|Han, K - Northwest Agriculture And Forestry University|
|Saporito, Louis - Lou|
|Mcgrath, J - University Of Maryland|
|Reiter, M - Virginia Polytechnic Institution & State University|
|Tingle, S - University Of Delaware|
|Allen, A - University Of Maryland Eastern Shore (UMES)|
|Wang, L - Northwest Agriculture And Forestry University|
Submitted to: Soil and Tillage Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/3/2014
Publication Date: 10/8/2014
Citation: Han, K., Kleinman, P.J., Saporito, L.S., Mcgrath, J.M., Reiter, M.S., Tingle, S.C., Allen, A.L., Wang, L.Q., Bryant, R.B. 2014. Phosphorus and nitrogen leaching before and after tillage and urea application. Soil and Tillage Research. 44:560-571. DOI 10.2134/jeq2014.08.0326.
Interpretive Summary: Managing nutrient runoff from agricultural soils is a priority in areas where water bodies are impacted by nutrient loadings. On artificially drained soils of the Delmarva Peninsula, bordering the Chesapeake Bay, phosphorus leaching is a perennial problem as few remedial management practices have been proven. We sought to test the potential to curtail phosphorus leaching with tillage from Delmarva Peninsula soils that possessed high levels of phosphorus. While tillage clearly impacted the principal pathway for phosphorus leaching, soil macropores, sources of phosphorus in the soils studied were too diffuse to target with tillage alone. Results point to the need for diversified management strategies that employ multiple practices to address all nutrient sources within these phosphorus enriched soils.
Technical Abstract: Leaching of nutrients through agricultural soils is a priority water quality concern on the Atlantic Coastal Plain. The objective of this study was to assess the effect of tillage on leaching of phosphorus (P) and nitrogen (N) from no-till soils of the Delmarva Peninsula, evaluating low and high nutrient status members of three dominant agricultural soils under no-till management. Soil columns were collected and irrigated over a 16 week period to assess trends in P and N leaching. Mehlich-3 P values were above agronomic recommended levels, and P was vertically stratified in all of these no-till soils. An initial six weeks of irrigation to establish a baseline of leaching response was followed by two weeks of drying. A subset of columns was then subjected to simulated tillage (0-20 cm) in an attempt to curtail transfers of surface nutrients via macropores. Urea (145 kg N/ha) was then broadcast to the surface of all soils (tilled and untilled), and the columns were irrigated for an additional eight weeks to assess trends following tillage and urea application. Comparison of leachate recoveries representing rapid flow and slow flow from tilled and untilled columns following treatment confirmed the potential to manipulate flow fractions, albeit with mixed results across soils. In the finer-textured soil we observed that tillage destroyed soil macropores, thereby impeding preferential flow and forcing greater matrix flow. Tillage had no significant impact on P leaching losses, despite significant vertical stratification of soil P that suggested tillage could prevent macropore transport of P from the surface to the subsoil. However, tillage did curtail losses of applied urea in leachate in two of the three soils, confirming the study’s premise that tillage would destroy macropore pathways transmitting surface constituents to the subsoil. Relatively high levels of soil P below the 20-cm depth of simulated tillage likely served as the source of P enrichment of leachate waters.