Adsorption and desorption of phosphorus (P) and nitrogen (N) by stalk residues may influence the concentrations of P and N in runoff. A laboratory study was conducted to measure the effects of P and N constituents in solution on adsorption and desorption of P and N by maize, soyabean, and wheat stalk residues. Experimental variables included type of stalk material (maize, soyabean, and wheat), inorganic nutrients in solution (PO4-P and NO3-N; PO4-P and NH4-N; NO3-N and NH4-N; and PO4-P, NO3-N, and NH4-N), solution concentration (0, 6, 12, and 24 micro g g-1 residue), and stalk immersion period (25, 250, 2500, 25 000, and 86 400 seconds). The initial concentration of each of the P and N constituents in a particular test solution was the same (0, 6, 12 or 24 micro g mL-1). Maize-stalk residues released PO4-P, NO3-N, and NH4-N. The quantity of PO4-P released generally increased as the length of time the maize stalks were immersed became greater. The presence of P and N constituents in solution in general did not affect the quantity of NO3-N released by maize-stalk residues. Soyabean-stalk residues released PO4-P and adsorbed relatively small amounts of NH4-N. Wheat-stalk residues released PO4-P, and adsorbed NO3-N and NH4-N. The presence of stalk residues, P or N solution concentration, and residue immersion period may influence P and N concentrations of overland flow. The amount of P and N adsorbed or desorbed by residue materials can be significantly different if more than one nutrient constituent is present in solution.
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