The application of organic carbon, such as crop residue, animal manure, and compost, improves the physical, chemical, and biological dimensions of agricultural soil. Soils rich in organic carbon have the potential to sustain and improve crop yields while minimizing environmental externalities. The incorporation of organic carbon into marginal soils has various high order impacts on smallholder farmers, including improved food security, higher household income, broader access to education for youth, and more reliable public health outcomes. However, soil organic carbon levels and soil erosion prevention efforts fall far below soil loss tolerance rates globally. A randomized controlled trial (RCT) called the Wanging'ombe Soil Health Trial was conducted in the Southern Highlands of Tanzania to establish the extent to which soil health test data changes smallholder farmer behavior related to organic carbon application.