SOYBEAN (GLYCINE-MAX) RESPONSE TO AC-263,222 AND CHLORIMURON AS INFLUENCED BY SOIL-MOISTURE

Field experiments conducted in 1992 and 1993 evaluated differential re sponse of 20 soybean cultivars to POST application of AC 263,222 or ch lorimuron, as influenced by soil moisture. Natural rainfall was supple mented with overhead sprinkler irrigation to achieve three moisture re gimes: excessive (12.5 cm/wk), optimum (5 cm/wk), and low (non-irrigat ed). Chlorimuron and AC 263,222 injured soybean. Excessive moisture di d not increase soybean injury with chlorimuron for any of the cultivar s tested compared to optimum moisture; however, 17 of 20 cultivars wer e injured more by AC 263,222 in combination with excessive moisture th an optimum moisture. AC 263,222 reduced the height of five cultivars. Photosynthetic rate of several cultivars was reduced by both AC 263,22 2 and chlorimuron. Neither herbicide affected the number of nodes per main stem or seed weight; however, pod numbers were reduced for severa l cultivars with both herbicides. In the low moisture regime, AC 263,2 22 delayed the maturity of 18 of 20 cultivars with 'Hutcheson' maturit y delayed 7.1 d. Excessive moisture when combined with AC 263,222 redu ced yields for 12 cultivars, compared to five cultivars with chlorimur on. Under optimum moisture conditions, AC 263,222 reduced the yield of 10 cultivars, whereas chlorimuron reduced the yield of 9 cultivars. L ow moisture stress only resulted in a yield reduction with 3 cultivars treated with AC 263,222.