I quoted wikipedia because there is some good info but not exactly a credible source. Lack of experience or education is not my problem.
So can anybody tell me exactly how nutrients get into the leaf? How polar substances pass through the waxy coating then through polar cell walls?
I found a few abstracts but not the full article.
Essential plant nutrients are mainly applied to soil and plant foliage for achieving maximum economic yields. Soil application method is more common and most effective for nutrients, which required in higher amounts. However, under certain circumstances, foliar fertilization is more economic and effective. Foliar symptoms, soil and plant tissue tests, and crop growth responses are principal nutrient disorder diagnostic techniques. Soil applications of fertilizers are mainly done on the basis of soil tests, whereas foliar nutrient applications are mainly done on the basis of visual foliar symptoms or plant tissue tests. Hence, correct diagnosis of nutrient deficiency is fundamental for successful foliar fertilization. In addition, there are some more requirements for successful foliar fertilization. Foliar fertilization requires higher leaf area index for absorbing applied nutrient solution in sufficient amount, it may be necessary to have more than one application depending on severity of nutrient deficiency. Nutrient concentration and day temperature should be optimal to avoid leaf burning and fertilizer source should be soluble in water to be more effective. Foliar fertilization of crops can complement soil fertilization. If foliar fertilization is mixed with postemergence herbicides, insecticides, or fungicides, the probability of yield response could be increased and cost of application can be reduced. [ABSTRACT FROM AUTHOR]
Fageria, N. K. et al. "Foliar Fertilization of Crop Plants." Journal of Plant Nutrition 32, no. 6 (June 2009): 1044-1064. Academic Search Premier, EBSCOhost (accessed July 18, 2009).
Foliar fertilization is an agricultural practice of increasing importance in practical terms. Since nutrient sprays are mostly applied as water solutions, the focus of the article was placed on the penetration of ionic, polar solutes through the leaf surface, although the mechanisms of cuticular penetration of lipophilics are also taken into consideration. In theory, application of foliar nutrient sprays may indeed be a more target-oriented and environmentally friendly fertilization method since nutrients are directly delivered to the target organism in limited amounts, thereby helping to reduce the environmental impact associated with soil fertilization. However, response to foliar sprays is often variable and not reproducible due to the existing lack of knowledge of many factors related to the penetration of the leaf-applied solution. To overcome the current “spray and pray” situation, there is a need to critically analyze the major factors involved and the existing experimental approaches to safely assess the penetration mechanisms, which is the final aim of this review. Beginning with the significance of foliar fertilization in agriculture, a historical overview regarding foliar uptake related studies is given, with especial emphasis on the penetration of solutes through the cuticle and stomata. The existing models of cuticular and stomatal uptake are analyzed separately considering among other factors the physico-chemistry of the solution including the role of adjuvants and the effect of the environment. Methods employed to estimate the process of cuticular and stomatal penetration of solutes are critically assessed. Finally, conclusions related to multidisciplinary research perspectives for improving the efficiency of foliar sprays are drawn. [ABSTRACT FROM AUTHOR]
Fernández, V., and T. Eichert. "Uptake of Hydrophilic Solutes Through Plant Leaves: Current State of Knowledge and Perspectives of Foliar Fertilization." Critical Reviews in Plant Sciences 28, no. 1/2 (January 2009): 36-68. Academic Search Premier, EBSCOhost (accessed July 18, 2009).
. Its crucial to administer extra control when foliar feeding your plants as its easier to burn or rot your plants, timing and other conditions are very important. For me, its just not worth the hassle....