Abstract:

【Objective】This study aims to investigate the effects of incorporating green manure and rice straw, along with reduced nitrogen (N) fertilizer application, on rice population quality, grain yields, N absorption, and grain quality in a Chinese milk vetch (Astragalus sinicus L.)-rice (Oryza sativa L.) rotation system. The goal is to lay a theoretical foundation for reducing N input, enhancing efficiency, and improving grain quality in rice cultivation. 【Method】 A field experiment was conducted in Hanzhong City, Shaanxi Province, from 2019 to 2021, utilizing a randomized block design with four treatments: 1) Chinese milk vetch application with no straw returning and conventional nitrogen application (GN₁₀₀); 2) Incorporating winter-planted milk vetch and rice straw into the field with conventional nitrogen application (GSN₁₀₀); 3) Incorporating winter-planted milk vetch and rice straw into the field with a 20% reduction in nitrogen fertilizer (GSN₈₀); 4) Incorporating winter-planted milk vetch and rice straw into the field with a 30% reduction in nitrogen fertilizer (GSN₇₀). During the full heading and maturity stages, aboveground biomass and grain yield were measured, and N content and accumulation in aboveground biomass were analyzed. Additionally, the appearance quality, protein and amylose contents, and gel consistency were assessed. In 2021, an experiment was conducted to examine the nitrogen release characteristics of Chinese milk vetch (CMV) or the combined use of CMV and rice straw, with samples collected on various days to determine the total N content of decomposition residues. 【Results】 The field experiment results demonstrated that the incorporation of CMV and rice straw significantly promoted aboveground rice growth from the full heading stage to maturity, with a notable increase in the population growth rate of 39.83% compared to GN₁₀₀. Over two years, the average annual yield of "Huanghuazhan" increased by 3.08%, 7.21%, and 3.92% under the GSN₁₀₀, GSN₈₀, and GSN₇₀ treatments, respectively, when compared to GN₁₀₀. Incorporating CMV and rice straw enhanced the dry matter of panicle during the full heading stage and maturity, facilitating dry matter transportation to the panicle after the full heading stage. Compared to GN₁₀₀, the contribution rate of dry matter to the panicle after the full heading stage was 1.93%, 23.59%, and 14.43% under GSN₁₀₀, GSN₈₀, and GSN₇₀ treatments, respectively. The incorporation of CMV and rice straw increased N accumulation in rice stems and panicles at the maturity stage, with GSN₈₀ showing the highest improvement. In comparison to GN₁₀₀, the average anaual N accumulation in rice stems and panicles at the maturity stage increased by 40.74% and 23.20%, respectively. Rice quality improved significantly with the increasing years of CMV and rice straw incorporation. When compared to GN₁₀₀, the incorporation of CMV and rice straw reduced amylose and protein contents in rice while enhancing gel consistency. This resulted in a decrease in amylose content by 7.54% to 17.10% and protein content by 4.28% to 5.88%, along with an increase in gel consistency by 2.64% to 12.51%. Moreover, GSN₈₀ and GSN₇₀ had the most substantial positive effects, significantly reducing chalky grain percentage and chalkiness degree of rice. The nylon net bag decomposition experiment revealed that the incorporation of CMV and rice straw increased the nitrogen supply level in the later stages of rice growth, with a significant increase of 11.97% in cumulative nitrogen release during the 106 to 146 days of decomposition compared to CMV being returned to the field alone. 【Conclusions】 In a rotation system of CMV and rice, incorporating CMV and rice straw into the field improves soil N supply during the late stages of rice growth, promoting dry matter accumulation, N absorption, and N transport after the full heading stages. This leads to a reduction in protein and amylose content and an increase in gel consistency, appearance quality, processing quality, and taste quality of rice. However, a 20%-30% reduction in N fertilizer is more conducive to establishing a high-yield population and achieving the synergistic improvement of yield and rice quality. Therefore, the incorporation of CMV and rice straw into the field with a 20%-30% reduction in N fertilizer may be an environmentally friendly cultivation technique suitable for the synergistic enhancement of yield, reduced fertilizer use, and improved quality of indica rice.

Key words: Chinese milk vetch-rice rotation, rice straw incorporation, reduced nitrogen application, nitrogen absorption, rice quality

摘要：

【目的】 研究紫云英稻草联合还田与氮肥减量配施对水稻群体质量、产量、氮素吸收和稻米品质的影响，以期为水稻减肥、增效和提质提供理论依据。【方法】 田间试验于2019－2021年在陕西汉中进行，采用随机区组设计，设置4个处理：1）稻草不还田+常规施氮(GN₁₀₀)；2）紫云英稻草联合还田+常规施氮(GSN₁₀₀)；3）紫云英稻草联合还田+氮肥减量20%(GSN₈₀)；4）紫云英稻草联合还田+氮肥减量30%(GSN₇₀)。水稻齐穗期和成熟期调查地上部生物量和籽粒产量，分析地上部含氮量和氮素累积量，测定籽粒外观品质、加工品质、蛋白质含量、直链淀粉含量和胶稠度。紫云英及紫云英+稻草氮素释放特征试验于2021年在水稻季进行，采用尼龙网袋填埋法，在埋设的第9、20、31、40、50、69、87、106、125、146天取样品测定腐解残体全氮含量。【结果】 与GN₁₀₀相比，紫云英稻草联合还田各处理显著促进水稻齐穗期至成熟期地上部生长，其中群体生长速率显著增加39.83%。与GN₁₀₀相比，GSN₁₀₀、GSN₈₀、GSN₇₀处理下稻谷两年平均增产3.08%、7.21%和3.92%。紫云英稻草联合还田处理提高水稻齐穗期和成熟期穗干物质量，促进水稻齐穗期后干物质向穗的转运。与GN₁₀₀相比，GSN₁₀₀、GSN₈₀和GSN₇₀处理下齐穗期后干物质对穗的贡献率两年平均增幅分别为1.93%、23.59%和14.43%。紫云英稻草联合处理提高了成熟期茎和穗氮素累积量，与GN₁₀₀处理相比，GSN₁₀₀、GSN₈₀和GSN₇₀处理成熟期茎和穗氮素累积量两年平均增幅分别为40.74％和23.20％，且均表现为GSN₈₀最高。稻米品质随着紫云英稻草联合还田年限的增加而明显改善。与GN₁₀₀相比，紫云英稻草联合还田处理显著降低稻米直链淀粉和蛋白质含量，并能提高胶稠度，其中，直链淀粉降幅为7.54%~17.10%，蛋白质含量降幅为4.28%~5.88%，胶稠度增幅为2.64%~12.51%，且GSN₈₀和GSN₇₀改善效果更佳。同时，GSN₈₀和GSN₇₀显著降低稻米垩白粒率和垩白度。尼龙网袋腐解试验结果显示，紫云英稻草联合还田显著提高水稻生育后期土壤氮素供应水平，在填埋后106~146 d腐解期内氮素累积释放量较紫云英单一还田显著增加11.97%。【结论】 紫云英-水稻轮作下紫云英稻草联合还田，可提高水稻生育后期土壤氮素供应，促进水稻齐穗期后干物质积累、氮素吸收和氮素转运，提高水稻产量，降低稻米蛋白质和直链淀粉含量，增加胶稠度，提高稻米外观品质、加工品质和食味品质，而减氮20%~30%条件下更有利于构建高产群体，实现水稻产量和稻米品质协同提高。紫云英稻草联合还田氮肥减量20%~30%适宜优质籼稻增产、减肥、提质。

关键词: 紫云英-水稻轮作, 稻草还田, 氮肥减量, 氮素吸收利用, 稻米品质