Phosphate Transformation under Continuous Submergence in Rice-Barley Rotation

Total inorganic soil P increased in all the plots receiving high water-soluble phosphate (WSP) in straight (TSP), mixed (75% or 100% WSP with urea) and complex (NP-53.7% WSP) fertilizers. Diammonium phoshate however, showed comparatively lower value in both the years. The Al-P was the second dominating fraction next to Ca-P in the first year and Fe-P in the second year indicating the conversion of Al-P to Fe-P with passage of time.

Inorganic phosphate fractionation studies indicated that phosphatic fertilizers containing 50 to 75% WSP are needed for rice crop even under flooded condition as they transform to Fe-P (Fe-P, RSFe-P and occluded Fe-P) which in turn contributes significantly to available P in alkaline alluvial soils with high Ca content whereas water insoluble sources (DCP and RP) are inferior in such soils because of their reversion to insoluble calcium phosphate compounds. The grain production of rice was associated with Fe-P and that of barley with Ca-P in rice-barley sequence.