How much do you know about boron?

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By Fabiano Silvestrin, Principal Advisor, Global Market Development Agriculture, U.S. Borax

The majority of researchers and farmers have recognized the importance of boron in agriculture. Boron is necessary for proper plant nutrition. And, boron-deficiency can significantly affect crop yields.

Types of borates

Although its clear crops need boron, there is still debate as to what sources of boron are best in agriculture. There are basically two classifications of borates:

1. Those where the original source material has gone through a refinement process. Unsurprisingly, these are known as refined borates. Examples include boric acid, disodium octaborate tetrahydrate, borax decahydrate, borax pentahydrate, and anhydrous borax.
2. Those borates which have had no refinement process. These are called mineral or unrefined borates. Examples include hydroboracite, colemanite, and ulexite.

Borate solubility by type

The more soluble a product is, the more boron is available to the plant. The solubility of borates depends on the source material and the interaction of the boron with sodium (Na), calcium (Ca), and magnesium (Mg). The more Mg and Ca a borate has the less soluble this mineral will be.

Most of the borate fertilizers used in agriculture, come from the following boron ores:

Hydroboracite (CaMgB₆O₁₁6H₂O)
Calcium and magnesium borate which is practically insoluble in water (solubility of 0.8 g/L at 20° C)

Colemanite (Ca₂B₆O₁₁5H₂O)
Calcium borate which has low water solubility (4.7 g/L at 20° C)

Ulexite (NaCaB₅O₉8H₂O)
Calcium and sodium borate which has partial solubility in water (10.9 g/L at 20° C)

Kernite (Na₂B4O₇4H₂O)
Sodium borate, which is water soluble (19.0 g/L at 20° C)

Tincal, also known as borax, (Na₂B₄O₇10H₂O)
Sodium borate which is water soluble (26.5 g/L at 20° C)

Refined borates such as boric acid (H₃BO₃) and disodium octaborate tetrahydrate (Na₂B₈O₁₃.4H₂O) are highly soluble in water having solubility of 47.2 g/L and 97.0 g/L at 20° C, respectively. Because of this, they are widely used to produce liquid fertilizers for foliar fertilization and fertigation.

What is borax?

Many people think that there is only one type of borax. But, in addition to several other products, U.S. Borax produces three different forms:

1. Borax decahydrate (Na₂B₄O₇ • 10H₂O): About 11.4% boron
2. Borax pentahydrate (Na₂B₄O₇ • 5H₂O): About 15% boron
3. Anhydrous borax (Na₂B₄O₇): About 21.3% boron

The water solubility of each type of borax will depend upon the degree of hydration. Because borax decahydrate has a greater solubility in water and a lower percentage of boron, it is not widely used in agriculture. Rather it is mainly used in a variety of industrial manufacturing end uses, including as a laundry detergent booster.

On the other hand, borax pentahydrate (sold commercially by U.S. Borax as Granubor® and Fertibor®) and anhydrous borax are very efficient sources for use as fertilizers.

Borates in the field

When it comes to borated soil fertilization, growers should be concerned about using efficient boron sources capable of releasing 100% of the present boron and making boron available when plants really need the nutrient.

Not all boron sources are created equal: Research shows that not all boron sources are equal in their ability to provide plants with soluble boron throughout the season. In the tests below, all samples were of similar particle size.

Refined borates from U.S. Borax

U.S. Borax agriculture products are fully refined to remove impurities and maximize potential plant uptake. This process results in a pure, natural product that provides optimized nutrition throughout the growing season.

The U.S. Borax refining process involves several important steps:

1. We mine high-quality sodium-borate ore that is naturally low in calcium and other contaminants
2. We dissolve the ore in water
3. We settle the dissolved borate liquor to remove impurities
4. We cool the liquor and then further wash and filter the resulting crystal slurry
5. We dry the refined slurry to produce dry borate crystals
6. We check our products for purity, solubility, consistency, and optimal granulation
7. We constantly conduct and review field tests and other research to improve our products and services

For more information, visit our agriculture web site at: https://agriculture.borax.com/ or contact one of our regional agriculture experts.