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In the present study, the interactive effect of irrigation and nitrogen (N) on biomass and physiological characteristics of amaranth and the influence of zeolite in this interaction were investigated. A 2-year field experiment was conducted as split-plot factorial in a randomized complete block design in three replicates. The main factor consisted of different levels of deficit irrigation (DI) such as irrigation after 40 (DI 1), 60 (DI 2), and 75% (DI 3) depletion of soil available water. The subplots derived from a combination of different factors including nitrogen rates (zero (N 0), 80 (N 1), 160 (N 2), and 240 (N 3) kg urea ha −1) and zeolite levels (zero (Z 0) and 10 (Z 1) ton ha −1). Reduction of soil moisture resulted in a decrease in the amount of chlorophylls, carotenoids, protein, maximum quantum yield of photosystem II (F v /F m ratio), and biomass of amaranth. In contrast, it resulted in the increase of antioxidant enzyme activity, soluble carbohydrates, and proline. However, nitrogen application led to an increase in the contents of chlorophyll, carotenoids, protein, antioxidant enzyme activity, F v /F m ratio, and biomass of amaranth and a decrease in the soluble carbohydrates and proline. Zeolite treatment by increasing the content of chlorophylls (16%), carotenoids (19%), protein (25%), F v /F m ratio (11%) as well as enchantment of soluble carbohydrate content and antioxidant enzyme activity and by decreasing the proline content (40%) moderated the adverse consequences of water-deficit stress and improved biomass of amaranth. In general, the use of zeolite along with the lowest rate of nitrogen fertilizer (80 kg urea ha −1) reduced the harmful effects of the oxidative stress caused by water scarcity and improved the growth conditions for the plant and thus produced maximum biomass of amaranth plant under moderate and severe deficit irrigations.

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This study’s primary purpose was to investigate the possible amelioration of limited irrigation conditions by mycorrhiza (AMF), vermicompost, and green manure for lingrain plants. This experiment was accomplished as a factorial based on the completely randomized design with three replications. The first factor was green manure (without green manure and with Trifolium pratense as green manure); the second factor consisted of Rhizophagus irregularis mycorrhiza, vermicompost, a combination of mycorrhiza and vermicompost and none of them, and also the third factor was irrigation regime (full irrigation and late-season water limitation). Green manure, vermicompost, and mycorrhiza single-use enhanced the plant’s underwater limitation conditions compared to the control. However, vermicompost and green manure or mycorrhiza developed a positive synergistic effect on most traits. Combining green manure with the dual fertilizer (mycorrhiza + vermicompost) resulted in the vermicompost and mycorrhiza synergistic effects, especially under limited irrigation. Consequently, the combination of green manure, mycorrhiza, and vermicompost experienced the highest amount of leaf relative water content, root colonization, leaf nitrogen, chlorophyll a, chlorophyll b, carotenoids, antioxidant enzymes activity, grain yield, and oil yield, which would lead to more resistance of plants to limited irrigation conditions.

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