Mitigation of Mombasa Grass ( Megathyrsus maximus ) Dependence on Nitrogen Fertilization as a Function of Inoculation with Azospirillum brasilense

ABSTRACT Using biological inputs to improve the efficiency of nitrogen fertilizers represents an alternative for the cultivation of grasses in tropical regions. Azospirillum brasilense is a species of plant growth promoting bacteria widely studied and used in inoculants. Thus, this study aimed to evaluate the performance of Mombasa grass ( Megathyrsus maximus ) in association with A. brasilense and nitrogen (N) fertilization. The study was conducted under field conditions in Araguaína-Tocantins State, between December 2017 and May 2018. The treatments were arranged in randomized blocks, in a 5 × 2 factorial arrangement, with five doses of N fertilization (0, 25, 50, 75, and 100 kg ha-1) combined with two inoculation treatments (inoculated and non inoculated), in four replicates. For the number of tillers and root production, the inoculation efficiency varied as a function of the supplied N doses. However, the percentage of leaf N was higher for inoculated plants regardless of the application of nitrogen. In the absence of nitrogen fertilization, it was possible to increase forage production by up to 36 % with inoculation.摘要：利用生物输入手段提升氮肥利用效率，是热带地区禾本科牧草栽培的可行替代途径。巴西固氮螺菌（Azospirillum brasilense）是一类被广泛研究并应用于微生物菌剂的植物促生细菌。本研究旨在评估巴西固氮螺菌配施氮肥对莫桑比克草（Megathyrsus maximus）生长性能的影响。本试验于2017年12月至2018年5月在托坎廷斯州阿拉瓜伊纳地区开展大田试验。试验采用5×2因子随机区组设计，设置5个氮肥施用量梯度（0、25、50、75、100 kg·ha⁻¹），搭配2种接种处理（接种组与未接种组），共设置4次生物学重复。结果表明，对于分蘖数与根系生物量，接种处理的效率随氮肥施用量的变化呈现显著差异。但无论是否施用氮肥，接种处理植株的叶片全氮占比均显著高于未接种植株。在不施加氮肥的条件下，接种处理可使牧草产量最高提升36%。