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. With more accurate forecasts, the system can reduce the risk of under-application of N. A perfect 3-week forecast would increase uptake by an average of 2 kg N ha −1, and increase profit nationally by £23M per annum but have negligible impact on losses. These improvements appear to be systematic and could be expected to be achieved with any recommendation system that makes explicit use of post-application weather.