Therefore, large quantities of Ca are required in the pod zone for direct absorption by pegs and pods. This requires continuous replenishment of Ca in the pod zone. Lack of Ca leads to unfilled pods (also termed as pops), small pods, and high incidence of pod rot. In addition, plants deficient in Ca will also have poor growth and development. Deficiency of Ca is commonly observed in non-calcareous soils. It is recommended that Ca be supplied to groundnut cultures during flowering as top dressing with gypsum (calcium sulfate). Gypsum is a byproduct of the fertilizer industries and is the cheapest and most readily available form of Ca.
Gypsum is easily soluble in water and should be applied at the time of flowering and incorporated into the soil in the pod zone. Application of gypsum at flowering supplies Ca over a 60 days period. Depending on soil tests about 250-500 kg/ha of gypsum is recommended for groundnut production. Other sources of Ca include ground limestone, which is common in southeastern United States and parts of Australia. Calcium chloride is not recommended due to high cost and high leaching losses. Iron (Fe) - Groundnut is very susceptible to Fe deficiency when grown in calcareous and alkaline soils. It is often called as lime-induced Fe chlorosis.
Deficiency symptoms are characterized by inter-venial chlorosis of
young and newly emerging leaves. Under severe deficiency the
complete leaves turn yellow or white and die. Fe-deficiency can significantly
decrease growth and yield of crops. In groundnuts grown in calcareous soils, Fe-deficiency
decreases leaf area and dry matter production of leaves, stems and root,
leading ultimately to yield losses of 20%. Severe Fe-deficiency decreases root
growth and elongation. In most legumes including groundnut, early nodule
development after nodule initiation is most sensitive to Fe-deficiency. In
groundnut, Fe-deficiency decreases the number of excisable nodules, nodule
mass, number of bacteroids and concentrations of leghemoglobin, nitrogenase
activity and nitrogen fixing ability.
Fe-deficiency does not limit the growth of rhizosphere populations of peanut Bradyrhizobium, and there is no effect on root infection processes or nodule initiation. This suggests that nodule development processes are more sensitive to Fe-deficiency than nodule initiation processes. Soil application of iron is not often recommended as soils are generally rich in Fe, especially in the tropics and subtropics, and applied Fe is generally fixed and is not available to plants.
As soil application of most Fe sources is generally
less effective, foliar application is widely used for correction of
Fe-chlorosis. Both inorganic and organic Fe sources are effective as foliar
sprays. Spraying of FeSO4 solution with some surfactant is very effective in
correcting Fe-chlorosis in many crops. However, because of the poor
translocation of applied Fe within the plant, the applied Fe does not readily
move from sprayed parts to other parts of the plants.
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