Phosphorus mineralization in an alluvial soil as influenced by organic manure addition and time of incubation

Abstract

Transport of phosphorus (P) from agriculture often causes eutrophication of surface water systems, which is particularly a concern in alluvial soil regions because of coarse texture and intermediate water and cation exchange capacity. Organic residues are increasingly being applied to soil because of their ability to increase soil organic carbon that also improves soil physical, chemical and biological properties. However organic manures contain variable amounts of phosphours, which upon mineralization gets released, and is of environmental concern. To evaluate the risk of P losses, an experiment was carried out in an alluvial soil with three manures viz., farm yard manure (FYM), oil cake and pig manure, incubated at the rate of 4, 40, 80 t ha-1 for a period of 2, 72, 168, 336, 480, 1440, 2160 hours at constant temperature and moisture and net phosphorus mineralized was evaluated. It was found that the three manures differed widely in their C, N and P content and C/N and C/P ratios and consequently the mineralization pattern differed. FYM had higher C/P ratio as compared to oil cake and pig manure; consequently the net P mineralized in pig manure was the highest at all rates of P addition followed by oil cake and FYM throughout the time intervals studied. It was concluded the there was greater risk of P losses from high doses of pig manure addition in alluvial soils as compared to oil cake and FYM. Hence it was suggested that manures with different C/P ratios could be mixed to maintain a reasonably high P supplying capacity in soil at the same time the risk of P losses could be avoided.