Virginia Cooperative Extension"
Foliar Feeding of Plant Nutrients
Virginia Vegetable, Small Fruit and Specialty Crops
November 2002; Volume 1, Issue 11
Charlie O'Dell, Ext. Horticulturist Emeritus, Virginia Tech
<<For many years, horticulturists and agronomists have largely subscribed to the belief that foliar feeding of plant nutrients is an idea of dubious merit>>
<<Dramatic and fast correction of such nutrient deficiencies are generally always seen from such foliar applications. >>
<<Dr. H.B. Tukey, renowned plant researcher and Head of Michigan State University's Department of Horticulture back in the 1950's, working with research colleague S.H. Wittwer at MSU, first proved conclusively that foliar feeding of plant nutrients really works. Researching possible peaceful uses of atomic energy in agriculture, they used radio-active phosphorous and radio-potassium to spray plants, then measured with a Geiger counter, the absorption, movement and utilization of these and many other nutrients within plants. They found plant nutrients moved at the rate of about one foot per hour to all parts of the plants. Comparing efficiency of plant use of foliar-fed nutrients versus soil-applied nutrients near roots, they found foliar feeding provided about 95 percent efficiency of use compared to about 10 percent of use from soil applications! Likewise, speed of absorption and use by foliar applications was immediate, whereas from soil applications absorption and plant use both were very slow, thus providing a major benefit of foliar feeding where a specific plant nutrient deficiency may exist, be it major or minor plant nutrient. >>
<<.....this very important finding was published, but only in research journals and symposia proceedings. These findings rarely found their way into the ranks of Extension educators or their grower-focused publications and other teaching materials or programs. >>
The full article:http://www.ext.vt.edu/news/periodicals/commhort/2002-11/2002-11-03.html
Another informative article (in Acrobat PDF format):
<<Foliar applications are often timed to coincide with specific vegetative or fruiting stages of growth, and the fertilizer formula is adjusted accordingly. Applications may also be used to aid plants in recovery from transplant shock, hail damage, or the results of other weather extremes. In terms of nutrient absorption, foliar fertilization can be from 8 to 20 times as efficient as ground application (1). However, this efficiency is not always achieved in actual practice. Often, failures result from inattention to the principles of foliar feeding?>>http://www.attra.org/attra-pub/PDF/foliar.pdf
I hope this helps...