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Salt stress limits the crop yield in semiarid regions. Appropriate nitrogen sources mitigate salt stress in some species. Horticulturists prefer to use ammonium when growing Italian zucchini cv. Caserta, because ammonium is cheaper compared to nitrate. In this study, we evaluated the comparative effects of nitrate and ammonium ions on the growth, physiological responses, and production of Italian zucchini under salt stress conditions. An experiment was conducted in a greenhouse, in a hydroponic system, with two nitrogen sources (nitrate and ammonium), combined with five levels of irrigation water electrical conductivity (0.5; 2.0; 3.5; 5.0, and 6.5 dS m−1), in 2 × 5 factorial scheme and randomized block design, with four replicates. Cultivation extended up to 50 days, and we access the growth, gas exchanges, photochemical efficiency, energy quenching, and production components. Ammonium causes flower abortion in Italian zucchini and no fruits formed, regardless of the salt stress conditions. The growth, gas exchanges, photochemical efficiency, and production of the nitrate-fed plants outperform ammonium-fed plants. The water with electrical conductivity greater than 3.5 dS m−1reduced growth, gas exchange, photochemical efficiency, energy efficiency, and production of the Italian zucchini fed with nitrate. Nitrate is appropriate to grow Italian zucchini under salt stress conditions.