Effects of in-row and interrow subsoiling and time of nitrogen application on growth, stomatal conductance and yield of strip-tilled corn

The use of in-row subsoilers in conservation tillage systems in soils underlaid by tillage pans increases rooting depth, root proliferation and water infiltration. Interrow subsoiling 5 weeks after planting, to coincide with sidedress nitrogen applications, might be a practical method for further increasing infiltration of water from irrigation and high-intensity showers. Corn (Zea mays L.) was strip-till planted and grown under irrigation for 2 years at one location and 1 year at another to study the effects of subsoiling, placement and timing of nitrogen application (157 kg ha-') on plant growth, stomatal conductance and yield. Treatments included (1) not subsoiled, N applied at planting; (2) subsoiled in-row at planting, N applied at planting; (3) not subsoiled, N applied 5 weeks after planting; (4) subsoiled in-row at planting, N applied 5 weeks after planting; (5) subsoiled interrow, and N applied 5 weeks after planting; and (6)subsoiled in-row at planting and interrow 5 weeks after planting, N applied 5 weeks after planting. Nitrogen applied 5 weeks after planting resulted in higher yields than when applied at planting. In-row subsoiling at planting, interrow subsoiling 5 weeks after planting and subsoiling in-row at planting plus interrow 5 weeks later resulted in increased stomatal conductance between irrigations. Delaying N application resulted in decreased stomatal conductance in treatments that were in-row subsoiled at planting. Grain yields were lower without than with subsoiling, especially when N was applied at planting. When water was not limiting, subsoiling interrow 5 weeks after planting was as effective in increasing grain yield as in-row subsoiling at planting. In one test, the highest grain yield (9.96 t ha-') resulted from the cumulative effect of subsoiling in-row at planting plus interrow 5 weeks later.