Study on Correlation of Soil Properties and The Forms of Inorganic Phosphorus in Phosphorus recommendation in Qazvin Calcareous Soils

With the aim of evaluating the effective indices on P uptake efficiency under different cultivation patterns in calcareous soils, this research was designed and conducted in four experiments. In the First experiment, Phosphorus Fractions of selected calcareous soils of Qazvin province, Iran and their relationships with soil characteristics were studied as basic information on the status of phosphorus fractions in soil and understanding of soil chemistry that influence soil fertility. Amount and distribution of P in different fractions of 20 soil samples of Qazvin province, were determined by sequential extraction method. Their relationships with each other and with soil characteristics were determined. The ranges of soil characteristics and the amount of different P forms relative to the total P were determined to be as follows: clay from 18 to 52%, organic carbon (OC) from 0.28 to 1.3%, calcium carbonate equivalent (CCE) from 5 to 35%, active calcium carbonate (ACCE) from 2.9 to 19%, cation exchange capacity (CEC) from 15 to 34 cmol(c) kg-1 , Total P (Pt) from 700 to 1040 mg kg-1, dicalcium phosphate (Ca2-P) from 1.6 to 42, (1.1% of Pt ), octaclsium phosphate (Ca8-P) from 72 to 314, being (20.6% of Pt), apatite (Ca10-P) from 262 to 697 (45.1% of Pt), Al-Phosphate (Al-P) 15 to 55 (3.9% of Pt), Fe-Phosphate (Fe-P) 8.4 to 35 (2.5% of Pt), occluded P (O-P) from 5.9 to 33 (2.4 of Pt), olsen-P from 2.9 to 42 and solution P 0.47 to 13 mg kg-1. Soils were classified as Entisol , Inceptisol and Aridisol with clay mineralogy (2:1). The following order for inorganic phosphorous fractions: Ca10-P Ca8-P Al-P Fe-P O-P Ca2-P was determined. Simple correlation coefficients showed that clay had a positive and significant correlation with Fe-P and O-P. Organic-C had a negative significant correlation with Ca10-P and Pt. CEC had a positive significant correlation with Al-P, O-P, Ca10-P and Pt. A significant correlation was also observed between the P forms themselves, which is presumably a reflection of the existence of a dynamic relation between the chemical forms of an element in soil. Path analysis showed the positive direct effect of CCE on apatite and showed negative correlation between clay and CCE and positive correlation between CCE, exchangeable Ca and Ca10-P. Second experiment: The effects of growing corn plant on inorganic P fractions in 20 soils were studied in a factorial experiment and randomized complete blocks design (RCBD) in green house with three replicates to examine the influence of two levels of P fertilizers (0, 50 mg kg-1) for 20 selected soils with corn variety (SC 704). In a 6 weeks growing period variation of Olsen-P and soil inorganic phosphorus fractions and other factors in plant were studied. The results indicated that, effects of soil type and P fertilizer levels on inorganic P fractions were significant. So that all of P fractions except Ca10-P with application of P fertilizer increased. Ca2-P and Olsen-P had the most increase. In the blank treatments, after six weeks in most of the soils Ca2-P, Al-P, Fe-P, O-P and Ca10-P decreased and Ca8-P and Olsen-P increased while for phosphorus applied treatments in most of soils P fractions increased and the highest increase was for Ca2-P. The range of agronomical efficiency, physiological efficiency, percent recovery and fertilizer efficiency were different among the soils. There was a positive linear regression between P uptake and Olsen-P, Ca2-P, Al-P, Pt. Critical level of P in soil with Cate-Nelson method 9 mg kg-1, sufficiency level of P in shoot of corn using DOP method 0.23%, C coefficient of Mitcherlich-Bray model 0.21 was obtained.