Extractable Phosphorus Contents of Some Soils of Bangladesh and Their Correlation with Phosphorus Concentration in Rice Leaves

Abstract

To observe the availability of phosphorus by different extraction methods in some cultivated soils of Hathazari Upazilla of Chittagong District, this study was carried out with 36 surface soil samples (0 - 15 cm) belonging to six soil series, namely Bijipur, Pahartali, Mirsarai, Manu, Raojan and Noapara. Physical and chemical characteristics of the soils were also determined with an objective of identifying the soil factor(s) regulating P extractability. Three P extraction methods, namely Olsen (0.5 M NaHCO3, pH 8.5), Mehlich-3 (0.2 N CH3COOH + 0.013 N HNO3 + 0.015 N NH4F + 0.25 N NH4 NO3 + 0.001 M EDTA) and Bray & Kurtz-1 (0.03 N NH4F + 0.025 N HCl) were used. There was a wide variation in the extractability of P ranging from low to high categories. Olsen method extracted the largest amount of P (2.07 - 45.36 mg·kg-1) while Bray & Kurtz-1 extracted the smallest amount (1.02 - 21.79 mg·kg-1). The mean extractable P in soils was found to be in the order of Olsen > Mehlich-3 > Bray & Kurtz-1. Soil pH was the most dominant factor in determining P extractability. Available P was negatively correlated with percentage of clay, organic carbon and CEC and positively correlated with pH. Although the three methods extracted different amounts of P from soil, values of P extracted by the different methods were strongly correlated among themselves and with the leaf phosphorus concentration of rice growing in these soils.