O nitrogênio como mitigador do estresse salino nas mudas de maracujazeiro amarelo

The poor chemical quality of water, especially in arid and semiarid regions, almost always precludes the practice of irrigated agriculture, thus demanding the adoption of techniques that mitigate the deleterious effects of excess salt on soil and plants. The aim of this research was to evaluate the effectiveness of nitrogen fertilization in mitigating the negative effects of excess salt in irrigation water on the growth of yellow passion fruit seedlings grown in a greenhouse in plastic tubes containing 0.65 dm3 of substrate. The treatments were organized in randomized blocks, in accordance with a 5 × 3 factorial scheme – five electrical conductivities of irrigation water (0.3, 1.0, 2.0, 3.0, and 4.0 dS m?1) combined with three levels of nitrogen fertilizer (no nitrogen fertilization and 150 mg dm?3 of N derived from either ammonium sulfate or urea). Evaluations were performed 80 days after sowing and consisted of measuring the seedling height, stem diameter, number of leaves, leaf area, leaf nitrogen content, leaf concentration of chlorophyll a and b and total chlorophyll, specific leaf area, leaf area ratio, and Dickson quality index. An increase in the electrical conductivity of irrigation water hindered the production of yellow passion fruit seedlings. Nitrogen fertilization, with urea or ammonium sulfate, mitigated the effects of irrigation water salinity and favored the growth and quality of yellow passion fruit seedlings. Yellow passion fruit seedlings with a minimum quality standard (DQI) can be produced with irrigation water with salinity of 1.8 dS m?1, which means they can be considered as moderately sensitive. The higher quality provided by nitrogen to the yellow passion fruit seedlings made them more tolerant to salinity, allowing the use of water with salinity of 2.1 and 2.5 dS m?1 under fertilization with ammonium sulfate and urea, respectively.