Soils in which all three minerals contribute equally to their texture are called loam soils and thought to be best for agriculture. Soil quality can also be distinguished by a variety of soil characteristics. Color can indicate specific soil properties, especially as it relates to water and oxygen content. For example, dark soils typically indicate significant organic matter content; red and yellow soils indicate the presence of iron which is left behind as water leaches the more soluble minerals; and, saturated soils which are poorly aerated are often found to have a hue of grey, blue or green.
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Texture , often based on the mineral component of the soil, helps to measure soil productivity as it relates to drainage and fertility. At the extremes, the larger particle and very fine particle soils are less productive.
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The structure of the soil—its aggregation —is a measure of soil strength from sandy to clay to rocky soils. Again, it is the mid-level soils that provide the greatest stability necessary for functional use. Related to both texture and aggregation, porosity of the soil is extremely important for the transport of both water and oxygen. Chemical characteristics are also important for determining the quality of the soil. Soils that are particularly able to hold and exchange ions groups of atoms are more fertile.
The ion content of the soil makes it possible for important nutrients—calcium, potassium, and magnesium—to be changed into a form that is beneficial for plant growth.
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For example, while most plants prefer a pH closer to neutral 7 , others have a preference for either acidic or alkaline soils. In addition, if a soil is toward one extreme or the other, fertilizer to lower pH or lime to raise pH can be used.
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In addition to the minerals from the weathering of rocks, healthy soils contain millions of different bacteria, plants, and other organisms which are added to the soil as organic matter, called humus, when they die and decompose. As soils form, layers—called horizons—build up, each with its own distinct characteristics and composition reflecting different timelines and weathering processes. Soils are dynamic ecosystems composed of a combination of minerals, organic matter, and living organisms thought to be one of our most fundamental natural resources.
Vital, healthy soils are critical in cycling nutrients and necessary in sustaining plant growth. Without the oxygen and food supplied by plants and crops, life on Earth would not be possible, so the quality of soil ecosystems is a matter of considerable importance. Soil ecosystems can be damaged through the force of nature or by poor management practices. Significant amounts of topsoil are lost through erosion, a natural process caused by water and wind.
It can also be exacerbated by human activities, such as land clearing, poor farming methods, and the addition of pollutants. Modern agricultural practices often include the use of fertilizers to increase soil productivity; however, their use can cause nutrients to leach out of the soil, add heavy metals, or cause other environmental damage. There is now considerable research being done to improve both soil management and agricultural practices.
As population increases, there will be a greater demand for food resources and maintaining healthy soils will be critical to minimize erosion and maintain soil fertility and productivity. Sometimes it happens more suddenly. The destruction of millions of acres of carbon-rich Indonesian peatlands for palm oil plantations is helping to drive climate change today. Low carbon levels leave the ground nutrient-poor, requiring ever-greater amounts of fertilizer to support crops.
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They also make for thin soil that is vulnerable to erosion and less able to retain water, so yields suffer quickly in times of drought. To bring levels back up, a set of techniques known as carbon farming, or regenerative farming, encourage and complement the process by which plants draw carbon dioxide from the atmosphere, break it down and sequester carbon into soil. They include refraining from tilling, or turning, the soil; mixing crops together rather than growing large fields of just one type; planting trees and shrubs near or among crops; and leaving stalks and other cuttings on fields to decay.
Brown keeps his fields planted for as much of the year as possible to minimize nutrient loss. When he mixes clover and oats in the same field, the clover fixes nitrogen into the soil.
After the oats are harvested, livestock graze the clover and leave their manure behind. Such strategies have allowed him to stop using synthetic fertilizers and pesticides, reducing costs. And the rich soil not only yields higher volumes, but the crops are more nutritionally dense than those grown on depleted land, he says. The land will be better next year. There is some momentum behind a shift. Lal called the target unrealistic, but said achieving just a quarter of that sequestration would be meaningful.
In a generation, he said, agriculture could become carbon neutral, removing all the emissions it creates, for example through the energy used by farm equipment. That number is likely to increase, he said, as multinational institutions and wealthy nations start incorporating carbon sequestration incentives into existing aid to farmers in poor countries. Bockel added. Programs known as payment for environmental services, in which governments or others pay farmers for stewardship of land, are another potential avenue.
With that kind of support, the industry could be ready to do things differently, said Ceris Jones, a climate change adviser at the National Farmers Union in Britain.
Another obstacle is the lack of an agreed-upon system for measuring carbon sequestration in soil, which will be required as the basis for any payments, Mr. Toensmeier said. Technically, though, many elements of carbon farming are ready to be put into practice quickly, he said.