Seasonal Changes in Growth and Yield of Sugarcane Plants in Southwestern Islands of Japan : I. Progress of leaf-emergence on main stem

Abstract

We traced the progress of the leaf-emergence on the main stem of sugarcane plants and examined relationships between seasonal changes in the leaf-emergence and climatic factors, effective heat unit summation for unfolding leaf turning point of leaf-emergence rate and leaf number at the beginning time of floral induction. Four varieties, F160, NCo310, H37-1933 and H32-8560, were used as materials and were planted monthly from June in 1980 to May in 1981 in Ishigaki Island, southwesternmost island of Japan. Results obtained were as follows. 1. Quadratic regression relationships were found between mean soil temperature at a depth of 5 cm and days from planting to first emergence (Fig. 2). By those equations obtained in the four varieties, it was estimated that the optimum soil temperature minimizing the days to the first emergence was 31°to 33°C. 2. The seasonal changes showed in the progress of the leaf-emergence on the main stem were summarized as follows: May to September; period of rapid increase in the leaf-emergence rate, October to November; period of gradual increase in the rate, December to February; period of slight increase in the rate, March to April; period of gradual increase in the rate (Fig. 3). 3. Mean air temperature was significantly correlated with leaf-emergence rate during unfolding 20 leaves on the main stem (Fig. 5, Table 1). Using linear regression equation (y=ax-b) obtained between the leaf-emergence rate (y) and mean air temperature (x), it was derived that lower limit of effective temperature and effective heat unit summation for unfolding leaf were given b/a and l/a, respectively. In three varieties of F160, NCo310 and H37-1933, the lower limit of effective temperature and effective heat unit summation were 11.1-11.4°C and 81.3-90.9°C, respectively. Those in H32-8560 were 9.9°C and 106.4°C, respectively (Table 2). 4. The leaf-emergence rate on heading stems during two months before unfolding flag leaf was faster than that on non-heading stems during the same period (Fig. 4). Therefore, it was suggested that turning point of the leaf-emergence rate existed about two months before unfolding the flag leaf when coincided with time of flower bud differentiation. 5. In the plants of NCo310 and H37-l933 planted in June and July of 1980, some stems headed by January in 1931, others did not. The difference of heading among stems is considered to arise from plant age at the beginning time of floral induction, when is estimated to be at the beginning of September in Ishigaki Island. From relationships between leaf number on the stem at the beginning of September and heading percent by January in 1981, it was satisfactory to consider that plant age in the leaf number at the time of ripness to flower was 6 in H37-l933 and was 15 in NCo310 (Table 3).