Estimated nutrient leakage from arable land in different bioeconomy scenarios for two areas in central Sweden, determined using a leaching coefficient method

Knowledge of future developments in agriculture and how these will affect nutrient leakage from arable land is important in efforts to achieve good ecological status of surface waters. This study assessed the impact of five scenarios for a bioresource-based economy, involving use of renewable biological resources from land and sea, on nitrogen (N) and phosphorus (P) leakage from arable land to surface-waters and groundwater. The scenarios (developed in an earlier study) were applied to two areas in central Sweden, leaching region LR-6 (5350 km2) and catchment C6 (19 km2). Using the NLeCCS calculation system to produce leakage coefficients, we evaluated the changes in total N and total P leakage from arable soil. The leakage coefficients described agricultural management practices and climate conditions representing the leaching region LR-6 in Sweden and the baseline year was 2016. The scenarios varied from a baseline in terms of crop combination (relative area of different crops) and extent of mitigation measures (e.g. delayed tillage date, buffer zone width and relative area, and catch crop). Expected consumption of meat varied in the scenarios, with lower consumption meaning fewer cattle and consequently less grass ley. The scenarios was supplemented with calculations of introducing mitigation mea-sures up to their maximum potential. In leaching region LR-6, calculated baseline leakages was 10.5 kg N ha-1 year-1 and 0.87 kg P ha-1 year-1, values that varied in the scenarios by-4% to 5% (N) and-6% to 19% (P). In catchment C6 calculated baseline leakages was 7.1 kg N ha-1 year-1 and 1.11 kg P ha-1 year-1, and the values in the scenarios varied by-15% to 2% (N) and-5% to 5% (P). Assuming maximum potential of the mitigation measures decreased leakage further, by up to-19%. Crop combination had a major impact on total N and P leakage in the scenarios. Leakage increased when the amount of grass ley in the rotation decreased, but remained relatively unchanged when the crop combination change only involved annual crops. Frequency of the mitigation measures increased in all scenarios, with associated decreases in N and P leakage that counteracted the increased leakage caused by changes in crop combination. The most effective mitigation measure was catch crop for N leakage and delayed soil tillage for P leakage