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J. W. DORAN E T AL.
soil that we generally allude when we speak of a farm as good or bad’ (after
Storr-Best, 1912, p. 28).
Maintaining a fertile soil, then, was of paramount importance to the philosophers. Practices suggested to maintain soil fertility included the use of rotations
that incorporated green-manuring or legume crops, application of livestock manure to soil, and fallowing. The Georgics of Virgil, translated by Lewis (1940),
outlined numerous methods for maintaining soil fertility. Regarding crop rotation
and fallowing, Virgil wrote: “So too are the fields rested by a rotation of crops,
and unploughed land in the meanwhile promises to repay you” (Book 1, I. 8283). On using livestock manure, he noted: “Whatever plantations you’re setting
down on your land, spread rich dung and be careful to cover with plenty of earth”
(Book 11, 1. 346-347).
Sensitivity to soil characteristics was evident in the cropping practices advocated by the philosophers. Cropping to the character of the land was the rule, not
the exception. This belief was expressed by Varro when he wrote: . . . the
same soil is not equally suited for all kinds of produce . . . for it is better to plant
crops that do not need much nutriment on thinner soil” (after Storr-Best, 1912,
p. 28, 63). Cropping to specific soils was suggested by both Cat0 and Varro.
Cato, in De Agriculturu, wrote: “Where the soil is rich and fertile, without
shade, there the corn-land ought to be. Where the land lies low, plant rape,
millet, and panic grass” (after Harrison, 1913, p. 42).
Using senses of sight, taste, touch, and smell, the philosophers set down
qualitative guidelines for evaluating soil and its suitability to promote growth of
particular crops. Soil color was used often in their treatises as an indicator of
productivity, with black soils considered the most productive and suitable for
corn production. Saline or acid soils were identified by a simple taste test recommended by Virgil: “The taste of fresh water strained through sour soil will twist
awry the taster’s face” (after Lewis, 1940, Book 11, 1. 246-247). The soil’s
physical condition was considered an important component for successful crop
production. In his classification of farmland, Varro found crumbling soils of
medium texture to be ideal for farming: . . . the kind of land which will repay
cultivation . , . easily crumbles when dug, and neither resembles ashes in texture, nor is very heavy” (after Storr-Best, 1912, p. 36). Similarly, Columella
classified “rich and mellow” soils best for crops and pasture (after Simonson,
1968). Pliny used his sense of smell to test soil. He considered the musty odor of
freshly plowed soil to be the most telling assessment of a soil’s quality: “It is the
odor which the earth, when turned up, ought to emit, and when once found, can
never deceive any person: and this will be found the best criterion for judging the
quality of the soil’’ (after Harrison, 1913, p. 91). Interestingly, this same criterion
is currently being considered by the USDA National Soil Tilth Laboratory for use
as a potential indicator of soil health (T. Parkin, 1995, personal communication).
SOIL HEALTH AND SUSTAINABILITY
l ! h H AND
C E N T U R Y SCIENTISTS AND PRACTITIONERS
The nineteenth century brought widespread concern over a potential food
crisis caused by a rapid increase in human population. As the need to increase
food production was apparent, chemists sought to understand better relationships
between soils and plants. Initial work focused on the concept that plants fed
directly on soil humus. This theory, put forth by Wallerius in the middle of the
eighteenth century, was developed further during the first half of the nineteenth
century by Thaer and von Wullfen (Usher, 1923). They believed organic matter
in soils had to be kept at or near original levels to maintain fertility and avoid
reductions in crop yield. Humus, therefore, was considered a primary indicator
of soil quality. Research by these scientists indicated levels of soil humus to
decrease under cultivation. This finding resulted in predictions that, without
additions of organic matter, soils in central Europe would quickly be exhausted
causing significant declines in crop yield (Usher, 1923).
The humus concept, though profoundly important for its time, was considered
simplistic and limited in scope because of its theoretical basis in phlogiston
chemistry (Krohn and Schafer, 1983). Among its foremost critics was Justus von
Liebig. Liebig acknowledged the importance of hunius as a critical component of
soil fertility, but claimed that a number of key elements were essential for plant
nutrition instead. Relying on methodological advances in organic elementary
analysis, Liebig found plant nutrient requirements could be estimated by analyzing the elemental concentrations in plants and soils and striking a balance between the amounts in the soil and those in the growing plant.
Liebig’s thesis centered on the concept that maintenance of soil quality for
growth of plants required the establishment of natural, unbroken cycles of essential plant nutrients within the soil. These cycles, however, were perceived as
nonexistent in agricultural practices of the time. According to Liebig, the nutritionally extractive characteristics of agriculture could only be offset by addition
of essential plant nutrients to the soil in the form of artificial fertilizers. By doing
this, producers could claim to develop a nonexploitative relation to nature “like a
wave motion within a cycle” (Liebig, 1862, after Krohn and Schafer, 1983).
This new paradigm of plant nutrition caught on rapidly and by the turn of the
twentieth century, agriculture had evolved into a major production industry.
Under this method of agriculture, soil had acquired the status of a “nutrient bin”
for plant roots (Simonson, 1968). In opposition to this form of agriculture was a
group of scientists and farmers of “privilege” who regarded soil as a living
resource. Sir Albert Howard, J. I. Rodale, Lady Eve Balfour, and William
Albrecht represented a handful of individuals who believed soil vitality (i.e., soil
life) to be a fundamental component of successful and socially responsible agriculture. By their standard, soil was a form of biological capital: capital that could
J. W. DORAN E T AL.
be used wisely by adoption of agricultural practices that relied on balanced
natural fertility, or unwisely through continued use of practices that relied on external inputs of artificial fertility. They accordingly held the view that the health
and prosperity of society depended upon the condition of the soil.
Agricultural systems that promoted soil vitality were strongly advocated by
this group. In their view, soil vitality was achieved by maintaining a balance of
growth and decay in the soil. This balance was considered to be absent in
conventional agricultural systems as a result of a disproportionate emphasis on
production (Howard, 1943). Sustainable agricultural systems were regarded as
balanced by relying upon vast natural reserves of decaying material. In terms of
agricultural management, this implied replenishing organic and mineral matter in
Application of compost to soil was generally accepted as the primary method
to maintain soil organic matter. J. I. Rodale, in Pay Dirt (1945), outlined 36
advantages of using compost, 15 of which were directly related to improving soil
health. Rodale strongly believed the value of compost could not be estimated by
chemical composition alone. In his view, the greatest value of compost was in its
potential to improve the biological and physical condition of the soil.
Although emphasized less than organic matter application, addition of mineral
constituents to the soil was encouraged. Howard regarded the success of Hunzan
agriculture to be partly due to the silt-size glacial material found in the irrigation
water (Howard, 1947, p. 177). Albrecht and Rodale both stressed the importance
of renewing the soil mineral fraction by suggesting the application of lime, wood
ash, and even rocks to soil.
Primary to the philosophy of this group was the belief that soil quality impacted plant, animal, and human health. Diet was considered to be the primary
determinant of good health, and nutrition for all terrestrial organisms began
“from the ground up” (Albrecht, 1975). So strong was this belief that they
claimed soil quality to be an important element of public health. Lady Eve
Balfour, in The Living Soil (1948), declared issues of soil management and
public health to be inseparable. In fact, she proposed that agriculture should be
looked upon as one of the health services, if not the primary health service.
Attainment of this status, however, depended on the need to clearly identify a
relationship between soil quality and public health using rigorous scientific methods; a difficult or impossible task.
IV. SOIL HEALTH AND HUMAN HEALTH
For much of modern agricultural history, the value of new farming techniques
and products was judged primarily, if not solely, on their ability to increase food
SOIL HEALTH AND SUSTAINABILITY
production. As discussed earlier, warnings of potential environmental damage
associated with modem agriculture were largely unheeded until recent decades.
The concept that the method of food production can have an additional direct
impact on animal and human health has recently developed, but only tentatively
in scientific circles. The proposal that any definition of soil quality or soil health
needs to incorporate the soil’s effect on human health as a component of equal
importance with productivity and environmental impact was perhaps first publicly articulated at the Conference on Assessment and Monitoring of Soil Quality
held at the Rodale Institute, Emmaus, Pennsylvania in July, 1991 (Papendick and
Parr, 1992; Rodale, 1991). Little headway has been made since then in defining
the indicators of soil quality and associated effects on human health.
There are three general avenues through which the soil may interact with and
affect the health of higher animals. First, there is the potential for direct poisoning of animals and people from contaminated soils. This is most likely to be
highly localized and may be the result of industrial accidents or improper use or
disposal of agrochemicals, industrial chemicals, or radioactive waste products.
While the seriousness of such toxic encounters with the soil is not to be taken
lightly, the likelihood of the general population being exposed to soils so highly
contaminated as to seriously affect health is very small, There are numerous
well-documented occurrences of pesticide poisoning (Hodges and Scofield,
1983; Culliney et al., 1992), but most acute farm chemical poisonings occur
before the chemicals are applied to the soil, generally during mixing, or during
the spray process itself when chemicals are air-borne (Soule and Piper, 1992;
NCAMP, 1990). Recent dramatic increases in certain fungal diseases, often
fatal, seen in patients suffering from immunodeficiency diseases such as AIDS
can be traced to soil origins (Sternberg, 1994). Although naturally occurring, and
not normally associated with unhealthy soil conditions, it appears that soil disturbances, whether natural, as from earthquakes, or human initiated, create the
conditions necessary for the spores to be propelled into the atmosphere in numbers sufficiently high to infect the human population.
A second, more widespread degree of interaction between soil health and
animal/human health occurs indirectly, through the soil’s influence on the quality
of water and air. It is well-recognized that there are serious public health concerns related to contaminated groundwater, streams, and other surface water
supplies, occasionally including acute toxicity, but more often associated with
development of cancer and other long-term debilitating diseases. Nitrate in
drinking water can cause the potentially fatal methemoglobinemia, or blue baby
syndrome, but can also have more insidious carcinogenic effects if transformed