Main content area

Transformation of fertilizer P in a Vertisol amended with farmyard manure

Reddy, K.S., Rao, A.S., Takkar, P.N.
Biology and fertility of soils 1996 v.22 no.3 pp. 279-282
Vertisols, phosphorus, nutrient availability, phosphorus fertilizers, mixtures, organophosphorus compounds, low input agriculture, application rate, animal manures, inorganic phosphorus
Availability, fixation, and transformation of added P were studied in a 16-week incubation experiment with a Vertisol amended with farmyard manure in pots with 500 g soil each. P availability, as measured by Olsen P, decreased for up to 8 weeks with various rates of added P, when no manure was applied. In the presence of farmyard manure, P availability decreased during the first 6 weeks and then showed a considerable increase from the 8th week onwards. P fixation increased for up to 8 weeks with the rates of P in the absence of manure. With manure application, P fixation increased only during the first 6 weeks and thereafter decreased continuously. Thus the presence of farmyard manure shortened the period of P fixation and promoted its availability. After 16 weeks of incubation, when manure and fertilizer P were applied together, P was transformed into labile organic (NaHCO3-P), moderately labile organic P (NaOH-P), and calcium-bound inorganic P (HCl-P). When manure was not applied. P accumulated predominantly as labile inorganic (NaHCO3-P), moderately labile inorganic (NaOH-P), and inorganic HCl-P. The application of farmyard manure enriched long-term P fertility through NaHCO3-P and NaOH-P and a short-term P supply as HCl-P. All fractions except inorganic NaOH-P showed good relationships with Olsen P.