Document Type : Research Article
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Abstract
The objective of this research was to evaluate the rhizospheric effects of wheat on phosphorus (P) release kinetics in 10 calcareous soils under rhizobox conditions. The kinetics of P release in the bulk and the rhizosphere soils were determined by successive extraction with 0.5 M NaHCO3 in a period of 2 to 840 h at 25 ± 1°C. The results of kinetics study showed that mean of released P after 840 h of extraction period in the rhizosphere soils (192 mg/kg) was significantly lower than the bulk soils (207 mg/kg). A plot of cumulative amount of P released from both the rhizosphere and the bulk soils showed a discontinuity in slope at 168 h. Thus, two equations were applied to segments of the total reaction time (2 to 168 and168 to 840 h). Release kinetics of P from the rhizosphere and the bulk soils conformed fairly well to parabolic diffusion, simplified Elovich, power function and first order models in two segments. The correlation results showed that P released after 168 and P release rate constants of simplified Elovich, parabolic diffusion and first order equations in the rhizosphere and the bulk soils were significantly correlated (p≤0.05) with wheat plant indices. In second segment, P release rate constants of Elovich, and parabolic diffusion equations in the rhizosphere and the bulk soils were significantly correlated with wheat plant indices (p≤0.1). The results of this research indicated that wheat rhizosphere caused decrease of the P release rate and P release amount and release rate of P are important factosr in supplying available P to plants.
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