KYAUNG GWIN, Myanmar - Farmer Zaw Naing was puzzled as he stared at the brand-new, unassembled tilling machine - equipment not seen in most of Myanmar's rice belt before the deadly cyclone.

Thousands of the tillers, donated by international and private aid donors, have been brought in to replace the water buffalo that once plowed the rice paddies but were killed by Cyclone Nargis on May 2-3.

But the tillers have brought new challenges for farmers like Zaw Naing who have been lucky enough to receive them.

As he unwrapped the plastic cover of a Chinese-made machine's red engine on a recent afternoon in this delta village, he confessed, "We don't know how to put it together. We have to wait for a mechanic to come."

If they manage to put a tiller together and learn to operate it, the farmers face yet another hurdle: They cannot afford the diesel fuel to power the machines.

The plan is for farmers in the devastated Irrawaddy Delta to rebuild livelihoods and begin producing the rice that feeds this impoverished country. But time is running out.

The rice planting season should have started by early June, when farmers here typically plow their fields with water buffalo and prepare to plant new seeds for the October harvest. The delta produces most of Myanmar's rice, and without immediate help, food security will be seriously threatened, international experts have warned.

The Agriculture Ministry has said 13,600 power tillers are needed to replace more than 280,000 cattle that died in the storm.

"I don't know how to use this machine. We only used buffalo in the past," said Zaw Naing, who lost his home in the cyclone and the 10 water buffalo that plowed his fields.

Local officials have told him to share the tiller with five other farmers in his village.

The U.S. Department of Agriculture said in an assessment last week that the delta normally produces about 60 percent of Myanmar's rice and that the outlook for this year's crop is "very uncertain" after the storm flooded paddy fields with sea water, damaged irrigation systems, and destroyed seed supplies.

Myanmar's Agriculture Ministry says it is sending experts to train farmers and will send 140,000 baskets - 2,900 tons - of salt-resistant rice seed to the delta, a fraction of what is needed.

U.N. Undersecretary-General Noeleen Heyzer issued a plea Friday for donations of one million gallons of diesel fuel to help farmers run the tillers.

Urgency and frustration were shared by farmer Tin Yein, whose wife, five farmhands and eight buffalo died in the cyclone. He spent a whole day recently lined up with 200 other farmers in Labutta, where dozens of donated tillers in a government warehouse were waiting to be distributed.

Farmers applying for the mechanical tillers must be accompanied by their village headmen, said Tin Yein, and his local official arrived too late that day.

"Normally, planting season starts May 15. I'm already a month late," said the farmer, who has 70 acres. Each harvest produced about 30,000 baskets of rice, enough to feed his family and earn $9,000 a year in income.

Tin Yein also wonders if he can afford the mechanical tiller. Each machine uses two gallons of diesel per acre, and government rations restrict each person to five gallons of fuel every few days. Fuel is available on the black market but for twice the official price of $2.70 per gallon.

"I have no money for diesel," he said, "because every day I struggle just to buy food."