Land degradation is an issue of increasing concern to most countries. It is a concept in which the value of the environment is affected by one or more combination of human induced processes acting upon the land. It also means the deterioration in the quantity of land or soil that affects phenomena such as floods and bushfires. The land degradation threatens not only the viability of agriculture, but also water quality, human health, biodiversity and the fundamental ecological processes on which all life depend.

The loss of arable land has been caused by a number of factors, many or most of which are tied to human development and agriculture used. The major causes are land clearance such as clear cutting and deforestation, agriculture activities, irrigation salinity and over drafting, livestock including overgrazing, pollution and industrialization.

Overgrazing is a common problem in many parts of Australia. It is caused by animals, generally sheep, cattle, or other feral animals, all concentrated in the one area, all feeding on the grass and shrubs. Grass and shrubs hold the soil firmly together. The removal of grass and shrubs leaves the soil bare and susceptible to wind and water erosion. The soil can be broken up or compacted by hooves, this makes the problem worse.

Irrigation salinity is when the irrigation water, used to provide water for crops and pasture, seeps down to the water table, with all the dissolved salts, rises and kills the crops and grass, as they are not used to the salty soils.

Deforestation is the complete removal of a forest ecosystem and conversion of the land to another type of landscape. It differs from clear-cutting, which entails complete removal of all standing trees but leaves the soil in a condition to regrow a new forest if seeds are available.

Over drafting is the process of extracting groundwater beyond the safe yield or equilibrium yield of the aquifer. Since every groundwater basin recharges at a different rate depending upon precipitation, vegetative cover and soil conservation practices, the quantity of groundwater that can be safely pumped varies greatly among regions of the world and even within provinces. Some aquifers require a very long time to recharge and thus the process of over drafting can have consequences of effectively drying up certain sub-surface water supplies.

Land Degradation Processes

The main outcome of land degradation is a substantial reduction in the productivity of land. The land degradation processes include soil erosion, nutrient depletion, salinization, desertification and soil acidification or alkalinisation.

Soil erosion is a natural process that removes soil from the land. The critical aspect of soil erosion for our purpose here is that the rate of the process is highly dependent on human actions. Natural rates of soil erosion are lower for soil with a good cover of vegetation than for bare soil. In fact, any human actions that uncover soil (farming, logging, building, overgrazing, fires, etc.) greatly enhance soil erosion rates.

Soil salinization is the concentration of salts in the surface or near surface of soils. It involves the processes of salt accumulation in the upper rooting zone so that many plants are inhibited or prohibited from normal growth. Human induced salinization is a major problem in drylands and is often associated with large-scale irrigation.

Dryland Salinity

When drylands are irrigated, the water evaporates quickly, leaving behind previously dissolved salts. These salts can collect, since there is little rain to flash the system. The salt in the soil inhibits the uptake of water by plant roots and the soil can no longer sustain a vegetative cover.

Irrigation Salinity

Irrigation salinity is when the irrigation water, used to provide water for crops and pasture, seeps down to the water table, with all the dissolved salts, rises and kills the crops and grass, as they are not used to the salty soils.

Nutrients loss is an important problem in regions of low-input agriculture, such as Africa. In such regions, when crops are harvested, essential nutrients are taken away in the crop and not replaced.

Desertification occurs whenever a non-desert area starts to exhibit the characteristics of a true desert. The term was coined by the United Nations in 1977. The main cause of desertification is not drought, but mismanagement of land, including overgrazing and felling of trees and brushwood for fuels.

Soil acidification is when certain chemicals are used on the soil, for various reasons including pesticides, removal of salt from the surface and the soil, acid rain, the growth of certain crops, certain animal wastes and etc, these chemicals are often absorbed into the soil and become part of the soil-structure. With these chemicals now part of the soil, the soil may become acidic and therefore crops and pastures will not grow. Soil acidification can lead to a productivity decline up to and equal to 50%.

Soil akalinisation is clay soils with high pH (> 9), a poor soil structure and a low infiltration capacity. Alkali soils owe their unfavorable physico-chemical properties mainly to the dominating presence of sodium carbonate which causes the soil to swell. Sometimes these soils are also referred to as (alkaline) sodic soils.

Effect of degradation

Several land degradation affected a significant portion of the arable lands, decreasing the wealth and economic development of nations. Land degradation cancels out advanced by improved crop yields and reduced population growth. As the land resource, base becomes less productive, food security is comprised and competition for dwindling resources increases. Thus, a downward eco-social spiral is created when lands are nutrient depleted by unsustainable land management practices resulting in lost soil stability leading to permanent change. Land degradation not only affects soil productivity but also have more significant impacts on receiving water resources. Since soil along with nutrients and contaminants associated with soil, are delivered in large quantities to environments. Land degradation therefore has potentially impacts on lakes and reservoirs that are designed to alleviate flooding provide irrigation and generate Hydro-Power.

In summary, land degradation includes soil erosion, salinization, soil acidification or akalinisation and desertification. The rate of degradation has increased dramatically with growth in human populations and technology. Severe land damage accompanies large-scale of agriculture. The continued loss of arable land will jeopardize our ability to feed the world population. Land degradation is a worldwide problem which includes both of the developed and developing countries.