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.