Rising atmospheric drying is causing losses in crop productivity worldwide, by triggering excessive plant water losses. Water-saving varieties are effective in limiting yield losses under atmospheric drying, but the genetic regions controlling this behavior are unknown. We screened hundreds of soybean (Glycine max) plants for their water losses in response to atmospheric drying and identified genetic regions controlling their responses. These findings open the way to breed for climate-smart, water-saving legumes that are better-yielding under current and future drought conditions.