南方稻田紫云英作冬绿肥的增产节肥效应与机制

Effects of milk vetch(Astragalus sinicus)as winter green manure on rice yield and rate of fertilizer application in rice paddies in south China

本文对我国南方稻田紫云英作冬绿肥以及紫云英与稻草共同利用的增产和节肥效应及其植物营养学、土壤微生物学等相关作用机制进行综述。2008—2019年间开展的11个联合定位试验结果(n=930)表明,冬种紫云英在不减肥或者减肥20%条件下增产效果显著,水稻产量增加幅度分别为6.53%和4.15%;在减施40%化肥时可保障水稻与常规施肥相比不减产。紫云英的增产和节肥效应随种植年限的增加而增强,5个联合定位试验连续7年的监测结果表明,冬种紫云英减施40%化肥条件下,紫云英种植第一年相对常规施肥增产0.87%,至种植第7年增幅为3.98%。紫云英与稻草联合利用是近些年稻区推行的重要技术模式,2016—2019年间开展的7个联合定位试验结果(n=342)表明,紫云英-稻草联合还田相对于单独稻草还田,水稻产量增加了11.71%。本文分别从优化水稻产量构成、促进水稻养分吸收、提升土壤肥力3方面阐释了紫云英作冬绿肥的增产、节肥机制。稻田冬种紫云英可增加水稻有效穗数和每穗实粒数,优化了产量构成。与常规施肥相比,紫云英配施减量化肥的水稻吸氮量增加了6.4%~6.9%,氮肥利用率提高了6.6%~31.1%。稻田种植紫云英使土壤碳、氮库得到培育,土壤活性有机碳含量和碳转化酶活性提高,土壤速效养分、土壤物理性状明显改善。以有机质和全氮为例,相比常规施肥处理,种植翻压紫云英后减施20%和40%化肥处理的土壤有机质含量分别增加3.95%和4.15%,土壤全氮含量分别增加1.22%和1.74%。在紫云英调控土壤微生物及氮转化机制方面,冬种绿肥有利于土壤微生物的生长繁殖,增强与微生物活性密切相关的土壤酶活性,并通过改变土壤微生物的群落结构及功能微生物影响土壤养分循环。紫云英配施减量化肥可提高土壤固氮菌丰度,通过合理的调控措施可优化紫云英的生物固氮作用。硝化作用对冬绿肥的响应在不同类型土壤中有较大差异,碱性水稻土中冬种绿肥可通过抑制硝化作用降低氮素淋失风险,氨氧化微生物群落结构的变化是冬绿肥影响硝化作用的重要机制。通过近十多年来的研究,逐渐明晰了我国南方稻田冬种紫云英的增产、节肥效应及其机制,为今后稻田绿肥的效应与机制研究提供了重要借鉴和参考。

In this paper,we collected data from previous investigations on milk vetch(Astragalus sinicus)as winter green manure,and co-incorporation of milk vetch and rice straw in rice paddy fields in south China to study the effects of milk vetch green manure on rice yield and chemical fertilizer application,and the mechanisms of plant nutrition and microbial ecology.Thus,a total of 930 datasets obtained from 11 joint experiments conducted from 2008 to 2019 were analyzed to address this objective.The results showed that incorporation of milk vetch together with application of 100% and 80% of conventional amounts of chemical fertilizer significantly increased rice yield by 6.53% and 4.15%,respectively.The incorporation of milk vetch into paddy fields also prevented decrease in the rice yield at 40% reduction in conventional chemical fertilizer application.The positive effects of milk vetch incorporation on rice yield and chemical fertilizer application increased with the planting years of milk vetch.For instance,a 7-year results of 5 joint experiments showed that milk vetch plants combined with 40% reduction of conventional chemical fertilizer increased rice yield by 0.87% in the first year,compared with conventional fertilization,and the increase rate reached 3.98% in the 7th year.Co-incorporation of milk vetch and rice straw was also an important management practice in rice-planting regions,and widely promoted in south China.A total of 342 datasets obtained from 7 joint experiments conducted from 2016 to 2019 showed that co-incorporation of milk vetch and rice straw increased rice yield by 11.71%,compared with rice straw incorporation alone.We also analyzed the data of rice yield composition,rice nutrient absorption,soil fertility and microbial ecology to understand the mechanisms underlying the increase in rice yield and reduction in chemical fertilizer due to milk vetch green manure.Winter planting of milk vetch increased the effective panicle number and number of grains per panicle,thus optimized rice yield composition.Compared with conventional fertilization,milk vetch combined with reduced chemical fertilizer increased rice N absorption by 6.4%-6.9%,and increased N use efficiency by 6.6%-31.1%.Planting of milk vetch increased soil carbon(C)and nitrogen(N)pool,promoted soil labile organic C contents and enzymatic activities in C transformation,increased soil available nutrients contents and improved soil structure.For example,incorporation of milk vetch combined with 20% and 40% of conventional chemical fertilizer reduction increased soil organic matter by 3.95% and 4.15%,respectively,and soil total N by 1.22% and 1.74%,respectively.The results also showed milk vetch incorporation regulated soil microbes and N transformation.Incorporation of milk vetch influenced soil nutrient cycling by promoting the growth of soil microorganisms and enzymatic activities associated with soil microorganisms,and changing the community structures and functional microbes.Milk vetch combined with reduced amount of chemical fertilizer increased the abundance of azotobacter,and the N fixation process of milk vetch could be optimized through reasonable regulation methods.Responses of nitrification to winter green manuring varied a lot in different soil types.For example,in alkaline paddy soil,winter green manuring inhibited nitrification potential thus reduced the risk of nitrate leaching,and the community changes in ammonia oxidizers was the important mechanisms.Overall,the incorporation of milk vetch as winter green manure has showed reliable effects in increasing rice yield and reducing chemical fertilizer application.The mechanism study also serves as an important reference for further studies on impacts of green manures in rice fields.