Most of the crops require 17 essential nutrients to grow normally. Carbon, hydrogen, and oxygen derived from the air comprise more than 90 per cent of the fresh plant tissue. Macronutrients derived from the soil and needed in large amounts are nitrogen (N), phosphorus (P), potassium (K), sulphur (S), calcium (Ca), and magnesium (Mg). Legumes are the exception because they fix N from the air. The soil supply of N, P, K, and S is often supplemented by fertilizer and manure.

The remaining essential nutrients derived from the soil are referred to as micronutrients, because they are needed in small amounts. They are boron (B), chloride (Cl), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo), nickel (Ni) and zinc (Zn). Micronutrients are important for plant growth, as plants require a proper balance of all the essential nutrients for normal growth and optimum yield.

Soil factors that affect the availability of micronutrients:

Organic matter

• Mineral soils very low in organic matter, such as Gray soils, may be deficient in micronutrients.
• Peaty and muck soils are likely to show micronutrient deficiencies. 

Soil texture

• Sandy soils are more likely to show micronutrient deficiencies than clay soils.

Soil pH

• Micronutrient availability generally decreases as the soil pH increases, with the exception of Mo.

Management, climatic and spatial variability

• Soil moisture and temperature are important. For example, cold, wet soils restrict root growth, reducing the volume of soil explored by the roots. Saskatchewan soils can be cool and wet in the spring, at which time micronutrient deficiencies may show up, but disappear when the soils warm up.
• Deficiency of one of the macronutrients (N, P, K, or S) may also restrict the ability of the plant roots to explore for other nutrients. For example, P is important for early root formation and growth.
• Micronutrient deficiencies generally appear as patches in fields because micronutrient levels can vary across landscapes. For example, Cu deficiencies in northeastern Saskatchewan occur on peaty and sandy patches and eroded knolls, whereas Cu deficiency can be widespread on sandy soils.
• Land application of livestock manure can increase the amount of available Cu and Zn.

Micronutrient Deficiency

The best ways to measure the performance of a micronutrient treatment is to determine if the yield increases; or, for some crops like potatoes an improvement in quality will cover the costs of the micronutrient application and return some profit.

Diagnosing micronutrient deficiencies in the field by assessing crop symptoms is difficult, even for trained agronomists. Look for "multiple evidence" before recommending a micronutrient for a whole field. A combination of crop symptoms in the field, tissue tests, soil tests, test strips, cropping history and other techniques can be used to confirm micronutrient deficiencies and economic yield responses.

Take soil and plant tissue samples from the affected and unaffected areas within the same field for a complete comparative analysis. This service is available from most soil testing laboratories. Call the laboratory for sampling details for a complete comparative test.

Many factors, such as macronutrient deficiency, drought, salinity, disease, insect, herbicide injury or other physiological problems can cause poor or stressed plant growth. Stressed growth may show symptoms similar to micronutrient deficiencies.

Crop nutrient deficiency symptoms may be specific to a crop. Some deficiency symptoms can look similar between micronutrients.