Adsorption and desorption of phosphorus and nitrogen by immersed stalks

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 corn, soybean, and wheat stalk residues. Experimental variables included type of stalk material (corn, soybean, and wheat), inorganic nutrients in solution (PO4-P and NO ₃-N; PO ₄-P and NH ₄-N; NO ₃-N and NH ₄-N; and PO ₄-P, NO ₃-N, and NH ₄-N), solution concentration (0, 6, 12, and 24 μg g ^-1 residue), and stalk immersion period (25, 250, 2500, 25000, and 86400 s). The initial concentration of each of the P and N constituents in a particular test solution was the same (0, 6, 12 or 24 μg mL ^-1). Corn-stalk residues released PO ₄-P, NO ₃-N, and NH ₄-N. The quantity of PO ₄-P released generally increased as the length of time the corn stalks were immersed became greater. The presence of P and N constituents in solution in general did not affect the quantity of NO ₃-N released by corn-stalk residues. Soybean-stalk residues released PO ₄-P and adsorbed relatively small amounts of NH ₄-N. Wheat-stalk residues released PO ₄-P, and adsorbed NO ₃-N and NH ₄-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.