Chloride fertilization increased maize shoot chloride levels and yield depending on soil moisture conditions

Growing crops on sandy soils becomes especially difficult during summer when rainfall is scarce, making drought conditions even more severe. The micronutrient chloride (Cl^-) can accumulate in plant shoot tissue reaching contents that are typical for macronutrients, assumed it is supplied and taken up in appropriate amounts. When this happens, it can act as an osmoticum, facilitating shoot hydration, reported previously under drought. So far, this cascade of events was only reported under in-door conditions with pot experiments and to the best of our knowledge, not under field conditions. Under field conditions, uncontrollable environmental effects may limit the positive processes. Therefore, we conducted a field trial to investigate, how chloride application may enhance drought tolerance during the whole growth period of maize grown for silage. The field trial was conducted on a sandy soil in northeastern Germany subjecting maize to different Cl^--fertilization treatments (0, 125, and 250 kg Cl^- ha^- 1 a^- 1; given together with calcium as counter cation) in the years 2020 and 2021. The setup allowed for the assessment of Cl^--fertilization of (i) water status, via shoot water content and rain use efficiency (RUE; kg FM ha^- 1 mm^- 1 per vegetation period), and (ii) biomass yield under field conditions. We found a significant increase of Cl^--content in shoot tissue following the Cl^--fertilization (125 and 250 kg Cl^- ha^- 1, respectively) in both years. However, only in the year 2021, the higher Cl^- plant tissue content (4.6 g Cl^- kg^- 1 DM under a treatment of 250 kg Cl^- ha^- 1) was associated with significantly higher shoot water content at harvest and rain use efficiency. In the year 2021, were precipitation in spring was sufficient for the crop water demand, chloride fertilization supported shoot hydration by acting as an osmoticum." In this year plants treated with 250 kg Cl^- ha^- 1 showed a significantly higher fresh biomass yield. However, the improved water status did not result in a stimulated carbon assimilation. But chloride-fertilization decreased the dry matter content of silage maize. For the first time, this study showed that Cl^--fertilization supported silage maize to cope with water scarcity on sandy soils.