The former prime minister is on trial for criminal negligence over the scheme and could face a decade in jail if convicted.
The charges were brought after the junta took power two years ago, claiming it had to restore order amid deadly protests against Yingluck's government.
Yingluck, whose older brother Thaksin Shinawatra was booted out as premier by a 2006 coup, is accused of failing to halt rampant corruption in the multi-billion dollar subsidy.
But the programme was panned by critics as financially ruinous and a naked attempt at vote-buying by the Shinawatra clan.
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The former head of the Thai Farmers' Network said farmers cooked the books alongside rice mill owners to claim the generous subsidy.
"They gave higher figures than the amount of rice they had," prosecution witness Ravee Rungraeung told the court.
"The extra money was shared between them. The rice mills had a computer programme -- one kept the real figure, and the other kept the figure they reported to the government... everyone knew it was going on."
The former premier denies wrongdoing and says the scheme was a genuine attempt to help rice farmers, mainly in the poor but populous north and northeast.
But the policy led to a 40 per cent fall in Thai rice exports after the government hoarded rice in a bungled attempt to push up its global price to fund the policy.
That led to massive stockpiles as markets turned away from the Thai grain, costing the country its title as the world's top rice exporter.
"We were the champion rice exporter for decades. But when the defendant's government bought rice at an unnecessarily high price... No one bought it from us anymore," Vichai Sriprasert, the head of the Thai Rice Exporters' Association, told the court.
Yingluck says the case against her is a politically motivated attack on her family.