Plant nutrients do not have to be soluble in water in order to enter the roots of plants. This statement is contrary to the long-standing belief of plant scientists, but its truth has recently been demonstrated by Dr. F. L. Wynd and his associates at Michigan State College.
Proof that undissolved nutrients can enter roots was established by growing plants in a finely ground, insoluble, glass-enamel substance called frit. Fused with the frit were two essential nutrient elements, iron, and manganese.
By their fusion with the frit, the iron and manganese were rendered insoluble. Yet both these elements were taken up by the plants growing in the fruit.
Dr. Wynd’s Work
Two important implications of Dr. Wynd’s work are:
(1) that leaching, or loss of nutrient solutions by the movement of soil water, is eliminated and
(2) that the pH, or relative acidity or alkalinity, of the soil, no longer governs the availability to plants of certain nutrient elements.
Leaching
It is well known to gardeners that the nutrients contained in soluble fertilizers (i.e., any of the commercial synthetic or chemical plant foods) can be quickly lost by an excessive movement of water through the soil.
On light, sandy soil, nutrients are washed down below the reach of shallow-rooted plants by long, heavy rains, and on sloping ground, the nutrients are washed away during long rainy periods.
The soil in greenhouse benches and in pots standing on benches also loses nutrients from the leaching action of excessive watering.
When a nutrient-containing frit is mixed with the soil to supply plants with their fertilizer requirements, however, loss of nutrients by leaching does not occur.
The frit, being an insoluble, solid substance, “stays put” no matter how much water passes through the soil, and the insoluble nutrients contained in the frit “stay put” also.
Soil Acidity
It is also well known to most gardeners that the pH, or relative acidity, of the soil, plays an important part in the culture of many plants. This is because the pH of the soil governs the availability to plants of various soluble nutrients.
For example, plants belonging to the heath family—rhododendrons, azaleas, mountain laurels, blueberries, etc.—become chlorine or yellow-leaved if they do not take up sufficient iron from the soil, But iron is available to plants only in relatively acidic soil.
In alkaline soil, iron is “locked up,” and plants like azaleas are ion-starved and become chlorotic even though iron is present -in adequate quantity in the soil.
When, however, an iron-containing frit is thoroughly mixed with the soil so that plant roots are in contact with frit particles, there are no symptoms of iron deficiency in the plants even if the pH is raised (i.e., the soil is made alkaline) to the point that would otherwise prevent plants from taking up enough iron.
This is because iron passes directly from the frit particles into the roofs of the plants without going into solution.
The importance of this is obvious: With the advent of frit—agricultural frit, as the nutrient-containing product is called—pH loses much of its “nuisance” value. “Acid-loving” and “alkaline-loving” plants can be grown in the same soil—acid or alkaline.
Laboratory Proof
The method by which Dr. Wynd demonstrated that plants could obtain nutrients from an insoluble, nutrient-combining frit is illustrated in the accompanying drawing.
In the illustration, container A holds a solution that carries all plant nutrients except iron and manganese. Container B is filled with fruit that contains only iron and manganese. Container C is filled with pure quartz sand containing no plant nutrients.
Every four hours, the air is pumped into container A through tube D until the solution in A rises through the Y-shaped tube E until it almost reaches the tops of the containers. B and C.
After seven minutes, the pressure is released, and the solution flows back into container A. The same kinds of plants are grown in both containers- B and C.
It will be seen that if the iron and manganese in the frit container B are soluble, they will become dissolved in the solution, which is pumped up from container A every four hours into container B (as well as container C) and then is allowed to flow hack into container A.
If that happens, the solution will eventually carry iron and manganese into container C and thus supply these nutrients to the plants growing in container C and those growing in container B.
In other words, if the iron and manganese in container B are soluble, the plants in both containers. B and C will eventually receive all nutrients—iron and manganese coming from container B and all the rest coming from the solution in container A—and both sets of plants will show normal, healthy growth.
But this is a lot -what happens? The plants in container B grow normally, but those in container C show unmistakable iron and manganese starvation symptoms.
The conclusions from the experiment, then, are these:
(1) The iron and manganese contained in the frit are not dissolved;
(2) The plants in container B get their iron and manganese directly from the frit and their other nutrients (ruin the solution;
(3) The plants in container C have access only to the nutrients in the solution and therefore are iron- and manganese-starved.
(Direct movement of nutrient elements from frit particles into plant roots has been explained by the phenomenon known to chemists as ion exchange.
It is not yet definitely known, however, whether the nutrient does or does not go into the solution at the actual point of contact with the root.)
Available Soon
Since the original experimental work Kith iron- and manganese-containing frits were conducted, rapid progress has been made in the development of fruits containing other nutrient elements, and extensive tests have been made to determine their usefulness in the cultivation of all kinds of plants.
At the present writing, an agricultural frit containing practically all the essential trace elements—iron, manganese, boron, copper, zinc, and molybdenum—has been perfected and has reached the production stage.
It is already being used to a limited extent commercially and, by next spring at the latest, will be available to home gardeners in various size packages.
Plants as diverse as farm crops like wheat rd navy beans, orchard crops like tree and hush fruits, and ornamental crops like roses, snapdragons, hydrangeas, chrysanthemums, and cinerarias, as well as many others, have all responded favorably to the use of agricultural frit in all kinds of soil.
As in all cases of plant feeding, the response of some plants has been greater than that of others, but in no instance has there been an absence of response or an unfavorable response.
Besides the fact that its nutrients do not leach from the soil and are available to plants over a wide pII range, the agricultural frit is notable for the fact that its effectiveness is extremely long-lasting and that it releases its nutrients slowly so that they do not injure plant roots.
However, gardeners who plan to try out agricultural frit as soon as it becomes available should remember that its value to plants depends upon its actual contact with their roots. It is of great importance, therefore, to thoroughly mix it with the soil.”
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