Surface runoff can be a problem when water application rates of continuously moving sprinkler irrigation machines exceed the infiltration capability of soil. The problem is aggravated with reduced sprinkler pressure operating conditions. Field studies were conducted over a 5 year period on farmer managed and researcher managed sites to evaluate the influence of an annual post-emergence, interrow subsoil tillage (IRT) practice on surface runoff, soil water content and corn ( Zea mays L.) grain yields. The IRT practice consisted of the operation of a flat-soled, straight shank between each corn row at a 250–300 mm depth immediately after a shallow (50 mm) cultivation when the corn was in the six to eight leaf stage of growth. A single, shallow cultivation was used as a control practice. Surface runoff for the IRT practice was a quarter of the control runoff on both the farmer and researcher sites. The IRT practice eliminated runoff during the early part of the irrigation season, but lost some of its effectiveness during the later part of the season. Soil water contents of the IRT soil profile were consistently equal to or greater than the control profile contents. Soil water contents for the IRT and control practices were equal at the time of inter-row tillage which indicated no residual effects between successive years. The largest soil water differences between the two tillage practices occurred near the end of the irrigation season. Irrigation management practices used in farmer cooperator fields caused a significant crop yield response to the IRT practice where corn yields averaged 9.0 t ha −1 and 10.0 t ha −1 for the control and IRT practices, respectively. Corn yields were also increased from 11.3 to 11.8 t ha −1 on a research site where significant increases in soil water contents were caused by the IRT practice during the last half of the crop season. No differences in corn yields were found on a second research site where significant soil water differences were not present.