Plants And Water Loss some info on growing plants in dry conditions

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Transpiration is a plant?s loss of water, usually through the stomates of leaves. Plants have guard cells to regulate the water loss. These guard cells open and close the stomates in response to various environmental conditions; darkness, lack of water within the plant, and extreme temperatures cause the guard cells to close the stomates while light, plentiful water, and favorable temperatures cause them to open the stomates. Some stomates must be open even in unfavorable conditions so that the plant can take in carbon dioxide.Dryland farming is the growing of crops in areas of little moisture without irrigation. It is important to control the amount of moisture lost so that there is enough to keep the plants living. The destruction of weeds and prevention of runoff are the most common ways to reduce moisture loss.Crops that can survive must be carefully selected. They can be either drought evasive or drought resistant. Drought evasive crops grow when conditions are not severe. Drought resistant crops can reduce transpiration but may not grow at all during harsh periods and resume growth when conditions are favorable.Greenhouses are structures which house plants and provide supplemental heat. Radiation enters the clear glass or plastic walls of the house and heats the soil. During the night, the soil slowly releases the heat and keeps the plants warm. The heat, as long wave radiation, is prevented from leaving the house at night, so it builds up and keeps the plants warm.During the summer, the sun shines brighter, so these greenhouses are usually kept in the shade to reduce transpiration. Some have precise environmental controls called phytotrons. Automatic watering, regulation of light and shade, addition of carbon dioxide, and the regulation of fertility control other environmental factors as well.