LEACHING AND SORPTION OF NITROGEN AND PHOSPHORUS BY CROP RESIDUE

Abstract

Overland flow from cropland areas often contains nutrients and residue materials can either contribute to runoffnutrient load through leaching or remove nutrients by sorption. Measurements were made of leaching and sorption of nitrogenand phosphorus from corn (Zea mays L.), soybean (Glycine max (L.) Merr.) and winter wheat (Triticum aestivum L. cv.Pastiche) residues placed in solutions containing inorganic nutrients. Variables used were type of residue material, nutrientconstituent, solution concentration, and residue / solution contact time. For a given residue material and nutrient constituent,four different solution concentrations were used (PO4 -P: 0 to 16 .g mL-1; NO3 -N and NH4 -N: 0 to 24 .g mL-1), and changesin solution concentration over five selected residue / solution contact times (25 to 86400 sec) were measured. Soybean andwheat residue contained relatively small amounts of NO3 -N and therefore had minimal impact on the NO3 -N content of thesolutions. An increase in initial solution concentration did not substantially affect PO4 -P leaching from corn and soybeanresidue but caused the amount of NH4 -N removed to decrease. As residue solution / contact time increased from 25 to 86400 s(1 day), the amount of PO4 -P leached from corn and soybean residue consistently increased. Wheat residue sorbed PO4-Pwith an increase in sorption generally resulting from greater residue solution / contact time. Thus, crop residue materialsappear to have the potential to influence the N and P content of runoff through leaching and sorption.