Suitability of Active Carbon As a Predictor of Soil Carbon Management.

Agricultural soil carbon (C) sequestration is one of the viable options to mitigate climate change effects. To evaluate the impact of continuous no-till (NT) on C sequestration, composite soil samples taken at 7.5 cm increments from 30 cm depth of conventionally tilled (CT) and 2 (NT₂), 23 (NT₂₃), and 44⁺ years (NT₄₄) of NT corn (Zea mays, L.) plots in northwest Ohio were analyzed for pH, bulk density (rb), total C, total N, active C, extractable (ext C), and soluble C (sol C). Results showed that increasing years of NT significantly decreased soil pH. Surface rb under NT decreased over time to values that were comparable to the rb of CT. Compared to CT, the soil in NT₂₃ and NT₄₄ had total C content 23 and 28% higher, respectively. Similarly, active C was 50 and 78% higher and total N was 11 and 16% higher. The NT had also a significantly greater ext C content compared with CT. The concentration of all the C fractions and total N decreased significantly with increased depth. Among the C fractions, active C was subjected to greater stratification than any other C fractions. Regression equations for NT at 10 yr increments over a 44 year period yielded total C sequestration rates of 594, 167, 71, and 23 kg ha^-1 yr^-1 in the 0 to 7.5, 7.5 to 15, 15 to 22.5, and 22.5 to 30 cm soil layers, respectively, for the first 10 years. Similarly, total N accumulation rates were 88, 22, 7, and 3 kg ha^-1 yr^-1, active C sequestration rates were 57, 25, 22, and 17 kg ha^-1 yr^-1, and ext C sequestration rates were 3, 1, 0.4, and 0.2 kg ha^-1 yr^-1. After 20 years of NT, the total C sequestration rates reached a plateau in all soil layers, and total N accumulation in the 0 to 7.5 cm soil layer also plateaued. After 15 years, the active C sequestration in the 0 to 7.5 cm soil layer had reached a plateau. Our results suggest that C sequestration “synthesizes” SOM that is distributed in different C fractions and is stoichiometrically linked with N accumulation or vice versa. Active C is a sensitive predictor of  soil organic matter management.