Number 29, Fall/Winter 1989
by David Cleveland and Daniela Soleri
"These are just a few examples of very simple water conservation techniques for dryland gardens based on a basic understanding of soils, plants, and water. The most important characteristic of this approach is not the specific solutions it can offer, but that it encourages development of local solutions. "
The following brief summary of water conservation in dryland gardens draws on both Western science and traditional knowledge and is based on material from the authors' 1990 book, Food from dryland gardens, published by the Center for People, Food and Environment (CPFE) in Tucson, Arizona. Regrettably, the book is now out of print.
Improving water use efficiency - that is, reducing water losses - is central to dryland garden management. Water is lost from dryland gardens in four ways: evaporation, transpiration, runoff, and deep percolation.
Hot, dry conditions encourage evaporation of water from the garden soil surface. The longer the water remains on or near the surface the more is lost through evaporation. Heavy soils keep water on or near the surface due to slow infiltration rates, and soil amendments such as organic matter and sand improve soil porosity, hastening water infiltration. Vertical mulches can be made using garden by-products such as maize, sorghum or sunflower stalks, or just sand, arranged in a vertical row or column in the garden bed. These create pathways in the soil through which irrigation water can travel quickly down to the root.
Another simple and effective method for reducing evaporation is the use of surface mulches to shade the soil and capture some of the water evaporating from it. Compost, leaf litter, pulled weeds, and other kinds of organic matter make good surface mulches which also improve the soil as they decompose.
Transpiration is the loss of water vapor from the plant and is an essential part of photosynthesis. However, the high temperatures, sunshine, and drying winds common in many drylands increase transpiration rates beyond those required by the plant for maintenance and harvest production. This stress-induced transpiration can be reduced by using shades, windbreaks, and mulches made from locally available materials such as palm fronds or maize stalks. In Egypt, for example, young tender seedlings are protected from drying winds and wind-borne sand by careful placement of maize or wheat stalks just upwind of the seedlings.
Mixed plantings combining garden crops of different forms and life cycles reduce both evaporation and transpiration. Larger plants in these mixtures, such as perennial fruit trees, provide shade and protection from winds while squash vines and other rambling plants spread out over the soil and act as living mulches.
Water from direct rainfall or irrigation may reach the garden but if not contained it will run off and be lost. Planting dryland gardens in sunken beds or depressions is a long tradition in many regions, for example, among Native Americans of southwestern North America, and in West Africa. This is an effective way to contain and concentrate water in the growing area, allowing time for the water to infiltrate and reach the root zone where garden plants can use it. Sunken beds are not washed away should a sudden heavy rainfall occur and the rainwater will be captured for garden use.
Water in the garden which moves down through the root zone and beyond is lost to garden crops. This deep percolation is a problem in areas where the soil is very sandy with a low water-holding capacity, and too much water is being applied to the garden, although limited deep percolation is needed to wash salts out of the root zone. The water-holding capacity of sandy soils can be improved by adding organic matter. Overwatering can be avoided by using a pole to test the depth of soil wetting. The pole will move down with ease through wet soil but then slows or stops when reaching dry soil. For good root development the soil should be wet to about 18 inches below the surface; much deeper than this for annual crops is probably a waste of water.
These are just a few examples of very simple water conservation techniques for dryland gardens based on a basic understanding of soils, plants, and water. The most important characteristic of this approach is not the specific solutions it can offer, but that it encourages development of local solutions. By doing so, it avoids the danger of promoting models that do not reflect local needs and resources.
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At the time that this article was originally published in hard copy (1989), Daniela Soleri and David A. Cleveland were co-directors of the Center for People, Food and Environment (CPFE), 344 South Third Avenue, Tucson, AZ 85701, U.S.A. At the time of uploading this article to the ALN web site (September 2000), the authors can be reached for comment as follows:
David A. Cleveland, Department of Anthropology and Environmental Studies Program, UC Santa Barbara, firstname.lastname@example.org
Daniela Soleri, Department of Anthropology, UC Santa Barbara, email@example.com
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