EFFECT OF WATER-TABLE LEVEL ON THE YIELD OF SOYBEAN GROWN UNDER SUBIRRIGATION DRAINAGE

Water deficit is a primary yield limiting factor in soybean [Glycine max (L.) Merr.]. A new concept in Midwestern irrigation is the use of the same drain lines for both subirrigation And drainage to provide a total water management system and water table control. The objectives of this research were to evaluate the potential of a subirrigation/drainage system, when used in combination with a soybean production system with known high yield potential, to increase average yields on a poorly drained soil in the humid Midwest and to identify an optimum water table level for soybean in this environment. A subirrigation/drainage research facility with drain lines spaced 20 ft apart was established at Wooster, OH, in the fall of 1984 on a Ravenna silt loam (fine-loamy, mixed, mesic Aeric Fragiaqualfs). Three different water table levels (16-, 22-, and 28-in. average depth) were compared over 4 yr (1985 through 1988) using four soybean cultivars ('Sprite 87', 'Hobbit 87', 'Asgrow 3127', and 'Williams 82'). A nonirrigated treatment was added in 1987 and 1988. All plots were planted in 7-in.-wide rows in late April or early May. Averaged over the four cultivars and 4 yr the highest yield was obtained with the highest water table (80.6, 73.0, and 67.9 bu/acre for the 16-, 22-, and 28-in. water table levels, respectively). Averaged over 2 yr, 1987 and 1988, there was a 43% yield advantage (80.2 vs. 56.0 bu/acre) for the 16-in. water table level over the nonirrigated treatment.