Certain soil conditions, such as pH, excess moisture, or cool temperatures, may render a nutrient or nutrients unavailable to the plant root.
Nutrient demand curves indicate that there are stages in a plant's life-cycle when demand for some nutrients may be greater than its physiological capacity to supply itself, even when these soil nutrients are available in abundant supply. This often occurs during the development of fruit or grain.
Data from trials on crops, show that increases in yield and/or grade results from applications of foliar nutrients during these periods of peak demand.
Foliar fertilisers can be designed to meet a plants specific needs for one or more micro and macro nutrients--especially trace minerals and enables you to correct deficiencies, strengthen weak or damaged crops, speed growth and grow better plants, which is of course, the bottom line.
Foliar applications can be targeted to a particular stage of crop development to achieve specific objectives and is an excellent way to "fine tune" a high fertility program.
Plant hormones, are specialised chemical substances produced by plants. Foliar fertilization is a particularly useful technique: and are the main internal factors controlling growth and development.
Hormones are produced in one part of a plant and transported to others, where they are effective in very small amounts.
Depending on the target tissue, a given hormone may have different effects.
Auxin, one of the most important plant hormones, is produced by growing stem tips and transported to other areas where it may either promote growth or inhibit it.
It also retards the abscission (dropping off) of flowers, fruits, and leaves.
Commercially, synthetic auxins are used to initiate adventitous roots from plant cuttings eg. in nurseries.
Weed control by another synthetic auxin, 2, 4-dichlorophenoxyacetic acid (2,4-D), is widespread as a selective herbicide against broadleaf weeds.