Contrasting Effects of Uncharged and Nitrogen-Charged Chabazite-Zeolite Amendment on Physiology, Growth and Nutrient Uptake of Barley (Hordeum vulgare) Under Drought

Zeolite amendment to arable soils has been proposed as a promising strategy to improve soil quality and crop performance, particularly under drought. Nevertheless, empirical evidence remains scarce. In this study, we evaluated the effect of uncharged and nitrogen-charged chabazite-zeolite amendment on barley growth, nutrient uptake and physiology (i.e., stomatal conductance, photosystem II efficiency and SPAD) under drought. Barley plants were grown in the greenhouse for nine weeks under optimal conditions before inducing a moderate, 2-week drought period. Our results show that amending soils with uncharged zeolite had no effect on the crop yield and nutrient uptake under water-sufficient conditions. In contrast, applying nitrogen-charged zeolites resulted in significant yield improvements (+90%) and nutrient uptake (+60–90%) as compared to control and uncharged zeolite amendment. Further, we observed a disproportional high uptake of calcium (+260–280%) as compared to other base cations with nitrogen-charged zeolite amendment, resulting in significant shifts in elemental ratios. Both zeolite amendments helped maintain stomatal conductance under drought, while only uncharged zeolite also mitigated declines in photosystem II efficiency under water-limited conditions. Against our anticipation, we observed significant reductions in aboveground biomass (−15%) as well as nitrogen (−20%), phosphorus (−29%) and magnesium (−25%) contents in the treatment receiving uncharged zeolite as compared to the unamended control under drought conditions. This suggests that a significant amount of nutrients must have been immobilized in the zeolite’s mineral structure. Therefore, while nitrogen-charged zeolite amendment represents a promising farming management strategy to improve crop productivity, uncharged zeolite amendment may lead to unintended negative outcomes. Our results highlight the need for further research to evaluate the pedoclimatic factors that determine the agronomic effectiveness of zeolite amendments.