Soil Test Crop Response Based Phosphorous Calibration Study for Maize in Daro Lebu district, West Hararghe Zone, East Oromia, Ethiopia

Abstract

A sound soil test-based crop response approach is critical for optimizing fertilizer application and enhancing crop productivity. Therefore, the study aimed to investigate soil phosphorus dynamics in the Daro Lebu district, West Hararghe Zone. Seventeen farmers' fields were selected for this study to determine the economically optimal nitrogen fertilizer application rate in the first year. In the subsequent second and third years, the study focused on assessing the phosphorus critical level and determining the phosphorus requirement factor. The initial findings showed that an optimum nitrogen rate of 69 kg ha⁻¹ was recommended in the first year. For the second and third cropping seasons, six phosphorus levels (0, 10, 20, 30, 40, and 50 kg ha⁻¹) were tested in combination with a constant nitrogen rate of 69 kg ha⁻¹. The experiment was arranged in a randomized complete block design with three replications to determine the phosphorus critical level and the phosphorus requirement factor. The study revealed low soil phosphorus levels, ranging from 0.98 to 19.9 ppm, and identified a critical phosphorus concentration of 14 ppm along with a phosphorus requirement factor of 4.71 ppm. The maximum maize yield of 4,827 kg ha⁻¹ was achieved with an application of 69 kg ha⁻¹ of urea and phosphorus rates determined based on the critical phosphorus value. This approach significantly increased yields compared to the control (2,636 kg ha⁻¹) and provided a substantial economic return of 15.52 ETB for every birr invested. However, validation of these results on similar farms is recommended before broader adoption.