Foliar feeding is a real effect but it has limits. It
is not used to provide all mineral nutrients except
possibly for epiphytes that have no root systems. It
can give crops a boost in mineral nutrients and
prevent or overcome certain deficiencies.
Micronutrient deficiencies in particular are often
solved by foliar feeding, especially iron deficiency,
called iron chlorosis, where there is plenty of iron
in the soil, it just is not available to the roots.
Other deficiencies that foliar feeding has corrected
include boron in plums and calcium in tomato fruit
(blossum end rot) and apple fruit (bitter pit). The
calcium deficiency in fruits cannot be corrected
quickly by adding calcium to the soil because the
fruit has such a low transpiration rate. California
citrus crops are often given a urea-zinc spray to give
them a boost.
Traynor, Joe. 1980. Ideas in Soil and Plant Nutrition.
Bakersfield, CA: Kovak Books. has a practical chapter
on foliar fertilization.
Alexander, A. (ed.) 1986. Foliar Fertilization.
DEVELOPMENTS IN PLANT AND SOIL SCIENCES Volume 22
Search for foliar feeding and foliar fertilization on
Try the agricola database for foliar feeding research
Probably the computerized Science Citation Index would
be a good place to look as well.
Blossum end rot in tomato
Cork Spot and Bitter Pit in Apples
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