Conservation agriculture practices have been successfully applied to improve crop yields in South America, but questions arose whether these practices can be successfully implemented in Africa. Here we show that a specific set of soil conservation practices called conservation farming (CF) using planting basins and hand hoes disseminated on 280 farms in Zambia on average failed to increase maize yields compared to traditional farming (TF). Average grain yield was low with 1.2 t ha⁻¹, but variation between farms was large with a variance of 32% for CF, ranging in individual farms from 0.02 to 2.8 t ha⁻¹. Yields on farms that declared to practice CF were more constrained by inappropriate management (P < 0.001 of multiple stepwise regression; 13% of total variability) such as lack of early planting and insufficient weeding (25% of total variability explained by management) than by site or climatic conditions. In contrast, yields under TF varied the most (26%) based on the amount and types of inputs. CF practices increased maize yields at rainfall below 1000 mm yr⁻¹, and in valley bottoms possibly due to the water-collecting properties of the planting basins, but decreased yields in lower slope and valley positions of higher rainfall regions above 1000 mm yr⁻¹ likely due to waterlogging. Observed management constraints in comparison to site or soil conditions highlight the critical importance of training needed to make complex interventions such as CF successful in areas where means and infrastructure are insufficient to provide farmers with external inputs.