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Difficult Agricultural Landscapes of Latin America |
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Well over one
third of Latin America is devoted to production of crops and
livestock. But farmers face persistent and daunting challenges in
maintaining - let alone improving — the productivity of up to half of
these lands. More than 40 percent of the agricultural landscapes of
Latin America have significant soil productivity constraints. Some of
these constraints are a direct consequence of the conditions under
which the soils themselves were formed — such as the low soil
fertility of the vast tropical savannas of the Amazon and Orinoco
river basins. Other constraints, like the high rates of soil erosion
from the often steep, tropical hillsides of Central America, are made
even worse by inappropriate methods of intensifying food production.
High Andean agroecosystems represent other challenging production
environments, as do now the overgrazed pastures and nutrient-depleted
croplands of the pampas. Irrigated areas throughout the region are
affected by waterlogging and the accumulation of harmful salts.
The hillside agroecosystems of tropical America cover about 1 million square kilometers in the Andean region and Central America — especially Honduras, El Salvador and Guatemala - and sustain an estimated 10 million small farmers in areas that were predominantly forested. Large commercial enterprises often acquire flatter lowlands for industrial export crops, leading to pervasive and still expanding use of hillsides for subsistence or low-level commercial food crop production. About half of these areas show signs of serious environmental degradation. This is often the case where agricultural and resource management practices have not kept pace with population growth. Inequalities in land distribution associated with insecure land tenure have lead to deforestation and overgrazing and other forms of over-exploitation. Soil erosion is by far the most important aspect of soil degradation in these tropical hillsides because of the intense rainfall, relatively steep slopes, and soil properties. Attempts to cultivate hillsides more intensively using traditional methods tend to accelerate loss of fertile topsoil. As a consequence, only a limited number of very resilient crops are able to flourish. In such cases, the capacity to meet even subsistence food needs can be seriously compromised, often resulting in the abandonment of non-productive lands and rural-urban migration. In the densely-populated hillsides, deforestation, overgrazing and soil erosion have important on-farm, community, and downstream consequences. Mitigating these problems can involve collective action across households and communities in entire watersheds. It also relies on communities gaining improved access to technologies, information and other forms of support. Tropical savannas consist of low shrubs and tough grasses and with, typically, a 4 to 6 month dry season and an annual rainfall of some 1,200 to 2,000 millimeters. Savannas occupy large parts of Bolivia, Brazil, Colombia and Venezuela and, despite their fertility problems, are perceived by some as the continent’s last great source of unlocked agricultural potential. In Brazil, technology development, extension, and soil liming practices have served to limit fertility constraints. But elsewhere crop yields in the savannas tend to be significantly less than those of other agroecosystems. But savannas do contribute an increasing share of total agricultural production, especially in Colombia, Venezuela and Brazil. Generally, the physical quality of these soils is good. They tend to be deep, well drained and easily cultivated — although "no-tillage" practices that improve soil condition are being increasingly adopted. However, the productivity of savanna soils is severely constrained by their very high acidity combined with low nutrient status, both major growth-limiting factors. Furthermore, many savanna soils contain high concentrations of aluminum and manganese that inhibit root development. A restricted root system severely limits yields by making crops more vulnerable to drought and unable to take up available plant nutrients. Other savanna soils contain iron sulfides that generate large amounts of sulfuric acid when exposed to air. Conversion to agricultural exploitation has exposed large areas of these soils. Acid leachate, plus the aluminum, iron and the heavy metals that this releases from soils, can cause significant environmental and economic problems. Research has shown that yields can be improved if the high levels of exchangeable aluminum can be reduced and if more nutrients are supplied. But chemical inputs, such as fertilizer and lime or gypsum to reduce soil acidity, are not affordable or accessible to all farmers and, by themselves, are often insufficient to sustain yields on a long-term basis. Breeding crops and pasture species for higher tolerance of these soil constraints, as well as designing more sustainable farming systems are some of the avenues currently being followed by — among others — Future Harvest scientists. The information for this text was compiled by Stanley Wood of IFPRI and edited with the author of From the Rural Heart of Latin America. |
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