Accumulation and Release of Nutrients by Immersed Stalks Collected on Selected Dates Following Harvest

The concentrations of phosphorus (P) and nitrogen (N) in runoff from cropland areas may be influenced by accumulation and release of P and N by stalk residues. A laboratory study was conducted to measure the effects of time since harvest and immersion period on accumulation and release of P and N by corn, soybean, and wheat stalks. Experimental variables included type of stalk material (corn, soybean, and wheat), time since harvest (six residue collection dates over an approximate 1-year period), and stalk immersion period (25 s (0.42 min), 250 s (4.2 min), 2500 s (42 min), 25,000 s (6.9 h), and 86,400 s (24 h)). The initial concentration of each of the P and N constituents in a test solution was 6 μg mL−1. The soybean, wheat, and corn residue released PO4-P at mean rates of 40, 69, and 141 μg g−1 residue, respectively. The amount of PO4-P that was released consistently increased as immersion period became greater. Corn and wheat residue either accumulated or released NO3-N depending on residue collection date. Soybean residue accumulated an average of 20 μg NO3-N g−1 residue. Wheat residue obtained on five of the collection dates accumulated an average of 13 μgNO3-N g−1 residue. Residue collection date also influenced accumulation of NH4-N by soybean and wheat residue. Corn residue released an average of 77 μg NH4-N g−1 residue. The type of crop residue material, the amount of time the residue has remained in the field following harvest, and residue immersion period were found to influence nutrient concentrations of solution