The details are always hardest to manage. It’s getting the small things right that determine whether we are successful or not. While it is important to have  proper soil pH and available calcium. Many farmers overlook the small details; like understanding that micronutrients are the catalysts for big yield gains. Boron is the catalyst that makes calcium, nitrogen, magnesium, phosphourus, carbon, and potassium more available to your crop.

Only a few of Earth's naturally occurring chemical elements make up living matter. Just six of them; carbon, hydrogen, nitrogen, oxygen, phosphorous and sulfur, make up for 99% of all living tissues. Nevertheless, other minerals or trace elements are crucial for all vital functions even if this may be in extremely low dosages. Some of these, such as iron, copper, cobalt, zinc or manganese, are required by all living forms. Boron is one of those crucial elements, proven essential for the structure of plants.

Any soil test you conduct should be a complete soil test such as Midwest Labs S3C test. That test includes, base saturation, including sodium, and a full micronutrient package. In many of the tests we look at, we see more and more test coming back with very low boron readings. Boron has been much overlooked in the past, but many are discovering the benefits of this micronutrient.

Boron Function

Adequate boron nutrition is critical for high yields and quality crops. The main functions of boron relate to cell wall strength and development, cell division, fruit and seed development, sugar transport, and hormone development. Boron affects sugar transport in plants, flower retention, pollen formation, and germination. Boron is needed in protein synthesis and is associated with increased cellular activity that promotes maturity, increases flower set, and fruit yield and quality. Boron also affects nitrogen and carbohydrate metabolism and water and sap flow in the plant.

Photosynthesis transforms sunlight energy into plant energy compounds such as sugars. For photosynthesis to continue, the sugars must be moved away from the site where they are made and stored or used to make other compounds. Boron increases the rate of transport of sugars to actively growing regions and to developing fruit (grain). Boron is essential for providing sugars which are needed for root growth in all plants and also for normal development of root nodules in legumes such as alfalfa, soybeans and peanuts.

Since boron is non-mobile in plants (like calcium), a continuous supply from the soil is required in all plant growing points. In mineral soils, release of boron is usually quite slow. Much of the available soil boron is held rather tightly by soil organic material. As organic matter decomposition occurs, boron is released with a portion being absorbed by plants, some leaching below the root zone area (especially in acid soil), or tied up under alkaline soil conditions.

Boron Deficiency and Excess

Boron deficiencies are found in acid soil, sandy soils, soils with low organic matter, and in regions of high rainfall. Borate ions (soluble boron) are mobile in soil and can be leached from the root zone. Boron availability also decreases on heavy clay and high pH soils. Soils with a high pH (at 7.5 pH boron becomes fixed) or which have just been heavily limed, have a limited amount of boron available for plant growth. Boron deficiencies are more pronounced during drought periods when root activity is restricted.

Plants deficient in boron continue to undergo cell division in growing tips, without cells changing into the proper type of cell. This results in cells that fail to becoming stem, leaves, and flower cells. As boron becomes deficient the vegetative growing point of the affected plant becomes stunted, deformed or altogether stop.

Boron does not often occur in toxic quantities in most arable soils. When toxic levels are reached, excessive boron can cause off color and stunting of plant growth. As boron concentrations in plant tissue increase to toxic levels, older foliage may exhibit leaf edge burning or necrosis. Some plants will also develop black spots on older foliage. High levels of boron can only be removed from soils through the leaching action of water flushing it below the active plant root zone.

Target Boron Levels

Depending on the crop, but for corn, shoot for 20 ppm in the soil. I have talked with many consultants in the past week and 5 ppm should be plenty. Boron can have negative impacts on soil biology when it get to high. Many soils routinely test less than 5 ppm and in many cases under 1 ppm.

For treating boron deficiency during the growing season apply 1-2 lbs of soluble boron. Plant tissue should read 2-75 ppm depending on the crop. More research will need to be conducted to further narrow the range.

Plant needs for boron can be applied as Granubor preplant broadcast to the soil or as Solubor or Solubor DF foliar sprays during the growing season.

Reference and Additional Reading

Boron, The Overlooked Essential Element

Boron is Essential for the Growth of Plants and Animals

US Borax

Midwest Labs Agronomy Handbook