Heavy metal distribution, relationship and prediction in a wheat-rice rotation system

To study the heavy metal contamination and its transfer patterns in a wheat-rice rotation system in Dingshu, a typical industry county in China, 52 pairs of complete crop samples and corresponding soil samples (0-20 cm) were collected from this area. All samples were detected for the total concentrations of six heavy metals. Available factions and main soil properties were also analyzed. The results showed that Cd, Ni, Pb and Zn in both soil had moderate accumulation and these elements in corresponding grains exceeded their standard values to some extent. Most of these metals had higher concentrations in the eastern and central regions in both crop grains and the corresponding soils, which were related to the strong human activities in this region. In particular, the distribution of Cd in both soils and crops exhibited the most significant spatial correlation, whereas Cr had opposite trends. These elements in wheat and rice grains was related to different influencing factors and varied with different heavy metals. Cross-correlograms further quantitated the spatial influencing factors of elements in soils and various organs on crop gains. Cd prediction models for rice and wheat grains were stimulated based on nonedible organs and soil properties with a maximum r(2) of 0.748. These models are helpful to predict Cd accumulation in grains within wheat-rice rotation systems and thus allow farmers to reduce threats of heavy metals by adopting certain agronomic practices in different periods.