Purple Soil Region Research Articles

The Quantification of the Ecosystem Services of Forming Ridges in No-Tillage Farming in the Purple Soil Region of China: A Meta-Analysis

The Quantification of the Ecosystem Services of Forming Ridges in No-Tillage Farming in the Purple Soil Region of China: A Meta-Analysis

Responses of soil microbial biomass carbon and microbial entropy to soil properties in typical sloping croplands of China under erosion conditions

Soil microbial biomass carbon (MBC) and microbial entropy play a crucial role in the carbon cycle of terrestrial ecosystems, while their responses to soil properties in typical sloping croplands under the impact of soil erosion remain poorly understood due to the complexity of the soil erosion process. In this study, we selected typical sloping croplands with different erosion levels for the four severely eroded soil types (black, loess, purple, and red soil) in China to assess the key controls of MBC and microbial entropy under the influence of soil erosion. The results showed that soil erosion significantly reduced the MBC content but increased the microbial entropy of sloping croplands in black soil region (BS) (22 %, 43.6 %), purple soil region (PS) (25.5 %, 26.2 %) and red soil region (RS) (28.9 %, 21.9 %), but not in loess soil region (LS). The soil physicochemical properties had significantly positive and negative correlations on the MBC and microbial entropy, respectively. The MBC and microbial entropy of these sloping croplands had different dominant drivers under soil erosion. Overall, our results revealed that changes in MBC and microbial entropy directly depended on the fundamental properties of the soil and soil erosion could indirectly affect the MBC and microbial entropy by directly affecting the physicochemical properties of soil. Thus, the impact of soil erosion on sloping croplands and the associated responses following changes in MBC and microbial entropy provide fresh insights into predicting the effects of soil erosion on carbon stability.

Effects of the Combining Straw Return with Urease Inhibitor on Ammonia Volatilization, Nitrogen Use Efficiency, and Rice Yield in Purple Soil Areas.

Straw return in rice (Oryza sativa L.) paddy has been heavily criticized for its potential to influence ammonia (NH3) volatilization loss due to irrational fertilizer N application. Therefore, improving the N fertilization strategies within residue straw systems is necessary to reduce N loss from NH3 volatilization. This study investigated how the incorporation of oilseed rape straw and the urease inhibitor affected NH3 volatilization, fertilizer N use efficiency (FNUE), and rice yields over two growing seasons (2018-2019) in the purple soil region. This study arranged eight treatments combined straw (2, 5, 8 ton ha-1, named 2S, 5S, 8S, respectively), with urea or urease inhibitor (UI, 1% NBPT) with three replicates, which included control (CK), UR (Urea, 150 kg N ha-1), UR + 2S, UR + 5S, UR + 8S, UR + 2S + UI, UR + 5S + UI, UR + 8S + UI, based on the randomized complete block method. Our results indicated that incorporating oilseed rape straw increased NH3 losses by 3.2-30.4% in 2018 and 4.3-17.6% in 2019 than the UR treatment, attributing to the higher NH4+-N content and pH value within floodwater. However, the UR + 2S + UI, UR + 5S + UI and UR + 8S + UI treatments reduced NH3 losses by 3.8%, 30.3%, and 8.1% in 2018 and 19.9%, 39.5%, and 35.8% in 2019, separately compared to their corresponding UR plus straw treatments. According to the findings, adding 1% NBPT significantly decreased NH3 losses while incorporating 5 ton ha-1 oilseed rape straw. Furthermore, adding straw, either alone or in conjunction with 1% NBPT, increased rice yield and FNUE by 0.6-18.8% and 0.6-18.8%, respectively. Otherwise, NH3 losses scaled by yield in the UR + 5S + UI treatment decreased significantly between all treatments in 2018 and 2019. These results suggest that optimizing the oilseed rape straw rate combined with 1% NBPT applied with urea efficiently increased rice yield and reduced NH3 emissions in the purple soil region of Sichuan Province, China.

Crop Residue Removal Effects on Soil Erosion and Phosphorus Loss in Purple Soils Region, Southwestern China

Background: Purple soil has a fragile structure and is highly vulnerable to soil erosion and phosphorus (P) loss risks. Despite this, the region is endowed with abundant crop residue resources. To ensure sustainable agricultural development in this area, we conducted a study to investigate the impact of crop residue removal on soil aggregate structure, soil erosion, and the risk of P loss. Methods: We conducted a three-year on-farm experiment and analyzed various soil parameters. These parameters include mean weight diameter (MWD), geometric mean diameter (GMD), soil aggregates with a diameter greater than 0.25 mm (R>0.25mm), saturated hydraulic conductivity, soil erosion estimated by RUSLE 2, total soil phosphorus (TP) concentration, geometric mean concentration of TP (GMC), and geometric mean concentration of TP adjusted for aggregate size (GMCd). Results: Retaining all crop residue can significantly improve soil saturated hydraulic conductivity, which was 2.56 times higher than the complete removal treatment. After three years of experimentation, compared to four months, the 50% residue removal treatment increased the GMCd by 32.7%, while the 0% removal treatment increased the GMCd by 16.6%. Both improvements were higher than the complete removal treatment. Partial or complete removal of the crop residue can reduce the soil aggregate stability and increase the risk of soil erosion and P loss. Conclusions: The GMC and GMCd have the potential to serve as indicators for evaluating soil P loss risk. Removing crop residues can cause the degradation of the structure of purple soil aggregates, thus resulting in increased soil erosion and P loss. It is not recommended to remove crop residues in the purple soil region to ensure sustainable agricultural development.

Adsorption of nitrate from interflow by the Mg/Fe calcined layered double hydroxides.

Nitrate loss in interflow caused serious nitrate pollution of neighboring water bodies in the purple soil region of China's Sichuan Province. In this study, Mg/Fe(Al)-calcined layered double hydroxides (Mg/Fe(Al)-CLDHs) with varied Mg/Fe(Al) ratios were synthesized for nitrate removal from interflow, and 3:1 Mg/Fe CLDH exhibited the best adsorption performance. The effects of initial pH, adsorbent dosage and co-existing anions on the adsorption performance were investigated by batch experiments. The best-fitting kinetic and isothermal models for nitrate adsorption were the pseudo-second-order model and Freundlich model, respectively, indicating that the adsorption process was a physical-chemical multilayer process. The maximum adsorption capacity of nitrate was 73.36 mg/g, which was higher than that of many other commonly used adsorbents. The adsorbents were characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), transmission electron microscope (TEM) and Brunauer-Emmett-Teller (BET) techniques, and the XRD and FT-IR results revealed that the adsorption mechanism involved original layered structure reconstruction and ion-exchange interaction. Under the coexistence of SO42- and Cl-, 75.63% nitrate in interflow could be removed after 6 h of adsorption. Overall, the synthesized Mg/Fe CLDH is an effective and low-cost nitrate adsorbent for in-situ nitrate removal.

The Crop Residue Removal Threshold Ensures Sustainable Agriculture in the Purple Soil Region of Sichuan, China

Sichuan, a hilly area in southwestern China, is recommended as a bioethanol production base because of its abundant crop residue resources. However, removing the crop straw for bioethanol may negatively affect soil fertility and productivity due to the local purple soil vulnerability. To explore the impact of crop residue removal on soil fertility and productivity and meet the needs of sustainable agriculture, we conducted a crop residue removal experiment by measuring the soil organic carbon (SOC), total nitrogen (TN), and total phosphorus (TP) contents, and crop yield in the purple soil region in southwest China. Soil erosion was also simulated by Revised Universal Soil Loss Equation version 2 (RUSLE 2). The results showed that soil erosion increased with the increase of the straw removal rate. Compared with 0% removal treatment, the SOC content reduced at other removal rate treatments, especially for long-term residue removal. The effect of residue removal on soil TN and TP was not consistent within one year. After two years, residue removal greater than 25% caused a decrease in TN by 1.6–3.7%, and straw removal greater than 50% caused a TP decrease by 8.5–9.3%. More than 25% of the residue removed reduced maize and canola yields, and TN and TP content. However, all crop residue removal treatments resulted in SOC content reduction and soil erosion deterioration. In conclusion, crop residue removal was not recommended due to agricultural sustainability in Sichuan, China.

Adaptive scale weighted fuzzy C-Means clustering for the segmentation of purple soil color image

The segmentation and extraction of the purple soil region from purple soil color image can effectively avoid the influence of background on recognition of soil types. A scale weighted fuzzy c-means clustering algorithm(SWFCM) is proposed for effective segmentation of purple soil color image. The main work is to establish the maximum difference optimization model with the mean of Gaussian distance between each pixel and each peak of the image histogram, and optimize the clustering number and the initial clustering centers. Then, the compactness of each class is defined to weight the Euclidean distance between the pixel and the clustering center and improve the optimization model of FCM for raising its clustering performance. Aiming at the problem of removing scattered small soil blocks in the background and filling holes in the purple soil region, the algorithm of extracting the boundary of the purple soil region and the algorithm of filling the purple soil region are proposed. Finally, the normal and robust experiments are carried out on the normal sample set and robust sample set. And the performances of relative algorithms are compared, which involves the previously released FCM algorithms and some methods for the segmentation of purple soil color image and our proposed algorithm. Experimental results show that performance of SWFCM is better and it can provide a high reference for adaptive segmentation of purple soil color images. Especially for robust experiment images, its average segmentation accuracy is improved by 6 . 64% ∼ 8 . 25 % compared with other purple soil segmentation algorithms.

Spatial variation of microtopography and its effect on temporal evolution of soil erosion during different erosive stages

Microtopography significantly influences soil erosion at hillslope scale. Currently, the influence of microtopography on temporal evolution of soil erosion is still unclear. A set of simulated rainfall experiments on three 2 m long, 1 m wide soil boxes under a rainfall intensity of 1.5 mm min−1 on a 20° slope were conducted in the Chinese purple soil region to quantify the spatial variation of microtopography and its effect on temporal variations of runoff and sediment yield during water erosion processes. Three local tillage practices: conventional tillage (CT), artificial digging (AD), and ridge tillage (RT) with different initial microrelief (smooth, rough, and very rough) were designed. The spatial heterogeneity of microtopography was characterized by directional derivatives, semivariogram, and fractal information dimension in terms of morphology and quantity. And we identified the temporal variability characteristics of runoff and sediment yield based on wavelet and rescaled range (R/S) analyses. The results indicated that the spatial variability of different tillage practices had strong or medium autocorrelations during different water erosive stages. The spatial autocorrelation scales of CT, AD, and RT were 6.10, 5.32, and 4.01 m, respectively. The fractal information dimensions of tillage practices at various erosive stages were RT > AD > CT. There was a certain range of Di critical values, which reflected the positive or negative effect on soil erosion. The Hurst indexes of the runoff time series were in the section between 0.632 and 0.718, and that of the sediment yield time series ranged between 0.741 and 0.846. The time series of runoff and sediment yield had long-range persistence and varied periodically every 12–16 min during water erosion processes. Overall, the dominant period and the persistence of runoff tended to decrease and increase respectively with the increase in microrelief, while the temporal variation in sediment yield was opposite to that of runoff. Characterization of the temporal variability characteristics of runoff and sediment yield response to microrelief changes would contribute to a better understanding of the hydro-geomorphological processes at hillslope scale.

Characteristics of nitrogen loss in sloping farmland with purple soil in southwestern China during maize (Zea mays L.) growth stages

Nitrogen (N) loss from agricultural nonpoint source pollution results in eutrophication. In this study, the characteristics of N loss were explored using simulated rainfall conditions during different maize growth stages (seedling, elongation, tasseling, and maturity) under different slope gradients (10°, 15°, and 20°), from May to August 2016. The surface runoff and sediment yield increased with increasing rainfall duration. As the slope gradient increased, surface runoff and sediment yield also increased, and N loss accelerated during the maize seedling stage. Interflow and N loss decreased as the slope gradient increased, and the maximum interflow and N loss were found during the tasseling and elongation stages of maize. Similarly, maximum average N losses were recorded during the maize seedling stage for both surface runoff and sediment yield (35.01 mg m−2 and 5.63 mg m−2, respectively), while the maximum interflow (163.91 mg m−2) was recorded during the elongation stage. The surface runoff and interflow accounted for 9.27%–45.90% and 50.79%–89.35%, respectively, of the average total nitrogen (TN) loss under different slope gradients and during different maize growth stages. Thus, we concluded that interflow was the main pathway for N loss. Surface runoff and interflow mainly contained dissolved total nitrogen (DTN), while nitrate nitrogen (NO3N) was the primary form of DTN during the different maize growth stages. Path coefficients and contribution rates of slope gradients were the highest for DTN loss in surface runoff and for ammonium nitrogen (NH4N) loss in interflow. The path coefficients and contribution rates of surface runoff, interflow, and sediment yield were the highest for TN, NO3N, NH4N, TN, DTN, NO3N, and TN loss, respectively. We concluded that surface runoff, interflow, and sediment yield were the main factors affecting N loss at our study site in the purple soil region of southwest China, followed by slope gradient and vegetation coverage.

Characteristics of Antibiotic Resistance Genes in Various Livestock Feedlot Soils of the Hilly Purple Soil Region

Given the potential risk posed by antibiotic resistance genes (ARGs) to the eco-environment in the hilly purple soil region, which has been intensively utilized by human, surface soil samples were collected from feedlots of pig, chicken, and cattle farms and were analyzed for the diversity and abundance of ARGs using high-throughput QPCR. In total, 79 ARGs and 5 mobile genetic elements (MGEs) were detected across all samples. Among these genes, multidrug resistance genes were the most abundant type of ARGs. More abundant and diverse ARGs were observed in feedlot soil samples from pig and chicken farms than those from cattle feedlot soils, and these samples showed different distribution patterns of ARGs. High abundance of MGEs and their significant correlation with ARGs (P<0.05) implied an important role of MGEs in the dissemination of ARGs in livestock feedlot soils.

Regional differences in the soil and water conservation efficiency of conservation tillage in China

The benefits of conservation tillage on water erosion control have been extensively tested in China, while few studies have involved their regional differences. We synthesized 81 recent publications about the water erosion control by conservation tillage in China, to explore the regional difference of conservation tillage and identify the optimal tillage methods of each region. The benefits of conservation tillage for runoff retention and sediment reduction are different in different regions due to the special environmental condition of each region. Conservation tillage demonstrated the lowest efficiency in the Northwest China Loess Plateau region and highest in the North China mountainous region, while no significant differences were found among other 4 regions. In the Northeast China black soil region, micro-basins tillage (MBT) is the optimal tillage method due to its greatest benefits in reducing runoff and sediment. In the North China mountainous region, the values of regional efficiency evaluation index (REEI) of runoff and sediment were both larger than 1 only by contour tillage with hedgerow (CTH), thus CTH will be the optimal tillage method in this region. In the Northwest China Loess Plateau region, some engineering measures should be the priority due to the limited benefits of conservation tillage. In the South China red soil region, no tillage with mulch (NTM) presented the greatest benefits on water erosion control and largest values of runoff and sediment REEI, thus CTH is the priority in this region. In the Southwest China purple soil region, though the values of runoff and sediment REEI by collecting soil to form ridges with no tillage (CSNT) are less than those by MBT, CSNT is the most suitable tillage method in this region. The small sample size leads to the unreliable results in the Southwest China karst region, thus more researches are needed in this region.

Effects of slope gradient on runoff from bare-fallow purple soil in China under natural rainfall conditions

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.

Effects of intercropping Chinese milk vetch on functional characteristics of soil microbial community in rape rhizosphere

The application of green manure is facing serious problems in purple soil region of southwest China. With the aim to explore the potential application of green manure, we examined the functional characteristics of soil microbial community in a system of Chinese milk vetch intercropped with rape. The innovations are the application of Chinese milk vetch in dry land of the southwest China and the establishment of new planting pattern of rape by providing empirical data. Results showed that the intercropping with Chinese milk vetch decreased the carbon resource use efficiency of microbial community in rape rhizosphere, especially for the utilization of carbohydrates. At the same time, Shannon index, Simpson index, and richness were reduced, but evenness index was increased by intercropping. Those results from cluster analysis and principal component analysis suggest that the soil microbial community composition was significantly different between monocropping and intercropping. The carbohydrates, amino acids and carboxylic acids were the sensitive carbon sources for differentiating the changes of the microbial community induced by monocropping and intercropping. Intercropping Chinese milk vetch could decrease functional activity, change community composition, and reduce diversity of soil microbial community in rape rhizosphere.

Surfactant-enhanced flushing enhances colloid transport and alters macroporosity in diesel-contaminated soil

Soil contamination by diesel has been often reported as a result of accidental spillage, leakage and inappropriate use. Surfactant-enhanced soil flushing is a common remediation technique for soils contaminated by hydrophobic organic chemicals. In this study, soil flushing with linear alkylbenzene sulfonates (LAS, an anionic surfactant) was conducted for intact columns (15cm in diameter and 12cm in length) of diesel-contaminated farmland purple soil aged for one year in the field. Dynamics of colloid concentration in column outflow during flushing, diesel removal rate and resulting soil macroporosity change by flushing were analyzed. Removal rate of n-alkanes (representing the diesel) varied with the depth of the topsoil in the range of 14%–96% while the n-alkanes present at low concentrations in the subsoil were completely removed by LAS-enhanced flushing. Much higher colloid concentrations and larger colloid sizes were observed during LAS flushing in column outflow compared to water flushing. The X-ray micro-computed tomography analysis of flushed and unflushed soil cores showed that the proportion of fine macropores (30–250μm in diameter) was reduced significantly by LAS flushing treatment. This phenomenon can be attributed to enhanced clogging of fine macropores by colloids which exhibited higher concentration due to better dispersion by LAS. It can be inferred from this study that the application of LAS-enhanced flushing technique in the purple soil region should be cautious regarding the possibility of rapid colloid-associated contaminant transport via preferential pathways in the subsurface and the clogging of water-conducting soil pores.

间作绿肥对油菜根际土壤碳氮及根际微生物的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 间作绿肥对油菜根际土壤碳氮及根际微生物的影响 DOI: 10.5846/stxb201610072007 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 公益性行业（农业）科研专项（201503127）；国家自然科学基金项目（31271673） Effects of intercropping green manure on soil carbon, nitrogen and soil microbial in rapeseed rhizosphere Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:在我国西南紫色土地区，农田生态环境极为脆弱，绿肥应用也面临严峻问题。为改善农田土壤健康状况，探索绿肥的应用途径，通过紫云英与油菜间作，重点探讨了绿肥紫云英对油菜根际土壤碳氮及其微生物特征的影响，同时与秸秆覆盖的效应作了比较，其创新性在于将绿肥紫云英应用于西南旱地，并且为建立新的油菜种植模式作铺垫。结果表明：与秸秆覆盖相比，间作绿肥紫云英是影响油菜根际土壤环境的主要因素。间作紫云英减少了油菜根际土壤碳、氮含量，改变了油菜根际土壤碳氮比。间作紫云英也减少了油菜根际土壤微生物量，改变了油菜根际土壤微生物群落结构，改善了油菜根际土壤通气状况，抑制了厌氧细菌的生长。 Abstract:In purple soil region of southwest China, the eco-environment is extremely fragile in farmlands, and the application of green manure is facing serious problems. In order to improve soil health and explore the application way of green manure, the effects of intercropping green manure (Chinese milk vetch) on soil carbon, nitrogen and soil microbial in rapeseed rhizosphere was examined and compared with those of straw mulching. Chinese milk vetch was innovatively applied in dry land so as to establish a new rapeseed planting pattern in southwest China. Results showed that, compared with straw mulching, intercropping Chinese milk vetch was the main factor to affect soil environment in rapeseed rhizosphere. Intercropping Chinese milk vetch substantially decreased the content of carbon and total nitrogen and changed the C/N ratio in rapeseed rhizosphere. It also decreased the total PLFA (phospholipid fatty acid), changed the structure of soil microbial community, improved the soil aeration condition and inhibited the growth of anaerobic bacteria in rapeseed rhizosphere. 参考文献 相似文献 引证文献

Combined effects of runoff and soil erodibility on available nitrogen losses from sloping farmland affected by agricultural practices

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 16.91mm, 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 9.83kgha−1mm−1. Meanwhile, soil erodibility under CT+OM, CT+SM, and CT+OM+SM were 8.49, 6.99, and 6.87kgha−1mm−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 NO3−–N and NH4+–N concentration in runoff water were markedly affected by rainfall events and agricultural practice. A significant logarithmic correlation between NO3−–N load and runoff depth was identified. NO3−–N was proven to be the main form of inorganic nitrogen loss; therefore, fertilizer application of NO3−–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.

Mechanisms of soil N dynamics following long-term application of organic fertilizers to subtropical rain-fed purple soil in China

In this study, a 15N tracing incubation experiment and an in situ monitoring study were combined to investigate the effects of different N fertilizer regimes on the mechanisms of soil N dynamics from a long-term repeated N application experiment. The field study was initiated in 2003 under a wheat-maize rotation system in the subtropical rain-fed purple soil region of China. The experiment included six fertilization treatments applied on an equivalent N basis (280 kg N ha−1), except for the residue only treatment which received 112 kg N ha−1: (1) UC, unfertilized control; (2) NPK, mineral fertilizer NPK; (3) OM, pig manure; (4) OM-NPK, pig manure (40% of applied N) with mineral NPK (60% of applied N); (5) RSD, crop straw; (6) RSD-NPK, crop straw (40% of applied N) with mineral NPK (60% of applied N). The results showed that long-term repeated applications of mineral or organic N fertilizer significantly stimulated soil gross N mineralization rates, which was associated with enhanced soil C and N contents following the application of N fertilizer. The crop N offtake and yield were positively correlated with gross mineralization. Gross autotrophic nitrification rates were enhanced by approximately 2.5-fold in the NPK, OM, OM-NPK, and RSD-NPK treatments, and to a lesser extent by RSD application, compared to the UC. A significant positive relationship between gross nitrification rates and cumulative N loss via interflow and runoff indicated that the mechanisms responsible for increasing N loss following long-term applications of N fertilizer were governed by the nitrification dynamics. Organic fertilizers stimulated gross ammonium (NH4+) immobilization rates and caused a strong competition with nitrifiers for NH4+, thus preventing a build-up of nitrate (NO3−). Overall, in this study, we found that partial or complete substitution of NPK fertilizers with organic fertilizers can reduce N losses and maintain high crop production, except for the treatment involving application of RSD alone. Therefore, based on the N transformation dynamics observed in this study, organic fertilizers in combination with mineral fertilizer applications (i.e. OM, OM-NPK, and RSD-NPK treatments) are recommended for crop production in the subtropical rain-fed purple soils in China.

Rainfall and tillage impacts on soil erosion of sloping cropland with subtropical monsoon climate — A case study in hilly purple soil area, China

Under global warming, storm events tend to intensify, particularly in monsoon-affected regions. As an important agricultural area in China, the purple soil region in the Sichuan Basin, where it has a prevailing monsoon climate, is threatened by serious soil erosion. Tillage operations alter runoff and soil erosion processes on croplands by changing the physical properties of the soil surface. To clarify the relationship between tillage and soil erosion in the purple soil region, three different tillage practices in this region were investigated at the plot scale over 4 years: bare land with minimum tillage (BL), conventional tillage (CT) and seasonal no-tillage ridges (SNTR) which was initially designed to prevent soil erosion by contoured ridges and no-tillage techniques. The results showed that although there were no significant differences in the surface runoff and soil erosion among the three practices, BL caused relatively high surface runoff and soil erosion, followed by CT and SNTR. Classification and comparison of the rainfall events based on cluster analysis (CA) verified that the surface runoff was not significantly different between most intensive event and long intensive events but was significantly different between most intensive and short and medium-duration events. Only the rainfall events with the highest rainfall intensity could trigger serious soil erosion, up to moo kg ha(-1) in the region. Further detailed investigations on the effects of tillage operations on the soil erosion in a subtropical region with a monsoon climate are needed to provide a basis for modeling catchments and designing better management practices.

Nitrogen and phosphorous concentrations in runoff from a purple soil in an agricultural watershed

Abstract Nutrient loss from purple soils has been reported to increase pollution of the Yangtze River. However, few studies have addressed the variations of nutrient concentration in runoff during natural rainstorms in the regions. Nitrogen and phosphorus concentrations in runoff waters from a small agricultural watershed, in the purple soil region of southwest China, were investigated for four natural rainstorms occurred in a conventional double cropping system (wheat–corn) and another six rainstorms in a new triple cropping system (wheat–corn–sweet potato). The NO 3 − concentrations in runoff for the observed rainstorms generally varied from 1.0 to 3.5 g m −3 , which were noticeably affected by flow rates. A significant logarithmic correlation between NO 3 − concentrations and flow rates for each rainstorm was identified. In contrast, the concentrations of NH 4 + and dissolved reactive phosphorus (DRP) in runoff fluctuated substantially without a noticeable trend for each rainstorm. Positive linear correlation between the concentrations of DRP and sediment for each rainstorm tested was found under the circumstances of double cropping system. In addition, the ratios of NO 3 − to NH 4 + for the loss amount in 10 rainstorms varied from 1 to 7 for the triple cropping system and 16–29 for the double cropping system. Furthermore, the ratios of the sum of NO 3 − and NH 4 + to DRP for the loss amount in 10 rainstorms ranged from 12 to 79 depending on the cropping systems. Nitrate nitrogen was proved to be the main form of inorganic nitrogen loss in runoff water in the purple soil region. Compared with the conventional double cropping system, the new triple cropping system tends to cause more NH 4 + loss. These findings would help develop the effective erosion control strategies and select a suitable cropping system to reduce potential pollution hazards.

Sediment flow behavior in agro-watersheds of the purple soil region in China under different storm types and spatial scales

Bedload sediment is not only a major pollutant, but can also act as a transporter of pollutants. Sediment flow behavior often reflects the characteristics of a watershed, such as land use and management. To clarify the behavior of sediment flow under different spatial scales and storm types in the Chinese purple soil area, the sediment flow behavior in three small agro-watersheds with different catchment areas, physical characteristics and land use types was investigated during natural rainfall events from 1999 to 2000. The results showed that there were three types of sediment hydrographs, waveform or linear with a low sediment concentration (1.13 ± 0.58 g l −1), logarithmic decrease (3.41 ± 4.13 g l −1), and compound linear and logarithmic decrease (9.58 ± 10.90 g l −1). During PP-type rainfall events (high-intensity rainfall occurred during the prophase of the rainfall process) and ML-type rainfall events (high intensity rainfall occurred during the middle of the rainfall event), the waveform or linear type sediment hydrographs or the logarithmic decrease type hydrographs were generated in each of the three agro-watersheds. However, sediment hydrographs produced by IM-type rainfall events (discontinuous rainfall with obvious segments) depended on the spatial scale of the watershed. As the spatial scale decreased, the hydrographs were transformed from the logarithmic decrease type to the compound type. In addition, it was found that the S = aQ b model could effectively simulate the sediment hydrologic process of a single rainfall event. The information provided in this study will help evaluate and prevent soil and water loss and non-point source pollution in the purple soil region.