LAUSR

Abstract Elevated nitrate levels in surface and ground waters on Prince Edward Island (PEI), Canada, are of concerns for both drinking water quality and aquatic habitat protection. These elevated nitrate levels have been closely linked to excessive nitrogen (N) leaching from land under intensive potato production. An improved understanding of the effects of conventional and alternative potato rotation systems and associated rotation crops on N leaching and potato tuber yield is needed to inform if the alternative rotation can impose less impact on water quality while maintaining the economic viability. We contrasted two field based, 3-year potato-based rotations: a potato-barley-red clover (PBC) rotation (conventional), and a potato-soybean-barley (PSB) rotation (alternative), from 2014 to 2017. Crop tissue N accumulation, soil mineral N and N concentrations in soil leachate were measured during the experimental period for assessing N dynamics and potential N leaching loss from the two systems. On a rotation basis, soil mineral N and N concentrations in leachate under the PBC rotation were significantly higher when compared with the PSB rotation after the planting of red clover. The overall N utilization efficiency of the PSB rotation was 1.6 times to that of the PBC rotation. Due to the high N surplus during the red clover and potato phase, total N surplus of the PBC rotation across the 3 years was significantly higher than that of the PSB rotation. A strong positive correlation was found between nitrogen surplus and average seasonal leachate nitrate concentration. On rotation crop level, potato and red clover phases produced most of the potential N leaching loss during the rotation cycles. The red clover phase accumulated the largest amount of N and produced the largest amount of N loss when compared with other rotation crops. Nitrogen leaching occurred primarily in the non-growing season, with different rotation crops demonstrating different leaching patterns. In the potato phase, N leaching occurred primarily between October and late December. Nitrogen leaching sourced from the red clover spanned a long-lasting process: the high mineralization rate and extended mineralization period of the residue led to carry-over of N leaching into the subsequent growing season. In addition, potato yield following the PSB rotation was 13.4% higher than the PBC rotation in 2017. These data suggested that the alternative PSB rotation could increase potato yields while reducing N leaching compared to the conventional PBC rotation.