Nitrogen Management, Nitrogen Use Efficiency, and Seed Yield and Quality of Creeping Signalgrass

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.