This group consists mainly of typical acid sulfate soils with extremely acidic condition ( plot at the surface < 4.5 ) They commonly occur along coastal plain on brackish water deposits. These soils have been used for paddy rice cultivation. However, without soil ameriolation, the yield is not good enough. Soils in this group are Chian Yai (Cyi), Mu Noh (Mu) and Onkarak (Ok).

Problems: Massive structure (crack when dry and stick when moist), very strong acid within 50 cm. depth, fixing plant nutrients and induce toxicity, lack of fresh water (acidity), water logging in rainy season.

Management for rice: Prepare and spread 1,000-2,000 kg/rai lime into moist soils, logging water into soils to leach acid and salt. Mix crop residue with soils and leave for 3-4 weeks or apply 50-70 days green manure with LDD organic fertilizer or 16-20-0 chemical fertilizer, 35-45 days after transplanting.Farm ponds are recommended to preserve water to be used in dry season or for second rice .

Management for vegetable or orchard: Raised bed to 6-8 meters wide with 1.0-1.5 meters width and 0.5-1.0 meters depth drainage canal. Spread 1,000-2,000 kg/rai lime into the top soils beds and logging water into soils to leach acid and salt. Soils improvement with 2-3 ton/rai compose or animal manure and chemical or LDD organic fertilizer. Mix 20-35 kg. compose fertilizer or animal manure with 7 kg of lime in 50*50*50 cm. pit for growing orchard. Apply chemical or LDD liquid organic fertilizer with compose and animal manure at vegetative growth, before and after harvest. Apply 1,000-2,000 kg/rai broadcast lime into acid sulfate soils.