Using beneficial fungi and bacteria to plant growth may reduce the leaf nitrate content and improve the quality of produced food. This study aimed to evaluate the isolated and combined effect of inoculation with Azospirillum brasilense and Trichoderma hazianum at two electrical conductivities on the nutrition and production of hydroponic arugula cultivation. The experiment was designed in randomized blocks, in a 4 x 2 factorial scheme, with five replications. The treatments consisted of inoculations (non-inoculated, A. brasilense, T. harzianum and co-inoculation) and two electrical conductivities (1.4 and 1.6 dS m-1). The isolated inoculation of T. harzianum and A. brasilense produced a higher root fresh mass, while the leaf chlorophyll index was higher with the inoculation of A. brasilense, concerning the other treatments. The inoculation of A. brasilense reduced the nitrate content in the arugula leaves. The inoculations and co-inoculation of A. brasilense and T. harzianum improved the yield components and plant nutrition, reduced the leaf nitrate content and promoted the biofortification of arugula leaves with Zn and Fe. In addition, the inoculation with T. harzianum increased the P and S leaf content.

Lettuce and arugula are the most cultivated leafy vegetables in hydroponic systems in the world, and the little information about Azospirillum brasilense effects in research in this system makes it necessary to verify the best method of inoculation of these bacteria. Therefore, this study aimed to verify the beneficial effects of inoculation methods of A. brasilense on plant growth and nutrition of lettuce and arugula grown in the hydroponic system. The study was conducted in a greenhouse with 30% shading. A randomized block design with five replicates in a 4 × 2 factorial scheme was used. Four A. brasilense inoculation methods (non-inoculated, foliar application, nutrient solution, and nutrient solution + foliar application) and two leafy vegetable species - arugula and lettuce - were evaluated. All inoculation methods improved plant height, shoot fresh and dry mass, root fresh and dry mass, fresh leaf yield, leaf chlorophyll index, accumulation of nitrogen, potassium, calcium, sulfur, phosphorus, iron, manganese, and copper and reduced nitrate accumulation in shoot and root of arugula and lettuce. Inoculation via nutrient solution + foliar application of A. brasilense is the most suitable for hydroponic arugula cultivation because it provides greater fresh leaf yield. All inoculation methods increased leaf yield in hydroponic lettuce. Hydroponic arugula and lettuce plants showed greater accumulation of nutrients and plant growth with less nitrate accumulation in the shoot under inoculation with A. brasilense.