Phosphate fractions of Kerala rice soils in relation to their occurrence and pedogenesis

Abstract

to their pedogenesis was conducted. The total P content varies between 816 and 917 ppm. The Fe-P fraction is the most dominant fraction in all the soils accounting for 21.8 to 39.3 per cent of the total P in the soils. AI-P is the second most abundant P fraction, accounting up to 12.7 to 25.8 per cent of the total P. The Ca-P fraction varies between 5.9 and 103 per cent. These soils contain only 6.0 to 9.5 per cent and 2.7 to 5.6 per cent respectively of reductant-P and occluded-P. The higher Ca-P incidence in the soils under marine influence has been attributed to the reaction of soluble Ca in the sea water with reduced Fe-P compounds and the formation of more insoluble Ca-P compounds. The results indicate that continuous alluviation by periodical floods in the formation of all the soils under study coupled with the marine influence in all the soils except the lateritic alluvium of the ribbon valleys of the midlands appear to maintain their juvenility.