PHOSPHORUS BIOAVAILABILITY IN CALCAREOUS AND SANDY SOILS

An incubation experiment was conducted under laboratory conditions to study the availability of ordinary super phosphate (OSP) at the rates of 0, 60 and 120 kg P₂O₅ fad.^-1 (0, 50 and 100% recommendation dose (RD)), either singly or combined with organic soil amendments i.e. chicken manure (CM) at the rates of 10 and 20 Mg fad.^-1 (1 and 2%), potassium humate (KH) at the rates of 1 and 2 Mg fad^-1 (0.1 and 0.2 %) and phosphorus dissolving bacteria (PDB) at a rate of 2 ml Kg^-1 soil through different incubation periods i.e. 10, 30, 60, 90, 120 and 150 days in the two different soils, the first was calcareous soil, collected from El-Noubaria Research Station beside El-Noubaria county, Northern Part of Tahreer Province. The second one was sandy soil, which collected from the Farm of the Faculty of Agriculture, El-Khattara District, Zagazig University, Sharkia Governorate. The obtained results can be summarized as follows: In absence of organic soil amendments and biofertilization (PDB), the highest average value of available phosphorus was obtained at the rate of 100% of RD (OSP) comparing with the other individual rates of (OSP). Wherever, in absence of biofertilization (PDB) all rates of (OSP) combined with 2% CM gave the greatest average value of available phosphorus if compared to the corresponded (OSP) rates combined with 0.2% KH in the two tested soils. The treatment of 100% of RD (OSP) + 2% CM + PDB in the two studied soils showed beneficial effect on the average value of available phosphorus if compared to the other treatments. The most (OSP) rates applied either singly or combined with organic soil amendments and/or biofertilization lead to the increase soil available phosphorus content after 60 days of incubation, while it decreased after  30, 90,120 and 150 days of incubation. The average values of available phosphorus for most treatments were greater in sandy soil than in calcareous one. Results showed that the use of half of the recommended dose of phosphatic fertilizer (OSP) combined with organic manures and/or biofertilizer (PDB) may reduce the phosphatic dose and production cost, consequently contamination soil salinity.