Distribution of Inorganic Phosphorus Fractions in a Calcareous Soil Amended with Poultry Manure and Phosphorus Fertilizer at Different Times of Incubation

Organic amendments considerably affect balance of nutrients such as phosphorus (P) by influencing the chemical, physical, and biological properties of soil. In the incubation study, the effects of two levels of P (100 and 200 mg kg-1) from two sources (poultry manure and KH2PO4) on inorganic P (Pi) fractions were investigated during 90 d (5, 15, 30, 45, 60, and 90 days). Phosphorus fractions were sequentially extracted with water (H2O-P), 0.05 M NaHCO3 (NaHCO3-P), 0.1 M NaOH (Al and Fe bound P) and 1 M HCl (Ca-P). The results showed that most of soil Pi in the control treatment was present in the HCl-P fractions (102-187.4 mg kg-1). Poultry manure and KH2PO4 application significantly increased NaHCO3-P, NaOH-P and HCl-P. Labile Pi fractions (NaHCO3-P and NaOH-P) were increased after organic and inorganic P amendments and then converted to most stable Pi fraction, Ca-P, by the end of the incubation period. This transformation was more severe for KH2PO4 amended soil indicating that poultry manure allowed P to be retained in more labile fractions for a longer period. Supporting this idea, highly significant correlation (r=0.81-0.93, P<0.01) was found between NaHCO3-P and available P in all incubation times. According to the results of the study, combined use of poultry manure and chemical P-fertilizer in calcareous soils could act as a source of plant available P.