紫云英还田与化肥减量配施对土壤氮素供应和水稻生长的影响

  【目的】  紫云英还田替代化肥是我国南方稻田可持续生产的重要措施。研究紫云英与化肥减量配施比例对水稻地上部群体特征与土壤氮素供应的影响，以期为实现水稻绿色可持续生产提供理论依据。  【方法】  定位试验始于2008年，设置了7个处理，包括不施肥(CK)，单施化肥(F100)，紫云英还田22.5 t/hm2配施化肥用量的100%、80%、60%和40% (MVF100、MVF80、MVF60和MVF40)，以及紫云英单独还田处理(MV)，其中磷肥用量不变。在水稻分蘖盛期、孕穗期和成熟期采样，分析水稻茎蘖动态变化、干物质积累与转运、地上部氮素积累量、氮素吸收利用率及根层土壤无机氮含量，计算各处理稻田土壤氮素表观损失量。  【结果】  与CK相比，F100处理提高了土壤无机氮含量和地上部氮素积累量，进而增加了干物质积累量24.01%～35.35%；虽然提高了不同时期的茎蘖数，却增加了无效分蘖，降低了成穗率。与F100处理相比，MVF80处理显著增加了水稻孕穗期和成熟期的土壤无机氮含量，提高了地上部氮素积累量，促进了干物质向穗中的转运，从而使成熟期的地上部干物质积累量和氮素积累量分别提高了7.14%和18.74%，尤其是使穗的干物质积累量和氮素积累量分别提高了10.96%和19.20%；而MVF100处理显著增加了成熟期土壤无机氮含量和地上部氮素积累量，最终使成熟期的地上部干物质积累量和氮素积累量分别提高了8.52%和24.54%，尤其是使秸秆的干物质积累量和氮素积累量分别提高了12.75%和46.13%。MVF60较F100处理显著提高了孕穗期的土壤无机氮含量，增加了孕穗期后干物质输入穗的量。与F100处理相比， MVF40和MV处理分别使氮素表观损失量显著降低了27.14%和63.83%，而MVF100处理使氮素表观损失量显著增加了36.15%，其他处理与F100处理无显著差异。  【结论】  紫云英还田替代适量化肥提高了稻田土壤氮素供应能力，促进了水稻关键生育时期的氮素吸收和积累，提高了氮肥吸收利用率，进而增加了干物质积累和转运，提升了成熟期干物质积累量尤其是穗的干物质积累量，同时可确保氮素表观损失不增加，最终实现了水稻绿色可持续生产。本试验紫云英还田条件下，减施20%化肥的综合效果较好。

Effects of Chinese milk vetch incorporation and chemical fertilizer reduction on soil nitrogen supply and rice growth

  【Objectives】  Chinese milk vetch (MV) incorporation with reduced chemical fertilizer application is a potential measure for the sustainable production of paddy fields in southern China. This study was designed to investigate how incorporating a proportional amount of Chinese milk vetch to the quantity of chemical fertilizer reduction impacts the aboveground population of rice and soil nitrogen supply. We aim to provide a theoretical basis for achieving green and sustainable rice production.   【Methods】  The experiment commenced in 2018 and had seven treatments, including no fertilizer application (CK), pure chemical fertilizer (F100), and MV incorporation at 22.5 t/hm2 together with 100%, 80%, 60%, 40%, and 0% of the pure chemical fertilizer (MVF100, MVF 80, MVF 60, MVF 40, and MV). All the treatments received an equal amount of P fertilizer. Samples (plants and soil) were collected at the peak of tillering, booting, and maturity stages. Data were collected on tiller number, dry matter accumulation and transport, aboveground N accumulation (ANA), N recovery rate (NRE), and soil mineral N content (Nmin). Also, we calculate the apparent N loss in paddy soil.   【Results】  Compared with CK, F100 increased Nmin and ANA and dry matter accumulation by 24.01%–35.35%. F100 increased the total tiller number across the growth stages, mainly in ineffective tillers with reduced panicle rate. Compared with F100, MVF80 (P<0.05) increased Nmin at the booting and maturity stages, promoted dry matter transportation to the panicle, and increased the aboveground dry matter and N accumulation at maturity by 7.14% and 18.74%. It also enhanced the dry matter and N accumulation in panicle by 10.96% and 19.20%, respectively. MVF100 (P<0.05) increased Nmin and ANA at maturity and the aboveground dry matter and N accumulation by 8.52% and 24.54%. Interestingly, the straw dry matter and N accumulation increased by 12.75% and 46.13%, respectively. Compared to F100, MVF60 (P<0.05) increased Nmin at the booting stage and increased the dry matter transfer into panicle after booting. Compared with F100, MVF40 and MV (P<0.05) reduced soil apparent N loss by 27.14% and 63.83%, respectively, while MVF100 increased it by 36.15%.   【Conclusions】  MV incorporation combined with the appropriate amount of chemical fertilizer could improve soil N supply capacity, promote N absorption and accumulation in the key growth period of rice, and increase dry matter accumulation and transport, especially in panicles. The combination of MV and chemical fertilizer did not increase the apparent N loss, which is conducive to attaining green and sustainable rice production. Under MV incorporation, the optimal chemical fertilizer reduction rate is 20%.