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[Objective] The present paper aimed to evaluate the potential of white clover (Trifolium repens L.) as forage grass and ecological engineering plant on paddy field ridges in southern China. [Method] The clover was planted on the ridge of paddy fields in Ilengnan, Ilunan province and Jiangyou, Sichuan province in the spring of 2015. Cabover-ground parts, mainly leaves and petioles, were harvested monthly from July of 2016 to June of 2017. Dry matter was weighted after desiccation in a stove at 105 °C for 15 minutes and 70 °C for 24 hours. Dry samples harvested in the same season were mixed after storing at -20 °C . The contents of crude protein, nitrogen, phosphorus and potassium of such mixed samples were then determined by the standard procedures. The antagonism experiment with Alternant her a philoxeroides was conducted by face-to-face cultivation in concreted circles located in a plastic greenhouse from July of 2017 to March of 2018. [Result] At the experiment site in Sichuan, the highest dry matter weight of the white clove was obtained at the first harvest and the dropped until January of 2017 and increase gradually till the end of the experiment. It dropped also in Ilunan after the first harvest but started to increase since August and reached the highest point in April of 2017. The contents of crude protein, nitrogen and phosphorus were the highest in the first quarter at both sites. The content of potassium was the highest in the third quarter at Jiangvou but in the second quarter at Ilengnan. In the antagonism experiment, the growth of A. philoxeroides under each treatment was obviously better than that of clover in the summer, but white clover grew significantly better than A. philoxeroides under each irrigation regime and dominated the community in terms of occupying area, fresh weight and dry weight. [Conclusion] White clover on paddy didges has shown strong regeneration ability both in Sichuan and Hunan and could be used as high-quality forage and green manure crop. It could strongly inhibit the growth of A. philoxeroides at low temperature and soil humidity. [ABSTRACT FROM AUTHOR]

Green manure is a natural clean organic source of fertilizer. Chinese milk vetch is the most popular winter green manure crop in rice-growing regions of China. In this study, a long-term field experiment was conducted at an experimental station managed by National Observation and Research Station of Farmland Ecosystem in Qiyang, China to explore suitable application amount of nitrogen fertilizer when returning green manure(Chinese milk vetch, Astragalus sinicus L.) to the field in the double-season rice area of southern Hunan. The double cropping rice experiment began from the winter of 2008. It lasted 9 years. A total of six treatments with different fertilization practices were included: 1) CK, without fertilization; 2) MV, Chinese milk vetch only; 3) FFP100%, conventional application rate of chemical nitrogen fertilizer; 4) MV+FFP100%, Chinese milk vetch combined with 100% conventional application rate of chemical nitrogen fertilizer; 5) MV+FFP80%, Chinese milk vetch combined with 80% conventional application rate of chemical nitrogen fertilizer; 6) MV+FFP60%, Chinese milk vetch combined with 60% conventional application rate of chemical nitrogen fertilizer. The yield of rice and soil nutrient content were measured. The nitrogen agronomic efficiency and nitrogen partial factor productivity, coefficient of variation and sustainable index of yield were calculated. The results showed that the treatments of green manure combined with different chemical nitrogen fertilizer application rate kept and even increased annual rice yield. The treatments of MV combined with reducing nitrogen application also increased the nitrogen agronomic efficiency and nitrogen partial factor productivity. Compared to FFP100%, the treatments MV+FFP100%, MV+FFP80% and MV+FFP60% resulted in the increase of long-term average of nitrogen agronomic efficiency by 34.63%, 64.91% and 115.26% in early rice, respectively, and by 29.69%, 56.23% and 72.09% in late rice, respectively(P<0.05). Compared to that of FFP100%, the long-term averages of nitrogen partial factor productivity of MV+FFP100%, MV+FFP80%, MV+FFP60% increased by 8.73%, 35.06% and 78.92% in early rice, respectively, and 7.51%, 32.90% and 68.06% in late rice, respectively. Among all the treatments, regardless of early and late rice, the treatment of MV+FFP60% had the smallest coefficient of variation of yield and the highest sustainable index. Soil organic matter, total nitrogen, total phosphorus and total potassium were not significantly different among the treatments of FFP100%, MV, MV+FFP100%, MV+FFP80%, MV+FFP60% (P>0.05). But, they were higher than the initial values in 2018. The treatment of Chinese milk vetch combined with 60% conventional application rate of chemical nitrogen fertilizer could achieve high and stable yield, and improve the nitrogen use efficiency and slowly improve soil fertility. Therefore, Chinese milk vetch combined with 60% conventional application rate of chemical nitrogen fertilizer was suggested as the best fertilization mode for double-cropping rice planting area in southern Hunan. In this case, the chemical fertilizer application rate could be decreased by 40% compared to the conventional fertilizer practice. [ABSTRACT FROM AUTHOR]

• Organic C inputs significantly increased SOC compared to synthetic fertilizer. • Organic amendment quality and soil water regimes influenced SOC sequestration. • Organic amendments increased soil hydrolase activity but decreased oxidase activity. • Applying green manure resulted in higher rice yield compared to rice straw. • Organic C quality may influence the SOC composition and its agroecosystem function. Both the quantity and quality of organic amendments can influence the accumulation of soil organic carbon (SOC) and agroecosystem functioning. However, the evidences of the effect of combination of quantity and quality of organic amendments on the paddy soil quality and rice yield are scarce. An ongoing field experiment was conducted in Hunan province of China to investigate the effect of different Chinese milk vetch (Astragalus sinicus L.) and rice (Oryza sativa L.) straw management practices on the soil biochemical properties and rice yield. The experiment consisted six treatments: applying Chinese milk vetch (MV), applying early-season rice straw (S), applying early-season and late-season rice straw (DS), applying Chinese milk vetch and early-season rice straw (SMV), applying Chinese milk vetch, early-season and late-season rice straw (DSMV), and unamended organic amendment (CK). Compared with CK, SOC content was significantly increased by 13.0%, 18.5%, 11.1%, 12.3%, and 23.0% for the MV, S, DS, SMV, and DSMV treatments, respectively. No significant correlation was found between SOC content and yearly carbon inputs. Application of organic amendments increased soil hydrolase activities (β-D-cellobiosidase, β-1,4-glucosidase, β-1,4-xylosidase, β-1,4-N-acetyl-glucosaminidase and phosphatase). The geometric mean of the assayed hydrolases followed the order: S > DSMV > SMV > DS > MV > CK. Phenol oxidase was significantly higher in CK than in the applied organic amendment treatments. The lowest ratio of β-1,4-glucosidase: phenol oxidase occurred in the S treatment, suggesting that S treatment decreased microbial substrate use efficiency. The yearly average rice yield was increased by 18.6%, 8.5%, 12.3%, 14.6%, and 24.1% for MV, S, DS, SMV, and DSMV treatment with respect to CK. There was no significant correlation between SOC content and rice yield. In general, after 4-year cultivation, our results highlight the effect of quality of organic amendments on the chemical properties of SOC and its nutrient supply. Applying high quantities of diverse organic amendments is suggested to increase SOC content and rice yield in red paddy soil. [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]