Effects of nitrogen fertilizer applied in autumn and winter on milk production from a tropical grass-legume grazed at four stocking rates

Abstract

The effect of applying 50 kg N ha-I in autumn and winter each year on milk yield of Friesian cows and dry matter yield and botanical composition of a green panic (Panicum maximum var, trichog1ume)- glycine (Glycine wightii cv. Tinaroo) pasture was measured over two years on the Atherton Tableland, north Queensland. Pastures were grazed at 1.3, 1.6, 1.9 and 2.5 cows ha-1. Milk yield and pasture yield were increased by nitrogen fertilization, particularly at the high stocking rates (P < 0.05). Increases in milk yield from mid-autumn to spring almost totally accounted for increases in annual milk production. Nitrogen fertilizer did not decrease the yield of legume, but legume content of the pasture was reduced in the second year (P < 0.01). Response by non-leguminous species to nitrogen increased (P < 0.05) with stocking rate, a change associated with decreasing legume contents of the pastures. Average fat corrected milk (FCM) yield per cow from mid-autumn to spring was restricted by less than 1600 kg pasture D.M. on offer cow-I or 2500 kg D.M. ha-1. When compared at the same dry matter yields, FCM yield was always higher from nitrogen fertilized pastures than from pastures not recieving fertilizer nitrogen.