Irrigation through Subsurface Drains

Field experiments were conducted to determine the feasibility of subirrigation on a Lumbee sandy loam soil. Results for the water table response to tile line subirrigation with tile spacings at 7.5 m, 15 m, and 30 m are presented and compared to predictions from theoretical design equations. The results indicated that water could be supplied to the root zone at a rate more than sufficient to supply plant needs for the 7.5 m and 15 m, but not for the 30 m spacing. Theoretical calculations showed that, in this soil, a water table depth range of 30 cm from directly over the tile lines to midway between tile lines could be maintained with a spacing of 19.2 m. An equation was derived for the upward movement of the water table during the early stages of subirrigation. Comparisons with the results of field tests showed that, except for an initial lag period, the equation can be used to accurately predict the water table rise midway between tile lines.