Nitrogen management of forage grasses for nutrition, seed production, and nutrients in residual straw

Abstract: The objective of this work was to evaluate the nutrition, accumulation of nutrients in residual straw, pure seed yield, and seed quality of the tropical forage grasses 'Mombaça' and 'Xaraés' subjected to topdressing with nitrogen fertilizer management. Field experiments were carried out in the municipalities of Rancharia and Presidente Prudente, in the state of São Paulo, Brazil. The treatments included a control (without N topdressing) and four N fractionation forms at different forage stages: 150 kg ha-1 N, at the vegetative phase (VP); 150 kg ha-1 N, at the beginning of the reproductive phase (RP), between panicle initiation and the prebooting stages; 100 kg ha-1 N, at VP plus 50 kg ha-1 N at RP; and 50 kg ha-1 N at VP plus 100 kg ha-1 N at RP. Fertilization with N as topdressing, regardless of the N fractionation form, increased N concentration in the flag leaf and in residual straw, and the quantities of N accumulated by 'Mombaça' and 'Xaraés' forage grasses. The application of all or most N in the VP increased the quantities of residual straw and of P and K accumulated by the 'Mombaça' forage grasses. The application of all or most N in the RP provided a greater pure seed yield and N use efficiency in both forage grasses. The seed physiological quality of the forages is not affected by fertilization with N topdressing.

摘要：本研究旨在评估氮肥追肥（topdressing）管理模式下，热带饲草‘Mombaça’与‘Xaraés’的养分含量、残留秸秆养分积累量、纯种子产量及种子品质。田间试验于巴西圣保罗州拉查里亚（Rancharia）与总统普拉登特（Presidente Prudente）两市开展。试验设置不施氮肥追肥的对照组，以及4种不同饲草生育期的氮肥分施方案：1）营养生长期（vegetative phase, VP）施150 kg·ha⁻¹氮肥；2）生殖生长期（reproductive phase, RP，即穗分化始期至孕穗前期）施150 kg·ha⁻¹氮肥；3）营养生长期施100 kg·ha⁻¹氮肥+生殖生长期施50 kg·ha⁻¹氮肥；4）营养生长期施50 kg·ha⁻¹氮肥+生殖生长期施100 kg·ha⁻¹氮肥。无论采用何种氮肥分施模式，氮肥追肥均可提升‘Mombaça’与‘Xaraés’饲草旗叶及残留秸秆中的氮素浓度，同时增加两种饲草的氮素积累总量。将全部或大部分氮肥施于营养生长期，可提升‘Mombaça’饲草的残留秸秆量与磷、钾积累量。将全部或大部分氮肥施于生殖生长期，则可提升两种饲草的纯种子产量与氮肥利用效率。此外，氮肥追肥对两种饲草的种子生理品质无显著影响。