The Influence of Soil Organic Carbon and Climate Variability on Crop Yields in Kongwa District, Tanzania

This study assessed the influence of soil organic carbon (SOC) accumulation and climate variability on crop yields in Kongwa District, central Tanzania. In doing so, climate data and soil samples were collected from Mnyakongo and Ugogoni villages through soil sampling, interviews and surveys. Walkley-Black method, Mann-Kendall test, and MS Excel were used to analyze SOC, climate, crop yields respectively. The results exhibited that the accumulation of SOC was significantly greater in soils under organic fertilization (1.15 and 0.80 MgC ha^-1 at soil 0-20 cm and 20-30 cm depth) than under no-fertilization (0.35 and 0.30 MgC ha^-1 at 0-20 cm and 20-30 cm) and decreased with increasing soil depths. Under these two soil treatments, the average yields for maize, sorghum and millet were almost 1.8 tn ha^-1 under organic fertilization and 0.6 tn ha^-1 under no-fertilization. Specifically, maize yields ranged from 1.5 to 2.2 tn ha^-1, while both sorghum and millet had 1.1-1.7 tn ha^-1. Therefore, yields were significantly higher under organic fertilizations than under no-fertilizations. Besides, the mean annual rainfall or temperature (1980‒2020) fluctuated at a decreasing (R² = 0.21) or an increasing trend (R² = 0.30). Comparatively, the yields for maize, sorghum or millet fluctuated at a decreasing trend at R² = 0.07, 0.05, or 0.85, respectively. Correspondingly, it was found that the temporal increase in rainfall and temperature had positive (R² ~0.5) and negative (R² ~0.3) correlations with crop yields, respectively. In contrast, the decline in rain's intensity and frequency had negative impacts on crop yields. Thus, both SOC and climate correlated with crop yields.