CORRELATION OF SOIL PROPERTIES WITH PHOSPHATE FIXATION IN SOME ALKALINE-CALCAREOUS SOILS OF NORTHWEST INDIA

Effects of soil properties on the rate of phosphate fixation and transformation of added phosphate into different inorganic P fractions were examined on 28 alkaline and calcareous soils of different agroclimatic zones of Haryana and Uttar Pradesh, India. Surface samples were treated with 200 mug P g-1 soil and incubated at 25 +/- 2-degrees-C and at 60% water holding capacity. Available P was determined at 7, 14, 28, and 56 days of incubation. The rate of decrease of available P was satisfactorily described by a second-order kinetic rate equation. Clay, organic carbon, Al, Fe, and cation exchange capacity (CEC) was positively and pH was negatively related with rate constant. An 81.7% variation in rate constant was due to soil properties, while clay content alone contributed a 78% variation. CaCO3 affected the rate constant only in soils not varying in other properties. The variation due to soil properties in the transformation of added phosphate into different inorganic P fractions was: saloid-P 77.7%, Al-P 43.9%, Fe-P 49.0%, Ca-P 80.9%, and available P 79.9%, while the partial contribution of CEC to saloid-P, pH to Al-P, CaCO3 to Ca-P, and clay to available P was maximum. The transformation of added phosphate into saloid-P decreased logarithmically with increasing CEC, clay, active Fe, and organic carbon content. The transformation into Ca-P increased and into Fe-P decreased linearly with increasing pH and CaCO3 contents. The recovery of added P into available P was increased by 9.29% with a one unit increase in pH, while a 1% increase of clay decreased it by 0.62%. The contribution of inorganic P fractions to available P was 86.0% in these soils.