With the new emphasis on sustainable agriculture comes a reawakening of interest in soil health. Early scientists, farmers, and gardeners were well aware of the importance of soil quality and organic matter to the productivity of soil. The significance of soil organic matter, including living organisms in the soil, was understood by scientists at least as far back as the 17th century. John Evelyn, writing in England during the 1670s, described the importance of topsoil and explained that the productivity of soils tended to be lost with time. He noted that their fertility could be maintained by adding organic residues. Charles Darwin, the great natural scientist of the 19th century who developed the modern theory of evolution, studied and wrote about the importance of earthworms to the cycling of nutrients and the general fertility of the soil.
Around the turn of the 20th century, there was again an appreciation of the importance of soil health. Scientists realized that “worn-out” soils, whose productivity had drastically declined, resulted mainly from the depletion of soil organic matter. At the same time, they could see a transformation coming: Although organic matter was “once extolled as the essential soil ingredient, the bright particular star in the firmament of the plant grower, it fell like Lucifer” under the weight of “modern” agricultural ideas (Hills, Jones, and Cutler, 1908). With the availability of inexpensive fertilizers and larger farm equipment after World War II, and the availability of cheap water for irrigation in some parts of the western United States, many people working with soils forgot or ignored the importance of organic matter in promoting high-quality soils.
[Organic matter was] once extolled as the essential soil ingredient, the bright particular star in the firmament of the plant grower . . .
As farmers and scientists were placing less emphasis on soil organic matter during the last half of the 20th century, farm machinery was getting larger. More horsepower for tractors allowed more land to be worked by fewer people. Large four-wheel-drive tractors allowed farmers to do field work when the soil was wet, creating severe compaction and sometimes leaving the soil in a cloddy condition, requiring more harrowing than otherwise would be needed. The use of the moldboard plow, followed by harrowing, broke down soil structure and left no residues on the surface. Soils were left bare and very susceptible to wind and water erosion. New harvesting machinery was developed, replacing hand harvesting of crops. As dairy herd size increased, farmers needed bigger spreaders to handle the manure. More passes through the field with heavier equipment to spread fertilizer and manure, prepare a seedbed, plant, spray pesticides, and harvest created the potential for significant amounts of soil compaction.
A new logic developed that most soil-related problems could be dealt with by increasing external inputs. This is a reactive way of dealing with soil issues—you react after seeing a “problem” in the field. If a soil is deficient in some nutrient, you buy a fertilizer and spread it on the soil. If a soil doesn’t store enough rainfall, all you need is irrigation. If a soil becomes too compacted and water or roots can’t easily penetrate, you use an implement, such as a subsoiler, to tear it open. If a plant disease or insect infestation occurs, you apply a pesticide.
Are low nutrient status; poor water-holding capacity; soil compaction; susceptibility to erosion; and disease, nematode, or insect damage really individual and unrelated problems? Perhaps they are better viewed as symptoms of a deeper, underlying problem. The ability to tell the difference between what is the underlying problem and what is only a symptom of a problem is essential to deciding on the best course of action. For example, if you are hitting your head against a wall and you get a headache—is the problem the headache and aspirin the best remedy? Clearly, the real problem is your behavior, not the headache, and the best solution is to stop banging your head against the wall!
What many people think are individual problems may just be symptoms of a degraded, poor-quality soil.
What many people think are individual problems may just be symptoms of a degraded, poor-quality soil. These symptoms are usually directly related to depletion of soil organic matter, lack of a thriving and diverse population of soil organisms, and compaction caused by use of heavy field equipment. Farmers have been encouraged to react to individual symptoms instead of focusing their attention on general soil health management. A new approach is needed to help develop farming practices that take advantage of the inherent strengths of natural systems. In this way, we can prevent the many symptoms of unhealthy soils from developing, instead of reacting after they develop. If we are to work together with nature, instead of attempting to overwhelm and dominate it, the buildup and maintenance of good levels of organic matter in our soils are as critical as management of physical conditions, pH, and nutrient levels.
A skeptic might argue that the challenges described above are simply the result of basic economic forces, including the long-run inexpensive cost of fossil fuel and crop inputs (although this is changing), and the fact that environmental consequences and long-term impacts are not internalized into the economic equation. It could then be argued that matters will not improve unless the economic incentives are changed. We argue that those economic motivations are already present, that sustainable soil management is profitable, and that such management will cause profitability to increase with greater scarcity of resources and higher prices of crop inputs.
This book has four parts. Part 1 provides background information about soil health and organic matter: what it is, why it is so important, the importance of soil organisms, and why some soils are of higher quality than others.
Part 2 includes discussions of soil physical properties, soil water storage, and nutrient cycles and flows. Part 3 deals with the ecological principles behind—and practices that promote—building healthy soil. It begins with chapters that place a lot of emphasis on promoting organic matter buildup and maintenance. Following practices that build and maintain organic matter may be the key to soil fertility and may help solve many problems. Practices for enhancing soil quality include the use of animal manures and cover crops; good residue management; appropriate selection of rotation crops; use of composts; reduced tillage; minimizing soil compaction and enhancing aeration; better nutrient and amendment management; good irrigation and drainage; and adopting specific conservation practices for erosion control. Part 4 discusses how you can evaluate soil health and combine soil-building management strategies that actually work on the farm, and how to tell whether the health of your soils is improving.
Table of Contents
- About the Authors
- Healthy Soils
- Organic Matter: What It Is and Why It's So Important
- Amount of Organic Matter in Soils
- The Living Soil
- Soil Particles, Water, and Air
- Soil Degradation: Erosion, Compaction, and Contamination
- Nutrient Cycles and Flows
- Soil Health, Plant Health, and Pests
- Managing for High Quality Soils: Organic Matter, Soil Physical Condition, Nutrient Availability
- Cover Crops
- Crop Rotations
- Animal Manures for Increasing Organic Matter and Supplying Nutrients
- Making and Using Composts
- Reducing Erosion and Runoff
- Preventing and Lessening Compaction
- Reducing Tillage
- Managing Water: Irrigation and Drainage
- Nutrient Management: An Introduction
- Management of Nitrogen and Phosphorus
- Other Fertility Issues: Nutrients, CEC, Acidity, and Alkalinity
- Getting the Most From Routine Soil Tests
- Taking Soil Samples
- Accuracy of Recommendations Based on Soil Tests
- Sources of Confusion About Soil Tests
- Soil Testing for Nitrogen
- Soil Testing for P
- Testing Soils for Organic Matter
- Interpreting Soil Test Results
- Adjusting a Soil Test Recommendation
- Making Adjustments to Fertilizer Application Rates
- Managing Field Nutrient Variability
- The Basic Cation Saturation Ratio System
- Summary and Sources
- How Good Are Your Soils? Field and Laboratory Evaluation of Soil Health
- Putting It All Together