The Influence of Soils on Human Health

By: Eric C. Brevik, Ph.D. (Department of Natural Sciences, Dickinson State University) & Lynn C. Burgess, Ph.D. (Department of Natural Sciences, Dickinson State University) © 2014 Nature Education

Citation: Brevik, E. C. & Burgess, L. C. (2014) The Influence of Soils on Human Health. Nature Education Knowledge 5(12):1


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Soils are important for human health in a number of ways. Approximately 78% of the average per capita calorie consumption worldwide comes from crops grown directly in soil, and another nearly 20% comes from terrestrial food sources that rely indirectly on soil (Brevik 2013a). Soils are also a major source of nutrients, and they act as natural filters to remove contaminants from water. However, soils may contain heavy metals, chemicals, or pathogens that have the potential to negatively impact human health. This article will summarize some of the more important and direct relationships between soils and human health.

Quality Food Production and Food Security

Quality food production and food security have several components, including the production of sufficient amounts of food, adequate nutrient content in the food products, and the exclusion of potentially toxic compounds from the food products (Hubert et al. 2010). Soils play a major role in all of these areas of quality food production and security.

Influence of Soils on Crop Yield and Food Security

Food security is achieved when all people have access to sufficient, safe, and nutritious food (Food and Agriculture Organization of the United Nations, 2003). Food security is central to human health (Brevik 2009a; Carvalho 2006), and the ability to produce nutritious crops in sufficient amounts depends on soil properties and conditions. In particular, soils that have well-developed structure, sufficient organic matter, and other physical and chemical properties conducive to promoting crop growth lead to strong yields and are thus important for food security (Reicosky et al. 2011; Brevik 2009b). Soil degradation, which includes soil erosion and loss of soil structure and nutrient content, decreases crop production and threatens food security (Brevik 2013b; Pimentel & Burgess 2013; Lal 2009) (Figure 1). Soils that contain substances such as heavy metals, which may be toxic to humans, can pass those substances on to humans through crop uptake, leading to unsafe foods that compromise food security (Hubert et al. 2010; Brevik 2009a).

Soil degradation along the top of the hill has left the soils unable to support strong plant growth. Soil degradation over large areas may threaten food security.

Figure 1: Soil degradation along the top of the hill has left the soils unable to support strong plant growth. Soil degradation over large areas may threaten food security.

Photo by Gene Alexander, USDA NRCS

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The Soil Biota

By: Ann-Marie Fortuna (Dept. of Crop & Soil Sciences, Washington State University) © 2012 Nature Education
Citation: Fortuna, A. (2012) The Soil Biota. Nature Education Knowledge 3(10):1

A ‘biological universe’ exists in a gram of soil. Find out how the soil biota within this tiny universe transform energy, create and modify their habitat, influence soil health, and aid in the regulation of greenhouse gases.

In his famous poem, The Auguries of Innocence, the poet William Blake wrote:

“To see a world in a grain of sand,

And a heaven in a wild flower,

Hold infinity in the palm of your hand,

And eternity in an hour.”

In a similar vein, one might see the ‘biological universe’ in a single gram of fertile soil, approximately a teaspoon in size, containing all the domains (Bacteria, Archaea and Eukarya) and elements of life! The majority of life on Earth is dependent upon six critical elements: hydrogen (H), carbon (C), nitrogen (N), phosphorus (P), oxygen (O), and sulfur (S) that pass through, and are transformed by, soil organisms (the soil biota). The process of biogeochemical cycling is defined as the transformation and cycling of elements between non-living (abiotic) and living (biotic) matter across land, air, and water interfaces (Madsen 2008). Biogeochemical processes are dependent upon the biota in the soil or pedosphere, the outermost layer of the Earth that is composed of soil and subject to soil formation processes. It exists at the interface of the lithosphere (rock), atmosphere (air), hydrosphere (water), and biosphere (living matter). This article addresses the role of soil biota in the pedosphere using ecological principles that link soil organisms and plants to biogeochemical processes occurring within the soil in natural and managed ecosystems.

Aggregates: Model of a Pedosphere

Soil texture (fineness or coarseness) affects plant rooting, soil structure and organic matter content. Soil texture and structure determine the pore-size distribution, soil water holding capacity and the amount of water to air-filled pore space in soil aggregates that provide habitat for soil organisms. Aggregates can be broadly classified into macroaggregates (>250 µm) and microaggregates (20-250 µm) (Six et al. 2004). An aggregate is a naturally formed assemblage of sand, silt, clay, organic matter, root hairs, microorganisms and their “glue” like secretions mucilages, extracellular polysaccharides, and hyphae (filaments) of fungi as well as the resulting pores. Soil aggregates often contain fine roots that grow into soil pores (Figure 1) associating aggregates with the rhizosphere “the zone of soil under the influence of plant roots” (Sylvia et al. 2005). Persistent binding agents like organic matter and metals stabilize microaggregates. The temporary binding agents (polysaccharides and hyphae) produced by soil organisms aid in the formation of macroaggregates contained within the more stable microaggregates. These macroaggregates function as “ecosystems or arenas of activity” (see: Arenas of Activity in the Pedosphere of a Forest) (Beare et al. 1997, Coleman et al. 2004). Thus, an aggregate is a unit of soil structure that could be considered as a very small-scale model of a pedosphere. One can visualize all the interactions of gases, water, organisms and organic and inorganic constituents at the “microscale” hence the “glimpse of the universe” in a gram of soil (Figure 1).

A soil aggregate or ped is a naturally formed assemblage of sand, silt, clay, organic matter, root hairs, microorganisms and their secretions, and resulting pores.

Figure 1: A soil aggregate or ped is a naturally formed assemblage of sand, silt, clay, organic matter, root hairs, microorganisms and their secretions, and resulting pores.
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The Rhizosphere – Roots, Soil and Everything In Between


 David H. McNear Jr. (Assistant Professor of Rhizosphere Science) © 2013 Nature Education 

Citation: McNear Jr., D. H. (2013) The Rhizosphere – Roots, Soil and Everything In Between. Nature Education Knowledge 4(3):1

What is the Rhizosphere and how can understanding rhizosphere processes help feed the world and save the environment? This article will review the critical biogeochemical processes occurring at the plant root-soil interface.

Meeting the Global Challenge of Sustainable Food, Fuel and Fiber Production

Soil is one of the last great scientific frontiers (Science, 11 June, 2004) and the rhizosphere is the most active portion of that frontier in which biogeochemical processes influence a host of landscape and global scale processes. A better understanding of these processes is critical for maintaining the health of the planet and feeding the organisms that live on it (Morrissey et al., 2004). There is a small but concerted effort under way to harness the root system of plants in an attempt to increase yield potentials of staple food crops in order to meet the projected doubling in global food demand in the next 50 years (Zhang, et al. 2010; Gewvin, 2010). These efforts are being done in the face of a changing global climate and increasing global population which will inevitably require more productively grown food, feed and fiber on less optimal (and often infertile) lands; a condition already encountered in many developing countries (Tilman, et al, 2002). Meeting the global challenges of climate change and population growth with a better understanding and control of rhizosphere processes will be one of the most important science frontiers of the next decade for which a diverse, interdisciplinary trained workforce will be required.

The Rhizosphere Defined

In 1904 the German agronomist and plant physiologist Lorenz Hiltner first coined the term “rhizosphere” to describe the plant-root interface, a word originating in part from the Greek word “rhiza”, meaning root (Hiltner, 1904; Hartmann et al., 2008). Hiltner described the rhizosphere as the area around a plant root that is inhabited by a unique population of microorganisms influenced, he postulated, by the chemicals released from plant roots. In the years since, the rhizosphere definition has been refined to include three zones which are defined based on their relative proximity to, and thus influence from, the root (Figure 1). The endorhizosphere includes portions of the cortex and endodermis in which microbes and cations can occupy the “free space” between cells (apoplastic space). The rhizoplane is the medial zone directly adjacent to the root including the root epidermis and mucilage. The outermost zone is the ectorhizosphere which extends from the rhizoplane out into the bulk soil. As might be expected because of the inherent complexity and diversity of plant root systems (Figure 2), the rhizosphere is not a region of definable size or shape, but instead, consists of a gradient in chemical, biological and physical properties which change both radially and longitudinally along the root.

Schematic of a root section

Figure 1

Schematic of a root section showing the structure of the rhizosphere.

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What Are Soils?

In this article readers are introduced to the many facets of soils – their unique characteristics and diversity, the ecosystem services that soils provide, and their use and misuse.
Soils are dynamic and diverse natural systems that lie at the interface between earth, air, water, and life. They are critical ecosystem service providers for the sustenance of humanity. The improved conservation and management of soils is among the great challenges and opportunities we face in the 21st century.

Soil is… a Recipe with Five Ingredients

Soil is a material composed of five ingredients — minerals, soil organic matter, living organisms, gas, and water. Soil minerals are divided into three size classes — claysilt, and sand (Figure 1); the percentages of particles in these size classes is called soil texture. The mineralogy of soils is diverse. For example, a clay mineral called smectite can shrink and swell so much upon wetting and drying (Figure 2) that it can knock over buildings. The most common mineral in soils is quartz; it makes beautiful crystals but it is not very reactive. Soil organic matter is plant, animal, and microbial residues in various states of decomposition; it is a critical ingredient — in fact the percentage of soil organic matter in a soil is among the best indicators of agricultural soil quality ( (Figure 3). Soil colors range from the common browns, yellows, reds, grays, whites, and blacks to rare soil colors such as greens and blues.

Relative sizes of sand, silt, clay.

Figure 1

Relative sizes of sand, silt, clay.

© 2013 Nature Education All rights reserved. View Terms of Use


Sustainable Agriculture


Sustainable Agriculture

By: Brodt Sonja (UC Sustainable Agriculture Research and Education Program and Agricultural Sustainability Institute), Six Johan (Department of Plant Sciences, UC), Feenstra Gail (UC Sustainable Agriculture Research and Education Program and Agricultural Sustainability Institute), Ingels Chuck (University of California Cooperative Extension, Sacramento County) & Campbell David (Department of Human and Community Development, UC) © 2011 Nature Education 

Citation: Brodt, S., Six, J., Feenstra, G., Ingels, C. & Campbell, D. (2011) Sustainable Agriculture. Nature Education Knowledge 3(10):1

History and Key Concepts

Agriculture has changed dramatically since the end of World War II. Food and fiber productivity has soared due to new technologies, mechanization, increased chemical use, specialization, and government policies that favored maximizing production and reducing food prices. These changes have allowed fewer farmers to produce more food and fiber at lower prices.

Although these developments have had many positive effects and reduced many risks in farming, they also have significant costs. Prominent among these are topsoil depletion, groundwater contamination, air pollution, greenhouse gas emissions, the decline of family farms, neglect of the living and working conditions of farm laborers, new threats to human health and safety due to the spread of new pathogens, economic concentration in food and agricultural industries, and disintegration of rural communities.

A growing movement has emerged during the past four decades to question the necessity of these high costs and to offer innovative alternatives. Today this movement for sustainable agriculture is garnering increasing support and acceptance within our food production systems. Sustainable agriculture integrates three main goals – environmental health, economic profitability, and social equity (Figure 1). A variety of philosophies, policies and practices have contributed to these goals, but a few common themes and principles weave through most definitions of sustainable agriculture.

Sustainable agriculture.

Figure 1

Sustainable agriculture gives equal weight to environmental, social, and economic concerns in agriculture.

© 2011 Nature Education Courtesy of Brodt et al. All rights reserved. View Terms of Use


Soil: The Foundation of Agriculture

Throughout human history, our relationship with the soil has affected our ability to cultivate crops and influenced the success of civilizations. This relationship between humans, the earth, and food sources affirms soil as the foundation of agriculture.

Human society has developed through utilization of our planet’s resources in amazingly unique, creative, and productive ways that have furthered human evolution and sustained global societies. Of these resources, soil and water have provided humans with the ability to produce food, through agriculture, for our sustenance. In exploring the link between soil and agriculture, this article will highlight 1) our transition from hunter-gatherer to agrarian societies; 2) the major soil properties that contribute to fertile soils; 3) the impacts of intensive agriculture on soil degradation; and 4) the basic concepts of sustainable agriculture and soil management. These topics will be discussed to demonstrate the vital role that soils play in our agriculturally-dependent society.

Agriculture and Human Society

Human use and management of soil and water resources have shaped the development, persistence, decline, and regeneration of human civilizations that are sustained by agriculture (Harlan 1992, Hillel 1992). Soil and water are essential natural resources for our domesticated animal- and plant-based food production systems. Although of fundamental importance today, agriculture is a relatively recent human innovation that spread rapidly across the globe only 10,000 to 12,000 years ago (Diamond 1999, Montgomery 2007, Price & Gebauer 1995, Smith 1995), during the Agricultural Revolution. This short, yet highly significant period of time, represents less than 0.3 % of the more than four million years of human evolution as bipedal hominids and ultimately Homo sapiens. In agriculturally-based societies during the last ten millennia, humans have developed complex, urban civilizations that have cycled through periods of increasing complexity, awe-inspiring intellectual achievement, persistence for millennia, and, in some instances, perplexing decline (Trigger 2003). In many cases, stressed, declining civilizations adapted, or reemerged, into new or similar complex cultures (Schwartz & Nichols 2006). Through such fluctuations, we have remained dependent on a relatively small number of crop and animal species for food, and on integrated soil-water systems that are essential for their production. There is no doubt that our modern human society has developed to the point that we cannot exist without agriculture.

It is clear that agriculture sustains and defines our modern lives, but it is often disruptive of natural ecosystems. This is especially true for plant communities, animal populations, soil systems, and water resources. Understanding, evaluating, and balancing detrimental and beneficial agricultural disturbances of soil and water resources are essential tasks in human efforts to sustain and improve human well-being. Such knowledge influences our emerging ethics of sustainability and responsibility to human populations and ecosystems of the future.

Although agriculture is essential for human food and the stability of complex societies, almost all of our evolution has taken place in small, mobile, kin-based social groups, such as bands and tribes (Diamond 1999, Johanson & Edgar 2006). Before we became sedentary people dependent on agriculture, we were largely dependent on wild plant and animal foods, without managing soil and water resources for food production. Our social evolution has accelerated since the Agricultural Revolution and taken place synergistically with human biological evolution, as we have become dependent on domesticated plants and animals grown purposefully in highly managed, soil-water systems.

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History of Agricultural Biotechnology: How Crop Development has Evolved


History of Agricultural Biotechnology: How Crop Development has Evolved

Have you ever wondered where our agricultural crops come from? And what were they like thousands of years ago, or hundreds of years ago? Our food crops today are in fact very different from the original wild plants from which they were derived.

About 10,000 years BC, people harvested their food from the natural biological diversity that surrounded them, and eventually domesticated crops and animals. During the process of domestication, people began to select better plant materials for propagation and animals for breeding, initially unwittingly, but ultimately with the intention of developing improved food crops and livestock. Over thousands of years farmers selected for desirable traits in crops, and thus improved the plants for agricultural purposes. Desirable traits included crop varieties (also known as cultivars, from “cultivated varieties”) with shortened growing seasons, increased resistance to diseases and pests, larger seeds and fruits, nutritional content, shelf life, and better adaptation to diverse ecological conditions under which crops were grown.

Over the centuries, agricultural technology developed a broad spectrum of options for food, feed, and fiber production. In many ways, technology reduces the amount of time we dedicate to basic activities like food production, and makes our lives easier and more enjoyable. Everyone is familiar with how transportation has changed over time to be more efficient and safer (Figure 1). Agriculture has also undergone tremendous changes, many of which have made food and fiber production more efficient and safer (Figure 1). For example in 1870, the total population of the USA was 38,558,371 and 53% of this population was involved in farming; in 2000, the total population was 275,000,000 and only 1.8% of the population was involved in farming. There are negative aspects to having so few members of society involved in agriculture, but this serves to illustrate how technological developments have reduced the need for basic farm labor.

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