With the continuous improvement of living standards, people's awareness of health and environmental protection has significantly increased. As a result, there is now a growing demand for vegetables that are free from pollution. Pollution-free vegetables are those in which the levels of harmful substances, such as pesticides, nitrates, heavy metals, and pathogens, comply with national safety and health standards. First, pesticide residues must not exceed permissible limits—these vegetables should not contain banned, highly toxic, or high-residue pesticides, and other pesticides should remain within the maximum allowable limits set by the government. Second, the content of nitrates and nitrites must also be within safe levels. Third, the presence of "three wastes" (waste gas, waste water, and solid waste), heavy metals, and pathogenic microorganisms should not exceed acceptable thresholds. Among these factors, the levels of heavy metals, nitrates, and nitrites are closely related to the proper use of fertilizers. There are various challenges in producing pollution-free vegetables, and one of the most critical factors is the correct selection and application of fertilizers.
When choosing fertilizers, it is essential to select types that do not harm the environment or compromise the nutritional quality of the vegetables. The following fertilizer categories are suitable for the production of pollution-free vegetables:
1. **Organic manure** includes farmyard manure, commercial organic fertilizers, compost, sludge manure, cake manure, biogas manure, green manure, and crop straw. Compost should meet the requirements of NY/T 394-2000, the "High-Temperature Composting Hygienic Standards." Commercial organic fertilizers should comply with the "Standards for Permissible Content of Contaminants in Organic Fertilizers" (NY/T 5018).
2. **Microbial fertilizers** include humic acid-based, rhizobia, potassium bacteria, phosphorus bacteria, and composite microbial fertilizers. The number of viable microorganisms must meet the requirements outlined in section 4.1 of the "Microbial Fertilizer" standard (NY227), and hygiene indicators must conform to the "Integrated Product Harm Index" specified in the same standard.
3. **Inorganic mineral fertilizers** consist of nitrogen, phosphate, and potash fertilizers. For nitrogen sources, iron-based or urea-based fertilizers are recommended. Phosphate and potash fertilizers must meet the health standards outlined in NY/T 394-2000. It is advisable to use calcined phosphate for phosphorus fertilizers, with impurity control limits such as ≤0.004% arsenic (As), ≤0.01% cadmium (Cd), and ≤0.002% lead (Pb) per 1% P₂O₅. For potash, potassium sulfate is preferred, with impurity limits of ≤0.004% As, ≤3% chloride (Cl), and ≤0.5% sulfuric acid per 1% K₂O.
4. **Trace elements** such as calcium, magnesium, copper, iron, boron, zinc, molybdenum, and manganese can also be included in fertilizers to support plant growth and improve vegetable quality.
By carefully selecting and applying the right fertilizers, farmers can effectively reduce the risk of contamination and ensure the production of safe, healthy, and environmentally friendly vegetables. This approach not only meets consumer demands but also supports sustainable agricultural practices.
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