Integrating alfalfa (Medicago sativa L.) with corn (Zea mays L.) for grain will increase biodiversity, reduce the negative environmental impact of corn monoculture and increase farm profitability. The objectives of this research were to evaluate forage productivity and nutritive value, along with stand establishment of alfalfa in a corn grain system in Iowa, Minnesota, and North Dakota. The experimental design was a randomized complete block with four replicates at each site. Treatments included were: sole corn (i.e., check; T1), sole alfalfa (T2), alfalfa intercropped into corn (T3), a prohexadione-treated alfalfa intercropped with corn (T4), and a spring-seeded alfalfa in the year after intercropping (T5), which was planted in plots with T1 the previous year. All sites had below normal rainfall in 2016 and 2017. Corn grain yield was significantly lower when intercropped with alfalfa (T3 and T4) compared with the check corn crop (no alfalfa, T1). Corn grain yield reduction ranged from 14.0% to 18.8% compared with the check (T1). Corn biomass yield was reduced by intercropped alfalfa (T3 and T4) by 15.9% to 25.8%. In the seeding year, alfalfa seasonal forage yield was significantly greater when corn competition was absent in all environments. The intercropped alfalfa from the previous season (T3 and T4) had almost double the forage yield than the alfalfa in the seeding year (spring-seeded alfalfa; T5). In the second production year, there were no meaningful forage yield differences (p > 0.05) across all treatments, indicating alfalfa in intercropping systems does not affect forage yield past the first production year. Prohexadione-calcium, a growth regulator, did not affect alfalfa stand density, forage yield and nutritive value. The forage nutritive value was dependent on harvest date not the alfalfa intercropping treatments. Results of our study suggest that establishing alfalfa with corn is feasible and can be a potential alternative for the upper Midwest region. However, when under drought conditions, this system might be less resilient since competition between alfalfa and corn for soil moisture will be intensified under drought or moisture-limited conditions, and this will likely depress corn grain yield. Research targeted to reintroduce perennial crops into the current dominant corn–soybean systems in the US Corn Belt is urgently needed to improve stability and resiliency of production systems.

Introducing cover crops is a form of ecological intensification that can potentially reduce local, regional and global environmental impacts of soybean cropping systems. An assessment of multiple environmental impacts (global warming potential, eutrophication, soil erosion and soil organic carbon variation) was performed on a continuous soybean system in the U.S. upper Midwest. Four sequences were assessed and compared: a soybean cropping system with winter camelina, field pennycress, or winter rye as cover crop, plus a control (sole soybean). Cover crops were interseeded into standing soybean in Year 1, while in Year 2 soybean was relay-cropped into standing camelina or pennycress. Rye was terminated before sowing soybean. When compared with the control, sequences with cover crops showed lower eutrophication potential (4–9% reduction) and soil erosion (5–32% reduction) per ha year⁻¹, in addition to a lower global warming potential (3–8% reduction) when the cover crop was not fertilized. However, when the economic component was included in the assessment, and the results expressed per USD net margin, the sequences with cover crops significantly reduced their performance in all categories of impact considered. A further optimization of field management for camelina and pennycress is recommended to make the cropping system more sustainable.