SODIC SOIL TOPOSEQUENCE RELATED TO FOCUSED WATER-FLOW

Present concepts of sodic soil formation do not adequately account for observed variability of sodic soil properties on many landscapes in N orth Dakota. A conceptual model was developed to explain sodic soil ge nesis related to water and salt movement on a coarse-loamy till landsc ape in central North Dakota. The relationship between subsurface water flow and sodic soils was determined by monitoring soil water using ne utron attenuation and water wells at three contiguous landform positio ns. Electrical conductivity, major ions, and water-dispersible clay we re determined on extracts from selected soil samples from each landfor m position. Typic Argiaquolls, characterized by low salinity (electric al conductivity [EC] < 2.0 dS/m), occurred at the wetland position and were areas of recharge to groundwater. Typic Natraquolls also occurre d at the wetland position but were characterized by high salinity (EC > 5.0 dS/m) and were areas of groundwater discharge. Udic and Leptic N atriborolls were areas of groundwater discharge at the intermediate an d upland positions. Udic Haploborolls were hydrologically inactive are as at the upland position. Variations in sodic soil development were a ttributed to the concentration of water flow (focused flow) into speci fic areas of groundwater discharge or recharge. The most important fac tors that affected the direction and intensity of focused flow were st ratigraphy and landform position.