Effect of Zeolite on Nitrogen Use Efficiency and Physiological and Biomass Traits of Amaranth (Amaranthus hypochondriacus) Under Water-Deficit Stress Conditions

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 (DI1), 60 (DI2), and 75% (DI3) 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.