Soil Science Division, Bangladesh Institute of Nuclear Agriculture, Mymensingh 2202, Bangladesh.
* Department of Soil Science, Bangladesh Agricultural University, Mymensingh 2202, Bangladesh.
An investigation was undertaken with an dbjective of identifying the soil factor(s) regulating P extractability and delermining its critical limit for wetland rice. The study was made with four extractants in 19 selected soils of Bangladesh. The extractants ability to extract P followed the order: 0.05N HCI + 0.02N H2SU4 ≈ 0.25N NaHCO3-0.01N EDTA-0.01N NH4F ≈ 0.5N NaHCO3, pH 8.5 > 0.03N NH4F - 0.025N HCI. Possible reasons for variations in the amount of P extracted are discussed. Influence of soil pH was most dominant in P extraction. For the soils with low pH (< 6.0) the amounts of P removed by different extractants were positively correlated with organic matter content, whereas such correlation was negative in soils with high pH (> 6.0) indicating the stability of phosphorus-organic matter complexation at high pH Nelson's method (HCI + H2SO4) of P extraction was found most suitable for rice with 14 ppm as its critical limit.
P extraction, soil pH, critical limit, rice
