Panicum maximum cv. Aries Establishment under Weed Interference with Levels of Light Interception and Nitrogen Fertilization

ABSTRACT: The aim of this study was to evaluate the establishment of the pasture of Panicum maximum cv. Aries in an environmentally protected area under levels of interspecific interaction with the weed community. The experiment started after sowing P. maximum, and it was carried out in a randomized block design with four replications and the following factors: 3 light interception levels, 2 nitrogen rates, and 7 weekly sampling dates along pasture establishment (3x2x7). The light interception treatments, determined by photosynthetically active radiation, were given by mowing weeds over the canopy of P. maximum at 40% and 70% light interception, and no mowing (uncontrolled growth of weeds and P. maximum). Topdressing application of nitrogen in the form of urea was performed or not (0 or 200 kg N ha-1). The plant community was evaluated by number of species, dry matter accumulation, and density, and phytosociological indices were determined. The relative importance and dry matter accumulation of P. maximum were greater after nitrogen fertilization, which favored the species against weed competition. In contrast, there was lower weed density without nitrogen fertilization. Mowing weeds at 40% of light interception enabled P. maximum to accumulate more dry matter, while there was no difference between mowing weeds at 70% light interception and growing the forage crop freely with weeds. Reducing weed light interception as well as nitrogen fertilization, and consequently reducing the competitive ability of the weed, favored the establishment of P. maximum in diversified agro-ecosystems.

摘要：本研究旨在评估受环境保护区域内，白羊草（Panicum maximum cv. Aries）牧草地在与杂草群落存在种间互作梯度下的建植效果。本实验于播种白羊草后启动，采用随机区组设计（randomized block design），设置4次重复，包含3个光照截留水平、2个氮肥施用量梯度，以及沿牧草地建植周期的7个每周采样节点（因子组合为3×2×7）。光照截留处理基于光合有效辐射（photosynthetically active radiation）确定，具体操作为在白羊草冠层上方修剪杂草，分别维持40%、70%的光照截留率，以及不进行修剪（即杂草与白羊草自由生长，无人工控除处理）。氮肥以尿素（urea）为肥源进行表层追肥，设置0 kg N ha⁻¹与200 kg N ha⁻¹两个施用量梯度。本研究通过物种数、干物质积累量（dry matter accumulation）与种群密度对植物群落进行评估，并计算植物社会学指数（phytosociological indices）。结果显示，施加氮肥后，白羊草的相对重要值与干物质积累量均显著提升，使其在与杂草的种间竞争中占据优势；反之，未施加氮肥时杂草种群密度更低。将杂草修剪至40%光照截留率时，白羊草的干物质积累量更高；而70%光照截留率的修剪处理与杂草自由伴生的处理组间无显著差异。降低杂草对光照的截留量并配合氮肥施用，进而削弱杂草的竞争能力，可促进多物种农业生态系统中白羊草的建植。