“No one trusts the national government’s safety standards,” said Ichio Muto, 59, who farms organic mushrooms in Nihonmatsu, 25 miles northwest of the Fukushima Daiichi plant. “The only way to win back customers is to tell them everything, so they can decide for themselves what to buy.”

Mr. Muto is one of 250 farmers in Nihonmatsu who started a makeshift radiation-testing center at a local truck stop. On a recent morning, he and a half-dozen other farmers gathered in the truck stop’s tiny kitchen. There, they diced daikon, leeks and other produce before putting them separately into a $40,000 testing device that was donated by a nongovernmental group.

The farmers test samples of every crop they grow, and then they post the results on the Internet for all to see. Mr. Muto knows firsthand how painful such full disclosure can be: he destroyed his entire crop of 110,000 mushrooms after tests revealed high radiation levels.

But such efforts do not address one of the biggest questions asked by consumers: whether farming should be allowed at all in areas near the plant.

Farmers like Mr. Muto say they have no choice because they have seen little if any compensation and must make a living. So far, Fukushima Daiichi’s operator, Tokyo Electric Power, has offered full compensation only to farmers in the zones that were evacuated, which were within 12 miles of the plant, and a larger area to the northwest, where winds carried much of the fallout.

That approach is in line with the government’s basic stance since the accident: limiting as much as possible the size of the land area affected in this densely populated nation. Officials admit that many people question the wisdom of allowing farms so near the plant to operate, but they say that once they stop farming in an area because of radiation, it will take years to persuade the public to allow them to start again.