Phosphorus and nitrogen leaching before and after tillage and urea application.

Leaching of nutrients through agricultural soils is a priority water quality concern on the Atlantic Coastal Plain. This study evaluated the effect of tillage and urea application on leaching of phosphorus (P) and nitrogen (N) from soils of the Delmarva Peninsula that had previously been under no-till management. Intact soil columns (30 cm wide × 50 cm deep) were irrigated for 6 wk to establish a baseline of leaching response. After 2 wk of drying, a subset of soil columns was subjected to simulated tillage (0-20 cm) in an attempt to curtail leaching of surface nutrients, especially P. Urea (145 kg N ha) was then broadcast on all soils (tilled and untilled), and the columns were irrigated for another 8 wk. Comparison of leachate recoveries representing rapid and slow flows confirmed the potential to manipulate flow fractions with tillage, albeit with mixed results across soils. Leachate trends in the finer-textured soil suggest that tillage impeded macropore flow and forced greater matrix flow. Despite significant vertical stratification of soil P that suggested tillage could prevent leaching of P via macropores from the surface to the subsoil, tillage had no significant impact on P leaching losses. Relatively high levels of soil P below 20 cm may have served as the source of P enrichment in leachate waters. However, tillage did lower losses of applied urea in leachate from two of the three soils, partially confirming the study's premise that tillage would destroy macropore pathways transmitting surface constituents to the subsoil.