YIELD POTENTIAL OF SOYBEAN GROWN UNDER A SUBIRRIGATION DRAINAGE WATER MANAGEMENT-SYSTEM

Combination subsurface irrigation/drainage systems to manage water (add or remove) on poorly drained soils is a relatively new concept in the humid Midwest. The objective of this research was to evaluate the yield potential of a subirrigation/drainage system, when used in combination with a soybean [Glycine max (L.) Merr.] production system with known high yield potential, on a poorly drained soil at Wooster, OH. The water table was maintained on a Ravenna silt loam soil (fine-loamy, mixed, mesic Aeric Fragiuqualfs) by subirrigation at an average depth of 39 cm. Water table depth ranged from 25 cm over the drain line to 53 cm at the midpoint between drain lines which were spaced 6 m apart. Five cultivars (Sprite, Sprite 87, Hobbit 87, Asgrow 3127, Williams 82) and two row spacings (18 and 76 cm) were compared in 1985 and 1986. In 1987, the five cultivars were all planted in 18-cm rows and compared at two water table levels (the 1985 and 1986 level and a non-irrigated naturally varying depth). Averaged over the five cultivars, the constant water table produced a 3-yr average yield of 5392 kg/ha. In 1987 there was a 2051 kg ha-1 or 58% yield advantage for the subirrigation/drainage system over non-irrigation (5563 vs 3512 kg ha-1). The 1985, 1986 mean yield advantage for 18-cm rows compared to 76-cm rows was 1010 kg ha-1 or 23%. These results indicate that with a properly managed subirrigation/drainage system, combined with a soybean production system with high yield potential, long-term average soybean yields of 5300 kg ha-1 should be possible in the humid Midwest.