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Soil Biology and Land Management Soil Quality – Soil Biology Technical Note No. 4 Soil Biology and Land Management Table of contents The goal of soil biology management.......................................... 2 Why should land managers understand soil biology?.................. 2 The underground community....................................................... 4 What controls soil biology? ......................................................... 5 General management strategies ................................................... 7 Considerations for specific land uses......................................... 10 Cropland.............................................................................. 10 Soil Quality – Soil Biology Forestland............................................................................ 13 Technical Note No. 4 Rangeland............................................................................ 15 Assessment and monitoring....................................................... 17 January 2004 Summary.................................................................................... 19 NRCS file code: 190-22-15 References and further resources............................................... 19 Other titles in this series: #1 Soil Biology Primer Introduction #2 Introduction to Microbiotic Crusts The purpose of this technical note is to provide information about the #3 Soil Biology Slide Set effects of land management decisions on the belowground component of the food web. It points out changes in soil biological function that land managers should look for when changing management practices. This information is not a set of prescriptive guidelines, but is designed to increase awareness and prompt field trials. NRCS Soil Quality http://soils.usda.gov/sqi The goal of soil biology management The goal of managing the soil biological knowledge to support the development of community is to improve biological functions, detailed management strategies. A particular including forming and stabilizing soil structure, practice may have the desired result in one cycling nutrients, controlling pests and disease, situation but have little effect in another because and degrading or detoxifying contaminants. biological communities respond to the interaction of multiple factors including food Research shows that management practices and sources, physical habitat, moisture, and impacts disturbances impact soil biological functions of historical land use. Therefore, before a new because they can 1) enhance or degrade the product or practice is applied to a large parcel of microbial habitat, 2) add to or remove food land, it should be tested on a limited area and resources, or 3) directly add or kill soil results should be monitored in comparison to an organisms. Although management practices are untreated plot. known to impact soil biology, there is limited Why should land managers understand soil biology? associations for nutrient exchange. Even applied Energy and the food web fertilizers may pass through soil organisms Through agriculture, the sun’s energy is before being utilized by crops. converted into food, feed, and fiber. However, Soil stability and erosion most of the solar energy captured by plants is not directly harvested when crops are gathered; Soil organisms play an important role in forming instead, it feeds the belowground food web. and stabilizing soil structure. In a healthy soil Feeding the “underground livestock” is essential ecosystem, fungal filaments and exudates from to productive forests, rangeland, and farmland. microbes and earthworms help bind soil Figure 1 shows how energy is recycled particles together into stable aggregates that repeatedly through belowground soil organisms. improve water infiltration, and protect soil from The soil food web is part of energy, nutrient, and erosion, crusting, and compaction. Macropores water cycles. The energy cycle begins when the formed by earthworms and other burrowing sun’s energy is captured by the plant-based creatures facilitate the movement of water into (aboveground) food web. Nutrient availability is and through soil. Good soil structure enhances governed by the detritus-based (belowground) root development, which further improves the food web. The water cycle is also influenced by soil. the interaction of plants, soils, and soil Water quality and quantity organisms. By improving or stabilizing soil structure, soil organism dynamics help reduce runoff and Functions of the soil food web improve the infiltration and filtering capacity of Nutrient cycling soil. In a healthy soil ecosystem, soil organisms In a healthy soil ecosystem, soil biota regulates reduce the impacts of pollution by buffering, the flow and storage of nutrients in many ways. detoxifying, and decomposing potential For example, they decompose plant and animal pollutants. Bacteria and other microbes are residue, fix atmospheric nitrogen, transform increasingly used for remediation of nitrogen and other nutrients among various contaminated water and soil. organic and inorganic forms, release plant available forms of nutrients, mobilize phosphorus, and form mycorrhizal (fungus-root) Page 2 of 20 Soil Biology and Land Management Plant health Complexity and function A relatively small number of soil organisms Many soil biological functions emerge from the cause plant disease. A healthy soil ecosystem complex interactions of soil organisms and are has a diverse soil food web that keeps pest not predictable by adding up the activity of organisms in check through competition and individual soil organisms. How well the soil predation. Some soil organisms release community performs each of these functions compounds that enhance plant growth or reduce depends in part on the complexity of the disease susceptibility. Plants may exude specific biological community. Complexity is a factor of both the number of species and the different substances that attract beneficial organisms or kinds or functions of species. Greater repel harmful ones, especially when they are complexity may imply more diversity of under stress, such as grazing. functions and more redundancy of functions, and For more information about what lives in the therefore more stability. For example, when soil and how they function, see the “Soil multiple populations of microbes convert ammonium to nitrate, even if one population Biology Primer” (Tugel and Lewandowski, dies out, the function (nitrification) will continue 1999), and the soil biology glossary on the to be performed. Functional redundancy is the NRCS Soil Quality web site. underlying idea behind the "insurance hypothesis," which states that biodiversity insures ecosystems against declines in function. Figure 1. The plant-based (aboveground) and detritus-based (belowground) food webs. Arrows represent energy flow (commonly measured in carbon units). Of the aboveground organic matter entering the pool of soil organic matter, 60%-80% of the carbon is eventually lost as CO2. (Based on Chapin et al., 2002, Fig. 11.12.) Herbivores CO2 Plants Carnivores Plant-based food web Microbivores Decomposers (protozoa, (bacteria, fungi) nematodes) Soil organic matter Detritus-based food web Predators (mites, some beetles, centipedes, etc.) Stabilized organic matter (Heterogeneous pool of slowly decomposable, physically protected, compounds) Soil Biology and Land Management Page 3 of 20 The underground community Soil organisms can be grouped by size as shown termites, scarab beetles, and earthworms, are in figure 2, or by functions as described below “ecosystem engineers” that physically change (Wardle, 2002; Coleman & Crossley, 1996). the soil habitat for other organisms by chewing and burrowing through the soil. Microbes Decomposers (decomposers) living within their guts break Bacteria, actinomycetes (filamentous bacteria), down the plant residue, dung, and fecal pellets and saprophytic fungi degrade plant and animal consumed along with the soil. residue, organic compounds, and some pesticides. Bacteria generally, but not Mutualists exclusively, degrade the more readily Mycorrhizal fungi, nitrogen-fixing bacteria, and decomposed (lower C:N ratio) materials, some free-living microbes have co-evolved compared to fungi, which can use more together with plants to form mutually beneficial chemically complex materials. (See boxes on associations with plants. Mycorrhizae are pages 7 and 8.) Bacteria often degrade what they associations between fungi and plant roots in can of a particular material; then fungi which the fungus supplies nutrients and perhaps decompose the remainder. water to the plant, and the plant supplies food to the fungi. These fungi can exist inside Grazers and predators (endomycorrhizae) or outside (ectomycorrhizae) Protozoa, mites, nematodes, and other organisms the plant root cell wall. The common arbuscular “graze” on bacteria or fungi; prey on other mycorrhizae (AM or VAM fungi) are species of protozoa and nematodes; or both endomycorrhizae. graze and prey. Grazers and predators release plant-available nutrients as they consume Pathogens, parasites, and root feeders microbes. Often organisms specialize in one Organisms that cause disease make up a tiny type of prey, such as either bacteria or fungi. fraction of the organisms in the soil, but have Certain collembolans (springtails) even been most studied by researchers. Disease- specialize on specific species of fungi. Other causing organisms include certain species of organisms are generalists and will feed on any bacteria, fungi, protozoa,
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