Changes in Phosphorus Fractions in Manure and Phosphorus Fertilizer Amended Soil of Southwestern Nigeria

Phosphorus (P) fractions are important forms of P in the soil which determines P availability, an important ion in the soil for plant use. Incubation study was conducted in the laboratory for ten weeks to study the changes in selected P fractions in an Alfisol (Iwo soil series) in the southwestern region of Nigeria amended with poultry manure and single superphosphate (SSP).
The soil was collected from the experimental field of the Institute of Agricultural Research and Training, Ibadan, Nigeria. Poultry manure at 0, 5, 10, 15 and 20 t ha-1 was applied in combination with single superphosphate (SSP) at 0, 15, 30, 45 and 60 kg P ha-1. The treatments were replicated three times and phosphorus fractions (Organic P, Fe-P, Al-P, occulded P and residual P) were determined before and at two weekly interval during the incubation studies using the Chang and Jackson method.
Significant increases in Fe-P and Al-P fractions were observed to the 6th week of incubation after which it started decreasing when poultry manure was applied solely and in combination with SSP. The sole application of SSP i.e. at 30 kg P ha-1 of SSP increased the recalcitrant P fractions while poultry manure reduced it. When Fe-P extractable with NaOH i.e. NaOH-Pi builds up it acts as a sink for P and this is achieved more when the poultry manure was combined with SSP. Application of 20 t ha-1 of poultry manure in combination with 30 kg P ha-1 of SSP increased the Fe-P availability and therefore a potential sink for P.