The best way is by sending a tissue sample to a laboratory for analysis, since you can recognize deficiencies before they have damaged the crop plant very much. If you wait for visual symptoms, the plant has already been damaged, and some yield will be lost. Visual symptoms can be something as simple as purplish colored leaves in grass crops such as maize (corn), which indicates a phosphate deficiency.
No, Pica is not a contagious condition. Pica is generally caused by a mineral deficiency, and someone with a mineral deficiency can't pass that deficiency on to others.
Dwarfism is zinc deficiency. hypothyroidism is iodine deficiency.
I think it would be a deficiency is a vitamin or mineral. Increase the relevant vitamin or mineral to optimum levels.
iron
Often it is a mineral deficiency that causes the twitch - usually a magnesium deficiency.
Iron.
mineral deficiency
iodine
Please clink on the link below. It's relating to mineral deficiencies in animals.
phosphorous
iodine
B) Goitre. Goitre is commonly caused by iodine deficiency, which is a mineral essential for the thyroid gland to produce thyroid hormones. Beriberi is caused by thiamine (vitamin B1) deficiency, scurvy is caused by vitamin C deficiency, and night blindness is caused by vitamin A deficiency.