BORON deficiency is the most common and widespread of all micronutrient deficiencies.

In most agricultural soils BORON is associated with the soil organic matter. With decades of cultivation the organic matter content of our soils has decreased substantially. Therefore, the principal source of BORON has also substantially decreased.

Most BORON enters the plant passively with the transpiration stream (mass flow).

When transpiration is reduced, the uptake and translocation of BORON is reduced.

Factors that reduce transpiration include high humidity and soil moisture being either too high or too low.

BORON is relatively immobile in the plant. BORON availability in the soil decreases as soil pH rises above 6.5 pH. BORON can be leached from the soil profile in high rainfall areas.

BORON deficiencies can be overcome with multiple foliar sprays and/or multiple injections into drip tape. Foliar and Drip application rates of SOLUBOR (20.5% B) of 1 lb./Acre (= 0.2 lb. B) are common. Applications should be repeated at 7 – 10 day intervals. BORON deficiencies can be prevented with applications of BORON in preplant and sidedress fertilizers. Other sources of BORON are Borax (11% B), Boric acid (17% B), Sodium pentaborate (18% B) and Sodium tetraborate (21% B). Caution – most liquid BORON formulas contain very low amounts of actual B (2 – 4 %). Be sure to use enough.

BORON deficiency symptoms may be described as abnormal or retarded elongation of growing points and/or apical meristems. Leaves are misshapen, wrinkled, thicker and darker in color. Leaves and stems are brittle due to poor cell wall formation or the accumulation of phenols. In Monocots(Grasses), the leaves will spiral or twist. In Dicots(Broad leaf plants) the leaf tip will not form completely or will be malformed. Dicots require 3 – 4 times more BORON than Monocots.

BORON interacts with other elements in the soil and in the plant.

CALCIUM and BORON must be in balance for proper plant growth. The plant can not properly metabolize calcium when BORON is low and vise versa. CALCIUM inhibition of BORON uptake is noted on high pH soils.

Low levels of BORON in the plant affect PHOSPHORUS incorporation into cells and P containing compounds. The adsorption of P may be reduced by half at the roots of BORON deficient plants.

High NITROGEN and/or POTASSIUM levels can decrease the BORON level in plants. Increasing N and/or K decreases the CALCIUM level and the Ca:B ratio in plants.

Most crops require approximately 2-3 lbs. of elemental BORON per acre. Crops that have a high BORON requirement are the Brassica crops – turnip, broccoli, cauliflower, cabbage, and brussel sprouts; Also, alfalfa, clover, asparagus, sugar beet, table beet, celery, apple, pear, and grape. Watermelons and other cucurbits are unique in that they have a high CALCIUM requirement and demand an adequate BORON supply. Cotton, also, has a high BORON requirement. BORON toxicity can occur at 10X required rates or above. Some sensitive crops are peach, grape & fig.

In Citrus, on the same branch, toxicity symptoms on old leaves and deficiency symptoms on new leaves have been observed (B is relatively immobile).