Maturity selection but not sowing date enhances soybean productivity and land use in a winter camelina–soybean relay system

Enhancing crop diversification is needed to ensure sustainable food and energy production in the soybean [Glycine max (L.) Merr.] and maize (Zea mays L.) dominated cropping systems of the US Midwest. Relay-cropping soybean with winter camelina [Camelina sativa (L.) Crantz] is a means to sustainably intensify food and energy production while adding cropping system diversity. However, soybean yields in relay systems tend to be less than a full-season monocrop. We hypothesized that improved soybean selection and seeding date for relay cropping could minimize this yield gap, thus increasing agricultural land use productivity. A 2-year field study was conducted to determine the effects of soybean maturity and seeding date (SD) on winter camelina and soybean yields and land use productivity. Three soybean genotypes differing in maturity (MG) were relayed into winter camelina at rosette (SD1), bolting (SD2), and first flowering (SD3) growth stages. The soybean MGs were MG0.2, MG1.1, and MG1.7 representing early, standard, and late maturity, respectively, for the study region. The MG1.1 sown at SD2 was grown as sole crop check using conventional practices (CP). Results demonstrated that SD3 decreased camelina seed yield compared with SD1 and SD2. Soybean yield in the relay system was greatest for the MG1.7 genotype, and averaged across SD1 and SD2, was just 11.6% less than the sole crop CP check. Relaying soybean MG1.7 at SD2 produced 43% greater total (camelina +soybean) oil yield and greatly improved land use efficiency compared with CP. Appropriate soybean genotype selection can enhance winter camelina–soybean relay system productivity and land use efficiency.