Contents - Previous - Next

Part I: The present situation

Land and water resources
Traditional approaches to land conservation and the consequences

Land and water resources

Present potential

In order to develop sustainable systems of agriculture that satisfy the present and future needs of the region, there must be reliable information on the potential of the region's land and water resources.

The potential of some 96 percent of cultivable lands is limited by rainfall or soil factors and 29 percent of drylands are threatened by desertification. The areas with favourable soil and climatic conditions are mainly found in the southern cone of South America in temperate or subtropical climates.

The region as a whole is subject to much less agricultural exploitation than other parts of the world, such as the Near East or the Asian continent. This is due to a lower population pressure which results in a greater proportion of the land, including potentially cultivable areas, remaining under forest.

The region also possesses considerable freshwater reserves. Available data show that, for most countries, the average freshwater supply is satisfactory and exceeds 5000 m³ per person per year. However, the value varies from as little as 195 m³ per person per year in Barbados to 73416 m³ per person per year in Paraguay. In large areas of coastal Peru and northern Chile the freshwater supplies are less than 1 m³ per person per year.

The region possesses one of the largest freshwater reserves in the world, where water availability in the Amazon basin exceeds 300000 m³ per person per year. In this region the abundance of water gives rise to seasonal flooding which restricts the utilization of the most fertile soils located in the alluvial plains.

Of all water available for agriculture, livestock and industry, agriculture is the main consumer of water, using 60-70 percent to irrigate 13 million hectares. In areas where water is scarce, conflicts arise among agriculture, domestic consumption and industry; the serious problems of competition for water in Mexico City and Lima are well known. Although the expansion of irrigated areas has been limited in the last decade, many projects have been initiated to improve and rehabilitate existing irrigation schemes.

Water quality has been affected by discharge of sewage and industrial waste into rivers and the limited available data present a rapidly deteriorating trend. A symptom of this was the outbreak of cholera at the beginning of the 1990s which, in addition to the loss of human life, resulted in estimated costs of the order of US$ 200 million. Less dramatic, but of equal importance from an economic viewpoint, is the alarming increase in suspended sediment concentrations in many rivers, which causes additional costs for the maintenance of irrigation canals and the dredging of navigable rivers.

Limitations

In 1992, the Latin American and Caribbean Commission on the Environment emphasized that inappropriate land use is the most serious environmental issue. This results in soil erosion, desertification, loss of soil fertility, the deterioration of pastures and forests, salinization of irrigated lands and the under-utilization of good agricultural land.

The region can be subdivided into several clearly differentiated agro-environments with specific potentials and limitations, briefly described as follows:

Steeplands

Insidious processes of soil erosion in densely populated steeplands are causing a crisis that is progressively diminishing local people's capacity to produce even their subsistence food requirements. Average daily food intake in these zones is below the regional average of 2673 kcal/person. Soil erosion is also forcing large numbers of small-scale farmers to migrate to cities, or to forested areas in the lowland tropics, which constitute the agricultural frontier in many Andean countries. As in many other mountainous environments in the world, soil erosion with implied loss of production is becoming the most pressing environmental problem in these areas.

Drylands

Dryland areas constitute approximately 15 percent of Latin America and are found in a great variety of landscapes, ranging from the Pacific coastal zone, to the Chaco plains, to the semi-arid Pampa grasslands; one-third of these areas is threatened by desertification. Drylands are classified on the basis of aridity indices into hyperarid, arid, semiarid and dry sub-humid zones. In none of these zones does the annual precipitation exceed 65 percent of the annual potential evapotranspiration.

Within the dryland zones are irrigated areas that contribute significantly to food production; in Mexico irrigation provides more than 50 percent of the total food production. Irrigated areas also contribute a significant proportion of the agricultural exports of Chile, Brazil and other countries.

Dryland areas are very susceptible to desertification caused by climatic variations and human activities, such as overgrazing, overirrigation and inadequate drainage, expansion of cultivation into fragile soils, deforestation and overexploitation of vegetation for domestic use. The productivity of irrigated areas is also in danger because of poor quality water and diminishing water supplies. An estimated 10-15 percent of the irrigated areas in arid zones are degraded by waterlogging and salinity and once degraded their rehabilitation becomes very expensive.

Humid tropics

In the humid tropics the conversion of forested land to cropland and pastures is most rapid. It has been caused by migration from other, densely populated regions and by present economic development trends. The creation of croplands has led to loss of soil organic matter, accelerated erosion and increased sediment loads in rivers and lakes. It has also given rise to losses of important plant and animal species due to direct destruction and to changes in their habitats. In the Amazonian region in particular, new settlers have been granted permission and encouraged to extract timber and to establish crops or pastures. However, the nature of the soils, vegetation and climate and restricted land use suitability have seldom been taken into account. In some regions, especially those with high rainfall, transformation of the natural ecosystem has caused pronounced land degradation and loss of productive capacity. To date it is estimated that more than 800000 km² of forest in the Amazonian region have been felled due to the combined effects of population pressure, poverty and the commercial exploitation of cattle, timber and minerals.

Grazing lands

The grazing lands include subtropical and temperate grasslands in the south of the continent, seasonal pastures of the high altitude Andean regions and tropical savannahs and pastures of the Amazon basin. Due to socioeconomic reasons the number of cattle frequently increases as the area of pastures decreases. Overgrazing is the main cause of degradation of natural pastures, resulting in a rapid decline in productivity. In large watersheds this can result in damage such as gully erosion and contaminated water supplies in the lower-lying areas of the catchment that will entail high rehabilitation costs.

Many of the soils under cultivated pastures are of low fertility and pasture productivity generally diminishes with time due to poor management. The risks of deterioration are accentuated by the steep topography and short length of growing periods in the Andean highlands.

Under these conditions water and wind erosion can severely deteriorate the soils, cause sediment accumulation in river channels and reservoirs and lead to flooding, waterlogging and salinization.

Wetlands

Wetlands occupy 11 percent of the region and are most common in Central America, the southern cone, in the Orinoco valley, in the north of Bolivia, southeast Brazil and Mexico. Smaller areas of wetlands are also frequently found in a wide variety of topographic and edaphic situations. The principal limitations are the lack of drainage and the high risk of flooding. Although the soils are very varied in terms of texture and acidity, the majority are well supplied with nutrients and can be very productive if adequately drained and protected from flooding. The potential effects of drainage on the hydrology of the surrounding land and on the environment, including plant and animal (bird) diversity need to be considered before such conversion.

Acid savannahs

The acid savannahs, consisting predominantly of low shrubs and tough grasses, occur mainly in the vast Cerrado region of Brazil where they occupy 112 million hectares of rolling landscape. They correspond mainly to a sub-humid environment with a 4-6 month dry season and an annual rainfall of 1200-2000 mm. The soils are physically good, deep, well drained and easy to plough, but suffer from a very low chemical fertility due to high acidity, low nutrient content and-very high aluminium saturation. However, with good management that includes the application of considerable quantities of fertilizers and lime, the land can become very productive. Nevertheless, the application of fertilizers and lime is very costly and is not sufficient on its own to sustain yields. The soils are very susceptible to erosion and if the management practices do not ensure an adequate soil cover and provide effective conservation, erosion can rapidly degrade the soils so that they are soon abandoned.

Small island environments

The Caribbean, which consists predominantly of island environments, deserves special attention. The small proportion of agriculturally suitable land provides few opportunities for production and leads to an enforced, intensive use of the limited lands available. These limitations become even more serious due to the ever-growing population pressure. This situation exists on almost all of the islands, both large and small, with the possible exception of the Dominican Republic and Cuba, where the agro-ecological conditions are more similar to those of continental environments.

The formulation of National Action Programmes for sustainable natural resource use and management will need to take account of the great variety of island environments, the physiography, climate and cultural aspects, as well as tourism with its ever-increasing impact.

Traditional approaches to land conservation and the consequences

AFTER MANY YEARS OF IMPLEMENTING CROSS-SLOPE PHYSICAL BARRIERS FOR SOIL AND WATER CONSERVATION, MANY FARMERS ARE STILL NOT CONVINCED OF THEIR BENEFITS AND RIGHTLY REGARD THEM AS ADDITIONAL COSTS.

In the traditional approach to land conservation emphasis was placed on three factors: physical conservation structures, the need for soil conservation specialists and the requirement that farmers comply with the recommended conservation measures.

Even nowadays, many farmers do not associate these practices with increased productivity or higher profits and most farmers consider physical conservation structures merely as additional costs. Most soil conservation structures were implemented as part of aid programmes with subsidies and many of the structures were abandoned as soon as the subsidies ceased.

Government bodies created to combat the problems of soil erosion and runoff emphasized physical aspects related to soil type, hydrology and engineering. These physical aspects contrast with the more socioeconomic concerns of extension agencies and farmers, which have tended to accentuate the lack of coordination between the work of extensionists and soil conservation specialists.

Traditional approaches only achieved limited success, even when recommended soil conservation structures were implemented. As a result, soil erosion has in general not been controlled and productivity continues to decline in extensive areas affected by erosion.

The guidelines in this document introduce new concepts and methods for the implementation of soil conservation measures and the development of sustainable agriculture.

Traditional soil tillage practice using animal traction

Contents - Previous - Next