Haiti's rice farmers are dismayed. It's nearly harvest time in this fertile valley where the bulk of Haiti's food is grown, and they're competing once again with cheap U.S. imported rice.

Just down the road, vendors are undercutting them, selling the far less expensive grain. Subsidized U.S. rice has flooded Haiti for decades. Now, after the Jan. 12 quake, 15,000 metric tons of donated U.S. rice have arrived.

"I can't make any money off my rice with all the foreign rice there is now," said Renan Reynold, a 37-year-old farmer who makes an average of about $600 a year. "If I can't make any money, I can't feed my family."

Last month's catastrophic earthquake that killed an estimated 200,000 people and spurred emergency food needs for more than 4 million has raised a familiar predicament for aid organizations — how to help without undermining Haiti's fragile economy.

This nation born nearly 200 years out of a slave revolt hasn't been able to feed itself for more than two decades and now imports most of its food.

Since the quake, aid groups have spearheaded cash-for-work programs, some of which intend to help struggling farmers pay for seed. They're also helping with irrigation and crop diversification projects and working with Haiti's government to analyze soil.

But little is being done to change endemic problems, according to Jean Andre Victor, a Haitian agronomist. He is among analysts who believe Haiti needs radical agricultural reforms — not constant food aid.

"There's a long history in Haiti of groups like USAID flooding the market with rice and other imports," said Victor. "This is not what we need. We need real help and that means completely changing the agricultural system."

Agricultural production accounted for nearly half of gross domestic product in the 1970s. It now amounts to less than a third.

And U.S. rice imports have long eclipsed Haitian production, due in part to smaller local yields because of environmental degradation and the lowest rice import tariffs in the Caribbean community.

The earthquake has only exacerbated needs in farming provinces. The government says more than a half-million people have fled the capital for provinces, which lack the infrastructure and food to sustain such a population surge. The coming rains will only make things worse.

When the earthquake hit, Haiti was recovering from about $1 billion in crop damage from 2008 tropical storms. Now, farmers lack cash to buy seeds for the planting season that begins in two weeks, and food prices have already risen 10 percent since the quake.

Aid organizations say families caring for displaced people are spending their savings to feed new arrivals and consuming food stocks.

"Rural areas experiencing the highest levels of displacement from Port-au-Prince and surrounding areas are the most affected," said Dick Trenchard, Assessments Coordinator for the U.N.'s Food and Agriculture Organization in Haiti.

The U.S. Agency for International Development, which has been working in Haiti for decades, is providing more than $400 million in earthquake aid with U.S. taxpayers set to give some $113 million in food aid alone this year.

But U.S. farmers also stand to benefit from the earthquake.

Last year, Washington paid farmers some $12.9 billion in subsidies, which critics say have unfairly deflated international prices. That makes it harder for poorer nations to develop their economies by expanding markets abroad.

Paul O'Brien of Oxfam America says the lessons of the harm of flooding a country like Haiti with subsidized rice should have been learned a long time ago.

"The days are gone when we can throw up our hands in terms of unintended consequences; we know now what these injections can do to markets," he said. "The question we want asked is what is being done to guarantee long-term food security for Haitians."

Haiti's 2008 food price riots prompted President Rene Preval to announce subsidies that would lower the price of rice. And still, there is plenty of malnutrition.

Some 2.4 million Haitians — out of a population of nearly 10 million — cannot afford the minimum daily calories recommended by the World Health Organization.

With planting season just weeks away for crops including beans and spinach, the Haitian government is looking at ways to boost agricultural production.

But donors often sink more money into emergency aid than such long-term projects.

The U.N. Food and Agriculture Organization has warned only 8 percent of a $23 million appeal to help Haiti revive food production has been funded.

James Woolley, a senior agronomist working with USAID in Haiti, said the multiple challenges that must be addressed in order to boost production include the country's small farming plots and persistent litany of natural disasters.

One way of attacking the problem of getting Haiti to be able to feed itself again is to focus on diet.

Before the 1970s, Haitians only ate rice once or twice a week, getting starch from other local staples like sorghum and manioc, Woolley said.

Today, rice is a staple but often U.S.-subsidized rice costs less than locally grown crops. On Friday, a 25-kilogram (55-pound) bag of US rice cost about $36, compared with $60 for the same size sack of Haitian rice.

USAID said it is investigating reports that bags of donated rice are being sold on the market and studying whether its policies in Haiti are having adverse effects on local markets.

"USAID conducts regular analyses in Haiti and across the world to make sure that our food aid does not serve as a disincentive to local production," Moira Whelan, a spokeswoman for USAID in Washington, D.C., said in an interview Thursday.

Whelan would not respond, however, when asked what the analyses had determined in Haiti.

U.S. intervention in Haitian agricultural policy is not without precedent.

In the 1970s, fearing indigenous pigs could spread swine fever, the United States — in conjunction with USAID — moved to replace all of Haiti's hearty Creole pigs with pigs from Iowa. The end result was the fragile U.S. pigs often became sick, preferred expensive feed and had fewer litters.

Reynold, meanwhile, stands hunched over the small rice paddy he rents from a property owner and hopes opportunity will come out of Haiti's latest crisis.

He needs cheap credit, cheaper fertilizer and more government aid, he said.

"Each year, it gets harder to survive."

A frightening new aftershock Wednesday forced more earthquake survivors to live on the capital's streets or sent them fleeing to perhaps even worse conditions in the countryside.

A flotilla of rescue vessels, meanwhile, led by the U.S. hospital ship Comfort, converged on the capital. They are helping fill gaps in still lagging global efforts to bring water, food and medical help to hundreds of thousands of people who are surviving in makeshift tents or simply on blankets or plastic sheets under the tropical sun.

The strongest tremor since Haiti's cataclysmic Jan. 12 earthquake struck at 6:03 a.m., just before sunrise while many were still sleeping. From the teeming plaza near the collapsed presidential palace to a hillside tent city, the 5.9-magnitude aftershock lasted only seconds but panicked thousands of Haitians.

"Jesus!" they cried as rubble tumbled and dust rose anew from government buildings around the plaza. Parents gathered up children and ran.

Up in the hills, where U.S. troops were helping thousands of homeless, people bolted screaming from their tents. Jajoute Ricardo, 24, came running from his house, fearing its collapse.

"Nobody will go to their house now," he said, as he sought a tent of his own. "It is chaos, for real."

A slow vibration intensified into side-to-side shaking that lasted about eight seconds — compared to last week's far stronger initial quake that seemed to go on for 30 seconds.

Throngs again sought out small, ramshackle "tap-tap" buses to take them away from the city. On Port-au-Prince's beaches, more than 20,000 people looked for boats to carry them down the coast, the local Signal FM radio reported.

But the desperation may actually be deeper outside the capital, closer to last week's quake epicenter.

"We're waiting for food, for water, for anything," Emmanuel Doris-Cherie, 32, said in Leogane, 25 miles (40 kilometers) southwest of Port-au-Prince. Homeless in Leogane lived under sheets draped across tree branches, and the damaged hospital "lacks everything," Red Cross surgeon Hassan Nasreddine said.

Hundreds of Canadian soldiers and sailors were deploying to that town and to Jacmel on the south coast to support relief efforts, and the Haitian government sent a plane and an overland team to assess needs in Petit-Goave, a seaside town 10 miles (15 kilometers) farther west from Leogane that was the epicenter of Wednesday's aftershock.

The death toll was estimated at 200,000, according to Haitian government figures relayed by the European Commission, with 80,000 buried in mass graves. The commission raised its estimate of homeless to 2 million, from 1.5 million, and said 250,000 people needed urgent aid.

Many badly injured Haitians still awaited lifesaving surgery.

"It is like working in a war situation," said Rosa Crestani of Doctors Without Borders at the Choscal Hospital. "We don't have any morphine to manage pain for our patients."

The damaged hospitals and emergency medical centers set up in Port-au-Prince needed surgeons, fuel for generators, oxygen and countless other kinds of medical supplies, aid groups said.

Dr. Evan Lyon, of the U.S.-based Partners in Health, messaged from the central University Hospital that the facility was within 24 hours of running out of key supplies. Wednesday's aftershock was yet another blow: Surgical teams and patients were forced to evacuate temporarily.

Troops of the 82nd Airborne Division were providing security at the hospital. A helicopter landing pad was designated nearby for airlifting the most critical patients to the U.S. Navy hospital ship Comfort.

The great white ship, 894 feet (272 meters) long, with a medical staff of 550, was anchored in Port-au-Prince harbor and had taken aboard its first two surgical patients by helicopter late Tuesday even as it was steaming in.

It joined the aircraft carrier Carl Vinson and other U.S. warships offshore, along with the French landing craft Francis Garnier, which carried a medical team, hundreds of tents and other aid.

The seaborne rescue fleet will soon be reinforced by the Spanish ship Castilla, with 50 doctors and 450 troops, and by three other U.S.-based Navy vessels diverted from a scheduled Middle East mission. Canadian warships were already in Haitian waters, and an Italian aircraft carrier, the Cavour, also will join the flotilla with medical teams and engineers.

U.N. humanitarian chief John Holmes said at U.N. headquarters in New York that it's believed that 3 million people are affected, with 2 million of those needing food for at least six months.

At the hillside tent camp, set up on a golf course where an 82nd Airborne unit has its base, the lines of hungry and thirsty stretched downhill and out of sight as paratroopers handed out bottled water and ready-to-eat meals as fast as helicopters brought them in.

In one sign of normality, women were seen carrying baskets of cauliflower, sweet potatoes and sugar cane into the city from farms in the hills. Some food and water was on sale in Port-au-Prince's markets, but prices had skyrocketed.

"We need money, man. I don't have enough to buy anything," said a newly homeless man who gave his name as Ricardo, who was seeking work, food and shelter.

Looking over the golf course scene, 82nd Airborne Capt. John Hartsock said, "This is the first time I've seen it this orderly."

President Rene Preval stressed the relative quiet prevailing over much of Port-au-Prince. People understand, he told French radio, "it is through calmness (and) an even more organized solidarity that we're going to get out of this."

Concerns still persisted that looting and violence that flared up in pockets in recent days could spread. The European Commission's report described the security situation as "deteriorating."

But U.S. troops — some 11,500 soldiers, Marines and sailors onshore and offshore as of Wednesday and expected to total 16,000 by the weekend — could be seen slowly ratcheting up control over parts of the city. The U.N. was adding 2,000 peacekeepers to the 7,000 already in Haiti, and 1,500 more police to the 2,100-member international force.

Other small signs of normalcy rippled over Port-au-Prince: Street vendors had found flowers to sell to those wishing to honor their dead. One or two money transfer agencies had reopened to receive wired money from Haitians abroad. Officials said banks would open later this week.

But Wednesday's aftershock, the stench of the lingering dead, and the tears and upstretched hands of helpless Haitians made clear that the country's tragedy will continue for months and years as this poor land counts and remembers its losses.

After the tremor's dust settled, street merchant Marie-Jose Decosse walked past the partly collapsed St. Francois de Salles Hospital in Carrefour Feuille, one of the worst-hit sections of town. She raised her arms to the sky, and spoke for millions.

"Lord have mercy, for we are sinners! Please have mercy on Haiti," she shouted.

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Associated Press writers contributing to this report included Alfred de Montesquiou, Tamara Lush, Kevin Maurer, Michelle Faul and Bill Gorman in Haiti; Edith M. Lederer at the United Nations; Emma Vandore and Elaine Ganley in Paris, and Aoife White in Brussels.