Cropping System Effect on Soluble and Sediment-Bound Phosphorus Losses

Abstract

There is a growing interest in corn silage utilization due to changes in animal farmdynamics and favorable economics compared to alfalfa. The extent of residue cover influencesrunoff production and soil losses, and hence, these changes will affect the off-site migration ofphosphorus (P). Since high-cut silage will increase residue cover, this method could conceivablyminimize water quality degradation that would otherwise result from harvesting corn for silage. Weexamined cropping system effects on sediment and P losses from no-till fields planted in corn.Treatments included conventional corn grain (CG) and silage (CS-L) and non-conventional, high-cut (24-26) silage (CS-H). Each treatment received one of three manure treatments: no manure,application in fall or spring. Simulated rainfall (76 mm/hr; 1 h) experiments were performed in springand fall 2002, runoff from 2.0 m x 1.5 m plots collected and a sub-sample analyzed for totalsediments, dissolved reactive phosphorus (DRP), and total phosphorus (TP).<br><br>Compared to CS-L, CS-H was effective in reducing sediment and P losses; the reductions weregreatest in fall runoff and were enhanced by manure addition. Runoff depth, sediment load, DRPload, and TP load were reduced by 50% when no manure was added and by 85% with manureapplied in either season. Although sediment, DRP, and TP concentrations were higher undermanure application, the secondary effect of enhanced infiltration resulted in lower values on a loadbasis. Reductions were smaller following spring rainfall. DRP concentration was sensitive tomanure application timing while TP concentration was not. Compared to the no manure treatment,DRP concentrations in runoff from all crop treatments were five times greater following springmanure application, while TP concentrations were highest under no manure. Preliminary data onparticle size distribution in transported sediments reveal an increased concentration of fines (< 2 m)on manure-applied plots. Recently applied spring manure protected the soil the most, but leads tothe preferential selection of finer particles.