Different agricultural practices affect soil carbon, nitrogen and phosphorous in Kilombero -Tanzania

Converting natural and semi-natural vegetation to agriculture is currently the most significant land use change at global scale. This conversion leads to changes in soil nutrients and increased CO2 emissions. However, knowledge of how soil organic carbon and nutrients change under various farming management is still limited, especially for small scale farming systems. This study evaluated the effects of different farming systems on soil organic carbon (SOC), total nitrogen (TN) and total phosphorous (TP) in subsistence farming at Kilombero, Tanzania. We applied an in-situ experimental setup, comparing maize and rice farming with and without irrigation and difference in fertilizers, with replicated soil sampling at five soil depths to a depth of 60 cm. The results show that irrigation had a positive effect on profile-averaged concentrations of SOC and TN, while fertilization had a positive effect on TN. Higher concentrations and stocks of TN were found in maize field soils compered to rice fields. In the vertical profile, irrigation and fertilization had positive effects on concentrations of SOC and TN of top soil layers, and the interaction between irrigation and fertilization extended the effect to deeper soil layers. Our results indicate that moderate irrigation and fertilization can help to improve carbon storage and nutrient availability (TN) in small-scale farming soils in Africa.