氮素水平对直播冬油菜-杂草竞争关系的影响及机制

Weed control is essential for high and stable yield of direct-seeded winter oilseed rape. Reasonable nitrogen (N) fertilization could enhance crop competition against weeds, and is therefore one feasible and important means to achieve ecological weed control. In previous studies we have found that the competitions between oilseed rape and weeds were significantly influenced by N fertilization levels. However, the underlying mechanisms and their intensities that determine the patterns of oilseed rape-weed competition with varied N levels are unclear. To fill this gap, based on our previous field results and findings, this proposal plans to conduct further micro-plot controlled experiments in multiple sites as well as pot experiments. The main aims are to 1) further investigate weed community dynamics at different growth stages of oilseed rape, as influenced by N rates; 2) to identify variations in critical N concentration and sensibility to N rates between oilseed rape and dominant weed species, and N rate effects on N nutrition indexes and accumulative N deficit values, which would elucidate the interrelation between oilseed rape-weed community dynamics and competition patterns, as regulated by N rates; 3) to clarify N rate effects on the critical period for oilseed rape-weed competition by means of model analysis. The results of this project will provide theoretical and technical support for scientific fertilization and ecological weed control in winter oilseed rape production.

杂草防控对保障直播冬油菜稳产高产至关重要，通过合理施氮提高油菜竞争力是实现生态控草的重要途径。本项目组前期研究表明：油菜与杂草竞争关系受到氮素供应水平的显著调控，但不同氮素水平下决定油菜杂草竞争格局的作用机制及强度尚未明确，亟待深入研究。基于此，本项目拟在原有定位试验数据基础上，通过多点田间微区控制试验、盆栽培养试验明确施氮水平对油菜生育期内杂草群落演变的影响规律，分析油菜和优势杂草氮临界浓度和氮响应敏感性的差异，以及施氮对其氮素营养指数、氮素积累-亏缺值的影响，进而揭示供氮水平调控杂草群落演变与油菜杂草竞争格局的互馈机制；通过模型分析明确氮素供应水平对油菜杂草竞争关键期的影响规律，为冬油菜科学施肥和生态控草提供理论依据和技术支撑。

通过合理施氮提高油菜竞争力是实现生态控草的重要途径，对保障直播冬油菜稳产高产至关重要，但氮素水平调控杂草群落演变及与油菜竞争格局的作用机制及强度尚未明确。基于此，本研究利用长期定位试验平台，开展了不同施肥模式下杂草群落演变与杂草-油菜养分竞争试验研究，分析了施肥模式对杂草生物量、种类、密度、生物多样性以及油菜生长、产量及养分吸收的影响；设置多点大田试验，研究氮素水平、控草时期和播种密度等调控措对施油菜/杂草的生长、养分吸收、油菜产量及氮肥利用效率的作用。结果表明：1. NPK平衡施肥促进油菜生长、养分吸收和产量形成，降低田间光透射率，加剧油菜-杂草的光竞争，强烈抑制杂草，特别是优势杂草生长，不施氮处理则提高相对竞争力弱的杂草物种的丰度。不同杂草对油菜产量的影响存在差异，优势杂草氮素吸收显著影响油菜产量，油菜生产中应在合理施氮的基础上加强对目标优势杂草的防控；2. 油菜产量随播种密度和施氮量增加，当施氮量超过180 kg ha-1， 或油菜播种量超过4.5- 6 kg ha-1 时，油菜产量增幅不大。适当提高油菜播种量可帮助减少氮肥用量，达到 “以密省肥” 的目的。3. 施肥和控草显著抑制杂草生长，促进油菜产量提高。油菜生长和产量对施氮量的响应强于杂草。随施氮量增加，杂草-油菜竞争关键期缩短。这些结果表明合理的施氮水平可调控杂草群落演变，提高油菜的相对竞争力，促进作物养分吸收、生长和产量形成。研究结果可为油菜科学施肥和生态控草提供理论和技术支撑。