EFFECT OF ADDED ROCK PHOSPHATE AND COMPOST ON SOIL PHOSPHORUS FRACTIONS AFTER DIFFERENT INCUBATION PERIODS

Surface clay Soil samples were collected from EL Hamoul, Kafr El-Sheikh governorate and air dried. Each of plastic pot from the experiment pots was filled with 500 grams from these samples. Three rates from rock phosphate (0, 1 and 3%) and three from compost (0, 2, and 4%) were added to and mixed with these experiment soil samples in the pots and incubated in three periods (0, 30 and 90 days) in the lab condition. This experiment was arranged in three replicates using a completely randomized block design. Samples from these applications were taken after each of the three incubation periods. Phosphorus fractions were measured in the taken samples according to Hedley sequential fractionation scheme. The determined P fractions were: (1) P-NaHCO3,(2) P-NaOH, (3) P- HCl/H2SO4, (4) P-residual and (5) Total P. Obtained results could be summarized as follows. The increasing rates of added compost led to an increase in P-NaHCO3 fraction comparing with control treatment. While the increasing rates of added rock phosphate led to a decrease in this fraction and gave the lowest value. The addition of compost and rock phosphate together led to increase in P-NaHCO3 fraction more than each of them alone. The increase of the incubation period led to an unnoticeable and insignificant decrease in this fraction of phosphorous. P-NaOH fraction represents 2.8 % of the total phosphorous. P-HCl/H2SO4 fraction increased with increasing incubation periods, phosphate rock and compost were. The residual P fraction was decreased with increasing incubation period.