The role of autumn crop-coverage in nitrate leaching: A Daisy model scenario analysis comparing catch-crops and winter cereals across multiple sites and climatic conditions in Denmark

Understanding the intra-annual dynamics of nitrogen (N) turnover across entire crop rotations is essential for minimizing N losses, as these dynamics carry legacy effects spanning agrohydrological years. While catch-crops (CCs) are widely adopted to mitigate N leaching, there is uncertainty of how their effectiveness varies across soil conditions and climates. This study used the agroecological model Daisy to evaluate regional variations, caused by differences in soil- and climatic-conditions, on N leaching in crop rotations with varying proportions of CCs, spring-, and winter-cereals as crop cover. This study utilized four soil types, from coarse sand to clay, and constructed eight 24-year crop rotation scenarios to quantify how differing levels of CC and winter cereal cover reduced annual N leaching and affected other key N-dynamics. Results confirmed that soil type alone could not explain differences in N leaching across crop rotations, but conditions such as early CC termination, restricted root development, high autumn precipitation, and percolation patterns, meant that winter wheat as an autumn cover could be equally effective as CCs in reducing annual N leaching. Although increasing CC-cover generally led to a near-linear reduction in N leaching, the magnitude of reduction varied depending on soil, CC species, and annual weather variability, ranging from 9 to 75 %. Differences between rotations could be largely explained by accounting for the intra-annual dynamics of N cycling. Finally, the high annual and site-specific variability in N leaching highlights the need for adaptive management strategies to ensure consistent reductions under increasingly unpredictable weather conditions.