Boron is a mineral that we find lacking in so many soil and leaf tests around the world. It often involves a simple, inexpensive correction, and yet it is so often neglected. You will soon understand the price of that neglect.
This missing mineral is often thought of as the ‘sidekick’ for calcium, but for those of you old enough to remember Tonto from The Lone Ranger, this particular version of an indispensable companion is not like the abused servant from that silly show. Boron is a standalone star in both plant and human nutrition and you are about to discover the yield-enhancing dynamics of this mineral.
Let’s begin by looking at where boron comes from and how it is stored in the soil. Boron is the only non-metal trace mineral. It is a commonly occurring mineral, often mined from dried salt lakes, most of which are found in California and Turkey. It is found in rocks and soil solution as boric acid and it can be complexed and stabilised with humus. In fact, this is how it is stored in the soil. Humus is, in effect, the boron storehouse.
There is no synthetic boron. It is all naturally mined, and there is virtually no difference between the technical grade and the agricultural grade, as both have over 99% purity and no contaminants.
The boron content of borax is 11.2% boron, while boric acid contains 17.5% boron. It can be further concentrated as sodium borate, with 21% boron, which is more soluble and often favoured by time-starved farmers.
Boron is an anion that becomes much less available in alkaline soils. It is easily leached from light soils, and soils with low organic matter often suffer from boron deficiency. Tropical soils also sponsor leaching, but one of the major players in induced boron deficiency is our misuse of NPK fertilisers. Both nitrogen and potassium will antagonise boron uptake when mismanaged.
Over 90% of the boron in a plant is found in the cell wall. It is at least as important as calcium and silicon in terms of proactive pest management, through the strengthening of that wall. This is actually a trio that may be to regenerative agriculture what the NPK trio is to the chemical extractive model. In fact, we will soon consider some other aspects of the interplay between calcium, boron and silicon.
The Top Ten Functions of Boron
Boron is notoriously lacking in the majority of farming soils, and correction of this shortage can prove a profitable strategy. Boron is essential for optimum growth, development, yield and quality, and the absolute minimum requirement is 1 ppm on a soil test. Most broadacre soils struggle to make 0.5 ppm of boron, and this neglect can prove costly. Let’s look at the critically important roles of boron.
1) Root growth – Boron is primarily involved in the structural and functional integrity of the cell wall and membrane. Boron deficiency dramatically inhibits root elongation due to impaired cell division. Boron is typically thought of as a mineral for improved pollination and seed set, however, in this context, it is just as important at the start of the season.
2) Misshapen fruit – This impaired cell division also leads to deformed flowers and fruit. Classic symptoms of boron deficiency include bumpy, misshapen fruit, hollow broccoli stems, crosswise cracking of celery stalks, shot berries in grapes, internal and external cork in apples, cracked carrots and flower shedding in multiple varieties.
3) Improved fruit-to-flower ratio – Boron has a major impact on lengthening the pollen tube, which can dramatically impact pollination and improve the fruit-to-flower ratio. A great example of this is the avocado tree, which can have huge numbers of flowers, but most of them do not become fruit. This boron hungry crop can respond wonderfully to a combination of fertigated and foliar boron. The fruit-to-flower ratio is increased and, with the current prices for this crop, your small boron investment can reap huge rewards.
4) Boron, the ‘steering wheel’ – This mineral is a hugely important calcium synergist. The oft repeated statement, “calcium is the trucker of all minerals and boron is the steering wheel”, requires some explanation. A great example of that synergy relates to the middle lamella. This is the cement-like lining between adjacent cells. Boron drives the formation of calcium pectate, which is of critical importance for strengthening the middle lamella and the cell wall for plant protection. In the absence of this super-resistant material, invading fungi are more able to use their enzymes to break down these barriers and feast upon the insides of the cell. Cell walls become much more resistant to maceration by fungal pathogens when good levels of calcium pectate are present.
5) Improved mineral uptake – Boron sponsors ion fluxes of minerals across the cell membrane and into and out of the cell. Research has demonstrated that these improved ion fluxes are particularly relevant to calcium, potassium and phosphorus. However, boron also increases uptake and availability of other plant nutrients, including nitrogen, zinc, iron and copper.
6) Nitrogen fixation – In legume crops, boron is an essential requirement for nitrogen fixation for both Rhizobium and Actinomycetes species. The lack of a pinkish-red interior in legume nodules is a classic sign of boron deficiency, and it is a signpost of poor nitrogen fixation.
7) Protein formation – Boron also plays a pivotal role in nitrogen metabolism, as it is required (along with molybdenum) for the nitrate reductase enzyme that converts nitrates through to protein.
8) Photosynthesis – Boron deficiency can also negatively impact the most important of all plant processes, photosynthesis. This occurs due to disruption of chloroplast membranes (‘the sugar factory’) and messing with the stomatal openings required to capture CO2 for photosynthesis.
9) Disease protection – Boron complexes with phenolic compounds to provide protection from free radicals and disease. In its absence, there is a damaging excess of certain phenols, as I will describe later.
10) Filling the seed head – Boron can have a big impact upon filling the seed head. When cereal grains like corn and wheat are lacking boron, the top of the seed head fails to fill. There is also much less likelihood of seed sterility in wheat fertilised with boron.
Boron and Disease
One of the diseases most commonly linked to boron deficiency is club root in brassicas. Here, it is common to see overapplication of nitrogen negatively affecting the uptake of both calcium and boron, and the club root screams, “you beauty!”
Both Fusarium wilt and Verticillium wilt in multiple species have also been linked to a lack of this mineral.
Powdery mildew can be related to boron deficiency, but it can also be linked to manganese, zinc and sulphur deficiencies. Therefore, a separate foliar application of manganese sulfate and zinc sulfate may also be productive (these metallic trace elements are too acidic to be combined in the same tank as soluble boron without sedimentation occurring, which is likely to block your spray equipment). Always combine 300 grams per hectare of NTS Fulvic Acid Powder™ with both of these applications to increase uptake and to chelate the manganese and zinc cations.
Rust can also be linked to a boron shortage, but it can also arise when copper and manganese are missing.
Tobacco mosaic virus (TMV) can also have a boron link along with excess phosphorus, as viruses need phosphate to replicate. Sulphur is also an important mineral to protect against this disease and it is no accident that high phosphorus which shuts down sulphur, is implicated in TMV.
9 Little-Known Tips About Boron
1) Boron is an important mineral for single-celled bacteria and algae, but it is of much less importance for fungi and yeasts. In fact, it can be fungicidal and should not be included with fungi based biological brews.
One bacteria with a particularly strong requirement for boron is Azotobacter, the free-living, nitrogen-fixing dynamo. Zinc and molybdenum are the other trace mineral essentials for this N-fixer. I always try to include a little of these three minerals when I apply these organisms to the soil or leaf.
2) In seriously boron-deficient soils, it is always a good idea to address this mineral both in the soil and via the leaf as a foliar. In fact, there is a direct parallel here relative to magnesium uptake in humans. In that case, we see that a long term magnesium deficiency can reduce the uptake of magnesium through the gut lining. That’s why it is so productive to bypass the gut with transdermal magnesium. There is a similar finding relative to boron. In a 2010 study by Victoria Fernandez et al, we learnt that chronic boron deficiency in the soil can limit boron absorption through the leaves. I always favour the inclusion of NTS Stabilised Boron Granules™ with a starter blend to ensure that the soil route has been addressed. This practice will then ensure that the pre-flowering boron foliar spray will offer maximum benefit.
3) Boron has been shown to seriously increase the efficacy of fungicides including benomyl and zineb, but it must always be used as boric acid for this purpose rather than sodium borate (e.g. Solubor). All fungicides are more effective in acidic conditions. Sodium borate is alkaline, so you are effectively giving with one hand and taking with another. It is a little like the humic acid/fulvic acid story. Humic and fulvic acid can increase uptake of farm chemicals by over 30%, however, humic acid is also very alkaline and is not chemically compatible with most chemicals. That’s why you should always use fulvic acid, if you wish to combine humates with chemicals.
4) Boron can also impact the performance of natural fungicides. In a 1997 study by Duffy et al, biocontrol activity with Trichoderma koningii was improved in the presence of adequate boron. Interestingly, in that same study, alkaline soils sponsored poor Trichoderma performance and high phosphorus was another limiting factor. You would have to wonder about the burning capacity of DAP/MAP when they ionise near the roots and the Trichoderma is subjected to the sizzling heat of raw phosphoric acid. That’s one reason why you always buffer these acid phosphates with humic acid.
5) Boron deficiency can also impact other beneficial soil life, as it can limit the plant exudates provided by the plant to stimulate specific soil life. If you are a banana plant, for example, with a particularly high need for manganese, then you combine specific nutrients with your glucose root exudates to encourage proliferation of the manganese-reducing organisms that make manganese available to you. These nutrients are provided through the root cell membranes, which are compromised during boron deficiency.
6) Boron can become toxic at certain applications. In fact, it can even be used as a herbicide. The maximum rate of borax that can be broadcast over one hectare, at one time, is 15 kg per hectare in low calcium soils. However, that rate can be safely increased to 25 kg per hectare when sufficient calcium is present. I remember the wonderful American consultant, Neal Kinsey, citing an early failure in his consulting career. He had recommended a need for considerable lime and 25 kg of borax. The grower reasoned that he couldn’t afford the lime this season so he applied just the boron to his calcium-deficient soils. He was not too impressed when the excess boron application killed his corn crop.
7) Boron opens the trapdoor that allows the proceeds of the day’s photosynthesis to be distributed throughout the plant. This includes the 30% sugars gifted to the soil life each day. In this context, the soil life pay quite a price for this deficiency. A refractometer can pick up this problem – i.e., when the brix in the late afternoon is the same as the brix levels in the morning, translocation has stopped and the plant is effectively constipated. Here’s the mechanics of this phenomenon for those of you who like to understand how things work:
Boron deficiency impacts photosynthesis, and that reduced activity decreases the carbohydrate accumulation in the petioles. Studies have shown that this, in turn, leads to an accumulation of carbohydrates in the leaves, because the glucose can not be transported to the other parts of the plant.
8) Low boron directly impacts the medicinal value of the food you are producing. Boron deficiency sponsors lower levels of vitamin C and glutathione within the plant. This is due to a drain on both of these antioxidants through constantly neutralising the excess free radicals created by this deficiency. This also creates a less resilient plant, with a greater need for chemical intervention.
I will explain how this phenomenon occurs. Boron deficient plants accumulate unnaturally high levels of two phenolic compounds called caffeic and chlorogenic acid in their upper leaves – deficiency symptoms of immobile minerals like boron and calcium always show up in the younger leaves first. Excess caffeic acid kills growing tips and clogs conducting tissues. This imbalance also sponsors the overproduction of polyphenol oxidase, which oxidises these acids and further damages the young leaves, which become discolored and brittle. This can eventually lead to the dieback that is a feature of boron deficiency. Vitamin C and glutathione arrive to neutralise the free radical fires generated by this imbalance, and are hence depleted in your produce.
It’s always important to realise that the medicinal value of food is determined by how that food was produced. In one UK study of vitamin C levels in fresh produce, they found a significant percentage of oranges that contained no vitamin C at all. If you shut down boron with excess N and K (common in citrus), then vitamin C can be seriously depleted, as I have just described.
9) While too much potassium can shut down boron, too little boron can limit the transport of potassium to the stomata where it is required for stomatal opening. Sluggish stomata can impact respiration and hinder the uptake of CO2, for that all-important photosynthesis.
Boron is an unstable, highly leachable trace mineral that should always be monitored, particularly prior to flowering. In fact, boron foliar sprays before flowering can offer amongst the best cost-to-benefit ratio of any farm input.
Humus is the boron storehouse and humus is two-thirds depleted in most of our soils. Hence, applied boron should always be combined with humic acid, to create a stable boron humate.
Boron is absolutely integral to a healthy, resilient crop in every farming scenario and yet it is so often overlooked. This mineral is a prime example of the multiple benefits associated with a Nutrition Farming® approach, where we return to root causes to solve problems.