On farm verification of soil test-based phosphorus fertilizer recommendations for bread wheat (<i>Triticum aestivum</i> L.) on the vertisols of central highlands of Ethiopia

Abstract

Phosphorus is the most limiting nutrient in most of soils of highlands of Ethiopia. Mathematical models that integrate the soil test indices with fertilizer requirements can be important for phosphorus fertilizer recommendation. This study was conducted to verify the recommended soil test based calibration equation for phosphorus (P) fertilizer for two consecutive years on 16 farmers’ fields. Before planting, the initial soil P level was analyzed and ranged from 5.8 to 11.4 ppm. Based on the P calibration model of Debre Berhan Agricultural Research Center (DBARC), the phosphorus requirement ranged from 17 to 120 P2O5 kg ha−1. Nevertheless, in the second year, the initial P level was between 5.04 and 14.29 ppm and the need for P2O5 ranged from zero to 110.4 kg P2O5 ha−1 with DBARC model. In contrast, with agronomic phosphorus fertilizer recommendation, the need for P2O5 was 138 kg ha−1 for both locations for the two years. The first year result revealed that soil test based fertilizer application save 51% of the P2O5 applied compared to the agronomic fertilizer recommendation (138 P2O5 kg ha−1). However, in the second year DBARC and GARC model, could reduce P2O5 fertilizer applied by 65.94 and 44.2%, respectively. The first year result indicated that DBARC model had a mean grain and straw yield penalty of 0.8% and 0.7% compared to the agronomic phosphorus fertilizer recommendation. Similarly, in second year the penalty could be found to be 10.3% and 7.8%. The result also indicated that DBARC P calibration model had the higher net benefit of 19,088 ETB ha−1. The same was true for benefit cost ratio. Therefore, from this study, it is recommended that soil test based fertilizer recommendation shall be used for farmers and hence the P critical and P factor for the test crop were found to be 12.56 and 6.41, respectively.