Could Winter Annual Crop Increase No-till Double-Crop Soybean Yield in Kentucky?.

Double-cropping soybean (Glycine max L.) after a winter annual crop is common in Kentucky. The winter annual that precedes double-crop soybean may affect yield in Kentucky. Producers and agronomists have reported greater double-cropped soybean yields when preceded by winter canola (Brassica napus L.) instead of winter wheat (Triticum aestivum L.). Explanations for these yield differences remain unresolved. The objectives of this study are to determine: (1) plant populations, and yield of double-crop soybean following four winter annual treatments; and (2) emergence and biomass of soybean produced in rhizosphere soil when grown in greenhouse (GH) and cold chamber (CC) environments. Three winter annuals (canola, barley (Hordeum vulgare L.), wheat) and a non-planted control (fallow) were established in fall 2014 and fall 2015 at the University of Kentucky Research and Education Center near Princeton, KY (37.1092^o N, 87.8820^o W). Double-crop soybeans were established in summer 2015. All crops were managed according to University of Kentucky recommendations for no-till production. Immediately following winter annual harvest, rhizosphere soil cores were collected for GH (Princeton, KY) and CC experiments (Lexington, KY) (38.0406^oN, 84.5037^oW). Soybean yield did not differ among treatments in 2015: 2.90 t ha^-1 after barley, 3.05 t ha^-1 after canola, 3.00 t ha^-1 after wheat and 3.05 t ha^-1 after fallow. Although differences among winter annual treatments were not found for soybean emergence in GH or CC, soybean emerged in 7 days in GH versus 9 days in CC. Root length, shoot length, and biomass in the GH environment also did not differ among treatments. However, differences were found in the CC environment. Root length was longest for wheat and fallow rhizosphere soil and shortest for canola and barley (P<0.0015). Shoot length was also longest for wheat and fallow than for barley and canola (P<0.0976). Total biomass for wheat and fallow was greater than barley which was also greater than canola (p<0.0001).  The study is currently being repeated at two locations.