A study on planting season, varieties and harvesting times affection biochemical properties in cassava roots was conducted on six cassava varieties; Rayong 1, Rayong 60, Rayong 90, Rayong 5, Kasetsart 50, and CMR33-57-81. The data collection was harvested at 6, 8, 10, and 12 months after planting. This experiment was studied on Warin soil series (loamy sand) at Kham Talaesoa Farm, Nakhon Ratchasima in early (May) and late (October) rainy season, 1996. The result of this study indicated that Rayong 90 and Kasetsart 50 gave high average starch content both early and late rainy planting season. Planting in early and late rainy season gave highest starch content at 8 and 12 months after planting, respectively. There were significant differences in the average content of starch among planting season.

Biochemical properties in cassava roots like lipid and protein decrease starch viscosity, (Leach et al., 1959) and cause the rancidity of cassava starch. Phenolic compounds causes darkening of cassava starch. Moreover, the toxicity of cyanide and dense fiber arise. Which make difficulties in industrial starch production process. (Hughes et al., 1994). The result of the study found that Rayong 90 gave low lipid, protein, and fiber content. While Rayong 5 gave low cyanide and phenolic compounds content. Both lipid and phenolic compounds content were low at 6-8 months after planting. Protein and fiber content were low at 12 and 10 months after planting, respectively. Cyanide content was low during rainy season and high during dry season. Soil moisture content negatively correlated with cyanide content. There were no significant differences of the average contents of lipid, cyanide and phenolic among planting season.

Amylose content and amylose size which determine physicochemical properties of starch (Leach et al., 1959) were no significant differences among cassava varieties. Harvesting cassava at early rainy season caused the reduction of amylose content and amylose size, due to their regrowth whilst amylose hydrolysis was processed to be glucose and used as the energy source to produce their vegetative growth.