Nutrient Elements in Fertilizer

The "big three" in nutrient elements are nitrogen, phosphorus, and potash. They are the ones that must be declared on the bag of fertilizer you buy.

Nitrogen, Potassium, and Phosphorus
The three figures, such as in a combination of 5-10-5, mean that the bag contains 5% nitrogen, 10% phosphorus, and 5% potash.

These elements do not occur in pure form but as compounds with other materials. When they are elements in an organic fertilizer, they can be highly complex and are unavailable to plants until they have been digested or broken down into simpler forms by soil organisms. These organisms are partially dormant at temperatures below 60 degrees F. and grow progressively more active up to about 90 degrees F. Thus organic fertilizers are not too effective in early spring on hardy crops. However, because they add organic matter, they have one value not possessed by pure chemical or mineral fertilizers.

One argument used against chemical fertilizers is that they "burn" foliage. This is true, but only when they are misapplied. If used in excess - if not watered in - many fertilizer salts are so "thirsty" that they will actually suck water out of leaves and roots. Water is a vital elements in plant nutrition. In fact, some plants are 90% water. The answer to burning is to water in any chemical fertilizer as soon as applied. Fertilizers in solution simply do not burn.

Whether applied in organic or chemical form, all plant nutrients must be broken down into near elemental form before they can be taken up by roots. Plants cannot distinguish between nitrogen, phosphorus, or potash from the breakdown of organic matter and the same elements from a chemical source.

Minor Elements
Actually, these are minor in amounts used by the plants, not in their effects on growth. Of these ,iron is the one most commonly in short supply. The rest are practically always present from decaying organic matter when this material is used freely, and when pH is held between 6.0 and 6.9.

A convenient way to apply iron is in the form of ferrous ammonium sulfate, applied in solution. Four oz. of ferrous sulfate and 4 oz. of ammonium sulfate, dissolved in 3 gals. of water, form a solution that can be applied to soil directly, or even to a lawn if applied with a sprinkling can while walking at a moderate pace across the grass. If applied too liberally, it can turn grass a blackish-green for two or three weeks.

Iron deficiency shows up as a yellowing of the foliage and is particularly conspicuous on pin oaks.