Fertilizations and soil management for maintaining and increasing the productivity of cassava cultivated soils

Study on the Relative Responses to Fertilizer of Three Cassava Varieties in Warin Soil Series : To assess the relative potential response to fertilizer of a newly improved cassava variety MKU2-151 developed by cassava variatal improvement projects of the KURDI Kasetsart University, an experiment was established on Warin soil series in the farmer's field during normal rainy season from June 1985 to June 1986. A split-plot design was used having 3 main plots and 3 sub-plots each replicated three times. Three cassava varieties in main plot comprise MKU2-151, Rayong-1 and Rayong-3 whilst three fertilizing treatments in sub-plot were three rates of mixed fertilizer grade 15-15-15 i.e. 0,100 and 200 kg./rai. Fertilizer materials were divided into halves and applied two times by localized placement to each plant at 1 and 4 months after planting. Cuttings were planted in 6x7 sq.meter plot at 1x1 m. spacing. During plant growth stage, observations were made on cutting germination at 3 weeks after planting. At harvest at 12 months old, measurements comprise plant height and number of shoot and primary branch, fresh top and root weight, harvest index and starch content in fresh root. Comparing the varietal response, by average, the differences in number of shoot,primary root, harvest index, fresh top and root as affected by fertilization were not large or significant. However, cassava variety MKU2-151 out yielded Rayong-1 and Rayong-3 varieties among which variety Rayong-3 gave the lowest root yield. Regardless of varieties, addition of mixed fertilizer grade 15-15-15 at various rates i.e. 0, 100 and 200 kg./rai resulted in marked increase in all growth and yield observed except that of the starch content in fresh root in which the starch content decreased as fertilizer rates increased. In term of root yield, cassava variety MKU2-151 gave the highest response to fertilization followed by Rayong-3 and Rayong-1 varieties respectively. Regarding starch content in the fresh root, Rayong-3 variety contained significantly higher starch content than those found in MKU2-151 and Rayong-1 varieties.