CHARACTERIZATION OF SOIL-FERTILIZER P REACTION-PRODUCTS AND THEIR EVALUATION AS SOURCES OF P FOR GRAM (CICER-ARIETINUM L)

Laboratory studies on the characterization of soil-fertilizer P reacti on products were carried out by reacting three - soils occurring in a toposequence in the plateau region of Bihar (India) with saturated sol utions of diammonium orthophosphate (DAP), triple superphosphate (TSP) and ammonium polyphosphate:(APP) for 1 hour and 24 hours. The reactio n products (precipitates) formed in the solutions after 120 days of in cubation were isolated and identified through X-ray diffraction techni que. Results indicate the formation of Brushite [CaHPO4 . 2H(2)O), Str engite (FePO4 . 2H(2)O), Variscite (AIPO(4) . 2H(2)O) and Fe-4 (P2O7)( 3) as major soil-fertilizer P reaction products in these soils with or tho-and polyphosphates as source of phosphorus. Pot cultures were used to evaluate the relative efficiency of reaction products (Struvite, B rushite, Variscite and Strengite), orthophosphates (DAP and SSP) and p olyphosphate (APP) as sources of P for gram (Cicer arietinum L.) in a typical acid soil. Results indicate significant response of gram to di fferent sources and level of added P The dry weight and P uptake at 0, 6 and 12 mg P kg(-1) soil were 0.406, 0.519 and 0.609 (g pot(-1)); an d 0.289, 0.428 and 0.575 (mg P pot(-1)), respectively. Among the sourc es, struvite proved to be superior or equally effective as APP, DAP or SSP as sources of P for gram. Uptake of P also varied significantly w ith different P sources and levels of P application. Strengite was lea st effective in enhancing yield and P uptake by the crop.