Simple Formulation of the Soil Water Effect on Residue Decomposition

Soil water content, θ, is a major factor affecting residue decomposition, but simple formulation of this factor is often lacking. We observed that θ significantly (P < 0.001) affected the residue decomposition constant, k _d. When θ varied from 0.09 g g^?1 to 0.23 g g^?1, k _d ranged from 0.009 to 0.013 d^?1 and from 0.009 to 0.022 d^?1 for residues with carbon to nitrogen ratio (C/N) > 30 and C/N < 25, respectively. A θ factor was formulated in terms of the field capacity θ _FC and the air‐dry θ _d in the form f _w = (θ ? θ _d) / (θ _FC ? θ _d), and this was used to modify the potential k _d as θ varied. Coupling f _w with a first‐order residue decomposition equation resulted in the prediction of the decomposition of four residue types in the greenhouse (R² = 0.94; relative root mean square error, RRMSE, = 0.06) and in the field (R² = 0.93; RRMSE = 0.11).