Studies On Safe Utilization Technology Of Cd Exceeding Standard Farmland In Typical Sewage Irrigation Areas

In the north of China,due to lack of resources,sewage is often used for agricultural irrigation,and the problem of cadmium(Cd)pollution in farmland soil caused by sewage irrigation and the quality and safety of crops produced in the soil have attracted more and more social attention.In this study,Cd-contaminated farmland soils in typical sewage irrigation areas were collected.Based on soil characteristics of sewage irrigation areas,combined with species sensitivity distribution(SSD)model,salt-tolerant and low-Cd-absorbed vegetables and wheat cultivars were screened for Cd-contaminated soil under salt stress conditions so as to provide reference for safe use of the contaminated soil.The effects of intercropping different herbaceous plants with water spinach and wheat on plants uptake and translocation of Cd and the mechanism of interspecific interaction were studied,and the remediation effect of different herbaceous intercropping on Cd-contaminated soil was evaluated in order to provide a basis for safe production and side restoration of Cd-contaminated farmland.The main results are as follows:1.Under salt stress,the salt tolerance index(STI)of the shoots of 15 different leafy vegetables ranged from 0.591(Watercress)to 1.023(Celery).Under the salt stress,the fresh weight Cd content of 15 different leafy vegetables ranged from 0.236 to 1.790,and the fresh weight Cd enrichment coefficient ranged from 0.179 to 1.356,which both followed the order of Watercress> Water spinach> Pterocladia tenuis> Chrysanthemum nankingense> Leek> Oilseed rape> Flowering cabbage> Spinach> Amaranth> Lettuce> Wuta-cai> Leaf lettuce> Chinese cabbage> Celery> Leaf mustard.By combing the species sensitivity distribution(SSD)frequency of cadmium biocentration factors(1/BCF)and salt tolerance index(STI),Leaf mustard,Celery,Chinese cabbage and Leaf lettuce were screened as the leafy vegetables cultivars characteristed with the low-Cd absorption and high salt tolerance.2.Significant difference(p<0.05)was observed for the growth inhibition to salt stress among the 10 wheat cultivars,obvious growth inhibition was observed for Zhongmai 415 and Zhongyou 206.The measured salt tolerance index(STI)for Zhongmai 415 and Zhongyou 206 were 0.542 and 0.591 respectively.Cd biocentration factors(BCF)by the shoots of different wheat cultivars ranged from 0.338 to 0.970,the BCF of Cd by roots ranged from 3.01 to 5.71.The distribution frequency based on the BCF-shoot among wheat cultivars followed the order of Zhongmai 996> Lunxuan 1690> Zhongmai 415> Zhongmai 1062> Zhongmai 175> Zhongyou 9507> Zhongmai 816> Zhongmai 14> Lunxuan 987> Zhongyou 206.Zhongmai 996 and Lunxuan 1690 were screened as the wheat cultivars characteristed with the low-Cd accumulation and high salt tolerance.3.After intercropping water spinach with Gaodan grass,Sudan grass and Pennisetum,the shoot Cd content of water spinach decreased significantly,and the Cd decrease rate(%)reached 34.0%,35.8% and 34.3% respectively,however,the uptake of Cd by water spinach was promoted with intercropping with Chicory,Amaranth,Clover,Alfalfa and Milk vetch resulting in increased shoot Cd content.Significant difference of the uptake and transfer of Cd by herbs was also observed in this study,the shoot Cd for herbs ranged from 1.81mg/kg to 12.87mg/kg,with a maximum variation of 7.1 times.The removal rate(%)of Cd from the soil ranged from 0.35% to 1.49% among the treatments.The removal rate(%)of Cd from the soil for the intercropping with Gaodan grass,Sudan grass,Pennisetum reached 1.46%,1.49% and 1.48% respectively.4.After intercropping wheat with Gaodan grass,Sudan grass,Chicory and Amaranth,the Cd content of shoots of wheat decreased by 6.51%~20.71% compared with monocropped wheat(W),and the content of grains also reduced by 2.54%~29.66% compared with W.Among the six herbs intercropped with wheat,the aboveground Cd content of several herbaceous plants except ryegrass was significantly higher than that of the corresponding monocropped herbs.In the rhizosphere soil of WG,WS,WC and WA,the available Cd content decreased by 12.96%~38.89%,the Eh value decreased significantly by 3.64%~9.35%,and the DOC content was significantly lower than W by 9.21% to 19.68% compared with wheat monoculture(W).Correlation analysis showed that lowering pH value and increasing Eh value and DOC content could increase the bioavailability of Cd in rhizosphere soil of plants.