How far might medium-term weather forecasts improve nitrogen fertiliser use and benefit arable farming in the England and Wales?

Because of the interest in the value of medium-term weather forecasts to UK agriculture, we attempt to quantify this value for N fertiliser use with arable crops. Model systems such as SUNDIAL provide arable N fertiliser advice by modelling the N supply from soil, but poor knowledge of future weather reduces accuracy. A weather generator was used to produce sets of simulated weather of a range of accuracies and durations, for 10 regions in England and Wales. In a series of computer simulations, we tested the effect of prior knowledge of weather following the date of N fertiliser application on the efficiency of use of applications using SUNDIAL. The changes in N leaching, denitrification and crop N uptake due to the forecast quality were calculated. Yield and gross profit changes were estimated from N uptake, for the arable industry in England and Wales. Changes in losses were small. With a perfect forecast, there was a small decrease in leaching (approximately 1 kg N ha−1), and still less change in denitrification. The increase in crop uptake due to a perfect 27-week weather forecast was 6 kg N ha−1, and the increase in farm profit in England and Wales amounted to £68M per annum.