Leaching of Nitrogen, Phosphorus, and Organic Carbon From Wheat Straw Residues: II. Loading Rate

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Abstract
Using a rainfall simulator, wheat straw residue (Triticum aestivum L.) in 1.0‐m2 pans was subjected to simulated rainfall. Runoff from the wheat residue was sampled as a function of time and analyzed for PO43−‐P, NH4+‐N, NO3−‐N, and organic carbon (OC). Rainfall at 25 mm h−1 was applied for 1 h to five residue weights equivalent to field loading rates of 2200, 4500, 6700, 9000, and 11 200 kg ha−1. As loading rates increased from 2200 to 9000 kg ha−1, both concentrations and losses of PO43−‐P, NH43−‐N, and OC increased, whereas those of NO3−‐N decreased. During individual runoff events at all loading rates, PO43−‐P, NH4+‐N, and OC concentrations increased relatively rapidly to a maximum concentration in runoff and then decreased during the remainder of the 1‐h runoff event. The relationship of nutrient concentrations with time were described by a power function Y = aXb and to runoff by a hyperbolic equation of the form Y = 1/(a + bX). The quantity (kg ha−1) of nutrients leached from the wheat residue followed the order C > P > N. For all loading rates, percentage N (NH4+‐N + NO3−‐N) and C leached from the wheat residue was < 10 g kg−1, compared with 240 to 430 g kg−1 for P.