Use of a three-compartment model to evaluate the dynamics of cover crop residues

Abstract

Cover crop (CC) residues protect the soil from erosion and their permanence on the surface islargely influenced by theirbiochemicalconstituents. Simulation models have been proposed to evaluate the decomposition of residues in soil. Most of these models have taken in to a ccountone or several compartments to describe the organic residues, each decomposing according to first or de rkinetics. In this study, the dynamics of CC residue decomposition by applying mathematical models was described. The kinetics of decomposition of residues was obtained from a laboratory incubation experiment. Three CC shoot residues were applied on the soil surface and incubated for 362 days (withe ight sampling times). Total 72 samples (pots) were placed at random in a green house unde controlled conditions of temperature (25 ± 1°C). The basic treatment design consisted of pots in which CC residue (24 pots for each specie), oven-dried, was covered. The residues of oats, vetch and clover cutinto 2–3-cm particles and were added to pots at 5.4, 5.4 and 2.7 g dry matter, respectively, which corresponded to biomass rates of 6, 6 and 3 Mg ha−1, respectively. This rate is equivalent to that observed in field experimental plots. There sults from the application of the three-compartment model (LIG, C + H and NSC, with their decomposition rate constants) for simulating decomposition of different CC residues showed a better fit witht he real data than the estimation from the negative exponential equation. Oats and vetch residues decomposed the most than clover, where k values were 3.6 × 10−3,3.7 × 10−3 and 5.3 × 10−3 day−1, respectively. The three compartment model (non structural carbohydrates, cellulose–hemicellulose and lignin) to simúlate residue decomposition presented a close fit between simulated and measured data. The decomposition rate constant (k) of CC can be used to estímate how long residues willre main in thefield and how they could affect soil organic carbon.Vetch residues initially showed a fast decomposition rate. They lost over 40% in the first 21 day safter being placed in incubation pots, which allow edhigh N-availability in the soil. Oats residues decomposed more slowly and caused temporary N-immobilization in thesoil, with a late partial release between 3 and 4 months after the residues were placed in the pots. Decomposition rates foroats, vetch and clover residues were different, where as the processes of mineralization and immobilization were enhanced by the C:N ratio of each CC. The decomposition dynamics of the CC can be described by a simple equation in the médium term, or else a three compartment model can be used for more accurate descriptions in the short term.