Response of soybeans to planting date in south-eastern Queensland. III.* Agronomic and physiological response of cultivars to planting arrangements

Abstract

Results from five field experiments, designed to evaluate the response of several soybean cultivars to planting arrangement, and conducted at two locations in south-eastern Queensland during 1967–1972, are reported. Response to planting arrangement varied depending on cultivar maturity type, planting date, and availability of moisture during growth. Averaged over cultivars and planting arrangements, seed yields for irrigated soybeans were highest for December plantings, and declined as planting was delayed. A cultivar x planting date interaction was apparent. For December planting dates, yields of all cultivars were generally highest in 50.8 cm rows. A cultivar x plant population interaction occurred, with yields of the later-maturing cultivars maximized at lower plant population levels than for the earlier cultivars. When the planting date was delayed beyond December, yields of all cultivars were maximized in narrow row-high density treatments. Yields of the narrow row-high density late plantings were equivalent to, and in the case of the late-maturing cultivars, greater than, the highest December yields. Wide row widths (101 .6 cm) were consistently lower-yielding, regardless of cultivar and planting date. Seed yields were reduced substantially by periods of severe moisture stress during growth. The relative performance of cultivars of differing phenology depended primarily on the coincidence of periods of severe stress with critical stages of development, viz. pod and seed development. In the environments involving periods of severe moisture stress, seed yields were maximized in row widths narrower than 50.8 cm, and at the lowest plant populations used (c. 95,000 plants per ha). Such treatments most closely approached low density-equidistant spacings in these studies.