LOS TEJOCOTES, Mexico -- Mixteco Indian farmers used to bury cigarettes, candy and a cactus-based brew called pulque in their cornfields to give thanks to the land.
Over the last few years, the age-old tradition has died out.
"There's no reason to anymore, because the land no longer gives," said Policarpo Bautista Salazar, 56 years old.
Bald hillsides scarred with deep gullies glare down at Los Tejocotes, named after the native fruit trees that once grew in abundance here in the southern state of Oaxaca. Only a few trees remain from the thick forest that blanketed the mountains.
All across Mexico, farmers are discovering the same thing: The land no longer gives.
The United Nations Environmental Program says Mexico loses an average of 870 square miles of arable land each year to desertification -- forests or jungles transforming into barren land. It is caused mainly by overlogging, overfarming and overgrazing.
Faced with infertile soil, about 900,000 people leave Mexico's arid and semi-arid lands every year, the U.N. program says. Many wind up in the slums of Mexico's overcrowded cities.
If desertification continues at its current rate along with the population growth, the country that introduced the world to corn may be unable to feed itself in 30 years, scientists say.
"If Mexico doesn't revamp its agricultural policies, we are going to face desertification of barbaric proportions," said Juan Estrada Berg Wolf, a scientist with Mexico's National Commission on Arid Zones.
Any change is unlikely soon. The three leading candidates in the July 2 presidential election propose more farm production with no plans for healing the land, Mr. Estrada said.
More than 60% of Mexico's farmland is severely degraded, the National Institute of Geographic Statistics and Information says. An additional 30% is in varying stages of ecological decay.
Down the road from Los Tejocotes, the tiny village of Guadalupe Llano Grande clings to the brittle earth.
Elderly farmers poke at the exhausted land as if goading a stubborn mule.
"Over there is the last field I've had to abandon," said Pedro Pablo Martinez, 70, pointing with a broken machete to an area behind the community's half-built church.
The village is among the poorest in Mexico. In the church's basement is a statue of the Virgin of Guadalupe with a dollar bill in her praying hands. Next to her is a crucifix of what people say is "The Christ of Safe Travels."
"We ask them to make sure nothing happens to those who've left to seek a better life," Mr. Martinez said.
Guadalupe Llano Grande is a town of elderly men, women and small children, its young people gone in search of better lives. Mr. Martinez's sons all went to California. Two wash dishes at restaurants; the third was killed five years ago by gang members in Los Angeles.
Decades of too much logging, farming and grazing has ruined the land, said Mr. Estrada, who is conducting a study analyzing the correlation between government policies and land degradation.
The government knew decades ago that if its farmers continued to pump the land with chemicals to boost production the soil would eventually collapse, but officials refused to consider more restrained practices, Mr. Estrada said.
"This is big business," he said. "The policies have supported the quasi-state and multinational companies that sell the improved seeds, chemical fertilizers, pesticides and machinery."
They also support the political parties, Mr. Estrada said. The government farm aid program, Procampo, puts local leaders in charge of distributing vouchers for farmers to buy the products at a discount.
"But if you don't vote for them, you're not going to see your voucher," farmer Bautista Salazar said.
Farmers have nicknamed the program "PRIcampo," alluding to Mexico's long-ruling Institutional Revolutionary Party, or PRI by its Spanish initials.
"The program opens the doors to a lot of manipulation to benefit those in power," Mr. Estrada said.
Pascacio Taboada, spokesman for the Agriculture Secretariat said it is possible irregularities occur, given that Procampo has 714 support centers that distribute about $1 billion to more than 3 million farmers each year. But he insisted such occurrences are rare since the program is monitored by the farmers themselves, who elect local Procampo representatives.
"The system works," he said. "You can bet if someone believes they are getting ripped off that they report it."
He disputed contentions that the secretariat's policies are designed to benefit agrochemical businesses and political powers. The government has reduced pesticide use and promoted organic farming wherever possible, Taboada said. But, he added, the bottom line is production.
"Our goal is to make use of our natural resources for the benefit of man. I suppose we could leave the land alone, which would be best for the environment, but then how would we produce?" he said. "I don't deny that the resources are running out, but the demand is growing. We can't wait."
Alejandro Santiago Salazar, a Mixteco farmer, started using fertilizers in the early 1970s when officials came to this isolated region as part of the Green Revolution, a campaign started in Mexico in 1944 to combat world hunger. Sponsored by the Rockefeller Foundation, it promoted new seed varieties, fertilizers and pesticides to boost grain yields.
During the first few years, Salazar's corn production boomed. But over time, the Oaxacan land, which had been farmed for thousands of years, became a chemical junkie, requiring stronger fertilizers and more pesticides to produce.
Heavy fertilizer use disrupts the ecological balance. It overdoses the land on nitrogen, causing the soil to shut down its natural production of nutrients, Mr. Estrada said.
The nitrogen also kills humus, a spongy, slow-decomposing organic material that not only provides nutrients to soil but also increases the soil's ability to hold water, curbing runoff, he said.
The new plant varieties introduced under the Green Revolution also brought more pest invasions, requiring more pesticides.
"Fertilizer burned the land, and now we can't grow anything without it," Mr. Salazar said.
Fertilizer is a key demand of the People's Revolutionary Army, a leftist guerrilla group in Oaxaca and Guerrero. In April, the Campesino Organization of the Southern Sierra in the state of Guerrero blocked city hall in the state capital for a week to demand 500 tons of fertilizer.
Mr. Estrada said the answer to restoring land lies in Mexico's past, when farmers grew crops suited for each region's ecosystem, and in manual labor, organic material and longer fallow periods.
For instance, farmers grew corn with beans in the same field. Beans replace the nitrogen that corn depletes from the soil. Pre-Hispanic farmers also did not use plows, which break down the soil's structure, Mr. Estrada said.
In addition, they let fields rest for more than a decade. While that is no longer feasible, Mr. Estrada believes that if growers used less fertilizers and more organic material the land could heal with shorter fallow periods.
"It's possible the Mexican countryside can recover," he said. "But it'll take a fight."
Many farmers are just quitting.
The states with the greatest land degradation also have the highest rates of migration. In Guanajuato, 43% of the land is degraded, while more than a quarter of the land in Jalisco and Michoacan is spent.
In Oaxaca, Mexico's southernmost state, 75% of the towns are losing population. Land erosion is the principle reason, according to a report last October to the Mexican Senate from human rights organizations.
A leading Mixteco expert, anthropologist Michael Kearney of the University of California, has watched fertile Oaxacan fields turn into bedrock over the years -- and has seen the young leave.
"They either have to migrate or starve," he said.: