Evaluation of Phosphorus Response and Fertilizer Recommendations for Wheat Grown on Andosols in the South-Western Ethiopian Highlands

A phosphorus response trial on wheat was carried out on Andosols at 3 locations at highlands of South-western Ethiopia in the main growing seasons of 2017-2018. There were seven treatments, containing  six rates of phosphorus fertilizer (0, 10, 20, 30,40 and 50 kg P ha-1) and a farmer’s practice as a positive control (18-38-6 kg N-P2O5-S ha-1), laid down in a randomized complete block design which replicated 3 times. The yield variation among treatments without P and P treatments indicates 90% of the area showed a yield increase due to P application. Application an external P inputs improved the wheat yield as much as 39% higher compared to the treatments without external P inputs. Olsen available soil P levels in samples taken 21 days after sowing positively responded to different phosphorous fertilizer doses. The critical P level for ninety present relative yields was 14.3 mg kg-1. All the soil samples analyzed had Olsen P values of <10 mg kg-1. The use of 40 kg P ha-1 which produced the maximum wheat grain yield of all treatments can be recommended. It is logical to recommend a minimum of 5 kg P ha-1 each year, in addition to the optimum recommended P rate. Additional field experiments are necessary to evaluate the interactions among P response and different factors that limits white yields and local management practices.