Assessment across the United States of the Benefits of Altered Soybean Drought Traits

A number of plant traits have been suggested to ameliorate the effects of water deficits on crop yield. A quantitative response across a range of years and location is needed because many traits that could be beneficial in dry years might also be detrimental in wet years. This analysis was undertaken using a robust simulation model of soybean [Glycine max (L.) Merr] development and growth to quantify yield changes as a result of modification of five traits: rooting depth extension, rate of leaf area development, decreased stomata conductance at high soil water content, reduced maximum transpiration rate, and drought-tolerant nitrogen fixation. Simulations were done for 50 yr of weather data for 2655 grid locations of 30 km by 30 km size in the United States. Slow rate of rooting development was a neutral or negative trait in most locations. Slow leaf area development proved beneficial in less than half the years and in wetter years it resulted in yield losses. Water conservation both by early decrease in stomata conductance with soil drying and by reducing the maximum transpiration rate resulted in yield increases in many locations in 70% or more of the years. Both traits resulted in only small yield decreases in the wet years. Drought-tolerant nitrogen fixation had the greatest benefit of all traits with a yield gain in more than 85% of the years at nearly all locations, and in those cases with no yield increase there was only a very small yield loss.