Nitrate leaching for a three-year potato rotation in Prince Edward Island, Canada

Intensive potato practices in Prince Edward Island, Canada can negatively impact groundwater, the sole source of drinking water for the province, and have been associated with increased frequency of anoxic events in downgradient coastal ecosystems. In this study (2009-2015), two cycles of a three-year potato rotation (potato-barley-red clover) implemented on a field scale (2.4 ha) at the Harrington Experimental Research Farm of Agriculture and Agri-Food Canada, located 10 km north of Charlottetown, were modelled using Root Zone Water Quality Model (RZWQM), a one-dimensional model that simulates plant growth and the movement of water, nutrients and pesticides in the root zone, to better understand the nitrogen (N) dynamics and magnitude of nitrate leaching under the various rotation phases. The main inputs of N were mineral fertilizer (150 kg, 51 kg and 0 kg N ha-1 y-1 for potatoes, barley and red clover, respectively) and mineralization of N from soil organic matter (60 - 90 kg N ha-1 y-1, depending on the rotation phase). For the red clover phase, biological N fixation provided an additional input of N (40-170 kg N ha-1 y-1). Plant uptake was the most important process for removal of N from soil (195-226 kg kg N ha-1 y-1 for potatoes, 80-103 kg N ha-1 y-1 for barley and 83-215 kg N ha-1 y-1 for red clover) and was followed by leaching, which was greatest for potatoes (67-76 kg N ha-1 y-1), followed by barley (31-37 kg N ha-1 y-1) and clover (27-36 kg N ha-1 y-1). The greatest nitrate leaching occurred in the fall after harvest when the crop cover was absent and the infiltration was high (e.g., maximum leaching of 33 kg N ha-1 y-1under potato in November 2014). Elevated nitrate leaching also took place in mid-spring when residual soil N was mobilised by increased percolation due to snowmelt (e.g., maximum leaching of 23 kg N ha-1 y-1 at the end of the clover phase in April 2014). The results of this research, including the calibrated plant growth models for each rotation phase can be used for developing sustainable management practices aimed at reducing nitrate leaching while maintaining agricultural yield as well as for assessing the impact of future climate changes on both yield and environmental footprint associated with potato production practices.