The effect of drought and nitrogen fertiliser addition on nitrate leaching risk from a pasture soil; an assessment from a field experiment and modelling.

Background: A combination of field experiment and modelling tested the hypothesis that dry summers increase the risk of nitrogen (N) leaching from pasture owing to a combination of: soil N accumulation in a dry summer; slow recovery of drought-affected pasture in the autumn; and the resultant inefficient use of fertiliser N by the pasture.

Results: In the experiment, pasture response to urea and apparent N recovery in autumn after the drought was half that of irrigated pasture (7 vs 13 kg dry matter kg N; 28 vs 52% apparent recovery; P < 0.05).