By Anneliese Abbott
Is there a connection between soil fertility and human health?
In the 1940s, this was one of the hottest topics in the soil conservation movement. Researchers had just discovered that vitamins played a critical role in animal and human nutrition, and from the 1920s to 1950s they found that a score of mineral elements — especially trace elements like manganese, boron, copper, zinc, iron, and molybdenum — were essential for plant, animal and human health.
The discovery of certain trace elements cleared up centuries-old confusion about what caused the geographic distribution of some mysterious animal and human diseases. The most famous discovery was that iodine deficiencies in certain soils caused endemic goiter and cretinism. The solution was simple — add a little bit of iodine to salt for both animals and humans, and the goiters and other iodine deficiency symptoms disappeared. Similarly, soil deficiencies of selenium and cobalt were linked to several animal diseases, which could be treated with supplements.
Quite logically, the link between soil deficiencies of these three elements and diseases in both humans and animals made many people wonder what role soil fertility might play in human nutrition. “Even if you prescribe the right sort of food, how are you going to know that your carrots, or meat or greens come from a soil that has packed them full of minerals?” an Ohio conservation educator named Ollie Fink asked in 1941.
It was an important question. If infertile soils produced mineral-deficient plants and the animals eating those plants suffered from mineral deficiencies, then wouldn’t the humans eating those deficient plants and animals also suffer from ill health? Were fruits and vegetables always healthy, or only if they were grown on fertile soils?
These were the questions that many people were asking in the 1940s. And they turned to one main source for information on the connection between soil and health — William A. Albrecht.
Albrecht and Nutritional Geography
William A. Albrecht (1888-1974) earned his PhD in soil science from the University of Illinois in 1919, joined the staff at the University of Missouri sometime between 1914 and 1916, served as chair of the Department of Soil Science from 1938 to 1959, and continued working at as a professor emeritus until the 1960s. Albrecht was a man of diverse interests, studying a variety of topics such as inoculating legumes with microbes to enhance nitrogen fixation, cation exchange on clay particles and the importance of calcium in plant nutrition.
Albrecht’s interest in the connection between soil fertility and nutrition seems to have started in the 1930s, when he became aware of a “nutritional geography” hypothesis that suggested a causal link between infertile soils and unhealthy people in certain regions of the United States. During World War II, the US Navy studied the dental health of over 70,000 recruits and found that young men from the Midwest had lower rates of tooth decay than those from the Northeast. Other studies found that the healthiest young men drafted during World War II came from the Northwest and Midwest.
When Albrecht looked at the maps of the data from the Naval Dental Survey, he immediately jumped to the conclusion that differences in the underlying soils were responsible for these variations in health. The following summary of the “Albrecht Hypothesis” is drawn mainly from volumes 1, 2, and 8 of the Albrecht Papers, especially volume 2, which is a reprint of Albrecht’s 1958 book Soil Fertility and Human Health.
The best soils in the world, Albrecht argued, were those formed under grass. Grass, with its associated legumes, was the perfect food for cows — important producers of high-quality animal protein for the American diet. In much of the midwestern United States — especially the Great Plains — prairie grass was the predominant vegetation before European contact. These lush, fertile prairies had supported enormous populations of buffalo, wild bovines with similar nutritional requirements to domestic cattle.
In contrast, the soils of the East Coast were so leached and infertile that they couldn’t grow “proteinaceous” grass, only “carbonaceous” trees. No thundering herds of buffalo greeted the first Europeans to land on the East Coast; the land was so barren that when they found a few turkeys, “they were so thankful that we have had to be thankful for them every year since.”
The difference between the soils of these two regions, Albrecht explained, was largely due to rainfall. In the semiarid Great Plains, soils were under “construction” and were rich in fertility, especially calcium. These calcareous soils naturally grew protein-rich grass, perfect for fattening bison. In contrast, the soils in the humid regions of the East were under “destruction,” where rainfall had leached out so much of the original fertility that only “carbonaceous” trees could grow. Albrecht even argued that no “human life form” or cow could survive on leached eastern soils — completely disregarding the large number of Native Americans who had lived in his “carbonaceous” regions before European contact, or the ruminants like deer, elk and moose that had browsed the forests.
Some of the assertions that Albrecht made about ecology and plant physiology were inaccurate, even for the time. For example, he thought that a plant first formed “the woody structure that makes up its bulk” and then, “if soil conditions are right, the plant will store up a supply of the raw materials of protein, vitamine, and mineral compounds.” Most plant scientists, even in the 1940s, would have realized that plants grow protein-rich, tender leaves and stems first and form hard, woody stems later. Despite these misconceptions, however, his hypothesis that soil fertility affected animal health was still worth putting to the test.
Albrecht decided that the best way to test his hypothesis was by conducting animal feeding studies, or “biological assays of soil fertility,” as he called them. His first experiment, conducted from 1939-1941, involved feeding two groups of lambs lespedeza hay from limed and unlimed soils.
To Albrecht’s elation, there was a huge difference between treatments in the first season — the lambs on the limed soils gained nearly 50 percent more weight than those fed hay from the unlimed soils. Unfortunately, however, these results did not really mean anything because much of the hay had been ruined by rain and Albrecht had brought in outside hay, not grown under controlled conditions, to supplement the feed. In the second season, when the lambs were actually only fed hay from the correct soils, those on the limed soils gained an average of 16 percent more weight, though Albrecht didn’t statistically analyze the data or check to make sure that the vegetational composition of the two fields was the same.
One of Albrecht’s favorite feeding studies was done by his graduate student Eugene McLean around 1942. McLean fed fertilized and unfertilized lespedeza hay grown on five geographically distinct Missouri soils to rabbits to see if their growth was affected. The results seemed exciting: Rabbits fed hay from some unfertilized soils were much larger than those fed hay grown on other unfertilized soils. Also, the rabbits fed on fertilized hay were bigger than those fed unfertilized hay grown on the same soil type.
Albrecht frequently cited this study as proof that some soils were better at growing animals than others and could result in drastically different body types. But contemporary critics pointed out that the data were not statistically analyzed, that the number of experimental animals (8 per treatment) was rather small, and that no one analyzed the mineral content of the soils or hays. The biggest flaw in the experiment was that the hay from the poorer fields contained little lespedeza and was mostly grass and weeds — much less nutritious for rabbits.
All the study really showed was that some fields were better for growing lespedeza than others, that fertilization could improve lespedeza growth, and that rabbits grew larger when fed lespedeza than when fed grassy and weedy hay. It didn’t convincingly demonstrate that there was any nutritional difference in the lespedeza itself. But it did inspire other researchers to conduct better-designed experiments on the soil-nutrition relationship.
The possibility of a connection between soil and health was such a hot topic that, in 1939, the USDA established an entire Plant, Soil, and Nutrition Laboratory on the campus of Cornell University in Ithaca, New York. This state-of-the-art building, completed in 1941, contained a well-equipped laboratory, a greenhouse, and field facilities for conducting experiments with plants and animals. Research at this laboratory was a collaborative, interdisciplinary effort, combining the expertise of specialists in soil science, plant science, animal science, and nutrition. Its stated goal was “to improve the health and performance of human beings and farm animals by showing how they may be provided with nutritionally superior food and feed.”
One of the first hypotheses to be tested at the Plant, Soil, and Nutrition Laboratory was whether the mineral constituents of the soil significantly altered the nutritional composition of crops. Several researchers, including Firman Bear at Rutgers University, had found that crops grown in different regions of the United States often had varying mineral concentrations. If these differences were due to the amounts of mineral elements in the soils, then it seemed logical that fertilization with deficient elements could increase their concentration in plants.
But what the researchers quickly found was that the relationship between soil and plant nutrient composition was extremely complicated. The mineral composition of crops grown on the Ithaca soils did not change significantly even with extremely large fertilizer applications. And contrary to the findings of Albrecht, the researchers at Cornell found that lambs fed fertilized and unfertilized forages showed no difference in growth.
One of the early topics investigated at the USDA laboratory was how soil fertility and type might affect the vitamin C content of tomatoes. As the researchers explained in the 1948 USDA bulletin Factors Affecting the Nutritive Value of Foods: Studies at the U.S. Plant, Soil, and Nutrition Laboratory, they discovered that tomatoes grown in Wyoming, California, and Wisconsin had significantly different vitamin C concentrations than those grown in New York. But when they brought in soil samples from these other states and grew tomatoes in pots on the Cornell campus, they all had the same vitamin C content. After testing several other variables, they discovered that the amount of sunlight reaching developing tomato fruits was actually the most important factor affecting vitamin C levels; soil had no effect on this particular nutrient.
By the mid-1950s, the USDA researchers had come to an unexpected conclusion: fertilization could increase crop yields, or make it possible to grow a wider variety of crops (such as legumes), but it did not consistently affect the mineral or vitamin content of crop plants. Other factors, such as climate (soil type, rainfall, sunlight, temperature, etc.), type of plant, and variety of crop had much more influence over the nutritional quality of foods. Since climate cannot really be modified in a given location, the focus of the laboratory shifted toward breeding more nutritious varieties of crops, a project still in progress today.
The MSU Cow Study
One of the best-designed biological assays of soil fertility, as Albrecht would have called it, was an interdisciplinary study conducted at Michigan State University from 1945 to 1955 to test the effect of fertilization on dairy cow health. This study was conducted on a 210-acre “badly depleted farm” that the researchers determined had never been fertilized or even manured except for a few fields near the barn. It was a golden opportunity to see if fertilizer really could increase the nutritional quality of crops.
To make the most of this unique opportunity, the MSU researchers decided to raise two herds of dairy cows, one given feed grown on fertilized soil and one given feed from the unfertilized soil. Since the unfertilized soil couldn’t grow alfalfa or clover, the cows in both herds were fed an identical diet of corn, winter wheat, oats, soybeans, and grass hay, carefully balanced by animal nutritionists. This would make sure that any differences in cow health were due to actual differences in crop mineral composition, not because they were eating different kinds of plants.
After ten years and three or four generations of dairy cows, the results of this study were presented at a 1955 MSU symposium and published in a book titled Nutrition of Plants, Animals, Man. To the surprise of almost everyone involved, the plant scientists discovered that there was no significant difference in the protein or mineral content of the soybeans, corn, and brome hay grown on the fertilized and unfertilized soils. Only fertilized timothy plants had significantly higher levels of protein and minerals than unfertilized ones.
The animal scientists discovered that the cows in both herds were equally healthy. The only significant difference was that the Jersey cows on the unfertilized ration produced significantly more milk than those on the fertilized feed for the first couple years, but the differences evened out after the hay on the fertilized land was cut earlier to compensate for its more rapid growth.
The nutritionists analyzed milk samples from both herds and found no significant difference in total solids, butterfat, total nitrogen, lactose, ash, calcium, phosphorus, magnesium, manganese, carotene, vitamin A, amino acids, or B vitamins. There was also no significant difference in the health of lab rats fed on the milk from the two herds.
Though it may not have been what anyone expected, the results of this study were pretty clear. Fertilization had made no difference—either positive or negative—on the nutritional quality of the feed grown on the experimental soils. It increased yields and productivity, but it did not necessarily make the plants themselves any more nutritious.
Was Albrecht wrong? Does soil fertility actually have no effect on human or animal health? As with most controversial issues, the reality turned out to be a lot more complicated than a simple “yes” or “no” answer. Soil health and fertility certainly has a major impact on plant growth, and thus on the amount and quality of vegetation available for animals and humans to eat. Healthy plants grown on healthy soils often show increased resistance to pests and diseases. Soils that can grow higher yields of healthy plants can support a larger number of healthier animals. For these reasons alone, improving soil health is a desirable outcome.
Unfortunately, one reason that little research has been done on the connection between soil and nutrition since the 1950s was that some people took Albrecht’s ideas too far and claimed that it might be possible to eat a properly balanced diet containing lots of “protective foods” like vegetables and milk and still suffer from deficiency disease if those vegetables and milk were produced on depleted soils. There never was any evidence to support this claim, but it provided plenty of material for agronomists to discredit organic and eco-farmers who claimed that fertilization practices were a major cause of degenerative diseases in the United States.
By the way, I do still recommend that people read the Albrecht Papers. They are fascinating documents from a historical perspective, and Albrecht was an entertaining writer with a memorable way of phrasing important concepts. Just remember that he was a fallible human like the rest of us, he sometimes made mistakes, and he was stepping somewhat outside of his area of expertise when he made claims about animal and human health. None of that should detract from the significant contributions he made to the soil science of his day, or to the eco-agriculture movement of the 1970s and beyond.
Anneliese Abbott is a graduate student in the Nelson Institute for Environmental Studies at the University of Wisconsin-Madison. She holds a B.S. in plant and soil science from The Ohio State University and is the author of Malabar Farm: Louis Bromfield, Friends of the Land, and the Rise of Sustainable Agriculture. She can be contacted at firstname.lastname@example.org.”