Increased knowledge about secondary nutrients and micronutrients, including plant requirements, nutrient sources, and methods of application, has resulted in their increased use. Improvements in soil testing and plant analyses have provided more knowledge about plant needs and the wide variations in plant responses to these nutrients. Higher crop yields and the use of high-analysis NPK fertilisers also have resulted in increased needs for these nutrients.

The secondary nutrients are calcium, magnesium, and sulphur. Concentrations of these nutrients in plant tissues generally are lower than those of the primary nutrients (nitrogen, phosphorus, and potassium) but are higher than those of the micronutrients. The eight micronutrients are boron, chlorine, copper, iron, manganese, molybdenum, selenium and zinc. Because chlorine deficiencies rarely occur in nature, most discussions on supplying micronutrient fertilisers are confined to the other seven micronutrients. It is very important to keep in mind the “barrel of von Liebig”. Von Liebig was a scientist who first made it very clear that the yield of a plant was limited by the nutrient that is present in the environment in the least quantity relative to its demands, in other words if one of the essential plant nutrients (either primary, secondary or micronutrient, is deficient, plant growth will be poor, even when all other essential nutrients are abundant.

Nowadays agriculture focusses very much on Nutrient Use Efficiency, so more yield per unit of supplied nutrient, and in achieving this goal the role of micronutrients will be very important since only small quantities can have massive effect, examples being the addition of B and Zn to fertilisers in Ethiopia, and Zn in grain fertilisers in Turkey, Greece, Spain, etc.

In addition, there is increasing interest in the potential benefits of fortifying crops with these nutrients as a way to improve the quality of the human diets in certain parts of the world. See these pages for detailed information about the production aspects of secondary and micronutrients.

References

1. Follett, R. H., L S. Murphy, and R. L. Donahue. 1980. Fertilizers and Soil Amendments, Prentice• Hall Inc., Englewood Cliffs, NJ, U.S.A.

2. Portsch, S. (Ed.). 1991. The Role of Sulphur; Magnesium and Micronutrients in Balanced Plant Nutrition, Potash and Phosphate Institute of Canada, Saskatoon, Saskatchewan.

3. Mortvedt, J. J., and F. R. Cox. 1985. “Production, Marketing and Use of Calcium, Magnesium and Micronutrient Fertilizers,” IN Fertilizer Technology and Use, 0. P. Engelstad (Ed.), 3rd. Ed., Soil Science Society of America, Madison, WI, U.S.A.