Management-Induced Soil C Sequestration Index.

Carbon sequestration is related to soil quality. A sensitive test to evaluate soil’s performance as a sink or source of CO2 is important for sustainable management of agroecosystems. A randomized block design in 2 (tillage system) x 3 (crop rotation) factorial arrangement was laid-out to evaluate the impact of tillage and crop rotation (1990 to 2007) on soil microbial activity. Tillage treatments (conventional tillage, CT and no-till, NT) were factored into continuous corn, corn-soybean, and corn–soybean-wheat-cowpeas rotation. Ten soil cores were collected at 0-7.5, 7.5-15, 15-22.5 and 22.5-30 cm), 2-mm sieved, and analyzed for sequential extraction of different C fractions, such as total microbial biomass (C_mic), particulate organic C (POC), non-humic C, humic acid, fulvic acid, humin, and total C (C_org) with soil pH, electrical conductivity (Ec), and bulk density (rb). An additive approach was used by summation and average of normalized C into a single integrator as C sequestration index (C_index). Datum of each individual C fraction (C_o) was normalized (C_i) on a scale [³0, ≤1] relative to the maximum value of that particular C fraction (C_max) in the data set, C_i = (C_o C_max^-1). Equal weight was assign to each C_i. By summing all the C_i’s and then dividing by the number of C_i’s, the C_index calculated. Results showed that Cindex was significantly (0.45 vs. 0.34) higher in NT than CT at all soil depths. Both CC and CSW (0.42 and 0.40) had higher Cindex than CS (0.37). The Cindex significantly decreased with increasing soil depth. Stepwise multiple regression analysis showed that Cmic, POM-C and CT had significant relationship with Cindex. Cmic accounted 86% variability in Cindex while CT and POM-C accounted 72 to 76% variability in Cindex. Routine measurement of Cmic can be used as an early and sensitive indicator of management induced soil C sequestration.