Phosphorus fractions in soil amended with empty fruit bunches and phosphate fertilizer - An incubation study

In an incubation experiment,p was added to the rengam series soil through empty fruit bunches (efb) alone (38 mg p kg-1 soil),p fertilizer alone (900 mg p kg-1 soil),and p fertilizer added together with efb (938 mg p kg-1 soil). the p fertilizers used were triple superphosphate (tsp),gafsa (tunisia) phosphate rock (gpr) and christmas island phosphate rock (cipr). for each month during the six-month incubation,soil p fractions,namely iron oxide-coated strip p (pi),bray 2 p,naoh p,occluded p,ca p,organic p,microbial biomass p,total p,amount of p dissolved (dp) from phosphate rock (pr),and exchangeable ca were determined. the percentage dissolution of tsp,gpr and cipr was 94.8%,31.3% and 26.6% of added p,respectively,following the chemical reactivity of the materials. addition of organic residues (efb) only had a significant effect on the dissolution of cipr. however,the results show a positive influence of organic residues added with p fertilizer which stimulated the formation of microbial biomass p (four times more than with p fertilizer added alone),organic p (about two times more than with p fertilizer added alone),and less movement into the inorganic p fractions. addition of organic residues led to the continued increase in dissolution of pr with time,over the six months of incubation,compared to when pr alone was added to the soil; this might be due to the additional sinks for p (biological transformation of p) and ca (increase in ca-exchange sites).