Influence of Different Moisture Regimes on the Transformation of Applied Phosphate in Rice Soils and Its Availability to Rice Plants

The influence of three moisture regimes, namely, (i) air dried, (ii) submerged, and (iii) moist at field capacity, prior to flooding on the transformation of applied P in soils and its availability to rice plants was studied with three rice soils of West Bengal. The results showed that the moist treatment could maintain a higher amount of added P in the water soluble, salold bound and Truog's available form in the Canning soil, which was neutral to slightly alkaline in reaction and contained lesser amount of free Fe₂O₃ as compared to the other two soils, but no such effect was found in the Sriniketan soil, which was acidic in reaction and contained higher amount of free Fe₂O₃. The moisture condition prior to flooding did not appear to influence the transformation of applied P into Al-P form. The transformation into Fe-P was lower under submerged treatment as compared to that in the air dried and moist treatments. The latter treatment was found to cause lower fixation as Ca-P. Transformation into reductant soluble Fe-P with each of the three soils studied was very small and as such no effect of the moisture treatments could be observed.

The moist treatment was found to record higher increase in dry matter yield over the no-P control and higher P concentration in the plant material, as compared to that in the other moisture treatments. The total uptake of applied P during 60 day period of growth was very low, but it was found to be highest under the moist treatment.