Effects of Compost and Mineral Sulfur Fertilizers on Phosphorus Desorption at Wujiraba Watershed, Northwestern Highlands of Ethiopia

Phosphorus fixation, which is responsible for low availability of P, is one of the major problems of crop growth in acidic soils such as Nitisols. It is one of the most chronic problems for crop yield decline in Wujiraba watershed. Therefore, an incubation study was conducted for two months to investigate the effects of compost and S fertilizers on P desorption in strongly acid soils (pH/KCl 4.53) and low P content (Bray II P 4.8 mg kg-1). After air drying, grinding and passing through 2 mm sieve, 200 g of soil was placed to each pot. The experimental treatments included three rates of compost (0, 5 and 10 t compost ha-1) and S (0, 15 and 30 kg S ha-1) fertilizers were laid down in CRD with three replications. At the end of the incubation period, the analyzed data result revealed highly significant (P ≤ 0.001) difference in available P by interaction effects of compost and S fertilizers whereby the highest (22.8 mg kg-1) was recorded in pots treated with high dose of compost (10 kg compost ha-1) and nil S fertilizer rates which increased by 301% relative to the control. Unlike compost, S fertilizer amendment resulted in a decrease in available P but increase in exchangeable acidity and Al contents of the soil. Therefore, this work showed a decline in P fixation and exchangeable Al with the application of compost, which, is a cost effective measure on strongly acid soils that can benefit farmers cultivating soils which are deficient in available P nutrient.