Abstract
The effects of water table control on the growth of spring- and summer-sown carrots were evaluated in a field with andosol soil. Carrot cultivars, 'Koyo-2-gou' for spring-sowing and 'Hamabeni-5-sun' for summer-sowing, were grown on ridges of width 70 cm and height 12 cm. Treatments of water table control were as follows: (1) maintained at 15 cm below the ridge surface until seedling emergence (i.e. USE15) and (2) maintained at 42 cm below the surface after USE15 (i.e. M42) , (3) maintained at 52 cm below the surface after USE15 (i.e. M52) , (4) maintained at 52 cm below the surface for one month after USE15 (i.e. M52M) and (5) not controlled (Control). The seedling emergence rate was higher for treatments with the water table controlled than for the Control. At the five-leaf stage, the growth of Control and USE15 were less than for M42 and M52 treatments. For spring-sowing, the root weight at harvest time was higher for M52 than the Control treatments. Furthermore, when there was heavy rainfall, the incidence of root cracking was lower for M52 than the other treatments because of much less fluctuation in soil moisture for M52. Even when the water table was controlled, the root form was long and thin when the temperature in the later growth stage was high, as the root form depends on temperature. For summer-sowing, the treatment of water table that were maintained at 52 cm depth were discontinued when it rained after about one month passed since the treatment was started; however, any further rain after this time did not result in injury from excess-moisture and root weight was increased. The incidence of root cracking was low even for treatments in which the water table was temporarily controlled.
