Healthy soil is vital for agriculture, for forestry, and for the functioning of Earth’s natural systems. As a renewable resource, once depleted of it’s productivity, it may renew itself over a very long and slow time. We’ll reduce it’s ability to support life if we have careless or uninformed practices.
Soil characteristics vary from place to place, they’re defined basically by temperature and amount of rain. Soil in the Amazonian rainforest, in northern Brazil is less productive than the soil of temperate grassland in Kansas. This difference is due to the amount of rain that falls in the Amazon, because the water leaches minerals and nutrients from topsoil; also the warm temperatures speed the decomposition of leaf litter and the uptake of nutrients by plants, in a way that humus remain small in the thin topsoil layer.
Kansas prairie, in the other hand, has a lower rainfall, which means that the leaching is reduced and the nutrients remain within reach of plants’ roots. Plants return nutrients to the topsoil when they die, maintaining its fertility. The thick and rich topsoil of temperate grasslands can be farmed repeatedly with minimal loss of fertility if farming techniques like no-till and reduced tillage are used.
Therefore, most of the world’s soils are not ideal for agriculture, but that does not stop our world’s population to grow 80 milion people a year, which means that we are pressing lands into cultivation that are unsuitable for farming, which causes considerable damage to soil. Thw world loses anually 5-7 milion ha (12-17 milion ac), about the size of West Virginia.
Some consequences of careless use of the soil are:
- Erosion – removal of material from one place and its transport toward another by the action of wind or water. The arrival of eroded material at a new location is called deposition. Erosion and deposition are natural processes that help to create soil. Productive soils are produced by deposit of eroded sediment in river valleys and deltas by flowing water;
Even though erosion is a natural process, it becomes a problem for ecosystems and agriculture because it occurs more quickly than soil is formed and tends to remove the topsoil, which is the most valuable soil layer for living things. People have made fertile lands more vulnerable to erosion by overcultivating fields through poor planning or excessive tilling; overgrazing rangelands with more livestock than the land can support; clearing forests on steep slopes or with large clear-cuts.
Soil is protected from wind and water by grasslands, forests, and other plant communities. Vegetation breaks the wind and slows water flow. Plant roots hold soil in place and take up water. The removal of these plants accelerates erosion.
- Overgrazilng – when sheep, goats, cattle, or other livestock graze on the open range, they feed on grasses. If the livestock population do not exceed a range’s carrying capacity and it does not consume grasses faster than they can be replaced, grazing may be sustainable. However, when too many animals eat too much of the plant cover, the plant regrowth is impeded and the replacement of biomass is prevented.
Overgrazing worsen damage to soils, natural communities, and the land’s productivity for grazing. All this happens because when livestock remove too much plant cover, soil is exposed and made vulnerable to erosion. Like I’ve said before, erosion makes it difficult for vegetation to regrow, in a way that the cycle of lack of cover provoking more erosion is perpetuated.
Another consequence is non-native weedy plants invasion. Plants that are less palatable to livestock may invade denuded soils and outcompete native vegetation in the new, modified environment. Overgrazing also compact soils and alter its structure. Compacted soil is hard for water to infiltrate, to be aerated, and for plants’ roots to expand or to conduct cellular respiration.
Overgrazing is a greater cause of desertification. Humans keep a total of 3,4 billion cattle, sheep, and goats, and rangeland declaration is estimated to cost $23,3 billion per year.
- Clearing forests – is the cut of all trees in ane area. Clear-cutting is cost-efficient in the short term, however, has severe impacts on forest ecosystems. It may mimic natural disturbance events like fires, tornadoes or windstorms, and destroy or displace ecological communities, provoke soil erosion, and sunlight penetration to ground level might change microclimatic conditions, in a way that new types of plants replace those of the native forests;
- Desertification – is the loss of more than 10% of productivity due to erosion, soil compaction, forest removal, overgrazing, drought, salinization, climate change, depletion of water sources, and other factores. Severe desertification can expand desert areas and create new ones in once-fertile regions. This has occured in areas of the Middle East, that have been farmed and grazed for long periods of time.
Desertification affects one-third of the planet’s land area and costs tens of billions of dollars a year for people in over 100 countries. A 2007 United Nations report estimated that desertification, worsened by climate change, could displace 50 milion people in 10 years. China loses $6.5 bilion annually. Desertification causes gigantic dust storms called dust bowl.
- Dust bowl – erosion of millions of tons of topsoil by strong winds. It’s caused by the removal of native grasses and the break down of soil structures. They might travel up to 2,000 km (1,250 mi). In the 19th and early 20th centuries, homesteading settlers spread through Oklahoma, Texas, Kansas, New Mexico, and Colorado. Farmers grew wheat and ranchers grazed thousands of cattle, both on unsuitable land. In 1930, a drought exarcerbated the ongoing impacts and the dust storms begun. Some areas lost 10 cm (4 in) of topsoil in a few years.
These problems made the US government, the state and local government increase support for research into soil conservation measures. The Soil Conservation Service (SCS) was created and started to work with farmers to develop conservation plans for individual farms. The SCS teams include soil scientists, forestry experts, engineers, economists, and biologists. Nowadays, the SCS is called Natural Resources Conservation Service, and it serves as a model for similar efforts elsewhere;
- Salinization – buildup of salt in surface soil layers. It is more common in arid areas where precipitation is minimal and evaportion rates are high. This happens because of irrigation. Irrigation have allowed dry and unproductive regions into fertile farmland. However, overirrigation saturates soil with water in a way that waterlogging, when the water table rises to the point that water bathes plant roots, might occur. This is bad because it deprives the plant roots of access to gases and suffocates them.
Salinization occurs because if the area is to arid, the evaporation of water from the topsoil may pull water rich in dissolved salts upward through the soil from lower horizons. When the water evaporates at the surface, its salts precipitate, turning the soil surface white.
Salinization inhibits production of one-fifth of all irrigated cropland globally, and cost more than $11 billion a year. The best way to prevent it is avoid planting crops that require a great deal of water in areas that are prone to the problem. A second way is to irrigate with water low in salt content, since the irrigation water often contains some dissolved salt. And a third way is to irrigate efficiently, supplying no more water than the crop requires. These mesures minimize the amount of water that evaporates and hence the amount of salt that accumulates in the topsoil;
- Fertilizers – like overirrigation might result on salinization, overapplying fertilizers can cause chemical damage to soil with severe pollution problems. Plants require nitrogen, phosphorous and potassium to grow, altogether with other nutrients. These nutrients are removed from soil as the plants grow, and leaching likewise removes nutrients. If agricultural soils come to contain too few nutrients, crop yields decline, that’s when fertilizers are used. There are two main types of fertilizers, inorganic and organic. Organic fertilizers can provide some benefits that inorganic cannot. The proper use of these compounds improves soil structure, helps to retain nutrient and increase the water retaining capacity; erosion is prevented.
In order to prevent these consequences, there are agricultural techniques that can be used.