Cover crop–based organic rotational no-till soybean production has attracted attention from farmers, researchers, and other agricultural professionals because of the ability of this new system to enhance soil conservation, reduce labor requirements, and decrease diesel fuel use compared to traditional organic production. This system is based on the use of cereal rye cover crops that are mechanically terminated with a roller-crimper to create in situ mulch that suppresses weeds and promotes soybean growth. In this paper, we report experiments that were conducted over the past decade in the eastern region of the United States on cover crop–based organic rotational no-till soybean production, and we outline current management strategies and future research needs. Our research has focused on maximizing cereal rye spring ground cover and biomass because of the crucial role this cover crop plays in weed suppression. Soil fertility and cereal rye sowing and termination timing affect biomass production, and these factors can be manipulated to achieve levels greater than 8,000 kg ha−1, a threshold identified for consistent suppression of annual weeds. Manipulating cereal rye seeding rate and seeding method also influences ground cover and weed suppression. In general, weed suppression is species-specific, with early emerging summer annual weeds (e.g., common ragweed), high weed seed bank densities (e.g. > 10,000 seeds m−2), and perennial weeds (e.g., yellow nutsedge) posing the greatest challenges. Due to the challenges with maximizing cereal rye weed suppression potential, we have also found high-residue cultivation to significantly improve weed control. In addition to cover crop and weed management, we have made progress with planting equipment and planting density for establishing soybean into a thick cover crop residue. Our current and future research will focus on integrated multitactic weed management, cultivar selection, insect pest suppression, and nitrogen management as part of a systems approach to advancing this new production system.

Cover crops can provide ecological services and improve the resilience of annual cropping systems; however, cover crop use is low in corn (Zea mays L.)–soybean [Glycine max (L.) Merr.] rotations in the upper Midwest due to challenges with establishment. Our objective was to compare three planting methods to establish cover crops (winter rye [Secale cereale L. ‘Rymin’], red clover [Trifolium pretense L. ‘Medium’], hairy vetch [Vicia villosa Roth], field pennycress [Thlaspi arvense L. ‘MN‐106’], and a mixture of oat [Avena sativa L.], pea [Pisum sativum L.], and tillage radish [Raphanus sativus L.]) (MIX) in corn at the seven‐leaf collar stage. Planting methods included directed broadcast into the inter‐row (DBC), directed broadcast with light incorporation (DBC+INC), and a high‐clearance drill (DRILL). The DRILL method achieved greater fall biomass than DBC for all species except pennycress, and DRILL and DBC+INC increased red clover and hairy vetch spring biomass compared with DBC. Cover crops did not affect corn grain or silage yield and reduced yield of the subsequent soybean crop by 0.4 Mg ha−1 (10%) only when poor termination of hairy vetch occurred at one site. Cover crops with >390 kg ha−1 of spring biomass reduced soil nitrate‐N compared with the no‐cover control. These results support that cover crops can be interseeded into corn at the seven‐leaf collar stage in the upper Midwest to reduce soil nitrate‐N while maintaining corn and subsequent soybean yields; however, effective cover crop termination is critical to avoid competition with the subsequent soybean crop.

Core Ideas Reduced lignin and reference cultivars did not differ in forage accumulation. Forage accumulation was greater with a fall harvest or a 40‐d cutting schedule. Reduced lignin alfalfa averaged 8% less acid detergent lignin and 10% greater neutral detergent fiber digestibility. Cutting treatments with shorter harvest intervals increased forage nutritive value. Delaying reduced lignin alfalfa harvest increased forage mass and maintained quality. Reduced lignin alfalfa (Medicago sativa L.) cultivars have the potential to increase the feeding value of alfalfa for livestock by improving forage fiber digestibility and to increase harvest management flexibility. The objectives were to compare the forage accumulation and nutritive value of reduced lignin and reference alfalfa cultivars when subject to diverse cutting treatments in the establishment and first production year. Research was established in 2015 at four locations in Minnesota. Reference alfalfa cultivars 54R02, DKA43–22RR, WL 355.RR, and the reduced lignin cultivar 54HVX41 were subject to cutting treatments with variable intervals between harvests. Cultivar by cutting treatment interactions were not significant (P > 0.05), but cultivar and cutting treatment effects were significant. Cultivars did not consistently differ in forage accumulation. Establishment year forage accumulation was greater when a fall harvest was taken, and first production year forage accumulation was generally greatest when alfalfa was harvested on a 40‐d cutting schedule. Compared to reference alfalfa cultivars, 54HVX41 had an average of 8% less acid detergent lignin (ADL) and 10% greater neutral detergent fiber digestibility (NDFD) but was similar in crude protein (CP) and neutral detergent fiber (NDF) concentrations. Cutting treatments with shorter harvest intervals increased forage CP and NDFD and decreased NDF and ADL concentrations. With a 5‐d harvest delay, 54HVX41 harvested on a 35‐d harvest interval had a 21% gain in forage mass and a 3% reduction in relative forage quality (RFQ) compared to reference cultivars harvested on a 30‐d harvest interval, which could allow for increased management flexibility.

The limited time available for cover crop establishment after maize (Zea mays L.) and soybean [Glycine max (L.) Merr.] harvest is one of the main reasons for low cover crop adoption in the upper Midwest. Therefore, a 2-yr multilocation study was conducted to evaluate winter annual cover crops establishment, their effect on main crop grain yields, and soil water content when interseeded into standing maize and soybean. Treatments were three interseeding dates (broadcasting at R4, R5, and R6 growth stages for maize, and R6, R7, and R8 for soybean) and three cover crops (win-winter rye [Secale cereale L.] plus a no cover crop control). Cover crop establishment and growth varied with interseeding date across locations and seasons for both maize and soybean systems. Averaged over the years, rye produced more green cover and biomass than the oilseeds in spring. However, at the northern-most site, the greatest (40%) green cover was recorded from pennycress and indicates its potential as a cover crop. Seeding date and cover crops did not negatively affect maize or soybean grain yields or soil water content. Generally, cover crop establishment and growth were better in the soybean system than maize due to better light penetration. Further research is needed to develop better suited cultivars and/or agronomic management practices for interseeding into maize. The results of this study indicate that producers could integrate these covers to diversify and add ecosystem services to soybean production practices.Abbreviations: PAR, photosynthetic active radiation; PC, pennycress; PLS, pure live seeds; PPD, plant population density; WC, winter camelina.

A 3 site‐year study was conducted to investigate the impact of roller‐crimped rye (RC) (Secale cereale L.) mulches on soil N immobilization and subsequent effects on weed suppression and soybean [Glycine max (L.) Merr.] yield. Treatments consisted of: (i) RC, (ii) conventional tillage with neither rye cover crop nor weed control measures (WC), (iii) conventional tillage plus herbicide weed control (CT+HB), and, (iv) roller‐crimped rye plus herbicide (RC+HB). The rye biomass varied between the sites with 4400, 8300, and 7084 kg ha−1 dry matter (DM) for Goldsboro 2009, Kinston 2009, and Kinston 2010, respectively. During the season, the flow of soil inorganic N was monitored via ion‐exchange probes and by direct extractions at two depths (0–10 and 10–25 cm) every 2 wk. Tissue data was collected every 2 wk on soybean and redroot pigweed (Amaranthus retroflexus L.) to determine the C/N ratio. For all sites, peak N immobilization occurred between 4 and 6 weeks after planting (WAP), indicated by a reduction in soil inorganic N. Results from the ion‐exchange probes showed similar trends of the extractable soil inorganic N at all sites. Pigweed C/N ratios revealed a growing divergence between the two systems, with a severe N deficiency in the RC. Even with varying rye biomass production across environments the RC system created an extremely low N environment, suggesting that when a cereal cover crop is paired with a legume cash crop, reduced weed crop interference may result, with little reduction in soybean yield.

Core Ideas Winter annual oilseed crops are being used in annual cropping systems to add value. We explored trade‐offs in oilseed yield and provision of ecosystem services. Oilseed cover crop yield was greatest when harvested late rather than early. Pennycress and camelina reduced N in the soil profile compared to soybean alone. To gain additional value from land during winter fallow periods in corn (Zea mays L.)–soybean [(Glycine max (L.) Merr.] rotations, growers in the Upper Midwest are considering winter annual oilseed crops such as field pennycress (Thlaspi arvense L.) and winter camelina [Camelina sativa (L.) Crantz]. The objective of this study was to (i) explore trade‐offs between soybean and winter oilseed crop yield as influenced by timing of winter oilseed crop harvest and of soybean planting, and (ii) evaluate how inorganic soil N was affected by the presence or absence of pennycress or camelina. Field experiments were conducted at three sites in Minnesota to evaluate yield of field pennycress and camelina winter oilseed crops planted in a double‐crop system or planted early or late in a relay‐cropping system. Soybean grain yield was reduced in one of the three sites in 2014 and at all sites in 2015. However, the addition of a winter oilseed crop in a relay‐ or double‐crop system increased the total oilseed production. The optimal cropping strategy for achieving maximum total oilseed crop yield was dependent on environment. Winter oilseed crop yield tended to be greatest when harvested late rather than early in either a relay‐ or double‐crop system. Pennycress and camelina significantly reduced inorganic soil N along the entire soil profile compared to soybean alone, especially in the spring (53–72%) and autumn (18–19%) when the potential for N loss is greatest. Pennycress and camelina, when integrated with soybean in a late‐planted relay‐ or double‐crop system, increased total crop yield while providing critical ecosystem services.

Agriculture in the Upper Midwest of the USA is characterized by a short growing season and unsustainable farming practices including low-diversity cropping systems and high fertilizer inputs. One method to reduce the magnitude of these problems is by integrating a winter annual into the summer-annual-dominant cropping system. For this reason, pennycress (Thlaspi arvense) has garnered interest in the agricultural community due to its winter annual growth habit and potential for industrial oil production, making it an ecologically and economically desirable crop. Despite decades of research focusing on pennycress as an agricultural weed, little is known about its best management practices as an intentionally cultivated crop. The majority of agronomic research has occurred within the past 10 years, and there are major gaps in knowledge that need to be addressed prior to the widespread integration of pennycress on the landscape. Here we review relevant agronomic research on pennycress as a winter annual crop in the areas of sowing requirements, harvest, seed oil content, seed oil quality, cropping strategies, ecosystem services, and germplasm development. The major points are as follows: (1) there is little consensus regarding basic agronomic practices (i.e., seeding rate, row spacing, nutrient requirements, and harvest strategy); (2) pennycress can be integrated into a corn (Zea mays)soybean (Glycine max) rotation, but further research on system management is required to maximize crop productivity and oilseed yields; (3) pennycress provides essential ecosystem services to the landscape in early spring when vegetation is scarce; (4) breeding efforts are required to remove detrimental weedy characteristics, such as silicle shatter and high sinigrin content, from the germplasm. We conclude that pennycress shows great promise as an emergent crop; however, current adoption is limited by a lack of conclusive knowledge regarding management practices and future research is required over a multitude of topics.

Cover crop mulches have been successful in reducing weed severity in organic soybeans. This study examined six rye cultivars (SRCs) used as cover crops to determine which were most adapted for use with a roller-crimper in the southeastern U.S. To be an effective mulch, a rye cultivar must produce high biomass and reach reproductive growth stage to facilitate mechanical termination via the roller-crimper prior to soybean planting. Rye cultivars were planted at three locations in North Carolina over the 2009 and 2010 growing seasons. Each rye cultivar was mechanically terminated via a roller-crimper implement. Rye cover crops were terminated on two dates and soybeans were immediately no-till planted into the mulch. In 2009, all rye cultivars produced greater than 9000 kg ha −1 rye biomass dry matter (DM) with the exception of Rymin at Plymouth (2009), but in 2010 only the early flowering cultivars produced in excess of 9000 kg ha −1 DM. There were no detectable soybean yield differences between the SRCs and the weed-free checks, and weed control was excellent across all SRCs at both Plymouth and Salisbury (2009). After an unseasonably cold and wet winter in 2010, the late flowering rye cultivars were not fully controlled by the early termination date due to delayed maturation (less than 65% control at 2 WAP) whereas the early flowering cultivars were fully controlled (100% control at 2 WAP). Rye biomass production was below 9000 kg ha −1 DM for the late flowering and dough development rye cultivars. The early-terminated rye plots had greater weed coverage across all SRCs than those from the late termination date (P < 0.01). However, weeds did not impact soybean yield for either of the termination dates. Soybean yield in 2010 was modeled with rye biomass and soybean population used as covariates, and for both termination dates, soybean yield was proportional to rye biomass production. Early flowering rye cultivars offer producers the widest range of termination opportunities that best coincide with their cash crop planting dates.