A study on cassava [Manihot esculenta] - Rice [Oryza] double cropping in upper paddy field [at Ban Sok-ta-ling, Amphoe Ban-phai and Ban Muang, Ban Sam-chan, Amphoe Muang, Changwat Khon Kaen, Thailand]

The study consisted of 3 experiments and one survey. The results showed differences in both root yield and overall growth of cassava grown at different locations. Cassava grown at Ban Sam Jan and Ban Phai gave equivalent yields, but lower yield was obtained at Ban Moung. Discrepancy in yields of cassava grown at three sites could be attributed to the differences in soil fertility, particularly potassium. Performances of cassava grown in upper paddy fields in different positions along the toposequence were compared in the second experiment. There was no significant difference in the root yield of casava planted at the 3 spots (i.e., higher, middle, lower) of upper paddy fields. However, the final yield of cassava harvested from the "lower" part of the field seemed to be lowest presumably due to premature loss of leaves by diseases. The early growth of cassava was better for this "lower" paddy fields, presumably due to the higher available nitrogen and phosphorus in the soil. Optimum soil moisture content and high potassium were the reason for consistently good growth of cassava on the highest part of the upper paddy field. The third experiment evaluated the effect of cassava residue on yield of the subsequent rice crop. There was no significant difference among yields of rice grown alone or after cassava. To determine the impact of growing cassava after rice on the farm households, a survey was conducted in a village known to have long establishment of rice-cassava system (i.e., Ban Soak Taling). The results showed that the rice-cassava cropping pattern was quite important to the low-income farm households with small upland and/or no other alternative activities. However, growing cassava on the upper paddy field appeared to be extensively adopted in the drought season when rice transplanting could not be done. In such circumstances, cash obtained from cassava grown in upper paddy fields became an important component in the total household income