Submitted to: Journal of Environmental Quality
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/27/2006
Publication Date: 7/5/2007
Citation: Khoshgoftarmanesh, A.H., Chaney, R.L. 2007. Preceding affects cadmium and zinc of wheat grown in saline soils of central Iran. Journal of Environmental Quality. 36:1132-1136. Interpretive Summary: Excessive dietary cadmium can cause human disease (renal tubular dysfunction). Previously, paddy rice has been the cause of observed Cd disease due to soil and food contamination. Recently it has been observed that application of phosphate fertilizers with high cadmium levels had occurred in Iran for about 30 years, and under the conditions of their soils, wheat grain may accumulate high enough Cd levels to comprise lifetime risk to consumers. It is recognized that high soil chloride levels increase uptake of Cd by most plant species and these soils are saline and continue to be irrigated with chloride rich waters. Part of the area is Zn deficient which substantially increases Cd accumulation in wheat grain. In addition, the preceding crop in a crop rotation may affect Cd accumulation in wheat grain. Wheat is important as it is the dietary staple grain of the Iranian people. The present study was conducted to learn if preceding crop affected Cd accumulation in wheat grain in the Cd contaminated soils in Iran. Two farm fields with significant Cd enrichment were cropped with cotton or sunflower in 2001, and the crop residue removed. In the Fall of 2001 wheat was sown and harvested in 2002. All plant tissues and soils were analyzed for Cd and Zn using appropriate quality assurance. Although sunflower shoots accumulated significantly more Cd than did cotton shoots, with the removal of the crop residues, wheat accumulated significantly lower concentrations of Cd in grain grown on soils following sunflower than following cotton. Thus one farming practice that can reduce the concentration of Cd in wheat grain of Iran even on these Cd enriched soils is growing sunflower and removal of the crop residue before growing wheat. When combined with Zn fertilization, crop rotation management can help farmers achieve the limits allowed for Cd in wheat grain.
Technical Abstract: Enhanced Cd concentrations in wheat grain produced on saline soils of central Iran have been recently reported. Considering that wheat bread is a major dietary component for the Iranian people, finding some practical approaches to decrease Cd concentration in wheat grain were investigated. Thus, the purpose of this study was to investigate the influence of sunflower-wheat and cotton-wheat rotations on reducing labile Cd and its uptake by wheat in salt-affected soils. Two field experiments with different levels of Cd contamination (1.5 and 3.2 mg total-Cd kg-1 dry soil) and two different rotations (cotton-wheat and sunflower-wheat) were conducted in Qom province, central Iran. Seeds of cotton (Gossypium L.) or sunflower (Helianthus annuus L. cv. Record) were planted in plots. After harvesting of the plants (sunflower and cotton residues were removed in accordance with local practice), wheat (Triticum aestivum L. cv. Rushan) was seeded in all plots. Before and after wheat harvest, soil Cd concentrations were extracted using 0.04 M EDTA and 1 M CaCl2. Cadmium concentrations were determined in the shoot and grains of plants. For both studied soils, the concentrations of Cd extracted by EDTA and 1 M CaCl2 were significantly (P<0.05) greater after cotton than after sunflower. Accordingly, the total amount of Cd in sunflower shoot was significantly (P0.05) greater than in the cotton shoot. Shoot Cd content in wheat plants grown after cotton and sunflower were significantly different and in particular, wheat shoots after cotton accumulated more Cd (2-4 times) in their shoots. In particular, wheat grain Cd concentration after sunflower was much lower than after cotton. The results of this study showed that sunflower in rotation with wheat in salt-affected soils of central Iran significantly reduced the risk of Cd transfer to wheat grain.