Zinc Deficiency in Peanut
Zinc deficiency in peanut plants is characterized by leaf deformation and reduced growth, restricted development of new leaves and reduced internode length. Wide chlorotic stripes are found on the portion of the leaf nearest to the petiole and leaves become brittle. Moreover, reddish pigments accumulate in stems, petioles and leaf veins. Zinc deficiency may occur together with iron deficiency and symptoms are mixed up. However, in the case of iron, the chlorosis extends to the whole leaf, whereas with zinc the deficiency is mainly observed on the leaf bottom. Foliar or soil applications increase zinc concentrations in plant tissues. With the exception of a few rare cases, the addition of zinc as foliar or soil applications increase yields and quality of the nut significantly.
Zinc deficiency is mainly a problem in alkaline (high pH), sandy soils that are low in organic matter. High levels of soil phosphorus and calcium (calcareous soils) also affect the availability of zinc to plants. In fact, phosphorus application can show antagonistic effects on zinc uptake. The addition of calcium- rich materials such as limestone or chalk (liming), offsets soil acidity and also reduces the uptake of zinc by the plants (even though the levels in the soil remain unchanged). Zinc deficiency can also become a problem when soils are cool and wet during the vegetative phase. Sufficient ranges in peanut leaves is considered to be 20 to 60 mg per kg of dry plant tissue. Critical values are in the range of 8-10 mg per kg.
Application of organic manure to the seedbed, or to the field a few days after transplanting reduces the odds of observing zinc deficiency.
Recommended rates of application depend on soil type and pH, and on the original concentrations of zinc in leaves. Apply foliar sprays of Zinc Sulphate 0.2-0.5 % at weekly intervals (3 sprays) after noticing symptoms. Seed coating with zinc is another way to make the micro-element available to plants. The effectiveness of soil applications can vary greatly depending on the parameters mentioned above and are in the range of 5 to to 10 kg of zinc per hectare. Be aware that higher fertilization rates can lead to zinc toxicity.