Effect of Applied Lime and Mineral Phosphorus Fertilizer on Phosphorus Transformation in Acid Soils of West Wollega, Ethiopia

Prevalent occurrence of P deficiency in strongly acid soils is one of the major problems limiting crop production in high rainfall regions of Ethiopia where Phosphorus (P) fixation, nutrient leaching and soils erosion are common. This work investigated effect of liming and applied mineral P on the P transformation of acid soils of West Wollega, Ethiopia. To study the P transformations, P fractionation was carried out to determine distributions of P in the various P pools. The soils were categorized as strongly acidic in which the pH (H2O) values varied between 4.35 and 4.82. Cation exchange capacity (CEC) of the soils ranged from 20 to28 cmolc kg-.1 Lime requirements to raise the soil pH to target values of 5.5, 6.5 and 7.2 varied from 4.27 to 8.18 tons CaCO3 ha-1. The total P contents of the studied soils ranged from 298.46 to 392.12 mg kg-.1 Available P( Bray I-P, Mehlich 3-P and CaCl2-P) ranged from 1.12 to 1.82 mg kg-1 and considered as very low available P content. On average, distributions of applied P in the various fractions of the soils followed the order: iron bound P (Fe-P) > aluminum bound P (Al-P) > calcium bound P (Ca-P) > easily soluble P (ES-P) > reductant soluble P (RS-P). Clay content was highly positively correlated with total P, Fe-P, Ca-P, organic P and Bray I -P (r = 0.86, 0.76, 0.88, 0.89 and 62 respectively at p < 0.01 and p < 0.05). CEC was significantly correlated with total P, Fe-P, Ca-P, organic P (r = 0.92, 0.98, 0.89 and 0.78 respectively at p < 0.001 and p < 0.01). Desorption of P in the Fe-P and Al-P fractions were highly affected by the pH while desorption of P in the other fractions were modestly affected. The recovered mean percentages of the applied P were different among the soil types and P treatments ranging from 44.30% to 90.83%. This indicates that with proper lime treatment and optimum mineral P application, plant availability of P be increased in acid soils that highly fix applied P fertilizer. Key words: P fractions, lime requirement, available P. P transformation, P recovery