NOT far from the legendary mining town of Tombstone, Ariz., Bob Hopp runs a modest cattle spread -- 26 square miles of mesquite-covered desert country, typical of the region. The land, dust dry for much of the year is sparsely grassed except for a 100-acre section that contrasts sharply with the surrounding scrub lands. It boasts a solid grass cover that to the casual observer belongs in better-watered prairie country much farther north. After any rain, the area draws cattle like a magnet. In Mr. Hopp's words, ``they come running.''
When encroaching suburbia caused the Hopp family to sell their original ranch near Tucson four years ago, they bought this one specifically because of those 100 grass-rich acres. Remarkably, this cover had not even existed some six years earlier. Without the development of a method for embossing the soil surface, it never could have been established so readily in the arid environment.
Land imprinting, as it is called, adds a waffle-like texture to the soil, forming indentations that capture and absorb rainwater that simply runs off untreated land. The indentations also provide a series of microclimates that promote germination and protect grass seedlings during the critical early growth period.
The magazine Irrigation Journal, which followed early imprinting trials, reported on 500 acres near Fort Huachuca, Ariz. The land had been imprinted and seeded with perennial grasses. Within 10 months, it had accumulated 2,900 pounds of grass an acre, compared with 50 pounds an acre on adjacent non-imprinted (but similarly seeded) land. Within 18 months, the yield was 4,100 pounds of grass per acre, which Irrigation Journal noted was well above yields of the ``lush'' Kansas Flint Hills region with an annual rainfall double that of the Arizona region.
The Australians, Israelis, and Argentinians with arid climates of their own to contend with, also are experimenting with land imprinting.
Robert M. Dixon, who developed the technology and coined the term land imprinting, was a soil scientist with the United States Department of Agriculture in Tucson for many years. He noted that Arizona's soils, in common with arid regions worldwide (less than 15 inches of rain a year), tend to form a smooth, hard crust on the surface. When the occasional rains, often heavy, do fall, most of the water runs off the land and down the gulleys like water draining from a paved road. The region's most scarce resource simply runs to waste and a vicious cycle of desertification is set in motion. According to the Irrigation Journal, bare, compacted soils often have infiltration rates one-tenth that of grasslands.
If he could develop a system that would hold rainwater long enough for it to soak into the soil, Dr. Dixon reasoned, then surely grass could be encouraged to return to the area. (Decades of overgrazing denuded what was - when settlers first arrived - relatively well-grassed land.) Another need was to eliminate the competing mesquite bush without using chemical herbicides that contribute still further to topsoil degradation and compaction.
Dixon's answer was a large heavy roller with projections, or imprinters, welded on the surface. When the roller is towed across the land, the projections form funnel-like impressions in the ground. They also grind up the mesquite bush, scattering it on the land as a moisture-conserving mulch. When rain falls, seed, water, and nutrient-rich litter are funneled into the depressions.
In a now moist environment, sheltered and fed by decaying mulch, the seed sprouts. During the first few vulnerable days, the hollow also protects the seedling from searing winds.
Shortly after land imprinting was developed and had proved itself, Dixon noticed that it closely duplicated a natural phenomenon -- the imprints made by hoofed animals, such as buffalo, in the the wild. Domesticated cattle will do the same thing if not too many are confined to an area. The United Nations Food and Agriculture Organization referred to this form of imprinting in the May 1986 issue of Ceres magazine as an ``easily observed, but generally ignored function of nature.'' Of Dixon's approach to land imprinting the article said: ``[its] mechanical simplicity hides a sophisticated concept.''
Any farmer with a tractor can pull an imprinter across his lands, and because the technology is so simple and relatively inexpensive (a ready-to-roll imprinter costs about as much as a small car) it seems tailor-made to halt desert encroachment in many Third World areas. A smaller roller, pulled by a team of oxen or donkeys, would work as effectively, Dixon feels. He has also designed a hand imprinter that farmers working an acre or two might find acceptable.
Cost of land imprinting in the United States, including amortization and the farmer's time, currently averages around $20 an acre ($10 for imprinting and $10 for seed), according to Dixon. Some ranchers have treated only 10 percent of their land, doing so in strips. Experience has shown that the revegetated strips, if not overgrazed, slowly spread to the untreated areas. ``This way,'' says Dixon, ``the effective cost of imprinting is reduced to $2 an acre.''
Dixon and some associates have established the Imprinting Foundation, a nonprofit organization open to members from around the world. Its efforts are designed to develop land imprinting still further and any other techniques that might be better ways of revegetating the land. Says Dixon, ``I guess our main thrust is directed towards reversing global desertification.''
The Imprinting Foundation, 1231 E. Big Rock Road, Tucson, AZ 85718.