Maintaining Dutch potato yields with less N inputs: great promise for lowering N surplus

In arable farming systems in Northwest Europe high yields are obtained, but they are coupled with high nitrogen (N) application rates and losses. Lowering application rates and thereby increasing resource use efficiency and reducing emissions to the environment is essential to move towards a more sustainable agriculture. In this study, we aimed to quantify and explain variability in nitrogen use, surplus and efficiency for ware potato production in the Netherlands. Over two growing seasons, we closely monitored 96 ware potato fields and assessed variability in yield and management. Average total N input was 448 kg N/ha on clay soils (range: 271-978 kg N/ha) and 319 kg N/ha on sandy soils (range: 155-525 kg N/ha). Nitrogen use efficiency was on average 44% on clay soils and 59% on sandy soils. Thresholds for desired N surplus were achieved in only 4% of the fields on clay soils and 19% of the fields on sandy soils. Regression analysis showed that N input was the most significant contributor for explaining variability in N surplus, while it hardly affected yield. In addition, there was a small effect of year and irrigation on N surplus. Hence, lowering N input rates is the most effective way to reduce N surplus, while yields can be largely maintained. Relatively low N use efficiency suggests that there is also an economic loss for farmers. However, a simple cost benefit analysis showed that risk aversion may partly explain farmers’ rationale with regards to N application rates well above crop demand.