Assessment of Phosphorus Availability in Acidic Soils of Ebonyi State, South East Nigeria

This study assesses phosphorus availability and the factors controlling it in the strongly acidic soils of Ebonyi State, located in Nigeria's South East geopolitical zone. Phosphorus deficiency is one of the most widespread nutritional constraints on crop production in tropical acidic soils, where low pH promotes fixation by aluminium and iron oxides, rendering applied fertiliser phosphorus unavailable to crops and necessitating high and costly application rates. Using a descriptive analytical design, surface soil samples were collected from 45 farms across Afikpo, Abakaliki, and Ezza South local government areas. Samples were analysed for pH, organic carbon, total phosphorus by acid digestion, available phosphorus by the Bray-1 and Mehlich-3 methods, exchangeable aluminium, and free iron oxide content by dithionite-citrate-bicarbonate extraction. Phosphorus sorption isotherms were determined at six solution concentrations for a subset of 15 soils. Findings revealed that 82 percent of sampled soils had pH below 5.2, with exchangeable aluminium above 1.5 cmolc/kg in 68 percent of samples. Available phosphorus by Bray-1 was below 10 mg/kg in 79 percent of farms. Phosphorus sorption was strongly related to free iron oxide content (r = 0.81) and inversely related to pH (r = -0.76). Soils with higher organic carbon showed significantly lower phosphorus sorption maxima, highlighting the role of organic matter in reducing fixation. The study recommends liming combined with organic matter additions as a prerequisite for efficient phosphorus fertiliser use in Ebonyi State. Keywords: phosphorus availability, soil acidity, Ebonyi State, phosphorus sorption, acidic soils.