Study On The Ecological Safety Threshold Of Cadmium In Agricultural Soil Under Different Farming Systems

The ecological safety threshold of heavy metal in agricultural land is an important basis for the environmental quality benchmark and standard revision of agricultural land soil.It is affected by many factors,and most of the current research focuses on the physical and chemical properties of soil,crop varieties and types,etc.The impact of the farming system in the activity has not been considered,especially the research on the ecological safety threshold of heavy metals in agricultural land under different farming systems based on the species sensitivity distribution method has not been reported.Therefore,based on the species sensitivity distribution method,this paper selects three main farming systems-Xiangtan,Hunan,Hechi,Guangxi,and Shaoguan,Guangdong——the typical cadmium contaminated areas in southern China—as rice–fallow,rice–rice,and rice–vegetable.Through field experiments in two consecutive years?2018-2019?,the ecological safety thresholds of agricultural land soil cadmium in different areas under the same farming system and different farming systems in the same area were derived,and their rationality was demonstrated.The main research results are as follows:?1?The change of basic soil properties under different farming systems in the same area is generally not significant?p>0.05?.One-way ANOVA analysis of soil pH,soil organic matter,cation exchange capacity and total soil cadmium content under different farming systems in the same area showed that the soil pH,soil,rice-rice and rice-vegetable farming systems in Xiangtan,Hunan,Hechi,Shaoguan,Guangdong,and Shaoguan,Guangdong soil organic matter,cation exchange capacity and soil total cadmium content have some differences,but the overall change is not significant?p>0.05?.?2?The sensitivity of crops to cadmium under different farming systems in the same area has obvious differences within and between species,and the sensitivity of crops to cadmium in different areas under the same farming system also has obvious differences,but the crops under different test cycle conditions The order of sensitivity to cadmium is basically the same,and rice varieties and vegetable varieties with high cadmium sensitivity and high enrichment ability,low sensitivity and weak enrichment ability,and medium sensitivity and enrichment ability are selected.?3?The ecological safety thresholds of soil cadmium in agricultural land under rice-fallow,rice-rice and rice-vegetable farming systems in Xiangtan,Hunan Province in 2018 and 2019 are 0.35,0.27,0.31mg·kg-1 and 0.33,0.28,0.26 mg·kg-1;Guangxi Hechi was 0.46,0.38,0.23 mg·kg-1 and 0.48,0.38,0.25mg·kg-1,respectively,which showed that rice-holiday was greater than rice-rice and rice-vegetable farming systems.In Shaoguan,Guangdong,2018 and 2019,the ecological safety thresholds of soil cadmium in agricultural land under rice-fallow,rice-rice and rice-vegetable farming systems were 0.27,0.24,0.29 mg·kg-1 and 0.27,0.23,0.32 mg·kg-1,respectively.Showing that rice-vegetable is larger than rice-fallow and rice-rice farming systems.?4?Based on the BCF of crop cadmium in different regions and the corresponding soil physi cal and chemical properties,the bioavailability models of cadmium in soil-rice and soil-vegetabl e systems were lgBCF=-1.385p H-1.640lgSOM-0.468lgCEC+10.865?R²=0.704,p<0.01,n=240?and lgBCF=-0.201p H+1.070lgSOM-0.622lgCEC-0.484?R²=0.646,p<0.01,n=60?.Using the above mod el to normalize the BCF of crop cadmium in different regions,the intra-species variation coeffi cients decreased significantly,indicating that the normalization process can eliminate the effect o f soil physical and chemical properties on crop cadmium enrichment.?5?The ecological safety thresholds of agricultural land soil cadmium in Xiangtan,Hunan,Hechi,Guangxi,and Shaoguan,Guangdong under the rice-fallow farming system in 2018 and 2019 are 0.25,0.23,0.24 mg·kg^-11 and 0.29,0.28,0.28 mg·kg^-1,respectively.Under rice-rice farming system 0.22,0.21,0.25 mg·kg^-11 and 0.23,0.23,0.23 mg·kg^-1.Under rice-vegetable farming system 0.25,0.27,0.23mg·kg^-11 and 0.21,0.23,0.23 mg·kg^-1,respectively.Under the same farming system,the ecological safety thresholds of agricultural land soil cadmium in different regions are not obvious,and the differences in ecological safety thresholds of agricultural land soil cadmium in different test cycles are not significant.