EVALUATION OF SIMULATED FALL FREEZE, PLANTING DATE, AND CULTIVAR MATURITY IN SOYBEAN

In the northern fringe of the U.S. soybean [Glycine max (L.) Merr.] gr owing area, early planting dates of late-maturing cultivars would effe ctively increase growing season length and may increase yield. However , growing late maturing cultivars increases the risk of fall freeze da mage. Planting early also increases the risk of a spring freeze. Our o bjective was to evaluate the effects of varying both planting and fall freeze dates on yield, reproductive stage, and U.S. Grain Grades of f our soybean cultivars. A factorial arrangement of four cultivars, thre e planting dates, and three fall freeze dates were evaluated in a tota l of five environments across 2 yr. Cultivars included two from Maturi ty Group 0, which were considered adapted to the geographical region, and one each from Maturity Group I and II, which were considered unada pted, due to their late maturity. The first and second fall freeze dat es were simulated by applying paraquat herbicide with a specially desi gned sprayer. Temperatures were warmer than normal in 1991 and cooler than normal in 1992. Increasing the length of the growing season by ea rly planting of late maturing cultivars did not result in increased yi eld. However, there was a yield advantage for early planting of adapte d cultivars when an early fall freeze occurred, A fall freeze near the R6 stage generally did not degrade grain quality.