Sodium is involved in osmotic (water movement) and ionic balance and is required for some plants.
Cobalt is required for nitrogen fixation in legumes and in root nodules of nonlegumes because it is a component of enzymes essential for nitrogen fixation. Deficient levels could result in nitrogen deficiency symptoms.
Silicon is found as a component of cell walls. Plants with supplies of soluble silicon produce stronger, tougher cell walls creating a mechanical barrier to the mouth parts of piercing and sucking insects. Silicon significantly enhances plant heat, drought and cold tolerance. Foliar sprays of silicon have also shown benefits reducing populations of aphids on field crops. Tests have also found that silicon can be deposited by the plants at the site of infection by fungus to combat the penetration of cell walls by the attacking fungus. Improved leaf erectness, stem strength and prevention or depression of iron and manganese toxicity have all been noted as effects from feeding soluble silicon. Silicon is known to be essential to some members of poaceae (grasses) but has shown benefits to a wide variety of plants.