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Corn Irrigation Scheduling in Humid Regions on Sandy Soils with Tillage Pans¹

Several droughts during the past decade in humid regions of the USA, especially the Southeast, have intensified the interest in supplemental irrigation. One objective of this study was to evaluate the effect of supplemental irrigation in a humid environment on corn (Zea mays L.) production on an Atlantic Coastal Plain soil having a tillage pan. A second objective was to evaluate two alternative techniques for scheduling supplemental irrigation in humid regions The study, conducted on a Wagram soil (Arenic Paleudu1ts)-Norfolk soil (Typic Paleudults) from 1979 to 1981, employed a split plot design with water level (irrigation scheduling) as the main block. Water levels were control or dryland (Wl), scheduled irrigation water applications based on a computerized water balance model (W2), and scheduled water applications based on tensiometer measurements (W3). Subplot treatments were time of N application in 1979 and 1980 and cultivation intensity in 1981. Compared with a normal rainfall of 447 mm during the growing season, 464, 262, and 220 mm fell during 1979, 1980, and 1981, respectively. The average amount of irrigation water applied over the 3-yr period based on the water balance model was 40 mm greater than the 3-yr average of 179 mm applied based on the tensiometers. Grain yield as affected by subplot treatment was not significantly different for any year. Mean grain yields for the 3-yr period were 2.58, 7.73, and 8.14 Mg ha–1, for treatments W1, W2, and W3, respectively. Either irrigation scheduling method offers large yield improvements in drier years, but no significant yield difference occurred for the two scheduling techniques. In the wetter year 1979, irrigation increased yield by 2.45 Mg ha–1, whereas in the dryer years of 1980 and 1981 the increases were 6.53 and 7.06 Mg ha-', respectively.

Key Words: Tensiometer • Nitrogen split application • Allowable depletion • Soil water pressure • Rooting depth

² Professor and assistant professor of soil science, North Carolina State Univ., Raleigh, NC and professor of agricultural engineering, Clemson Univ., Clemson, SC, respectively

Received for publication August 20, 1984.