CULTIVAR MATURITY AND POTENTIAL YIELD OF SOYBEAN

Soybean (Glycine max (L.) Merrill) cultivars from maturity groups 00, I, III, and V were grown in the field to evaluate the relationship between the length of the total growth cycle and potential yield. Cultivars from maturity group 00 and I were grown in narrow rows (0.38 m) to obtain maximum insolation interception. The length of the vegetative growth period increased by 35 days from maturity group 00 to V. Plant size (total nodes per plant and maximum vegetative mass in g m-2) also increased with increasing maturity group. All cultivars reached maximum insolation interception soon after initial flowering. The crop growth rate of control plots (measured between growth stages R1 and R5) was not related to plant size. Shade (30 and 63%) from growth stage R1 to R7 was used to create variation in crop growth rate within a cultivar. For each cultivar, the number of seeds m-2 increased linearly with increasing crop growth rate. After adjusting for cultivar differences in individual seed growth rate, there were no cultivar differences in seeds m-2 at a constant crop growth rate. Thus, seeds m-2 was related to crop growth rate, not to the size of the plant. The maturity group 00 cultivar tended to have a shorter seed-filling period but there were no consistent differences among the others. These data suggest that the longer vegetative growth period of later-maturing cultivars does not provide a higher yield potential and that shorter-season cultivars may have equal yield potential if exposed to a similar environment.