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Purple soils (0-20 cm layer) located in a restoration region of Hengyang, South-central China were examined under six different land use types, comprising: natural grassland (NGL), artificial grassland (AGL), artificial shrub and grassland (ASGL), artificial shrub land (ASL), slope farmland (SFL), and artificial forest land (AFL) . The effects of different land use types on soil physico-chemical and biological properties were analyzed. Soil quality under different land use types was evaluated by using principal component analysis (PCA) . The results showed that: total nitrogen, alkali-hydrolyzable nitrogen, and available phosphorus content under AGL, ASGL, and SFL were significantly higher than for the other three land use types (P＜0. 05), while soil pH value, bulk density, and capillary porosity in AGL, ASGL and SFL were significantly lower than those of the other types (P＜0. 05), and there was no significant difference in available potassium content among the six land use types (P＞0. 05) . Total phospholipid fatty acids (PLFAs) concentration; bacterial, fungal, and actinomycete contents; urease, sucrase, phosphatase, and protease activities; and the contents of soil microbial biomass carbon and soil microbial biomass nitrogen were significantly higher in AGL, ASGL, and SFL than the other land use types (P＜0. 05) . There were strong correlations among all fertility factors apart from readily available potassium content. PCA showed that AGL, ASGL, and SFL land use types were more beneficial for the recovery of soil quality in the restoration region. [ABSTRACT FROM AUTHOR]

【Objective】This study aims to investigate the adsorption-desorption characteristics of phosphorus (P) in soils applied with ammonium polyphosphates (APPs) of different polymerization distribution, and to compare these characteristics with those of soils applied with traditional orthophosphates (monoammonium phosphate, MAP; diammonium phosphate, DAP）. It can provide a theoretical basis for the efficient use of APP.【Method】Three kinds of APP (18-58-APP, 16-60-APP and 11-37-APP, whose N-P2O5-K2O were 18-58-0, 16-60-0 and 11-37-0, and the distribution of polymerization degree were 1-2, 1-4 and 1-7, respectively), MAP and DAP were used as test fertilizers. The fertilizers were applied to calcareous and acid purple soils and then were incubated for 56 days. The adsorption-desorption characteristics of P and the physicochemical properties of the soils were determined.【Result】Both Langmuir and Freundlich equations fit the adsorption characteristics of P in the two purple soils well (R² = 0.825-0.997). In the calcareous purple soil, compared with MAP and DAP applied soils, the APP-treated soil showed a 15.1%～20.7% decrease in P adsorption rate and a 4.5%-164.9% increase in desorption rate. The Langmuir KL, adsorption free energy (|ΔG|）, and Freundlich KF values of the APP-treated soil decreased by 20.4%-54.0%, 3.3%-10.6%, and 23.8%-43.8%, respectively, indicating a reduction in the binding force of soil for P. The 11-37-APP treated soil showed the largest changes in these values (KL, |ΔG| and KF values were reduced by 40.8%-54.0%, 7.2%-10.6% and 43.6%-43.8%, respectively). In acid purple soil, the impact of different P fertilizers on the adsorption-desoprtion characteristics of P was not significant, but APP-treated soil tended to reduce P adsorption and promote P desorption. Correlation analysis showed that pH, iron and aluminum oxides, and Olsen-P were significantly correlated with P adsorption parameters in calcareous purple soil and soil Olsen-P was significantly correlated with P adsorption parameters in acid purple soil. APP application in calcareous purple soil decreased complexed iron and aluminum oxides while increased free iron and aluminum oxides, resulting in decreased P adsorption and increased desorption. Compared to calcareous soil, acid purple soil had a lower available P content and a stronger adsorption capacity, making the adsorption-desorption characteristics less susceptible to the influence of different P fertilizers in the short term.【Conclusion】The adsorption-desorption characteristics of P in APP-treated purple soils were influenced by the soil properties and the APP’s polymerization distribution. The significant changes were observed in calcareous purple soil, especially for 11-37-APP with a broader polymerization distribution. [ABSTRACT FROM AUTHOR]

Abstract The identification and quantification of the ecological risks, sources and distribution of heavy metals in purple soils are essential for regional pollution control and management. In this study, geo-accumulation index (Igeo), enrichment factor (EF), pollution index (PI), potential ecological risk index (RI), principal component analysis (PCA) model and geographical detector (GD) were combined to evaluate the status, ecological risk, and sources of heavy metals (HMs) in soils from a typical purple soil areas of Sichuan province. The results showed that the average contents of As, Cd, Cr, Cu, Hg, Ni, Pb and Zn in purple soil were 7.77, 0.19, 69.5, 27.9, 0.077, 30.9, 26.5 mg/kg and 76.8 mg/kg, and the Igeo, EF and RI of topsoil Hg and Cd in designated area was the highest, and the average contents of Hg and Cd in topsoil were obviously greater than respective soil background value in Sichuan province and purple soil. The hot spots for the spatial distribution of 8 HMs were mainly focused in the southwest and northeast of the designated area, and there were also significant differences for 8 HMs distribution characteristics in the profile soil. Cu comes from both anthropogenic and natural sources, Zn, Ni and Cr mainly come from natural sources, but As, Pb, Hg and Cd mainly derived from human activities. GD results showed that soil texture (X18), altitude (X4), total nitrogen (TN), clay content (X3), sand content (X2) and silt content (X1) had the greatest explanatory power to 8 HMs spatial differentiation.This study provides a reference for understanding the status and influencing factors of HM pollution in typical purple soil, and lays a theoretical foundation for the environmental treatment of purple soil in China.

The identification and quantification of the ecological risks, sources and distribution of heavy metals in purple soils are essential for regional pollution control and management. In this study, geo-accumulation index (Igeo), enrichment factor (EF), pollution index (PI), potential ecological risk index (RI), principal component analysis (PCA) model and geographical detector (GD) were combined to evaluate the status, ecological risk, and sources of heavy metals (HMs) in soils from a typical purple soil areas of Sichuan province. The results showed that the average contents of As, Cd, Cr, Cu, Hg, Ni, Pb and Zn in purple soil were 7.77, 0.19, 69.5, 27.9, 0.077, 30.9, 26.5 mg/kg and 76.8 mg/kg, and the Igeo, EF and RI of topsoil Hg and Cd in designated area was the highest, and the average contents of Hg and Cd in topsoil were obviously greater than respective soil background value in Sichuan province and purple soil. The hot spots for the spatial distribution of 8 HMs were mainly focused in the southwest and northeast of the designated area, and there were also significant differences for 8 HMs distribution characteristics in the profile soil. Cu comes from both anthropogenic and natural sources, Zn, Ni and Cr mainly come from natural sources, but As, Pb, Hg and Cd mainly derived from human activities. GD results showed that soil texture (X18), altitude (X4), total nitrogen (TN), clay content (X3), sand content (X2) and silt content (X1) had the greatest explanatory power to 8 HMs spatial differentiation.This study provides a reference for understanding the status and influencing factors of HM pollution in typical purple soil, and lays a theoretical foundation for the environmental treatment of purple soil in China. [ABSTRACT FROM AUTHOR]

Polyacrylamide (PAM) is a water-soluble polymer with strong cohesiveness and a strong water absorption capacity, and it has been widely used to modify soil structural stability. However, little information is available on the impact of PAM application on the aggregate-breaking process of purple soils in hilly areas of southwestern China. Therefore, the current study aimed to examine the influence of PAM application on the aggregate stability of purple soil in terms of different breakdown mechanisms at different hillslope locations. Three disruptive tests employing the Le Bissonnais method (FW, fast-wetting sieving; SW, slow-wetting sieving; and WS, wet-stirring sieving) were used to determine the mean weight diameter (MWD), geometric mean diameter (GMD), and mass fractal dimension (D) of the soil aggregates, and soil erodibility factor (K) was calculated as an index of soil anti-erodibility. Overall, the major aggregate-breaking mechanism for purple soils was the following: SW (differential swelling) > WS (mechanical breakdown) > FW (slaking). The content of water-stable aggregates (>0.25 mm) obviously rose after PAM application, with the most significant influences shown under FW. A significant difference in MWD was observed between PAM application and without polyacrylamide application (CK) under WS (p < 0.05). However, there was a significant difference in GMD between PAM and CK (p < 0.05) under FW and SW. In comparison with CK, D value in PAM under FW and SW was significantly reduced, mainly at the slope locations of 0 and 20 m. A descending order of FW, WS, and SW was found on the basis of K value at different slope locations. These findings contribute to improved understanding of proper application of soil amendments to control soil and water loss in purple soils. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Northwest A & F University - Natural Science Edition is the property of Editorial Department of Journal of Northwest A&F University (Natural Science Edition) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Polyacrylamide (PAM) is a water-soluble polymer with strong cohesiveness and a strong water absorption capacity, and it has been widely used to modify soil structural stability. However, little information is available on the impact of PAM application on the aggregate-breaking process of purple soils in hilly areas of southwestern China. Therefore, the current study aimed to examine the influence of PAM application on the aggregate stability of purple soil in terms of different breakdown mechanisms at different hillslope locations. Three disruptive tests employing the Le Bissonnais method (FW, fast-wetting sieving; SW, slow-wetting sieving; and WS, wet-stirring sieving) were used to determine the mean weight diameter (MWD), geometric mean diameter (GMD), and mass fractal dimension (D) of the soil aggregates, and soil erodibility factor (K) was calculated as an index of soil anti-erodibility. Overall, the major aggregate-breaking mechanism for purple soils was the following: SW (differential swelling) > WS (mechanical breakdown) > FW (slaking). The content of water-stable aggregates (>0.25 mm) obviously rose after PAM application, with the most significant influences shown under FW. A significant difference in MWD was observed between PAM application and without polyacrylamide application (CK) under WS (p < 0.05). However, there was a significant difference in GMD between PAM and CK (p < 0.05) under FW and SW. In comparison with CK, D value in PAM under FW and SW was significantly reduced, mainly at the slope locations of 0 and 20 m. A descending order of FW, WS, and SW was found on the basis of K value at different slope locations. These findings contribute to improved understanding of proper application of soil amendments to control soil and water loss in purple soils.

Abstract Rill erosion is one of the most important processes affecting soil detachment. Therefore, the quantification of the soil detachment process is important to establish a basic process-based erosion prediction model. The objective of this study was to assess the contributions of the hydraulics parameters and sediment content to the soil detachment rate of purple soil. Purple soil was collected from a typical hilly region in Sichuan, China. Six scouring experiments were conducted in two 1 m × 2 m boxes at six different flow discharge rates (2, 4, 6, 8, 10, and 12 L min−1) in an upslope drainage area (0.30 m2) with a 15° slope. The results show that the soil detachment rate greatly changes during the rill development stage and the soil detachment rate varies at a sediment content of 0.15 g L−1. Furthermore, the soil detachment rate is negatively related to the sediment content. The relationships between the sediment content and hydraulics parameters can be described with a negative power function. The soil detachment rate is positively related to the stream power; the relationship can be described with a linear function. The comprehensive relationship between the soil detachment rate and sediment content and stream power can be described with a binary linear equation. The proportional contribution of the sediment content to the soil detachment rate is 80.65% and that of the stream power is 19.35%. The sediment content has a negative effect on the soil detachment rate in rills. The stream power has a positive effect; it induces soil detachment. The negative effect of the sediment content on the soil detachment rate is influenced by the stream power. This study provides new insights into the effects of the sediment content and hydraulics on the rill erosion process. Highlights • We provided a new insight for revealing the detachment mechanism of rill erosion in purple soil area. • We figured out the contribution rate of sediment content and hydraulics parameters to soil detachment rate. • Using sediment content and stream power to forecast rill erosion intensity was feasible. • Soil detachment process model was established based on sediment content and hydraulics parameters. [ABSTRACT FROM AUTHOR]

Rill erosion is a serious concern in the hilly region of China with purple soil, and maize is extensively cultivated in this region. Evaluations of the dynamic mechanisms of rill erosion in sloping farmland areas are particularly important during the maize growing season to determine whether rill erosion can occur. A new ridge tillage (RT) system was designed using local agricultural methods in China. Twelve artificial rainfall experiments were conducted in three 1 × 2 m experimental plots with a slope of 15°, which is a typical slope in the study area. The rainfall intensities were designated as 1.0, 1.5, and 2.0 mm min−1. The rainfall experiments were performed in the field to determine the characteristics of run‐off and sediment transport related to rill erosion processes during different stages of maize growth and to analyse how hydraulic parameters and the sediment yield of the rill erosion process are related. The results showed that rill flow patterns were mainly classified as subcritical transition flow during all the growth stages of maize. The effects of hydrodynamic parameters on the sediment yield were ordered as follows: Reynolds number > stream power > Froude number > shear stress. The total sediment yield varied by stage as follows: seedling stage > jointing stage > mature stage > tasseling stage. The sediment yield and run‐off rate exhibited a linear relationship that was well described at the hillslope scale. To initiate soil loss in sloping farmland areas with purple soil during the maize growing season, the critical hydrodynamic shear stress and stream power must be at least 46.505 Pa and 1.541 N m−1 s−1, respectively. [ABSTRACT FROM AUTHOR]

Flow hydraulics play important roles in soil erosion and loss of soil nutrients. A better understanding of the relationship between flow hydraulics and nutrient losses will improve chemical transport modeling. The laboratory experiment was conducted to determine flow hydraulics' effects on total nitrogen (TN) loss. The impacts of rainfall intensities (0.6, 1.1, 1.61, 2.12, and 2.54 mm·min-1) and slope gradients (10°, 15°, and 20°) on TN loss were also studied. Selected soils were derived from purple sandy shales, which are the main parent materials in Wangjiaqiao watershed, southern China. Results show that negative linear relationships (R2 = 0.71) were observed between the rate of Manning roughness coefficient to average flow depth and the unit area runoff-associated TN transport rate. There was a good linear relationship between the unit area sediment-associated TN transport rate and Reynolds numbers (R2 = 0.90), flow velocity (R2 = 0.87), and stream power (R2 = 0.73), while Froude numbers, Darcy-Weisbach and Manning friction coefficients were not good hydraulic indicators of the sediment-associated TN loss of purple soil. The equation including stream power and flow velocity may have a better correlation coefficient (R2 = 0.94). [ABSTRACT FROM AUTHOR]

Purple soil bunds are embankments constructed along the contour on purple soil sloping farmlands, and play a key role in controlling soil erosion. The soil shear strength makes a significant influence to the bund stability; however, few reports have documented how purple soil shear strength responds to the soil physical properties. The main goal of the present study was to determine how indicators of soil shear strength vary with the soil water content and dry density. In this study, we collected soil samples from 3 purple soil bunds in Zhong County, in the Three Gorges Reservoir Area in China, and performed an unconsolidated undrained triaxial compression test to study the soil shear strength in terms of the cohesion ( c ), internal friction angle ( φ ), and the principal stress difference ( σ 1 – σ 3 ). The test results show that when the dry density was constant and the soil water content increased, the soil cohesion increased and then decreased, and the results fitted to a quadratic curve. As the soil water content increased, the internal friction angle of the soil bunds decreased and displayed a first-order exponential decay. As the soil water content increased and the confining pressure remained constant, the principal stress difference decreased rapidly. When the soil water content was constant and the dry density increased, the soil cohesion, internal friction angle, and the total principal stress difference increased, although at different rates. In general, the water content had a greater effect on the cohesion, internal friction angle, and the principal stress difference than the dry density, but there were little or no interaction between water content and dry density. Furthermore, except when the water content was 6%, the stress–strain characteristics were similar across the range of water contents. For a low water content, fixed confining pressure, and an increasing dry density, the curves gradually changed from the hardening type to the weak hardening type and then to the softening type. In most cases the curves corresponded with the hardening type as the confining pressure increased. [ABSTRACT FROM AUTHOR]

Purple soil is highly susceptible for overland flow and surface erosion, therefore understanding surface runoff and soil erosion processes in the purple soil region are important to mitigate flooding and erosion hazards. Slope angle is an important parameter that affects the magnitude of runoff and thus surface erosion in hilly landscapes or bare land area. However, the effect of slope on runoff generation remains unclear in many different soils including Chinese purple soil. The aim of this study was to investigate the relationship between different slope gradients and surface runoff for bare-fallow purple soil, using 5 m × 1.5 m experimental plots under natural rainfall conditions. Four experimental plots (10°, 16°, 20° and 26°) were established in the Yanting Agro-ecological Experimental Station of Chinese Academy of Science in central Sichuan Basin. The plot was equipped with water storage tank to monitor water level change. Field monitoring from July 1 to October 31, 2012 observed 42 rainfall events which produced surface runoff from the experimental plots. These water level changes were converted to runoff. The representative eight rainfall events were selected for further analysis, the relationship between slope and runoff coefficient were determined using ANOVA, F-test, and z-score analysis. The results indicated a strong correlation between rainfall and runoff in cumulative amount basis. The mean value of the measured runoff coefficient for four experimental plots was around 0.1. However, no statistically significant relationship was found between slope and runoff coefficient. We reviewed the relationship between slope and runoff in many previous studies and calculated z-score to compare with our experimental results. The results of z-score analysis indicated that both positive and negative effects of slope on runoff coefficient were obtained, however a moderate gradient (16°-20° in this study) could be a threshold of runoff generation for many different soils including the Chinese purple soil. [ABSTRACT FROM AUTHOR]

Loess and purple soils are two very important cultivated soils, with the former in the loess region and the latter in southern sub-tropical region of China, featured with high-risks of erosion, considerable differences of soil structures due to differences in mineral and nutrient compositions. Study on soil erodibility ( K r ) and critical shear stress ( τ c ) of these two soils is beneficial to predict soil erosion with such models as WEPP. In this study, rill erosion experimental data sets of the two soils are used for estimating their K r and τ c before they are compared to understand their differences of rill erosion behaviors. The maximum detachment rates of the loess and purple soils are calculated under different hydrodynamic conditions (flow rates: 2, 4, 8 L/min; slope gradients: 5°, 10°, 15°, 20°, 25°) through analytical and numerical methods respectively. Analytical method used the derivative of the function between sediment concentration and rill length to estimate potential detachment rates, at the rill beginning. Numerical method estimated potential detachment rates with the experimental data, at the rill beginning and 0.5 m location. The K r and τ c of these two soils are determined by the linear equation based on experimental data. Results show that the methods could well estimate the K r and τ c of these two soils as they remain basically unchanged under different hydrodynamic conditions. The K r value of loess soil is about twice of the purple soil, whereas the τ c is about half of that. The numerical results have good correlations with the analytical values. These results can be useful in modeling rill erosion processes of loess and purple soils. [ABSTRACT FROM AUTHOR]

Purple soil, a loamy entisol dominating the hilly central Sichuan basin in the upper reaches of Yangtze River, is low in organic matter content and abundant in macropores that form the rapid transport network for water and solutes including pesticides. However, effects of soil's macroporosity on transport of pesticides has not been quantitatively explored and simulated at the column scale. In this study, we explore the transport of 3,5,6-trichloro-2-pyrdionl (TCP), a main pesticide degradation product, in purple soil through experiments and simulations on typical farmland categories, including rice-rape and vegetable farmland. Soil water retention characteristics (SWRCs) and physical properties are measured to learn the hydraulic parameters and porous structures of the soil. Batch experiments are conducted to obtain the adsorption coefficient of TCP on soil, and breakthrough curves of Br − (a conservative tracer) in undisturbed soil columns are applied to evaluate the hydrodynamics of TCP transport. The two-region model is used to simulate the transport processes, and the parameters are obtained by inversion simulation. It is found that TCP transport in purple soil exhibited complex patterns and is strongly affected by both chemical and physical non-equilibrium. A higher pollution risk on water body of rice-rape field is due to the stronger preferential flow and better pore connectivity despite the larger macroporosity observed in vegetable field. These results can provide useful data and modeling approach for evaluating the risk of pesticide leaching toward groundwater. [ABSTRACT FROM AUTHOR]

Agricultural non-point source pollution of nitrogen (N) and phosphorus (P) exerts a key influence on aquatic environment safety. Purple soil and sloping cropland make up the highest proportion of all soil types and land-use pattern in the up and middle reaches of Yangtze River. Therefore, a study on nutrients balance for risk assessment in sloping cropland of purple soil will contribute to the understanding of the causes of eutrophication in aquatic environment in China. The Organization for Economic Cooperation and Development (OECD) have developed the soil surface nitrogen balance indicator to estimate potential N pollution through measuring the difference between agricultural inputs and outputs. Based on this indicator, we established a framework, a methodology, and a database for calculating the N and P balance for typical sloping cropland of purple soil in TGR region, and evaluated the impact of nutrients balance on agricultural production and environment. For the basic watershed of Xinzheng unit, which mainly consists of sloping cropland of purple soil, N and P inputs were 755 and 107 kg ha −1 a −1 , with 68.4% of N and 56.1% of P inputs originating from chemical fertilizer. The N and P outputs were 482 and 60 kg ha −1 a −1 ; the N in crops and P in straw accounted for 23.5% and 45.6% of total outputs, respectively. The N and P surplus intensities were 273 and 47 kg ha −1 a −1 , much higher than the respective risk thresholds of 180 kg ha −1 a −1 and 35 kg ha −1 a −1 , indicating a risk of N and P potential pollution in aquatic environments via cropland discharge. It is essential to utilize proper fertilization methods and improve fertilizer use efficiency in sloping cropland of purple soil in China. [ABSTRACT FROM AUTHOR]

The adsorption behaviors of 3,5,6-trichloro-2-pyridinol (TCP) are explored by experiment and simulation on typical farmland of purple soil in southwestern China. Samples are collected from three farmlands with seasonal crop rotation of wheat-corn, rice-rape and vegetables respectively, and isothermal adsorption, breakthrough curves (BTCs) of packed and intact soil column experiments are tested. Adsorption parameters are also obtained by inversion simulation of appropriate model. The results reveal that the adsorption varies substantially in different farmlands and environmental conditions. Isothermal adsorption displays a decrease trend from the soil with crop of wheat-corn to rice-rape, then vegetables, and the main influencing factor is content of clay and silt. Langmuir model fits the isothermal adsorption best (R2= 0.99), and the estimated adsorption capacity (qm) of soil is 2.73, 1.19 and 0.55 mg/g, corresponding to the sample from farmland of wheat-corn, rice-rape and vegetable, respectively. However, the adsorbed amount by unit mass is almost the same in packed columns because of the incomplete interaction between TCP and soil, accounting for 0.59–3.24% ofqm. In intact soil columns, the adsorption on TCP decreases further, 0.13–1.15% ofqm. Thomas model fits TCP's adsorption well in packed soil columns (R2≥ 0.97) but poorly in intact soil because of the preferential flow, and the fact that the more intensive the preferential flow, the poorer is the performance of the model. [ABSTRACT FROM PUBLISHER]

The Sichuan Basin is the main agricultural production area of the upper reaches of the Yangtze River and is also an extremely important ecological area because it is rich in biodiversity and has complex and diverse landscape types. The dominant soil type, purple soil, is prone to rapid soil erosion and weathering processes because it is shallow and rich in phosphorus and other nutrients. Field experiments were conducted to reveal the effects of precipitation and topography characteristics on nonpoint source pollutants from purple soil. The results showed that total phosphorus (TP) load and TP concentration both increased with increasing rainfall amount, and there was an initial time of runoff and sediment yield before runoff generation. Moreover, the TP load generally increased with precipitation intensity as setting a coincident value of rainfall amount; however, the difference between TP load at 30 and 60 mm/h was minimal as was the difference between 90 and 120 mm/h. Similarly, TP concentration increased with increasing precipitation intensity. In terms of topographical conditions, TP load increased with increasing gradient, but began to decline when the gradient was about 20°, which indicates that 20° is the critical gradient for TP loss. There was a significant positive correlation between gradient and TP concentration when the gradient was <15°, whereas the increase in TP concentration slowed as the gradient increased. [ABSTRACT FROM AUTHOR]

Crust restoration is increasingly being done but we lack quantitative information on soil improvements. The study aimed to elucidate the dynamics involving soil microbial biomass carbon and soil dissolved organic carbon in the re-vegetation chronosequences of a hillslope land with purple soil in Hengyang, Hunan Province. The soil can cause serious disasters with both soil erosion and seasonal drought, and also becomes a typical representative of ecological disaster area in South China. Using the space-for-time method, we selected six typical sampling plots, designated as follows: grassplot community, meadow thicket community, frutex community, frutex and arbor community, arbor community, and top-level vegetation community. These plots were established to analyze the changes in soil microbial biomass carbon, soil microbial quotien, dissolved organic carbon, dissolved organic carbon/soil organic carbon, and soil basal respiration in 0–10, 10–20, and 20–40 cm soil layers. The relationships of these parameters with soils physic-chemical properties were also determined. The ecological environment of the 6 plant communities is similar and typical; they denoted six different successive stages of restoration on hillslopes with purple soils in Hengyang, Hunan Province. The soil microbial biomass carbon and soil basal respiration contents decreased with increasing soil depth but increased with re-vegetation. By contrast, soil microbial quotient increased with increasing soil depth and re-vegetation. From 0–10 cm soil layer to 20–40 cm soil layer, the dissolved organic carbon content decreased in different re-vegetation stages. In the process of re-vegetation, the dissolved organic carbon content increased in the 0–10 and 10–20 cm soil layers, whereas the dissolved organic carbon content decreased after an initial increase in the 20–40 cm soil layers. Meanwhile, dissolved organic carbon/soil organic carbon increased with increasing soil depth but decreased with re-vegetation. Significant correlations existed among soil microbial biomass carbon, soil microbial quotient, dissolved organic carbon, soil basal respiration and soil physic-chemical properties associated with soil fertility. The results showed that re-vegetation was conducive to the soil quality improvement and the accumulation of soil organic carbon pool of the hillslope land with purple soil in Hengyang, Hunan Province. [ABSTRACT FROM AUTHOR]

This study examines the technical efficiency (TE) differences among typical cropping systems of smallholder farmers in the purple-soiled hilly region of southwestern China. Household-, plot-, and crop- level data and community surveys were conducted to explore TE levels and determinants of typical cropping systems by using a translog stochastic frontier production function. Results indicate significant difference in TE and its determinants among cropping systems. The mean TEs of the rice cropping system (R), the rice-rape cropping system (RR), the rice-rape-potato cropping system (RRP), and the oil cropping system (O) are 0.86, 0.90, 0.84, and 0.85, respectively, which are over 1.17 times higher than those of the maize-sweet potato-other crop cropping system (MSO) and the maize-sweet potato-wheat cropping system (MSW) at 0.78 and 0.69, respectively. Moreover, Technical inefficiency (TIE) of different cropping systems is significantly affected by characteristics of the household as well as plot. However, the impact of land quality, mechanical cultivation conditions, crop structure, farming system, farm radius, household type, cultivated land area per capita, and annual household income per capital on TIE vary by cropping system. Additionally, output elasticity of land, labor, and capital, as a group, is greater than the one of agricultural machinery and irrigation. Finally, when household-owned effective agricultural labor is at full farming capacity, optimal plot sizes for the R, RR, RRP, MSO, MSW, and O cropping systems are 1.12 hm, 0.35 hm, 0.25 hm, 2.82 hm, 1.87 hm, and 1.17 hm, respectively. [ABSTRACT FROM AUTHOR]

The susceptibility of purple soil and intensive tillage render the land prone to erosion under heavy precipitations in a sloping cropland in southwestern China. This study aimed to improve the evaluation of the potential benefits of surface protection tillage and organic matter addition to decreasing nutrient losses. A field plot experiment under natural rainfall conditions was conducted, which employed four management practices: conventional downslope tillage system as control (CK), contour tillage (CT) with organic matter addition (CT + OM), CT with wheat straw mulching (CT + SM), and CT combining straw mulching and organic matter addition (CT + OM + SM). Runoff depth, nutrient loads, and soil erodibility were used to estimate the effects of straw mulching and organic matter addition. Results indicated that the runoff depth under CK was largest during the experimental period, with an average of 16.91 mm, and runoff coefficient average was 32%. Compared with CK, the runoff depth under CT + OM, CT + SM, and CT + OM + SM were reduced by 19%, 34%, and 50%, respectively. A significant difference in soil erodibility indicator among the four treatments was indicated (p < 0.05); CK achieved the highest value, whereas CT + OM + SM obtained the least value. In addition, the contour cultivation (i.e., CT approaches) were more sustainable than the downslope tillage system (i.e., CK). Soil erodibility under CK was 9.83 kg ha −1 mm −1 . Meanwhile, soil erodibility under CT + OM, CT + SM, and CT + OM + SM were 8.49, 6.99, and 6.87 kg ha −1 mm −1 , respectively. These values were 14%, 29%, and 30% lower than that of CK, respectively. CK was more susceptible to accelerated erosion compared with the plots with a surface cover or organic addition. This greater erodibility resulted in higher runoff, sediment yield, and associated nutrient loss for CK. The runoff-associated nitrogen losses were mainly controlled by the runoff rate and soil erodibility (p < 0.05). Variations in NO 3 − –N and NH 4 + –N concentration in runoff water were markedly affected by rainfall events and agricultural practice. A significant logarithmic correlation between NO 3 − –N load and runoff depth was identified. NO 3 − –N was proven to be the main form of inorganic nitrogen loss; therefore, fertilizer application of NO 3 − –N should be reduced in the purple soil region. Soil erodibility significantly influenced the available N losses (p < 0.01), which was best described by a positive logarithmic correlation. Soil nutrient concentration also played an important role in nitrogen loss. However, further research is needed to understand the dynamic interactions between soil erodibility as well as soil and nutrient losses. Results indicated that surface protection by CT + OM + SM is one of the good management practices to reduce soil loss by water erosion in regions with intense agricultural activity. [ABSTRACT FROM AUTHOR]

Copyright of Chinese Journal of Applied Ecology / Yingyong Shengtai Xuebao is the property of Chinese Journal of Applied Ecology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Soil shear strength is an important indicator of engineering design and an essential parameter of soil precision tillage and agricultural machinery and equipment design. Although numerous studies have investigated the characteristics of different soil shear strengths, only a few of these works have paid attention to soils containing considerable quantities of rock fragments. To date, most studies on the effects of rock fragments on the shear strength have paid attention to the role of rock fragments with sizes >2 mm. The effects of rock fragments <2 mm in soil are generally ignored. Similar to rock fragments >2 mm, the presence of rock fragments <2 mm could also change the mechanical properties of soils. Thus, in the present study we evaluated the potential influence of <2 mm rock fragments on soil shear strength via an unconsolidated undrained (UU) triaxial compression test. Our results were as follows: (1) A certain quantity of <2 mm rock fragments presented in purple soils developed from clay rocks; and an appropriate quantity of <2 mm rock fragments could improve the shear strength of soils. (2) The different PSDs of soils containing <2 mm rock fragments mainly caused variations in the internal friction angle of soils. (3) The shear strengths of the two mudstone-developed red-brown and gray-brown purple soils was more sensitive to water than that of the shale-developed coarse-dark purple soil. As the soil water content increased from 9% to 23%, the changes in the cohesion, internal friction angle, shear strength, and the maximum principal stress difference were smaller in the coarse dark purple soil than in the two other soils. We therefore concluded that <2 mm rock fragments in purple soils exerted important effects on soil shear strength. A better understanding of the differences among the shear strength features of purple soils could help improve the design of agricultural machinery and equipment. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Agro-Environment Science is the property of Journal of Agro-Environment Science Editorial Board and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Soil infiltration capability is the hot spot topic of soil erosion studies and soil physical and chemical properties have great influence on it. A new infiltration method point - source infiltration method was used to precisely evaluate the infiltration capability in different purple soil land - use types. And correlation analysis on soil physical and chemical properties and soil infiltration capability of different land - use types was performed. Results showed that: (i) there is a large difference among soil physical and chemical properties in different land - use types, soil water content, non - capillary porosity, capillary porosity, content of > 0.25 mm aggregates and organic matter content in the top soil are greater than those in the subsoil; (ii) soil infiltration capability showed differences among different land - use types. Land use showed great effects, in general, the order of decrease on initial infiltration rate and average infiltration rate was: woodland slope > slope farmland > grassland, the order of decrease on steady infiltration rate was : slope farmland > woodland > grassland and the time reaching stable state was : slope farmland > woodland > grassland; (iii) correlation analysis showed that there was a significantly positive correlation between initial infiltration rate and wet sieve MWD value and structural damage rate, and it had a significantly negative correlation with capillary porosity; (iv) steady infiltration rate and non - capillary porosity showed the significantly positive correlation, and it had a significantly negative correlation with the soil bulk density; (v) the average infiltration rate and non - capillary porosity and structural damage rate showed a positive correlation and the correlation coefficient was large and there was a negative correlation between average infiltration rate and soil bulk density and capillary porosity, and the absolute value of correlation coefficient was relatively large. The results of this study can provide the theoretical basis for soil infiltration study in purple soil area. [ABSTRACT FROM AUTHOR]

Soil erosion along with soil particles and nutrients losses is detrimental to crop production. We carried out a 5-year (2010 to 2014) study to characterize the soil erosion and nitrogen and phosphorus losses caused by rainfall under different fertilizer application levels in order to provide a theoretical evidence for the agricultural production and coordinate land management to improve ecological environment. The experiment took place under rotation cropping, winter wheat-summer maize, on a 15° slope purple soil in Chongqing (China) within the Three Gorges Region (TGR). Four treatments, control (CK) without fertilizer, combined manure with chemical fertilizer (T1), chemical fertilization (T2), and chemical fertilizer with increasing fertilization (T3), were designed on experimental runoff plots for a long-term observation aiming to study their effects on soil erosion and nutrients losses. The results showed that fertilization reduced surface runoff and nutrient losses as compared to CK. T1, T2, and T3, compared to CK, reduced runoff volume by 35.7, 29.6, and 16.8 %, respectively and sediment yield by 40.5, 20.9, and 49.6 %, respectively. Regression analysis results indicated that there were significant relationships between soil loss and runoff volume in all treatments. The combined manure with chemical fertilizer (T1) treatment highly reduced total nitrogen and total phosphorus losses by 41.2 and 33.33 %, respectively as compared with CK. Through this 5-year experiment, we can conclude that, on the sloping purple soil, the combined application of manure with fertilizer is beneficial for controlling runoff sediments losses and preventing soil erosion. [ABSTRACT FROM AUTHOR]

Summary Rills are commonly found on sloping farm fields in both the loess and the purple soil regions of China. A comparative study on rill erosion between the two soils is important to increase research knowledge and exchange application experiences. Rill erosion processes of loess and purple soils were determined through laboratory experiments with the volume replacement method. Water was used to refill the eroded rill segments to compute eroded volume before sediment concentration distribution along the rill was computed using the soil bulk density, flow rate, and water flow duration. The experimental loess soil materials were from the Loess Plateau and purple soil from the southwestern part of China, Chongqing City. A laboratory experimental platform was used to construct flumes to simulate rills with 12.0 m length, 0.1 m width, and 0.3 m depth. Soil materials were filled into the flumes at a bulk density of 1.2 g cm −3 to a depth of 20 cm to form rills for experiments on five slope gradients (5°, 10°, 15°, 20°, and 25°) and three flow rates (2, 4, and 8 L/min). After each experimental run under the given slope gradient and flow rate, the rill segments from the upper slope between 0–0.5, 0.5–1, 1–2, 2–3, …, 7–8, 8–10, and 10–12 m were lined with plastic sheets before be re-filled with water to determine sediment concentration after the eroded volumes was measured. Rill erosion differed between the two soils. As purple soil started to erode at a higher erosive force than loess soil, it possibly exhibits higher resistance to water erosion. The subsequent erosion process in the eroding purple rill was similar to that in the loess rill. However, the total erosion in the eroding loess rill was more than that in the eroding purple rill. The maximum sediment concentration transported by the eroding purple rills was significantly lower, approximately 55% of those transported by the loess rills under the same flow rate and slope gradient. Hence, less purple sediments can be transported compared with loess sediments. These findings were validated through comparison with existing studies. The results indicate that the research methods and experiences on rill erosion can be inter-exchanged between the loess and purple soils. [ABSTRACT FROM AUTHOR]

Ammonium adsorption and desorption properties by purple soils with different pH were studied. The results showed that the adsorption and desorption amounts of NH4+ by purple soils increased with the increase of NH4+ concentration, regardless of soil pH values; the largest adsorption and desorption amounts of NH4+ by purple soil at pH 6.0 were 10.3 and 7.96 mg/g, respectively; the largest adsorption and desorption amounts of NH4+ by purple soil at pH 7.2 were 12.8 and 4.62 mg/g, respectively; the largest adsorption and desorption amounts of NH4+ by purple soil at pH 8.0 were 13.5 and 2.23 mg/g, respectively. The isothermal adsorption kinetics of NH4+ by purple soils fits the Freundlich equation best (R>0.95). This study shows that the adsorption of NH4+ by purple soils with different pH values is multi-molecular layer uneven surface adsorption. [ABSTRACT FROM AUTHOR]

As a fundamental characteristic of soil physical properties, the soil Particle Size Distribution (PSD) is important in the research on soil moisture migration, solution transformation, and soil erosion. In this research, the PSD characteristics with distinct methods in different land uses are analyzed. The results show that the upper bound of the volume domain of the clay domain ranges from 5.743μm to 5.749μm for all land-use types. For the silt domain of purple soil, the value ranges among 286.852~286.966 μm. For all purple soil land-use types, the order of the volume domain fractal dimensions is DclayDsilt(U)>Dsand (U)>Dsand and Dsilt>Dsilt(U)>Dsand>Dsand(U), respectively. As it is compared with all Dvi, the Dsilt has the most significant correlativity to the soil texture and organic matter in different land uses of the typical purple soil watersheds. Therefore, Dsilt will be a potential indictor for evaluating the proportion of fine particles in the PSD, as well as a key measurement in soil quality and productivity studies. [ABSTRACT FROM AUTHOR]

The relationship between soil fauna groups and different fertilization regimes has been of continuous concern. Little attention has been paid to the response of soil fauna to changes in soil fertility. Thus, the aim of this study was to investigate the response of soil fauna communities to fertilizer management practices, to explore the inter-relationships between soil fauna communities and fertilization regimes so as to identify soil fauna species or groups that are sensitive to changes in soil fertility. This long-term fertilization experiment was conducted with a no fertilizer control and six fertilization regimes: CK (control, no fertilizer), N (synthetic N fertilizer), NPK (synthetic fertilizer: nitrogen, phosphorus and potassium), OM (pig manure), OMNPK (pig manure plus nitrogen, phosphorus and potassium), RSD (crop residues returned) and RSDNPK (crop residues returned with nitrogen, phosphorus and potassium). The application of organic fertilizers (i.e., pig manure or crop residues) promoted the diversity of the soil fauna communities due to the abundant organic matter the fertilizers supplied for the communities’ survival and development. Furthermore, organic–inorganic compound fertilizers (i.e., treatment of OMNPK or RSDNPK) were beneficial for richness and diversity of soil fauna communities due to their abundance of organic matter and supply of nutrients. Indices of soil fauna communities (i.e., TI, the DG (density-group) index, the number of individuals of Nemata, Lumbricida, Collembola and Oribatida) showed the same trend with an increase in the soil organic matter. Therefore, indices of soil fauna communities can be applied to indicate certain features of soil fertility, such as soil organic matter content, but they cannot be used to reflect integrated assessment for soil fertility. [ABSTRACT FROM AUTHOR]

Soil organic carbon (SOC) sequestration impacts on food security and climate change and may be affected by soil microbes in fertilized croplands. A 12-year field experiment under the rice–wheat system was used to evaluate the effect of the long-term fertilization on the SOC accumulation, culturable soil microbes, and their interaction in purple paddy soil. Results showed that varied fertilizations resulted in a significant increase of the SOC content and stock in the plow layer, as well as rise in populations of major soil microbes, including bacteria, actinomycetes, and fungi compared with no fertilization. Soil with combined application of chemical NPK fertilizer and organic amendment (pig manure or rice straw return) on average had the highest organic carbon content and stock, amounts of bacteria, actinomycetes, and fungi, which were 7.8%, 5.8%, 75.8%, 130.5%, and 16.2% higher than the NPK fertilization alone. Fertilization differentially altered populations of the functional anaerobic bacteria in paddy soil. With the combined application of chemical NPK fertilizer and organic amendment, soil displayed higher amounts of anaerobic cellulolytic bacteria, anaerobic fermentative bacteria, hydrogen-producing acetogen, methanogenic bacteria, denitrifying bacteria, and sulphate-reducing bacteria than that with the NPK fertilization alone or no fertilization. Populations of all three major soil microbes showed significantly positive correlations with the SOC content, indicating their interaction was of mutual promotion. Data suggest that the combined application of the NPK fertilizer with organic amendment especially by the rice straw return is recommended to sustain the soil biological fertility and mitigate the emission of the greenhouse gas by the SOC sequestration in purple paddy soil. [ABSTRACT FROM PUBLISHER]

Major element compositions and chemical weathering features of the purple soils and their corresponding rocks in the Red Sichuan Basin, China were studied in this paper to infer the diagenetic features of the purple rocks and the pedogenetic features of the purple soils. The results showed that all of the rock and soil samples, except those from Yibin, have strongly similar major element compositions and the distribution patterns of their major element compositions are similar to those of the upper continental crust. Chemical index of alteration, chemical index of weathering and NaO/KO indicate that the purple soils and rocks have similar chemical weathering intensities, whereas the AlO-CaO* + NaO-KO (A-CN-K) relationship, suggests that chemical weathering was strong during diagenesis of the purple rocks, but weak during pedogenesis of the purple soils. Variations in major element compositions of the purplish rock samples, except that from Yibin, do not primarily reflect differences in compositions of the sediment source, sediment recycling and potassium metasomatism, and therefore the effects of chemical weathering on the major element compositions were mainly dependent on climate condition and the residence time of material exposed to chemical weathering. Chemical weathering of the purple rocks reached only moderate degrees under the general influence of warm and humid climate during Jurassic and Cretaceous. Warmer and more humid climate conditions partly resulted in stronger chemical weathering of rocks in the southern region of the basin than in the central and western region, whereas shorter residence time of material in upslope position partly resulted in weaker chemical weathering of rocks in the eastern region than in the central and western region. The same climate and stable tectonic setting led to comparable chemical weathering intensities of rocks in the Ziliujing and Jiaguan Formations. Gradually colder and dryer climate from Early Jurassic to Middle Jurassic then to Late Jurassic and shorter residence time in tectonically active setting of Middle Jurassic and late Late Jurassic resulted in the following order of chemical weathering intensity of the purple Jurassic rocks: Ziliujing Formation ≫ Shaximiao Formation ≈ Suining Formation > Penglaizhen Formation. [ABSTRACT FROM AUTHOR]

In this study, the current situation of pluriactivity in mountainous and hilly rural areas of Sichuan province was analyzed using representative sample survey data and natural factor data calculated based on 30 m-resolution DEM and GIS. Moreover, using logistic regression model, a quantitative analysis was conducted on factors influencing pluriactivity in terms of individuals, households, communities and natural environmental conditions. The results showed that, (1) only 17.77% of rural laborers in mountainous and hilly areas of Sichuan province were engaged in pluriactivity. Geographically, pluriactivity was mainly chosen according to the 'proximity principle', and was concentrated in construction and service industries; (2) the following factors have a significant influence on whether rural laborers in hilly areas engage in pluriactivity: gender, number of years of education, marriage, number of laborers and time to towns. Those with little influence include: age, health, family size, arable land per capita and per capita income, whether there are elderly people over 75 years and children less than 3 years. According to the main factors affecting pluriactivity, the government should enhance vocational skills training for rural laborers in mountainous and hilly areas, especially for female laborers, further improve transport accessibility and encourage rural laborers, especially female laborers to move into pluriactivity to increase the income of farm households. [ABSTRACT FROM AUTHOR]

Quantification of soil spatial and temporal variability at watershed scale is important in ecological modeling, precision agriculture, and natural resources management. The spatio-temporal variations of soil nitrogen under different land uses in a small watershed (12.10 km) in the hilly area of purple soil at the upper reaches of the Yangtze River in southwestern China were investigated by using conventional statistics, geostatistics, and a geographical information system in order to provide information for land management and control of environmental issues. A total of 552 soil samples (0 to 15 cm) from 276 sites within the watershed were collected in April and August of 2011, and analyzed for soil total nitrogen (STN) and nitrate nitrogen (NO3-N). We compared spatial variations of STN and NO3-N under different land uses as well as the temporal variations in April (dry season) and August (rainy season). Results showed that STN contents were deeply affected by land-use types; median STN values ranged from 0.94 to 1.27 g·kg, and STN contents decreased in the following order: paddy field > forestland > sloping cropland. No significant difference was found for STN contents between April and August under the same land use. However, NO3-N contents were 23.26, 10.58, and 26.19 mg·kg in April, and 1.34, 8.51, and 3.00 mg·kg in August for the paddy field, sloping cropland and forestland, respectively. Nugget ratios for STN indicated moderate spatial dependence in the paddy field and sloping cropland, and a strong spatial dependence in forestland. The processes of nitrogen movement, transformation, absorption of plant were deeply influenced by land use types; as a result, great changes of soil nitrogen levels at spatial and temporal scales were demonstrated in the studied watershed. [ABSTRACT FROM AUTHOR]

Abstract: Cadmium (Cd), through human activities, has severely accumulated in purple soil. Purple soil is considered as one of the most important types of agricultural soil in Southern China. In this study, we investigated the release of Cd from 13 purple soils with a wide range of total Cd content collected from vegetable fields and forestlands in Sichuan Basin. Soil batch extraction and column leaching experiments were conducted to determine the influence of chemical speciation, soil properties, soil water contact time, and soil/water ratio on the release characteristics of Cd from soil. Results indicate that Cd release was primarily present in exchangeable, carbonate-bound, and organically bound fractions. Moreover, precipitation-induced, long-term saturated conditions enhance the release of Cd from soil to water. Multiple regression analysis also shows that the release of Cd from soil is related to pH level, organic matter amount, and total Cd content in native soil. This finding explains the Cd release variation of 86% and 95% during batch extraction and column leaching experiments, respectively. Finally, this investigation provides a more convenient way of evaluating potential ecological risks of Cd in purple soil by determining the properties of several common soil types. [Copyright &y& Elsevier]

This study was conducted to investigate the effect of waterlogging on copper, lead and cadmium fractionation in Chinese purple soil. Heavy metals were added to purple soil at 80 % field capacity and waterlogging regimes as nitrate salts of 500 mg kg of copper and lead, and 5 mg kg of cadmium. Metals in the incubated soil samples were fractionated termly from 1 to 35 days by the sequential extraction procedure. Under both treatments, the heavy metals spiked in the soil were transformed slowly from the exchangeable fractions into more stable fractions, whereas their residual fractions barely changed. The transformation process of exchangeable fraction in soil was estimated by Elovich kinetic equation for the above incubation periods, and the constant B in Elovich equation was applied to reflect the transformation rates of metal speciation. It was found that waterlogging incubation could immobilize heavy metals, resulting in decreased lability and availability of the metals in purple soil. The effect of waterlogging on the redistribution of heavy metals in purple soil might be mainly related to the changes of pH, potential redox and hydrous oxides in varying soil-water systems. [ABSTRACT FROM AUTHOR]

Abstract: Soil aggregation is a crucial soil property that affects a wide range of physical and chemical processes in soil ecosystems. Arbuscular mycorrhizal (AM) association is recognised as an important promoter of soil aggregation through the action of individual roots, mycelia and an insoluble, glue-like and hydrophobic proteinaceous substance, which is (at least partly) of AM fungi origin, named glomalin-related soil protein. Considering the increasing application of commercial AM inoculants, we addressed how the soil aggregates respond to the hyphal functions of AM inoculation in the field with a resident AM community. To this end, we introduced a new system in which the hyphae were separated by mesh and regular rotation to break the ingrowing hyphae as a control and to demonstrate the causal link between the hyphae and soil aggregates under conditions simulating natural parameters. The results showed the following: (i) the hyphal length was positively correlated with the mean weight diameter (r = 0.384, P < 0.05), geometric mean diameter (r = 0.257, 0.05 < P < 0.10) and easily extractable glomalin (r = 0.296, P < 0.05); (ii) the colonisation rate of the roots in the cores was increased by constantly severing the extraradical mycelium and (iii) the colonisation rate of the control plant roots (approx. 10%) was significantly lower compared to those inoculated with AM fungi (ranging from 34% to 54%). It was concluded that the hyphal networks of AM inoculations can promote the formation and stability of soil aggregates under conditions that closely simulate those occurring in nature. [Copyright &y& Elsevier]

Aims: A 3-year field experiment (October 2004-October 2007) was conducted to quantify NO fluxes and determine the regulating factors from rain-fed, N fertilized wheat-maize rotation in the Sichuan Basin, China. Methods: Static chamber-GC techniques were used to measure soil NO fluxes in three treatments (three replicates per treatment): CK (no fertilizer); N150 (300 kg N fertilizer ha yr or 150 kg N ha per crop); N250 (500 kg N fertilizer ha yr kg or 250 kg N ha per crop). Nitrate (NO) leaching losses were measured at nearby sites using free-drained lysimeters. Results: The annual NO fluxes from the N fertilized treatments were in the range of 1.9 to 6.7 kg N ha yr corresponding to an NO emission factor ranging from 0.12 % to 1.06 % (mean value: 0.61 %). The relationship between monthly soil NO fluxes and NO leaching losses can be described by a significant exponential decaying function. Conclusions: The NO emission factor obtained in our study was somewhat lower than the current IPCC default emission factor (1 %). Nitrate leaching, through removal of topsoil NO, is an underrated regulating factor of soil NO fluxes from cropland, especially in the regions where high NO leaching losses occur. [ABSTRACT FROM AUTHOR]

The water erosion prediction project (WEPP) model is a popular water erosion prediction tool developed on the basis of the physical processes of water erosion. Although WEPP has been widely used around the world, its application in China is still insufficient. In this study, the performance of WEPP used to estimate the runoff and soil loss on purple soil (Calcaric Regosols in FAO taxonomy) sloping cropland was assessed with the data from runoff plots under simulated rainfall conditions. Based on measured soil properties, runoff and erosion parameters, namely effective hydraulic conductivity, inter-rill erodibility, rill erodibility, and critical shear stress were determined to be 2.68 mm h, 5.54 × 10 kg s m, 0.027 s m and 3.5 Pa, respectively, by using the recommended equations in the WEPP user manual. The simulated results were not good due to the low Nash efficiency of 0.41 for runoff and negative Nash efficiency for soil loss. After the four parameters were calibrated, WEPP performed better for soil loss prediction with a Nash efficiency of 0.76. The different results indicated that the equations recommended by WEPP to calculate parameters such as erodiblity and critical shear stress are not suitable for the purple soil areas, Sichuan Province, China. Although the predicted results can be accepted by optimizing the runoff and erosion parameters, more research related to the determination of erodibility and critical sheer stress must be conducted to improve the application of WEPP in the purple soil areas. [ABSTRACT FROM AUTHOR]

This study provides a combined dataset on N loss pathways and fluxes from sloping cropland in the purple soil area, southwestern China. A lysimeter experiment was conducted to quantify nitrate leaching (May 2004–May 2010) and N2O emission (May 2009–May 2010) losses. Nitrate leaching was the dominant N loss pathway and annual leaching fluxes ranged from 19.2 to 53.4 kg N ha−1, with significant differences between individual observation years (P < 0.05). Direct N2O emissions due to N fertilizer use were 1.72 ± 0.34 kg N ha−1 yr−1, which corresponds to an emission factor of 0.58 ± 0.12%. However, indirect N2O emissions caused by nitrate leaching and surface runoff N losses, may contribute another 0.15–0.42 kg N ha−1 yr−1. Our study shows that nitrate leaching lowered direct N2O emissions, highlighting the importance for a better understanding of the tradeoff between direct and indirect N2O emissions for the development of meaningful N2O emission strategies. [Copyright &y& Elsevier]

Summary: Bioavailable phosphorus (P) losses due to agriculture activity in a purple soil watershed in the Sichuan Basin of Southwestern China were monitored to define the hydrological controls of P transport. Our results indicate that the proportion of P that was transported in particulate form increased in the rainy season, and that the mass of total bioavailable P (BAP) loads exhibited seasonal fluctuations, wherein the majority (over 90%) was observed to have been exported between June and September. The proportion of bioavailable dissolved P (BDP) in the BAP discharge budget in the watershed varied between 11% and 15% during the monitoring period. The bioavailable particulate P (BPP) and BDP concentrations of stream water under rainstorm events increased by over 40% in comparison to their annual mean concentrations, and the annual BAP load was primarily dominated by the loads that occurred during rainstorm events in the study year. BAP concentration in groundwater significantly fluctuated with the seasons, and the ratio of total BAP in groundwater to that in surface water gradually increased during the rainy season. Thus, the impact of agriculture on the water quality of this watershed becomes clearly evident. [ABSTRACT FROM AUTHOR]

The worldwide extension and intensification of farming during the last century has led to ecosystem degradation and caused a series of environmental problems. Conservation of ecosystem services in agricultural regions has been implemented by top-down government actions or initiated by resilience scientists in the developed countries, but little attention was paid in the developing countries, especially in some remote mountainous regions. The present paper presents a case study showing how local farmers obtained both maximal societal outcomes and agroecosystem conservation interests in the absence of distinct boundaries between agricultural and protected ecological areas in the densely populated purple-soiled hilly region of southwestern China. The local community (Yanting County) has developed a mosaic agricultural-forestry-fishery-stock breeding system with spatially targeted land uses, diverse agricultural productions and multiple ecological partnerships. It indicates that the local farmers have hereditarily perceived sound strategies on maximizing sustainable societal outcomes and optimizing tradeoffs among macro-market, state policy, new technological facility and ecological reinforcement. [ABSTRACT FROM AUTHOR]

Research on the effects of soil erosion on soil productivity has attracted increasing attention. Purple soil is one of the main soil types in China and plays an important role in the national economy. However, the relationship between erosion and the productivity of purple soils has not been well studied. The purpose of this research was to determine if soil depth, which is dependent on the rate of erosion, has an influence on crop yield and growth. Plot and pot experiments at different soil depths were performed. Results indicate that soils from different parental materials had different growth features and crop yields due to the differential fertility of the derived soils. The yield reduction rate increases exponentially with the depth of eroded soil (level of erosion). The yield reduction rate per unit eroded soil horizon (10 cm) is approximately 10.5% for maize and wheat. [ABSTRACT FROM AUTHOR]

Abstract: The potential for using 7Be measurements to document soil redistribution associated with a heavy rainfall was estimated using 7Be method on a bare purple soil plot in the Three Gorges Reservoir region of China. The results were compared with direct measurement from traditional approaches of erosion pins and runoff plots. The study shows that estimation of soil losses from 7Be are comparable with the monitoring results provided by erosion pins and runoff plots, and are also in agreement with the existing knowledge provided by 137Cs measurements. The results obtained from this study demonstrated the potential for using 7Be technique to quantify short-term erosion rates in these areas. [Copyright &y& Elsevier]

Rainfall runoff is a critical hydrological process related to soil erosion and agricultural non-point pollution. In this study, 25 simulation experiments on rainfall were carried out in five runoff plots. Rape ( Brassica campestris) was planted on the downslope of the plots. Experiments were conducted when the vegetation coverage reached 80%. Each plot was subjected to five rainfall events differing in intensity. The results showed: (1) the runoff coefficients of overland flow and subsurface flow were less than 0.6 and 0.005, respectively; (2) the discharge of overland flow was the quadratic function of time; (3) runoff coefficient was the function of slope gradient and rainfall intensity. When the slope gradient increased from 8.7% to 46.6%, the runoff coefficient of overland flow first increased and then decreased. The runoff coefficient reached the maximum when the slope gradient was within the range of 17.6%-36.4%; and (4) the process of subsurface flow generation included the increasing phase and recession phase. Discharge was a logarithm function of time in the increasing phase, and an exponential function in the recession phase. Runoff coefficient of subsurface flow decreased first and then increased when the slope gradient varied from 8.7% to 46.6% and was not correlated with rainfall intensity. [ABSTRACT FROM AUTHOR]

The deposition flux of Be was measured in the range from 0.4 to 5.2 Bq md, with a mean value of 2.6 Bq md, during the period of May 31, 2009-May 31, 2010 in the Three Gorges Reservoir region, China. The low annual deposition flux of Be was probably due to the adsorption of Be within high altitude clouds and the Qinling-Daba Mountain's barrier and blocking effects on the cold air during winter months. There was a seasonal trend for Be deposition, showing a spring maximum and winter minimum, which may be attributed to the seasonal folding of tropopause in spring and little rainfall amount in winter. A strong positive correlation ( R = 0.67) between Be deposition flux and rainfall was observed. The depth distribution of Be in undisturbed purple soil profiles suggested that the nuclide was mainly distributed within the top 20.0 kg m (~1.5 cm) of soil in depth and the maximum concentration occurred at a depth of 3.0 kg m (~0.2 cm), then the concentration declined quickly and exponentially with depth. The seasonal inventories of Be in soils were consistent with the values calculated from the atmospheric fluxes, which shows a great potential for using Be as a tracer to assess soil redistribution in purple soil areas of China. [ABSTRACT FROM AUTHOR]

This paper presents the results of laboratory experiments showing the effects of rock fragments contained in three different purple soils of the Sichuan basin of southwest China. The experiments investigated how these rock fragments alter the soil's physical, chemical, and agronomical characteristics such as infiltration and evaporation. We found that the infiltration rate, whether horizontal or vertical, in the three soils has the following order: gray brown purple soil < reddish brown purple soil < brown purple soil. With increasing rock fragment contents the accumulated infiltration decreases, while the total time decreases first and then increases. The minimum occurs at approximately 10-20% of fragment content by weight. The infiltration rate also changes with the distance. In the 0-5 cm range, the initial infiltration rate increases with increasing rock fragment contents, while in the 5-10 cm range, the slope of infiltration curve increases with increasing rock fragment contents. With increasing distance, the slope gradually decreases and finally reaches a stable value. The presence of rock fragments reduces soil water content, the minimal value appearing when the rock fragments were on top of the soil column (soil + rock sample), decreasing with increasing rock fragments for other samples mixed with fragments. Under the constant 40°C temperature, the accumulated evaporation and evaporation rate are minimal for soils covered by rock fragments, and the accumulated evaporation decreases with increasing rock fragment for other soil samples. However, the evaporation rate increases with increasing rock fragments in the first 4 days and decreases thereafter. [ABSTRACT FROM AUTHOR]

Use of anionic polyacrylamide (PAM) to control phosphorus (P) losses from a Chinese purple soil was studied in both a laboratory soil column experiment and a field plot experiment on a steep slope (27%). Treatments in the column study were a control, and PAM mixed uniformly into the soil at rates of 0.02, 0.05, 0.08, 0.10, and 0.20%. We found that PAM had an important inhibitory effect on vertical P transport in the soil columns, with the 0.20% PAM treatment having the greatest significant reduction in leachate soluble P concentrations and losses resulting from nine leaching periods. Field experiments were conducted on 5m wide by 21m long natural rainfall plots, that allowed collection of both surface runoff and subsurface drainage water. Wheat was planted and grown on all plots with typical fertilizer applied. Treatments included a control, dry PAM at 3.9kgha−1, dry PAM at 3.9kgha−1 applied together with lime (CaCO3 at 4.9tha−1), and dry PAM at 3.9kgha−1 applied together with gypsum (CaSO4·2H2O at 4tha−1). Results from the field plot experiment in which 5 rainfall events resulted in measurable runoff and leachate showed that all PAM treatments significantly reduced runoff volume and total P losses in surface runoff compared to the control. The PAM treatments also all significantly reduced water volume leached to the tile drain. However, total P losses in the leachate water were not significantly different due to the treatments, perhaps due to the low PAM soil surface application rate and/or high experimental variability. The PAM alone treatment resulted in the greatest wheat growth as indicated by the plant growth indexes of wheat plant height, leaf length, leaf width, grain number per head, and dried grain mass. Growth indexes of the PAM with Calcium treatments were significantly lesser. These results indicate that the selection and use of soil amendments need to be carefully determined based upon the most important management goal at a particular site (runoff/nutrient loss control, enhanced plant growth, or a combination). [Copyright &y& Elsevier]

Abstract: To characterize the phytoextraction efficiency of a hybrid poplar (Populus deltoids × Populus nigra) in cadmium contaminated purple soil and alluvial soil, a pot experiment in field was carried out in Sichuan basin, western China. After one growing period, the poplar accumulated the highest of 541.98±19.22 and 576.75±40.55μg cadmium per plant with 110.77±12.68 and 202.54±19.12g dry mass in these contaminated purple soil and alluvial soil, respectively. Higher phytoextraction efficiency with higher cadmium concentration in tissues was observed in poplar growing in purple soil than that in alluvial soil at relative lower soil cadmium concentration. The poplar growing in alluvial soil had relative higher tolerance ability with lower reduction rates of morphological and growth characters than that in purple soil, suggesting that the poplar growing in alluvial soil might display the higher phytoextraction ability when cadmium contamination level increased. Even so, the poplars exhibited obvious cadmium transport from root to shoot in both soils regardless of cadmium contamination levels. It implies that this examined poplar can extract more cadmium than some hyperaccumulators. The results indicated that metal phytoextraction using the poplar can be applied to clean up soils moderately contaminated by cadmium in these purple soil and alluvial soil. [Copyright &y& Elsevier]