Fixation of soluble forms of fertilizer phosphorus in salt affected soils of Ramanathapuram and Trichy districts and acid soil of Ariyalur district of Tamil Nadu

Soluble phosphorus (P) applied through phosphatic fertilizers is quickly converted into low soluble P compounds in soil.  For evaluating fixation ability of P fertilizers laboratory incubation experiments were conducted with saline, sodic and acid soils. Phosphatic fertilizers selected were single super phosphate (SSP), diammonium phosphate (DAP), monoammonium phosphate (MAP), monopotassium phosphate (MPP) and 19:19:19 N, P2O5, K2O % (All-19). Fixation of P was computed based on the amount of P recovered after addition of P in the soil in increasing levels. At a typical P addition at 16 kg ha-1 the results were compared in all soils. In saline soil, high fixation of P occurred when DAP (12.18 kg ha-1) and MPP (11.28 kg ha-1) were applied. In sodic soil, high fixation of P resulted when SSP (7.10 kg ha-1) was applied. In acid soil, high fixation of P occurred when All -19 (12.64 kg ha-1), MAP (12.40 kg ha-1), SSP (12.22 kg ha-1), and DAP (11.74 kg ha-1) were applied. With all forms of phosphatic fertilizers fixation of added P occurred to the extent of 57.9 to 79.0 per cent in acid soil, 55.0 to 70.5 per cent in saline soil and 25.5 to 44.4 per cent in sodic soil. In saline soil availability of P might be higher for SSP and All-19 compared to ammonium/ potassium phosphate fertilizers. On the other hand, MPP, MAP and All-19 may be preferably applied in sodic/ acid soils alternative to SSP or DAP for realizing higher P release in soils from added fertilizers for the benefit of crop utilization