Low nitrogen fertiliser rates and stage of maturity influence nitrogen fractionation and in vitro ruminal nitrogen degradability in tropical grasses.

Abstract

This study evaluated the interactive effects of low rates (0, 25, 50 and 75 kg N ha−1) of nitrogen (N) fertilizer application and stage of maturity on total N, N fractions and in vitro ruminal N degradability in Brachiaria hybrid, Megathyrsus maximus and Paspalum atratum. The grasses were harvested at 4, 8 and 12 weeks regrowth, except for P. atratum that was harvested at 6 and 12 weeks. There was a significant N fertilizer rate × stage of maturity interaction (p < 0.001) on total N, buffer soluble N (BSN), buffer insoluble N (BISN), acid detergent insoluble N (ADIN) and in vitro ruminal N degradability (ND) in all grass species. Total N, BISN and in vitro ruminal N degradability increased linearly with N fertilizer rate up to 50 kg ha−1 in Brachiaria hybrid and M. maximus and were highest in grasses harvested at 4 weeks maturity. Nitrogen fertilization rate was positively correlated with total N, BISN (r = 0.70 to 0.97) and ND (r = 0.60 to 0.98) in Brachiaria hybrid and M. maximus forage. We concluded that N fertilisation rate of 50 kg ha−1 per application interval is adequate to improve N, N fractions and N degradability of tropical grass forage.