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close this bookAmaranth to Zai Holes, Ideas for Growing Food under Difficult Conditions (ECHO; 1996; 397 pages)
View the documentOther ECHO publications
View the documentAbout this book
View the documentAcknowledgements
Open this folder and view contents1: Basics of agricultural development
Open this folder and view contents2: Vegetables and small fruits in the tropics
Open this folder and view contents3: Staple crops
Open this folder and view contents4: Multipurpose trees
Open this folder and view contents5: Farming systems and gardening techniques
Open this folder and view contents6: Soil health and plant nutrition
Open this folder and view contents7: Water resources
Open this folder and view contents8: Plant protection and pest control
Open this folder and view contents9: Domestic animals
Open this folder and view contents10: Food science
Open this folder and view contents11: Human health care
Open this folder and view contents12: Seeds and germplasm
Open this folder and view contents13: Energy and technologies
Open this folder and view contents14: From farm to market
Open this folder and view contents15: Training and missionary resources
Open this folder and view contents16: Oils
Open this folder and view contents17: Above-ground (urban) gardens
View the document18: What is ECHO?
View the documentAdditional ECHO publications
Open this folder and view contentsECHO development notes - issue 52
Open this folder and view contentsECHO development notes: issue 53
close this folder28 additional technical notes about tropical agriculture
View the documentA few alternate seed sources that we commonly use
View the documentAmaranth - grain and vegetable
close this folderArid region farming primer
View the documentIntroduction
View the documentAgricultural techniques for arid lands
View the documentCitrus propagation and rootstocks
Open this folder and view contentsCucurbit seeds
Open this folder and view contentsDry farming
View the documentMuscovy ducks for png villages
View the documentFruit crops
View the documentFruit vegetables
View the documentGrain crops
View the documentGround covers and green manures
View the documentGreen manure crops
View the documentIndustrial crops
View the documentThe lablab bean as green manure
View the documentLeafy vegetables
View the documentLeguminous vegetables
View the documentThe moringa tree
View the documentRecipes to learn to eat moringa
View the documentMiscellaneous vegetables
View the documentThe poor man's plow
View the documentPulses (grain legumes)
View the documentRabbit raising in the tropics
View the documentLetter from fremont regier, mennonite central committee, Botswana (and earlier in Zaire)
View the documentRoots and tubers
View the documentSunnhemp as a green manure
View the documentThe sweet potato
View the documentTropical pasture and feed crops
View the documentThe velvet bean as green manure
Open this folder and view contentsPrinciples of agroforestry
Open this folder and view contentsGood nutrition on the small farm


Why this primer is desirable. In every region of the world it is necessary to find or develop appropriate techniques for agriculture. A large part of the surface of the world is arid, characterized as too dry for conventional rain fed agriculture. Yet, millions of people live in such regions, and if current trends in population increase continue, there will soon be millions more. These people must eat, and the wisest course for them is to produce their own food. Yet, the techniques are so varied that only a very large volume would cover the entire subject. This publication is only a primer, an introduction to appropriate techniques. More extensive treatments are mentioned in the bibliography. In many cases the most suitable techniques for a particular region may be those already developed by the local inhabitants. In some cases it will be difficult to improve on local techniques, but at times even simple and inexpensive innovations may be almost revolutionary. This bulletin suggests that one must begin to improve local agriculture in arid zones by learning what is already there. Then both techniques and plants that may be useful in specific situations are suggested.

Definitions and degrees of aridity. Arid implies prolonged dryness, and is used with respect to the climate itself, and the land below it. In such regions the ability to produce agricultural crops is restricted. Usually on arid lands the potential evaporation of water from the land exceeds the rainfall. The land may be characterized according to the degree of aridity as dry forest, chaparral or brushland, grassland or savannah, or desert. The word, "arid" does not adequately characterize the soils, however, for they may vary in many ways. Often they are alkaline or saline.

Several degrees of dryness must be recognized. The first is where the dry climate is modified by seasonal rainy seasons. In such a region it might be possible to produce a wide range of annual crops during the short rainy season, enough to sustain animals and feed mankind, although few food or feed trees might be feasible without special techniques.

The second situation is a year round aridity, sometimes modified by light or irregular rains, which might make production of crops impossible.

The third situation is where water is brought in by wells, canals, or other means so that normal agriculture can exist, in spite of the aridity of the climate. This primer concerns the first two situations, but not the third. There are techniques suitable for all arid regions.

Principal arid regions of the world. The arid regions of the world are often very extensive, but in the tropics it is common, even on a small island, to find arid regions not far from regions of abundant rainfall. Some of the larger arid regions are:

However, while the above mentioned regions may constitute the most arid regions, nevertheless, there are many more areas, large and small, where aridity is a problem.

Water. Water is absolutely necessary for all plant and animal life. Plants have evolved that are capable of living and reproducing in semi arid, arid, and even desert regions. However, as aridity increases, fewer and fewer species are adapted, and the potential biomass is reduced.

Plants are adapted to aridity by several mechanisms. There are plants with a short life cycle that can germinate, grow, and produce during a very short period of available moisture. There are plants with deep or extensive root systems which have the ability to gather water over a wide area. There are plants which store up water in their tissues and release it very slowly. There are plants that are protected from water loss by wax or other impediments. There are plants with very small or narrow leaves, thus reducing water loss. There are plants in which the tissues themselves can withstand much desiccation without dying. Crop plants in arid regions may have any or a combination of such mechanisms.

Water that falls in arid regions may be of little use for crop plants because the amount is too small to penetrate the soil sufficiently, or it may run through a porous soil too quickly, or it may run off too quickly. Furthermore, weedy species may be so adept at utilizing scarce water that they rob the water from crops. On the other hand, some soils can store water so efficiently that is possible to grow crops in such soils over an extensive period of drought.

Water from rivers, lakes and wells in arid regions may have problems of quality, especially the presence of excess minerals. The use of irrigation water might lead to the accumulation of salts in the soil resulting in alkalinity or salinity, which might then limit crop production. The removal of salt from the soil is very difficult.

In all arid regions a major challenge is to manage water appropriately. The purpose of such management is to obtain water, to conserve it, to use it efficiently, and to avoid damage to the soil.

Heat and Wind. The major effects of heat and wind are to increase the rate of evaporation of water, and thus to increase the effects of aridity. Wind may also cause mechanical damage to crops. Both are combatted by changing the microclimate. The effects of winds can be reduced by windbreaks (lines of trees perpendicular to the direction of prevailing winds). Some useful tall species are tamarisk, casuarina, and eucalyptus. A windbreak can consist of trees and other plants of varying height. As a general rule, a windbreak is effective over an area two and a half times the height of the tree. One must remember, however, that a windbreak may also rob crops of light, water and nutrients. Thus, the advantages of a windbreak must be weighed against the disadvantages in any particular environment. Windbreaks can also be constructed of non-living materials, which are likely to be expensive.

Heat is received principally from the sun and can be reduced by shading. But, shading also reduces the yields of plants. A light shade such as that below a coconut planting or a protective screen or lathwork can be useful in reducing heat and retaining moisture, with only a minimum loss of yield.

Soils. Soils of the arid tropics are highly variable, as they are in any climate. Nevertheless, it is possible to make some generalizations about such soils. Because of the low rainfall and consequently reduced plant growth, organic material is produced slowly. Yet, again because of low rainfall, it may be broken down slowly as well. The amount of organic material in the soil, and thus the potential fertility, is likely to be high in semi-arid zones, low in deserts.

Because of low rainfall in desert soils minerals derived from breakdown of rocks are not leached from the soil. In some cases where the soil is periodically flooded or irrigated the soil might be saline as well. Such soils support few crops.

Soils of the semi-arid and arid zones might support few plants on the surface, but a good part of the biomass might be in the soil itself as roots. Shrubby desert plants often have very hard woody roots that may be a physical barrier to agriculture.

Disease and Pest Problems. Arid regions have their fair share of disease and pest problems. However, these may often be quite different from those of wetter regions. Nematodes are often a severe problem in sandy soils. No general rules are useful, and indeed, agriculture anticipates diseases and pests, and their parasites as well.

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