Speciation Variation and Bio-Activation of Soil Heavy Metals (Cd and Cr) in Rice-Rape Rotation Lands in Karst Regions.

Jiachun Zhang,Guiting Mu,Xianfei Huang,Zhenming Zhang,Hui Fang

doi:10.3390/ijerph18031364

Abstract

Heavy metals in soil are in a high background state in Karst areas, and agricultural activities will affect the bioactivity of heavy metals. The heavy metal (Cd and Cr) bioactivity and their activation effects in rice-rape rotation lands in Karst areas were studied based on field experiments and laboratory analysis, and the influencing factors of heavy metal activity were analyzed based on the physical and chemical properties of soil. The results suggest that the residual fraction was the largest and the exchangeable fraction was the smallest for both Cr and Cd in rice-rape rotation lands in Karst areas. During the rice-rape rotation process, Cd and Cr tended to be released from the residual fraction and transformed into the other four fractions. The fractions with high bioactivity, including the exchangeable fraction and carbonate fraction, increased to different degrees. Rice-rape rotation could activate the activity of soil Cd and Cr in Karst areas. It is also revealed that the activity of soil Cd and Cr in Karst areas was closely associated with soil pH and electric potential (Eh). In the 0–20 cm soil layer, Cr showed a significant negative correlation with pH (r = −0.69, p < 0.05), while both Cr and Cd showed significant negative correlations with Eh, and the correlation coefficients were −0.85 (p < 0.01) and −0.83 (p < 0.01), respectively. In the 20–40 cm soil layer, Cr showed significant negative correlations with Eh, and the correlation coefficient was −0.95 (p < 0.01). No significant correlation between the activity of soil Cd and Cr and soil mechanical composition was observed. This study revealed that special attention should be paid to changes in pH and Eh in consideration of heavy metal activity in the rice-rape rotation process.

Highlights

Cultivated land resources are fundamental materials for human survival and development, and they are nonrenewable resources [1]
0–20 cm soil the layercontents except during period, During the period rape growth, of Crthe in harvest the 20–40 cmas soil layer were listed in Table
During the period of rice growth, the 0–20 cm soil layer in the seedling and bolting periods, and an inverse phenomenon the contents of Cd in both the 0–20 cm and 20–40 cm soil layers decreased during the was observed florescence and harvest periods

Summary

Introduction

Cultivated land resources are fundamental materials for human survival and development, and they are nonrenewable resources [1]. China’s cultivated land area is 122 million hectares, and the world’s existing cultivated land is 136,911 million hectares. China’s cultivated land area accounts for 7% of the world’s existing cultivated land area. In China, cultivated land resources are limited, and reserve resources are insufficient [2]. Since the 1950s, the production performance and utilization value of soil have been declining due to the rapid development of modern industrial and agricultural production, the large application of pesticides and chemical fertilizers, and the continuous invasion of atmospheric dust and sewage on farmland [3]. The degradation of farmland soil quality is a serious threat to food security. The effect of these efforts is not obvious, and feasible methods are still in the research process [5]

Objectives

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Results

Conclusion