Phosphorous Sorption as Affected by P Sources in Soils Varying in Organic Matter Content

摘要

The effect of four phosphatic fertilizer materials viz., diammonium phosphate (DAP), single super phosphate (SSP), ammonium nitrophosphate (ANP) and narmadaphos (NP) on the adsorption and desorption behaviour of four soil samples exhibiting variationin organic carbon was studied in a laboratory incubation experiment. There existed a wide variability in the amount of P to be added through different sources to obtain a specific equilibrium P concentration in soils varying in organic carbon. Langmuir adsorption maxima (a) values decreased with increasing organic carbon content df soils, irrespective of the source of P addition. On the other hand, bonding energy values (b) exhibited a reserve trend irrespective of the soil and P source. Computation of'a' and 'n' values pertaining to Freundlich isotherms and supply parameter constants (k_1 and k_2) also exhibited more or less the similar trend. A decrease in Dm values "occurred with increase in organic carbon content. Among the P carrier, Dm values followed the following trend-DAP>SSP>ANP>NP. Likewise, Kd values exhibited an increase with an increase in organic carbon content. In a low organic carbon soil, upto 15 days reaction time, dicalcium phosphate (DCP) was the main P compound. Later on, it wasfound to be octcalcium phosphate (OCP) upto 60 days beyond which conversion of tricalcium phosphate (TCP) and hydroxy apatite (HA) was observed at 120 and 180 days equilibration time. Application of P through different P sources to a low OC soil changedthese to dicalcium phosphate dihydrate (DCPD) within 24 h reaction period, which continued to persist till seven days of incubation. In high OC status soil, DCPD was the main P compound after 24 h of equilibration time. This compound continued to exist at 60 days reaction time and got converted to OCP afterwards (upto 180 days).