Soil organisms both serve as a source of nutrients for plant growth and drive the transformations of nutrients that make them available to plants. The collective carbon content of all soil bacterial cells is comparable to that of all plants on earth, and their total nitrogen and phosphorous contents are far greater than that of all vegetation, making these microorganisms the primary source of indispensable nutrients for life. Plants fix carbon from the atmosphere, but they require macro and micronutrients that are absorbed from the soil to create biomass and transfer nutrients and energy. Soil microbes and microfauna interact with abiotic factors – temperature, pH, moisture content- and drive these transformation processes. Soil micro, meso and macrofauna play a key role in the physical breakdown of plant residues, allowing the soil microorganisms to liberate the nutrients and energy bound up in the plant material. The role of soil organisms in agriculture has many beneficial effects beyond plant nutrition. For example, soil microbiota such as arbuscular mycorrhizal fungi and nitrogen fixing bacteria can minimise cost and dependence on synthetic nitrogen fertilizers in agriculture, and enhance soil fertility and environmental sustainability, including reducing greenhouse gas emissions from the energy-intensive manufacture of nitrogen fertilizer.
The role of soil biodiversity in addressing global climate change cannot be understated: the soil community’s activities can contribute either to the emission of greenhouse gases or to absorbing carbon into soils from the atmosphere. As part of the natural functions and ecosystem services provided by soils, a healthy soil stores more carbon than that stored in the atmosphere and vegetation combined. Carbon is either fixed or released from soils, depending the activity of the soil organisms and driven by soil conditions. Carbon is fixed into soils through the transformation of plant and animal detritus, and also some bacteria and archaea can fix carbon by using atmospheric CO2 as their energy source. Beyond their direct role in the carbon cycle, soil organisms are also critical for efforts to reduce overall greenhouse gas (GHG) emissions from agriculture. Globally, agricultural ecosystems contribute 10 to 12 percent of all direct anthropogenic GHG emissions each year, with an estimated 38 percent resulting from soil nitrous oxide emissions and 11 percent from methane in rice cultivation. Soil microorganisms are involved in every step of nitrogen and carbon transformations that yield these greenhouse gases, and managing the soil environment to minimise emissions is a key objective in sustainable soil management.
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Sources:
learning.edx.org
http://www.fao.org/