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

Abstract

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.