Micronutrient Formulations

There’s a vast and often bewildering product range to choose from. Whatever your purchasing decision, it’s essential that the micronutrients in your chosen product are in a form that makes them available to the plant.

For fertiliser products, this means that they mustn’t get locked up in the soil. While most micronutrients will remain in the soil after application, both manganese and boron will leach in certain circumstances. With foliar sprays, the nutrient must be able to get into the plant. As a result, the elements must be soluble so that they can be taken up across the leaf surface. Another important consideration is that they are non-toxic and safe for crop use.

  • Boron – both techniques should be used together. Soil testing before planting is recommended and a value less than 0.8mg/litre of dry soil is considered to be a risk. Foliar tests also provide a good guide to potential shortfall, with a value below 5-100mg/kg of dry matter, depending on the crop, indicating a possible deficiency.
  • Chlorine – deficiency can be diagnosed by soil or leaf analysis. However, chlorine is rarely deficient and a crop’s requirement can usually be met by chlorine in the soil and in rainfall.
  • Manganese – soil testing can be variable and should be backed up by foliar analysis to confirm a diagnosis, with a value lower than 20mg/kg dry matter indicating a possible problem.
  • Zinc – leaf analysis is also the most useful diagnostic guide, where less than 15mg/kg may indicate a shortfall.
  • Nickel – foliar analysis is again the best guide, with leaf concentrations less than 0.1 mg/kg dry matter highlighting a possible deficiency.
  • Copper – leaf analysis is not a reliable indicator of a plant’s copper status, so soil analysis is the solution. A value lower than 1mg cu/litre of dry soil is a warning sign.
  • Molybdenum – deficiency can be diagnosed by either method.
  • Iron – neither soil testing nor foliar analysis is especially useful.
  • Boron – death of growing tips and a stunted, bushy habit. In sugar beet, blackening at the leaf base and beneath the crown is characteristic, while carrots often have a darkening on the root surface.
  • Chlorine –wilting leaves, and as the deficiency becomes more severe, leaf curling and shrivelling, together with a spotty necrosis.
  • Manganese – pale, limp foliage, with spotty necrosis, reflecting the role of this element in antioxidant processes.
  • Iron – up to 90% of leaf iron is found in the chloroplasts, so deficiency symptoms include interveinal yellowing in younger leaves.
  • Zinc – the most common sign of zinc deficiency is interveinal chlorosis and “little leaf”, which is thought to be caused by altered auxin metabolism.
  • Copper – chlorosis in younger leaves, often followed by distortion of the leaf.