SOYBEAN (GLYCINE-MAX) CULTIVAR RESPONSE TO AC-263,222 AS INFLUENCED BY SUPPLEMENTAL IRRIGATION

In field studies conducted over two years, soybean cultivars 'Deltapin e 415', 'Forrest' 'Asgrow 6785', 'Centennial', 'Sharkey', 'Terra Vig 6 16', 'Hartz 6686', and 'Pioneer 9791' responded similarly to POST appl ication of AC 263,222. With supplemental overhead irrigation of 5.1 cm weekly for 4 wk initiated 21 d after herbicide applications, mature s oybean height for the cultivars averaged 18% less than that of the unt reated check for 27 g/ha AC 263,222, but only 8% less when not irrigat ed. Although non-irrigated soybean seed yield following AC 263,222 app lication the first year was not reduced compared with the untreated ch eck, with irrigation seed yield reductions of 12 and 32% were noted fo r 13 and 27 g/ha AC 263,222, respectively. Seed yield the second year was not negatively affected with herbicide application whether soybean was irrigated or not irrigated. For individual years, seed yield for the untreated irrigated and non-irrigated checks was similar. In the f irst year soybean yield following AC 263,222 at 13 and 27 g/ha with ir rigation was 16 and 30% lower, respectively, than when soybean was not irrigated. Decreases in soybean 100-seed weight accompanied the yield reductions.