Soil Fertility and Nutrient Use: Micronutrient Fertilizers

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Pub 811: Agronomy Guide > Soil Fertility and Nutrient Use > Micronutrient Fertilizers

Excerpt from Agronomy Guide for Field Crops
Order OMAFRA Publication 811: Agronomy Guide for Field Crops

• Table 9-5. Manganese Soil Test Interpretation
• Manganese
• Zinc
  • Table 9-6. Zinc Soil Test Interpretation
• Copper
• Boron
  • Table 9-7. Adjustment of Nitrogen Requirement, Where Crops Containing Legumes Are Plowed Down
• Iron and Molybdenum

Apply micronutrient elements only on competent advice or where experience has proven their application to be necessary. Generally, make soil applications during soil preparation and foliar applications during the growing season. Include a spreader sticker in micronutrient sprays applied directly to crop foliage.

¹ These values are indices of manganese availability based on extractable soil manganese and soil pH.

Do not combine micronutrient elements with insecticide or fungicide sprays unless the manufacturer's directions indicate that this may be done.

Manganese

Preventing and Correcting Manganese Deficiency

The general symptom of manganese deficiency is interveinal chlorosis of leaves, which begins on the younger foliage. Later, the whole plant may be affected. Cereals show manganese deficiency as a general yellowing and stunting, occasionally with grey specks on the leaves. The crops most susceptible to manganese deficiency are soybeans, dry edible beans and cereals.

Manganese is less available at high soil pH, so it is important not to add more lime than is needed to correct soil acidity. For materials and rates to correct a deficiency, consult the individual crop chapters under Micronutrients. Interpretation of the manganese soil test is found in Table 9-5, Manganese Soil Test Interpretation.

Zinc

Preventing and Correcting Zinc Deficiency

Corn is the main crop that may show zinc deficiency in Ontario. Zinc deficiency has been reported in beans in other areas but it appears to be rare in Ontario. High phosphorus in the soil and/or in the fertilizer can cause or increase the severity of zinc deficiency. Apply only the recommended amount of phosphorus. Use of animal manures can prevent or reduce zinc deficiency. Erosion control can prevent deficiency of zinc by maintaining the topsoil.

¹ These values are indices of zinc availability based on extractable soil zinc and soil pH.

Zinc deficiency can be prevented by application of zinc fertilizer to the soil at a rate of 4 kg/ha (3.6 lb/acre). Broadcasting up to 14 kg/ha (12.5 lb/acre) will correct a deficiency for 3 years, but do not band more than 4 kg/ha (3.6 lb/acre). Foliar sprays can be useful to correct a deficiency after the symptoms have appeared, provided this is done early in the growing season. Interpretation of the zinc soil test is found in Table 9-6, Zinc Soil Test Interpretation.

Copper

Copper soil tests are quite unreliable on Ontario soils, but plant analysis is useful. Copper is unlikely to be deficient on mineral soil, except perhaps on very sandy soils. Copper deficiency does occur on organic soils and is best diagnosed by plant analysis. When organic soils are first brought into cultivation, apply copper to the soil at 14 kg/ha (12.5 lb/acre) for each of the first 3 years.

Boron

Boron is required for alfalfa, particularly on sandy or gravelly soils with low water-holding capacity. Deficiencies are more common in Central Ontario than in the rest of the province. Boron deficiency occurs most frequently during dry weather, and the response to boron may be inconsistent. It has not been possible to develop a reliable soil test. Plant analysis is useful as a predictor of boron requirements as are visual symptoms on the plants. For rates of boron to correct a deficiency, see Micronutrients.

Boron is needed only in very small quantities, and since an overdose is toxic, take extreme care in its use. Boron deficiency has not been diagnosed in cereals, peas or beans in Ontario, and boron applications to these crops or applied to other crops in the year preceding them can be toxic. Do not band boron.

¹ Applies where the legume stand is thick and over 40 cm (16 in.) high.
² For all crops other than corn. For adjustments to corn fertilizer requirements, see Corn Nitrogen Rate Worksheet.

Iron and Molybdenum

Iron and molybdenum have not been found to be deficient in field crops in Ontario.

Changes in Crop or Management

Fertilizer requirements on the OMAFRA soil test report are specific to selected crop and management. Adjustments in fertilizer requirements may be needed if changes are made in manure application or if legumes are going to be incorporated. For fertilizer adjustments, see Table 9-7, Adjustment of Nitrogen Requirement, Where Crops Containing Legumes Are Plowed Down, this page. Changing the crop from the original soil test recommendation will require a new fertilizer recommendation. This can be obtained by looking up the appropriate table under the specific commodity chapter in this publication.