HYDRAULIC CONDUCTIVITY OF TILL SUBSOIL IN NORTH DAKOTA

Abstract

ABSTRACT Soil monoliths were used to evaluate the natural drainage from a soil profile having slowly permeable glacial till below 1.0 m. Each monolith was 2.5 m by 2.5 m by 2.3 m deep. The bottom of each monolith was not disturbed, leaving the natural continuity of the soil within the monolith to the soil below the monolith. The sides were encased with plastic to prevent horizontal water movement from the monoliths. Evaporation was minimized by covering the tops of the monoliths with plastic. A total of 676 mm of water was applied in 29.4 mm applications, three times each week during an eight-week period. Water drained from the top 1.8 m of the soil profile at a rate of 0.6 mm/day for the last 7 days of the test, 50 to 57 days after the last water application. Average hydraulic conductivity of the monoliths ranged from 15.4 mm/day at a matric potential of -2.19 kPa (measured at 2.0 m) to 2.13 mm/day at a matric potential of -9.21 kPa. These drainage and hydraulic conductivity data show that the natural drainage of these soils is sufficient to prevent water table formation or salinity accumulation under properly managed irrigation.