Soil fertility constitutes the 5 percent that is the plant ash. It is the handful of dust that makes up the corresponding percentage in the human body. Yet it is the controlling force that determines whether Nature in her fabricating activities shall construct merely the woody framework, with leaf surfaces catching sunshine and with root surfaces absorbing little more than water or whether inside that woody shell there shall be synthesized the innumerable life-sustaining compounds.

Soil fertility determines whether plant foods of only fuel and fattening values, or plant foods capable of body service as complicated as growth and reproduction, shall be grown in a given area. Because the soil accounts for only a small percentage of our bodies, we are not generally aware of the fact that this 5 percent can predetermine the fabrication of the other 95 percent into something more than mere fuel.

Realization is now dawning that a global war is premised on a global struggle for soil fertility as food. Historic events in connection with the war have been too readily interpreted in terms of armies and politics and not as actions calculated to mobilize soil fertility. Gafsa, merely a city in North Africa, was rejuvenation for phosphorus-starved German soils. Nauru, a little island speck in the Pacific, is a similar nutritional savior to the Japanese. Hitler’s move eastward was a hope looking to the Russian soil-fertility reserves. The hoverings of his Graf Spee around Montevideo and his underground workings in Argentina, much more than being maneuverings for political or naval advantage, were designs on that last of the world’s rich store of less exploited soil fertility, to be had in the form of corn, wheat, and beef. Some of these historic martial events serve to remind us that “an empty stomach knows no laws” and that man is in no unreal sense an animal that becomes a social and political being only after he has consumed some of the products of the soil.

In view of our youthfulness as an extensive country, our different geographic areas have registered themselves mainly as differences in body comfort, whether hot or cold, wet or dry. Because of the free flow of foods and food constituents by means of cheap transportation, we have not been cognizant of the differences in quality as well as in kinds of foods produced in adjoining districts that differ in soil. We have not yet marked out our country into smaller patchwork districts with distinctive local colorings, as the Old World has in the opinion of visitors from the New World. Limitations in travel, difficulties in food delivery, and all the other restrictions now making us more local will soon emphasize differences and deficiencies according to the soils by which we live.

The regions of major rural land uses as mapped by F.J. Marschner. Though the main natural vegetation types — forest, grassland, and desert shrub — are indicative of major rural land uses, other factors are influential. In the eastern corn belt, originally timber covered, forestry now scarcely exists, because the fertility of the soil and the gentleness of the surface relief favor crop production.

The effect of fertilizer treatment of soils is indicated by this chart. It measures in pounds against days the gain in weight of sheep which were fed equal amounts of hay (and supplements) grown on soils essentially similar but given different fertilizer treatments.

Vegetation has been distinguished by names of crop species and by tonnage yields per acre. Plants have not been considered for their chemical composition and nutritive value according to the fertility in the soil producing them. This failure has left us in confusion about crops and has put plant varieties into competition with one another rather than in support of one another. Now that the subject of nutrition is on almost every tongue, we are about ready for the report that vegetation as a deliverer of essential food products of its own synthesis is limited by the soil fertility.

Proteinaceousness and high mineral contents of distinct nutritive values are more common among crops from soils receiving comparatively low rainfall and in less leached areas, as, for example, in the midwestern part of the United States. Hard wheat — so called because of its high protein content, which makes it useful in the milling of the patent flour for light bread — is commonly ascribed to regions having lower annual rainfalls. Soft wheat is similarly ascribed to areas of more abundant rain. The high calcium content, the other liberal mineral reserves, and the pronounced activities of nitrogen within the less leached soil must be accepted as the reasons for this distinction, in view of the fact that experimental trials supplying these fertility items to the soil in regions of high rainfall can result in hard wheat where soft wheat is common.

The proteinaceous vegetation and the synthesis by it of many unknowns which, like proteins, help to remove hidden hungers and encourage fecundity of both man and animal are common in the prairie regions marked by the moderate rainfalls. It is fertility of the soil, rather than low precipitation, which gives the Midwest, or those areas bordering along approximately the 97th meridian, these distinctions: (1) selection of it as a feeding ground by the thundering herds of bison, which multiplied to untold numbers on the buffalo grass; (2) the wheat which, taken as a whole rather than as refined flour, is truly the staff of life; (3) areas where cattle, on unhampered range, nourish themselves so well that they reproduce regularly without being pampered; and (4) the more able-bodied selectees for military service of whom seven are chosen out of ten, in contrast to seven rejected out of ten in one of the southern states where the soils are more exhausted of their fertility.

An array of native vegetation from western Kansas (17-inch rainfall) to eastern Kansas (37-inch rainfall). This calls attention to the buffalo’s location on lime-laden soils with proteinaceous, mineral-rich but sparse vegetation named for him, rather than on the leached soils with more bulky, carbonaceous growths farther east. (Drawing by Schantz.)

Protein production, whether by plant, animal, or man, makes demands on the soil-given elements. Body growth among forms of higher life is a matter of soil fertility and not one of photosynthesis only. It calls for more than rainfall, fresh air, and sunshine.

Heavier rainfall and forest vegetation characterize the eastern United States, where the soils have been leached of much fertility. Higher temperatures in the southern areas have made more severe the fertility-reducing effects of the rainfall. Consequently, vegetation there is not such an effective synthesizer of proteins. Neither is it a significant provider of calcium, phosphorus, magnesium, or the other eight or more soil-given fetus-building nutrients. Annual production of vegetation per acre is large, particularly in contrast to the sparsity of that on the western prairies. The East’s production is highly carbonaceous, however, as the forests, the cotton, and the sugar cane testify. The carbonaceous nature is contributed by air, water, and sunlight more than by the soil. Fuel and fattening values are more prominent than are aids to growth and reproduction.

Fertilizer treatments of the soil register their beneficial effects in the plant, but more noticeably in the physiology of the animal as indicated by better weight, wool, fur, bones, or other body products and functions. On the left, the rabbit and the bones record the results of lack of soil treatment, in contrast to the effect of treatment measured by similar gauges on the right.

Here is a basic principle that cannot be disregarded. It has signal value as we face nutritional problems on a national scale. It is, of course, true that soils under higher rainfalls and temperatures still supply some fertility for plant production. Potassium, however, dominates that limited supply, to give prominence to photosynthesis of carbonaceous products. The insufficient provision of calcium and of all the other requisite elements usually associated with calcium does not permit the synthesis, by internal performances in plants, of the proteins and many other compounds of equal nutritive value. The national problem is largely one of mobilizing the calcium and other fertility elements for the growing of protein and not wholly one of redistributing proteins under Federal controls. As the distribution pattern of soil fertility is etched on the map, it delineates the various areas of particular success or particular trouble in nutrition. It coincides also with the regions where the starving plants can be given relief by particular soil treatments.

Life behaviors are more closely linked with soils as the basis of nutrition than is commonly recognized. The depletion of soil calcium through leaching and the almost universal deficiency of soil phosphorus affect animals directly, since their bones are the chief body depositories for these two elements. In the forest, the annual falling of leaves and their subsequent decay, to pass their nutrient elements through the cycle of growth and decay again, are almost a requisite for tree maintenance. Forest soils offer very little fertility and offer it very slowly. Is it any wonder then that dropped antlers and other skeletal forms are eaten by animals to keep calcium and phosphorus in their cycle? Pregnant squirrels gnaw bones in their nests. Deer will select in their browse those trees that have been given fertilizers in preference to those that have not been treated. Pine-tree seedlings along the highway, transplanted from fertilized nursery soils, are eaten by deer while the same species in the adjoining forests go untouched. Wild animals truly “know their medicines,” which they take as plants from particular levels of soil fertility.

In going from midwestern United States eastward to the less fertile soil, we find that animal troubles increase and become a serious handicap to meat and milk production. The condition is no less serious as one goes south or southeast. The distribution patterns of milk fever, of acetonemia, and of other reproductive troubles that so greatly damage the domestic animal industry parallel the soil-fertility pattern. Troubles in the milk sheds of eastern and southern cities are more a challenge for the agronomists than for the veterinarians.

Experimental soil treatments have demonstrated the important roles that calcium and phosphorus can play in animal physiology and reproduction. Applied on adjoining plots of the same area, their effects on sheep were registered as differences in growth per unit of feed consumed and as differences in the quality of the wool. Rabbits also grew more rapidly and more efficiently on hay grown where limestone and superphosphate had both been used than where phosphate alone had been used.

The influence of soil fertilizers registers itself pronouncedly in the entire physiology of the animal, seemingly so far removed from the slight change in chemical condition in the soil. This fact was indicated, in the study mentioned, not only by differences in the weight and quality of the wool but in the bones and more pronouncedly in semen production and reproduction in general. Rabbit bones varied widely in breaking strength, density, thickness, hardness, and other qualities beside mass and volume. Male rabbits used for artificial insemination became sterile after a few weeks on lespedeza hay grown without soil treatment, while those eating hay from limed soil remained fertile. When the hays were interchanged during the second feeding period, a corresponding interchange of sterility and fertility took place between the groups of animals. This factor of fertility alone is an economic liability on less fertile soil but is a great economic asset on the soils which either are more fertile naturally or are made so by soil treatments.

Notwithstanding our attempt to relegate the cow into the lower levels in the biotic pyramid, even down to that of plants and microbes that alone can live on chemical ions not requisite as compounds, she still clings to her instincts of selecting particular grasses in mixed herbages. Fortunately she strikes up a partnership with the microbes in her paunch, with the result that some seven essential vitamins are synthesized there for her. We tend to forget, however, that these paunch dwellers cannot be refused in their demands for soil fertility to enable them to meet this expectation. England’s allegiance in wartime to the cow as a ruminant that can carry on these symbiotic vitamin syntheses, and England’s reduction of pigs and poultry that as nonruminants cannot do so, are more effective in bringing the soils more directly into efficient service for national nutrition than we have been prone to believe.

The instincts shown by animals are compelling us to recognize soil differences: Not only do the dumb beasts select herbages according as they are relatively more carbonaceous or proteinaceous but they select offerings from the same kind of grain according to the different fertilizers with which the soil has been treated. The fact that animal troubles are engendered by the use of feeds in mixtures only should be weighed against the fact that hogs select different corn grains from separate feeder compartments with disregard of hybrids but with particular and consistent choice among grains produced by different soil treatments. Rats indicate the same discrimination by cutting into the bags of corn that were chosen by the hogs but leaving uncut the bags holding the corn the hogs refused. Surely the animal appetite that calls the soil fertility so correctly can be of service in guiding animal production by means of soil treatments.

Curt P. Richter of the Johns Hopkins Hospital has pointed to a physiological basis for such fine distinctions by rats. Deprived of insulin, for example, they ceased to take sugar. But dosed with insulin, they increased consumption of sugar in proportion to the insulin given. Fat was refused in the diet similarly in accordance with the incapacity of the body to digest it.

Now that we are thinking about putting blanket plans over states, countries, and possibly the world as a whole, there is need to consider whether such regulations can blot out the economics, customs, and institutions which have established themselves as a counterbalance to the soil’s fertility, if not, indeed, as a mirror image of the distribution pattern of soil fertility. Since any civilization is actually premised on its resources rather than on its institutions, changes in the institutions cannot usefully be made in disregard of so basic a resource as the soil.

Researchers in soil science, plant physiology, ecology, human nutrition, and other sciences have given but a few years of their efforts to human welfare. These contributions have looked to hastened consumption of material surpluses from unhindered production for limited territorial use. They are now to be applied to production, and a production that calls for use of nature’s synthesizing forces for food production more than to simple nonfood conversions. When our expanded chemical industry is permitted to turn from wartime to peacetime pursuits, it is to be hoped that a national consciousness of declining soil fertility can enlist our sciences and industry into rebuilding and conserving our soils as the surest guarantee of the future health and strength of the nation.