Kinetic to Saturation Model for Simulation of Soil Organic Carbon Increase to Steady State

Abstract

Core Ideas We evaluated SOC dynamics in a long‐term soil tillage and N fertilization experiment. We proposed a kinetic to saturation model for long‐term simulation of SOC dynamics. The model was accurate in C‐depleted soils and accounted for SOC saturation process. The use of mathematical models predicting SOC dynamics can provide relevant information about the C storage potential of agricultural soils. We evaluated three mathematical models (first‐order kinetic, C saturation, and a proposed kinetic to saturation) predicting SOC dynamics and steady‐state SOC of a Hapludoll from central Kansas. The study was based on a long‐term experiment (17 yr) assessing soil tillage systems (chisel tillage [CT] and no‐till [NT]) and N fertilizer sources (168 kg N ha−1 as NH4NO3 [MF], cattle manure [OF], and a control treatment without N [CO]. The soil under NT (0–5 cm) had significant SOC accumulation (>0.23 Mg C ha−1 yr−1) regardless of fertilization source, while the CT soil had negligible changes in SOC (<0.12 Mg C ha−1 yr−1) without the addition of organic fertilizer as an external C source. Organic fertilization increased the original SOC by 56 and 192%, reaching steady state at 15.9 and 28.0 Mg ha−1 in CT and NT soils, respectively. The SOC predicted by all three models had significant correlations (r > 0.80, p < 0.05) with measured SOC. However, the C saturation model overestimated the measured SOC under C‐depleted conditions, failing RMSE and lack‐of‐fit tests, while the first‐order kinetic model overestimated NT OF steady‐state SOC by up to 58% in relation to the maximum SOC storage capacity determined for NT soils. The SOC predicted by the kinetic to saturation model agreed with both measured SOC and the maximum SOC storage capacity of NT soils. The kinetic to saturation model can be used for long‐term simulation of SOC dynamics in soils that are either C depleted or close to saturation.