Soil Management and Crop Quality

Kenneth C. Beeson.

The term "crop quality" means both marketable quality and nutritional quality of a crop. A potato with yellowish flesh and of small, irregular size can be unusually high in vitamin C. It would have high nutritive value, but the housewife would not be inclined to buy it.

Nature has not always combined two aspects of crop quality in one package, and man has seldom improved matters in his efforts to breed plants and manage soil so as to produce crops that are both attractive and high yielding.

Nutritional quality is hard to define. A crop may be rich in a vitamin or one of the mineral elements, such as iron. The importance of each component in terms of man or a specific domestic animal is not always clear. Each species of animal has a different set of nutritional requirements.

The horse can survive and be healthy on a pasture where cows fail to thrive and reproduce normally. Sheep may not even survive on the same pasture. The difference in the response of each animal in this instance could be due to their different requirements for the mineral element cobalt. Hence, if cobalt is determined in the laboratory by chemical means, the interpretation of the results in terms of nutritional quality must be made with respect to the particular animal involved.

Our knowledge concerning nutritional quality is still quite limited.

First, all of the factors that enter into this entity in crops are not known. Studies in research laboratories attempt to identify some of these unknown factors. One that apparently is required by the chicken and another that the rabbit (and possibly the growing calf) seems to need are two clues being investigated.

Secondly, we recognize that there is a definite and desirable balance among the factors comprising nutritional quality. Thus the nutrition of an animal may be upset if calcium is too high in relation to phosphorus in a forage.

The measurement of nutritional quality by a laboratory method or groups of methods is not possible. Only partial estimations can be made. For this reason, no single unique value can be assigned to a food or a feed to express its nutritional quality. It follows, of course, that no laboratory measurement of the overall nutritional quality of a food or feed has ever been made.

1. Known areas in the United States where mineral-nutritional diseases of animals occur. The dots indicate approximate locations where troubles occur. The lines not terminating in dots indicate a generalized area or areas where specific locations have not been reported.

We are not entirely without a handle in dealing with this important matter, however. The animal itself is a good indicator of nutritional quality of the feed it consumes. Certain standards for growth, reproduction, and lactation can be used as bases for evaluating nutritional quality of one food or feed, at least in terms of another. We can compare corn and wheat, clover and timothy, or two sources of timothy by feeding them to a test animal. We can supplement the tests with laboratory determinations of individual nutritive constituents of the crop. These methods have limitations of basic importance, but if we recognize the limitations we can make an intelligent appraisal of the nutritional quality of crops and the factors affecting it.

DIFFERENT CROPS can exhibit different levels of nutritional quality.

Legumes, for example, will contain 2 to 10 times the amount of calcium ordinarily found in timothy or similar grasses when all are grown on the same kind of soil. The legumes contain more protein and cobalt than the grasses.

The content of phosphorus, however, will not differ materially between these two classes of forage crops.

A study of several hundred samples of mixed hay from New York farms illustrates the importance of legumes. If the hay contained 25 percent of a legume, the cobalt content was always high enough to meet the needs of cattle. Timothy from the same farms often failed to supply sufficient cobalt.

The protein of wheat may have a higher biological value for certain animals than does the protein from corn. The iron in spinach may be less available nutritionally than the iron in turnip greens.

Such differences in nutritional quality in different kinds of crops emphasize the importance of producing the kind of crop we want wherever we may need it. To do that requires an understanding of the cultural factors Involved.

Alfalfa is one of our best forage crops. Its production in abundance guarantees healthier animals and more animal products, such as meat and milk, for our human population. Alfalfa will not grow satisfactorily on many soils in the Eastern States unless boron is applied to them.

Citrus fruit, a good source of vitamin C, could not be produced in abundance in this country without the help of zinc, copper, and, in some regions, molybdenum.

Potatoes, an important source of energy, vitamin C, iron, and copper, cannot be produced in abundance on many soils unless magnesium is added to the soil.

These mineral nutrients have been especially limiting in crop production because different crops have different requirements for them.

Most crops respond to applications of nitrogen, phosphorus, and potassium to the soil. But not all crops have the unusually high requirements for boron as does alfalfa, for example. Hence, we now recognize that supplements of boron, in addition to nitrogen, phosphorus, and potassium, make possible the production of alfalfa of high nutritional quality where only poor-quality grasses grew before.

The nutritional quality of crops as grown on all soils is not the same.

Some soils do not supply enough cobalt to a forage crop to meet the needs of cattle and sheep. Some soils do not Supply enough phosphorus. Others do not supply copper or iodine.

In contrast to these deficiencies, there are soils that supply elements like selenium and molybdenum in excessive or harmful amounts to the vegetation. The management of such soils generally requires a choice of methods best suited to the particular environment, the nature of the farm enterprise, and the nature of the deficiency or toxicity.

Feeding the deficient mineral element directly to the animal is a common method of correction.

In the dairy regions of the Northeast, for example, cobalt is added to most commercially prepared concentrates. Salt with added cobalt can be purchased. In this manner the normally low-cobalt grass, hays, and pasture herbage of this region are adequately supplemented. The mineral form of cobalt is as effective in this respect as is the cobalt in the crop. Only about 0.003 part of 1 ounce of cobalt is required by a sheep in a day. Somewhat more is required by the cow.