Modeling spatial and temporal optimal N fertilizer rates to reduce nitrate leaching while improving grain yield and quality in malting barley

Barley is one of the most important Scottish crops with major economic implications for the Scottish economy because of its use in whisky and beer production. Managing nitrogen (N) fertilizer at field scale for barley is difficult because of the complexity to simultaneously achieve profitability, malting quality and reducing N losses to groundwater. The aim of this study was to model spatial and temporal optimal N fertilizer rates to reduce nitrate leaching while improving grain yield and quality in malting barley. A calibrated and validated crop growth model (DSSAT) was used to identify the optimal amount of N fertilization rates to be applied in the field. The optimal amount of N fertilizer varied between 120 and 140 kg N ha(-1) (as average over the 34 years) to maximize the economic return, grain N% and minimize environmental impact. The malting barley premium paid to farmers varies with N content thus affecting marginal net return, with variation ranging from 500 to 2000 GBP ha(-1). The use of long-term weather data for the simulations allowed the calculation of outcomes from 34 different growing seasons. This information combined with the different premium levels paid to farmers can be helpful in identifying the possible combinations between grain quality premium-N fertilizer-weather conditions. Modelling the long-term data showed that the simulated N leaching (kg N ha(-1)) was highly variable between years and the greatest trade-off was for the amount of N leached. The overall the applied N fertilizer rate had a strong effect on the risk of a trade-off developing over the 34 different growing seasons.