Soil salinization is a major threat to agricultural ecosystems. Consequently, an understanding of agro-ecosystem functions affected by increasing levels of soil salinity is critical for land management. The purpose of this research was to determine the effects of soil salinity on corn and soybean growth and soil microbial activity in southeastern North Dakota soils with naturally occurring soil salinity. A field study assessed corn and soybean yield, and a laboratory study assessed microbial respiration in response to increasing salinization. Both corn and soybean yield were significantly impacted by salinity in sandy loam soils, declining after a threshold of 4.57 dS m-1 and 2.98 dS m-1, respectively. These thresholds are higher and lower than previously established threshold tolerances for corn and soybean, respectively. Microbial respiration in sandy loam soils could not be significantly explained by ECe, potentially indicating a community composition that has acclimated to sulfate-based salinity in these soils.