Quality as Feed, Not Only Quality as Crop, Demonstrates Effects of Soil Fertility
CROP YIELDS HAVE LONG been measured by the amount of the plant mass. If crops are grown for the simple purpose of selling them, and if we measure the returns by the greatest monetary income from more pounds or bushels sold, then bigger plants may be the reason for making soils more fertile. In a broader sense, it is the fertile soils that make the plants grow bigger. Though there may be big plants of some kind that grow big on soils that are not very fertile for other plants, one cannot conclude, therefore, that any big vegetative mass proves the soil to be fertile. One can reason the converse of this quite safely, however, and say small, spindly, sick plants are indicators of an infertile soil.”
Certain “big” plants are more apt to be indicators of fertile soils than others. But for that, one must know something about what the plant is creating or making while it is growing. Crops, like the legumes, which are said to be “hard to grow,” are usually indicators of fertile soils when they are making big plants and especially a big output of seed. It is this reproductive aspect, the activity of making new cells, of creating proteins—through which alone life keeps flowing—and of multiplying its parts and its species that really reports the fertile soils. Plants in Nature are big and numerous because they have been multiplying themselves via production of more protein. The production of protein by plants is the real index of the fertility of the soil under the plants.
Perhaps you have never thought that what we consider plant growth is not necessarily multiplication of cells, for which more protein must be created by the biosynthetic, or life, processes of the plant. Instead, it may be only a case of blowing up to larger volume the cells laid down in embryonic age. It may be making bigger those cells by putting in more water or more sugar and other carbohydrates of photosynthetic origin. In the watermelon, and other cucurbits, this is the case. So the so-called “growth” reflects mainly the air, water, and sunshine going into the resulting products of sugar equivalent and not the fertility coming up from the soil to convert those carbohydrates into proteins, as we expect it to be done by legumes.
But when the plant’s embryo is the place where the cells are all laid down, even in very miniature, then the truly growth process there calls for much soil fertility and that in balanced proportions of the different nutrient elements. Even a watermelon requires a fertile soil in a certain sense, but we are apt to be misled in believing that the increasing size of the plant or the increasing amounts of plant product are necessarily proof of fertile soils. That fact has been demonstrated for soybean plants readily by shifting the fertility ratio, or the balance between calcium and potassium. We associate the function of the latter with the plant’s production of vegetative mass; the former is connected with the output of protein by the biosynthetic conversion of the photosynthetic products or carbohydrates into protein. Thus by unbalanced soil fertility we may be misled to believe that big plants mean big soil. But with balanced fertility, we are correct and fertile soils really mean big plants in terms of much protein.
There is no fallacious reasoning in saying that less fertile soils give us the small, sick plants, when on other soils along side the plants are large. In the same field one can demonstrate this fact easily. Applications of the elements deficient in the soil soon show their effects in terms of bigger plants. Nitrogen on grasses in the pasture as a result of urine droppings is a well known example in the spots of tall-growing plants. Lime on legumes like the sweet clover and alfalfa, magnesium on soybeans, zinc on fruit trees, copper on clovers in Australia and numerous other soil treatments draw their lines of differences clearly out in the field.
The sickly conditions of the plants give various signs and symptoms. Celery with its dark areas in the stalk when boron is insufficient; white-colored soybean leaves except for green veins when magnesium is deficient in the soil, reddening leaves of cotton under potassium deficiency, clustered small leaves in rosette-like forms of fruit trees needing more zinc from the soil or from spray applications, are all telling us that infertile soils make not only small but also sick plants.
We are gradually coming to realize that plant growth is a creative activity by a life form demanding proper nourishment if that growth is to go forward effectively. Bigger plants generally testify to a fertile soil, especially if bigger yields of seed and more extensive cell reproduction rather than just cell enlargement are the reasons for bigness. Conversely, small sickly plants are true indicators of poor nutrition of them by the soil. Closer observation of our plants and more knowledge of the symptoms of plant hunger are bringing us around to feed our plants via the soil rather than turn them out to rustle for themselves. On fertile soils alone can our crops be truly big in the food-creating services we expect of them.