Trace elements, or micronutrients, are required in small quantities by plants and animals, though a small deficiency can critically affect growth and development. A deficiency of the micronutrient boron (B) is commonly observed in many parts of New Zealand.

Boron is usually considered only necessary for plants, however, research has shown that B influences metabolism and growth in animals, highlighting its importance.

In plants, B plays an important role in carbohydrate metabolism and protein synthesis and assists with the movement of calcium and sugars into the growing parts of the plant. It is also important for seed set and pollination and it is common practice to apply B to brassica and root crops to aid in preventing brown heart and hollow stem.

A deficiency in legumes displays as a bushy appearance due to the death of the stem tips and the development of short stems.

The plant’s leaves may be misshapen and become crinkly. A B deficiency is more likely to occur in soil types that are free-draining and have low organic matter as these soils lose B through leaching.

For spring-sown brassica crops, B must be applied as close to sowing as possible to reduce the risk of brown heart. If there are localised underlying deficiencies identified from leaf tissue testing, once the crop has been established, applying B through foliar applications may help.

Plant herbage analysis is essential to determine the trace element status. A herbage test assists to confirm if visual symptoms are related to a B nutrient deficiency and are not related to fungal diseases such as dryrot and scelrotinia.

Soil tests should still be undertaken well before the crop is sown to assess soil B levels. Do not use the results in isolation to determine a plant deficiency. A plant tissue sample of clover only, or the youngest mature leaf in brassicas, for analysis is recommended. When taking a clover plant tissue test, the concentration of B is at its lowest in winter and early spring, so test for B in clover during the summer when they are rapidly growing.

If tissue tests show a B deficiency, even after B was applied at sowing, prompt remedial action is required using a foliar application of formulated B as this method is quick, accurate, and cost-effective.

Soil testing well before the sowing date of brassicas and legumes is critical to establish background B soil levels and it is best practice to include B in a base fertiliser plan. Follow up with tissue testing to identify if B is deficient. If a deficiency is present, a foliar application of B provides rapid uptake and even spread of the product applied.

For help taking a herbage test, or to identify a boron deficiency in your crops, contact your local PGG Wrightson Technical Field Representative.