Sediment and phosphorus losses in snowmelt and rainfall runoff from three corn management systems

Limited comparisons of sediment and phosphorus (P) loss dynamics from agricultural fields under snowmelt and rainfall runoff conditions exist despite significant differences in underlying particle detachment and transport processes during these two periods. A systems approach was used on three hydrologically isolated hillslope tracts from which rainfall runoff and snowmelt data were collected over an 18-month period under different residue and manure management systems: corn-grain, corn-silage, and corn-silage with fall manure application. Particulate-bound P dominated overall losses for all the monitored events. While higher mass loads of sediments and P were exported in rainfall runoff, the concentrations of dissolved P forms and organic matter were higher in snowmelt. During the rainfall runoff period, both sediment and P losses were inversely related to the percent residue cover, with the highest coverage corn-grain site producing the lowest levels. In contrast, manure P input prior to melt events, rather than percent residue, dictated P loss patterns during the snowmelt period. Consequently, median P and volatile solids concentrations in snowmelt were higher for the manured site than from the non-manured sites. Importantly, the dissolved P load from the manured field was higher during the snowmelt period compared to the rainfall runoff period. Differences in organic matter sources (manure vs. crop residue) produced sediments with contrasting solids-P signatures, with those from manured corn-silage site enriched both in volatile solids and P Interestingly, the residue cover-manure interplay and the mode of runoff generation had no significant effect on the sediment and P mass distribution in various particle size classes. Our results are expected to improve understanding of P loss pathways and facilitate development of better predictive tools for P transport by enhancing insight on sediment and P mass distribution in different size classes under contrasting row-crop production systems and from different modes of runoff generation.