Assessment the Effect of Different Planting Pattern (Rice-Wheat, Corn-Wheat) and Growth Stage on Soil Chemical Properties

Conducting research on monitoring contaminated fields by heavy metals is necessary in order to achieve sustainable agriculture, increase product quality and keep public health. This study was carried out using split plot experiment based on randomized complete blocks design with three replications during 2014-2015 in Shavor Agricultural Research Center in order to evaluate the effect of cropping systems and different growth stages on arsenic content and other chemical properties of conventional cultivation. The main factor consisted of planting pattern at two levels (rice-wheat and corn-wheat), and the sub-factor included different growth stages in three levels (Tillering, flowering, and maturity). The results of the analysis of variance showed that the effect of cultivation system on concentration of arsenic, cationic exchange capacity, electrical conductivity, soil organic matter, phosphorus concentrations, pH, and concentration of soil lime was significant at 1% level. The effect of different growth stages on all traits except of electrical conductivity (at 5% level) was non-significant. The interaction effects of the treatment on all traits were non significant. According mean comparison rice-wheat cropping system had more arsenic concentration (8.68 mg.kg-1) than corn-wheat cropping system (6.73 mg.kg-1). Comparison of different growth stages showed that soil electrical conductivity decreased over time; therefore, the lowest concentration was found in maturity stage (2.62 ds.m-1) that was affected by continuous irrigation. Arsenic and phosphorus are absorbed via similar system by plants because of they are analog; so low concentration of phosphorus and high concentration of arsenic lead to the activation of the absorption system which results in increased absorption of arsenic compared to phosphorus. Finally use of phosphorus fertilizers based soil test is recommended according standard of soil and water Institute.