Extractable phosphorous of the Karaj soils as affected by solid and liquid forms of phosphate fertilizer.

Granulated phosphate fertilizers, are the common forms of P-fertilizers that is now applied in Orchards. On the other hand, soil injection of liquid P-fertilizers is one of the most suitable and cheapest methods for orchards. Application of liquid, instead of solid P-fertilizers, almost changes reactions type and/or rate between fertilizer and soil. One of the consequences of these changes is a probable difference in fertilizer recommendation. Prediction of liquid fertilizer recommendations, according to the literatures is not possible. So, the present research was conducted to evaluate the effectiveness of liquid (suspension) vs solid (granulated) triple super phosphate, on increasing of available P in two soil samples of Karaj region. A granule, or the same amount of liquid P-fertilizer was added to soil samples in laboratory. In another treatment, H2SO4 was also added to liquid fertilizer for evaluation the effect of suspension acidification on soil available P. Soil available P was determined after 14, 36 and 165 days. Results showed that after 14 days and in soil sample 1, acidified liquid P-fertilizer caused 31 percent more available P than solid P-fertilizer. liquid P-fertilizer without acid, caused no significant increase in soil available P. In soil sample 2, there was no difference between liquid and solid P. In longer period of time, solid P-fertilizer was more effective than liquid one. After 36 days, solid P-fertilizer caused 127 and 44% more available P in soil samples 1 and 2 respectively and after 165 days, 455 and 133%. Acidified liquid P-fertilizer showed no difference compared to no acid treatments. As there are some reactions between P-fertilizers and soil Fe and Zn, and on the other hand, there are some difficulties for plant to absorb these two elements in calcareous soils of Iran, we evaluate the effect of liquid and solid P-fertilizer on available soil Fe and Zn. Results indicated the form of the fertilizer had no effect on the availability of these elements. It is concluded that if the time of soil injection of liquid P-fertilizer is in accordance to the high demand of the tree, the same amount of liquid P is need as the granulated solid P-fertilizer. Key words: Liquid phosphate fertilizer- Solid phosphate fertilizer- soil available phosphate- soil injection of fertilizers