Effect of Nitrogen Sources on the Phenological Phases of Italian Zucchini Under Salt Stress

Salt stress is one of the most significant abiotic factors limiting plant growth and crop productivity worldwide, especially in arid and semiarid regions. We aimed to investigate nitrogen fertilization strategies using nitrate and ammoniacal sources during different phenological phases of Italian zucchini cv. Caserta to alleviate salt stress. The experiment was conducted in a greenhouse using a randomized block design with four replications. The treatments were as follows: T1 = entire cycle with nitrate nitrogen + 0.50 dS m−1 (control); T2 = entire cycle with nitrate nitrogen + 4.5 dS m−1 (salt stress); T3 = 50% nitrate nitrogen + 50% ammoniacal nitrogen + 4.50 dS m−1; T4 = ammoniacal nitrogen during the vegetative phase + nitrate nitrogen during the reproductive phase + 4.50 dS m−1; T5 = nitrate nitrogen during the vegetative phase + ammoniacal nitrogen during the reproductive phase + 4.50 dS m−1; T6 = entire cycle with ammoniacal nitrogen + 4.50 dS m−1. Under salt stress conditions, Italian zucchini cv. Caserta showed a leaf area of 5783 cm2 compared to an average of 4521 cm2 under salt stress. Similarly, production per plant reached 1361 g in the control, while under salt stress it averaged only 442 g. However, under salt stress, T2 resulted in higher production compared with T3, T4, T5 and T6, although it was still lower than T1. The use of ammoniacal nitrogen throughout the cycle or during the reproductive phase caused flower abortion. Under salt stress, the application of ammoniacal nitrogen during the vegetative phase (T4) or a 1:1 ammonium–nitrate ratio throughout the cycle (T3) resulted in yields that were comparable to those achieved with nitrate-only fertilization (T2).