BAAC President Apirom Sukprasert said the number of farming households signing up for the scheme exceeds the target by 90,000, totalling 4.4 million, so an additional 2.6-billion-baht budget is required.
Even more funds could eventually be sought because some farmers in southern areas have yet to register, he said.
Typically, rice in the south is harvested a few months later than in other regions.
The government's farm aid measures include price guarantees for certain crops.
Earlier, officials budgeted 24.8 billion baht for subsidies in the 2018-2019 crop season that started last November, aimed at 4.31 rice farming families who delayed paddy sales to stabilise prices.