Management of irrigation and fertilization in greenhouses, if not done correctly, can cause soil salinization. The use of water treated with very low-frequency electromagnetic resonance fields (WVLF) can reduce salinization effects on the photosynthetic and biometric systems. Thus, the purpose of the research to evaluate the metabolism of photosynthesis and the impact of WVLF on the cultivation of tomato crops subjected to different levels of fertigation. For this, the gas exchange parameters were evaluated, as well as chlorophyll a fluorescence, sugar contents, sucrose, chlorophylls, and phaeophytins and fruit production. The gas exchange parameters had greater activity when subjected to irrigation with electromagnetic water, consequently the production of sugar and sucrose increased. Photosynthetic System II showed less salinity effect, being favored by very low-frequency electromagnetic resonance fields. The production increased by 20% for the dose of 2.5 d·Sm⁻¹ of WVLF reducing the effects caused by higher doses. Hence, the induction of water by electromagnetic fields can provide less damage to the photosynthetic system and to the cultivation of the tomato crop when subjected to saline stress and, consequently, favor the production of fruits by this crop under such conditions.