Phosphorus fractions in calcareous soils amended with P fertilizer and cattle manure

Studies on phosphorus (P) reactions over time and the role of organic matter in calcareous soils are important for developing P fertilizers and manure management practices. This study was conducted to determine the effects of time, soil properties and manure on Olsen-P and its chemical forms in calcareous soils. Eight soil samples were treated with two levels of inorganic P (0 and 300 mg kg− 1) and two levels of manure (0 and 1%, w/w). Olsen-P was determined at 2, 5, 10, 30, 60, 90 and 150 days of incubation. Phosphorus fractionated to NaCl + NaOH-P, citrate bicarbonate (CB-P), citrate bicarbonate dithionate (CBD-P), acetic acid-sodium acetate (OAc) and HCl (HCl–P) after 5, 30 and 150 days. Olsen-P, in P-treated soils, showed a positive correlation with the NH4OAc extractable Al and active CaCO3. Increases in recovery as CBD-P revealed that Fe oxides play an important role in P sorption during 0–30 days. The relative distribution of P fractions and Olsen-P followed the order of HCl–P > OAc-P > Organic-P > CBD-P > Olsen-P > NaCl-NaOH-P. The CB-P fraction was not measurable. Application of manure along with P increased the recovery of applied P and recovery as CBD-P compared with the P treatment. In general, manure application had an appreciable and different impact on the chemical fractions of P in calcareous soils as P from manure gradually turned into available forms over the time.