Soil Test Crop Response Based Phosphorus Calibration Study for Maize in Negele Arsi District of Western Arsi Zone Oromia

A phosphorus calibration study based on soil testing for maize was carried out in the Negele Arsi district, located in the Western Arsi Zone of Oromia, during the main cropping seasons spanning 2014 to 2016. The primary objectives were to establish the critical phosphorus level (Pc) and determine the phosphorus requirement factor (Pf) for maize, as well as to formulate soil test-based, site-specific phosphorus fertilizer recommendations. The experiment utilized a randomized complete block design (RCBD) with a factorial setup involving five nitrogen application rates (0, 23, 46, 69, and 92 kg ha<sup>-1</sup>) combined with three doses of phosphorus (0, 46, and 92 kg ha<sup>-1</sup>) to identify the optimum nitrogen rate for maize cultivation. During the subsequent two years of the study, a fixed nitrogen rate of 69 kg/ha (identified as optimum) was applied across all plots with varying phosphorus levels of 0, 10, 20, 30, and 40 kg ha<sup>-1</sup> to pinpoint the phosphorus critical value and requirement factor. Soil samples were collected from the composite surface layer at each site before planting and again 21 days post-planting. Results revealed that the highest maize grain yield, averaging 7108 kg/ha, was achieved with an application of 69 kg N/ha alongside 46 kg P<sub>2</sub>O<sub>5</sub>/ha. The combination of 69 kg N/ha with 69 kg P<sub>2</sub>O<sub>5</sub>/ha yielded the maximum net return of 209,806 Birr per hectare. The study concluded that the phosphorus critical level for maize production in these soils is 31 ppm, with a phosphorus requirement factor of 3.06. These values merit validation through further trials before recommending for broader application.