Characterization of the Weed Flora in Rice Areas under Distinct Cropping Systems and Herbicide Managements

ABSTRACT: The aim of this study was to evaluate the occurrence of weeds in flooded rice areas, as a function of planting system and herbicide programmes in the previous cropping year. The experiment was installed in field conditions, in randomized complete blocks design, arranged in factorial scheme 3 x 2, with eight replications. In factor A, treatments consisted on conventional tillage, minimum tillage and no till cropping systems, coupled to the application (traditional control) or not (semi-ecological system) of herbicides (Factor B). One year after rice cultivation, preceding the planting of the next cropping season, phytosociological evaluations of the weed communities present in the treatments were carried out. We assessed the overall infestation level and weed species composition, which were classified by their respective density, frequency and dominance abilities. We also estimated the diversity coefficients of Simpson and Shannon Weiner, and the sustainability coefficient of Shannon; treatments were also grouped by similarity in weed species composition. Rice growing systems (traditional or semi-ecological) promote remarkable differences in weed occurrence. Herbicide-based crops select specific companion weed species, but crop rotation or winter cover crops are not a sine qua non condition for success since a good herbicide programme is planned. For the Semi ecological system, crop rotation, thick winter soil mulching and association with animal presence and grazing are essential for the short, medium and long-term inhibition of weeds.

摘要：本研究旨在评估淹水稻田的杂草发生情况，其影响因素为前一季种植制度与除草剂施用方案。本试验设置于大田环境，采用完全随机区组设计，按3×2因子方案布置，共设8次重复。因子A的处理包括常规耕作、少耕和免耕种植制度，结合因子B的除草剂施用（传统防控体系）或不施用（半生态体系）两种设置。在水稻种植一年后、下一茬作物播种前，对各处理组中的杂草群落开展植物社会学调查。本研究评估了杂草总体侵染程度与物种组成，并通过密度、频度和优势度对各杂草类群进行分类。同时估算了辛普森（Simpson）多样性指数、香农-威纳（Shannon-Weiner）多样性指数以及香农可持续性系数；并根据杂草物种组成的相似性对各处理组进行聚类分组。水稻种植制度（传统或半生态）会对杂草发生情况造成显著差异。依赖除草剂的种植体系会筛选出特定伴生杂草物种，但只要规划合理的除草剂施用方案，轮作或冬季覆盖作物并非成功的必要条件。对于半生态体系而言，轮作、厚层冬季土壤覆盖以及配合动物活动与放牧，是短期、中期和长期抑制杂草的必要措施。