The following experiments were conducted in three phases during 2001-2003 in a randomized complete block design to study the effects of organic materials and phosphate solubilizing bacteria on phosphorus availability in phosphate rock through isotopic dilution technique. The first phase of the experiments was performed on field to study the main effects of treatments on corn crop( Zea mays L.), the second phase was carried out on field to study the residual effects of treatments on barley crop ( Hordeum vulgare L.), and the third phase in a greenhouse to study the treatments effects on P derived from soil (Pdfs), P derived from fertilizers (Pdff), and to determine fertilizer use efficiency (FUE) in corn crop grown in pot soils labeled with radioactive phosphorus (32P). After crop harvest in each phase, dry matter yield, total dry matter percentage, crop growth rate (CGR), P and Zn content in leaf, total P yield, P derived from fertilizer (Pdff), fertilizer use efficiency (FUE), agronomic efficiency (AE) and soil available phosphorus (Pa\a) were determined for corn crop while straw and grain yield, harvest index, as well as thousand kernel weight were determined for barley. The following results were obtained: Main effects of treatments on dry matter yield, total dry matter percentage, crop growth rate (CGR), fertilizer use efficiency (FUE), agronomic efficiency (AE)
and the rate of fertilizer derived P (Pdff), were statistically significant (P<0.01), but the main effects of treatments on height, P and Zn content in leaf, total phosphorus yield (TPY) and Pay. were not significant. Residual effects of treatments on straw yield, grain yield, thousand kernel weight, harvest index and agronomic efficiency were not statistically significant. The results in this research demonstrated that phosphate rock along with organic matter and phosphate solubilizing bacteria increased the rate of P derived from fertilizer (Pdff) as well as increasing the yield indices for corn crop. As for main effects, treatments with organic matter and phosphate solubilizing bacteria were more effective than treatments with either organic matter or phosphate solubilizing bacteria. Therefore, treatments with organic matter and phosphate solubilizing bacteria can be recommended for increasing main effects on corn crop.
)