Causative Factors of Low Water Use in a Typical Upland Irrigation District of West Japan

An on-farm questionnaire survey was carried out in a typical upland irrigation district of western Japan to investigate factors which influenced water use during the 1994 early crop growing season. The survey included irrigation frequency, type and area of crops grown, farm labour, irrigation equipment and others ; the variables were investigated by a form of quantification theory (`suryouka-riron 1 and 2') . The partial correlations for the full-time farm households indicated that water use was most influenced by crop type while farm labour was the most influencial factor in the part-time farm households ; cropped area was least sensitive to water use in both cases. The combined farm households indicated an optimum irrigation frequency of 5 to 6 irrigations per month. About two-thirds of the irrigators preferred applying water during the morning and evening periods possibly to avoid the extremely hot, afternoon, weather usually associated with summer. Quantification method type 2 indicated that irrigation frequencies of 4 to 7 times per week were mostly on farms of about 0.1 to 0.4 ha which also grew various crops as the main crop. 3 to 4 irrigations per week were mostly on leafy vegetables usually grown on farms of about 0.5 to 0.9 ha and with water mostly applied through drip hoses. Irrigations of 1 to 2 times per week were usually on wet fruits mostly grown on farms of about 0.1 to 0.9 ha with water mostly applied through drip hoses and normal hoses. Irrigations of 1 to 2 times per month were mostly on grass (lawn) usually grown on farms of more than 1 ha with water mostly applied through sprinklers. The various on-farm factors identified in this study were hence associated with crop production, farm management and socio-economics ; their influence on water use may have resulted in less water usage compared to the designed water duty of crops grown in the district.