Trace Elements in Plant Nutrition, Boron, Copper, Iron, Manganese, Molybdenum, Zinc

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Trace Elements in Plant Nutrition

These are elements that are vital to plant growth but are only required in minute amounts, very much like vitamins in human diets. They are known as micro-nutrients because of the tiny amounts found in normal soils.

For the average home vegetable grower micro nutrients are an acedemic rather than a practical subject. Identifying micro nutrient deficiencies is difficult even for experts and usually requires laboratory analysis. With iron deficiency, even laboratory analysis is difficult.

Luckily for us, most of these deficiencies are very rare and rotation, use of compost and manures will cure them.

Boron (B)

Boron is necessary for calcium to perform its functions in the plant but too much boron is also harmful to the plant. Excess use of magnesium sulphate will also cause a boron imbalance. The symptoms of boron deficiency are poor development of the growing tip of the plant. It is more likely in soils with pH above 6.5.

Confirming boron deficiency is a job for laboratory analysis. Adding borax to the soil will correct the deficiency but borax is also a herbicide. For garden growers who are unlikely to want to pay for professional testing and recommendations the best advice is to avoid over use of magnesium sulphate, rotate and use plenty of home made compost.

Copper (Cu)

Copper deficiency is rare but can occur on sandy, peaty and chalky soils with their high pH levels. It is required for root formation. Once again it requires professional analysis to confirm and to determine a proper course of action to rectify. Usually the single use of a copper sulphate based fungicide (Bordeaux mixture) will re-stock the soil for as long as you are likely to grow on it.

Excess copper is very toxic to plants and to people. In plants it causes reduced growth, yellowing of the foliage, and stunted root development

Iron (Fe)

Iron deficiency causes yellowing of the leaves and a general lack of vigour. It is fortunately rare but unfortunately hard to both diagnose or determine by laboratory analysis.

Generally not something the home grower needs to concern himself with but should you suspect you have it then use sulphate of iron fertilizer

Manganese (Mn)

Manganese deficiency is often caused by over liming and is most often found on peaty and sandy soils with a high pH. Symptoms are similar to iron deficiency and can be confirmed by laboratory analysis of the leaf. Susceptible crops include peas and beets.

Adding sulphur to the soil, which will increase the acidity (decreasing pH) will solve the problem.

The following micro-nutrients are rarely lacking and analysis and remedy are professional jobs. Normal additions of composts and manures will resolve deficiency problems. Excess in the soil will probably be due to industrial contamination.