Skip to main content

Micronutrients for arable soils

By Gavin Elrick, Consultant, SAC Consulting

For farmers to minimise their carbon footprint it is essential that cereal and oilseed rape crops are grown to maximise their yield with efficient utilisation of the main nutrients Nitrogen (N), Phosphate (P), Potash (K), magnesium (Mg) and Sulphur (S). The key to efficient utilisation of these main nutrients starts with knowing your soil nutrient status and soil pH, aiming for an optimum pH of between 6.0 to 6.2.
With the focus on getting the pH and major nutrients on target, micronutrients can often be overlooked as an additional cost when requesting a standard soil analysis. The table below shows the most common micronutrient issues affecting cereals and oilseed rape and suggests possible treatment options:

Micronutrient Conditions that exacerbate the deficiency Micronutrient Important for Treatment Options
Boron (B) Organic soils, alkaline and calcareous soils sandy soils, dry soils, cold wet soils and high levels of nitrogen (N). Germination and early seedling growth in brassicas, boosts flowering, grain yields and oil content in oilseed rape crops. Nodulation and N-fixation in legumes.
Can be toxic to cereals at levels just above optimum levels so care must be taken when treating deficiencies.
Boronic fertilisers in seedbed or as a foliar spray of Boric acid, Borax, Solubor or other products containing other boron compounds.
Copper (Cu) Organic soils, alkaline and calcareous soils sandy soils, dry soils, fluffy seedbeds, and soils with high levels of phosphorus (P) Better crop establishment, tillering, improved winter hardiness, improved disease resistance, better grain quality, grain set and yield. In oilseed rape improves flowering, grain yield and oil content of grain. Boronic fertilisers in seedbed or as a foliar spray of Boric acid, Borax, Solubor or other products containing other boron compounds.
Manganese (Mn) Organic soils, calcareous soils, dry soils, sandy soils, high nitrogen conditions. Increase grain fertility, grain numbers and yield. Soil applications of copper oxychloride and copper oxysulphate. Foliar applications of copper oxychloride, chelated copper products and proprietary copper or “cocktail” products
Zinc (Zn) Organic soils, alkaline and calcareous soils sandy soils, dry soils, cold wet soils, and soils with high P levels Increase plant fertility, grains per ear and improves grain quality. Cereals are more susceptible than oilseed rape to zinc deficiency. Can be applied as a soil or foliar spray of zinc-containing products.

Deficiencies can be exacerbated where efforts have been made to increase soil pH and fertility to higher levels; this, in turn, can reduce optimum yields. Soil analysis for micronutrients should be carried out before crop establishment in order that remedial measures can be carried out prior to or during the growing season.

This article from Farming for a Better Climate was funded by the Scottish Government as part of Scotland’s Farm Advisory Service and first published in the Farming Scotland Magazine in September 2020.