The necessity of irrigation for sugar cane produced in Okinawa (Department of Agricultural Engineering)

1)本研究は宮古本島における1962年7月∿1969年2月の降雨記録と夏植えサトウキビの生産高から降雨量, 有効雨量および不足水量と単位面積当りの収量との関係を調べ, サトウキビに対するかんがいの必要性を検討したものである。2)夏植えサトウキビの全生育期に約3,300mmの降雨量があるが, 約1,300mmしか利用されず約500mmの水分量は不足している。3)土壌水分に不足をきたしているのは主に植え付け翌年の7月∿9月すなわち水分消費量およびサトウキビの伸長量が最大値を示す最盛期である。4)全生育期の降雨量と単位収量との間には明確な関係はないが, 最盛期においてはほとんど比例関係を示す。5)全生育期の有効雨量と単位収量の間にはほゞ比例関係があるが, 最盛期においてはこの関係がはっきりしている。6)全生育期の不足水量と単位収量の間にはほゞ反比例関係があるが, 最盛期においてはこの関係が明確にあらわれている。7)以上の結果沖縄における夏植えサトウキビの単位収量を上げるためにはかんがいは必要で, 植え付け翌年の7月∿9月においては特に必要である。1. This study was made to investigate the necessity of irrigation for the sugar cane. The study was done by examining the relations between the yield of the sugar cane and rainfall, availabla rainfall and soil moisture deficiency. Material for this study consisted of the yield of the sugar cane planted in summer and the data of rainfall for Miyako Island for July 1962 to February 1969. 2. Althouth there is about 3,300mm of rainfall at Miyako Island during all the vegetation period, the available rainfall is only about 1,300mm and about 500mm is deficient. 3. Soil moisture deficiency mainly occurs for July to September in the year following the planted year, when consumptive use of water and growth rate of the sugar cane are at maximum. 4. The relations between yield of the sugar cane per 10 ares and total rainfall for all the vegetation period are not clear, but it is almost directly proportional for the period from July to September in the year following the planted year. 5. Yield of the sugar cane per 10 ares is nearly in direct proportion to the total available rainfall for all the vegetation period and the relation is clearer for the period from July to September in the year following the planted year. 6. Yield of sugar cane per 10 ares is nearly inversely proportional to the total soil moisture deficiency for all the vegetation period and the relation is found more clearly for the period from July to September in the year following the planted year. 7. Therefore irrigation is necessary in order to increase the yield of the sugar cane planted in summer. Especially, it is absolutely necessary for the period from July to September in the year following the planted year