Growth rates of three cassava varieties (Manihot esculenta Crantz) under varying population densities

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Abstract
Summary: The effect of variety and spacing on growth, development and yield of cassava and the relationship between growth, development and yield in three cassava varieties were investigated during the 1971 and 1972 growing seasons. Msitu Zanzibar outyielded Aipin Valenca and these two varieties in turn outyielded Amani 4026/16. The varietial effect was associated with differences in the rate of bulking. Increase in plant density led to an increase in the yield of tubers per hectare, the mean increase with increasing plant density being greater in Aipin Valenca than in either Amani 4026/16 or Msitu Zanzibar. Increase in plant density from 12000 to 18000 plants/ha led to a decrease in root tuber yield in Amani 4026/16. The calculated optimum density for maximum yield was 6·7, 6·4 and 5·6 plants/m2 respectively for Msitu Zanzibar, Aipin Valenca and Amani 4026/16. The spacing effect on tuber yield was associated with differences in the rate of bulking. Aipin Valenca was usually taller than the other varieties and, in general, increase in plant density increased the height of the plants.Final total dry matter/m2 was greater in Aipin Valenca and Msitu Zanzibar than in Amani 4026/16 and, with the exception of the last variety, total dry matter/m2 increased with increasing plant density. Total dry matter produced per plant was greater in Msitu Zanzibar than in Aipin Valenca and these two varieties had greater dry weight per plant than Amani 4026/16. In the three cassava varieties, the dry weight per plant increased with decreasing plant density.A greater proportion of the total dry matter was diverted into the root tubers of Aipin Valenca and Msitu Zanzibar than in Amani 4026/16. Generally, increase in plant density decreased the proportion of total dry matter diverted into the root tubers. Mean crop growth rate increased with increasing plant density while mean net assimilation rate and relative growth rate decreased with increasing plant density. Amani 4026/16 and Aipin Valenca had a greater mean crop growth rate and a greater net assimilation rate than Msitu Zanzibar. Mean relative growth rate was greater in the latter than in the former two varieties.Leaf area index and leaf area duration were greater in Msitu Zanzibar than in the other two varieties and these tended to increase with increasing plant density.There was a close and positive relationship between rate of bulking and root tuber yield and the lack of a positive relationship between leaf area duration and tuber yield is discussed.