Abstract
Effectiveness of residual phosphate was determined in 13 Pakistani soil series and an English soil, by the isotopic exchange method. Phosphate (31P) was added to each soil to fulfill the maximum P sorption capacity. The soils after addition of phosphate were incubated at 10, 25 and 45 °C for 365 days to extend the observations equivalent to many years under field conditions. After one year of incubation, exchange with carrier free 32P was measured. Results showed that the isotopically labile P (E values) decreased as temperature increased. A poor correlation was found between CaCO3 and E values suggesting that high pH (Na), organic matter and reactivity of CaCO3 control the ability of CaCO3 in these soils to decrease labile P. The labile P in these soils decreased as the Olsen P decreased with time and this relationship was well described by the power equation. A linear relationship between solution P (intensity factor) and labile P (quantity factor) was found in these soils. It is concluded from this study that the residual effectiveness of phosphate varies from soil to soil, and increasing time of contact and temperature have a marked effect on its amount in a soil.
S. Javid*, D.L. Rowell2. (2010) Assessment of residual effectiveness of applied phosphate by the 32P exchange method , The Journal Soil & Environment , Volume 29, Issue 2.
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