Farmers’ soil knowledge, fertility management logic and its linkage with scientifically analyzed soil properties in southern Ethiopia

Abstract Background Farmers’ locally have acquired knowledge from generations of experience and experimentation that fit local conditions. Yet, the scientific approach less used farmers’ soil knowledge (FSK) and site-specific soil information. The objectives of this study were to investigate FSK and rationality; to demonstrate how FSK relates to scientifically analyzed soil properties; and to explore the implemented soil management practices and crop performances in selected districts of Wolaita zone, southern Ethiopia. A total of 789 farmers were included, and their fields were evaluated. Data on farmer’s soil nomenclature, soil physicochemical property, soil fertility management practices and crop yield performance were recorded and analyzed. Results Farmers describe and classify their soils using holistic approach. Soil nomenclature and classification indicators are relatively homogeneous over large area. Accordingly, seven soil types common over large area were identified. Mostly, soil types perceived fertile by farmers (e.g., Arrada bita) were found better in measured physicochemical properties than infertile soil types (e.g., Lada bita, Zo’o bita). Simple regression analysis revealed a declining trends of soil properties with a decrease in fertility of farmers soil types such as soil bulk density (r 2 = 0.78), pH (r 2 = 0.53), available phosphorous (r 2 = 0.83), total exchangeable bases (r 2 = 0.71), copper (r 2 = 0.64) and zinc (r 2 = 0.69). Farmers are rational to allocate the scarce fertilizers. They apply more chemical fertilizer when soil type was getting poor in soil fertility (r 2 = 0.61), whereas it was opposite for manure (r 2 = 0.85). Furthermore, crop response and farmers’ soil type also demonstrated an observable relationship where yield was declining with a decrease in fertility level of farmers’ soil types. Conclusions Farmers understand within farm soil variability and exploit soil fertility differences of their field. This is supported with noticeable relationship with scientifically analyzed soil properties, fertility management strategy and crop responses. It suggests that FSK is relevant for site-specific soil management. Yet, FSK is deficient to identify yield-limiting nutrients, implying it has to be complemented with scientific soil knowledge. Additionally, further investigation to systematically link both approaches is also suggested