Agronomy notes


Borax counts some of the world’s leading boron agronomists among its staff. These agronomy notes have been compiled in response to commonly asked questions about boron’s role in plant nutrition.
Boron Deficiency Symptoms

Boron Deficiency Symptoms

Plants initially may not exhibit obvious symptoms of nutrient deficiencies other than a slower growth rate, which may be due to other factors. When moderate or severe nutrient deficiencies occur, most crops exhibit visible symptoms which are typical for deficiencies of a particular nutrient. Knowledge of boron-deficiency symptoms can help in diagnosing deficiencies. Symptoms should be confirmed with results of soil tests and plant analyses, and appropriate corrective action taken.

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The Role of Boron in Flowering and Fruit, Nut and Seed Formation

The Role of Boron in Flowering and Fruit, Nut and Seed Formation

One of the important functions of B in plant nutrition is its role in fostering pollen growth and development, which is important in seed set and the resulting fruit, nut and grain production. Therefore, it is important to know the available B status for specific crops and the environmental conditions which may reduce B availability prior to, and during the critical period just before and during seed set. One or more foliar sprays of a B source such as Solubor®, depending on the specific crop, can help ensure that there is sufficient available B at this critical period.

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Boron Mobility in Various Plant Species

Boron Mobility in Various Plant Species

Boron is a micronutrient required for all plant nutrition. While it has been generally accepted that boron is phloem-immobile in plants, recent research has shown that boron is mobile in the phloem tissue in a number of species. Diagnosis of boron deficiencies and the most efficient methods of boron application differ in plant species with respect to boron mobility or immobility. Knowledge of the relative mobility of boron within a particular plant species will improve the ability to diagnose boron deficiencies and supply the needed boron for optimum crop production.

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Functions of Boron in Plant Nutrition

Functions of Boron in Plant Nutrition

Boron is a micronutrient required for all plant nutrition. The main functions of boron relate to cell wall strength and development, cell division, fruit and seed development, sugar transport, and hormone development. Some functions of boron interrelate with those of nitrogen, phosphorus, potassium and calcium in plants. Balanced nutrition is essential for optimum crop growth. Soil application of Granubor® 2 or foliar sprays of Solubor® or can be used to ensure an adequate B supply for optimum growth.

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Boron applications for Coastal Bermudagrass

Boron applications for Coastal Bermudagrass

Boron is essential for all plant growth. It aids in the transfer of sugars and nutrients from leaves to reproductive organs, and increases pollination and seed development. Coastal bermudagrass requires a supply of available boron, especially during rapid vegetative growth. Some Coastal bermudagrass varieties may respond to applied boron, especially on sandy soils in high rainfall regions, or with adverse weather conditions during the growing season. Where needed, a preplant application of Granubor® 2 with the early-season top-dressed NPK fertilizer generally will ensure an adequate supply of boron.

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Boron applications for improved cotton yields

Boron applications for improved cotton yields

Boron is essential for all plant growth. It aids in the transfer of sugars and nutrients from leaves to fruit, and increases pollination and seed development. Cotton requires an available supply of boron – especially during the boll development stage – or boll shed may occur, which reduces yields. Multiple foliar sprays of Solubor® applied alone or with insecticides will ensure an adequate supply of boron during flowering and boll development. Preplant soil application of Granubor® 2 plus foliar sprays of Solubor® during the season are recommended for soils testing low in available boron.

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Boron applications for improved peanut quality and yields

Boron applications for improved peanut quality and yields

Boron is essential for all plant growth. It aids in the transfer of sugars and nutrients from leaves to fruit, and increases pollination and seed development. Peanuts requires an available supply of boron, especially during the pod development stage, or “hollow heart” may occur, possibly reducing quality and yields. One or more foliar sprays of Solubor® applied alone or with insecticides will help ensure an adequate supply of boron during flowering and pod development. Preplant soil application of Granubor® 2 plus foliar sprays of Solubor® during the season are recommended for soils testing low in available boron.

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Boron applications for increased apple production

Boron applications for increased apple production

Boron is essential for all plant growth. It aids in the transfer of sugars and nutrients from leaves to fruit, and increases pollination and seed development. Apples require an adequate supply of available boron, especially during flower formation and fruit set. Foliar sprays of Solubor® during the dormant season, pre-pink and early bud stages will ensure an adequate supply of boron during the critical stages of flowering and fruit development. Apples are sensitive to over-applications of boron, and boron toxicity can result if the recommended boron application methods and rates are not carefully followed.

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Boron applications for increased grape production

Boron applications for increased grape production

Boron is essential for all plant growth. It aids in the transfer of sugars and nutrients from leaves to fruit, and increases pollination and seed development. Grapes require an adequate supply of available boron, especially during flowering and fruit set. Multiple foliar sprays of Solubor® applied alone or with insecticides will ensure an adequate supply of boron during the critical stages of flowering and berry development. Preplant soil application of Granubor® 2 plus foliar sprays of Solubor® during the season are recommended for soils testing low in available boron.

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Boron applications for increased soybean yields

Boron applications for increased soybean yields

Boron is essential for all plant growth. It aids in the transfer of sugars and nutrients from leaves to reproductive organs, and increases pollination and seed development. Soybeans require an adequate supply of available boron, especially during flowering and seed development. Multiple foliar sprays of Solubor® will ensure an adequate supply of boron during this stage of growth. Foliar sprays of Solubor® can be combined with other field treatments, such as insecticides, to reduce costs. Preplant soil application of Granubor® 2 plus foliar sprays of Solubor® during the season are recommended for soils testing low in available boron.

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Boron applications for increased yields of high-yield field corn and sweet corn

Boron applications for increased yields of high-yield field corn and sweet corn

Boron is essential for all plant growth. It aids in the transfer of sugars and nutrients from leaves to reproductive organs, and increases pollination and seed development. Corn requires a supply of available boron, especially during tasseling and silking. Where needed, a preplant application of Granubor® 2 or a foliar spray of Solubor® prior to these stages of growth generally will ensure an adequate supply of boron. Only certain varieties of field corn under high-yield conditions – and some sweet corn varieties – may respond to applied boron, especially on sandy soils in high rainfall regions, or with adverse weather conditions during the critical stages of tasseling and silking. In order to avoid toxicity, application rates of boron and methods should be followed.

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Boron in forestry production

Boron in forestry production

Boron deficiency is the most common micronutrient limitation in forest plantations. It occurs in many countries, particularly in exotic plantations of eucalypts and pines, but also in plantations and natural stands of native species on soils altered by macronutrient fertilization, liming, fire or erosion.

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Fruit tree foliar nutrient sprays

Fruit tree foliar nutrient sprays

Foliar nutrient sprays are commonly applied to fruit trees. Boron is immobile in most plant tissues so boron may not be readily transported to developing flower buds. Solubor® can be effectively applied with dormant oil-insecticide sprays during the dormant stages of most fruit trees.

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Yields of pistachio increased with boron application

Yields of pistachio increased with boron application

  • Recent research results in California have shown that foliar applications of Solubor® have increased pistaschio yields.
  • The best time for foliar application is from the late dormant to the early bud stages.
  • Soil applications of boron are not as effective as foliar applications in supplying sufficient boron for flowering.
Brown, Ferguson, and Picchioni worked with 1,000 pistachio trees in California over a 4-year period to
investigate the role of boron (B) nutrition and review current B recommendations. Cumulative 3-year yields
of pistachio per tree from foliar and soil-applied B are given in the table shown here. Their results show
greater yields were definitely obtained with foliar application of Solubor®. The best application rate shown in
this research was 5 pounds of Solubor® in 100 gallons of water. The best time to use a foliar application was
from the late dormant to early bud stages of development.

Soil-applied B at 2 to 8 ounces per tree affected yields sometimes. Soil-applied B results were not as
consistent, nor as dependable as a foliar application.

Pistachio yield was only one measurement that Brown, Ferguson and Picchioni made on trees. They
documented several influences of foliar-applied B at the critical late dormant to early bud stages. Boron
increased pollen viability, fruit set, and leaf B concentrations, but decreased blanking percentage. All of these
measurements lend support to applying 5 pounds of Solubor®/100 gallons of water per tree at the right time.

DOWNLOAD PDF FOR TABLE
 

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Soybeans

Soybeans

Boron fertilization of soybeans has been shown to increase grain yield at locations across the world when the boron supplying power of the soil is inadequate even though soybeans are listed as tolerant to boron deficiency. University research has found soybean yield increases ranging from 2-17.91 bushels per acre due to application of boron to boron deficient soybeans.

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Boron reactions in soils

Boron reactions in soils

Boron deficiencies in crops are found mainly on low organic matter soils and on acid, sandy soils in humid regions. Organic matter is the storehouse for most of the available boron (B) in soils. Boron deficiencies frequently are associated with drought periods, because root activity decreases in the surface soil layer. Balanced soil fertility, which gives improved plant vigor and root growth, results in optimum uptake of B and other plant nutrients.

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Does manure contain enough boron?

Does manure contain enough boron?

Animal manures contain varying concentrations of most plant nutrients. The average boron content of animal manure is 0.03 lbs./ton. Assuming an application rate of 10 tons/acre, the resulting boron rate of 0.3 lbs./acre may not be sufficient for high-boron requiring crops, such as alfalfa. Supplemental boron applications should be based on yield goals for the specific crop and on results of soil tests and/or plant analyses.

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Effects of sodium in borax on soils and crops

Effects of sodium in borax on soils and crops

Sodium is found in all soils and crops. Soils in humid regions, where most boron (B) deficiencies occur, contain about 50-150 lbs./acre of sodium in the surface 6-inch layer, but soils in drier regions may contain higher levels of sodium. While borax contains some sodium, one lb. of B/acre as borax only supplies about 0.9 lbs. of sodium/acre. Application of boron at recommended rates would result in an application of only 1-2 lbs. of sodium/acre, which would not significantly affect soils and crops.

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Fertilize before boron deficency symptoms occur for optimum yields

Fertilize before boron deficency symptoms occur for optimum yields

Visual symptoms of boron deficiency may not occur until the deficiency has become moderate or severe. At this stage, slower growth may have reduced the yield potential for the crop. Use the results of soil tests and/or plant analyses to help assess the potential for boron deficiencies to ensure adequate boron supplies for the crop.

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Plant tissue testing for boron

Plant tissue testing for boron

Plant analysis can be a valuable tool in determining the general nutritional status of crops during the growing season. Accurate interpretation of plant analyses data requires that plant tissue samples be carefully collected and handled prior to shipment to the laboratory. Knowledge of the normal boron sufficiency range in a given crop helps to interpret the analytical results and to diagnose a possible boron deficiency.

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Soil tests for available boron

Soil tests for available boron

Boron deficiencies may be suspected on coarse-textured soils where organic matter content is low, on soils with a pH above 6.0, and on recently limed soils. Soil testing and plant analyses are both helpful in assessing the potential boron-supplying capacity of the soil and the current boron status of the plant. Recent research has shown that three commonly used soil tests, the Mehlich-1 and -3 tests and the DTPA test modified to include sorbitol, also may be used to determine available boron in soils. The hot water test (HWT) is the most common, however. The critical value of available boron in a soil test may be affected by soil and the environment, which must be considered in interpreting soil test results.

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Differences in Boron Fertilizer Sources

Differences in Boron Fertilizer Sources

Boron was first shown to be an essential micronutrient for plant growth and development by Warington in 1923. Boron is essential for all plant growth, aiding in the transfer of sugars and nutrients from leaves to fruit and increasing pollination and seed development. Growers should know the relative boron needs for each specific crop, as well as the water soluble available boron supply in the soil, to determine the optimum rate and method of applying sufficient boron for optimum yields.

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Solubility of Solubor in Liquid Fertilizers

Solubility of Solubor in Liquid Fertilizers

The recommended soil application rate of boron generally ranges from 0.25 to 2.0 lbs. of B/acre.
Because it is difficult to separately apply these low rates of boron fertilizers to soil, granular or fluid NPK
fertilizers generally are used as carriers of boron. Such application assures more uniform application of boron to the soil and also eliminates the cost of separate applications. Soluble boron sources such as Solubor® may be easily mixed with fluid fertilizers to provide the recommended boron rates for crops.

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Amounts of Solubor to Mix into Spray Tanks to Supply Desired Boron Rates

Amounts of Solubor to Mix into Spray Tanks to Supply Desired Boron Rates

Foliar applications of boron generally are more effective than soil applications in supplying sufficient boron for flowering and reproductive development in crops. Solubor® is highly water soluble, and is commonly applied in foliar sprays. It is also compatible with most pesticides, so it also can be applied in these sprays. Because the season for the most effective foliar application of boron is short, foliar sprays must be
prepared quickly and accurately.

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Relative Plant Tolerance to Available Boron Supply

Relative Plant Tolerance to Available Boron Supply

Boron is essential for all plant growth. It aids in the transfer of sugars and nutrients from leaves to fruit, and increases pollination and seed development. Plant species vary considerably in their tolerance to the boron supply in the root environment. Plant species also vary considerably in their boron requirement. Reports show that many of those crops with higher boron requirements also usually have a greater tolerance to higher levels of available boron, so applying recommended boron rates and methods should not result in problems with excessive boron. Growers should know the relative boron needs for each specific crop as well as the available boron supply in the soil to determine the optimum rate and method of applying sufficient boron for optimum yields.

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How Much Will Increased pH Affect Pesticide Efficacy?

How Much Will Increased pH Affect Pesticide Efficacy?

Efficacy of some pesticides may be affected by increased pH of the pesticide tank mixes. Solubor® may increase the pH of unbuffered solutions. Inclusion of an appropriate buffer to control the pH of tank mixes is suggested for those pesticides whose efficacy is known to be reduced by increased pH.

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Boron for profitable alfalfa

Boron for profitable alfalfa

Alfalfa has a higher boron requirement than most crops. Results of soil tests and/or plant analyses can be used to assess the available boron status for this crop. For optimum yields of high quality alfalfa, it is essential to maintain adequate supplies of available boron throughout the growing season. Boron fertilizers can be topdressed with potassium and/or phosphate fertilizers in the spring, or after the first harvest of established alfalfa, or as foliar sprays.

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