Abstract
Heavy application of fertilizers containing nitrogen and phosphorus to soils causes surface water quality degradation because the nutrients flow out of the agronomic systems and enter water bodies in large quantities, causing algal blooms and eutrophication. Extensive studies focusing on phosphorus as a surface water pollutant from agronomic systems have been conducted in the many regions of the United States, however, there has been a lack of studies completed in the semiarid Palouse region of eastern Washington and western Idaho. The goal of this research was to better understand how no-till farm management has temporally altered soil P availability for off-site transport through an artificially drained catchment at the Cook Agronomy Farm in Pullman, WA. Preferential flow pathways were also characterized in extracted cores. Dissolved reactive P (DRP) concentrations in subsurface drainage from an artificial drain exceeded TMDL threshold concentrations during numerous seasonal high flow events over the two-year study time frame. Soil analyses of samples collected in 1998, 2008, and 2015 show a highly variable distribution of water-extractable P across the sub-catchment area, and translocation of P species deeper into the soil profile since implementing no-till practices. We hypothesized that a greater network of macropores from lack of soil disturbance allow for preferential flow of water rich in dissolved nutrients deeper into the subsurface and to the artificial drain system. Simulated flow experiments on soil cores from the study site showed large-scale macropore development, extreme variability in soil conductivity, and high P adsorption potential for the soils, suggesting a disconnect between P movement through macropore soil and subsurface drainage water rich in DRP at the artificial drain line outlet.