Boron Deficiency in Coffee
Boron is the most often deficient micronutrient in coffee cultivation. Boron’s primary role in coffee is to act as a key component in a number vital process such as cell division, root development, cell wall formation, and calcium uptake.
Boron is necessary for:
- Root growth and functioning uptake of water
- Growth of internodes
- Fruit setting
- Fruit size
- Drought and disease resistance
Deficiency causes the death of the terminal growing point. The later development of secondary branches (sometimes as many as seven at the same node) below the dead terminal bud gives the typical fan-like effect. In severe cases the secondary branches quickly die resulting in the typical dieback of terminal sections of the new shoots. Such dieback can be distinguished from that caused by disease by the associated leaf symptoms and, if necessary, by analysis of young leaves.
What does boron deficiency look like?
When a plant is boron deficient, the leaves are typically misshapen and smaller in size. They are often narrow and twisted with irregular edges and have a leathery texture. The internodes are short, leaf tips may fail to develop properly, and the apical portion may then turn a pale olive/green color. In contrast, the basal portion of the leaf remains a deep dark green. It has been suggested that this apical chlorosis is due to a local calcium deficiency which may be the result of boron deficiency reducing calcium translocation.
Defoliation can occur. The underside of the midrib of both chlorotic and otherwise healthy older leaves may become suberized.
Production will be seriously reduced because of poor fruit formation. In nutrient solution studies, it has been demonstrated that boron deficiency does not seem to affect flowering but that, in contrast, fruiting is markedly reduced. In controlled experiments, no fruit was produced even though flowering was regular. This is in accord with work demonstrating that coffee shows a peak demand for boron (and for calcium) just after flowering and when the formed cherry is developing.
When do symptoms appear?
Terminal dieback and the development of crinkled leaves towards the end of a dry period and at the start of the rainy season (due to reduced boron absorption from the dry upper soil layers) are often the first signs that the coffee plant is suffering from boron deficiency.
Symptoms are also particularly noticeable at flowering and after liming due to the reduced availability of soil boron. Boron is mainly used on coffee to prevent the occurrence of the transient deficiency symptoms rather than to correct severe deficiencies which result in considerable branch dieback.
How much boron is enough?
Coffee removes significant amounts of boron from the soil each year. Once a plant shows signs of deficiency it cannot fully recover. Flowering may be regular however no fruit may be produced.
Always consult your local department of agriculture to check the proper dose rates. Rates of boron fertilization should be based on yield goals along with soil tests and/or plant analyses.
Timing your boron application
- High demanding periods for boron are after harvest, blooming, fruit setting, and fruit growth.
- Boron may be applied in dry or fluid blends. With dry bulk blend fertilizer, broadcasting before planting is recommended, using Granubor® 2.
- Boron in liquid suspensions may be applied broadcast before planting, banded at planting, or sidedressed, using Fertibor® in suspensions.
- Boron in liquid fertilizers may be broadcast before planting, banded at planting, side dressed, or fertigated using Solubor®. This material may also be mixed with pesticides or, in aqueous spray, applied to foliage.