Micronutrients like Boron (B) are as important as the primary and secondary nutrients in plant nutrition. However, the amounts of micronutrients required for optimum nutrition are much lower. Micronutrient deficiencies are widespread because of increased nutrient demands from the more intensive cropping practices.
A primary function of B relates to cell wall formation, so B-deficient plants may be stunted. Sugar transport in plants, flower retention, and pollen formation and germination also are affected by B. Seed and grain production are reduced with low B supply. Boron-deficiency symptoms first appear at the growing points. This results in a stunted appearance (rosetting); barren ears due to poor pollination; hollow stems and fruit (hollow heart); brittle, discolored leaves, and loss of fruiting bodies. Boron deficiencies mainly occur in acidic, sandy soils in regions of high rainfall and in those with low soil organic matter. Borate ions are mobile in soil and can leach from the root zone. Boron deficiencies are more pronounced during drought periods, when root activity is restricted.
Recommended application rates of B are rather low (0.5 to 2 pounds per acres), but growers should follow them carefully, since the range between B deficiency and toxicity in most plants is narrow. Uniform application of B in the field is very important for that reason.
Soil tests and plant analyses make excellent diagnostic tools to monitor the micronutrient status of soils and crops. Helpfully, deficiency symptoms of these nutrients are highly visible in most economic crops, so growers can readily identify them and begin managing the problem. Micronutrient recommendations are based on soil and plant tissue analyses, the type of crop and expected yield, management level, and research results.
Include soil tests in B fertilization programs, first to assess the level of available B and later to determine possible residual effects (buildup). The most common soil test for B is the hot-water-soluble test. This test is more difficult to conduct than most other micronutrient soil tests, but most B-response data have been correlated with it.
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.