EFFECTS OF GROWING-SEASON AND IRRIGATION REGIME ON GROWTH, WATER-USE,AND YIELD OF ROSE PLANTS

The effects of growing season and irrigation regime on growth, water u se (soil evaporation and transpiration), and yield of rose plants were investigated. Rooted cuttings of 'Carl Red' roses were grown in a gre enhouse and watered at the four following soil moisture tensions, i. e . 3, 10, 32, and 50 kPa (pF 1.5, 2.0, 2.5, and 2.7, respectively) duri ng summer, fall-winter, and winter-spring seasons. In all seasons the best plant growth was obtained with the 3 kPa treatment which simultan eously coincided with the largest amount of water use. In the other tr eatments, as the soil moisture tension was increased, the amount of wa ter use decreased and growth was inhibited. There was no effect of irr igation regime on water use per unit plant growth. The amount of water use per ten days varied within and among seasons. We postulate that t he variations among seasons were caused by irradiation and temperature changes; whereas, those within season were caused by the difference i n plant size, especially the leaf area. As the soil moisture tension w as increased, the days to flowering from pinching or harvest increased , and the number, quality and marketability of cut flowers decreased. Based on these results, we recommend that the optimal soil irrigation tension for greenhouse rose production is kept at 3 kPa throughout the growing season.