| dc.description | The aim of this work was to study the effects temperature and microbial activity on the decrease kinetic of availabile P in two different soil types. Surface soils were sampled from Guilan and Hamadan provinces in north and northwest of Iran with temperate and semiarid climates. The availability of P in soil samples was studied in two (sterile and unsterile) conditions after addition of 400 mg P kg-1 soil as KH2PO4. Treated soil samples incubated in field capacity up to 2880 h at 15 and 28 0C in 3 replicates. Separate batches were taken after 0.16, 0.5, 1, 3, 12, 24, 48, 168, 336, 720, 1440, 2160, and 2880 h for extraction with 0.5 M NaHCO3- Temperate soils had higher clay content, cation exchange capacity (CEC), organic carbon (OC), total nitrogen, biological activity, amorphous and crystalline Fe and Al, but semiarid soils had higher sand content, pH, equivalent carbonate calcium (EEC), available P and K. Soil properties and sterilization had significant effect on P bioavailability after soil treatment with P fertilizers. The temperate soils with high affinity surface sites for P sorption compared to semiarid soils, had a lower available P in each time of extraction. Soil sterilization reduced the rate of P sorption/precipitation processes in initial step. The NaHCO3-extractable P in sterilized soils decreased continuously in first 30 days of soil incubation. After that soil available P did not decrease in sterilized soils significantly. However in unsterile soils after the initial decrease of available P, the bioavailability of P due to soil microbial activity increased. In sterile soils the first order equation, second order equation, Elovich kinetic equation, and power function equation could describe the adsorptive/precipitate process. The second order model and Elovich kinetic equation were selected to express the sorption/precipitation behavior in sterile soils because of the high R² values. The models selected suggest that the sorption mechanism in sterile soils is greatly chemisorption process. However in unsterile soils incubated at 15°C the suitability of the tested equations was considerably low. This study showed that soil biological activity had considerable effects on available P and its decrease kinetic after P addition to soil. | |
