Numerous investigations have shown that soybeans [Glycine max (L.) Merr.] will give a significant yield response to irrigation, especially when the supplemental water is applied during reproductive development. However, the majority of these results have been obtained with soils ranging in texture from silt loam to sandy loam. Since soybeans are frequently grown on finer-textured soils, we conducted field experiments in 1979 and 1980 on Sharkey clay (Vertic Haplaquept, very-fine, montmorillonitic, thermic), a soil representative of that occurring in about 3 750 000 ha of the alluvial plain of the Mississippi River. Variables included initiation of furrow irrigation at the prebloom (V), beginning of bloom (BL), beginning of pod set (PS), and beginning of pod fill (PF) stages, plus a nonirrigated (NI) treatment, and three cultivars representing Maturity Groups V (‘Bedford’), VI (‘Tracy’), and VII (‘Bragg’). Data were collected for seed yield, mature plant height, lodging, xylem pressure potential, leaf area, and seasonal soil moisture status. In the ‘wet’ year of 1979, yields from irrigated Bedford and Tracy were not significantly greater than the respective NI yields of 2754 and 3368 kg ha−1. The PF treatment of Bragg produced a yield of 3630 kg ha−1, however, and this was significantly higher than the yields of all other treatments of Bragg, as well as all treatments of Bedford. In the dry year of 1980, all irrigation treatments of all cultivars increased yields above the NI treatment, although the PF treatment yields were only about one-half of those from PB or BL treatments, which were nearly equal. Seed yield was highest from Bragg and lowest from Bedford in all cases. Lodging was not significantly affected by any irrigation treatment. Mature plant height was significantly increased only in the BL treatment of Bedford in 1980. Measurements of xylem pressure potential, leaf area, and soil water potential in 1980 indicated that the NI plots were severely stressed; thus, response to irrigation should have been expected. These results show that irrigation of soybeans growing in a clay soil should be initiated at or near bloom in a dry year, and at any period of stress during reproductive development in a “wet” year.