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, C ₀ (μg CO ₂-C g^-1) than maize-elephant grass (Pennisetum purpureum) rotations. The C ₀ 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, m ₀ (μg CO₂-C g^-1 day ^-1), was significantly (P < 0.001) related to the soil water content, θ. The m ₀ 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, f _w, formulated as: fw = [θ-θ_d/ θ_FC-θ_d], where θ _d and θ _FC were the air-dry and field capacity soil water content, respectively, adequately described the variation of the m ₀ with respect to soil water (R ² = 0.91; RMSE = 1.6). Such a simple relationship could be useful for SOC modeling under variable soil water conditions.