Early-maturing soybean cropping system: III. Protein and oil contents and oil composition

Expanding production of early-maturing soybean [Glycine max (L.) Merrill] cultivars in the southeastern USA has exposed such cultivars to a wide range of environmental conditions during seed-fill. Temperatures during rids growth stage influence levels of specific fatty acids, particularly of the unsaturated fatty acids. Our objective was to evaluate the grain quality responses of early-maturing cultivars to the wide range of planting dates in the southeastern USA. Protein and oil contents, along with fatty acid profiles, were assessed for cultivars from Maturity Group (MG) 00 through IV using late April, mid-May, early June, and late June planting dates on a well-drained Maury silt loam (fine, mixed, mesic Typic Paleudalf) in 1990 through 1993. Across years and cultivars, delayed planting increased protein content and linolenic acid levels and reduced oil content and oleic acid levers, but had little or no influence on palmitic, stearic, or linoleic acid levels. The higher seed-fill temperatures associated with early planting were strongly 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 cultivars. However, the oleic acid response to seed-fill temperatures strongly depended on cultivar maturity. Oleic acid revels of early-maturing cultivars were much more sensitive to seed-fill temperatures than were those of later maturing cultivars. While overall effects of environment on grain quality characteristics may be relatively small, perhaps the quality of new low linolenic acid cultivars could be amplified through culture under the warmer conditions of the southeastern USA.