Rice Cultivation under Drip Irrigation with Plastic Film Mulch in the Kanto Area of Japan

A drip irrigation system with plastic mulch film was evaluated in terms of growth, yield, and water productivity (WP) using three leading paddy rice cultivars (Japonica) in the Kanto area of Japan. A cultivation with drip irrigation and plastic film mulch in the upland field (DI) and continuous flooding cultivation in a paddy field (CF) were conducted in 2015 (DI) and 2016 (DI and CF). The amounts of irrigation and total water supply (irrigation and precipitation) were 715 mm, 599 mm, and 905 mm and 1620 mm, 1379 mm, and 1687 mm for DI in 2015, DI in 2016, and CF in 2016, respectively. The percentages of irrigation for DI in 2015 and 2016 compared to those of CF were 79% and 66%, respectively. The grain yields in 2015 were higher than those in 2016 for DI. The DI in 2016 showed significantly lower grain yields compared to those of CF, representing 74% to 85% of the CF which were attributed to lower leaf area indexes in DI. There was no significant difference in WP between DI and CF, between years and among cultivars, ranging from 0.25 to 0.30 kg m^-3, showing an offset of the reduction in irrigation water by lower yields in DI. The rice cultivation system under drip irrigation with plastic film mulch showed a large water-saving effect, no physiological damage due to water stress and a slight reduction of grain yield compared to that of the paddy field.