Abstract

The current methods of predicting P availability in rice soils need reconsideration. Anaerobic conditions due to submergence of the soil creates problems of assessment of this nutrient element. A pot experiment using three soils of Tamil Nadu and IR 22 rice as the test crop was conducted. Soils equilibrated with diammonium phosphate at the rate of 100 kg/ha were transplanted with rice. The moisture levels, viz., submer- gence, field capacity and wetting and drying were maintained. Soil samples were drawn at stages and analysed for available phosphorus by Olsen's. Bray's No. 1, 0.01M CaCl and water extraction methods. Phosphate potential (1/2 pCa + pH.PO,) was calcula- ted for these soil samples and all these values were correlated with phosphorus uptake and yield at the crop. In assessing the phosphorus availability under different moisture regimes. the suitability of buffer curves was indicated and discussed.

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