设施黄瓜菜田土壤镉污染预测模型及阈值研究

Prediction model and threshold of soil cadmium contamination in cucumber greenhouses

为指导设施栽培的安全生产,以设施黄瓜为研究对象,通过连续2年镉(Cd)污染微区试验,对设施黄瓜菜田土壤Cd污染预测模型及阈值开展研究。结果表明,设施黄瓜土壤全量Cd和有效态Cd含量均与黄瓜Cd含量呈极显著的线性、对数、幂函数和指数关系,其中,全量Cd含量以指数预测模型的相关系数最高,有效态Cd含量以线性预测模型的相关系数最高。依据国家食品卫生标准,利用呈极显著相关的模型,提出了基于土壤pH≥7.5且质地为壤土的设施黄瓜土壤全量Cd和有效态Cd的风险阈值分别为2.13mg·kg^–1和0.26mg·kg^–1。利用土壤敏感性指标脲酶活性对该阈值进行验证,结果表明土壤全量Cd污染达2.74 mg·kg^–1时才会引起土壤脲酶活性显著下降,而≤2.13 mg·kg^–1的土壤全量Cd含量并未对土壤脲酶产生明显影响。可见,通过土壤脲酶指标验证后确定的阈值是可行的;并推荐当土壤中全量Cd>0.8 mg·kg^–1且Cd≤2.13 mg·kg^–1(pH≥7.5)时,选择黄瓜替代其他风险作物能够满足食用农产品质量的安全要求。该研究结果可为我国北方土壤Cd污染地区设施黄瓜的安全生产提供科学理论依据。

The accumulation of heavy metals in soil is difficult to reverse,and this threatens China’s agricultural safety.Nevertheless,the current implementation of heavy metal standards involves determining the risk screening value based on the pollutant items and pH value.However,there is a risk of contamination in edible agricultural products,which cannot meet quality and safety standards.In order to guide the selection of suitable crops for different soil types to avoid the risk of cadmium(Cd)pollution and to fully utilize land under the premise of safe production,thresholds for Cd pollution of different crops in different soil types need to be developed urgently.A Cd pollution micro-plot experiment with cucumber as the research object was conducted for two consecutive years to establish a prediction model and threshold of Cd pollution in greenhouse soils.The results showed that the total Cd and available Cd in greenhouse cucumber soil exhibited significant linear,logarithmic,power functions,and exponential relationships with the Cd content in cucumbers.The total Cd content showed the highest correlation coefficient according to the exponential model,while the available Cd content had the highest correlation coefficient according to the linear model.On the basis of soil conditions with pH≥7.5 and loamy texture,the risk thresholds for total Cd and available Cd in facility cucumber soils were proposed to be 2.13 mg·kg^–1 and 0.26 mg·kg^–1,respectively,based on extremely significant correlation models and national food hygiene standards.The proposed threshold was further verified by the soil urease activity;thereby,it was concluded that soil Cd contents less than or equal to 2.13 mg·kg^–1 had no significant effect on soil urease.Hence,the determined thresholds are feasible after soil urease verification.When the Cd content in the soil is greater than 0.8 mg·kg^–1 and less than or equal to 2.13 mg·kg^–1(soil pH≥7.5),cucumbers can be recommended to replace other risk crops to meet the quality and safety requirements of edible agricultural products.The results of this study provide a scientific and theoretical basis for cucumber planting in the Cd-contaminated soil area of northern China,and thus hold practical significance.In this study,referring to the large body of existing research on the threshold value of vegetable soil Cd,the threshold value of soil Cd obtained by the soil sensitive soil index of urease activity and by constructing a cucumber soil Cd mathematical model are mutually confirmed,and a safe and reasonable threshold value of soil Cd under the experimental conditions is obtained.