Chemical fractionation of phosphorus in calcareous soils of Hamedan, western Iran under different land use

We investigated the effects of land uses on P distribution and availability in selected calcareous soils under different management practices. KCl-P (labile P), NaOH-P (Fe-Al-bound P), HCl-P (Ca-bound P), and residual P (Res-P) fractions at 0-30 cm depth were determined for soils planted to garlic, orchard, pasture, potato, leafy vegetables, and wheat. Trends in P distribution between chemical fractions were similar between land uses. Ca-bound P was the most abundant P fraction in the soils, constituting between 61% and 78% of the total P, whereas P associated with labile was less abundant (<2%). Soils under leafy vegetables and wheat along with pasture presented the highest and lowest values in all fractions of P, respectively. Labile P generally was highest for leafy vegetables and potato. Labile P and Fe-Al-bound P comprised <1.4% and 8% of total P, respectively. Residual P ranged from approximate to 14% (potato and garlic) to 31% (pasture). Long-term fertilization increased P allocation to inorganic fractions, as Ca-bound P contained 78% of total P for potato and garlic and 74% for leafy vegetables but 61% for pasture. A strong positive correlation between labile P and Fe-Al-bound P (r = 0.534, p < 0.01), labile P and Ca-bound P (r = 0.574, p < 0.01), Ca-bound P and Fe-Al-bound P (r = 0.504, p < 0.01), Olsen-P and CaCl2-P (r = 0.821, p < 0.01) was found. Principal-component analysis showed that the first four components accounted for most of the variation, 32.5%, 16.9%, 12.9%, and 7.9% of total variation, respectively.