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The Role of Boron: Much More Than a Synergist
American consultant, Gary Zimmer, coined the term “Calcium the trucker of all minerals and boron the steering wheel” and he correctly highlighted the critically important, synergistic relationship between these two minerals. It is a simple fact that you will be disappointed in your lime response if your soils are boron deficient because calcium does not provide its many benefits in the absence of boron. During a recent trip to New Zealand I was speaking with a dairy farmer who had made a considerable investment in lime but had seen very few benefits from the exercise. Upon further investigation I found that his soil tests revealed a massive boron deficiency! In fact, he had just 0.1 ppm of boron in his soils when he required a minimum of 1 ppm. He had created this deficiency through burning out his organic matter reserves with large applications of urea and then leaching boron with centre pivot irrigation. Organic matter is the boron storehouse as it is the only component of the soil that has the positively charged sites to attract and retain this negatively charged trace mineral (anion). As your organic matter declines so does your boron, as it is the most leachable of all trace elements. However this dairy farmer’s boron neglect cost him more than a poor lime response. There was virtually no clover on his entire property because legumes are boron-hungry and will struggle when boron drops to these levels. The lack of clover was also related to urea abuse as legumes never thrive in high N situations. When most people think of legumes they think of nitrogen fixation and the associated reduced requirement for applied N. However, legumes offer more than this. Legumes constantly release organic acids which are invaluable in solubilising locked-up phosphorus (over 70% of applied phosphate becomes insoluble) and they also make calcium more bio-available which is beneficial to both soil organisms and plants. So you get nitrogen, calcium and phosphorus from legumes and you don’t get a good legume to grass ratio without boron. These calcium and legume links should offer enough motivation for you to manage boron nutrition but this highly leachable trace element provides several other benefits.
Boron and Biology
Photosynthesis is the most important process on the planet because this is where we get our food. In an almost miraculous process, the plant combines sunlight, water and carbon dioxide to produce the glucose building blocks that are the basis of carbon chemistry. The grower’s chief role is to manage chlorophyll, the green pigment that houses the sugar factories. If there are pale colours, stripes or blotches in the leaf then you failed as a chlorophyll manager and will pay the price in terms of yield or increased pest pressure. The plant translocates 50% of all of the glucose it produces down to the roots each night, and 60% of this is squirted out into the root zone (the rhizosphere) to feed the hoards of microorganisms surrounding the roots. In the most classic example of the universal law, “give and you shall receive”, the plant is rewarded many fold for its glucose gift. In return for their daily feed, the soil microbes fix nitrogen from the atmosphere, solubilise locked-up phosphorus, recycle minerals from crop residues, remove toxins, produce plant growth stimulants and protect the plant from pathogens. What has this mutually beneficial deal got to do with boron? Well, quite a lot as it happens. There is a little trapdoor in each chloroplast which opens just before dusk to allow the glucose, intended for the roots, to flow freely from the factory. Boron governs the opening of this trapdoor. If your plants are boron deficient the glucose stays trapped in the chloroplast and the beneficial bugs, who deliver all nutrients to the plant, miss out on their daily tucker. In this situation a foliar spray of $3 worth of soluble boron becomes one of the best cost-to-benefit investments you will ever make because the whole give and take system falls flat on its face without boron. A refractometer is an invaluable tool for early detection of a boron deficit. Brix levels in the leaf should always be lower in the morning, following translocation of half of the sugars down to the roots overnight. If levels have not changed overnight, then you have detected a boron deficit and should correct it as a matter of urgency.
Flowering and Fruit Formation
It is my firm belief that there is no crop that will not benefit from a foliar spray of boron prior to flowering (except in very rare cases of boron toxicity in the soil). We like to see luxury levels of boron in the leaf tissue but this is rarely achieved. The boron requirement is much higher for reproduction than for vegetative growth as boron increases flower production and retention, pollen tube elongation and germination and seed and fruit development. Avocados are an incredibly boron-hungry crop and their very low fruit to flower ratio can be substantially improved with a foliar spray of boron at pre-flowering. The boron increases the length of the male pollen tube and improves the pollination process. It is common to see the top 25% of corn cobs not fill due to a boron shortage. I always recall visiting a corn grower in Kunnanurra who was facing a 25% yield loss on 1000 acres of table corn for the sake of an inexpensive boron foliar. He had assumed that because his starter fertiliser contained some boron the poor pollination must be due to a lack of bees. In actual fact, his irrigated, low carbon soils had lost the boron through leaching by the time his crop reached the boron draw-down time at reproduction. It was a stark and expensive lesson in the importance of leaf analysis before flowering. It can make a big difference getting things right at the business end of the season. Poor pod set in soybeans is another consequence of poor boron nutrition that could be avoided through early diagnosis with leaf analysis and a timely foliar spray of boron.
Cell Strength and Cell Division
In a synergistic process, not unlike bone development in humans and animals, boron is involved in cell wall strength as it moves calcium into the cell walls. Boron has also been shown to increase the solubility of silica in the soil, which further increases cell strength. It is a good idea to apply boron to the soil in late winter to sponsor the uptake of soluble silica before spring. This also improves calcium transport into the plant through improved, silica-based development of phloem and xylem (like building better highways). Good levels of calcium are required for the extra cell division needed during the spring flush. Boron is actively involved in cell division in its own right and this is why it is common to see misshapen fruit and vegetables where cell division was compromised due to boron deficiency during fruit formation. Rosetting (stunting) of plants can occur due to inadequate cell division in the growing shoots and this is particularly common in lucerne. A combination of boron compromised cell strength and cell division is responsible for hollow stems in broccoli. Never purchase these boron deficient vegetables as they are virtually guaranteed to have required more chemical intervention than otherwise. Dieback in vines crops can also be related to a boron related deficiency.
Plant Hormone Regulation
Plant hormones, like animal hormones, regulate many growth and reproductive functions. Flower initiation, fruit development, cell wall and tissue formation and root elongation are all influenced by hormones. Boron plays an important role in regulating plant hormone levels. This is yet another reason for your pre-flowering foliar spray of boron as there is such a strong hormonal presence during reproduction.
We have concluded that boron nutrition is never to be overlooked but what is the best type of boron to use and at what rates?
Boron and Biology
Photosynthesis is the most important process on the planet because this is where we get our food. In an almost miraculous process, the plant combines sunlight, water and carbon dioxide to produce the glucose building blocks that are the basis of carbon chemistry. The grower’s chief role is to manage chlorophyll, the green pigment that houses the sugar factories. If there are pale colours, stripes or blotches in the leaf then you failed as a chlorophyll manager and will pay the price in terms of yield or increased pest pressure. The plant translocates 50% of all of the glucose it produces down to the roots each night, and 60% of this is squirted out into the root zone (the rhizosphere) to feed the hoards of microorganisms surrounding the roots. In the most classic example of the universal law, “give and you shall receive”, the plant is rewarded many fold for its glucose gift. In return for their daily feed, the soil microbes fix nitrogen from the atmosphere, solubilise locked-up phosphorus, recycle minerals from crop residues, remove toxins, produce plant growth stimulants and protect the plant from pathogens. What has this mutually beneficial deal got to do with boron? Well, quite a lot as it happens. There is a little trapdoor in each chloroplast which opens just before dusk to allow the glucose, intended for the roots, to flow freely from the factory. Boron governs the opening of this trapdoor. If your plants are boron deficient the glucose stays trapped in the chloroplast and the beneficial bugs, who deliver all nutrients to the plant, miss out on their daily tucker. In this situation a foliar spray of $3 worth of soluble boron becomes one of the best cost-to-benefit investments you will ever make because the whole give and take system falls flat on its face without boron. A refractometer is an invaluable tool for early detection of a boron deficit. Brix levels in the leaf should always be lower in the morning, following translocation of half of the sugars down to the roots overnight. If levels have not changed overnight, then you have detected a boron deficit and should correct it as a matter of urgency.
Flowering and Fruit Formation
It is my firm belief that there is no crop that will not benefit from a foliar spray of boron prior to flowering (except in very rare cases of boron toxicity in the soil). We like to see luxury levels of boron in the leaf tissue but this is rarely achieved. The boron requirement is much higher for reproduction than for vegetative growth as boron increases flower production and retention, pollen tube elongation and germination and seed and fruit development. Avocados are an incredibly boron-hungry crop and their very low fruit to flower ratio can be substantially improved with a foliar spray of boron at pre-flowering. The boron increases the length of the male pollen tube and improves the pollination process. It is common to see the top 25% of corn cobs not fill due to a boron shortage. I always recall visiting a corn grower in Kunnanurra who was facing a 25% yield loss on 1000 acres of table corn for the sake of an inexpensive boron foliar. He had assumed that because his starter fertiliser contained some boron the poor pollination must be due to a lack of bees. In actual fact, his irrigated, low carbon soils had lost the boron through leaching by the time his crop reached the boron draw-down time at reproduction. It was a stark and expensive lesson in the importance of leaf analysis before flowering. It can make a big difference getting things right at the business end of the season. Poor pod set in soybeans is another consequence of poor boron nutrition that could be avoided through early diagnosis with leaf analysis and a timely foliar spray of boron.
Cell Strength and Cell Division
In a synergistic process, not unlike bone development in humans and animals, boron is involved in cell wall strength as it moves calcium into the cell walls. Boron has also been shown to increase the solubility of silica in the soil, which further increases cell strength. It is a good idea to apply boron to the soil in late winter to sponsor the uptake of soluble silica before spring. This also improves calcium transport into the plant through improved, silica-based development of phloem and xylem (like building better highways). Good levels of calcium are required for the extra cell division needed during the spring flush. Boron is actively involved in cell division in its own right and this is why it is common to see misshapen fruit and vegetables where cell division was compromised due to boron deficiency during fruit formation. Rosetting (stunting) of plants can occur due to inadequate cell division in the growing shoots and this is particularly common in lucerne. A combination of boron compromised cell strength and cell division is responsible for hollow stems in broccoli. Never purchase these boron deficient vegetables as they are virtually guaranteed to have required more chemical intervention than otherwise. Dieback in vines crops can also be related to a boron related deficiency.
Plant Hormone Regulation
Plant hormones, like animal hormones, regulate many growth and reproductive functions. Flower initiation, fruit development, cell wall and tissue formation and root elongation are all influenced by hormones. Boron plays an important role in regulating plant hormone levels. This is yet another reason for your pre-flowering foliar spray of boron as there is such a strong hormonal presence during reproduction.
We have concluded that boron nutrition is never to be overlooked but what is the best type of boron to use and at what rates?
