PHOSPHORUS SORPTION CHARACTERISTICS OF FOUR SOIL SERIES

A study was undertaken in order to find out the effect of incubation period s of phosphorus applied in soil samples of four series i.e. Gishkori, Buzdar, Sultanpur and Tikken with varying clay contents of 52, 48, 21 and 20% collected from Dera Ismail Khan, Khyber Pakhtunkhuwa, Pakistan. Soil samples were equilibrated in 20 ml aliquot of 0.01M CaCl2 solution containing 0, 20, 40, 60, 80, 100, 120 and 140µg mL -1 of P as KH2PO4. The samples were incubated at room temperature, shaked twice a day for 30 minutes for 2, 8 , 16 days and centrifuged at 10,000 rpm. The Gishkori soil series with the highest clay content a dsorbed highest quantity of phosphate followed by Tikken that adsorbed the least as contained 20% clay content. For varying equilibration periods, maximum sorption took place in first two days after which little absorption was observed. The study showed that Gishkori soil needed more P addition than other soil samples for plant growth. Beckwith plots showed greater slopes for Gishkori and Buzdar soils indicat ing more phosphate buffering capacities which would replenish the nutrient if solution is exhausted. While, their intercepts were small at zero phosphate sorption hence solution might contain less P for plant growth. Kew words: Phosphorus use efficiency, incubation, clay content, soil series, D era Ismail Khan, Pakistan.