Components of Soil

Soil Components:

Soils consist of four major components:
(1) mineral (or inorganic), (2) organic, (3) water, and (4) air. The relative proportions of these four soil components vary with soil type and climatic conditions. Review the approximate proportions (by volume) of the four soil components in a mineral soil under optimum conditions for plant growth. Image Source: Leslie Dampier

1. Mineral Components

Mineral particles are inorganic materials derived from rocks and minerals. They are extremely variable in size and composition. 

Primary minerals are formed at high temperature and pressure, under reducing conditions without free oxygen. These minerals are mainly present in soils as sand and silt particles. They are not crystallized and deposed from molten lava.

Secondary minerals are formed at low temperature and pressure through oxidation. They are the weathering product of primary minerals, either through alteration of their structure or through re-precipitation. Secondary minerals are usually present in soil as clay particles.

2. Organic Components

Soil organic matter (SOM) can be of plant, animal, or microbial origin and may be relatively fresh or highly decomposed and transformed.

Organic matter is an important soil component because it:

a)   holds soil particles together and stabilizes the soil, thus reducing the risk of erosion;  

b)   aids crop growth by improving the soil's ability to store and transmit air and water;

c)   stores and supplies many nutrients needed for the growth of plants and soil organisms;

d)   prevents or minimizes soil compaction;

e)   retains carbon from the atmosphere;

f)    reduces the negative environmental effects of pesticides, heavy metals, and many other pollutants.

SOM includes primary components that are inherited from plant and animal residues entering the soil. Primary components are sometimes referred to as non-humic substances. These compounds are relatively easily decomposed by microorganisms and they persist in soil for a brief  time (e.g. several months or years). They make about 20-30% of total SOM. These include

·         carbohydrates and several derivatives (monosaccharides, and polisaccharides such as cellulose, hemiscellulose)

·         amino acids and several derivatives (proteins)

·         lignin (condensed polyphenil-propane structures of extremely large molecular weight, very resistant to microbial decomposition)

·         lipids (a class of organic compounds which is a convenient analytical group rather than a specific type of compound. They include fats, oils, waxes, phospholipids, and resins)

·         a variety of other compounds.  

3. Soil Water

Water is the major transport agent for fluxes within and between terrestrial ecosystems. It is a prerequisite for all active life, and participates in geochemical cycles by weathering geological substrates, by leaching materials to groundwater and by moving ions and particles through the soil profile.

Soil water is part of the global hydrological cycle, which shows how water that falls as precipitation returns to the atmosphere through transpiration and evaporation. On a local scale, how well the soil stores water is of great importance to crop production and the vitality of the land.

Water and air constantly compete for pore space in soils. Most of the time soil pores are not full of water, but occasionally (after heavy storms or in swamps and bogs) some soils may be saturated with water and little or no air is present in pores. 

4. Soil Air

Soil pores, the voids between minerals, organic matter, and living organisms, are filled with air or water. There is a dynamic equilibrium between water and air content within a soil. When water enters the soil, it displaces air from some of the pores.

4.1. Composition of soil air

The composition of soil air is different from that of the atmosphere because it cannot readily mix with air above the soil. The metabolic activity of plant roots, microbes and soil fauna all affect the composition of soil air. For example, the concentration of carbon dioxide (CO₂) in soil (between 0.3 and 3%) is often several hundred times higher than the 0.03% found in the atmosphere. In extreme cases oxygen can be as low as 5-10%, compared to 20% in the atmosphere. Soil air has a higher moisture content than the atmosphere, with relative humidity approaching 100% under optimum conditions. (humidity is not as variable in soil as it is in the atmosphere).  The amount and composition of air in soil are dynamic and to a large degree are determined by water content and activity of soil organisms.  

Soil conservation

The protection of fertile topsoil erosion by wind and water and the replacement of nutrients in the soil, as by means of cover crops, terracing, contour farming, crop rotation, etc.

Soil conservation is using methods to save our soil from erosion or becoming contaminated with chemicals. This ensures we will have soil for planting and helps keep our animal and insect life healthy.

The prevention or reduction of soil erosion and soil depletion by protective measures against water and wind damage.

Management of soil so as to obtain the largest crop yields feasible and improve the soil at the same time.

10 Ways to Conserve Soil

1. Plant Trees: We all know that roots of trees firmly hold on to the soil. As trees grow tall, they also keep rooting deeper into the soil. As the roots of trees spread deep into the layers of soil, they hold it tightly, thus preventing soil erosion. Soil under a vegetative cover is saved from erosion due to wind as this cover acts as a wind barrier.
2. Build Terraces: Terracing is a very good method of soil conservation. A terrace is a leveled section of a hilly cultivated area. Owing to its unique structure, it prevents rapid surface runoff of water. Terracing gives the landmass a stepped appearance, thus slowing the washing down of soil. Dry stonewalling is a method used to create terraces in which stone structures are made without using mortar for binding.
3. No-till Farming: The process of preparing soil for plowing is known as tilling. No-till farming is a way of growing crops without disturbing it through tillage. The process of tilling is beneficial in mixing fertilizers in the soil, making rows and preparing the surface for sowing. But the tilling activity can lead to compaction of soil, loss of organic matter in the soil and the death of soil organisms. No-till farming is a way to prevent the soil from this harm.
4. Contour Plowing: This practice of farming on slopes takes into account the slope gradient and the elevation of soil along the slope. It is the method of plowing across the contour lines of a slope. This method helps in slowing the water runoff and prevents soil from being washed away along the slope. Contour plowing also helps in percolation of water in the soil.
5. Crop Rotation: Some pathogens tend to build up in soil if the same crops are cultivated again and again. Continuous cultivation of the same crop also leads to imbalance in the fertility demands of the soil. To save the soil from these adverse effects, crop rotation is practiced. It is a method of growing a series of dissimilar crops in an area. Crop rotation also helps in the improvement of soil structure and fertility.
6. Maintain Soil p^H: The contamination of soil by addition of acidic or basic pollutants and due to acid rains has an adverse effect on the soil p^H. Soil pH is an indicator of the level of nutrients in soil. The uptake of nutrients by plants also depends on the pH of soil. Maintaining the correct value of soil pH, is thus essential for soil conservation.
7. Water the Soil: We water plants, we water the crops, but do we water the soil? We seldom do. Watering soil is a good measure of soil conservation. Watering the soil along with plants growing in it is a way to prevent soil erosion caused by wind.
8. Salinity Management: The salinity of soil increases due to excessive accumulation of salts in the soil. This has a negative effect on the metabolism of crops. The salinity of soil is detrimental to the vegetative life in it. The death of vegetation leads to soil erosion. Hence, salinity management is an indirect way of conserving soil.
9. Promote Helpful Soil Organisms: Nitrogen-fixing and denitrifying bacteria are important constituents of the nitrogen cycle. They live in soil. Bacteria and fungi help keep the soil healthy. Organisms like earthworms help decompose organic material in the soil. They aid soil aeration and help it maintain porosity. Rodents too, help soil the same way. This increases the absorbing capacity of soil. Earthworms, through aeration of soil, enhance the availability of macronutrients. These helpful organisms boost soil fertility and help in soil conservation.
10. Grow Indigenous Crops: Planting native crops is beneficial for soil conservation. If non-native plants are grown, fields should be bordered by indigenous crops to prevent soil erosion, thus achieving soil conservation.

10 Ways to Conserve Soil

The task in finding ways to stop soil erosion becomes one of finding ways to conserve soil. There are several methods of soil conservation that can be achieved through agricultural practices and measures you take at home.

Agriculture Soil Conservation

1. Practice no till farming. With no till farming, crops are allowed to remain rather than being plowed under at the end of the season. This practice keeps soils anchored in place rather than having bare ground exposed to wind and water.

2. Use terrace farming. This type of farming uses the topography of the land to slow water flow through a series of terraces. This manipulation of the water flow prevents it from gathering speed and washing soil away from farmlands.

3. Practice contour farming. Contour farming replicates the effects of terrace farming, but on a smaller scale. Rather than planting crops in straight vertical rows, crops are planted following the contour of the landscape. Crops planted up and down hillsides create pathways for water to flow. Crops planted parallel to the land slow the flow of water that prevents soil erosion.

Home Methods

4. Reduce impervious surfaces. Impervious surfaces like driveways and patios allow precipitation to flow freely over them. Water flow gains momentum when moving over such surfaces and can then erode stream banks and lakeshores. A good compromise is to use paving stones rather than a concrete slab for your patio to allow the water to percolate down into the soil.

5. Plant a rain garden. A rain garden is a shallow depression in your yard, which will collect precipitation washing over impervious surfaces. It prevents soil erosion and gives you an opportunity to grow wetland plants.

6. Use a rain barrel. You can place a rain barrel underneath a downspout to collect the water that runs off of your roof. Your roof, after all, is another impervious surface. You can use the water you collect for your lawn and garden. In this way, you can conserve water and soil.

Resource Planning

7. Plant windbreaks. Windbreaks prevent soil erosion by slowing the force of the wind over open ground. You can plant trees or shrubs in your windbreak. In addition to preventing erosion, these plantings will prevent snow from drifting onto your driveway or into the road. They can also protect your home from wind damage.

8. Restore wetlands. Wetlands are one of the most effective ways to prevent soil erosion. Wetlands act as natural sponges, absorbing rainwater and preventing it from carrying the soil away. They also provide a habitat for birds and other wildlife and help prevent water pollution.

9. Plant buffer strips along stream banks. Buffer strips help hold stream banks intact during times of flooding. They also prevent runoff from entering waterways. Buffer strips can include a mixture of grasses, shrubs, and trees.

10. Re-establish forest cover. The re-establishment of forest cover provides an extensive, tree-root network that offers a long-term solution to soil erosion. It can function both as a windbreak and a means to anchor soils in place.