Effect of varieties, harvesting dates, rates of fertilizer on cassava yield and starch quality

Varieties, harvesting times and fertilizer rates have been reported as the cause of varietal differences in the yield of many crops. This work reports on the effects of these factors on root yield and quality of extracted starch of cassava (Manihot esculenta Crantz.). Three experiments were conducted at the Rayong Field Crop Research Center, Rayong Province, to compare the yield and starch quality of a large number of cassava clones. This was an in preliminary yield trial the clones were compared with Rayong 1 and Rayong 90. The clone CMR 35-65-14 was the highest root yield (5480 kg/rai) and CMR 35-22-196 was the highest in starch content (23.8 percent). The quality of starch from CMR 35-21-9 was the highest as demonstrated by the highest paste peak viscosity (337 RVU/3 gm at 14 percent moisture content). A further study was undertaken to investigate the yield and starch quality of cultivars namely Rayong 1, Rayong 5, Rayong 60, Rayong 90 and Kasetsart 50 at different harvesting times (6, 8, 10, 12, 14 and 16 monthes) during 1994 to 1996 at the same research center. By using Split Plot Design in Randomized Complete Block (RCB) 3 replications, it was found that among cultivars Rayong 90 gave the highest yield. The yield increased as the age of root increased. Rayong 1 and Rayong 60 root contained the lowest starch content. The starch content of all cultivars and their paste viscosity decreased in high rainfall periods. Fiber in the roots increased as the root growth progressed and after a period of high rainfall. Other physico chemical properties such as granular size, amylose content, and paste clarity showed no significant difference between varieties. The effect of fertilizer (15-15-15 formular) rates (0, 50, 100 kg/rai) on Rayong 1, Rayong 5, Rayong 60, Rayong 90 and Kasetsart 50 was evaluated by Split Plot Design in RCB 3 replications. Increasing rates of fertilizer resulted in increasing fresh root yield and root dry matter content, but no effect on chemical properties extracted starch was observed.