Influence of the nitrogen fertilization and of the cut age on the forage yield of the elephant grass.

Abstract

The study was carried out in Parnaíba, Brazil, aiming to evaluate the effects of three levels of nitrogen doses (150; 300 and 450 kgN.ha^-1) and five plant age at cutting (28; 35; 42; 56 and 84 days) on height, dry matter, and biomass yield of elephant grass, cv. Napier. The experimental design was in complete randomized blocks, with 4 replications. Plant height was significantly influenced by plant age and nitrogen dose (450 kgN.ha^-1). Plant dry matter, however, was influenced only by plant age. Plant dry matter yield significantly increased (P < 0.05) in line with plant age at cutting, with age at cutting of 84 days yielding the best results (18.93 t.ha^-1), followed by 56 days (9.48 t.ha^-1), and 42 days (5.02 t.ha^-1). Plant biomass obtained by cutting at 35 days (3.96 t.ha^-1) did not differ from cutting at 28 days (3.28 t.ha^-1). Application of 450 kgN.ha^-1 resulted in greater biomass yield (8.82 t.ha^-1), and did not differ (P< 0.05) from 300 kgN.ha^-1 (7.84 t.ha^-1), which in turn did not differ (P < 0.05) from 150 kgN.ha^-1 (7.75 t.ha^-1). Nitrogen application efficiency (51.66; 26.13 and 19.6 kgDM.kg^-1.N), regardless of plant age at cutting, was inversely proportional to nitrogen doses (150; 300 and 450 kgN.ha^-1).