Soil acidity is a growing problem in western North Dakota. High soil H+, alone or in combination of high Al3+ (a common problem in acid soil), inhibits plant growth and development, water/nutrient uptake, and interaction with soil microorganisms, resulting in reduced crop yield and increased sensitivity to other stresses (such as drought). Use of tolerant plants can help alleviate stress. Although there are soybean evaluation trials conducted in western ND that possibly encounter soil acidity, more detailed research is needed because of large variations of soil acidity (e.g. severity and spatial distribution) from site to site even in the same field. We are proposing this research to evaluate genetic differences of acidity tolerance in soybean. This project has two specific objectives: (1) quantify morphological and physiological responses of 25 soybean genotypes (including commercial varieties) to acidity in a hydroponic system and (2) validate the observations from the hydroponic system in a soil system with nodulation. Such information will help soybean growers who are challenged by soil acidity to address the problem directly. Our result will also assist soybean breeders identifying possible parental lines with high stress tolerance and providing reliable method/selecting index to facilitate the screening process.