Tillage, cropping, harvest, and nutrient management systems impacts on phosphorus loss with surface runoff: A research update

Eroded soil and phosphorus (P) impair several Iowa lakes and streams, and exported P contributes to hypoxia in the Gulf of Mexico. Most of the sediment and P originate from agricultural fields and stream banks. Phosphorus is lost from fields mainly by surface and subsurface transport processes, although delivery through water erosion and surface runoff accounts for the vast majority of the P reaching surface water bodies. The P lost with runoff can be classified into particulate P, dissolved reactive P (DRP), and bioavailable P (BAP). Particulate P includes forms in or attached to soil mineral and organic particles (sediment-bound P), and has been reported to account for 60 to 90% of P transported with surface runoff. Dissolved reactive P includes mainly orthophosphate P that was desorbed from soil, leached from plant residues, and dissolved from recently applied fertilizer or manure. Bioavailable P is an estimate of P available to algae and aquatic plants over a short period of time, and includes dissolved P and P weakly retained by soil constituents. A significant portion of the sediment-bound P becomes available to algae over a longer period of time