How to properly use micronutrient fertilizers

How to properly use micronutrient fertilizers

01 What exactly are secondary and micro-nutrient fertilizers? These nutrients comprise secondary elements (calcium, magnesium, and sulfur) and trace elements (such as zinc, boron, iron, manganese, copper, and molybdenum). They act like "vitamins" for crops; while the required quantities are small, a deficiency in any one of them can lead to problems.

For instance, boron directly affects crop flowering and fruiting; a deficiency can cause rapeseed plants to produce flowers but fail to set fruit, as well as lead to fruit malformation. Zinc influences the synthesis of plant auxins; a lack of zinc can result in "albino seedlings" in corn. Calcium is a component of cell walls; a deficiency can cause blossom-end rot in tomatoes and "dry heart rot" (tipburn) in Chinese cabbage.

The question now arises: why is there an increasing need to supplement secondary and trace elements? This is primarily due to the long-term, excessive use of nitrogen, phosphorus, and potassium fertilizers, which causes these elements to be rapidly depleted from the soil without being replenished.

02 How can you tell what nutrients a crop is lacking? The most accurate way to determine a nutrient deficiency is through soil testing; however, ordinary farmers can also assess the situation by observing the crop's growth.

When you notice abnormal symptoms in your crops, you should be on the alert: Are the leaves yellowing, deformed, or spotted? Is the growing point underdeveloped? Are the fruits misshapen or showing necrotic spots?

Different nutrient deficiency symptoms manifest in distinct ways. For example, iron deficiency causes the new leaves of crops to turn yellow while the veins remain green; zinc deficiency leads to shortened internodes and smaller leaves; and molybdenum deficiency affects root nodule formation in leguminous crops.

Another practical approach is to conduct a small-scale comparative trial: designate a small section of the field for the application of fertilizers containing secondary and micro-nutrients while leaving the rest untreated, then compare crop growth and yield.

03 Methods for the Proper Application of Secondary and Micro-nutrients - Soil Application: A Solid Foundation for Easier Management Later. Soil application is the primary method for supplementing secondary and micro-nutrients. Ideally, before sowing or transplanting, mix the micro-nutrient fertilizers thoroughly with decomposed organic fertilizer or slightly moist soil, and apply the mixture into furrows or planting holes along with the basal fertilizer.

Application rate is crucial; the amount of trace element fertilizer used per mu is generally quite low: 1–2 kg/mu for zinc sulfate and 0.5–1 kg/mu for borax. While the dosage may be increased slightly for fruit trees and vegetables, it generally should not exceed 3–5 kg/mu. It is important to note that most trace element fertilizers should not be mixed directly with phosphate fertilizers, as they can form insoluble compounds that mutually reduce fertilizer efficacy.

Foliar spraying: rapid correction with immediate results. When crops already exhibit symptoms of nutrient deficiency, foliar spraying is the fastest corrective method. Leaves absorb nutrients much more rapidly than roots, making this technique ideal for quickly replenishing nutrients during critical growth stages. Spray concentrations must be strictly controlled: 0.05%–0.25% for boric acid or borax, 0.02%–0.05% for ammonium molybdate, and 0.01%–0.02% for copper sulfate.

Seed treatment is a cost-effective way to ensure uniform and vigorous seedling emergence, particularly for the application of certain trace elements. For instance, coating peanut seeds with ammonium molybdate (at a rate of 15 grams per mu) or treating legume seeds with *Rhizobium* inoculants can enhance nitrogen-fixation efficiency. Seed soaking is another method; soaking peanut seeds in a ferrous sulfate solution for 4 to 5 hours can effectively prevent iron deficiency.

04 Keep these points in mind during application to avoid common pitfalls. Above all, avoid over-application. The margin between deficiency and toxicity for trace elements is narrow; even slight carelessness can lead to fertilizer burn. Pay attention to compatibility when mixing products; do not arbitrarily mix micronutrient fertilizers with alkaline pesticides or chemical fertilizers, as this can reduce efficacy. Improving the soil environment is fundamental. Deficiencies in secondary and trace elements often stem not from low total soil content, but from the elements being "fixed" and thus having low bioavailability. Improving soil's physical and chemical properties-such as by applying organic fertilizers or soil conditioners-can enhance the availability of these elements.

Tailor fertilization to the specific crop. Different crops have varying needs for secondary and micronutrients: corn and rice are sensitive to zinc; rapeseed and cotton are sensitive to boron; and legumes are sensitive to molybdenum and iron. Fertilizers containing these nutrients act like "special forces" for your crops-while the quantities used are small, their impact is crucial. By adhering to the principles of applying the right amount at the right time to address specific needs, you can maximize the return on your fertilizer investment. Next time you fertilize, take a moment to identify exactly what your crops are lacking before selecting the appropriate fertilizer and application method. Effective use of secondary and micronutrient fertilizers will result in more robust crop growth, enhanced disease resistance, and significant improvements in both yield and quality.