No farther. Subsistence farmers of Burkina Faso wrestle the encroaching desert into submission

WHEN Hamidou Banda and his wife, Kelsbyam Gamsore, first carried heavy rocks onto their fields and set them end to end in long, roughly parallel lines, their friends thought they were crazy. At first glance, their fields look flat. But the land has enough slope so that when the infrequent rains come, water runs quickly off the dry earth without soaking in. And precious topsoil washes away.

Their lines of rocks - about a foot high - form miniature dams that slow down the runoff and reduce erosion.

``Before the construction of the rock lines, I farmed in the same fields, but had smaller harvests,'' Mr. Banda explains, as he and his wife snip heads off the millet stalks they harvest by hand on eight acres here.

Banda is one of the pioneers in this West African country's six-year battle to fight the spreading Sahara and win back once-unusable farmland.

The near-desert in Burkina Faso - and in the nearby countries of Chad, Gambia, Mali, Mauritania, Niger, and Senegal - continues to expand at rates of up to 3 miles a year during dry periods, according to Hugh Lamprey, a regional representative for the World Wildlife Fund.

Only an average of 12 percent of the land in these countries is suitable for farming, and another 28 percent can support livestock, according to World Bank figures. For Burkina Faso, the figures are only 9 and 16 percent. And the situation here has been worsened by nearly two decades of drought.

But thousands of ambitious, small-time farmers have been taught to build these anti-erosion dams of rock and have constructed lines of them across their farms. Most have been trained by village volunteer groups organized by Naam, a 21-year-old private, Burkina Faso self-help group that is funded primarily by European development organizations. Oxfam, the British development and relief agency, has also helped with the training.

``I've never seen anything evolve so fast,'' says Peter Wright, a consultant to Oxfam who helped with some of the initial training in 1982.

Many farms that might have been abandoned by now are producing bigger crops with the rock lines than farms without them, according to two Swiss development experts.

And many other farms that had been abandoned for as long as 20 years are now back in use. With the rock dams, farmers are ``pushing the desert back a bit,'' Mr. Wright says.

Wright, and Antoine Ouedraogo, a Burkina Faso government official, say much of the desert expansion here is a result of livestock overgrazing.

Wright suggests restricting grazing on unplanted fields and relocating animals when ground cover is two-thirds consumed instead of waiting until it has been totally depleted. Also, he says, manure should be collected and dumped as fertilizer onto the fields, especially onto farms with anti-erosion rock dams.

Burkina Faso and Mali are both studying this approach.

Trees should also be planted along the rock line as a windbreak to slow dust erosion, and for use as timber, Wright adds.

``The problem in fighting the desert is to convince people that certain techniques are bad,'' Mr. Ouedraogo, an expert in rural development, says.

Unrestricted grazing, burning brush to clear land, and over-cutting trees are all bad practices here, he explains. But the country lacks the money it would need to teach that to all its farmers.

Rock lines, at least, offer an inexpensive - though back-bending - method for fighting the desert. The technology is simple.

Oxfam's Wright and Naam personnel have shown farmers how to find the contour lines (points of equal elevation) in their fields, along which the rocks are placed.

A plastic tube is attached to two poles that are held upright and a few yards apart. The tube is partially filled with water. One pole is held in place, where the first stone is set. The other pole is moved to the left or right until the water level in the tube is level. A line is then traced in the dirt between the two poles - this is the contour line.

Rocks are placed along this line very close to each other, but some tiny seepage space is allowed between them so that water flows down the slope over the entire field, but is slowed enough to allow some soaking in.

The effort seems to have paid off.

``We've eaten better since the construction of the rock lines,'' says Mrs. Gamsore, Hamidou Banda's wife.

Banda's family eats the millet they grow, but sell some of their vegetables. Cash from those sales have enabled Banda to buy a small, animal-drawn wagon that his wife now uses when she gathers wood.

He has also purchased a metal, animal-pulled plow, and materials for the new cement-walled, one-room home where he and his wife sleep. Most homes in this village have walls made of mud.

Last year, for the first time, the family bought seven sheep to fatten for market. It recently sold four of them.

Resting for a moment before setting off for a village meeting, Banda explained that the increase in crops has given him peace of mind. He has enough to eat, despite years of drought.

``I sleep well,'' he says. ``I'm not worried.''