Boron Deficiency in Maize
This deficiency can affect maize throughout its growth cycle but symptoms usually appear first on young leaves. The micronutrient is not very mobile, this is why the first symptoms usually appear on forming leaves. Boron deficiency may be expressed by shortened internodal growth and by narrow white and transparent necrotic spots that develop into brown waxy raised streaks as the deficiency develops. Acute boron deficiency will cause young leaves to become brittle, to twist and to produce wrinkled leaf tips. A lack of boron will result in stunted plant growth, smaller cobs, with less tightly packed kernels. Kernel rows will appear less regular.
At high soil pH, boron is in a chemical form that is not available for the plant. Soils with low organic matter content (<1.5%), weathered soils or sandy soils (prone to nutrient leaching) are also susceptible to boron deficiency. Application of boron may not correct the deficiency in those cases because it may remain unavailable for plant absorption. Symptoms on foliage might resemble those of other pathologies such as false spider mite, zinc deficiency or mild iron deficiency. Calcium deficiency may also result in the death of shoot and root tips, but young leaves below the shoot tip are not thickened and do not develop interveinal chlorosis.
Make sure to have healthy soils with a good organic matter content and a good water retention capacity and nutrients by applying farm manure or a compost mix of animal manure and leaves (ideal for sulfur and boron supply). This is a good long-term approach to remedy boron deficiency.
Prevention is key to avoid deficiencies in B and other nutrients. Apply fertilizers containing soluble boron compounds (borax) to the soil between seasons. Recommended rates are 1-1.5 kg B/ha on sandy, acid soils, or up to 4 kg B/ha on clayey, alkaline soils. Over-fertilization may result in boron toxicity, so aim for the lowest effective rate. Soil applications are recommended as leaves of many plants are damaged by direct boron application. Sandy soils may need a continued application of boron due to leaching. It is not recommended to mix boron sources with ammonium fertilizers.