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• Factors driving rice straw and milk vetch mixture (MR) decomposition were studied. • Non-additive synergistic effects on biomass loss were observed in 55.6% of the sampled MR. • MR enhanced fungal abundance by 19.6–30.6% compared to a single residue. • Bacteria contributed more to residue decomposition than did fungi in paddy soils. • The increase in Peziza sp. and Reticulascus tulasneorum may drive MR decomposition. The co-incorporation of rice straw (RS) and milk vetch (MV) into paddy fields has been increasingly applied as a sustainable farming practice in southern China. Our previous study revealed the contribution of bacteria to the co-decomposition of the RS and MV mixture, although additional underlying factors driving the co-decomposition process need to be clarified. The present study further determined the succession of fungal communities and enzyme activity in the co-decomposition process of the RS and MV mixture. The results showed that non-additive synergistic effects on biomass loss were observed in 55.6% of the sampled RS and MV mixture during the co-decomposition process, stimulating mixture decomposition. Overall fungal abundance was 19.6–30.6% higher in the RS and MV mixture throughout the study than in the single residue. Fungal diversity and community structure were mainly affected by the sampling date rather than the type of residue. Specifically, mixing RS and MV significantly increased the abundance of Peziza sp. and Reticulascus tulasneorum (lignocellulose- and lignin-decomposing fungi) and exhibited higher activities of C- and N-related hydrolases than monospecific residues. Random forest (RF) models showed that bacteria contributed more to the residue decomposition and activities of C-related hydrolases, N-related hydrolases, and oxidases than fungi. However, both RF and partial least squares path models revealed that fungal abundance and community structure directly or indirectly affected the residue decomposition rate. These findings showed that mixing RS and MV could stimulate their decomposition by enhancing C-related hydrolase activity and Peziza sp. and Reticulascus tulasneorum abundance. [ABSTRACT FROM AUTHOR]

Although widely studied in grassland and forest ecosystems, dissolved organic nitrogen (DON), an important form of nitrogen (N) lost through leaching, has received little attention in cropland ecosystem research. A global literature review and partial least squares path modeling (PLS–PM) were adopted to assess the quantity and composition of N leaching loss under different cropping systems, soil types, and management practices, as well as to identify the major factors controlling DON leaching. Annual total dissolved nitrogen (TDN, organic + inorganic N) leaching under different cropping systems ranged from 4.0 to 383.2 kg N ha−1. Vegetable and rice production systems showed the greatest and least TDN leaching, respectively. Across different cropping systems, DON accounted for 4.7%–34.9% of TDN in leachate. The NH4+–N form of N leaching is negligible in most upland cropping systems (<2.3%), but not so in lowland rice systems. The largest ratio of DON leaching to TDN leaching was found in a rice–wheat rotation (34.9%). Catch crop slightly increased DON leaching; however, it greatly decreased TDN leaching. Cropping systems in which animal manure or plant compost was applied or lowland rice was included showed a relatively high DON leaching ratio. Accordingly, in investigating DON leaching, more attention should be focused on cropping systems with manure application or lowland rice systems. Compared with climatic conditions and soil properties, field management practices (irrigation, chemical N input, and manure amendments) proved to be the factors most strongly influencing DON leaching. This suggests that optimizing water and N management practices is the most effective way of reducing the risk of DON leaching and increasing N use efficiency, particularly for vegetable and rice production systems. [ABSTRACT FROM AUTHOR]

The practice of co‐incorporating rice straw and leguminous green manure (such as Chinese milk vetch) into paddy soils has become increasingly popular in the last 10 years, although its effect on soil CH4 emissions and microbial community structure is poorly understood. In this study, data from a 2‐year pot experiment were used to reveal the effects of the co‐incorporation of rice straw and Chinese milk vetch on CH4 emissions and methanogenic and methanotrophic communities in paddy soil. Five treatments were chosen: CK (unamended control), CF (inorganic fertilizer), FM (inorganic fertilizer and Chinese milk vetch, 20 g 10 kg−1 dry soil, 4.5 t ha−1), FR (inorganic fertilizer and rice straw, 20 g 10 kg−1 dry soil, 4.5 t ha−1) and FMR (inorganic fertilizer and Chinese milk vetch and rice straw mixture, 5 + 15 g 10 kg−1 dry soil, 1.125 + 2.375 t ha−1). Overall, the soil CH4 emissions in the 2 years under all residue treatments (104.4–122.8 and 83.3–133.3 g CH4 m−2) were higher than those in CK (57.0 and 20.7 g CH4 m−2) and CF (71.8 and 21.9 g CH4 m−2) treatments. The FMR treatment decreased CH4 emissions when compared with FM and FR, especially in the second year. A higher abundance of methanogens (mcrA gene copies) was found under the plant residue‐treated soils (4.35 × 108 g−1 dry soil on average) and FM increased the abundance of methanotrophs (pmoA gene copies, 2.68 × 106 g−1 dry soil). Application of plant residues changed the methanogenic and methanotrophic community structures in comparison with CF (e.g., markedly increased the populations of Methanobacteriales and Methylomonas and suppressed Methanomicrobiales and Methylobacter populations). Methane emissions were significantly and positively related to the mcrA and pmoA gene copy numbers, as well as the mcrA/pmoA ratio. The partial least squares path model (PLS‐PM) indicated that the rice plant biomass (path coefficient = 0.64), the abundance of methanogens (path coefficient = 0.57) and the community structure of methanotrophs (path coefficient = −0.59) were determinants of CH4 emissions. Among the three residue‐treated soils, FMR showed the lowest CH4 emissions and was associated with a slight decrease in the mcrA/pmoA ratio and a significant increase in the Type I/Type II methanotrophs ratio. Thus, we recommend the co‐incorporation of Chinese milk vetch and rice straw as a sustainable fertilization pattern to improve the growth of rice and minimize CH4 emissions. Highlights: Residue application improves rice productivity (except for FR), soil fertility and CH4 emissions.Co‐incorporation of MV and RS reduces CH4 emissions in comparison with pure MV or RS addition.Residue application changes the community structure of methanogens and methanotrophs.The methanogenic abundance and the methanotrophic community structure determine the CH4 emissions. [ABSTRACT FROM AUTHOR]

Growing winter green manure is an effective method for improving nitrogen (N) management in paddy fields to enhance rice production. Ammonia oxidization is a key process in N cycling in these soils, but effects of green manuring on ammonia oxidizers have not been fully addressed for red paddy soils. The objective of this study was to investigate long-term impacts of winter green manure on abundance and diversity of ammonia oxidizers in rice paddy soils of Southern China. The field experiment established in 1982 included four treatments: rice-rice-winter fallow (RRF), rice-rice-ryegrass (RRG), rice–rice–rape (RRP) and rice–rice–milk vetch (RRV). The abundance and diversity of amoA genes from ammonia-oxidizing archaea (AOA) and bacteria (AOB) were quantified using quantitative PCR and 454 pyrosequencing, respectively. The AOA were more abundant than AOB in red paddy soils, with ratios of AOA to AOB from 36 to 1686. Long-term application of milk vetch increased the abundance of both AOA and AOB after green manures were incorporated. Some of the relative abundances of most abundant operational taxonomic units (OTUs) of AOA increased and others decreased after application of green manures, while most abundant OTUs of AOB remained unaffected. Redundancy analysis (RDA) found a clear separation between milk vetch and winter fallow, indicating that the community structure of AOA was influenced by application of milk vetch. Phylogenetic analysis showed that the most dominant OTUs of AOA and AOB were affiliated with Nitrososphaera and Nitrosospira , respectively. In conclusion, in red paddy soil, long-term application of milk vetch increased the abundances of AOA and AOB after incorporated. Moreover, long-term application of green manures had more profound influences on AOA community than on AOB in red paddy soils. [ABSTRACT FROM AUTHOR]

• Mixing milk vetch and rice straw (MR) shortened the decomposition process. • MR increased hydrolytic enzyme activity compared with its monospecific residues. • MR enhanced the monosaccharide decomposing bacteria abundance relative to rice straw. • MR enhanced the fiber decomposing bacteria abundance relative to milk vetch. • More interconnected and competitive relations existed between the bacteria in MR. The present study determined the dynamic changes of enzyme activity and bacterial community in rice straw (RS) and milk vetch (MV) co-decomposing process. Results showed that mixing RS and MV promoted decomposition. The mixture enhanced β-glucosidase and β-cellobiohydrolase activities relative to its monospecific residue during the mid-late stage of decomposition. The mixture enhanced Enterobacteriaceae (monosaccharide decomposing bacteria) abundance during the initial stage of decomposition, and the abundance of Hydrogenispora, Bacteroides , Ruminiclostridium, and Acidobacteriaceae that could hydrolyze fiber during the mid-late stage of decomposition relative to single RS and MV, respectively, which would benefit mixture decomposition. Furthermore, more interconnected and competitive relations existed between the bacteria in the mixture. These results indicated that mixing RS and MV promoted residue decomposition by increasing hydrolytic enzyme activities and changing bacterial community. This study concluded that co-incorporating RS and MV may be recommended as a promising practice for the efficient utilization of RS resources. [ABSTRACT FROM AUTHOR]

Rice–rice–green manure rotations in south China are characterized by high efficiency and good environmental performance, and the application of green manure plays an important role in N management. Nitrification is a key process in N cycling and is highly correlated with the N utilization of crops and with leaching losses. As a potential N loss pathway, the nitrification process and nitrifiers as affected by green manuring are of critical importance. A pot experiment covering green manure-double rice rotation was conducted to evaluate the effects of green manure and N fertilizer on soil nitrification and to achieve a mechanistic understanding of underlying processes in an alkaline paddy soil. Soil nitrification potential (NP) and the recovered nitrification potential (RNP) were measured. Relative contributions of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) in soil nitrification were studied using specific bacterial inhibitors. In the alkaline paddy soil, soil NP and nitrate concentrations were significantly decreased by green manuring but increased with increasing N fertilization. Soil nitrification was dominated by AOB and that the relative contributions of AOB to RNP ranged from 65% to 79% at different sampling stages despite the larger abundance of AOA amoA gene numbers. RNP and the contribution of AOB to RNP were significantly increased by N fertilizer, whereas the contribution of AOA was decreased by green manuring. We concluded that the application of inorganic N enhanced NP while green manures reduced it, which is consistent with the variation of observed soil nitrate concentrations. These results indicate that the utilization of winter green manure is an effective practice to improve N management in paddy rice. • Green manuring decreased nitrification potential in an alkaline paddy soil. • Recovered nitrification potential was increased by N fertilization. • Ammonia-oxidizing bacteria contribute more to nitrification in an alkaline paddy soil. • Green manuring in paddy fields offers the potential to reduce nitrate leaching. [ABSTRACT FROM AUTHOR]

• Soil nitrification potential increased with increasing amount of chemical fertiliser. • Green manuring changes the nitrification process by affecting recovered nitrification potential. • Green manuring directly affected the contribution of ammonia-oxidising archaea to nitrification. Rice–rice–green manure rotation is a cropping system that effectively maintains high yields and improves soil fertility. Nitrification, a critical process in N cycling, is affected by different fertilisation regimes, but the roles of ammonia-oxidising bacteria (AOB) and ammonia-oxidising archaea (AOA) in nitrification and their shift in abundance and diversity in response to long-term green manure application in alkaline paddy soil is poorly understood. In the present work, nitrification potential (NP), the contributions of AOA and AOB to nitrification, abundances, and communities of AOA and AOB were studied to mechanistically understand the effects of green manuring and fertilisation regimes on nitrification and ammonia oxidisers. Results showed that the combination of green manure and reduced chemical fertiliser increased grain yields. Soil NP increased with increasing amount of chemical fertiliser. The combination of green manure and different rates of chemical fertiliser promoted the soil recovered nitrification potential (RNP) and the contribution of AOB to nitrification (RNP AOB). Differences in AOA and AOB communities revealed that an increase in the abundance of Nitrosopumilus in AOA and a decrease in the abundance of Nirosomonas in AOB were observed in green manure treatment compared with those of chemical fertiliser treatments. Partial least squares path modelling showed that chemical fertilisation exerts direct effects on NP whereas green manuring markedly influenced RNP. For the relative contributions of AOA (RNP AOA) and AOB, RNP AOB were correlated with chemical fertilisation, whereas green manuring directly affected RNP AOA. In conclusion, green manuring changed the nitrification process by affecting RNP, whereas chemical fertiliser directly influenced NP. Changes in AOA composition and their impact on nitrification might reflect a mechanism worthy of further research. [ABSTRACT FROM AUTHOR]

• Four different representative N dilution curve approaches was compared. • WHCNS model performed well in simulating soil water and N supply. • The M2 method performed well using the minimum input parameters. • The smaller the crop water and N stresses, the larger the uncertainty of crop N uptake modeling. Crop nitrogen (N) uptake is a key process in soil-crop models. This process affects crop growth and soil N cycling and determines crop quality. However, crop N uptake modeling remains uncertain because of the various N dilution curve approaches adopted in soil-crop models. In this study, four different representative N dilution curve approaches (i.e., DAISY, M1; CERES and RZWQM, M2; EPIC, M3; and CROPSYST or STICS, M4) were incorporated into a soil-crop model platform (WHCNS), and their effects on crop N uptake and crop growth simulation under different water and N stresses were evaluated via global sensitivity analysis methods. The three-year field experiment data of winter wheat-summer maize rotation under different water and N management practices were used to test the model. Results showed that the WHCNS model performed well in modeling the supplies of soil water and mineral N. The values of statistical indices for crop N uptake, LAI, dry matter and yield simulation by the four methods were within the acceptable ranges, and had the relative mean square error (RRMSE) < 24 %, index of agreement (IA)> 0.81 and Nash and Sutcliffe index (NSE) > 0.37. However, the M2 method performed well using the minimum input parameters, and hence recommended to simulate crop N uptake in soil-crop models. In this study, the dataset of high water and N input treatment was more suitable for model parameter estimation to reduce uncertainty, and the datasets of middle and low water and N input treatments was appropriate to validate the model. These information were useful to guide selecting the modeling method and the model calibration dataset. [ABSTRACT FROM AUTHOR]

• Organic residue returns improve rice productivity but increase CH 4 emissions. • Residues application increases soil methane production and oxidation potentials, and mcrA , pmoA gene abundance. • The abundance of methanogens can serve as a proxy for predicting CH 4 emissions. • Residues application changes the methanogenic and methanotrophic communities. • Different residue impacts CH 4 flux by altering the microbial community and DOC level. Although rice straw return is widely recommended for maintaining or improving soil fertility and rice yields, it inevitably increases methane (CH 4) emissions. Effective measures to mitigate CH 4 emissions while guaranteeing grain yields are urgently needed. A 2-year mesocosm experiment was conducted. Six management systems, i.e., no residue (traditional management, CF), 100% rice straw (a popular practice among farmers, FR), 50% rice straw (F1/2R), leguminous green manure (FM), mixture of leguminous green manure and 100% rice straw (FMR), and a mixture of leguminous green manure and 50% rice straw (FM1/2R), were used. Compared with the CF, the organic residue returns could effectively improve rice productivity but increase the CH 4 emissions. Notably, when compared with the FR, both F1/2R and FM could reduce the CH 4 emissions, with equal crop yields, and FM1/2R not only increased the rice yields but also reduced the CH 4 emissions, whereas FMR increased the rice yields and the CH 4 emissions. Applications of organic residues significantly increased the soil methane production potentials (MPPs), methane oxidation potentials (MOPs), the abundances of methanogens and methanotrophs, and changed methanogenic and methanotrophic community structures in comparison with the CF. The partial least squares path model (PLS-PM) results showed that the MPPs had a strong direct effect on CH 4 emissions, whereas an abundance of methanogens could serve as a proxy for predicting CH 4 emissions. Moreover, relatively high MOPs associated with high Type I/Type II methanotroph ratios and relatively low dissolved organic carbon (DOC) concentrations were found to be central in lowering CH 4 emission fractions under the F1/2R and FM1/2R treatments. Above all, the combined utilization of leguminous green manure and rice straw exhibited potential prospects for the enhancement of rice yields and for the mitigation of CH 4 emissions, and the practice of mixing leguminous green manure with 50% rice straw performed the best of the treatments tested. [ABSTRACT FROM AUTHOR]

• Application of green manure and/or rice straw increased rice yield compared with F. • The FMS combined the advantages of FM and FS in improving soil fertility. • The FMS had the greatest effect on soil microbial community and enzyme activities. • Straw had more lasting effects on soil properties and rice yield than green manure. The cultivation of green manure or rice straw returns in southern China increases crop yields and soil fertility. Few studies have reported the effects of combining both management techniques on rice performance and soil fertility. A 3-year field study was carried out to analyse the impacts of the co-incorporation practice on soil microbial and biochemical parameters as well as crop yield. Five treatments were tested: (i) no-fertilizer (CK); (ii) chemical fertilizer (F); (iii) F plus green manure (FM); (iv) F plus rice straw (FS); (v) F plus green manure plus rice straw (FMS). The results showed that incorporation of green manure and/or rice straw increased double rice yields by 4.1% (FM), 4.7% (FS) and 9.6% (FMS) compared with F. The FMS treatment enhanced soil organic C (SOC), total N (TN), mineral N (N min), and available K (AK) levels by combining the advantage of FM in increasing TN and N min and the advantage of FS in increasing SOC and AK in comparison with F. The incorporation of green manure and/or rice straw stimulated microbial growth (total phospholipid fatty acids, PLFAs) and altered the soil microbial community structure relative to F, in which FMS had the greatest effect. The enzyme activities of β-glucosidase, β-cellobiosidase, N -acetyl-glucosaminidase, L-leucine aminopeptidase and phosphatase were higher in the green manure and/or rice straw application treatments than in the F treatment in the order FM ≈ FS < FMS. The partial least squares path model (PLS-PM) analysis indicated that green manure mainly influenced the abovementioned indices in the early rice season, while the effects of rice straw lasted until the late rice season. Our results suggest that co-incorporation of green manure and rice straw is a more effective practice for improving soil fertility and rice yields. [ABSTRACT FROM AUTHOR]

Fe-modified biochar (FB) and co-using Chinese milk vetch and rice straw (MR) are two effective ways for mitigating the cadmium (Cd) contamination in paddy fields in southern China. Nevertheless, the effects of FB combined with MR on Cd passivation mechanism remain unclear. In the current study, the strengthening effects of FB induced by MR were found and the mechanisms of the extracted dissolved organic matter (DOM) from the co-decomposition of MR on Cd alleviation were investigated through pot experiment and adsorption experiment. Pot experiment demonstrated that co-incorporating FB and MR decreased available Cd by 23.1% and increased iron plaque concentration by 11.8%, resulting in a 34.7% reduction in Cd concentrations in brown rice compared with addition of FB. Furthermore, co-using FB and MR improved available nutrients in the soil. The molecular characteristics of DOM derived from the decomposition of MR (DOM-MR) were analyzed by fluorescence excitation emission matrix spectroscopy-parallel factor analysis (EEM-PARAFAC) and Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR MS). Results showed that lignin/carboxylic-rich alicyclic molecules and protein/amino sugar were the main compounds, potentially involved in the Cd binding. Adsorption experiments revealed that the addition of DOM-MR improved the functional groups, specific surface area, and negative charges of FB, inducing the strengthening of both physisorption and chemisorption of Cd(II). The maximum adsorption capacity of Fe-modified biochar after adding DOM-MR was 634 mg g−1, 1.30 times that without the addition of DOM-MR. This study suggested that co-incorporating MR, and FB could serve as an innovative practice for simultaneous Cd remediation and soil fertilization in Cd-polluted paddy fields. It also provided valuable insights and basis that DOM-MR could optimize the performances of Fe-modified biochar and enhance its potential for Cd immobilization. Highlights: Chinese milk vetch and rice straw strengthened the Cd remediation by biochar. Soil DOM was the key influencing factor on soil Cd immobilization. DOM optimized the properties of biochar and produced richer functional groups. The combination of DOM and biochar had a higher specific surface area than biochar alone. DOM strengthened the physisorption and chemisorption capacities of Cd(II) on biochar. [ABSTRACT FROM AUTHOR]

Rice straw (RS) was incorporated into paddy soil together with leguminous green manure (e.g., Chinese milk vetch, Astragalus sinicus L., MV) in a mesocosm-scale experiment and the enzyme activity and composition of main microbial groups were measured. Mixing MV and RS caused a synergistic release of residual C and N, leading to a low C/N ratio at the middle and late decomposition stages of the mixture and shortening the time to complete decomposition. Furthermore, the highest abundances of Gram-negative (G−) bacteria and fungi and the highest activities of α- and β-glucosidase, β-cellobiosidase, β-xylosidase, N-acetyl-glucosaminidase, and acid phosphomonoesterase were observed in the residue mixture, especially at the middle and late stages of the experiment. The residue decomposition rate was positively correlated with residual N and mineral N concentrations. Most hydrolases and both oxidase (phenol oxidase and peroxidase) activities, and G− bacterial (especially 18:1 ω5c, Photobacterium) abundance explained the decomposition of mixing residues. In conclusion, co-incorporation of MV and RS could stimulate their decomposition by retaining a relatively low C/N ratio, enhancing G− bacterial abundance and hydrolase activities. Introducing leguminous green manures in paddy fields may be an effective way to accelerate the decomposition of rice straw. [ABSTRACT FROM AUTHOR]

Green manuring is an established strategy for soil nutrient enrichment; however, its effects on the soil microbiome remain unclear. In this study, we assessed the impact of green manuring on soil microbial diversity, functional profiles, and enzymatic activities in a pot experiment involving tobacco rotation with three types of green manure: smooth vetch, ryegrass, and radish. Our data revealed distinct temporal shifts in bacterial communities under diverse tillage while fungi communities showed obvious clustering between fallow and green manuring. Moreover, green manure-sensitive bacterial and fungal taxa constitute a greater proportion of total sequences than their fallow-sensitive counterparts, indicating a more pronounced influence of green manuring on microbial communities. Functionally, green manuring augmented the relative abundance of N-cycle-related genes and was strongly associated with elevated N-acetyl-glucosaminidase activity. Notably, a subset of green manure-sensitive microbes exhibited significant antagonistic interactions with the fungal pathogens Fusarium spp. and Fusarium solani, and synergistic interactions with the beneficial bacteria Pseudomonas spp. Collectively, these findings suggest that green manuring promotes an optimized soil environment characterized by efficient nutrient cycling and diminished pathogenicity, thereby providing a scientific basis for targeted microbiota manipulation in agricultural systems. [ABSTRACT FROM AUTHOR]

Aims: We studied the effects of green manuring on the gene level of microorganisms associated with nitrogen (N) fixation, nitrification, and denitrification in different paddy soils. Methods: Field experiments were conducted in Hunan, Jiangxi, Henan, and Fujian experimental sites in south China to investigate the responses of rice yield, soil properties, and functional genes to green manuring. The four treatments were no fertilizer application (NF), using milk vetch as green manure without chemical fertilizer (GM), winter fallow with chemical fertilizer (CF), and a combination of green manure and chemical fertilizer (GMCF). Results: The rice yield and N uptake significantly increased in GMCF. The nifH gene copies significantly increased in GMCF in the Jiangxi and Henan sites. Soil SOM, TN, NH4+-N, NO3−-N, AP, and AK were higher in GMCF than in the other treatments. For the nitrification process, the gene copies of ammonia-oxidizing archaea were higher than those of ammonia-oxidizing bacteria in all sites. The nirK and nosZ genes involved in denitrification were negatively correlated with soil properties. With the improvement of soil properties and rice N uptake, the denitrification process was inhibited in the GMCF treatment. The nirK gene was the most critical functional gene influencing rice yield among the tested genes. SOM was the most important factor among soil properties. Conclusions: The application of green manure improved soil properties and changed the abundance of the functional genes involved in N cycling. Green manure combined with chemical fertilizer increased rice yields and N uptake and inhibited the denitrification process. [ABSTRACT FROM AUTHOR]

In southern China, winter green manure is widely used in rice cropping systems for improving grain yields and soil fertility. Cd pollution has recently been reported in some of these paddy fields. Research on the in-depth understanding of how green manuring affects Cd absorption in rice is limited. This study aimed to investigate the impacts of different green manures, including single plantation and mixed plantation on the absorption of Cd by rice and explore the underlying mechanisms. Pot experiments demonstrated that compared with winter fallow–rice, green manuring treatments considerably decreased rice Cd content, promoted the conversion of bioavailable Cd fraction into a more stable form, induced the formation of iron plaque, and increased the content of humic-like fraction (HF) in soil dissolved organic matter (DOM). Treatment with mixed plantation resulted in a greater decrease in rice Cd content and an increase in HF and iron plaque contents than single plantation. Hydroponic experiments confirmed that both iron plaque and green manure-derived DOM significantly reduced the Cd content in rice seedlings. In conclusion, green manure incorporation is an efficient measure for the safe utilization of Cd-contaminated soil, and mixed plantation of different green manures exerts stronger effects. [Display omitted] • Green manuring significantly reduced Cd contents in rice tissues. • Green manuring enhanced humic-like fraction but reduced protein-like fraction. • Humic-like fraction and iron plaque were effective in immobilizing Cd. • DOM and iron plaque affected Cd mobility and bioaccumulation. • Mixed plantation of green manure is more effective in reducing Cd absorption. [ABSTRACT FROM AUTHOR]

Cultivation of green manure crops is important strategy for improving soil fertility in South China. Therefore, it is important to obtain plant varieties that can better accumulate nutrients during the green manuring phase. The present study evaluated the phosphorus (P) and potassium (K) uptake efficiencies of various winter leguminous species at two different sites. Varieties tested included six Chinese milk vetch cultivars (i.e., Minzi No.6, Ningbodaqiao, Wanzi No.1, Xiangzi No.1, Yijiangzi, and Yujiangdaye), as well as hairy vetch and common vetch, while ryegrass was planted as a control. All leguminous species showed higher ability for P and K absorption in the two sites compared to the ryegrass. Hairy vetch and common vetch performed better than all six Chinese milk vetch cultivars, and the highest biomass and P and K uptake capacities were observed in hairy vetch. Green manuring had different effects on soil enzymes. Phosphatase (87.0%) and leucine-aminopeptidase (163.8%) were increased by hairy vetch. β-glucosidase (143.4%) and N-acetyl-glucosaminidase (283.3%) were increased by Yijiangzi and Yujiangdaye, respectively, in Guangxi compared to the control. Xiangzi No.1 increased N-acetyl-glucosaminidase (352.6%), leucine-aminopeptidase (477.5%), phosphatase (591%), and β-glucosidase (786.0%) in Hunan compared to the ryegrass. Enzyme activities increased nutrient availability at both experimental sites. P and K uptake efficiencies significantly related with soil enzymes in Guangxi. It is suggested that hairy vetch has the largest capability for P and K uptake and might be a potential choice for improving P and K management in sustainable agriculture. [ABSTRACT FROM AUTHOR]

Aims: We studied the effects of mixing rice straw and hairy vetch plant residues in a subtropical paddy soil, on subsequent carbon (C) and nitrogen (N) dynamics.Methods: Using a theoretical framework, we designed two groups of experiments (involving equal amounts of residual C or N addition, referred to as either C or N treatments). Each experiment included mixed residues of rice straw and hairy vetch at different mixing ratios. Soils together with residues were incubated at 25 °C under waterlogged conditions for 100 days. Greenhouse gas (GHG) emissions and soil C and N fractions were measured continuously.Results: Both C and N treatments affected soil C and N dynamics, and these dynamics were quantitatively dependent on residue C/N ratios. The effect of residue mixtures on C and N dynamics could not be predicted from single residues, since there were non-additive effects of residue mixtures. Synergistic effects were generally more frequent than antagonistic effects. Residue mixtures tended to enhance CO2 and CH4 emissions in both C and N treatments but decreased N2O emissions in the N treatment. In the N treatment, dissolved organic C (DOC), dissolved organic N (DON), and microbial biomass C (MBC) concentrations increased. DOC and DON concentrations decreased in the C treatment. Residue mixtures enhanced the global warming potentials (GWP) of greenhouse gases (GHG) emitted from soil by non-additive synergistic effects. The C/N ratio of residue mixtures affected the non-additive responses of soil C and N dynamics, for example mixtures with a C/N ratio of 25 had higher CO2 emissions and DOC concentrations than those with a C/N ratio of 35 as a consequence of non-additive effects, however, CH4 emissions and MBC concentrations were higher in mixtures with a C/N ratio of 35 than in mixtures with a C/N ration of 25.Conclusions: These results indicated that non-additive effects can impact soil C and N dynamics and that residue C/N ratios play an important role in influencing non-additive effects. Applying a single residue to paddy soils may be better than residue mixtures from a GWP mitigation perspective. [ABSTRACT FROM AUTHOR]

Intercropping cereals with legumes is considered a promising option for improving productivity and sustaining soil health. However, the long-term effects of cereal and legume intercropping on soil carbon (C) storage and the physicochemical properties of soil profiles remain elusive. In the present study, an 11-year long-term field experiment was carried out on maize monoculture with zero (control) and conventional 375 kg ha−1 nitrogen (N) application rates (N375), as well as on pea and maize intercropping with zero N (Ps) and a 20% reduction in conventional N (PsN300). The crop yield was obtained each year. The cumulative changes in organic C, bulk density, and other physicochemical properties of the top 20 cm of soil at the beginning and end of the experiment, as well as their spatial changes along the 1 m soil profile at the end, were closely investigated. Greenhouse gas emissions were estimated based on reported emission factors. Pea and maize intercropping under reduced fertilizer N application maintained maize growth and grain yield and increased land use efficiency (land equivalent ratio 1.1) relative to monoculture with farmers' N inputs. After an 11-year intercropping, soil organic C concentrations increased by 6.7–12.4% in the top 0–20 cm layer and organic C stocks increased by 8.3–17.9%, and bulk density decreased by 6.4–14.2%. Intercropped soils with optimal N application (PsN300) sequestrated 14.8% more organic C in the 0–100 cm soil profile, particularly at depths of 40 cm and below, and the bulk density decreased by 7.0% on average compared with the monoculture with farmers' N practices. Such intercropping benefits for soil organic C storage and physical properties in the 1-m profile were associated with greater soil microbial biomass C and N and dissolved organic C and N in the profile. Meanwhile, compared to farmers' N and monoculture, intercropping under reduced N fertilizer application substantially decreased nitrate residues by 30.8% and GHG emissions by 17.8% per hectare or by 15.4% per ton grain yield, which was attributed to less N input, and downregulated enzyme activities involved in soil denitrification. Overall, this study showed that intercropping peas and maize with reduced N inputs is an environmentally sound strategy that improves soil physical quality and enhances deep C storage while reducing greenhouse gas emissions. • An 11-year intercropping of maize and pea with low to high N inputs were conducted. • Maize and pea intercropping maintained maize grain yield under reduced N inputs. • Long-term intercropping improved soil physical quality as indicated by lower soil bulk density in 1-m depth than monoculture. • Long-term intercropping increased subsoil C storage but reduced nitrate leaching. • Intercropping with optimal N inputs substantially reduced GHG emissions than monoculture. [ABSTRACT FROM AUTHOR]

Milk vetch (Astragalus sinicus L.; MV) is the most common winter green manure used in rice cropping systems in southern China. The utilization of MV can achieve the dual goals of soil fertilization and increased rice yield. Two long-term field experiments were conducted in Yujiang and Gaoan in Jiangxi Province, a typical double-rice cropping area, to explore the effects of 80 % conventional fertilizer for early rice supplemented with 15.0 (G1F80), 22.5 (G2F80), 30.0 (G3F80), and 37.5 (G4F80) t ha−1 MV on rice yield, soil fertility, nutrient uptake, and nutrient use efficiency. The results showed that, the yield data obtained from the 5-year (Gaoan) and 12-year (Yujiang) long-term experiments demonstrated that compared with conventional fertilization (F100), treatments with MV markedly increased the yield of early and late rice by 2.5–8.8 % and 5.6–10.9 %, respectively, and high rates of MV (G3F80 and G4F80) performed better in grain yields. The nitrogen (N) and potassium (K) uptake of early rice in Gaoan increased by 38.1 and 34.8 kg ha−1, respectively, and the N uptake of late rice in Gaoan and Yujiang increased by 11.7 and 62.6 kg ha−1 in G2F80, respectively, compared to that in F100. Compared with F100, treatments with MV significantly increased phosphorus (P) fertilizer recovery efficiency by 23.1–36.4 %, and the agronomic efficiency of N, P, and K fertilizers increased by 16.1–21.1 %, 13.9–19.6 %, and 15.7–21.4 %, respectively. Partial least squares path model analysis indicated that soil available P was the most important factor affecting the nutrient uptake of rice, and available K was the most important factor affecting fertilizer use efficiency. Our results suggested that 22.5 t ha−1 MV supplemented with 80 % chemical fertilizer is recommended for double-rice cropping sites to improve rice yield and crop uptake and the use efficiency of N, P, and K fertilizers. • Green manure with 80 % of N, P, and K fertilizer increased or maintained the multi-year yield. • Green manure with 80 % of N, P, and K fertilizer enhanced the grain N, P, and K uptake. • Green manuring increased the use efficiencies of N, P, and K fertilizer. • Application of 22.5 t ha−1 milk vetch with 80 % of chemical fertilizer can be recommended for double-rice cropping sites. [ABSTRACT FROM AUTHOR]

Green manuring is a potential method for reducing chemical N fertilizer input and reactive N losses to the environment that can achieve dual goals of food security and green development of agriculture. In this study, three long-term field experiments in south China and process-based model (WHCNS_LIXIM model) were combined to examine effects of long-term green manure substitution on soil N supply, crop N uptake, and N losses in rice production system. Results showed that green manure substitution significantly improves soil mineral N by 27.4–94.9% and 1.0–45.0% at jointing and maturity stages, respectively, compared with the use of chemical N alone. Moreover, 18.4–62.2% of crop N uptake increased at the maturity stage at Xinyang and Yujiang sites. The model demonstrated satisfactory performance in modeling dynamics of soil mineral N, crop N uptake, crop dry matter, and grain yield of the rice–green manure system with a determination coefficient (R2) > 0.967 and slope of linear regression equation (β) close to 1.0. Simulated N budgets presented that green manure reduces 20–40% of the chemical N fertilizer input and decreased 5.5%, 25.1%, and 30.6% of N losses by ammonia volatilization, leaching, and runoff, respectively, when green manure application rates (fresh matter) are less than 30 t ha−1. However, the total N loss increased with the increase of green manure application amounts when application amounts are larger than 30 t ha−1. These findings indicated that the further reduction of chemical N fertilizer was needed when the application amount of milk vetch was higher than 30 t ha−1. A milk vetch application of 15–30 t ha−1 was recommended to substitute 20–40% of chemical N fertilizer to improve crop N uptake and reduce N losses, and develop green rice production system in the study areas. • Long-term green manure substitution significantly improves soil mineral N. • Long-term green manure substitution enhances crop N uptake and reduces N losses. • The WHCNS_LIXIM model performed well in simulating soil mineral N and crop N uptake. • Milk vetch application of 15–30 t ha−1 was recommended to improve crop N uptake and reduce N losses. [ABSTRACT FROM AUTHOR]