Nanotechnology can prompt optimize approaches of fertilization with micronutrients for higher returns especially with plants grown on degraded soils e.g., saline soil. Finding out a suitable alleviant to alleviate salinity stress effects of soils is one of the tasks of workers in the field of plant nutrition. A little is known about the joint effects of potassium humate as soil addition plus foliar spraying with magnetite iron Nanoparticles on plants grown on salt-affected soil. So, a field trial was performed during two successive seasons of 2018/2019 and 2019/2020 aiming at evaluating the effect of potassium humate as soil addition (applied or not) as main plots and exogenous application of magnetite Fe3O4 NPs as subplots at different rates i.e, 0.0, 0.1, 0.5, 10 and 20 ng L-1 on the performance of onion plants at period of 90 days from transplanting as well as at harvest stage. Thefindings indicate that onion plants fertilized with potassium humate had growth, yield and quality traits better than the corresponding plants untreated with potassium humate. Regarding foliar application, increasing added rate of magnetite Fe3O4 NPs up to 0.5 ng L-1 stimulated growth and yield quality of onion, while the values of all studied parameters gradually decreased with increasing rate of magnetite Fe3O4 NPs more than 0.5 ng L-1 taking in consideration that plantstreated with NPs at rates of 10 and 20 ng L-1 had performance less than the plants grown without any spray as a result of appearing toxicity of Fe3O4 NPs. Generally, the best performance for onion plants grown on saline soil was recorded when plants were treated with potassium humate and magnetite Fe3O4 NPs at rate of 0.5 ng L-1 as a combined treatment. Thus, it can be concluded that the best joint treatment in the current study may can prompt optimize performance of plants grown under salinity conditions.