*4.2. Soil Organic C*

The SOC was significantly increased with biochar application. The general ANOVA did not show significant difference in SOC content between experimental years. However, differences in SOC content were observed between experimental sites. Higher SOC content was observed at LCB with a coarse textured sandy loam soil compared to Efaw with silty clay loam. Results averaged across experimental sites and years indicate a 19.3% increase in SOC under biochar soil amendment. The significant impact of biochar on SOC have been well documented [21,25,37]. For instance, Liu et al. [38] observed as high as 40% increase in SOC under biochar treatment. At just 8 t ha−<sup>1</sup> of biochar derived from wheat straw, Zhang et al. [39] observed 34–80% increase in SOC. Similarly, Gao et al. [33] reported that wood biochar application increased SOC by 33% at 20 t ha−<sup>1</sup> under tropical soils. Soil organic C increased at all biochar rates used in this study. The apparent and perhaps obvious reason for the increased SOC under biochar soil amendment is the fact that biochar contains high proportion of C by weight compared to other elements. In this study, the pine wood biochar used contained 87% organic C. Indeed, application of material with such high organic C content will certainly increase the SOC of the amended soil. With other factors constant, this implies that the increase in SOC following biochar application is dependent on the rate of biochar application. This notion is consistent with observation in the current study where SOC increased with biochar application rate. In addition, biochar is also known to persist in soil for a long period of time. In the latter case, some researchers have presented evidence on the stability of biochar in the soil and suggested its application as a strategy for soil C sequestration [40,41]. Therefore, application of biochar in agricultural soil are important both from the agronomic and environmental perspectives.
