Foliar Feeding
(Page 2 of 5)
May/June 1988
By Peter Donelan
Leaf sprays are also highly efficient fertilizers. Agricultural scientist S.H. Witter pioneered some of the first scientific studies into nonroot plant feeding in the early 1950s at Michigan State University. He found that the uptake of various plant foods was from 100% to 900% more effective when the nutrients were applied to the leaves instead of to the soil. Much soil fertilizer may never get used by plants. Water-soluble nutrients like nitrogen often wash out of the earth. (As much as 50% of the chemical nitrogen fertilizer used in this country leaches into our waterways—creating a complex of environmental problems.) Other nutrients may, through chemical reactions, be bound into a form unavailable to plants. For instance, 80% of the phosphorus applied through conventional fertilizers may get locked up in the soil. On the other hand, up to 80% of foliar-added phosphorus can be directly absorbed by the plants.
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Don't Forsake the Basics
Before you rush out and put your garden on a daily leaf spray schedule, stop and remember the basic tenet of organic agriculture: Feed the soil, not the plant. Many feel that the biggest mistake of modern chemical agriculture has been its lack of focus on the sustainable base of all the earth's production—the soil.
A healthy soil ecosystem rich in life and organic matter will help prevent nutrient loss due to leaching and chemical binding. It will even hold excess nutrients in storage until they are needed. For example, vesiculararbuscular mycorrhizae, fungi present in healthy live soil, increase the uptake of many nutrients, including phosphorus, and stimulate the growth of other beneficial soil microorganisms (such as nitrogen-fixing bacteria).
Fertilizers do not create fertility; building the soil does. In the long run, adding balanced, aged organic matter to your soil is the most efficient way to improve a garden. Foliar feeding, then, is best used as a supplement—a temporary or special procedure to boost production or help plants in a difficult growing situation.
SPRAYERS
A recycled (and thoroughly washed) window-cleaner bottle may be adequate for spraying houseplants, a small bed of herbs or an experimental half-row of tomatoes. But if you're going to foliar feed a full garden, you'll soon wish for a more sizable sprayer, one you can pressurize with a few pump strokes so it will mist continuously. MOTHER offered a design for a homebuilt two-liter sprayer back in issue 80. In addition, here are a few companies that offer sprayers (write for free catalogues):
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