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To mitigate the adverse effects of excessive mineral nitrogen fertilization on vegetative crops, it is imperative to decrease the doses of mineral nitrogen applied and explore alternative nitrogen sources to fulfill the plants' requirements. Therefore, a field experiment was conducted over two consecutive seasons (2022 and 2023) to examine the impact of bio fertilizer (either with seed inoculation with Azospirillum brasilense or without inoculation at 8 kg ha-1), as main factor, on the growth and productivity of spinach plants. The plants were subjected to varying doses of mineral nitrogen (25%, 50%, 75%, and 100% of the Nitrogen Recommended Dose NRD) as sub main treatments, while different liquid organic fertilizers none (control), compost tea at rate of 48 L ha-1, liquid biogas at rate of 48 L ha-1and vermicompost extract at rate of 48 L ha-1were evaluated as sub-sub treatments. Regarding bio fertilization, the results revealed that all growth and productivity parameters, including yield (Mg ha-1), plant height (cm), and No. of leaves plant-1 as well as the chemical composition of leaves, (N, P, K %) attained their peak values when treated with Azospirillum brasilense inoculation compared to untreated plants. For example, yield of plants treated with bio fertilization were 24.51 and 25.92 Mg ha-1 for 1st and 2nd seasons, respectively,while the yield of the plants grown without bio fertilization were 21.18 and 22.66 Mg ha-1 for 1st and 2nd seasons, respectively. On the other hand, as the nitrogen recommended dose (NRD) decreased, the values of these parameters declined. Among the liquid organic fertilizers studied, biogas emerged as the most effective (yield values of 24.79 and 26.8 Mg ha-1 for 1st and 2nd seasons, respectively), followed by vermicompost extract and then compost tea, all surpassing the control (yield values of 20.03 and 21.61 Mg ha-1 for 1st and 2nd seasons, respectively). Importantly, the presence of bio fertilizer alongside any of the liquid organic fertilizers under 75% NRD resulted in higher values for growth and productivity parameters compared to plants fertilized with 100% NRD without bio fertilizer and liquid organic fertilizer. Concerning soil properties, the interaction among treatments did not have a significant effect on the studied properties. However, there was a noticeable relative improvement in fertility parameters due to the application of both bio fertilizer and liquid organic fertilizer. Finally, it is recommended to incorporate Azospirillum brasilense inoculation and biogas, vermicompost extract, or compost tea as alternatives to mineral nitrogen fertilization, especially at lower NRD levels, to optimize spinach production while maintaining soil fertility.
Shabana et al. (Sat,) studied this question.