Phosphorus Sorption under Changing Soil Drainage Condition of a Wetland –Implications for Sustainable Intensification of Agriculture

Phosphorous is a major limiting factor for plant growth, and its behaviour varies significantly under different soil drainage conditions. Understanding the chemistry of phosphorus availability of wetlands remain imperative for sustainable management of paddies under intensive agriculture and this has not been well documented. A study was therefore conducted to investigate the effect of soil drainage condition on the phosphorus sorption capacity of some wetland soils in south-west Nigeria. Soil samples were taken at 0-30 cm (surface) and 30-60 cm (subsurface) soil depth across some land use types under dry and wet soil conditions, primarily during the rainy and dry seasons. Phosphorus sorption studies were carried out using standard protocols. The results showed that the phosphorus sorption isotherms for the soils had the characteristic L- shape and were best described by Langmuir II adsorption isotherm. The R2 values of the isotherms varied between 0.97 and 0.99. The adsorption maxima (Smax) ranged from 17.09 to 39.22 mg kg-1under wet condition while it ranged from 37.74 to 138.89 mg kg-1 in the dry soil. The P sorption capacities of the soils were higher in the dry soils which had Smax that were 4 to 6 times greater than those of the wet soil. Similarly, the specific P requirement (SPR) of the dry soils were higher than those of the wet soils. This suggests that P fertilizer requirement for crop production during the wet season is essentially determined by the quantity of P applied during the dry season and this should be taken into consideration in fertiliser management programs to avoid eutrophication.