Phosphorus sorption characteristics of lime amended Ultisols and Alfisols in humid tropical Western Ethiopia

Ultisols and Alfisols in humid Western Ethiopia are deficient in available phosphorus (P) but respond slightly to P fertilization. The study determined P sorption characteristics of five soils with and without optimum lime rate. Phosphorus sorption was conducted by equilibrating the soils with P solutions. Phosphorus sorption patterns of unlimed soils had no sorption maxima while limed soils had sorption maxima. The sorption data fitted to Langmuir model. The unlimed and limed soils had high P sorption capacity. The net zero equilibrium P concentration (EPC0) ranged from 0.007 to 0.012mg l-1. Standard phosphorus requirement (SPR) ranged from 759 to 831 and 441 to 1164mg kg-1 for soils and lime treatments, respectively. Langmuir adsorption maxima (bmax) ranged from 2072 to 2792 and 2352 to 2367mg kg-1 for soils and lime effect, respectively. Effect of soil types on sorption was not significant while lime significantly decreased SPR from 1164 to 441mg k g-1. The bmax of Alfisols increased while of Ultisols decreased with liming. The study suggested that Alfisols and Ultisols require 39 to 49 kg ha-1 and 63 to 75kg ha-1 to elevate solution P concentration to 0.1 and 0.2mg l-1, respectively. The study indicated that P fertilizer recommendations for most agronomic crops in Ethiopia were lower than SPR. With optimal lime rate, the recommended P fertilizer provides suboptimal SPR to provide 0.1 mg l-1 but require additional P fertilizer to achieve 0.2mg l-1. With optimum lime rate, P fertilizer recommendations should be developed through research for Alfisols and Ultisols of humid Western Ethiopia.Peer reviewe