Studying Inorganic Phosphorus Fractions in Cultivated and Virgin Fields around Yasouj

The present study was conducted to evaluate the effect of agriculture on phosphorus (P) accumulation and changes of inorganic P fractions in some soils around Yasouj. Ten pairs of agricultural and virgin fields adjacent to each other were selected and composite soil samples were taken of each land use in three replications from the depth of 0-30cm. After sample preparation, inorganic P fractions were determined by successive extraction with NaHCO₃ (NaHCO₃-P), NH₄OAc (NH₄OAc-P), MgCl₂ (MgCl₂-P), NH₄F (NH₄F-P), NaOH-Na₂CO₃ (HC-P), citrate-dithionite-bicarbonate (CBD-P), and H₂SO₄ (H₂SO₄-P). Statistical analysis was carried out based on paired factorial in a completely randomized design. Results showed that agricultural land use significantly increased all of the P fractions except HC-P at 1% level. Sum of the inorganic P fractions in agricultural fields were 64 to 318 mg kg^-1 higher than those of virgin soils. Averages relative increases of various fractions' were NaHCO₃-P 5.2%, NH₄OAc-P 18.8%, MgCl₂-P 8.4%, NH₄F-P 12.2%, HC-P 0.22%, CBD-P 15.1% and H₂SO₄-P 39.4%. Results indicated the high amount of P fertilizers application and accumulation in the region. In addition, results indicated that there was the probability of transformation of applied P to stable Ca-P compounds.