How Should Heavy Metals be Treated in the Return of Livestock Manure to the Field

The addition of some trace elements such as copper and zinc in feed is beneficial to improve feed utilization, increase the immunity of livestock and poultry and improve meat quality; as the proportion of heavy metals added to feed and heavy metals contained in feed materials is only about 5%-30% absorbed by animals, most of them are excreted with manure. The research results found that compared with the heavy metal content in feed, the heavy metal concentration in livestock manure has a significant enrichment effect, and the heavy metal concentration in manure is about 4 times of that in feed, so all livestock manure will inevitably contain a certain amount of heavy metal.

The most economical and effective way to implement the resource utilization of livestock manure is to return the manure to the field after harmless treatment. In developed countries with livestock industry such as the United States, Denmark and the Netherlands, livestock manure is mainly returned to the field for use. From the requirements of the manure return to the field in these countries, the focus is on the nitrogen and phosphorus content of the manure and the scientific return to the field according to the nutrient demand of crops and soil conditions. EU countries mainly based on the Nitrate Directive, the annual application of livestock manure per hectare of arable land should not exceed 170 kg; the U.S. implements the Integrated Manure Nutrient Management Program. These countries have not yet put forward limit requirements for heavy metals such as copper and zinc in the process of returning livestock manure to the field as manure, but mainly still have strict limit requirements for the amount of heavy metals added to feed. At the same time, feed manufacturers and breeding enterprises also strictly in accordance with the specification requirements to add heavy metals such as copper and zinc, to ensure the long-term safe application of livestock and poultry manure.

Copper and zinc are also essential micronutrients for normal growth and development of plants, livestock and poultry manure containing trace or moderate amounts of heavy metals returned to the use of the soil and crops will not have an impact, some studies have shown that a small amount of copper and zinc in manure has no significant adverse effects on the growth of oilseed rape and other plants, and even promote growth; however, when the concentration of copper and zinc in manure is too much, it will cause slow growth of seedlings, poor growth, plant dry matter quality At the same time, the health risk of crop absorption of copper and zinc entering human body through diet is very low, so the appropriate amount of heavy metals such as copper and zinc contained in livestock manure can be returned to the field.