Abstract
Pig manure (PM) is often highly enriched in heavy metals, such as Cu and Zn, due to the wide use of feed additives. To study the potential risks of heavy metal accumulation in the soil and rice grains by the application of PM and other organic manure, a four-year field experiment was conducted in the suburb of Shanghai, southeast China. The contents of Cu, Zn, Pb, and Cd in the soils and rice plants by the treatments of PM and fungal culturing residues (FCR) show a trend of annual increase. Those in the soils and rice by the PM treatment are raised even more significantly. Cu and Zn contents in the soil and rice roots by the PM are significantly higher than those by the non-fertilizer control (CK) during the four years, and Pb and Cd also significantly higher than CK in the latter two years. Heavy metals taken up by the rice plants are mostly retained in the roots. Cu and Zn contents in the rice plants are in the decreasing order of roots > grains > stems > leaves, and Pb and Cd in the order of roots > stems > leaves > grains. Cu, Zn, Pb, and Cd contents in the soils by the PM treatment increase by 73%, 32%, 106%, and 127% on annual average, and those in the brown rice by 104%, 98%, 275%, and 199%, respectively. The contents of Cu, Zn, Pb, and Cd in the brown rice of the treatments are significantly correlated with those in the soils and rice roots (p < 0.05), suggesting the heavy metals accumulated in the rice grains come from the application of PM and FCR. Though the contents of heavy metals in the brown rice during the four experimental years are still within the safe levels, the risks of their accumulative increments, especially by long-term application of PM, can never be neglected.
Highlights
Excessive application of chemical fertilizers often leads to agricultural diffuse pollution, causing the eutrophication of surface water and contamination of groundwater [1]
Cu content in the brown rice of Pig manure (PM) attains 2.94 mg/kg in the fourth year, which is 2.0, 1.1, and 1.2 times that of CK, AB, and FV, respectively. This suggests that the application of PM and fungal culturing residues (FCR) has already posed a risk of heavy metal accumulation in brown rice, and the risk caused by the application of PM is much higher
The applications of PM and FCR to the paddy fields raise the contents of OM and nutrients in the soils significantly and increase grain yield effectively
Summary
Excessive application of chemical fertilizers often leads to agricultural diffuse pollution, causing the eutrophication of surface water and contamination of groundwater [1]. Long-term application of PM significantly increases the contents of organic matter and nutrients in soils [4]. During the four experimental years, the contents of TK and AK in the PM, AB, and FV soils are significantly higher than CK (p < 0.05). During the four experimental years, the contents of Cu, Zn, Pb, and Cd in the PM, AB, and FV soils show a trend of annual increase, which are mostly higher than CK (Figure 6). Pb content in the PM soil in the latter two years is 1.9 and 2.1 times higher than CK (Figure 6c), and Cd content is 1.2 and 2.3 times hi5gohfe1r8 than CK (Figure 6d), respectively. Pb content in the PM soil in the latter two years is 1.9 and 2.1 times higher than CK (Figure 6c), and Cd content is 1.2 and 2.3 times higher than CK (Figure 6d), respectively
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