With reference to named areas explain how farming in both LEDC's and MEDC's can have a negative impact on soils What techniques can be used to improve soil quality?

Organic farming has recently become the 'fashionable' thing to do but it has had a good impact on soil quality. It is a sustainable method of farming, using no chemicals and maintaining agricultural diversity. Organic farmers use crop rotation to help the soil structure and use biological rather than chemical pest control. The soil nutrients are replenished by legumes and organic manure and a minimum use of heavy machinery means the soil is not compacted and allows free drainage.

In the past, agriculture had been very labour intensive but mechanisation has changed this and the introduction of heavy machinery replaces some of the jobs originally done by farm workers. The machines destroy the soil structure by compacting the soil particles, which makes it harder for air and moisture to penetrate the soil. In some places where this occurs the soil is no longer able to support plant life as when it rains the ground becomes a quagmire and when it is dry the surface is cracked and hard.

In places like East Anglia, farmers specialize in growing one crop. This monoculture means that all the plants extract only the nutrients that they all need, leaving a nutrient deficient soil. To rectify this farmers add more fertilizers to the soil that only adds to the negative impact farming has on soils. Generally in these areas the farmers remove trees and hedgerows to maximize the land they can farm and also so they can have easy access for their large machinery. These hedgerows and trees help hold the soil together and their removal leads to soil erosion.

In the LEDW, irrigation has been important in increasing yields. Along the Senegal River two new dams were completed and filled by 1991, with one of its intentions being to irrigate the land and increase productivity. It has increased some yields but it has resulted in a loss of biodiversity and a loss of pastureland, which is important to soil structure.

Soil erosion is a natural process and cannot be prevented but humans are adding to the amount of soil eroded. In China, India, Russia and the USA the losses total an estimated 13.6 billion tonnes per year. Reasons for this include deforestation and leaving the land fallow between crops. However, ploughing the soil in certain ways also increases soil erosion. By ploughing up and down the hillside creating gullies it channels the water and encourages it to erode downwards. It also loosens the surface particles and harms the soil structure. These factors can eventually lead to infertile soil. In the USA one of the ways they are attempting to reduce soil erosion is the Great Lakes Basin Programme where every $1000 spent saves 35kg of phosphorus, 13 kg of nitrogen and 174 tonnes of soil. It also helps to educate local people about techniques to reduce soil erosion. Other solutions are to reforest some of the land, conservation ploughing and restoring the wetlands. Around 31 500 tonnes of soil in this area are being saved each year.

Salinization is a big problem in areas of the world where conditions are arid or semi arid. These soils in these areas have high levels of salt and where evapotranspiration exceeds precipitation the water in the soil is drawn upwards taking the salt with it and depositing it in the surface layers of the soil. Humans however, can increase salinization. In southwest Australia around 14.6 million hectares of land have been cleared for grazing and cropping. This means that more precipitation can percolate into the ground, causing the salt to rise close to the surface. In these areas the water table is also higher. In southwest Australia it is estimated that 16% of land, including the best agricultural land will be affected by salinization. This in turn affects the water supply in the area as it will have an increased salt content and the water will not be fit for human consumption. Irrigation also adds to salinization as it raises the level of groundwater in the soil. As this water slowly evaporates it leaves a higher concentration of salts in the soil. The soil structure collapses and the bare ground is exposed to erosion from wind and water. To improve this kind of soil after salinization has happened can be an expensive process. Adding freshwater and drainage removes the salts in the soil and can only be done where there is a large freshwater supply and where the water table is low. To cope with the salty conditions, xerophytic and salt tolerant species of plants can be planted and by adding gypsum for example the salts can be converted into less harmful substances that can be leached from the soil.

Desertification is the process of land being turned into a desert and can be a result of human activity, particularly farming. One such area is the Sahel in North Africa, on the southern edge of the Sahara desert. It is thought to be mainly a result of rapid population growth, which has led to an increased pressure on the land. Some farmers have been forced to cultivate marginal areas that are more prone to erosion and others have repeatedly grown the same crop on the same piece of land thus overcultivating it and exhausting the soil. There has also been an increase in overgrazing as the drought in the region has caused nomadic tribes to stay in one area where there is water and grazed their cattle there, destroying the vegetation leaving bare soil open to erosion. The increase in population has also lead to an increase in demand for fuel that has led to greater deforestation. The exposed soil is baked dry and becomes cracked and loose so that it can be blown or washed away. Farmers have also practiced slash and burn which has made the land infertile. Around 250 000 hectares of land in the Niger alone are being lost to desertification. At the present time there are many projects that are trying to reduce desertification and improve soil quality. These are ideas such as using animal manure and crop stalks as fertilizer, terracing on steep slopes and providing windbreaks with fences or trees.

Farming can cause a lot of damage to the soil but if farmers take care and look to the future farming can be done sustainably and as organic farming shows, improve the soil.