Frequently Asked Questions

U.S. Borax is doing our part to combat global hunger by helping farmers efficiently grow abundant, healthy crops. How? By providing a clean, reliable source of boron, a micronutrient that plants—and people—need to thrive. Here, you’ll find answers to some of the queries we hear most often.

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Boron Micronutrient Questions

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General Questions

Boron Micronutrient Questions

What is the recommended maximum concentration of boron in irrigation waters for continuous use on all soils?
Irrigation waters containing 0.75 ppm boron may be continuously used on all soils. One acre-inch of water delivers 0.17 lbs boron per acre in waters containing 0.75 ppm boron. On fine-textured soils at pH 6.0 to 8.5, irrigation waters containing between 2.0 and 10.0 ppm boron may be used for up to 20 years, except for citrus which has a maximum recommendation of 0.75 ppm boron.

Source: Branson RL, et al. “Water Quality in Irrigated Watersheds.” J Environ Quality. 1975;4:33-40.
How much will increased foliar spray solution pH affect pesticide efficiency?
Pesticides vary in response to pH. Most pesticides take hours or days to break down and some are affected very little by moderate pH changes. Solubor® at a rate of 1 lb per 5 gallons of water will typically raise the solution’s pH to 8.0. Other liquid Boron fertilizers have pH higher than 8.0. There is no strong evidence that pest control has been affected where chemicals are mixed and sprayed immediately. Read Agronomy note: How much will increased pH affect pesticide efficacy? for more information.

Source: Gorsuch CS and Griffin RP. Extension Entomologists, Clemson University, Clemson, SC. 29634-0365.
What is the effect of boron on animals, such as cattle, consuming forage or hay where excessive rates of boron have been applied?
Cows fed 2.5 g B/day for 40 days were not affected in any way. This means that if hay contained 240 ppm boron (three times the normal level for alfalfa), a cow could eat 23 lbs of hay per day with no ill effect. An acute lethal dose where half of test animals (rats) died would be equivalent to 150 g boron per 500 lbs animal, or 1,380 lbs of alfalfa in one day if the alfalfa contained 240 ppm boron. Two-year studies with rats and dogs showed no effect on reproduction when 350 ppm boron was included in the diet, and no effect on fertility, lactation, litter size, weight, or appearance.

Read more about how boron deficiency affects forage crops.

Source: Sprague RW. The Ecological Significance of B. Valencia, CA: U.S. Borax, Inc.; 1972.
How much boron is supplied in manure?
The average farm manure contains 0.03 lbs of boron (B) per ton. If it is assumed that all of the boron in the manure is plant available, 10 tons of manure would supply 0.3 lbs of B. This rate of boron per acre per year will not supply alfalfa or many other crops with their total boron requirements.
 
Poultry manure contain approximately the same boron content as average farm manures, but in some situations, boron materials are applied to poultry house floors to control insects. Based on the maximum rate of boron applied and manure produced, boron-treated poultry manure will contain approximately 0.7 lbs of boron per ton. If it is assumed that all of the boron in poultry manure is plant available, 4 tons of poultry manure (the average rate applied per acre) would supply 2.8 lbs of B. This rate of boron per year would supply most crop boron needs. Untreated poultry litter however contains only 0.03 lbs of boron per ton, and the 4 ton rate would supply only 0.12 lbs of B. This rate of boron per acre would not supply most crop needs. Rates of supplemental boron and other plant nutrients applied in addition to manure should be based on yield goals along with soil tests and/or plant analyses.

Read Agronomy note: Does manure contain enough boron? for more information.

Source: Blanck FC. Handbook of Food and Agriculture. Reinhold Pub Co.; 1955. Chapter, Manure Analyses p. 91.
What is the importance of boron/calcium interaction?
Damage to plant tissues occur when calcium and boron get far out of balance. A good example of this was shown with peanuts when internal damage (hollow heart) was greatly increased where gypsum (calcium sulfate) was applied without boron, causing a wide shift in plant tissue calcium-boron ratio. Hollow heart of peanut completely disappeared where only 0.25 lbs/acre boron was applied along with the gypsum, bringing about approximately a five-fold decrease in the plant tissue calcium-boron ratio.

Source: Morrill LG, et al. “B Requirements of Spanish Peanuts in Oklahoma: Effects on Yield and Quality and Interaction with Other Nutrients.” Oklahoma Agr Exp Stn. 1977;MP-99.
 
How do boron and nitrogen interact in broccoli and other crucifers?
High ammonium nitrogen fertilization levels may increase pith calcium concentration (in cauliflower), resulting in a wide calcium-boron ratio and increased pith discoloration. Foliar sprays of boron reduced but did not eliminate discoloration.

Source: Bryan HH. Pith Discoloration and Breakdown in Cauliflower [dissertation]. Cornell University; 1964.
 
How accurate and precise are boron soil tests?
Soil scientists have found that the development of common soil test extractants, interpretations, and recommendations have to be limited to physiographic units and common soil characteristics. Boron soil testing is no exception. Soil texture, organic matter, and soil pH will strongly influence interpretation of the test results. The soil test methods used today accurately reveal the amount of plant available boron with an average precision of +/- 0.1 ppm B.

Read Agronomy note: Soil tests available for boron for more information.

Source: Gartley KL. “1999 Sample Exchange Results Soil, Plant and Manure Samples.” Mid-Atlantic Soil Testing and Plant Analysis Work Group, University of Delaware Soil Testing Laboratory. Newark, DE: 1999.
 
Why do crops grown on soils testing low in boron sometimes show no response to boron fertilization even when there is no other limiting factor?
On coarse- or medium-texture surface soils with fine texture subsoils, boron fertilizer from previous years may leach and accumulate in the subsoil where they are available to plant roots.

Source: Sedberry JE, Jr., et al. “Boron Investigations with Cotton in Louisiana.” LSU Agr Exp Sta Bull. 1969:635.
 
How rapidly does boron leach out of the topsoil?
Soil texture and the amount of water moving through the soil profile largely determine the potential for boron leaching. Soils with clay contents above 20% (sandy clay loam, clay loam, and finer texture) have a lower potential for boron leaching. Soils with less than 20% clay (sand, loamy sand, and sandy loams) are more likely to leach. An application of 4.4 lbs/acre boron was shown to leach out of the surface 8 inches of a sandy loam soil within six months. Boron applied at planting will normally remain available for the cropping season on most soils.

Read the following for more information:
Source: Touchton JT and Boswell FC. “B Applications for Corn Grown on Selected Southeastern Soils.” Agron J. 1975;67:197-200.
 
Would a 10% boron material in a bulk blend or a homogeneous complete fertilizer granule with 0.25% boron supply more granules per square foot with a better supply boron than a 15% boron material in a bulk blend?
It is true that for a given rate of boron applications, the number of granules per square foot is inversely proportional to the percent boron in the particle, eg based on a standard granule weight of 2.2 g/100 granular, a 15% material spread at the rate of 1 lb/acre boron would supply 3.15 granules/sq ft; a 10% material, 4.74 granules/sq ft; a 0.25% material, 189.3 granules/sq ft. Plant roots, however, contact only 1% of soil surface area. Boron moves to plant roots mainly by mass flow. Boron from 3.15 granules of the more concentrated 15% material would be more likely to sustain an adequate level of soil solution boron than would the boron from more granules with lower percentage boron concentration. In general, yield responses from granulated and from blended fertilizers have been similar.

Source: Aldrich SR. Illinois Fertilizer Conf. 1962.
 
Which method of boron application is superior–soil applied or foliar applied boron?
Both soil and foliar applications have been shown to be equally effective, depending on either convenience or circumstances. A low soil test boron would indicate the need to apply boron to the soil at planting. Foliar boron is applied to supply crops during maximum need at flowering and fruiting, or to correct a deficiency discovered after planting. Recommended boron application rates generally are higher for soil than for foliar applications.

Learn more: Boron Application

Source: Roberts RK, Gersman JM, and Howard, DD. “Soil and Foliar-Applied Boron in Cotton Production: An Economic Analysis.” J Cotton Science. 2000;4:171-177.
 

Product Questions

Are U.S. Borax products organic?
U.S. Borax fertilizers are listed appropriate for organic growers by the Organic Materials Review Institute (OMRI). Read more about all of our organic certifications.
How do you test your products for accurate boron content?
We use titration to measure wt.% of B2O3 at our Quality Lab in Boron, California. There, our experts routinely test U.S. Borax borate products. Learn more about our boron testing methods.
Is boron more plant-available from various liquid formulations than from wetable powders like Solubor?
The boron in all water-soluble sources is equally available to plants. The boron form taken up by plants is the boric acid molecule, whether through leaves or roots. In recent studies, all boron sources proved equally effective in increasing cotton and soybean dry weight, boron concentration or boron uptake. Boron uptake was highest with Solubor® (sodium borate) and tissue concentrations were higher or equal to those observed with the other boron sources.

Read more about the solubility of Solubor. 

Source: Guertal EA, et al. “Boron Uptake and Concentration in Cotton and Soybean as Affected by Boron Source.” Commun Soil Sci Plant Anal. 1998;29(19&20):3007-3014.
 
How do zinc, copper, and manganese sulfate react in spray mixes with Solubor?
Solubor® spray mixes of 1 or 2% Solubor concentration are commonly used. The pH of these mixes rises to around 8. At this pH, zinc sulfate converts to zinc hydroxide which is slightly soluble. (Copper and manganese also form hydroxides in pH 8 solutions.) The efficacy of the boron and zinc is not altered drastically as far as the plant is concerned, but agitation of the mix is important to maintain particle suspension. Acidifying agents in tank mixes can prevent precipitation.

Source: Handbook of Chemistry and Physics, 30TH ed. Cleveland, OH: Chem Rubber Pub Co; 1948.
 
Why is adding Solubor to high pressure nitrogen solutions not recommended?
The reaction of dry sodium borate with moisture produces boric acid and sodium hydroxide. The ammonium ion in the presence of excess hydroxyl reverts to ammonia and water. The ammonia volatilizes. In high pressure nitrogen solutions, with free ammonia, the evolution of ammonia is accelerated by adding sodium borate to the solution. If these nitrogen fertilizer materials (urea ammonium nitrate solutions, or dry ammonium nitrate blended with sodium borate fertilizer) are combined and incorporated directly into the soil, they can be used together.

Source: Winter KT, et al. “Ammonia Volatilization from Lime-Urea Ammonium Nitrate Suspensions Before and After Soil Application.” Soil Sci Soc Am J. 1981;45:1224-1228.
 
Can I buy products directly from U.S. Borax?
Please contact your local sales representative for more information about purchasing our industrial and agriculture products through us or one of our distributors.
Where can I get material safety data sheets or handling information for your products?
You can find information about safety and handling in the following places: Or send us an email at rtb.sds@riotinto.com and tell us which product you’re using
 
Can you send me copies of your product labels?
To request product labels, please contact your sales representative or customer service representative for more information.

General Questions

I am an agronomist or agricultural consultant looking for information on the use of boron or borates for crop health. Can you help me?
Yes! If you don’t find what you need on our web site, please contact our global agriculture team members with your questions.
Where do you get the borates you use in your products?
We operate California’s largest open pit mine in Boron, California. Read more about U.S. Borax Operations.
What if something is wrong with my shipment?
In the Americas:
  • For non-emergencies, contact Customer Service at (800) USBORAX (800-872-6729)
  • For emergencies, dial (800) 228-5635, extension 144
For all other regions, visit our customer service page to find your local representative.
 

U.S. Borax, part of Rio Tinto, is a global leader in the supply and science of borates—naturally-occurring minerals containing boron and other elements. We are 1,000 people serving 500 customers with more than 1,700 delivery locations globally. We supply 30% of the world’s need for refined borates from our world-class mine in Boron, California, about 100 miles east of Los Angeles.  Learn more about Rio Tinto

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