Leaching of Nitrogen, Phosphorus, and Organic Carbon from Wheat Straw Residues: I. Rainfall Intensity

Abstract

Knowledge of nutrients leached from crop residues will aid in understanding nutrient cycling in agricultural systems and in the development of small watershed chemical transport models. Using a multiple-intensity rainfall simulator, wheat straw residue (Triticum aestivum L.) was subjected to 25.4 mm simulated rainfall at intensities of 7, 12, 25, 53, and 105 mm h⁻¹. The wheat straw loading rate was 4500 kg ha⁻¹. Runoff was sampled as a function of time and analyzed for PO₄³⁻-P, NH₄⁺-N, NO₃⁻-N, and organic carbon (OC). Except for NO₃⁻-N, nutrient concentrations and losses were greater at the lower rainfall intensities. At each intensity, PO₄³⁻-P, NH₄⁺-N, and OC concentrations in runoff from the wheat straw increased rapidly to maximum values and then decreased with time. After maximum nutrient concentrations were reached, a power function, Y = aX^b, best described the relationship of nutrient concentrations with time, whereas a hyperbolic equation of the form Y = 1/(a + bX) best described the relationship of nutrient concentrations with runoff. The quantity (kg ha⁻¹) of nutrients leached from the wheat straw followed the order C > P > N as (NH₄⁺-N + NO₃⁻-N). Amounts of N as (NH₄⁺-N + NO₃⁻-N) and C leached from the wheat straw were ≤ 1% of the nutrient content compared with 80 to 140 g kg⁻¹ for P. This study also indicates that the variability in both the leachability and nutrient content of crop residues from different sources will be important, factors in the development of crop residue leaching models.