Soil: The Foundation of Agriculture
Sustainable Soil Management
Without sustainable soil management practices, soil can become degraded, eroded, compacted, toxic, and/or inhospitable for crop production. The importance of soil sustainability cannot be overstated in terms of utility, resources, and climate. It is key for food access, ecosystem services, and livelihoods. By understanding how the soil processes that support plant growth and regulate environmental quality are affected by management practices, it is possible to design sustainable soil management practices that can at least maintain if not improve soil health over time. The following list constitutes goals of sustainable soil management. The goals should not be viewed as a complete list, but rather a reference to be applied on a context specific basis.
Minimize Soil Erosion
Soil erosion, a major land degradation process, is caused by the weathering effects of water and wind. For land covered by native vegetation, natural erosion rates will tend to balance with soil production rates. However, typical agricultural tillage practice can disrupt this balance, causing levels of soil erosion to be one to two orders of magnitude higher than that of soil formation.
Sustainable Soil Management Practices
Rotating in high-residue crops—such as corn, hay, and small grain—can reduce erosion as the layer of residue protects topsoil from being carried away by wind and water. Conventional tillage produces a smooth surface that leaves soil vulnerable to erosion. Conservation tillage methods, on the other hand, such as no-till planting, strip rotary tillage, chiseling, and disking leave more of the field surface covered with crop residue that protects the soil from eroding forces.
Enhance Soil Organic Matter
Soil organic matter plays a central role in maintaining soil functions and preventing soil degradation. Soils constitute the largest organic carbon pool on the Earth and play a critical role in regulating climate and mitigating climate change through trade-offs between greenhouse gas emission and carbon sequestration. For this reason, soil organic matter is strategic for climate change adaptation and mitigation, and global stores of soil organic matter should be stabilized or increased.
Sustainable Soil Management Practices
To maintain or increase soil organic matter levels, inputs of organic matter must meet or exceed the losses of organic matter due to decomposition and crop harvesting. A period under perennial, grass-dominant pasture is an effective way of increasing organic matter in farm soils. Short-lived annual grasses are a source of dead roots; perennial grasses are a source of leaf matter. Even short periods (1–2 years) under pasture can improve soil structure, even though the actual increase in organic matter may be small.
Preserve and Enhance Soil Biodiversity
Soil biodiversity is the variety of life that exists within the soil, including bacteria, fungi, earthworms, insects, and nematodes. Beneficial soil microbes perform fundamental functions such as nutrient cycling, breaking down crop residues, and stimulating plant growth. While the role of microbes to maintain soil health and contribute to crop performance is clear, the soil biological component is extremely difficult to observe and manage.
Sustainable Soil Management Practices
In agriculture, soils that receive less manufactured inputs (e.g., chemical fertilizers and pesticides) generally have higher soil biodiversity. Grazing systems which encourage plant diversity usually have higher soil biodiversity, due to the greater availability of food resources from roots and litter, which support a greater variety of organisms in the soil. Soil organic matter levels supporting soil biodiversity should be maintained or enhanced through the provision of sufficient vegetative cover (e.g., cover crops, multiple crops), optimal nutrient additions, addition of diverse organic amendments, avoiding salinization, and maintaining or restoring vegetation such as hedgerows and plowed.
Prevent and Minimize Soil Salinization
Soil salinity in agriculture is the high concentrations of salts in the soil profile. The most familiar salt is sodium chloride but also can include sulfates, sodium, potassium, and carbonates and bicarbonates of calcium and magnesium. The process of salinization can occur either naturally or by anthropogenic activities. While salinity can improve soil structure, it can also negatively affect plant growth and crop yields.
Sustainable Soil Management Practices
Soil salinization can be prevented by implementing several strategies in the production management process. Surface cover should be optimized to reduce evaporation losses. Irrigation management should ensure sufficient water for plant growth and efficient drainage to avoid problems of salinization.
Prevent and Minimize Soil Acidification
Soil acidification is the term used to express the quantity of hydrogen (H⁺) and aluminum (Al3⁺) cations in soils. When levels of hydrogen or aluminum ions become too high—and the soil becomes too acid—the soil’s negatively charged cation exchange capacity (CEC) becomes “clogged” with the positively charged hydrogen and aluminum ions, and the nutrients (i.e., cations) needed for plant growth are pushed out.
Sustainable Soil Management Practices
Soil acidity can be corrected easily by liming the soil, or adding basic materials to neutralize the acid present. Lime will neutralize this acidity by dissolving, whereupon it releases a base cation (Ca2⁺) into the soil solution that reacts with the acidic components, hydrogen and aluminum ions. The most commonly used liming material is agricultural limestone, the most economical and relatively easy to manage source.
Prevent and Minimize Soil Compaction
Soil compaction occurs when soil is exposed to excessive foot and equipment traffic while the soil is wet and plastic. A major effect of soil compaction is the alteration of the soil’s physical (bulk density, soil strength, and porosity) and the hydraulic (infiltration rate and movement of water within the soil profile) properties.
Sustainable Soil Management Practices
The best way to minimize compaction is to avoid field activities that have the potential to damage the soil. Whenever possible, do not conduct field operations on wet soils. If possible, use controlled traffic lanes. Larger wheels and tires allow better flotation, whereas lower tire pressures reduce the load on the soil. Increase the tire’s “footprint” with larger wheel diameters. Apply manure in fall on drier soils.
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