Here are some striking examples of comparisons of foliar fertilisers versus soil applications.
Such ratios favouring foliar applications exist only under extreme conditions of soil fixation. Nevertheless, they single out the effectiveness of leaves as organs for absorption.
Related to the marked efficiency in absorption of nutritional sprays may be indirect effects of this method of applying fertiliser on other plant processes.
Comparative efficiency of foliar and soil applications of fertiliser.
|Approximate ratios of amounts required for comparable Authority responses|
|Nutrient and salt||Type of Crop||Foliar||Soil||Authority|
|Zinc (ZnSO4)||Annual crops||1||12||Lingle & Holmberg (1956)|
|Phosphorus (H3PO4)||beans,tomatoes||1||20||Wittwer, et al. (1957)|
|Iron (FeSO4)||grain sorghum||1||25||Withee & Carlson (1959)|
|Magnesium (MgSO4)||grain sorghum||1||100||Krantz (1962)|
|celery||1||50-100||Johnson, et al.(1957, 1961)|
Where isotopes showed that it was 8 -10 times more effective to foliar feed a plant as far as the amount of nutrients required and the speed with which those nutrients were utilized, the above authorities found the figure to be between 12 and 100 times more effective.
The readily- available nutrients are more easily utilised, as they are directly available to a plant and because they do not have to be dissolved by moisture before going into the soil solution and where they may be subjected to insolubalisation by incident anions such as carbonate, bicarbonate, hydroxide, etc, known as fixation.
Also important in foliar fertilisers, is whether or not the products being used are chelated. Chelation, allows a nutrient to "maintain its own identity" within the spray tank, and not get tied up by other nutrients or pesticides being used with it.
These days we have materials available which are ideally suited to spray applications.