IONIC ACTIVITIES OF PHOSPHORUS SPECIES IN RESPONSE TO VARYING pH IN SOILS OF KANO-RIVER-IRRIGATION PROJECT

Abstract

This study was carried out at the Kano River Irrigation Project (KRIP), Kadawa, Kano to determine the ionic activities of species and available forms of phosphorus at varying pH. Visual MINTEQ chemical equilibrium computer model software was used to simulate phosphorus species and phosphorus activity. A total of 37 irrigation sectors were identified in the area. Google earth was used to tag 60 sampling points randomly within both developed and undeveloped sectors of the project. Surface soil samples were collected at 20 cm depth using auger with fabricated steel augers. The samples were analyzed for their physical and chemical properties. Phosphorus availability and species were also analyzed at different soil pH classes (4, 5, 5.9, 6.4, 7.3, 8 and 9). In both experimental and simulated results, phosphorus availability initially increased then decreased with increase in pH of the soil solutions. There were variations in trends between species with H2PO4-, H3PO4, AlPO4, and FePO4 species increasing with decrease in pH while others such as HPO42-, PO43- and CaPO4- increased with increase in pH. Visual MINTEQ simulation output revealed that Fe, Al, Ca, organic matter and CO32- were responsible for the availability of P in the area depending on the pH. The optimum pH range that favors P availability in these soils was found to be between pH ranges of 5.5–7.3. This range is therefore recommended for farmers in the area.