Soybean Yield Response to Natural Soil Salinity Gradients in Richland County, North Dakota.

Soil salinization is a global issue, affecting 831 million ha of arable land and resulting in approximately US$ 27.3 billion in costs annually. Given the extent of soil salinity, it is imperative to obtain a better understanding of crop productivity in response to increasing levels of soil salinity under field conditions, as this knowledge is more pertinent to producers managing saline soils. The purpose of this research was to determine the effects of soil salinity on soybean growth on three quarter plots in Richland County, North Dakota for two growing seasons. Soybeans were planted on a sandy loam soil for the first year and a silty clay loam soil the second year of the study. Preliminary soil salinity gradients were established across each field using Geonics EM 38 apparent electrical conductivity data (EC_a).  The data was used in the construction of transects on each field that served as sampling gradients to measure crop yield.  EM 38 remotely-sensed salinity measurements were corroborated using both a saturated paste extract (EC_e) and 1:1 soil to water slurries (EC_1:1) on four composite soil samples collected at each point on the transects at five depths: 0-15 cm, 15-30 cm, 30-60 cm, 60-90 cm, and 90-120 cm. Crop yield was assessed using linear and non-linear regressions in an effort to understand crop yield in response to the depth weighted average EC_e. Preliminary results from year one of this study indicated that soybean yield began to decline at an depth weighted average EC_e between 2.5 and 3.0 dS  m^-1, which is substantially lower than the previous threshold estimates of 5.0 dS m^-1 established by greenhouse studies.