Abstract
Nitrogen pollution in agricultural systems is a globally pervasive issue. In dryland cereal grain production systems of the Palouse, current and historical management practices aimed to safeguard crop production from water or nitrogen co-limitation have direct effects on hydrologic partitioning and nitrogen cycling. This study compares hydrologic and nitrogen export at paired catchments under no-tillage and conservation tillage at Cook Agronomy Farm over a six-year period with variable precipitation. Crop yield, biomass, and nitrogen uptake were higher under no-tillage at Cook East (CE) than under conservation tillage at Cook West (CW) despite similar fertilization rates. Greater soil depth at CE and increased infiltration under no-tillage may have increased plant available water and led to improved crop performance. Runoff rarely occurred at CE and the increase in subsurface flow resulted in a positive water balance for most water years. Restrictive soil horizons and limited infiltration due to tillage practices at CW likely limited water retention, generated runoff annually, and increased water balance variability. Mean subsurface nitrate concentrations were correlated to soil inorganic nitrogen content in the fall at both sites, while post-harvest inorganic nitrogen content was tied to crop nitrogen uptake, highlighting how improved nitrogen use efficiency could reduce nitrate leaching. Reducing surface runoff through no-tillage, limiting fall fertilization, and using variable or split fertilizer management in conjunction with rotation management to maximize transpiration and nitrogen uptake and reduce subsurface discharge may lead to gradual reductions in in-stream nitrate loads.