Study on Direct Application Possibility of Phosphate Rock in Calcareous Soils.

The conjunction of calcareous parent materials and dry climate has resulted in the development of calcareous and alkali soils in large areas of Iran. Due to the high levels of Ca++ in soil solutions and high pH values, the soil nutrients, whose absorptions depend on pH, will become less available and thus limit the growth of crop plants. The objectives of this experiment was to test the possibility of using rock phosphate along with sulfur, thiobacillus (SOM), phosphate solubilizing microorganisms (PSM) to provide phosphorus to feed corn in calcareous soils. A completely randomized experiment with 15 treatments and 3 replications and 3 separate cuttings was carried out in the Soil and Water Research Institute greenhouse during 2001 for this investigation. The treatments included: T1=the controlT2= triple super phosphate (TSP)T3= phosphate solubilizing microorganisms (PSM)A= rock phosphate (A)T5= A+PSMT6= A+PSM+organic matter (OM)T7= A+OMT8= A+ sulfur (S)T9= A+S+OMT10= A+S+SOMT11= A+S+OM+SOMT12= A+S+SOM+ PSMT13= A+S+OM+SOM+PSMT14= A+S+PSMand T15= A+S. Planting, protection and cutting at three stages (4 weeks, 8 weeks and 12 weeks), and the analysis of data on dry weight yields, and the level of phosphorus absorption by plants were carried out similarly for all the treatments.The results show that for earlier cuttings when very little phosphorus from rock phosphate had been released and utilized by the plant triple super phosphate treated samples produced more dry weight. However, the dry weights of the later cuttings were significantly the same for triple superphosphate treated and rock phosphate treated plants. The results also showed that adding organic matter to any treatments containing microorganisms as the base treatment led to reduced yields which may be due to the type of organic matter to pure inorganic treatment mixtures except for A+S, however, resulted in yield increases. This finding emphasizes the negative effects of tea residue on phosphate solubilizing and sulfur oxidizing microorganisms. This experiment also showed that adding phosphate solubilizing microorganisms to sulfur or thiobacillus containing treatment mixtures would lead to lower yields indicating the negative effects of the two microorganisms. The efficiency of treatment 2 (triple super phosphate) was greater for the first and second cuttings and showed significant differences with respect to the other cuttings, whereas with the third cuttings even though the maximum yield was obtained with triple super phosphate treatment (14.66 gr/pot) it was significantly the same as T10 (12.67 gr/pot), T11 (12.37 gr/pot) and T12 (12.01 gr/pot) at 5% level.