有机肥连续施用对菜田重金属行为的影响——基于地球化学模型研究

2017年起，农业部连续多年出台化肥减量增效行动工作方案，要求适当增加有机肥投入，发展循环农业。但连续施用的有机肥进入土壤后，会对土壤pH、有机质和重金属含量等产生影响，改变土壤重金属行为。科学评估有机肥料施用的影响至关重要。仅通过总含量评估重金属污染风险被认为是片面的，不同化学提取剂提取的重金属含量不能完全代表实际污染状况。地球化学模型具有良好的适用性，比传统的提取方法能够更全面地解释重金属的行为。在集约化农业种植区黄淮海平原，多次施用不同比例的粪源有机肥于旱地菜田，并引入地球化学模型，结合pH依赖性浸出试验，明确连续施肥对菜田土壤重金属行为的主要影响机制。研究发现，有机肥中的铜锌含量远高于土壤中的含量，施用后，它们在土壤中的淋溶浓度随着施用比例增加而显著增加，最多可超过十倍以上，并且活性大大增加，与施肥后溶解性有机物含量的升高呈正相关。不同处理条件下的土壤重金属浸出趋势相似：在中性pH下浸出浓度最低，然后逐渐向强酸和强碱增加，呈现出V型变化。地球化学模型LeachXS展示出较好的模拟结果，其模拟值与实测浓度具有良好的相关性(71.02%)。模拟结果显示，有机肥的施用不会明显改变重金...

Effect and simulation of continuous application of organic fertilizer on heavy metal behavior in vegetable field soil based on geochemical model

Since 2017, the Ministry of Agriculture and Rural Affairs of China has introduced the action plan of chemical fertilizer reduction and efficiency improvement, which required an appropriate increase in organic fertilizer input and the development of circular agriculture. However, the continuous application of organic fertilizers into the soil will affect the soil pH, organic matter and heavy metal content, and change the soil heavy metal behavior. It is essential for scientific evaluation of the impact of organic fertilizer application. It is considered to be unilateral to evaluate the pollution risk only by the total content. The heavy metal content extracted by different chemical extractants cannot completely represent the actual pollution situation. The geochemical model has good applicability and can explain the behavior of heavy metals more comprehensively than the traditional extraction.In the Huang-Huai-Hai Plain, an intensive agricultural planting area, different proportions of manure-source organic fertilizer were continuously applied to dryland vegetable fields. A geochemical model was introduced, combined with a pH-dependent leaching test, to determine the main influence mechanism of continuous fertilization on soil heavy metal behavior. It found that the content of Cu and Zn in organic fertilizer was much higher than that in soil. After application, their leaching concentration in the soil increased significantly as the proportion of application increased, up to more than ten times, and the activity greatly increased, which was positively correlated with the increase in dissolved organic matter (DOM) content after fertilization. The soil under different treatments showed similar leaching trends. The leaching concentration of heavy metals appeared at a minimum at neutral pH, and gradually increased toward the strong acid and alkali (V-shaped). The geochemical model (LeachXS) showed good simulation results, and its estimated value had a good correlation (71.02%) with the measured concentration. The simulation results showed that the application of organic fertilizer would not significantly change the main adsorption process of heavy metals on the solid surface of the soil, but it could increase the leaching of heavy metals in the soil liquid phase by increasing the DOM and heavy metal content, thereby increasing the activity of heavy metals. Soil organic matter (SOM), Fe-Al (hdyr) oxides, clay, etc. determined almost all the leaching of heavy metals. Among them, SOM, including DOM and Particulate Organic Matter (POM), had greater adsorption and complexation of heavy metals than other substances, and was the most important factor affecting the behavior of heavy metals in soil between solid and liquid phases. With the increase in the proportion of organic fertilizer, the content of heavy metals (especially Cu, Zn, and Cr) of POM-bound increased significantly and was higher than other solid states. The increased content of the DOM-bound heavy metal directly led to their enhanced activity. For Ni and Pb, the content of Fe-Al (hdyr) oxides-bound was close to or higher than that of POM-bound, but the relationship with the fertilization ratio was not obvious. The application of pig manure with high DOM and high Cu and Zn content would significantly increase the accumulation of heavy metals in the soil and crops, and continuous application might cause extremely high pollution risks. When choosing continuous application of organic fertilizer from livestock and poultry manure, it is necessary to reduce its heavy metal content, and pay attention to possible pollution, to truly realize the healthy and sustainable development of organic recycling agriculture.