Consumptive water use and plant growth of watermelon as affected by irrigation and N fertilization

The effects of irrigation frequency and N supply on leaf and root water status and plant growth were studied on watermelon. The plants were grown in plastic tanks performed as drainage lysimiters. Two watering regimes were obtained by irrigating once or twice weekly. N was supplied at two rates within each watering regime (200 and 400 kg ha(-1)). Leaf and root water potentials, gas exchanges and plant growth were followed throughout the growing season. The plant cycle was more affected by irrigation frequency (+20 d with the highest irrigation frequency) than by the N supply (+10 d with the high-N treatment). Seasonal water consumption varied between 350 (low-N and low-frequency) and 480 mm (high-N and high-frequency). Leaf water potential decreased with increasing N rate and in the low-frequency treatment (-0.6 vs. -0.7 MPa). The decline in root water potentials was less severe. Treatments had a remarkable effect on both plant growth as dry matter production and on leaf area per plant. During the growing cycle root density was significantly affected by watering regime and N supply (+35% with high-N and high-frequency); the highest N rate in the wettest treatment increased root density in the 0-20 cm soil layer by 25%.