Depth to Fragipan in Cabot Silt Loam—Variability in a Characteristic Area

Abstract

AbstractA drainage research projec thas been established at East Franklin, Vermont on a Cabot silt loam to study and improve interception drainage methods. To be able to interpret the resulting data with greater meaning it was necessary to determine the variability of depth to fragipan and the relations between this variability, the slope of the surface, and the thickness of the Ap horizon. Two methods of determining depth to the fragipan surface were used. The more feasible one, auger borings taken on a 100‐foot grid was evaluated for precision in relation to the method of examining drain trench walls. Thickness of Ap horizon and the depth to the fragipan surface were measured at 161 locations 2 feet apart along tile drain trenches. Fragipan surface at 143 points over the research area was located by the auger grid system.The mean depth of the Ap horizon was 7.4 inches and 83% of the measurements fell in the 6‐ to 9‐inch range. Of all fragipan depths, 74% were in the 11‐ to 17‐inch range. Mean depth by augering was 13.9 inches; along the trench profile it was 14.4 inches. In this area of Cabot silt loam, the lower boundary of the Ap and the fragipan surfaces generally follow surface slopes. The auger method data follow the trend of the measurements derived from the trench profile.