Half of the surface of the Mekong Delta in Southern Vietnam has very acid soils (pH 3), due to the oxidation of pyrite into sulphuric acid. In these regions farmers are facing numerous problems, such as the toxic nature of the aluminium ion, the dwindling supply of available phosphates and the unsatisfactory growth of roots. Two regions of the delta have been studied:
- Hoa an: the soils are rich in phosphate, and they allow only one rice harvest a year, resulting in an extremely low standard of living.
- O mon: the soils are flooded in the rainy season and they are less oxidized and less acid. Three harvests a year are possible, but the yield of the second and third harvest is low because of diseases and the dessication of the top soil.
Local authorities suggest the cultivation of sugar cane or pine-apple during the dry season in Hoa an, while opting for the intercropping of soya or 'mungo' beans between two rice crops in O mon.
The author recommends better irrigation and considers the cultivation of sugar cane or pine-apple without any advantage, compared to the cultivation of rice. On the contrary, according to the author, a lot is to be gained by the intercropping of soya and beans.