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

DOI: 10.32474/OAJESS.2020.05.000208 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.