In a scenario of world population increase and climate change, an efficient use of water is key for agricultural production. Onion is one of the most profitable crops and can adapt to particular conditions of water stress. The objective of this research was to determine growing degree-days and accumulated radiation under non-stress conditions and yield of an F1 2000 hybrid of onion (Allium cepa L.) under water deficit (WD) and biofertilization in a semi-arid environment. An established nutrient requirement of 247 kg N, 240 kg P 2 O 5 (105 kg P), 240 kg K 2 O (199 kg K), and two irrigation factors were applied: normal irrigation with a daily and WD with a 3 d interval irrigation frequencies. The effect of biofertilization was evaluated through the inoculation of a microbial consortium (MC) in combination with four NPK fertilizer treatments. The crop accumulated 1334 degree-days and 1188 MJ m −2 ·d −1 at the time of harvest at 71 d after transplanting. The yield was 36 t·ha −1 , similar under both irrigation conditions; and the WD treatment resulted in a 35% water savings, a 47% and 65% increase in water use efficiency and modulus of elasticity, respectively. The MC resulted in a 50% NPK savings under non-limiting water conditions and produced a similar yield compared with the 100% NPK non-inoculated control. The lower irrigation frequency together with the 100% NPK fertilization dose without the MC and the use of the microorganisms and the 50% NPK treatment without water stress are recommended as agrosustainable practices for onion production.