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Boron in Agriculture
Koos Coetzee - MSc Soil Science • Christo Kritzinger Researcher
Boron deficiency is a common deficiency in crops. It is the most widespread micronutrient deficiency around the world and
causes large losses in crop production and crop quality. Boron deficiency affects vegetative and reproductive growth of plants,
resulting in inhibition of cell expansion, death of meristem, and reduced fertility.
Plants contain boron both in a water-soluble and insoluble form. In plants, the amount of water-soluble boron
fluctuates with the amount of boron supplied, while insoluble boron does not. The appearance of boron deficiency
coincides with the decrease of water-insoluble boron. It appears that the insoluble boron is the functional form while the
soluble boron represents the surplus.
Boron is essential for the growth of crops. The primary function of the element is to provide structural integrity to the cell
wall in plants. Other functions likely include the maintenance of the plasma membrane and other metabolic pathways.
Soil Conditions:
Boron is present in the soil in many forms, the most common being Boric Acid (H3BO3). An adequate amount of boron in
the soil is 4 mg/kg. If the boron content of the soil drops below 0.2 mg/kg then boron deficiency is likely to be observed.
Boron deficiency is also observed in basic soils with a high pH. Soils with low organic matter content (<1.5%) are also susceptible
to boron deficiency. Highly leached sandy soils are also characteristic of boron deficiency because the boron will not be
retained in the soil. Boron toxicity is also possible if the boron content of the soil is high enough that the plant cannot cope
with the excess boron. The levels at which boron is toxic to plants varies with different species of plants.
Boron Requirements:
Boron is an essential micronutrient which means it is essential for plant growth and development, but is required in very
small quantities. Although Boron requirements vary among crops, the optimum boron content of the leaves for most crops
is 20-100 ppm. Excess boron can result in boron toxicity and the toxicity level varies between plants.
Application of Boron:
X-Treem B Liquid (13% boron), X-Treem B Powder 130 (13% boron) or X-Treem B Power 200 (20% boron) can be applied to
soils to correct boron deficiency. Typical applications of actual boron are about 1.0 kg/hectare but optimum
levels of boron vary with plant type. Borax, Boric Acid or borate can be dissolved in water and sprayed or applied to soil as
a dust. Excess boron is toxic to plants so care must be taken to ensure correct application rate and even coverage. Leaves of
many plants are damaged by boron; therefore, when in doubt, only apply to soil. Application of boron may not correct
boron deficiency in alkaline soils because even with the addition of boron, it may remain unavailable for plant absorption.
Continued application of boron may be necessary in soils that are susceptible to leaching such as sandy soils. Flushing soils
containing toxic levels of boron with water can remove the boron through leaching.
Quality Boron Source
OPTIMUM RANGE
for most nutrients
}
Optimum Range for Boron
Hidden
hunger
Severe
deficiency
Typical doseresponse curve
for essential trace
elements in crops
Hidden
or mild
toxicity
Boron typical dose
responsive curve
Severe
toxicity
From: Micronutrients and Crop Production, An introduction: Alloway 2004
Functions of boron in the plant:
Once boron has been absorbed by the plant and incorporated into the various structures that require boron, it is unable to
disassemble these structures and re-transport boron through the plant resulting in boron being a non-mobile nutrient. Due to
translocation difficulties the youngest leaves often show deficiency symptoms first.
Boron is part of the dRG-II-B complex which is involved in the cross linking for pectin located in the primary cell wall and the
middle lamella of plant cells. This cross linking is thought to stabilize the matrix of plant cell walls.
Other important functions of boron in crops are: carbohydrate (sugar) metabolism, protein synthesis, germination and
pollination.
The B requirement is much higher for reproductive growth than for vegetative growth in most plant species. Boron increases
flower production and retention, pollen tube elongation and germination, and seed and fruit development.
A deficiency of B can cause incomplete pollination of corn or prevent maximum pod-set in soybeans.
Sugar Translocation:
Photosynthesis transforms sunlight energy into plant energy compounds such as sugars. For this
process to continue in plants, the sugars must be moved away from the site of their development,
and stored or used to make other compounds.
MoB
Advancing Boron Technology
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Boron increases the rate of transport of sugars (which are produced by photosynthesis in
mature plant leaves) to actively growing regions and also in developing fruits. Boron is
essential for providing sugars which are needed for root growth in all plants and also for
normal development of root nodules in legumes such as Lucerne, soybeans and peanuts.