Environmental Education Articles

Disappearing Land! - Soil Degradation

By Wisdom Dlamini - Swaziland National Trust Commission

A large proportion of Swaziland, prominently the range lands, are affected by severe erosion and land degradation. About 50% of the total land area in Swaziland is used for communal grazing. This obviously is the reason for the widespread soil erosion throughout the country. Overgrazing and poor range management is the evident cause for this serious land degradation. The indiscriminate cutting down of trees is another cause for this problem in Swaziland.

This can be seen all around the country where trees are cut down for various reasons like firewood, building and for 'fencing' off livestock from crop fields in the rural areas. One analysis of global soil erosion estimates that, depending on the region, topsoil is currently being lost 16 to 300 times faster than it can be replaced. Soil making processes are notoriously slow, requiring from 200 to 1000 years to form 2.5 centimetres of topsoil under normal agricultural conditions.

According to the World Resources Institute and the United Nations Environment Programme (1998), overgrazing is the main human-induced cause of soil degradation, more especially in Africa (679 million hectares). This is followed by vegetation removal (579 million hectares), agricultural activities (522 million hectares) and, overexploitation (133 million hectares). One study in 1994 estimated that soil degradation between 1945 and 1990 lowered world food production by some 17%. These losses are predicted to worsen as soil degradation continues. Though the total global harvest may not reflect such losses immediately, they may be noticeable in some areas where degradation is severe and progressing quickly. Soil erosion, salinisation and nutrient depletion are serious problems in large areas of Africa.

The Causes of Erosion

The process of raising the world's food has not always been kind to the environment. Many of the adverse environmental impacts resulting from agriculture are connected either to the loss of natural habitat that occurs when land is converted to agricultural purposes or to use (or misuse) of pesticides and fertilizers. Yet soil degradation has also been a factor, and one with implications for food production as well. Degradation comes in several forms, the best known of which is soil erosion. Most erosion is caused by water washing away the topsoil.

Over the past decade or so a widely stated objective in land resource management has been the adoption of strategies to ensure the sustainable use of land. Such an objective has been central to soil conservation ever since its emergence as an applied science in the 1930s. The aims of any policy dealing with sustainable use of soils are to maintain soil quality, properties, processes and diversity. The formulation of policies on sustainable development is thus on the agendas of national and international agencies. At the same time soil erosion continues to degrade the global land resource base. A wide range of economic, social, environmental, demographic and political factors interact to cause the dire situation that exists in many countries including Swaziland. Current concerns associated with the erosion of soils are the long-term impacts on soil quality, agricultural productivity, movement of pollutants, ecological diversity in streams and wetlands, river channel change and effects of flooding.

Erosion by water exists as soon as rainwater begins to move soil particles. Soil erosion starts the very moment raindrops beat the ground and it is at that moment, too, that the fight against erosion must start. How is it that areas once covered with lush vegetation are dry and arid today. The answer can be found by observing what is happening all around the country today: man is destroying the forests and the grass. There are three main causes of soil erosion in Swaziland and these are:

• Clearing of forests
• Bush and grass burning
• Overgrazing (the prominent one)

Clearings that have been managed in a bad way, unmindful of the risks of erosion, are therefore the primary cause of permanent erosion. Bush burning is an even more cause of desertification, whether it be wild, uncontrolled burning or the collection of firewood. Uncontrolled burning is completely unproductive and always vey destructive because it burns:

1. the seeds of annual plants
2. the bases of trees and their barks
3. vegetal matter on which insects and microorganisms which produce humus live

Each day, more trees are felled and burnt than forests can produce during the same period! Soil erosion is a natural process. It becomes a problem when human activity causes it to occur much faster than under natural conditions.

The Importance of Plants

Plants provide protective cover on the land and prevent soil erosion for the following reasons:

• plants slow down water as it flows over the land (runoff) and this allows much of the rain to soak into the ground;
• plant roots hold the soil in position and prevent it from being washed away;
• plants break the impact of a raindrop before it hits the soil, thus reducing its ability to erode;
• plants in wetlands and on the banks of rivers are of particular importance as they slow down the flow of the water and their roots bind the soil, thus preventing erosion.

The loss of protective vegetation through deforestation, over-grazing, ploughing, and fire makes soil vulnerable to being swept away by wind and water. In addition, over-cultivation and compaction cause the soil to lose its structure and cohesion and it becomes more easily eroded.

Erosion will remove the top-soil first. Once this nutrient-rich layer of soil is gone, few plants will grow in the soil again. Without soil and plants the land becomes desert-like and unable to support life - this process is called desertification . It is very difficult and often impossible to restore desertified land.

Preventing Soil Erosion

The aim of soil conservation is to obtain the maximum sustained level of production from a given area of land whilst maintaining soil loss below a threshold level which permits the natural rate of formation to keep pace with the rate of soil erosion. In addition, there may be a need to reduce soil erosion to control the loss of nutrients from agricultural land to prevet pollution of water bodies; to decrease rates of sedimentation in dams, rivers, canals, and ditches; and to limit crop damage by burial beneath water-transported sediments. In the longer term , erosion must be controlled to prevent land deteriorating in quality until it has to be abandoned and cannot be reclaimed, thereby limiting future use. The are various measures which can be used to conserve soil and these are:

1. Agronomic measures which utilize the role of vegetation to protect the soil against erosion;
2. Soil Management which is concerned with ways of preparing the soil to promote plant growth and improve its structure so that it is more resistant to erosion;
3. Mechanical or physical methods, often involving engineering structures such as terraces, gabions etc.

Preventing soil erosion requires political, economic and technical changes. Political and economic changes need to address the distribution of land in South Africa as well as the possibility of incentives to encourage farmers to manage their land sustainably.

Aspects of technical changes include:

• the use of contour ploughing and wind breaks;
• leaving unploughed grass strips between ploughed land;
• making sure that there are always plants growing on the soil, and that the soil is rich in humus (decaying plant and animal remains). This organic matter is the "glue" that binds the soil particles together and plays an important part in preventing erosion;
• avoiding overgrazing and the over-use of crop lands;
• allowing indigenous plants to grow along the river banks instead of ploughing and planting crops right up to the water's edge;
• encouraging biological diversity by planting several different types of plants together;
• conservation of wetlands.

Conclusion

Soil erosion is an interdisciplinary subject. It requires assessments of erosion risk; an understanding of the geomorphological processes at work and the factors controlling them; an understanding of agricultural systems and the organisational structure of the society in which they are practised; the ability to design farming systems which are economically acceptable, satisfy the aspirations of the farmer and result in sustained production without environmental damage; and the ability to implement any proposals and advise on the legislative framework to support them. Since Swaziland is a signatory to the Convention to Combat Desertification (CCD) and other international environment conventions, there must be serious commitment from government level. Therefore soil conservation requires the participation and the cooperation of every one since we all depend on soil for our food and other needs.

UMHLABA UYIMPHILO YETFU, WONGE!

References:

World Resources Institute, World Resources 1998-99- A Guide to the Global Environment (1998), UNDP, UNEP, WRI and the World Bank, Oxford University Press.

Government of Swaziland (Swaziland Environment Authority). Swaziland Environment Action Plan (1997) Vol.1

Environmental Education Articles