Boron (B) is a micronutrient that is essential for cell wall formation and rapid growing points within the plant, such as reproductive structures. Interestingly, while higher plants require B, animals, fungi and microorganisms do not need this nutrient.

Quick Facts

Boron improves seed set under stressful conditions.

Quick Facts

Although requred in small amounts, boron is a component of all cell walls in the plant.

Quick Facts

Boron deficiencies are more pronounced during drought periods, when root activity is restricted.

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The line between deficiency and toxicity is narrower than other essential nutrients. Farmers should apply at proper rate and with proper placement.

Quick Facts

Corn most effectively uses boron when it's applied through broadcast soil applications.

Dig Deeper

Boron (B) exists primarily in soil solutions as the BO33- anion – the form commonly taken up by plants. One of the most important micronutrients affecting membrane stability, B supports the structural and functional integrity of plant cell membranes. Boron-deficiency symptoms first appear at the growing points, and certain soil types are more prone to boron deficiencies.

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The need for boron was established in the late 20’s, but its role and function within the plant continues to be researched and better understood.

Boron deficiencies are widespread across North America. From a global perspective, B is the most widespread micronutrient deficiency after zinc.

More than 90 percent of B is found in cell wall structures. B deficiencies generally stunt plant growth by reducing cell wall extension at the growing point. Younger leaves show symptoms first, which indicates B is not readily translocated in the plant. Deficiency symptoms may include reduced flowering; thickened, curled, chlorotic leaves; and soft or necrotic spots in fruits and tubers. Boron deficiencies are more pronounced during drought periods, when root activity is restricted.

Crops remove B from the soil, in the form of boric acid H3BO30. Several factors influence B availability in the soil and uneven distribution within the soil is common. Organic matter is the most important reservoir for B. Extreme hot, dry conditions and extreme cold conditions may decrease O.M. decomposition and reduce the release of B into the soil solution. Plant availability is good over a wide range of pH, from 5.0 to 7.5. Boron is mobile in the soil and is subject to leaching. Leaching is of greater concern in sandy soils and/or in areas of intensive irrigation or high rainfall.

Crops vary widely in their need for B, and the line between deficient and toxic amounts is narrower than for any other essential nutrient. B should be used carefully, especially in rotations involving different sensitivities to B. It is important that B fertilizers are applied uniformly in broadcast applications rather than in-furrow situations. Boron placed close to the seed greatly reduces stand counts.

Dig even deeper into Boron

Source: Soil Fertility Manual (2006) by the International Plant Nutrition Institute (IPNI) and the Foundation for Agronomic Research (FAR).

Deficiency Symptoms

Symptoms of deficiency can vary across crop species, but similarities exist for how nutrient insufficiency impacts plant tissue color and appearance. Nutrient deficiencies are commonly associated with the physical location on the plant (i.e., whether the symptoms are primarily observed on older versus newly formed plant tissue), but these symptoms can spread as the severity of the deficiency progresses.

All photos are provided courtesy of the International Plant Nutrition Institute (IPNI) and its IPNI Crop Nutrient Deficiency Image Collection. The photos above are a sample of a greater collection, which provides a comprehensive sampling of hundreds of classic cases of crop deficiency from research plots and farm fields located around the world. For access to the full collection, you can visit IPNI's website.