NASA Kids is an excellent site for "kids" of all ages and provides an abundance of information, images, and interesting things to do on astronomy and the space sciences. In this lesson, students learn about sources of high-energy radiation and calculate student exposure to ionizing radiation over the past year. Soil is a thin layer of non-renewable natural resource separating our atmosphere from Earth's crust. It is composed of organic matter, inorganic mineral particles, air, water, and microscopic living organisms.
Man-made materials can also break down into soil, becoming part of it. I know of no soil scientist who would agree that soil is renewable simply because nutrients can be replaced.
I doubt few would even consider soil renewable within a lifetime, though under ideal conditions, much recovery can occur. So, the question becomes: How long does it take for a soil to recover from erosion, long-term tillage, compaction, acidification, salinization, etc.? Plants grow and die, organisms decompose the plant roots and residues, and in this way organic matter in the soil increases. In dry regions, there is little water to allow plant growth, so everything happens more slowly.
Another factor is relief. Soils on stable landscapes—uplands or lowlands, gently sloping to level—will be more likely to recover than soils on slopes.
Water running downslope erodes soil and deposits it at the bottom of the hill, or carries the sediments into streams or rivers and degrades water quality.
Even in natural, undisturbed landscapes, the least developed soils occur on slopes. This is the stuff in which a soil forms. Coarser materials sands tend to have more rapid soil development than finer materials clays and silts. If the soil is forming over bedrock, the process is even slower. If erosion removed the soil to expose the bedrock, that area may not be renewable for millennia.
When the rate of soil formation exceeds the rate of degradation, soils are renewable. In areas where degradation exceeds formation, soils are non-renewable at least until the next climate shift.
Some types of degradation can be managed to maintain productivity. Other kinds of damages may be irreversible. For example, acidification is common in humid regions or old soils, but is often managed with the addition of ground limestone products to raise the pH for crop production.
Salinization is the process of salts accumulating in a soil. Once soil becomes salinized, the only thing that will leach the salts out of the soil profile to make it productive again is good quality water. When that is not available from an aquifer or a river often because dams and reservoirs control floods so that water no longer covers the floodplain , the only other possible source is precipitation.
This mixture gives the overall texture of the soil, namely whether the soil is mainly sandy, loamy or clayey. Importantly, soil also contains organic matter , mainly in the top 20 cm. Organic matter comes from rotted and decomposed vegetation, broken down by soil organisms. Soil also contains varying amounts of water depending on the climate and the water holding capacity of the soil. The remaining important ingredient is air.
The amounts of each of these components varies in time and across the landscape. This is a magical mixture of ingredients that allows the soil to perform many vital needs of living beings. Home Introduction What is soil? Why does soil matter? Soil under the microscope Recognising types of soil Weathering and soil formation Properties of soil Soil character pH and soil acidity How do soils form? Why do soils differ? What is soil? Soil under the microscope. Recognising types of soil.
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