Management options to reduce nitrogen surplus in potato production in the Netherlands; a modelling approach

Nitrogen (N) overapplication leads to N surpluses and possible environmental problems. Overuse may particularly apply to cash crops which receive relatively high amounts of inputs, such as potato. To predict the effects of N fertilization regimes on crop production and to optimize N management, crop growth models can be used. In this study, we calibrated and evaluated the crop growth model WOFOST for potato and explored various management options to reduce N surpluses without yield loss. WOFOST was calibrated and evaluated on an experimental potato data set conducted over two growing seasons, at two locations, using five cultivars and under a combination of two irrigation regimes and three N fertilization regimes. The calibrated model was then evaluated on data from 94 farmers’ fields throughout the Netherlands. Next, three different management options to reduce N surplus were investigated: 1) close the efficiency yield gap, 2) reduce the N input without yield loss or soil mining, and 3) target 90 % of the water-limited yield without soil mining. WOFOST reproduced dry matter production and partitioning, and tuber N amounts from the experiments well. Also, WOFOST simulations matched the tuber dry matter production of farmers’ fields adequately throughout the season. Baseline N surpluses estimates were on average 2.6 times larger than the proposed maximum threshold values. All management options reduced the median N surplus to values slightly above or below these thresholds. However, both soil mining and N surplus above recommended threshold values still occurred in management option 1. In the other two options, it was possible on almost all fields with a clay soil to reach N surpluses below the recommended threshold values. The N surplus was slightly above the threshold value on sandy soils. Our work on the calibration and evaluation of WOFOST for potato under N-limited growth conditions allows using this model to assess N fertilization regimes and their effects on yield and the environment in potato production. We subsequently did such an analysis on data from Dutch farmers’ fields with potato. Only closing the efficiency yield gap was insufficient to prevent both soil mining and N surpluses above threshold values for more than half of the fields. However, it was possible to adjust the N input levels to either maintain current yields or obtain 90 % of the water-limited yields without soil mining on clay soils. Although adopting these management options also substantially reduced the N surplus for potato grown on sandy soils, the N surplus was still slightly above the recommended threshold value. • WOFOST was calibrated for modern potato cultivars under N limited growth conditions. • Farmers’ field data were used to explore management options to reduce N surpluses. • Closing potato efficiency yield gaps alone is often not enough to reduce N surpluses. • On clay soils, N surpluses can be reduced below threshold on clay without yield loss. • N surpluses can be strongly reduced on sand too, but median is still above threshold.