 For centuries, farmers have struggled to draw as much food as possible from the land. In arid regions of the world, the lack of water more than any other factor has limited the expansion of agriculture. But growing demands on the world's food supply have made it necessary to farm areas which until now have been uncultivated. A full third of the earth's land is dry and arid, yet more than 650 million people live in these regions. To increase the supply of water in desert lands, to make the desert bloom, simple inexpensive techniques are being developed through the science called water harvesting. The global problems of spreading desert lands are clearly evident in the arid southwestern United States. Here, not long ago, large herds of cattle once grazed. As in many other places, there were too many animals for the land to support. The grasses gave out, leaving only mesquite bush, cactus, and sand. To stop new deserts from forming and to reclaim already arid land, Bob Dixon, a soil scientist with U.S. Department of Agriculture, has invented a device that is showing promising results. Designed for use on barren, brush-covered terrain, the land imprintor is simple and effective. Onto a hollow steel drum, geometric shapes have been welded. Half of the drum imprints grooves into the soil, while the other half forms V-shaped pits. When filled with water, this land imprintor weighs almost two tons and easily crushes the brush into a mulch. With an attached planter, grass seed can be spread over the imprinted area, ooze direct rainwater to deep pockets that hold moisture and give the seed a chance to germinate. Just a year ago, only scrub brush and cactus grew here. Today, this well-established stand of grass is the result of one rolling with the land imprintor. No fertilizer or extra water was used. The land imprintor has applications in arid lands everywhere. Its construction is uncomplicated, inexpensive, and scaled-down models could be pulled behind oxen or mules. Soon, livestock will graze here again, but this time the herds must be kept small, or the land will quickly return to mesquite bush and sand. In the Sonora Desert of southern Arizona, the sparse and infrequent rainfall washes quickly over the crusted soil without benefit to the land. John Griggs and Dr. Gary Frazier, scientist with the Watershed Research Center, have for the past 15 years worked to find a practical and economic way to harvest rainwater for livestock use. While forage grasses are important, available drinking water is essential. In 1970, as one of their demonstration projects, 1,000 square meters of sloping desert ground were cleared of cactus and brush. A fiberglass matting was rolled directly onto the rough soil, then covered with asphalt and a protective aluminum paint. The fiberglass serves as a reinforcing fabric, and the asphalt provides waterproofing. Face material is pretty good, but the protective coating isn't working very well. It looks like it needs a new one on it. In the 10 years this catchment has been in place, very little maintenance has been necessary. Virtually all of the rain falling on this surface is harvested. From only 1 centimeter of rain, this catchment can produce over 8,000 liters of good drinking water. Many other surface materials for catchments are being evaluated. These long-term research studies measure the amount of runoff from various materials after each rainfall. The effects of wind, sunlight and temperature are carefully observed. Among the surfaces being tried are metal foil, gravel over asphalt, concrete, artificial rubber, paraffin wax, and gravel covered plastic. So far, no single ideal catchment surface for all conditions and locations has been found. Soils, climate and costs are too varied. But research has proven that water harvesting works. Treating a surface to increase runoff from rainfall will provide water, often in large quantities, without requiring fuel or power. However, once water has been collected in ponds and reservoirs, another serious problem must be faced. Evaporation. In arid countries, more water is lost through evaporation than is used productively. To stop the loss, hydrologists are testing various floating reservoir covers. Paraffin wax is inexpensive and forms a tight seal. Butyl rubber has proven effective, but is costly. Researchers have found that any materials which shield part of the exposed surface from the sun will help reduce the loss of stored water. Even ping-pong balls. Dr. Brent Clough of the University of Arizona has a simple concept to reduce evaporation. This is a water harvesting system feeding water into a compartmented reservoir. The reservoir has been divided up into compartments in order to reduce evaporation. Water is drawn first from the largest pond. As the level decreases, the remaining water is pumped into smaller compartments. Smaller surface areas reduce the evaporation loss. A low-cost, effective system for evaporation control. Arid lands can be successfully farmed with an age-old technique known as runoff agriculture. By preparing part of the soil surface as a watershed, rain will runoff onto the smaller cultivated area. Two centimeters of rain could concentrate as much as eight centimeters of water on the cropped area. Apricot, peach and plum trees have flourished in the Arizona desert under this system of water harvesting and runoff agriculture. Archaeologists have discovered that these same techniques were used 4,000 years ago in the deserts of the Middle East. Here at the University of Arizona's experimental farm near Tucson, several varieties of grapes have been grown successfully for the past 10 years. Runoff water, not absorbed by the plants, is channeled to a compartmented pond. A windmill provides energy to pump the water back onto the crops when needed. On a mesa in Northern Arizona, runoff agriculture is being tested on a mammoth scale. This demonstration project, a cooperative effort between the Navajo Indian Tribe, the University of Arizona and the U.S. Bureau of Mines, will reclaim land which until recently was covered with waste from a nearby coal mine. Water harvested from the compacted catchment surface is already being stored in ponds to be used for irrigation. Plans call for several solar collectors to be floated on the ponds. Not only will these slow down evaporation, but the sun's energy, when mirrored under the photovoltaic cells, will create electricity to keep the float aimed toward the sun and provide energy to irrigate the field in orchards. In another approach, for the past eight years, Dr. Dwayne Fink of the U.S. Water Conservation Lab has been studying the effect of microcatchment systems on a native desert bush, the jojoba. The jojoba thrives in the arid regions of Arizona, California and Mexico, and could grow well in many other countries. A hardy plant, it can survive in areas with extremely limited rainfall. The jojoba produces a high quality, multi-purpose oil which one day could be used in many ways. Dr. Fink has been experimenting with microcatchments covered with ordinary paraffin wax that channel rain to the base of the plant. A neutron soil probe records the moisture content at the root bottoms. Results from this study have proven that harvesting water with microcatchments has doubled the size and productivity of the jojoba. In southern Arizona, as well as in the Middle East and Australia, water management has a new innovative tool, laser leveling. This system enables farmers to level their fields with dramatic precision. Water for irrigation can then spread evenly over an entire field, reaching all crops in equal measured amounts. This rotating laser transmitter sends out a beam of light in an absolutely level plane. The laser receiver, mounted on an earth-moving machine, signals the scoop blade to dig in or raise up, maintaining a constant distance between the overhead plane of laser light and the earth's surface. In two days, this field will be leveled. 75 hectares, absolutely flat. With laser leveling, farmers in the southwest are now using far less costly water to irrigate. And at the same time, have substantially increased the productivity of their fields. The annual loss of crop land around the world is staggering. The deserts are expanding by 60,000 square kilometers every year. Still more land is being lost to overgrazing and erosion. If there is to be enough food in the future, this trend must be reversed. Using simple, appropriate technologies like water harvesting, much can be done to sustain and cultivate the arid lands of the world.