Manure and Crop Management Effects On Transport of Phosphorus and Nitrogen in Surface Runoff in a Corn Silage System.

Transport of P, N, and sediment via runoff from crop fields, especially where manure has been applied, can contribute to eutrophication and degradation of surface waters. We established a paired-watershed field site in central Wisconsin to evaluate surface runoff losses of nutrients and sediment from different manure/crop/tillage management systems for silage corn production. During the 2-yr calibration period the four 1.6-ha “watersheds”, or fields, were treated identically with fall dairy manure application and chisel plowing; and runoff was monitored, sampled, and analyzed for suspended sediment (SS) and total and dissolved forms of P and N. That management was maintained as a control in one watershed, while alternative management systems were carried out on the three treatment fields from Oct 2008 to Apr 2012: fall surface-applied manure with spring chisel plowing, fall-seeded rye cover crop with spring manure and chisel plowing, and fall manure and chisel plowing with field-edge grass-legume buffers. During the calibration period both concentrations and loads of SS and total and dissolved P and N varied by field, and more than 50% of runoff and dissolved P and N loads were from snowmelt runoff. Implementation of treatments significantly affected concentration and/or load of sediment and nutrients compared to the control. Fall surface-applied manure left over winter increased both concentration and load of dissolved P (DP) but not total P (TP), the latter a result of a decrease in concentration of sediment-bound particulate P, attributed to the mulching effect of surface manure. Fall-seeded rye cover reduced concentrations, but not loads, of SS, TP, and total N; effectiveness was limited by minimal fall growth due to difficulty achieving timely seeding. The vegetative buffer treatment reduced both concentrations and loads of SS, TP (but not DP), and total N, making it the most effective system evaluated in this study.