Soil Profile Characteristics in Relation to Drainage and Level Terraces

I N recent years there has been rapid expansion in the construction of terraces in Iowa as one of the measures for control of soil and water losses. On the Marshall, Monona, and Ida soils, areas 3 and 4 (Fig. i), level terraces operate satisfactorily. On the Grundy and associated soils, areas 5 and 6, graded terraces are required. Here the slowly permeable subsoil will not allow water to penetrate fast enough and overtopping or drowning out of plants in the terrace channel result. Between these two areas, the one where level terraces will work satisfactorily and the other where they will not work, is the Sharpsburg soil, area 2. This soil has a gradual gradation in characteristics from those of the Marshall soils to those of the Grundy soils. Requests have been received from Soil Conservation District Commissioners in this area for information or procedures that may be used in the field to separate sites on which level terraces may be safely used from those where failures are likely to be encountered. Drainage is also an important problem on several million acres of land in Iowa. It is recognized generally that the permeability of the soil largely determines the depth and spacing at which drain tiles should be placed. On the Edina soils, area 5, in southern Iowa, experiences by farmers indicate that it is not economical to tile drain these soils. The Taintor soils, area 2, in southeastern Iowa, will drain satisfactorily with tiles. Between these two areas are the Haig and associated soils, area 6, with a gradual gradation in soil characteristics from those of the Edina soils to those of the Taintor soils. Some farmers in this area are installing drain tiles despite the fact that in the past satisfactory drainage has not been obtained with tiles on numerous fields.