Cultivar and Planting Date Selection for Relay-Cropping Soybean with Winter Oilseeds.

Double- and relay-cropping soybean with winter camelina (Camelina sativa [L.] Crantz) and pennycress (Thlaspi arvense L.) have been shown to be viable cropping systems for the Upper Midwest. Relaying soybean with these winter oilseeds can result in greater total seed yield (i.e., both combined) and economic returns than a sole full-season soybean crop, while providing critical ecosystem services. However, optimum planting time and soybean cultivar selection for this relay system have not been studied. A field study was initiated in western Minnesota on a Barnes loam soil in 2015-2016 to evaluate three soybean planting dates from late April to mid-May using 0, I, and II maturity group (MG) cultivars; MG I is standard for the location. Initial results indicated that camelina and pennycress seed yields were unaffected by relay planting date or soybean cultivar. Generally, relayed soybean grain yields were affected by cultivar but not by planting date. The relay-cropped MG II cultivar planted in early May after winter oilseeds had already bolted, gave the highest grain yield in both the camelina (3642 kg ha^-1) and pennycress systems (3999 kg ha^-1). These yields were just 7% lower and 2% higher than the sole MG II full-season control, for the camelina and pennycress systems, respectively. Results so far indicate that using a longer MG soybean than standard for the region, along with a near normal planting date, helps to maximize relay-cropped soybean yields with winter camelina and pennycress.