Exploring the potential for top-dressing bread wheat with ammonium chloride to minimize grain yield losses under drought

The frequency and severity of drought is predicted to rise in many parts of the world. Considering that drought is the main constraint on rain-fed wheat crop production, both agronomic and genetic measures have been taken to minimize yield losses under drought. Beyond its role as a micronutrient, chloride also acts as an osmoticum, implicated in the regulation of stomatal aperture. This study explores the potential for chloride fertilization of Australian spring wheat (Triticum aestivum L.) to minimize grain yield losses caused by drought stress. For this, two drought tolerant commercial genotypes (Mace and Gladius) and a well-studied drought tolerant genotype used in Australian wheat breeding (RAC875) were grown in either watered or water restricted regimes under controlled conditions and treated with ammonium chloride, potassium chloride or ammonium bicarbonate, the latter two treatments served as controls for chloride and ammonium respectively. A significant increase in grain yield and grain number under drought was identified as a result of top-dressing RAC875 with ammonium chloride but not when top-dressed with the control fertilizers suggesting that this compound fertilizer can improve drought tolerance. Minimization of yield loss was accompanied by an increase in stomatal conductance and photosynthetic assimilation and a reduction in carbon isotope discrimination values. This study justifies further exploration of the agronomic potential of ammonium chloride fertilizers for use in rain-fed wheat production systems.