Effects of trees and nitrogen supply on macronutrient cycling in integrated crop–livestock systems

Abstract

AbstractResidue decomposition from pastures and crops plays an important role in nutrient cycling in integrated crop–livestock systems (ICLS). The objective of this research was to quantify dry matter decomposition and nutrient release—nitrogen, phosphorus, and potassium (N, P, and K, respectively), the most commonly required nutrients in tropical and subtropical agriculture—from pasture and soybean (Glycine max) residues of stocking and crop seasons in two ICLS (with and without trees, CLT and CL, respectively) and two N fertilization levels (90 vs. 180 kg N ha−1, N90 and N180, respectively, applied during the pasture phase). Litter bag incubations were set out in the December 2014 (soybean phase) and May 2015 (pasture phase), and retrieved after 7, 15, 30, 60, 90, and 120 d in each season. The total N, P, and K released from the pasture or soybean residues were related to the initial quantity of plant residues, which was reduced in the CLT systems, mostly for pasture residue (−60%), probably due to light reduction (−55%), rather than changes in litter quality and dynamics. Significant amounts of N (∼57 kg ha−1), P (∼11 kg ha−1), and K (∼58 kg ha−1) were cycled, particularly in CL and N180 treatments. The quantities of K released from pasture residues were enough to restore the quantity of K exported by soybean grains. Therefore, results reinforce the need to understand nutrient release patterns from residues to improve fertilization management.