Abstract
In order to determine the drip irrigation zone adequate to control drought stress, we investigated the influence of drought stress under different ratios of the irrigation zone on citrus trees. The results showed that there was a clear correlation between the irrigation zone and drought stress of trees. It was indicated that, in the case of young trees, a greater than 50% irrigation zone out of the root zone was required in order to protect them from overdryness. In the case of adult trees, over 19.5% was necessary for 13-year-old ‘Shiranui’, and over 14.2% for 21-year-old ‘Haraguchi-wase’. Drip tubes should be placed within 100 cm from trunks where fine roots are densely distributed. An appropriate irrigation time was estimated to be 20 minutes in granite soil, 20–60 minutes in basalt soil, and 60 minutes in andesite and volcanic ash soils. In addition, it was indicated that the dripper interval should be more than 20 cm in granite soil and more than 30 cm in the three other kinds of soil to reduce water wastage.
