Response of cucumber to drip irrigation water under a rainshelter

The experiments were conducted to evaluate the effects of different amount of irrigation water on the growth and yield of cucumber under a rainshelter from May to October for two seasons in Yamaguchi University, Japan. For spring experiment, the amount of irrigation water applied was 0.50, 0.75, and 1.00 times of water surface evaporation (Ep) measured by a standard 0.2 m diameter pan, regimes were denoted as Ep0.50, Ep0.75, and Ep1.00. Same method for autumn experiment, regimes were denoted as Ep0.75, Ep1.00, Ep1.25, Ep1.50, and Ep1.75. The results showed that amount of irrigation water significantly affected plant growth and fruit production. Plant height and biomass increased, but specific leaf weight (SLW, g/m2) decreased with increasing amount of irrigation water. The SLW and leaf blade water content were directly response to the applied irrigation water and soil water content, and the SLW of cucumber was decreased with the leaf blade water content increasing. The amount of irrigation water had significant effects on decreasing the leaf temperature, and the largest differences in leaf temperature with Ep1.75 regime were 2.1, 2.6, 4.7, and 5.8 °C for Ep1.50, Ep1.25, Ep1.00, and Ep0.75 regimes at noon. Plant biomass (dried stem and leaves), the number of lateral branches and production were highest for spring regime Ep1.00 and autumn regime Ep1.75 that the plant received the most amount of irrigation water. During the cucumber growth period of 5 months from May to September for the plant and fruit growth, the crop coefficient K should be more than 1.00 that is a guideline and it is better between 1.00 and 1.50, and the average irrigated water of 4.0–5.5 mm/day is necessary for plant and fruits growth. Therefore, applying water by drip irrigation in relation to the amount of water evaporated from a standard 0.2 m diameter pan is a convenient, simple, easy, and low cost method under a rainshelter.