Effect of Organic and Inorganic Amendments on Phosphorus Fractions in Soils under Submerged Condition

Abstract

A laboratory experiment was conducted to document the effect of organic and inorganic amendments on soil P fractions under submerged conditions and to gain understanding of the changes in different P pools under prolonged submergence. Initial soil samples were collected from cultivated rice fields in Sreepur (Aerie haplaquept), Bangladesh Rice Research Institute (BRRI) Farm, Gazipur (Vertic haplustept) and Satkhira (Vertic haplaquept) and were incubated (28° ± 2°C) under submerged conditions in plastic pots amending with cowdung, poultry manure @ 10 t ha^-1 each and triple super phosphate (TSP) @ 25 kg P ha^-1 individually. The Sui fractionation scheme [dividing soil P into six empirical fractions (solution-P, labile-P, inorganic-P, organic-P, acid-P and residual-P)], with some slight modification, was employed at two intervals, 60 and 120 days after submergence (DAS). The solution-P, labile-P and inorganic-P fractions were increased significantly due to the use of organic amendments but TSP did not increase those fractions significantly. The organic-P pool (NaOH-Po), although contributing the largest fraction of soil P, was not greatly affected by any of the amendments but it was noticeably reduced with the application of poultry manure. Acid-P (HC1 soluble-P) significantly increased due to the application of cowdung and poultry manure amendment and it jumped tremendously up to (140-1400%) at 120 DAS from that of 60 DAS. The relative change (%) in acid-P between two periods of measurement was found significantly higher in control than manure amendments. A slight increase in residual-P was observed due to the use of organic amendments. Three soils varied greatly in different P pools where Satkhira soil ranked at the top, followed by BRRI and Sreepur soil. Solution-P, labile-P and organic-P were larger at 60 DAS than at 120 DAS, while inorganic-P (NaOH-Pi) and acid-P were higher at 120 DAS than at 60 DAS due to the longer period of submergence. In addition, residual-P remained stable and these trends were very pronounced in the case of the poultry manure treated soils in most cases.