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This study investigated the extent to which statistical heterogeneity among results of multiple studies on soil organic carbon (SOC) sequestration rate in response to conventional tillage (CT) and no-till (NT) can be related to one or more characteristics of the studies. The analysis employed a random effect meta-regression technique using the data obtained from recently published experimental trials under continuous corn (CC) and corn soybean (CS) rotation system from selected Corn Belt states. Regarding the difference in the rate of SOC sequestration between NT and CT, our results shows that the percentage of heterogeneity in the true treatment effect that is attributable to between-study variability is 49%, whereas 51 % is attributable to within-study sampling variability. We find that 26% of the between-study variance is explained by the explanatory variables considered, and the remaining between-study variance appears almost zero. The regression results support the argument that the difference between NT and CT decreases as measurement depth increases. The results also show that the higher the initial SOC the higher the NT SOC sequestration rate relative to the CT sequestration rate. A test for publication biases in the analysis indicated no evidence for the presence of small-study effects.


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