EARLY-MATURING SOYBEAN CROPPING SYSTEM .3. PROTEIN AND OIL CONTENTS AND OIL COMPOSITION

Expanding production of early-maturing soybean [Glycine max (L.) Merri ll] cultivars in the southeastern USA has exposed such cultivars to a wide range of environmental conditions during seed-fill. Temperatures during this growth stage influence levels of specific fatty acids, par ticularly of the unsaturated fatty acids. Our objective was to evaluat e the grain quality responses of early-maturing cultivars to the wide range of planting dates in the southeastern USA. Protein and oil conte nts, along with fatty acid profiles, were assessed for cultivars from Maturity Group (MG) 00 through IV using late April, mid-May, early Jun e, and late June planting dates on a well-drained Maury silt loam (fin e, mixed, mesic Typic Paleudalf) in 1990 through 1993. Across years an d cultivars, delayed planting increased protein content and linolenic acid levels and reduced oil content and oleic acid levels, but had lit tle or no influence on palmitic, stearic, or linoleic acid levels. The higher seed-fill temperatures associated with early planting were str ongly correlated with increased oil content and oleic acid levels and reduced linolenic acid levels. Increasing seed-fill temperatures were closely associated with reduced linolenic acid levels for all six cult ivars. However, the oleic acid response to seed-fill temperatures stro ngly depended on cultivar maturity. Oleic acid levels of early-maturin g cultivars were much more sensitive to seed-fill temperatures than we re those of later maturing cultivars. While overall effects of environ ment on grain quality characteristics may be relatively small, perhaps the quality of new low linolenic acid cultivars could be amplified th rough culture under the warmer renditions of the southeastern USA.