石垣島のサトウキビ収量と気象の関係 : 時代による変化

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In Ishigaki Island of Nansei Shoto, the land improvement has begun by the government in 1976, because of the serious drought occurred in 1971. The sugar cane fields of uplifted coral reef were included in the areas of land improvement, because these fields with shallow soil layers were very weak for the drought. Therefore, the soils from the areas of "Kunigami Maji" have been dressed and mixed in the fields of the uplifted coral reef areas. Then, irrigation system with sprinkler was set in the land improvement areas. The relation between sugar cane yield and degree of drought which is expressed by water deficit (d) (mm/year) by the Thornthwaite method (1948) has examined in Ishigaki Island for the data from 1952 to 1987. The period was divided into 3: (1) Period I (1952-1959), in which the productivity was extremely low and yield per unit area (t/ha/year) was affected completely by drought, (2) Period II (1960-1977), in which the yield per unit area became higher through the introduction of cultivar NCo 310, and (3) Period III (1978-1987), in which the unit area productivity became slightly higher than the second period. Water deficit about 200mm/year did not cause serious drought for the productivity of sugar cane. It is considered that this fact was reflected by the land improvement including the irrigation system, the soil dressing and the shelter belts. The average yield of unit area per year in the three periods mentioned above was: In Period I, 37t/ha; in Period II, 66t/ha; and in Period III, 70t/ha. From Period II to III, the unit productivities increased less than 6%, against to the sharp increase (80%) from Period I to II. It is therefore suggested that higher productivity is expected in future through i) giving more organic fertilizer, ii) introduction of new varieties, iii) protection from soil erosion by heavy arainfall and drainage water, and iv) protection from wind damage and soil erosion by denser arrangement of shelter belts.
駒澤大学の論文

石垣島のサトウキビ収量と気象の関係 : 時代による変化

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