Nitrogen management, nitrogen use efficiency, and seed yield and quality of creeping signalgrass
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Nitrogen (N) fertilization management can affect the seed yield and quality of tropical forage grasses. Studies have shown the effect of N rates on tropical grass seed production, but no study has evaluated the effect of application timing of N on the N use efficiency (NUE) and seed yield and quality of creeping signalgrass [Urochloa humidicola (Rendle) Morrone & Zuloaga, syn. Brachiaria humidicola (Rendle) Schweick.]. Field experiments were conducted over two growing seasons in Santo Anastácio, São Paulo, Brazil, to evaluate the influence of N fertilization timing on plant nutrition, herbage mass, N uptake, NUE, and seed yield and quality of creeping signalgrass ‘Llanero’. The treatments included a control (no N application) and four treatments with N applied at different times (150 kg N ha−1 during the vegetative phase, 150 kg N ha−1 at panicle initiation [prebooting], 100 kg N ha−1 during the vegetative phase plus 50 kg N ha−1 at panicle initiation, and 50 kg N ha−1 during the vegetative phase plus 100 kg N ha−1 at panicle initiation). Topdressed N fertilization increased the concentration of N in the flag leaf by 35.9% (from 12.2 to 16.6 g kg−1) and increased the herbage N uptake by 99.7% (from 72 and 144 kg ha−1). Herbage mass was not affected by topdressed N fertilization. The greatest seed yield (64.2% or 136 kg ha−1 greater than the control, and an average of 22.5% or 64 kg ha−1 greater than the other N treatments) was observed in response to 100 kg N ha−1 applied during the vegetative phase plus 50 kg N ha−1 applied at panicle initiation, which resulted in improved NUE. Seed viability was greater in the treatments where all or most of the N was applied at panicle initiation. In addition, the seed germination percentage was positively affected by N fertilization, regardless of the N application timing.