitrogen and infiltrating irrigation nitrogen application, respectively) during fruit developmental periods. The results showed that the ¹⁵N derived from fertilizer (Ndff) in each organ displayed an order of IN > TN > ON at the fruit maturity stage, and significant difference was observed in Ndff values among the newborn organs (fruit, leaf and biennial branches). The total N contents and ¹⁵N absorption amount were highest in IN and lowest in ON. Compared with ON, the ¹⁵N utilization rates in TN and IN were increased by 41.63% and 68.60% respectively, and the ¹⁵N loss rates were decreased by 10.60% and 18.63% respectively. The residue amount of ¹⁵N-urea varied across different treatments and soil layers, showing an order of IN > TN > ON in 0-40 cm soil layer, and an opposite pattern in 60-120 cm soil layer. The ratio of ¹³C partition in fruit and storage organs (perennial branch, trunk and coarse root) under TN and IN was significantly higher than ON, and the highest value in the vegetative organs (leaf and biennial branches) occurred in ON, and lowest in IN. In addition, the yield, fruit hardness, soluble sugar and sugar-acid ratio quality index reached the highest value in IN. Our findings indicated that infiltrating irrigation nitrogen application could decrease nitrogen loss, thus increasing the absorption and utilization of nitrogen significantly by trees, and then optimizing the distribution of photosynthetic products, which was the preferred form to the yield and quality of apple tree.

Abstract:With the nitrogen application rate of 180 kg/hm², four nitrogen application ratios were designed in a field experiment, including base fertilizer:tillering fertilizer:panicle fertilizer=10:0:0 (T1), 4:3:3 (T2), 2:3:5 (T3), 0:3:7 (T4) respectively, to study the effect of postponing nitrogen application on rice yield formation and nitrogen dynamics in surface water of paddy field. The result showed that compared to T1, The treatments with 30% or even 50% of basal nitrogen fertilizer postponing to panicle fertilizer had no significant effect on rice grain yield, while the treatment with 70% of basal nitrogen fertilizer postponing to panicle fertilizer caused a significant decrease in rice grain yield. The peak concentrations of total nitrogen (TN) and total soluble nitrogen (DTN) in the surface water occurred after urea application for 1 day, NH₄⁺-N reached the peak on 1 day after basal fertilizer and tillering fertilizer and 3 days after panicle fertilizer, and then these 3 forms of nitrogen gradually reduced to basically close to the treatment with no urea application. These days between basal and tillering fertilization, 20 days after tillering fertilization and 9 days after panicle fertilization were the critical periods to control nitrogen loss from paddy field. After the urea application, DTN was the main part of the nitrogen in surface water of paddy field, and inorganic nitrogen (IN) was the major component in DTN, while NH₄⁺-N accounted for more than 64.0% of IN. The concentrations of TN, DTN and NH₄⁺-N in the critical periods for controling N loss during rice growth period were studied. Compared with T1, the concentrations of these 3 forms of nitrogen were decreased by 2.9%, 1.6%, 3.1% respectively in T2, decreased by 15.5%, 14.7%, 22.3% respectively in T3, and decreased by 16.1%, 22.9%, 34.1% respectively in T4. Considering the rice grain yield, T3 was determined to be the effective measure, as it could ensure rice grain yield and meanwhile effectively reduce the risk of nitrogen loss from paddy field.

Abstract:Substrate is an important component of ecological ditches, but its application in ecological ditch have been limited even there are few kinds of it can be employed, as high salinity in soil and water that caused by cold, limited rainfall, and strong evaporation in cold and arid areas in north China. Five kinds of common materials as zeolite, maifanite, anthracite, slag and fragment of waste brick were selected as test materials in this study, and the adsorption characteristics of ammonia nitrogen and phosphorus had been investigated by static adsorption test. Three kinds of substrates with good adsorption effect were combined in different proportions into ecological ditch substrates and matrix proportion combination with the best removal efficiency had been determination. The effects of temperature, pH, and salinity on the removal efficiency of ammonia nitrogen and phosphorus were also studied in the test. The experimental results showed that the removal rate of ammonia nitrogen and phosphorus reached maximum when the matching proportion of fragment of waste brick, zeolite and slag was 1:1:3, and its removal rate of ammonia nitrogen and phosphorus was higher than 90%. With the increase of temperature, adsorption capacity of ammonia nitrogen decreased, while adsorption capacity of phosphorus increased. A significant effect of pH was observed on the adsorption of ammonia nitrogen and phosphorus, the removal rate of phosphorus decreased with increment of pH. However the removal rate of ammonia nitrogen had increase first and then decrease with increment of pH, and the removal rate of was 91.78% when pH was 7. The removal efficiency of ammonia nitrogen and phosphorus decreased with the increment of salinity in solution, the effect of salinity on ammonia nitrogen adsorption was more significant than that of phosphorus. When salinity was less than 1%, the decrease of removal efficiency of ammonia nitrogen in solution was not obvious, removal rate of ammonia nitrogen and phosphorus was about 3%. The removal rate of ammonia nitrogen was only 68% when salinity was 2%, of which have decreased by 24% compared with its removal rate was 92% when salinity was 0.

Abstract:To examine the effects of excessive atmospheric nitrogen deposition on soil microbial carbon and nitrogen in Larix principis-rupprechtii plantation, we conducted fixed experiment plots and 5 years observation experiments to simulate the changes of microbial carbon, nitrogen, and soil respiration in soil of Larix principis-rupprechtii plantation with three nitrogen deposition treatments:CK (N₀:0 g/(m²·a)), light N level (N₁:8 g/(m²·a)), and severe N level (N₂:15 g/(m²·a)) to clarify the response of soil microorganism under excessive nitrogen deposition forest and the influence on soil carbon and nitrogen cycle. The results showed that the average content of soil microbial carbon and nitrogen was 1 098.93 and 97.31 mg/kg. In the May-October growing seasons respectively they showed a downward trend with the increase of soil depth. Light N addition promoted the increase of soil microbial carbon and nitrogen. Severe N addition inhibited the increase of soil microbial carbon and nitrogen. The content of soil microbial carbon and nitrogen increased from May to July and peaked in July, then decreased in August, slightly increased from September to October, and showed an "N" curve. The C/N of soil microbial was between 4.94 and 18.54, and decreased with the increase of N addition. The soil respiration rate of Larix principis-rupprechtii plantation was lower in May and June, continuously increased from July to August and reached the peak in August, then gradually decreased from September to October under different N treatments. The correlation analysis showed that soil respiration was significantly positively correlated with the content of soil total nitrogen, water content, microbial carbon and microbial nitrogen, and was positively correlated with soil organic matter. With the global change, the research results can provide important reference for further clarifying the impact of excessive atmospheric nitrogen deposition on carbon and nitrogen cycle in forest ecosystems.

Abstract:Interplanting is an important measure during the management of Cunninghamia lanceolata (Chinese fir) plantation. Phosphorus is one of the main limiting nutrient elements in the forests of southern China, but the effect of interplanting model on soil phosphorus is not clear. In this study, soil phosphorus fractions in surface soil (0-10 cm) were determined in different interplanting forests (young Chinese fir interplanting forest, mature Chinese fir interplanting forest) and young pure Chinese fir plantation. The results showed that:(1) Interplanting forests showed increased soil total phosphorus (including organic and inorganic phosphorus), microbial biomass phosphorus (MBP), and acid phosphatase activity (APA) compared with the Chinese fir plantation. Also, soil phosphorus contents were shown as mature Chinese fir interplanting forest > young Chinese fir interplanting forest > young pure Chinese fir plantation. (2) The contents of active phosphorus fractions were the lowest and NaHCO₃-Po dominated within the active components. Soil NaOH-Po was the main component of moderately active phosphorus, especially in the mature Chinese fir interplanting forest. The content of Residual-P was the highest among total phosphorus. (3) The mature Chinese fir interplanting with broadleaves trees showed significantly increased contents of resin extracted phosphorus (Resin-Pi), sodium bicarbonate extracted organic and inorganic phosphorus (NaHCO₃-Pi, NaHCO₃-Po), sodium hydroxide extracted organic and inorganic phosphorus (NaOH-Pi, NaOH-Po), sodium hydroxide residual extracted organic phosphorus (NaOHu.s-Po), hydrochloric acid extracted phosphorus (HCl-Pi), and Residual-P. There were no significant differences in soil total inorganic phosphorus, NaHCO₃-Po, NaHCO₃-Pi, HCl-Pi, NaOHu.s-Pi, and Residual-P contents between young Chinese fir interplanting forest and pure Chinese fir plantation. (4) There were positive correlations between soil phosphorus fractions and soil physical and chemical properties (such as soil total carbon and nitrogen, dissolved organic nitrogen, microbial biomass phosphorus, acid phosphatase activity) for different interplanting forests except for soil water content (P<0.05). Redundancy analysis (RDA) indicated that the changes in phosphorus fractions were mainly driven by MBP. Moreover, soil organic phosphorus (NaOHu.s-Po, NaOH-Po) and HCI-Pi was positively correlated with MBP. In conclusion, soil phosphorus availability in Chinese fir interplanting forests were higher than that in young pure Chinese fir forest, and soil nutrient status were also better.

Abstract:In view of low wheat yield and low soil fertility in the dry farmland of Loess Plateau, a study was carried out in a long-term localized experimental field in Lijiabao Town, near Dingxi, to study the effect of biochar (B) and straw (S) addition under three nitrogen levels (no nitrogen application, nitrogen application 50 kg/hm², nitrogen application 100 kg/hm²) (9 treatments in total) on soil organic carbon (SOC) and activated organic carbon in the middle Gansu region of Loess Plateau with the purpose of improving soil fertility and maintaining stable and increased yield. The results showed that compared with no nitrogen fertilizer (CNO), the other fertilization levels could all significantly increase the SOC content, and the effect of BN100 was the most significant as BN100 increased 84.7%, 69.3% and 47.8% of the SOC content in 0-5, 5-10 and 10-30 cm soil layers. The increase of the SOC content by BN0, BN50, and BN100 was significantly better than that of SN0, SN50, SN100, CN0, CN50, and CN100. Compared with SOC, the effect of SN100 on various active organic carbons (MBC, EOC, DOC, and HWOC) was the most significant, and significantly higher than that of CN0, CN50, and CN100. The effects of each treatment on the SOC content and its components showed identical trend as decreased with increment of soil depth. Compared with application of only nitrogen fertilizer, the correlations between SOC and its components were more significant in the treatments received biochar and straw. Addition of biochar showed more significant improvement of the SOC content, and straw addition showed more significant improvement of the soil active organic carbon content. Therefore, the results are of great significance to the improvement of soil microbial environment, the enhancement of soil fertility, the reduction of soil nutrient leaching, and the promotion of crop yield.

Abstract:In order to understand the effect of soil fertility under different rotation patterns of "grain, cash, and forage crops" in the semi-arid area of northwest China, seven rotation patterns, including corn-pea (C-Pe), corn-corn (C-C), 2-year alfalfa (2A), broomcorn-potato (B-Po), oat-corn (O-C), potato-oat (Po-O), pea-broomcorn (Pe-B), were set up in Yuanzhou District, Guyuan City, Ningxia Autonomous Region in 2017. The Indicators including the soil nutrient, enzyme activity and characteristics of culturable microbial community under different grain rotation cropping patterns were measured. Meanwhile, the soil fertility was comprehensively evaluated, which provide theoretical basis and practical guidance for local farming improvement. The results showed:(1) Different rotation patterns had significant effects on soil chemical properties. Compared with other rotation models, 2A was more conducive to the accumulation of soil nutrients. However, C-C mode increased the consumption of nutrients. The organic matter, total nitrogen, available nitrogen, available phosphorus, and available potassium content of C-Pe and Pe-B modes were significant higher than those of B-Po and O-C modes, moreover, rotation treatment had less effect on total potassium content. (2) Different crop rotation patterns had significant effects on soil enzyme activities. The soil urease and sucrase activities of 2A mode were significantly higher than those of other rotation patterns (P<0.05). The soil enzyme activity in C-C mode was the lowest, and the sucrase, the urease, and the alkaline phosphatase activities of O-C and Pe-B modes were significant higher than those of B-Po mode. (3) Different crop rotation patterns had significant effects on the number of soil culturable microorganisms. In crop rotation patterns, the number of soil microorganisms was dominated by bacteria, followed by actinomycetes and fungi with obvious vertical distribution of soil layers. Compared with other rotation models, the number of bacteria and the total number of microorganisms in 2A, C-C, and B-Po models decreased significantly and the number of fungi increased significantly (P<0.05), which was opposite to O-C mode. 4) Principal component analysis-numerical clustering method was used to comprehensively evaluate the soil fertility of 15 indicators of soil nutrient, soil enzyme activity, and soil microbial population under different rotation patterns. The results showed that the cumulative contribution rate of the two principal components extracted by principal component analysis was up to 89.38%. The first main component was composed of soil organic matter, total nitrogen, available nitrogen, total phosphorus, available phosphorus, available potassium, pH, sucrase, urease, and alkaline phosphatase, and the cumulative contribution rate was up to 63.56%. The second main component was composed of bacteria, fungi and microorganisms and cumulative contribution rate reached 25.82%. The overall score of each rotation pattern on the two principal components was ranked as 2A > Pe-B > C-Pe > O-C > Po-O > B-Po > C-C. The two principal component scores were further clustered, and seven models were divided into three categories:the first type (2A) had the best soil fertility; the second type (including Pe-B, O-C, C-Pe, Po-O, and B-Po modes) had better soil fertility; and the third type (C-C) had poor soil fertility. These research results may provide theoretical basis and practical guidance for the improvement of local farming methods.

Abstract:In order to reveal the effects of rubber litter covered on the surface soil physiochemical properties in different slop gradient, a field experiment was conducted. The four experimental treatments included leaf litter covered and litter removed in flat land, leaf litter covered and litter removed in slope land, respectively. The results showed that:(1) The soil water contents in flat land were higher than that in slope land during litter decomposition, moreover, it increased significantly at the treatments of litter covered compared with the treatments of litter removed in the condition of slope land. (2) There was a linear positive correlation between surface soil water content and precipitation, while the equation slop of slope land was larger than the flat land condition. (3) Treatments of litter covered in flat land and slope land increased the pH values by 0.09~0.74 and -0.09~0.47 units, respectively. (4) Total organic carbon, total nitrogen and C/N of treatments of litter covered increased significantly by 6.9%~68.5%,3.0%~44.8%,3.9%~16.2% respectively in flat land and 23.3%~95.0%,3.5%~52.5%,7.6%~27.9% respectively in slope land, compared with these of litter removed, while the increase rate in slope land was greater than that in flat land. (5) Compared with the treatments of litter removed, the treatments of litter covered increased significantly soil available phosphorus contents in slope land condition by 6.2%~48.1%, however, increased significantly soil available potassium contents in flat land by 16.4%~83.3% and in slope land by 12.8%~94.8%. In conclusion, rubber leaf litter covered could alleviate soil acidification, increase the water retention capacity and improve the conditions of soil nutrients.

Abstract:To evaluate the effects of dominant plants on controlling heavy metal pollution and the ecological restoration on indigenous zinc smelting slag dump, this study analyzed the effects of two naturally colonized and lushly grown plants (Chenopodium ambrosioides L. and Buddleja davidii Franch.) on the slag dump, basing on unrepaired blank slags. The effects of the two dominant plants on the main nutrient (nitrogen, phosphorus, and organic matter) and the content and occurrence mode of main heavy metals (Cu, Pb, Zn, and Cd) in the different particle size aggregates in rhizosphere and non-rhizosphere were examined. The results showed that the two naturally colonized dominant plants had significant effects on the main nutrient contents in the different size slags of rhizosphere and non-rhizosphere on the dump. Different plants had significantly different contributions to the organic matter in the rhizosphere and non-rhizosphere slags. The nutrient content had higher distribution in the size <1 mm aggregates. In addition to the total nitrogen content in the non-rhizosphere residue of B. davidii Franch. the nutrient content in the medium were wholly higher than in the blank waste slags. The growth of dominant plants significantly affected the content distribution and occurrence mode characteristics of main heavy metals (Cu, Pb, Zn, and Cd) in different size slags. Cu and Cd were mainly distributed in aggregates with sizes <0.25, 0.25~0.5 and 0.5~1 mm. Zn was mainly distributed in aggregates with sizes <0.25 and 2~5 mm. Pb had the highest content in four different aggregates which sizes were from 0.25 to 5 mm. The contents of Cu and Pb were reduced in the aggregates of various size slags, but the Cd content was improved in aggregates with size >5 mm. Among them, the proportion of acid-soluble Cu, Pb, and Zn decreased significantly, but the proportion of residual Zn and acid-soluble Cd increased in the size <5 mm aggregates. Principal component analysis showed that the plants had a high contribution to the nutrient, total Zn, and acid-soluble Cd content of the size <5 mm aggregates, but had little effects on the nutrient at the size >5 mm aggregate in the rhizosphere and non-rhizosphere. In summary, the vigorous growth of the two plants (C. ambrosioides L. and B. davidii Franch.) can effectively improve the nutrient status of lead-zinc smelting slags, and also reduce the potential risks of heavy metals Cu, Pb, and Zn to environmental ecology. Both plants can be used as pioneer-repairing species for lead-zinc smelting slags dump.

Abstract:This study selected the forest soils from 8 regions under different longitudes in the Loess Plateau as research objects, and explored the soil nutrients, soil microbial biomass and their ecological stoichiometry under different longitudes. The results showed that the contents of soil carbon, nitrogen and microbial biomass carbon, nitrogen and phosphorus overall gave a trend of decreasing first and then increasing with the change of longitudes. There was a coupling relationship between soil microbial biomass carbon, nitrogen and phosphorus and soil carbon and nitrogen, and the response to environmental factors was consistent. The spatial distribution of soil phosphorus content was stable. The soil carbon-nitrogen ratio was around 8, and the spatial distribution of soil organic carbon and total nitrogen was consistent. The soil microbial biomass carbon-nitrogen ratio was about 9, and the microbial biomass nitrogen-phosphorus ratio was about 5, which reflected that the soil microbial biomass carbon-nitrogen and nitrogen-phosphorus ratio were relatively stable, but the soil microbial biomass carbon-phosphorus ratio showed a trend of increasing first and then decreasing. Soil microbial biomass carbon, nitrogen and phosphorus had a strong correlation with soil moisture. Soil nutrients and soil microbial biomass carbon, nitrogen and phosphorus and their ecological stoichiometry were the result of the comprehensive action of environmental factors.

Abstract:Through a field experiment, the effects of organic surface covering materials on the physical and chemical properties of soil were studied. Taking soil from Morus alba L. tree holes in Yuan Ming Yuan Park as object, six treatments were set up as water-based polyurethane adhesive organic cover mats (A), water-based polyurethane and starch adhesive mixing ratio 9:1 organic cover mats (B), water-based polyurethane and starch adhesive mixing ratio 8:2 organic cover mats (C), water-based polyurethane and starch adhesive mixing ratio 7:3 organic cover mats (D), wood chip cover (M) and no cover treatment (CK). The coverage effect of different surface covering materials was evaluated by field coverage test. The results showed that:(1) Different surface covering materials have little effect on the soil bulk density, porosity, water holding capacity and other physical indexes, and soil pH values of different soil layers after covering the tree soil for one year. (2) Compared with CK, different organic surface covering treatments could increase the content of organic matter, alkali nitrogen, available phosphorus, and available potassium in soil. The effect of organic surface covering in 0-10 cm soil layer was more obvious than that in 10-20 cm soil layer. Comprehensively speaking, different surface covering materials could improve soil nutrient content, water-based polyurethane and starch adhesive mixing ratio of 8:2 organic covering mat (C) was the most suitable covering material for the exposed tree hole among the five organic surface covering materials.

Abstract:Soil is the necessary material basis for human survival and development, and changes in land use patterns directly affect soil properties. Taking Jiangxi red soil as an example, soils from five kinds of land use patterns:wasteland (HD), tea garden (CSY), citrus orchard (GJY), peanut land (HSD), and corn field (YMD) in upland red soil were used through field sampling and laboratory analysis to assess enzymatic activity and soil microbial diversity in surface soil (0-15 cm). The results showed that compared with the wasteland, the soil basal respiration of tea garden, citrus orchard, peanut land, and corn field increased by 93.33%, 79.71%, 9.12%, and 6.45%. The soil microbial biomass carbon of tea garden increased by 113.67% compared with the wasteland, while that of citrus orchard, peanut land, and corn field decreased by 12.35%, 6.84% and 87.57%. Compared with the wasteland, the activities of FDA hydrolysis in tea plantation, citrus orchard and peanut field increased by 51.99%, 44.04% and 25.55%, while the FDA hydrolysis activity in corn field decreased by 13.62%. The dehydrogenase activity in the tea garden and peanut field increased by 2.47% and 123.63% compared with the wasteland, the activity of urease in the citrus orchard increased by 35.70% compared with the wasteland, the catalase activity and sucrase activity were less affected by the five land use patterns. Compared with the wasteland, the total biomass of soil microorganisms in tea garden, citrus orchard, and peanut field increased by 11.11%, 5.56% and 2.78%, while the total biomass of soil microorganisms in corn field decreased by 13.89%. The soil bacterial species in tea plantation, citrus orchard and peanut field decreased by 9.09%, 4.55% and 22.73% compared with the wasteland, there was no difference in the number of soil fungi in different land use patterns. Compared with the wasteland, the species of soil actinomycetes in tea plantation and peanut field both increased by 16.67%, while the species of soil actinomycetes in citrus orchard decreased by 16.67%. The above results showed that compared with wasteland, citrus orchard, peanut land and corn field, the soil microbial diversity of tea garden is more abundant, and the community structure is relatively stable. Planting tea trees is more conducive to improving soil quality and maintaining soil fertility.

Abstract:Paddy soil has many kinds and large quantities of microbes, which will drive soil organic carbon mineralization and hold organic carbon pool. In this study, the paddy fields in Fuzhou Plain were used as test plots, and three kinds of treatments, such as biochar, slag, and biochar+slag, were applied to determine the effects of applied treatments on soil physical and chemical properties, microbial quantity, and organic carbon content in paddy fields, and the microbial role in the stabilization of soil carbon pools. The results showed that:(1) The application of slag and biochar could increase the quantity of microbes in paddy soil and the ratio of fungi/bacteria in soil, which was beneficial to the stability of soil carbon pool, and the effect of mixed treatments was more significant. (2) The three application treatments significantly increased the quantity of fungi and fungi/bacteria ratio in early rice jointing stage, and the fungi/bacteria ratio increased by 0.016, 0.015, and 0.018, respectively. The bacteria quantity was increased significantly. The single application and mixed treatments of biochar increased the quantity of aerobic bacteria in late rice jointing stage. The mixed application treatment significantly increased the quantity of aerobic bacteria in early maturity (p<0.05). (3) The slag application treatment significantly increased the soil DOC content in the early rice maturity stage, and the biochar application treatment significantly increased the soil SOC content in the early rice maturity stage. The mixed application treatment significantly increased the soil SOC content in the early rice jointing stage. Soil DOC significantly increased in the late rice jointing stage (p<0.05).The content of organic carbon in the early and late rice jointing stage was significantly higher than that in the maturitystage. (4) The physical and chemical properties, microbial quantity, and organic carbon content of paddy soils were positively affected. The soil of early paddy soil was significantly negatively correlated with soil MBC content, and it was significantly positively correlated with the quantity of fungi (p<0.01). The soil moisture content of late rice was positively correlated with DOC, aerobic bacteria, facultative anaerobic bacteria, and fungi. There was a significant negative correlation between MBC and anaerobic bacteria (p<0.05).

Abstract:In order to improve the utilization efficiency of water and nitrogen in the red soil under surge root irrigation, through an indoor fertilizer infiltration test, the soil infiltration capacity, wetting front migration, soil moisture, and the migration characteristics of ammonium nitrogen and nitrate nitrogen were studied under different fertilizer concentrations (0, 10, 20, 35, 60 g/L),and the relational model between cumulative infiltration volume, the wetting front migration distance and the fertilizer concentration were established. The results showed that:The cumulative infiltration volume, the wet front migration distance, and the migration and distribution of water and nitrogen in the wet body were all affected by the fertilizer concentration. At the same infiltration time, the cumulative infiltration volume and the wet front migration distance all increased with the increase of the fertilizer concentration, and they all had a power function relationship with the infiltration duration. At the end of irrigation, the greater the concentration of fertilizer was, the greater the soil moisture content was, and the greater the concentration of ammonium nitrogen and nitrate nitrogen was for the same soil depth, and the distribution of nitrate nitrogen was wider than ammonium nitrogen. With the redistribution of fertilizer solution, the position of maximum moisture content went down gradually, and the distribution of moisture content was more uniform. The changes of ammonium nitrogen and nitrate nitrogen concentration were different between the shallow and deep layer of soil. In the shallow layer, the concentration of ammonium nitrogen gradually decreased, while the concentration of nitrate nitrogen decreased first and then increased. In the deep layer, the concentration of ammonium nitrogen increased first and then decreased, while the concentration of nitrate nitrogen showed a gradually increasing trend. The research results could provide a theoretical reference for further study on the nitrogen transport and transformation of surge-root irrigation in the red soil region.

Abstract:In order to evaluate the fertigation mode of mango with high efficiency production in dry and hot region, a field mango experiment was carried out in dry and hot region of southwest by applying moistube fertigation technology. Four irrigation modes and three fertilization levels were set up with 7-year-old Guifei mango as experimental materials. Four irrigation modes were full irrigation (FI, 100% ET_C) in all fruit developmental stages and regulated deficit irrigation (RDI) in three growth stages. The deficit adjusted stage were flowering stage, expanding stage, and mature stage (RDI_FS, RDI_ES and RDI_MS), and the irrigation level in deficit adjusted stage was 50% ET_C, non-deficit adjusted stage was 100% ET_C. Three fertilization levels were high fertilizer (F_H), medium fertilizer (F_M), and low fertilizer (F_L). The effects of different water and fertilizer treatments on mango yield, water and fertilizer use efficiency, and photosynthetic characteristics were studied. The results showed that the P_n, G_s, and T_r of mango leaves were significantly reduced by water regulation deficit at different growth stages, while WUE_i of mango leaves was significantly increased. At the same irrigation level, P_n, G_s and T_r increased with the increase of fertilizer application, WUE_i increased first and then decreased with the increase of fertilizer application, and P_n, T_r and WUE_i increased with the increase of fertilizer application at maturity. Compared with FI treatment, RDI_FS significantly reduced the weight, yield, and PFP by 11.74%, 23.43% and 23.98%, RDI_ESdecreased by 21.09%, 20.29% and 20.50%, while RDI_ES and RDI_MS increased IWUE by 11.87% and 32.81%, respectively. Compared with F_M, F_H significantly reduced yield and IWUE by 4.17% and 4.06%, and F_L reduced by 6.75% and 6.67%, respectively. PFP decreased with the increase of fertilizer application. Compared with CK, except RDI_MSF_M treatment increased yield by 6.36% and RDI_MSF_L treatment did not increase significantly, the other treatments decreased by 3.14%~31.76%. Under RDI_MSF_L and RDI_MSF_M treatments, PFP and IWUE achieved maximum values of 363.93 kg/kg and 15.80 kg/m³, respectively, which increased significantly compared with CK. Therefore, considering yield and IWUE, RDI_MSF_M is the best moistube fertigation mode of mango in dry and hot region.

Abstract:Aiming at the problems of rice safety and quality caused by the activation of toxic heavy metals as a result of soil acidification in paddy soil of southern China, rice straw and husk were selected to produce biochar (reported as RSC and RHC respectively), the effects of different feedstocks biochar on the improvement of acidified soil and the availability of heavy metals were studied. Three biochar application rates (0, 20, 50 g/kg; CK, C1, C2), four soil acidification levels (pH 4.01, 4.25, 4.33, 4.58; L1, L2, L3, L4) were used in this study. The soil pH, total nitrogen, organic matter, available phosphorus, available potassium, and available Cu and Cd contents were determined after incubation for 60 days. Results showed that the RSC improved the pH of acidified soil significantly better than RHC, and the higher the amount of biochar applied, the greater the range increased. The C2 treatment of RSC increased the pH of four acidity levels soils by 0.68, 0.97, 1.29 and 1.71 units, respectively. Two biochar both could increase the contents of total nitrogen, available phosphorus, available potassium, and organic matter in soil. Among them, organic matter was significantly increased in all treatments, especially available potassium, and RSC was superior to RHC on enhancing the nutrients. RHC had no significant effect on soil available Cu content. C2 of RSC could reduce soil available Cu content more effectively than C1 treatment, and reduced the four acidity levels soils by 13.62%, 6.57%, 4.36%, and 7.88%, respectively. Available Cd content in L3 and L4 soils treated with RHC decreased significantly, with a maximum of 13.79% and 19.23% respectively. RSC reduced the maximum content of available Cd in four acidity soils by 20.00%, 25.81%, 20.69%, and 19.23%, respectively. Correlation analysis showed a significant negative correlation between soil pH and available heavy metal content. Rice straw biochar was more effective in improving acidified soils and decreased the availability of heavy metals such as Cu and Cd, and removed the available Cd in contaminated soils better than that of available Cu. Biochar had better effects on the increase of soil pH and available phosphorus content and the decrease of available Cd content in the soil with lower acidification degree, while the decrease of available Cu content was better in the soil with higher acidification degree. Soil pH is the main factor affecting the availability of heavy metals such as Cu and Cd regulated by biochar.

Abstract:A field experimental were conducted in acid paddy soil to study the influence of the fermented rapeseed residue as an organic fertilizer on soil organic matter (OM), pH value, microbial biomass carbon and nitrogen (MBC and MBN), three enzymes (acid phosphatase, ACP, urease, UA, and dehydrogenase, DH), and occurrence mode of Cd in soil. Path analysis was used to study the influence approaches and mechanisms of organic fertilizer application on soil Cd occurrence mode. The results showed that:(1) The application of organic fertilizer could significantly increase the OM content, alleviate soil acidity, significantly increase the concentrations of reducible Cd (Red-Cd) and oxidizable-Cd, and decrease the concentrations of acid extractable-Cd (Aci-Cd) in soil. (2) ACP, UA and DH activities and MBC and MBN concentrations in soil were showed gradually raised after organic fertilizer application. (3) Path analysis results showed that the reduction of Aci-Cd concentrations in soil after organic fertilizer application was mainly achieved by increasing of OM content, DH activity, and MBC concentrations in soil. The decision coefficients of soil OM content, soil DH activity, and MBC content were 0.846, 0.257 and -0.276, respectively, which reached the significant levels and suggested they are the main controlling factors of soil Aci-Cd content under organic fertilizer application.

Abstract:The physiochemical properties and nutrient contents in wetland soils and sediments in the Linfen segment of Fenhe River were explored, the soil status was assessed, and the ecoenvironmental quality of water was predicted. Totally 98 samples of soils and sediments were collected, and 11 indices including physiochemical properties and nutrients were analyzed. It was found the soil pH was 7.0~8.4, bulk density was 1.04~1.44 g/cm³, water content was 5.9%~17.5%, conductivity was 0.167~0.747 mS/cm, and soil texture types included loam clay and clay loam. The contents of organic matter, total N, total P, alkali-hydrolyzable N, available P, and available K were 8.7~39.8, 0.354~1.046, 0.389~1.444 g/kg, 12.9~50.3, 2.6~31.2, and 86.4~329.2 mg/kg, respectively. Correlation analysis showed that the indices of soils and sediments were significantly correlated with physical properties and textures respectively. Moreover, organic matter, total N, alkali-hydrolyzable N, and available K were correlated pairwise. Nutrient evaluation showed organic matter, total P and available P were at grade 4, total N was within grade 3 and 6, alkali-hydrolyzable N was at grade 5 and 6, and available K was at grade 2 and 3. The organic pollution degree of sediments was assessed as moderate, and the comprehensive pollution degree was evaluated as severe.

Abstract:In consideration of high organic matter content in biogas slurry of pig farm, and long cycle, high cost, and difficult to remove of other treatment processing, a binary co-precipitation system comprising an aqueous calcium oxide solution and AlCl₃ was applied to remove organic pollutants of biogas slurry. The effects of precipitant ratio, dosage, reaction time, and initial pH of biogas slurry on the removal of organic matter were investigated. The results showed that the maximum removal rate of organic matter reached 93% when the co-precipitant volume ratio was 1:2.5, the dosage was 1:1 (volume ratio), and the reaction time was 60 min at pH 9. The XRD, FITR, and SEM analysis of the precipitates before and after the reaction demonstrated that the co-precipitant could flocculate and precipitate organic matter by charge attraction with negatively charged organic matter, and complexation with normal valence metal ions in the biogas slurry. The precipitation reaction was rapid and could completely remove organic matter, and had good industrial application prospects in farm wastewater treatment.