Double-crop soybean germination, seedling growth, and seed yield differences when preceded by different winter annuals

Increasing sustainable grain and oilseed production is a significant challenge for US producers. Double-cropping soybean [Gly-cine max (L). Merr.] with a winter annual crop is one option to increase grain and oilseed production while reducing nutrient and sediment losses. Anecdotal observations that winter wheat (Triticum aestivum L.) limits double-crop soybean productivity are common, which is seemingly corroborated by documentation that winter wheat contains allelopathic compounds. Despite these observations and documented evidence, the winter wheat double-crop soybean system is prevalent in the mid-South. Investigations are lacking that document physiological differences in soybean plants when preceded by different winter annual crops. This study examined the effect of four winter annual treatments (wheat, canola [Brassica napus L.], barley [Hordeum vulgare L.], and a fallow, non-planted control) on soybean germination in the laboratory, seedling growth in a greenhouse, and harvest population and grain yield in field experiments at Princeton, KY, from 2014 to 2016. The only consistent finding was detected for seedling growth; soybean roots were shorter and lighter 1 mo after planting when grown in field-collected soil cores from wheat or barley crops. Differences were not detected for seed germination or seed yield. Based on results of this study and previously unpublished reports, it is possible that the anecdotal differences reported among winter annual crops may be due to an interaction between reduced root growth and environmental conditions, such as limited water or nutrient availability.