Short-term effects of crop rotation, residue management, and soil water on carbon mineralization in a tropical cropping system

The purpose of this study was to investigate the short-term effects of maize (Zea mays)-fallow rotation, residue management, and soil water on carbon mineralization in a tropical cropping system in Ghana. After 15 months of the trial, maize–legume rotation treatments had significantly (P < 0.001) higher levels of potentially mineralizable carbon, C0 (μg CO2–C g−1) than maize–elephant grass (Pennisetum purpureum) rotations. The C0 for maize–grass rotation treatments was significantly related to the biomass input (r = 0.95; P = 0.05), but that for the maize–legume rotation was not. The soil carbon mineralization rate constant, k (per day), was also significantly related to the rotation treatments (P < 0.001). The k values for maize–grass and maize–legume rotation treatments were 0.025 and 0.036 day−1 respectively. The initial carbon mineralization rate, m0 (μg CO2–C g−1 day −1), was significantly (P < 0.001) related to the soil water content, θ. The m0 ranged from 3.88 to 18.67 and from 2.30 to 15.35 μg CO2–C g−1 day−1 for maize–legume and maize–grass rotation treatments, respectively, when the soil water varied from 28% to 95% field capacity (FC). A simple soil water content (θ)-based factor, fw, formulated as: \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$f_{\text{w}} = \left[ {\frac{{\theta - \theta _{\text{d}} }}{{\theta _{{\text{FC}}} - \theta _{\text{d}} }}} \right]$$\end{document}, where θd and θFC were the air-dry and field capacity soil water content, respectively, adequately described the variation of the m0 with respect to soil water (R2 = 0.91; RMSE = 1.6). Such a simple relationship could be useful for SOC modeling under variable soil water conditions.