Phosphate relationships in acid-sulphate soils of Mbiabet swamp rice farm, Akwa Ibom State, Nigeria.

Abstract

A study was conducted in April 2006 to determine the phosphate relationship in acid sulphate soils of Mbiabet Swamp Rice farm in Akwa Ibom State, Nigeria. Soil samples were collected in the order of 0 – 1, 1 – 2, 2 – 5, 5 – 8, 8 - 10 and 10 - 15cm soil depths. Treatments consisted of potassium dihydrogen phosphate added to the swamp mud, cat-clay, and mud-clay in equal doses of 122 kg/ha P205, fitted into Latin square of 36 x 5 m swamp, except for the control plots. Limestone (CaC03) was applied to both fertilized and unfertilized plots at the rate of 50 kg/ha to reduce
the activity of alumimium. The distribution of phosphate in the top 10 cm of unfertilized plots at the fresh and dried mud showed that the bulk of the total phosphorus was in the organic and occluded forms. There was no saloid-bound phosphorus present in either the fresh or dried mud. The fixation of phosphorus was rapid, reaching the equilibrium within 50 - 75 hours. Fresh mud (except cat-clay) absorbed more phosphate than did dried mud and nearly 60 percent of the absorption took place within 6 hours. The soluble phosphate applied as solution to columns of air-dried swamp mud showed a decrease within 6 months, but calcium and organic phosphate increased. Saloid-bound phosphate with the water-logged cat-clay decreased considerably. The soils have great opportunities in rice production when given proper soil management.