Effect of Triple Superphosphate and Wheat Cultivation on Mineral Phosphorus Forms in Calcareous Soils of Qazvin Plain

Knowledge of soil phosphorus mineral forms is important in soil fertility and plant nutrition. This study was conducted to evaluate of mineral P fractions with addition of triple superphosphate fertilizer and wheat cultivation in incubation and greenhouse conditions. Incubation test was performed in three soil types: Dizan, Qaznin1 and Qaznin2 with various amounts of available P which in each soil 50 mg kg-1 P used from triple super phosphate. Soil's P fractions including: Ca2P, Ca8P, AlP, FeP, OP and Ca10P were measured at 0, 45 and 90 days of incubation based on a complete randomized block design with three replications. Results showed that soil type effect on fixation of mineral P under incubation conditions and Dizan soil ranked in the first place. In this soil, Ca2P: 67.5 and 73.8%, Ca8P: 74.5 and 59.7%, AlP: 31.9 and 50.3 %, FeP: 47.9 and 63.7%, OP: 50.7 and 60% and Ca10P: 62.8 and 69% were more than Qaznin1 and Qaznin2, respectively. By addition of 50 mg kg-1 P from TSP, concentrations of Ca2P and Ca8P increased in all soils and more in Dizan. The highest concentrations of Ca2P, Ca8P, AlP, FeP and OP achieved by T45 and Ca10P by T90 times. Greenhouse trial was conducted on three soils mentioned with 50 mg kg-1 P used from triple super phosphate and cultivated with wheat based on a complete randomized block design with three replications. The concentration of mineral P was higher than other soils under wheat cultivation in Dizan. Comparison of mineral P fractions under incubation and greenhouse conditions proved a reduction in P concentrations for Ca2P: 30.63, Ca8P: 12.1, AlP: 7.17 and FeP: 3.33 mg kg-1. The amount of P fixation forms (Ca2P) had an obvious decrease in association with wheat planting in the greenhouse.