SOYBEAN CULTIVAR RESPONSE TO PLANTING RATE AND TILLAGE

Previous research has shown that soybean [Glycine max (L.) Merr.] cultivar yield responses to tillage systems can vary in specific environments due to drought stress, diseases, or herbicides. In one of 3 yr in a previous study 'Mead' yielded 15% more in no-tillage than in tilled systems while 'Williams 82' yielded 8% less in no-tillage than in tilled systems. This was thought to be due to either a slight difference in plant populations between the two cultivars or genetic variability that could be used to develop tillage-specific cultivars. The study reported here was conducted to determine if planting rate of these two cultivars affected their responses to tillage. A 2-yr field study was conducted with two cultivars (Mead and Williams 82) at four planting rates (11.1, 34.6, 58.1, and 81.5 seeds m-2) and two tillage systems (no-tillage and triple disk). In 1986, the study was conducted on a Crete silt loam soil (fine, montmorillonitic, mesic Pachic Argiustoll), which is moderately well drained with slow permeability. In 1987, the study was conducted on a Hastings silt loam soil (fine, montmorillonitic, mesic Udic Argiustoll), which is well drained with moderately slow permeability. When averaged over planting rate, the cultivars responded similarly to tillage systems. Planting rate did not affect the responses of the cultivars to tillage system. Mead and Williams 82 appear to respond similarly to tillage systems in most environments regardless of planting rate.