Chapter 20

Soil depletion and plant and animal deterioration

THE data available on the subject of soil depletion and animal deterioration are so voluminous that it would require a volume to present them adequately. When we realize the quantities of many of the minerals which must enter into the composition of the bodies of human beings and other animals, we appreciate the difficulty of providing in pasture and agricultural soils a concentration of these minerals sufficient to supply the needs for plant growth and food production. If we think of growing plants and grasses in terms of average soil tilled to a depth of seven inches, we are dealing with a total of approximately two million pounds of soil per acre, of which two thousand pounds will be phosphorus in its various chemical forms, some of which will not be readily available for plants. If one-half of this phosphorus were present in an available form, there would be enough for only one hundred poor crops, utilizing ten pounds to the acre for the seed alone; or for forty good crops, taking twenty-five pounds per acre, assuming that the seed were to be removed from that land and not replaced. A sixty-bushel crop of wheat or corn per acre takes twenty-five to twenty-eight pounds of phosphorus in the seed. The soil is depleted of calcium similarly, though that mineral is not usually present in such limited amounts nor so rapidly taken away as is phosphorus. The leaves and stems of rapidly growing young plants and grasses are rich in calcium and phosphorus. As the plants ripen the phosphorus is transported in large amounts to the seed while most of the calcium remains in the leaves. A large part of the commerce of the world is concerned with the transportation of chemical elements as foods, chief of which are calcium and phosphorus. Whether the product of the soil is ultimately used as wheat for bread, milk and meat for foods, or wool and hides for clothing, every pound of these products that is shipped represents a depletion of soil for pasturage or for grain production.

    If we think of one hundred good crops constituting the limit of capacity of the best soils, and one-fourth of that for a great deal of the acreage of the tillable soil, we are probably over-generous. This problem of depletion may seem to many people unimportant, either because there has been no consciousness that depletion has been taking place, or because they believe that replenishment is a simple matter.

    In correspondence with government officials in practically every state of the United States I find that during the last fifty years there has been a reduction in capacity of the soil for productivity in many districts, amounting to from 25 to 50 per cent. I am informed also that it would cost approximately fifty dollars per acre to replenish the supply of phosphorus.

    Many people realize that farms they knew in their childhood have ceased to be productive because they have "run out." The movement of population to cities and towns is, in part, the result of the call of the social center and in part a consequence of the need of forsaking depleted soil. While there are many things that influence the movement from the farms, there is much to be learned from the government census reports which deal directly with farm acreage and values.

    If we relate the levels of life of human and domestic animals to the problem of soil depletion, we find two important groups of data. First, there are those which relate to specific land areas, some small and some very large; and second, those which relate to civilizations and groups, both large and small that have passed out of existence or are rapidly deteriorating. A study of the skeletons of the past and present often discloses a progressive breakdown. For example, we may mention the important anthropological findings of Professor Hooton of Harvard, who, in his examinations of various pueblos of the Western Plains, especially at the Pecos Pueblo where the progressive burials have been uncovered, has brought to light the calendar of a civilization extending over a thousand years. These findings show that there has been over the period of years a progressive increase in skeletal deformities, including arthritis and dental caries, together with a reduction in stature, suggesting a direct relationship to progressive depletion of the soil.

    In a recent magazine article, I have presented data (1) comparing the mineral content of different pasture grasses, and relating these to deficiencies in cattle. Unfortunately, space does not permit reviewing these data here in detail. They show that calcium varied from 0.17 per cent for a dry pasture grass in Arizona to 1.9 per cent in a Pennsylvania pasturage plant, to 2 per cent in a British Columbia pasturage plant, a range of over ten fold. Similarly, phosphorus was shown to vary from 0.03 per cent to 1.8 per cent, a range of sixty fold. Neither pasture animals nor human beings can eat a sufficient amount of low mineral plant food to provide the total mineral requirements of ordinary metabolism. In cases of overload, such as pregnancy and lactation in adults, and rapid growth in children, the demand is increased greatly. For example, a high-milk-production cow from southern Texas on a certain low mineral pasture will run behind her normal requirements about 60 grams of phosphorus and 160 grams of potassium per day. In that district large numbers of cattle were unable at the time to maintain their own bodies, let alone reproduce or provide milk. Many cattle in the district developed loin disease. It was found that moving them to another plot of ground where the soil was not depleted provided recovery.

    About thirty-seven billion dollars, or approximately 40 per cent of the cash income of salaries and wages of the people in the United States, is used for the purchase of foods. When we add to this the expenditure of energy by the people living on the land, it represents a total, probably exceeding fifty billion dollars a year that is spent for the chemicals that are provided in the foods, a large amount of which, perhaps 50 per cent, will have been expended for calcium and phosphorus, perhaps 25 per cent for other chemicals, and 25 per cent for special vitamin or activator carrying foods. Of this enormous transportation of minerals from the soil an exceedingly small proportion gets back to the tillable land in this country. Orr (2) states that "Consumption in the United Kingdom of live stock products mostly derived from grass lands has been estimated at about four hundred million pounds sterling per annum (nearly two billion dollars) ." This includes dairy products, meats and hides. Never in the history of the world has there been such a large scale depletion of the soil by transportation away from the tilled and pasturage areas. Sickness in the United States has been calculated to cost nearly half as much as food, and is increasing.

    An important discovery has been made with regard to the feeding of dairy cattle and other live stock: the nutritive value of young grass, when in a state of rapid growth, carries not only a very large quantity of minerals, but also digestible proteins in amounts that are approximately equivalent to those provided by the concentrated cereal cattle foods, such as linseed cake. It is observed also that not only do the milk products of such cows remain at a high level while the cows are on the rapidly growing young grass, particularly a rapidly growing young wheat grass or young rye grass, but the animals themselves are in better physical condition than when on grain concentrates. Further, that calves fed on the milk of those cows grow much more rapidly than they do when the cows are on other fodder and have a much higher resistance to disease. Grass, to provide these nutritional factors, must be grown on a very rich, well-balanced soil. A young plant, of necessity, produces a rapid depletion of soil. Minerals and other chemicals are removed and therefore there is need for adequate replacement.

    In Chapter 18 I have reported investigations made by Professors Meigs and Converse at the Beltsville Experimental Station, in which they have shown that feeding cattle on a grade of dried hay that was low in chlorophyll resulted in the development of dead or blind calves, and further that when the milk of these cows was fed to three normal calves they died in fifty-seven, sixty-two and seventy-one days respectively. These calves had been fed on whole milk until twenty days of age. They show that the main deficiency in this ration was vitamin A.

    Since mammals require milk in infancy and since it is the most efficient single food known, I have made a special study of milk and its products. The role of the vitamins and other activating substances in foods is quite as important and essential as that of minerals. These activating substances, in general, can be divided into two groups, those that are water-soluble and those that are fat-soluble, the former being much more readily obtained in most communities, than the latter. Since the fat-soluble and also the water-soluble vitamins are essential for mineral utilization and particularly since the fat-soluble activators are so frequently found to be inadequately supplied in diet and are usually more difficult to obtain, a special effort has been made to determine the level of these in dairy products in many different places for different seasons of the year. To accomplish this, I have obtained each year since 1927 samples of cream and butter, mostly butter, for analysis for their activator content. The work has rapidly extended so that for the eleventh year we are receiving now (1939) samples from several hundred places distributed throughout the world, usually once or twice a month throughout the year. Methods used for these studies are both biologic and chemical. These data are used in connection with morbidity and mortality statistics for the same districts.

    The progressive changing of the levels of life is shown by the morbidity and mortality statistics of the various areas of the United States and Canada. The American Heart Association publishes, from time to time, very important data relative to the number of deaths from heart disease in the various states of the Union. It is of interest to note that the highest mortality levels that are obtained are found in those states, in general, that have been longest occupied by modern civilizations, namely, the Atlantic States, the New England States, the Great Lakes States and the Pacific States. Their data published in their booklet ~tHeart Disease Mortality Statistics" and based on the United States Registration area reveal that the death rate per 100,000 population was 123 in 1900. The data sent me in November 1937 from the United States Census Bureau, Department of Commerce, in Washington, report the death rate from heart per 100,000 for 1934 as 239.9, in other words an increase of 86.9 per cent in thirty-four years. Figures provided by the Bureau of Census for England and Wales show the death rate per 100,000 to be 269.3; and for Scotland, 232. While the average figure for the United States Registration area of 224 deaths per 100,000 seems very high, it is exceedingly important to note that the New England States were much higher, leading the entire country. Massachusetts reported 307.3; New Hampshire, 323.1; Vermont, 310.8; New York, 302.1; Maine, 297.5. The rate of increase in the decade of 1921 to 1930 was 51.3 per cent for Delaware; 52 per cent for Connecticut, 51 per cent for Pennsylvania, 59.4 per cent for Missouri, 60.0 per cent for Washington; 55 per cent for Wisconsin; 64 per cent for Louisiana; 71 per cent for Florida; 63 per cent for South Carolina; 81 per cent for Montana; 61 per cent for Kentucky; and 51.9 per cent for North Carolina. Such rates of increase as these are cause for alarm.

    Sir Arnold Theiler, who spent a quarter of a decade studying the problems of nutritional deficiency diseases among pasture animals in South Africa, has discussed at length the reduction of phosphorus in available quantities for plant development as constituting, by far, the most important mineral deficiency. He reported data obtained from many countries through the world, indicating that the deterioration of cattle and sheep can be directly traced to an inadequate amount of phosphorus in the soil. He states, in discussing the relation of this problem to the conditions as they obtain in Australia, that: (3)

   Amongst the Australian data the figures showing depletion of phosphorus as a result of sale of products off the farm without adequate replacement by manuring, are interesting. Thus Richardson estimates that it would take two million tons of superphosphate to replace the phosphorus removed in the form of milk, mutton and wool. In the "ranching stage" of the development of a country the fact is often forgotten that the balance of Nature is frequently disturbed to the detriment of generations to come.

    It is important to keep in mind that morbidity and mortality data for many diseases follow a relatively regular course from year to year, with large increases in the late winter and spring and a marked decrease in summer and early autumn. The rise and fall of the level of morbidity with the changing season produces curves that are exceedingly regular for the same place from year to year. The distribution, however, is distinctly different for different latitudes and altitudes. It is further of special importance to note that the curves for the Southern Hemisphere, with its opposite seasons, are in reverse of those of the Northern Hemisphere, and have very similar levels for the same seasonal periods. I have obtained the figures for the levels of morbidity for several diseases in several countries, including the United States and Canada. I find that the distribution of the rise and fall in morbidity and mortality does not follow the sunshine curve but does follow the curve of vegetable growth. Accordingly, I have made studies by dividing the United States and Canada into sixteen districts, four from East to West and four from North to South. I have plotted by months the levels of mortality for heart disease and pneumonia in these various districts, from figures obtained from the governments of these two countries. Similarly, I have plotted curves for the vitamin content found in butter and cream samples obtained from these sixteen districts. When these are arranged in accordance with the levels by months they are found, in each case, to be opposite to the mortality from heart disease and pneumonia. It is also important to note that while these curves show a higher midsummer level of vitamins in dairy products in the northern tier of districts, the period of high level is shorter than in the more southern division. Two peaks tend to appear in the summer cycle of curves for the vitamins, one representing the spring period of active growth and the other, the fall period. These peaks are closer together in the north than in the south.

    A particularly important phase of this study is the finding of a lower level of vitamins throughout the year in those districts which correspond with the areas of the United States and Canada that have been longest settled, and consequently most depleted by agriculture. A similar study has been made based on the data published in a report by Tisdall, Brown and Kelley, (4) of Toronto. Their figures for children's diseases which included chicken pox, measles, nephritis, scarlet fever, hemorrhage of newborn, tetany and retropharyngeal abscess were arranged according to the incidence for each month. All of these diseases show a relatively high incidence during February and March, rising in December and January, falling during April and May, reaching a very low level in midsummer and then making a rapid increase during the autumn. These are opposite to the vitamin levels found in the dairy products of Ontario for the same months.

    In Chapter 3, I discussed data obtained during two summers in the Loetschental and other Swiss valleys. The Loetschental Valley has been isolated from contact with surrounding civilizations by its unique physical environment. For twelve hundred years during which time a written history of the valley has been kept, the people have maintained a high level of physical excellence providing practically all their food, shelter and clothing from the products raised in the valley. Cattle and goats provided milk, milk products and meat. The stock was carefully sheltered during the inclement weather and great care was used to carry back to the soil all of the enrichment. This, of course, is a process that is efficiently carried out in many parts of the world today. In this manner extensive depletion of the minerals required for food for animals and human beings may be prevented. Their practice is in striking contrast to that in many of the agricultural districts of the United States in which the minerals are systematically shipped from the land to the cities, there to be dissipated to the ocean through the sewerage system. Among many primitive races there is some attempt to preserve the fertility of the soil. For example, in Africa, many of the tribes that depend in part on agriculture, cleared off only a few acres in the heart of a forest and cropped this land for a limited number of years, usually less than ten. Great care was taken to prevent the loss of the humus both through drenching rains and wind erosion. The decaying vegetation and lighter soil that might be dislodged by the water were caught in the entanglement of roots and shrubbery surrounding the agricultural patch. The surrounding trees protect the soil from wind erosion. Care was taken not to form gullies, furrows and grooves that could carry currents of water and thus float away the valuable humus from the soil. This again is in contrast to conditions in other parts of the world, particularly in the United States. Sears (5) has stated that "Bare ground left by the plow will have as much soil washed off in ten years as the unbroken prairie will lose in four thousand. Even so, soil in the prairie will be forming as fast as, or faster than it is lost." In Nature's program, minerals are loaned temporarily to the plants and animals and their return to the soil is essential. To quote again from Sears.

    What is lent by earth has been used by countless generations of plants and animals now dead and will be required by countless others in the future. In the case of an element such as phosphorus, so limited is the supply that if it were not constantly being returned to the soil, a single century would be sufficient to produce a disastrous reduction in the amount of life.

    The history of preceding civilizations and cultures of mankind indicate the imbalances that have developed when minerals have been permanently transferred from the soil. There are only a few localities in the world where great civilizations have continued to exist through long periods and these have very distinct characteristics. It required only a few centuries, and in some profligated systems a few decades to produce so serious a mineral depletion of the soil that progressive plant and animal deterioration resulted. In such instances, regular and adequate replenishment was not taking place.

    The replenishment may be made, as in the case of the prairie with its plant and animal life, through a replacement in the soil of borrowed minerals, a program carried out efficiently by a few intelligent civilizations. The balance of the cultures have largely failed at this point. Another procedure for the replenishing of the depleted soils is by the annual spring overflow of great water systems which float enrichment from the highlands of the watersheds to the lower plains of the great waterways. This is illustrated by the history of the Nile which has carried its generous blanket of fertilizing humus and rich soil from the high interior of Africa northward over its long course through Sudan and Egypt to the Mediterranean, and thus made it possible for the borders of the Nile to sustain a population of greater density than that of either China or India. The salvation of Egypt has been the fact that the source of the Nile has been beyond the reach of modernizing influences that could destroy Nature's vast stores of these replenishing soil products. Where human beings have deforested vast mountainsides at the sources of the great waterways, this whole problem has been changed.

    A similar situation has occurred in China. Her two great rivers, the Yangtze and the Yellow River, having their sources in the isolated vastness of the Himalayas in Tibet, have through the centuries provided the replenishment needed for supporting the vast population of the plains of these great waterways. Together with this natural replenishment the Chinese have been exceedingly efficient in returning to the soil the minerals borrowed by the plant and animal life. Their efficiency as agriculturists has exceeded that of the residents of most parts of the populated world.

    The story in Europe and America has been vastly different in many districts. The beds of roots of trees and grasses that hold the moisture and induce precipitation have been rudely broken up. An important function of the plant and tree roots is the entanglement of dead plant life. Vegetation holds back moisture at the time of melting snows and rainy seasons so efficiently that disastrous floods are prevented and a continuing flow of water maintained over an extended period. Under the pressure of population more and more of the highlands have been denuded for agriculture; the forests have often been ruthlessly burned down, frequently with the destruction of very valuable timber. The ashes from these great conflagrations provided fertilizer for a few good crops, but these chemicals were dissipated rapidly in the swift flow of the water in which they were soluble, with the result that vast areas that Nature had taken millenniums to forest have been denuded and the soil washed away in a few decades. These mountainsides have become a great menace instead of a great storehouse of plant food material for the plains country of the streams. Loss of timber which was needed greatly for commerce and manufacture has been another disastrous result. The heavy rains of the spring now find little impediment and rush madly toward the lower levels to carry with them not the rich vegetable matter of the previous era, but clay and rocks which in a mighty rush spread over the vast plains of the lowlands. This material is not good soil with which to replenish and fertilize the river bottoms. On the contrary, it often covers the plains country with a layer of silt many feet deep making it impossible to utilize the fertile soil underneath.

    We have only to look over the departed civilizations of historic times to see the wreckage and devastation caused by these processes. The rise and fall in succession of such cultures as those of Greece, Rome, North Africa, Spain, and many districts of Europe, have followed the pattern which we are carving so rapidly with the rise and fall of the modernized culture in the United States.

    The complacency with which the masses of the people as well as the politicians view our trend is not unlike the drifting of a merry party in the rapids above a great cataract. There seems to be no appropriate sense of impending doom.

    An outstanding example of our profligate handling of soil and watersheds may be seen in our recent experiences in the Mississippi Basin. The Ohio River draining the western slopes of the Allegheny Mountains has gone on rampages almost annually for a decade carrying with it great damage to property and loss of life. Other branches of the Mississippi, particularly the Missouri, draining the eastern slopes of the Rocky Mountains have gone out of control so that vast areas are flooded with silt. There is now a concerted effort to stem this series of cataclysms by building dykes along the great waterways to raise the banks and dams in the higher regions of the watershed to hold back the floods. These artificial lakes become settling pools for the silt and soon lose their efficiency by being filled with the debris that they are holding back from the lower levels. An effort is also being made to reforest which is purposeful, but when we consider the millenniums of time that Nature has required to build the tanglewood of plant life, shrubbery and trees over the rocks and through the gullies to act as great defenses for holding back the water, these modern programs offer very little assurance for early relief.

    Another very destructive force is the wind. When surfaces are denuded either at high or low altitudes the wind starts carving up the soil and starts it on the march across the country. We call the demonstrations dust storms. When we travel through our Western States, it is not uncommon to see buildings and trees partially buried in these rolling dunes of drifting sand. When we were traveling across the desert of Peru in 1937, we saw in many places mountain-like dunes rolling slowly across the country, frequently so completely blocking former traffic routes that long detours were necessary. When we were flying over eastern Australia in search of groups of primitive aborigines, we saw great forests gradually being engulfed with these marching billows of sand so that most of the trees were covered to their tips.

    Few people will realize that it is estimated that only about 45 per cent of the land surface of the United States is now available for agricultural purposes and grazing. This includes vast areas that are rapidly approaching the limit of utility.

    In one of my trips to the Western States I visited a large ranch of some fifty thousand acres. I asked the rancher whether he was conscious of a depletion in the soil of the ranch in its ability to carry pasture cattle. He said that it was very greatly depleted, that whereas formerly the cows on the ranch were able to produce from ninety-three to ninety-five healthy calves per hundred cows annually, nearly all of sufficiently high physical quality to be available for reproductive purposes, now he was getting only forty to forty-four calves per hundred cows annually and usually only ten or eleven of these were physically fit for reproductive purposes. He stated also that he was able to raise as many calves for restocking the ranch on the plant food produced on the fifty acres to which he was applying a high fertilization program as on the rest of the fifty-thousand-acre ranch. Of late most of the calves for the ranch had to be imported from other states.

    In a city in the vicinity I inquired of the director of public health what the death rate was among their children up to one year of age. He stated that the figures were progressively increasing in spite of the fact that they were giving free hospitalization and free prenatal and postnatal care for all mothers who could not afford to pay for the service. This death rate had more than doubled in fifty years. I asked how he interpreted the increasing mortality rate among the infants and mothers. His comment was in effect that they could not explain the cause, but that they knew that the mothers of this last generation were far less fit physically for reproduction than their mothers or grandmothers had been.

    To many uninformed people the answer will seem simple. Those who are responsible for these programs, recognize the difficulty in replenishing the exhausted minerals and food elements in adequate quantity. I have been informed by the director of the department of agriculture of the state of Ohio that it would cost fifty dollars per acre to restore the phosphorus alone that has been exhausted during the last fifty to one hundred years. He stated that the problem is still further complicated by the fact that the farmer cannot go to a bank and borrow money to buy this fertilizer. If, however, he buys adjoining acreage to double his own, he can then borrow twice as much money as he can on his own farm. But this is not all of the difficulty. Recent data indicate that if sufficient phosphorus in a form easily available for plant use were supplied to the land at once, it would kill the plant life; it must be provided in a form in which by a process of weathering it is made slowly available for plant utilization. Phosphorus is only one of the minerals that is readily taken from the soil. Other minerals also are difficult to provide. I have been able practically to double the weight and size of beets in five weeks by the addition of a tablespoonful of ferric ammonium citrate to each square foot of garden soil.

    An important commentary on soil depletion is provided by the large number of farms that have been abandoned in many districts throughout the United States. The severe industrial depression which has thrown large numbers of shop and mill workers out of employment, has induced a considerable number of these to return to the land for subsistence. As one drives through farming districts that once were very fertile many farms are seen apparently abandoned insofar as tillage is concerned.

    In my studies on the relation of the physiognomy of the people of various districts to the soil, I have found a difference in the facial type of the last generation of young adults when compared with that of their parents. The new generation has inherited depleted soil. In many communities three generations of adults are available for study. The yardstick for these comparisons has been developed in the preceding chapters. It will be of interest for the readers to apply this yardstick to their own brothers and sisters in comparison with the parents and particularly their grandparents. The most serious problem confronting the coming generations is this nearly unsurmountable handicap of depletion of the quality of the foods because of the depletion of the minerals of the soil.


  1. PRICE, W. A. New light on the control of dental caries and the degenerative diseases. J. Am. Dent. Assn., 18:1889, 1931.
  2. ORR, J. B. The composition of the pasture. London, H. M. Stationery Office. E.M.B., 18, 1929.
  3. THEILER, A. and GREEN, H. Aphosphoris in ruminants. Nutrition Absts. and Rev., 1:359, 1932.
  4. TISDALL, BROWN and KELLEY. The age, sex, and seasonal incidence in children. Am. J. Dis. Child., 39:163, 1930.
  5. SEARS, P. B. Deserts on the March. Norman, University of Oklahoma Press, 1935.


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