Abstract
Although inorganic and organic manures with high concentrations of heavy metals can lead to accumulation or contamination of heavy metals in soils, there are few reports on the effects of long-term application of swine and green manures on the accumulation of heavy metals in rice grains in paddy soils. A long-term field experiment, which was established in 1990 in paddy soil in Hangzhou, China, was used to investigate the effects of inorganic and organic manures on the availability and accumulation of heavy metals in soil and uptake by rice plant. The results showed that long-term application of nitrogen, phosphorus and potash (NPK) plus green manure or swine manure, and swine manure only increased 202%, 146%, and 100% for total Cd, and 5.5%, 7.6%, and 6.6% for total Cu in rice grains, respectively compared to the control without fertilization. Total Zn in rice grain was significantly increased by 13.9% for the treatment of NPK plus green manure. The accumulation of Cd, Zn, and Cu in rice grains after long-term application of swine and green manures is due to the combined effects of the increased concentrations of total and EDTA extractable Cd, Zn, and Cu in soil and the changes of soil properties. Furthermore, the highest bioconcentration factor for Cd was found in the treatment of NPK plus green manure while for Zn and Cu it was observed in NPK treatment. Thus, it may be concluded that green manure and manure with increased Cd, Zn, and Cu in rice grain results in a potential risk of metal accumulation in paddy soils.
Highlights
Cadmium (Cd) is a toxic heavy metal
Compared with CK, soil pH, soil organic matter (SOM) and cation exchange capacity (CEC) were increased NPK(GM), M, and NPKM treatments compared with CK, while they were decreased by NPK application
69% in NPK-treated plots, respectively. These results showed that inorganic fertilizer, and combining the application of inorganic and green manure fertilizers, promoted the bioavailability of heavy metals in rice grains
Summary
Cadmium (Cd) is a toxic heavy metal. copper (Cu) and zinc (Zn) are biological elements, excessive amounts of Cu and Zn can be detrimental to crop growth and can be added to the environment through atmospheric deposition, agro-chemicals and inorganic fertilizers, animal manure, and sewage sludge, etc. [1,2]. Fertilization is a traditional method to improve soil fertility and increase crop yield, but many studies have reported that fertilization causes heavy metal accumulation in soil. Some fertilizers containing a certain amount of heavy metals, such as Cd, were found in phosphate fertilizers [3,4]. While phosphate rocks contain many other components, such as uranium, and the accumulation of uranium in fertilizers needs to be investigated [5,6]. Due to the higher accumulation of Cd, Zn, and Cu in food crops, our analysis was focused primarily on these elements. The application of N fertilizers has been shown to increase Cd concentrations in durum wheat by 50% [7]. The application of green manure can increase heavy metal solubility since it contains soluble compounds that
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