Spring and autumn nitrogen fertiliser effects, with and without phosphorus, potassium and sulphur, on dairy pastures: Yield and botanical composition

Experiments were conducted at three sites to study effects of different nitrogen (N) fertilisers (e.g. urea, ammonium nitrate, di-ammonium phosphate and ammonium sulphate), applied at 45 kg N ha-1, with and without phosphorus (P), potassium (K) and sulphur (S), on pasture dry matter (DM) yield and botanical composition. Autumn and spring applied N increased DM yield at all sites. Different N fertilisers generally produced similar DM yield increases. Where different N fertiliser types were balanced with respect to P, K and S there was a similar marginal, but usually nonsignificant (P≥0.05) increase in DM yield over unbalanced N fertiliser types. Average autumn N response efficiencies (excluding P, K and S) at Sites 1, 2 and 3 (after 47, 34 and 37 days, respectively) were 10:1 (10 kg DM per kg N), 16:1 and 13:1, respectively. Including P, K and S, N response efficiencies were 12:1, 17:1 and 15:1, respectively. Residual N response efficiencies without P, K and S (after 50, 41 and 29 days at Sites 1, 2 and 3, respectively), were 5:1, 5:1 and 3:1, respectively. When P, K and S were included, N residual response efficiencies were 6:1, 6:1 and 4:1, respectively. Average spring N response efficiencies at Sites 1, 2 and 3 (without P, K and S) after 29, 30 and 26 days, respectively were 9:1, 6:1 and 16:1, respectively. Including P, K and S, N response efficiencies were 12:1, 7:1 and 17:1, respectively. Residual N response efficiencies (excluding P, K and S) were 6:1, 6:1 and 7:1 at Sites 1, 2 and 3 after 21, 20 and 21 days, respectively. Including P, K and S, average N residual response efficiencies were 5:1, 7:1 and 8:1, respectively. The botanical composition of the pasture was unaffected by the application of N.