John Wallace, Weed Management Extension Specialist, Penn State University
In the coming year(s), Penn State will be leading a regional, SARE-funded project to better understand the agronomic, environmental, and economic challenges that prevent the adoption of cover crop interseeding in field corn. The team is comprised of Penn State and Cornell University researchers and extension educators, the New York State IPM program, and several cooperating Soil and Water Conservation Districts in PA and NY.
Interseeding cover crops early in the corn growing season (i.e., V4-V6) can potentially increase the benefits of cover cropping in growing regions that struggle to establish fall-sown cover crops. Previous studies and on-farm trials in our region have demonstrated the benefits of interseeding with specialized grain drills for improving establishment rates. Best management practices for early interseeding have also been developed for this region, including cover species selection and herbicide management.
However, there has been less documentation of conservation and soil health benefits associated with early interseeding compared to either winter fallow or post-harvest cover crop seeding. Understanding these benefits, and potential management tradeoffs, will help understand the return-on-investment of this practice. Finally, there is a general consensus that early cover crop interseeding works better in certain growing regions and production systems than others. Defining the geographic and agronomic fit for cover crop interseeding is one of our project objectives.
If you are interested in following the project, or participating in on-farm trials, please take a moment to complete this brief anonymous survey (link below). This information will help the projectteam prioritize on-farm trials and extension-outreach programming in the coming year(s).
Sandra Wayman1, Lisa Kissing Kucek2, Virginia Moore3, Lais Bastos Martins4, Matt Ryan1 1Soil and Crop Sciences Section, SIPS, Cornell University, 2USDA ARS Dairy Forage Research Center, 3currently: NC State University. Feb 2021: Plant Breeding and Genetics Section, Cornell University, 4Crop and Soil Sciences, NC State University.
Legume cover crops have room for improvement Winter annual legume cover crops are essential management tools for organic farmers; they fix nitrogen, improve soil health, and suppress weeds. Winter annual cover crops are planted in the early fall, overwinter, then grow vigorously in the spring and complete their life cycle in the summer. However, many farmers struggle with these cover crops. Poor emergence, low vigor, and winter kill are basic challenges that could be addressed through plant breeding. Unlike cash crops, cover crops have received relatively little attention from plant breeders in the past. Thus, even modest investments in germplasm improvement could return large benefits. The Sustainable Cropping Systems Lab is taking advantage of this opportunity to improve legume cover crops for organic farmers by participating in the national Cover Crop Breeding Network (Fig. 1). Sites across the U.S. are developing cover crop lines best suited to each region. Our goal is to develop new varieties that boost the sustainability of organic farms, using classical plant breeding methods rather than genetic engineering. We are working with three species of winter annual legume cover crops: hairy vetch (Viciavillosa), crimson clover (Trifoliumincarnatum), and winter pea (Pisumsativum) (Fig. 2).
Figure 1. Sites participating in the legume cover crop breeding program.Figure 2. Left, hairy vetch; top right, crimson clover; bottom right, winter pea.
The traits farmers want To inform our breeding efforts, we conducted a national survey of organic and conventional farmers to learn which cover crop traits were important to them (Fig. 3, Wayman et al 2017). We received 417 responses to the survey, and 87% of the respondents reported they used cover crops. Organic farmers reported placing greater value on the ecosystem services from cover crops than did conventional farmers. The top four traits chosen by respondents as important for legume cover crops were nitrogen fixation, winter hardiness, early vigor and establishment, and biomass production (Fig. 3).
Figure 3. Percentage of farmers (organic and conventional together) who rated the given traits for four focus cover crops as “important” or “very important” out of total of five rating levels (“not at all important” to “very important”). Numbers above bars indicate count of farmer respondents for each cover crop and trait. Stars on bars indicate significant differences between conventional and organic farmers for that particular trait and cover crop (chi-square test, * is P < 0.05, *** is P <0.001).
Genetic improvement The steps in developing better cover crop varieties for farmers are 1) create better genotypes through breeding nurseries, and 2) select the best new varieties through advanced line trials. Researchers at different sites in the project are selecting for different legume traits based on their region. In the legume cover crop nurseries planted at Cornell University, we are selecting for winter-hardiness in addition to early-flowering.
We began the breeding program with seeds of hairy vetch, crimson clover, and winter pea from commercially available varieties, lines from worldwide breeding programs, landraces selected by farmers, and PI (plant introduction) lines from the U.S. National Plant Germplasm System Germplasm Resources Information Network (NPGS GRIN) seed bank.
For five seasons, we have planted breeding nurseries of the three legume cover crop species at our Cornell University site. We selected plants based on fall vigor, low winterkill, spring vigor, early maturity, and soft seed. We culled undesirable plants before flowering, and saved seeds from the best plants to replant in the following year. We selected between 2.8% and 4.6% of the hairy vetch individuals across the breeding seasons, and between < 0.01% and 2.8% of crimson clover individuals.
For winter pea, the first year of the breeding program evaluated the performance of accessions from the National Plant Germplasm System. The results informed what material to include in breeding nurseries. For the following three seasons, we planted and selected early generation breeding lines originating from the USDA-ARS Grain Legume Genetics Physiology Research Center in Pullman, WA. The best 0.5 to 1.4% of the winter pea plants were chosen as new breeding lines, based on winter survival and vigor. In 2019, the winter peas experienced severe winter conditions 900 feet above Cornell University’s campus, where almost all the winter peas died from winterkill.
Advanced line trials In the 2018-2019 and 2019-2020 seasons, our breeding lines were tested against commercial varieties in multi-environment advanced line trials. Sites across the country (Fig. 1) grew replicated plots of breeding lines and commercial checks of each legume cover crop species. Each trial grew the legume cover crops alongside triticale to simulate grass-legume cover crop mixes typically grown by farmers. Breeding lines of each crop were compared with commercial check varieties to assess if our breeding program has produced something better than what is currently available to growers on the market. Lines were evaluated for emergence, winter survival, fall and spring vigor, flowering timing, disease, and biomass. The best lines of each species will be tested again in the 2020-2021 season, and performance of these lines will determine variety release and commercialization.
Nursery and advanced line trial performance Testing variety performance is currently underway. An analysis of the advanced line trials will identify if any lines perform well across the U.S., or if certain lines excel in specific regions. Ideally, we would find a few breeding lines performing well across all sites. Such “broadly adapted” lines could be sold as varieties nationwide. If certain lines are excellent in specific regions, however, seed companies are interested in selling lines as “regionally adapted” varieties. In the meantime, data from the breeding nurseries indicated patterns in regional performance. The results suggest different trends among species, which are detailed below.
Hairy vetch We found no hairy vetch line that performed best in both the fall and spring (Kissing Kucek et al. 2019). Instead a tradeoff between fall growth and spring growth was observed. As a result, the breeding program is screening and selecting for vigor at both times of the year, with the goal of finding ideal lines that have the best overall seasonal performance.
Over two seasons and a dozen U.S. sites (Fig. 1), we tested 16 hairy vetch breeding lines and six checks. Breeding lines developed by the Cover Crop Breeding Network beat the commercial check lines in both years. Winning lines, however, differed among sites. Colder northern environments had different winning breeding lines than warmer southern and western sites. Our Cornell University site proved to be an intermediate winter environment compared with the harsh upper Midwest and mild southeast and west. In cold winters like 2018-2019, Cornell University shared winning lines with MN, WI, and NE. In contrast, during warm winters like 2019-2020, NY was more similar to southern and western sites. These results suggest that the best performing lines in NY may vary depending on weather conditions, with warmer years in NY mimicking southern and Mid-Atlantic sites, and colder winters grouping NY with the northern Midwest. To select for resilient lines that can handle variable winter conditions, Cornell University breeding nurseries include material from warm and cold regions of the U.S.
The 2018 hairy vetch line from Cornell University was the second highest seed yielding in our OR trials, demonstrating 25% more seed yield than checks (Hayes and Azevedo, 2019). High seed yield is a very desirable trait for seed growers and seed companies.
Crimson clover Two commercially available varieties of crimson clover, ‘Dixie’ and ‘Linkarus’ were included as checks in our trials. ‘Dixie’ is a variety developed in GA that exhibits high forage biomass production, ability to reseed, and high amounts of hard seed (Hollowell 1953). ‘Linkarus’ is a highly productive winter hardy crimson clover which was developed in Germany. In general, we have seen ‘Dixie’ perform well in the southern locations, while ‘Linkarus’ performs better at northern locations. In the harsh NY winter of 2018-2019, our breeding lines beat both ‘Dixie’ and ‘Linkarus’.
In two seasons, we also evaluated crimson clover breeding lines for biomass production at Cornell University. Biomass production is important for all farmers, who often use crimson clover as a green manure. The crimson clover lines with the highest biomass production were included in the next season’s nursery. At our Cornell University site in 2018, ‘Linkarus’ had the highest biomass production, with 1.5 to 2.9 times more biomass production than ‘Dixie.’ Additionally, to compare top-performing lines from nursery selections at a dozen sites across the country, we tested 13 crimson clover breeding lines and 2 checks over two seasons. In the first season, a soft-seeded MD breeding line produced the most biomass, followed by ‘Linkarus’ and a Cornell University breeding line. In the second season, ‘Dixie’ produced the most biomass, followed by a MD breeding line.
Breeding lines have also been tested for seed yield in OR, where most crimson clover seed is produced. The two checks beat all breeding lines for seed yield (Hayes and Azevedo 2019). As a result, we have increased our focus on selection for seed yield in the crimson clover breeding program.
Winter pea In NY, winter peas have often been challenging for farmers due to poor winter survival. In the 2017-2018 season, 0.5% of plants were selected based on winter survival and vigor. Their seed is currently being increased so they can be included in future advanced line trials. In the 2019-2020 season, our Cornell University site experienced optimal weather to discriminate cold tolerance. Data from 39 new and different genotypes helped us choose the entries with the best potential to be increased for the advanced line trial.
Over two seasons, we tested 21 winter pea lines and five checks in our advanced line trial. In the 2018-2019 season, the winter pea advanced line trials did not survive at Cornell University and in MN due to harsh winter conditions. Southern locations (CA, GA, NC, OR) of the advanced line trials had overall higher biomass production than did the northern locations (MD, MO, NE, WI) in 2018-2019. Across all sites, our breeding lines performed better than the checks. Indeed, one of our breeding lines was in the top five performers across five different locations, showing good potential for release as a variety. Many of our breeding lines performed better than the two commercially available cultivars in the trial.
An additional observation for winter pea is that lines with the highest vigor in fall may have poor biomass production in the spring. This is not uncommon in peas; if the plants grow too much in the fall their exposed above-ground biomass is susceptible to frost damage and winter kill.
Next steps As part of this project, we will release varieties of legume cover crops adapted to specific regions. Our next steps include selecting for high-vigor and improved material in our nurseries, continuing advanced line trials with this new material, planting seed increases, and inviting farmers and seed company representatives to the breeding sites to evaluate the lines. We planted a third year of advanced line trials in 2020, after which we will determine if any lines are consistently high performers and good candidates for variety release.
Cover Crop Breeding Network team member coming to Cornell In February 2021, a Postdoctoral Scholar with the team, Virginia Moore, will join Cornell as an Assistant Professor with SIPS in the Plant Breeding and Genetics Section. Virginia’s program will focus on breeding for sustainable cropping systems. Virginia has been involved in the national Cover Crop Breeding Network as a project manager since 2019. She is currently based at USDA-ARS in Beltsville, MD, and completed her graduate work at the University of Wisconsin, with a MS in Agroecology and Agricultural & Applied Economics and a PhD in Plant Breeding & Plant Genetics. She sees plant breeding as a powerful tool to increase sustainability of cropping systems, with goals like a) reducing pesticide inputs through breeding for pest resistance, b) increasing cover crop adoption by developing regionally adapted cultivars, c) selecting crops for organic systems, and d) diversifying cropping systems through rotations and intercropping. She is excited to continue working in cover crop breeding and to take on new crops including alfalfa and other forages, hemp, and switchgrass.
Acknowledgements: Thanks to Gerald Smith for sharing data and resources. Thanks to Chris Pelzer, Katherine Muller, Dylan Rodgers, James Cagle, Nina Sannes, and Matt Spoth for help planting the nurseries.
References Hayes, R and M. Azevedo. 2019. Seed yield of hairy vetch and crimson clover breeding lines. Raw data available upon request.
Hollowell, E. A. 1953. Registration of varieties and strains of crimson clover (Dixie crimson, Reg. No. 1). Agron. J. 45:318-320
Kissing Kucek, L.; H. Riday; et al. 2019. Environmental influences on the relationship between fall and spring vigor in hairy vetch (Vicia villosa Roth). Crop Science. 59:1-9
Wayman, Sandra & Kissing Kucek, Lisa & B. Mirsky, Steven & Ackroyd, Victoria & Cordeau, Stéphane & Ryan, Matthew. (2017). Organic and conventional farmers differ in their perspectives on cover crop use and breeding. Renewable Agriculture and Food Systems. 32. 376-385. 10.1017/S1742170516000338.
Elson Shields, Entomology Department, Cornell University
The increased adoption of cover crops as a soil conservation and soil health building strategy is not without increased risk from insect pest problems. Increased insect pest risk can be managed with a combination of timely killing of the cover crop, pest scouting, and additional timely application of insecticide.
The best-case scenario for the management of the cover crop to reduce insect risk is to kill the cover crop far enough in advance that the cover crop is completely dead prior to the planting of the crop. Foliar feeding insects often can survive on the dying cover crop, and if the new crop emerges before the cover crop is completely dead, the foliage feeding insects simply move from the dying cover crop onto the newly emerged and tender crop plants. This is termed a green bridge.
The worst-case scenario for insect risk is to plant into a green cover crop which has been rolled prior to planting and then sprayed with an herbicide to kill it after the crop has been planted. This provides an excellent green bridge for the insects, like black cutworm larvae and armyworm larvae, to move directly onto the newly emerging crop.
Cover Crop Bridging Insects:
Black cutworm: Black cutworm is a long-ranged migrant which overwinters in the southern US. Moths typically arrive in NY during mid-April to early-May on the early weather systems. Moths are attracted to grassy areas, grassy cover crops, grass waterways, and fields with grassy weed problems. Eggs are laid on these plants and larvae begin feeding on these plants. In the situations where producers kill the cover crops or grassy weed areas with herbicide or tillage, the black cutworm larvae continue to feed on the dying plants for 1-2 weeks. When corn seedlings start emerging, the existing larvae then move from the dying plants onto the growing corn. Since black cutworm larvae do not start their cutting behavior until mid-size (L-4), the early larval development on the grassy weeds is a critical association with the economic association of black cutworm to seedling corn. In the situations where eggs are laid on emerging corn, corn development to V6, a stage where black cutworm has difficulty cutting occurs before the black cutworm develops to the larval stage where they begin cutting (L4).
Since black cutworm larval development on existing plants in the field prior to the planting and emergence of the corn is a critical component in the development of economic infestations, the management of the green plants prior to corn planting is important. Elimination of the green bridge between the cover crop and/or grassy weed cover at least 2 weeks before the emergence of corn seedling dramatically reduces the risk of a black cutworm infestation in NY corn fields. If the separation between the killing of the cover crop/grassy weeds and the emergence of the corn crop cannot be at least 14 days, the corn seedlings need to be scouted for the presence of foliar feeding, early cutting and the presence of larvae. To the trained eye, pre-cutting foliar feeding is very obvious and easily detected.
Armyworm: Armyworm is a long-ranged migrant similar to black cutworm, but often arrives 15-30 days later in NY. It overwinters in the southern US, and the moths emerging in April in the south use the weather systems to move long distances. When the moths arrive, they are attracted to grass hay fields or grassy cover crops. If the eggs are laid in the hay field, larvae will feed on the grass and only move when the field has been stripped, thus the name armyworm. Neighboring corn fields are then attacked by the larger marching larvae. When eggs are laid in a grassy cover crop, the larvae will feed on the cover crop until it is stripped before moving. If corn is emerging in the cover crop, they will simply move onto the young corn plants. Armyworm larvae are totally foliage feeders and do not cut plants like black cutworm. With timely scouting, this insect is easily controlled with an application of foliar insecticide. Usually, the infestation is missed until the field is stripped and the larger larvae are moving into a neighboring field.
Seed corn maggot: Seed corn maggot (SCM) adults (flies) are attracted to decomposing organic material. This organic matter can range from animal manures to decomposing plant material/killed cover crop. Fresh decomposing organic matter is more attractive to the flies for egg deposition than composted organic matter; although, SCM will also lay eggs in composted organic matter. Adult flies are present for egg laying from early May until late September. The highest risk fields for SCM problems would be a green manure crop covered with a thick layer of animal manure prior to planting the crop. High manure application rates without thorough incorporation before planting of large seed crops is a high SCM risk field. Damage from SCM is plant stand reduction, and without insecticide protection, plant stands can be reduced 30%-80%. The primary reason for insecticide treatment (Poncho, Cruiser, etc) on large seed crops (corn, soybeans) is protection against SCM-related plant stand loss. Under extremely heavy SCM pressure, the insecticide seed treatment can be overwhelmed, resulting in corn/soybean stand losses.
To reduce risk from SCM, cover crops should be killed and allowed to turn brown before planting the season’s crop. In addition, applications of manure should be subsurface rather than surface applied.
Wireworms: Adult wireworms (click beetles) are attracted to small grains, grass fields, run-out alfalfa fields which are mostly grass, and grass-based cover crops. Adult beetles search out these hosts during the growing season (June-August) and lay eggs. The larvae (wireworms) hatch and feed on a wide array of roots for multiple years. In cropping sequences where grassy/small grain/cover crops are present in the field during the June-August period, wireworms feeding on new seedlings and root crops can become an economic problem. While corn is technically a grass, wireworms do not find corn fields attractive for egg laying. However, small grains are very attractive. Generally, spring planted grains are more attractive than fall planted grains which mature in early summer. In conventional production systems, the insecticide seed treatment generally is effective at reducing the impact of wireworm feeding. However, in the organic production system, there are no effective rescue treatments for wireworm infestations/feeding damage. If grassy cover crops are the only grass in the cropping sequence, timely crop termination before June will reduce the attractiveness to wireworms for egg laying.
White grubs: In NYS, there are two different groups of white grubs which can be problematic. The first group is the native white grubs which have multi-year life cycles and the second group is the invasive annual white grubs (Japanese Beetle, European Chafer). Adults from both groups are attracted to grassy habitats to lay their eggs during mid-June to mid-July. Eggs hatch during August, and the larvae begin to feed on grass roots. In the case of the invasive annual white grubs, the larvae grow quickly and achieve more than 50% of development before winter. In the spring, the larvae resume development and are quite large when the grassy field is rotated to corn or soybeans and the new plants are quite small. Plant death is caused by these large larvae feeding on plant roots faster than the plant can generate roots. Larvae become adults in June and the cycle repeats. In the case of the native multiyear white grubs, the life cycle is similar but larval development requires 2-4 years depending on the species. Subsequent crops following the grassy/cover crop/small grain field are then impacted differently. With annual white grubs, the damage to the subsequent crop is confined to the following year only. In the case of native white grubs, subsequent crops could be impacted up to 4 years with declining damage levels each year.
The following two different cropping scenarios seem to place subsequent crops at higher risk. The most common case is the alfalfa field which has become mostly grass or a grass hay field which is then rotated into a large seed crop like corn or soybeans. The second scenario is the field which has been planted to a grass-based cover crop and not killed during the June-July egg laying period. In most cases, the insecticide seed coating on all corn and some soybean seeds reduce the impact of white grubs on subsequent crops. High white grub populations can overwhelm the insecticide, however.
Slugs: Increasing the organic soil cover with either the use of cover crops or last year’s crop waste increases the slug problem. In cool wet springs, which slow plant emergence and growth, damage from slug feeding can be severe. There is a little anecdotal evidence to suggest the presence of green cover reduces the slug damage because of the surplus of green tissue. In these cases, slugs miss the newly emerging plants and feed on the green cover crop.
By Brian Caldwell, Jeff Liebert, and Matthew Ryan
Soil and Crop Sciences Section, School of Integrative Plant Science, Cornell University
Interest in no-till planting soybeans into a rolled-crimped winter cereal cover crops is increasing among New York State organic grain farmers. This approach is also called “organic rotational no-till” because tillage is used to establish the cover crop in the fall. The rolled-crimped cover crop acts as mulch and helps suppress weeds in the summer. In addition to soil health benefits, this system has potential to save time and fuel by eliminating mechanical inter-row cultivation for weeds in organic soybean production.
In September of 2013, cereal rye, winter barley, and triticale were planted at an organically managed farm in Penn Yan, NY in anticipation of rolling-crimping them for no-till soybean planting the following spring. Two cultivars were planted per species: ‘Aroostook’ and a variety not stated (VNS) rye, ‘McGregor’ and ‘Verdant’ barley, and ‘TriCal 718’ and ‘TriCal 815’ triticale. The six cultivars across three species were arranged in a randomized complete block design with four replications, and plots were 15 x 15 feet to accommodate farm-scale equipment. Immediately prior to rolling-crimping, cover crop biomass was sampled from each plot. Cover crop biomass was determined by clipping the plants at the soil surface within a 5.4-ft2 (0.5-m2) quadrat, oven-drying the vegetation at 122°F for one week, and then weighing the dried samples. Weed biomass samples were collected approximately 15 weeks after soybean planting, which corresponds to the maturation of one of the most dominant weeds in the experiment, common ragweed (Ambrosia artemisiifolia L.). Weed biomass samples were collected, dried, and weighed as described for the cover crops, except 2.7-ft2 (0.25-m2) quadrats were used.
Soil types in this field were Cayuga silt loam and Honeyoye silt loam with 3-8% slopes. Soil test results showed the field was low in pH (5.7), P (3.8 lb/acre), and soil organic matter (2.0%).
This was an on-farm trial in conjunction with a series of experiments at the Musgrave Research Farm in Aurora, NY and the USDA Beltsville Agricultural Research Center in Beltsville, MD, which explored how different cultivars and termination timing of these three rolled-crimped winter cereal species affected weed suppression and soybean crop performance. Previous research suggested that optimal termination timing with a roller-crimper occurs when winter cereal cover crops have reached anthesis (flowering, Feekes growth stage 10.51), which is typically between late May and early June in the Northeast, depending on the winter cereal cover crop species. With anthesis signifying the transition from vegetative to reproductive growth, cover crop termination with a roller-crimper can be as effective as termination with synthetic herbicides (Ashford and Reeves, 2003; Davis, 2010; Mirsky et al., 2009).
Termination timing is particularly important for multiple reasons. If the cover crops are rolled prior to anthesis, termination can be incomplete and the cover crops will continue to grow, competing with soybean seedlings for light, water, and nutrients, and eventually producing seed that can become a weed later in the rotation. However, if termination timing occurs well past anthesis (i.e., too late), the winter cereal cover crops might similarly produce viable seed that can become a weed the following year, and late rolling will delay soybean planting, possibly reducing yield potential.
Winter cereals were planted with an Amazone Airstar Profi combination drill-power harrow on September 16, 2013, and terminated in 2014 on May 30 and June 5 with a 10-ft front-mounted roller-crimper (I & J Mfg., Gordonville, PA; Figure 1). The cover crops were drilled 1 inch deep in 5-inch wide rows with an Esch No-Till 5507 on the same day, and immediately after, rolling-crimping (Figure 2). Cereal grains can mature quickly in mid-May, which makes frequent growth stage scouting particularly important during that period of time. Feekes growth stages were 10.5, 10.54, and 11.1 for triticale, rye, and barley at the early termination date (May 30) and 10.54, 11.1, and 11.2 at the later date (June 5), respectively. These stages correspond to the onset of flowering (anthesis) through milky ripe for the early termination date, and the end of flowering through soft dough for the later date.
Figure 1. Front-mounted roller-crimper unit flattening a barley cover crop at the on-farm site. The blunt meal blades on the cylinder crimp, rather than cut, the cover crops. Filled with water, the roller-crimper weighs approximately 2600 lb.Figure 2. Indentations in the rolled cover crops represent soybean drilled in 5-inch rows at the on-farm site in 2014. Extra weight was added to the drill to help penetrate the thick mulch and hard, dry soil.
Cover crop biomass. Winter cereal biomass production at this site was relatively high, with over 8000 lb/acre for rye, 7000 lb/acre for triticale, and 5000 lb/acre for barley across both dates (Figure 3). After being rolled, the cover crops form a thick layer of mulch (Figure 4), which serves as the primary source of weed suppression in this system.
Figure 3. Cover crop biomass production at two termination dates in 2014. Error bars represent the standard error of the mean, and bars with the same letters represent values that are not significantly different at P < 0.05.Figure 4. Deep layer of weed-suppressive cover crop mulch.
Based on work by Teasdale and Mohler (2000), achieving at least 7000 lb/acre of cover crop biomass at termination is likely to result in good weed suppression when rolled-crimped in this system (Mirsky et al., 2012; Mirsky et al., 2013). Thus on both planting dates, the rye and triticale cover crops produced enough biomass to exceed the recommended threshold, but barley did not. However, too much cover crop biomass can also be a problem. Lodging of up to 60% of the plants in a given plot was observed in rye terminated at the late termination date. As coulters on no-till planters and drills are not typically designed to cut through large amounts of residue, lodged plants that lay diagonally or perpendicular to the direction of rolling-crimping and no-till planting can impede adequate soybean seed placement, which can reduce germination and potentially decrease soybean yield. Also, if hair-pinning (i.e., residue forced into the furrow) is particularly problematic, poor seed-to-soil contact can result in gaps in the canopy, which can reduce late-season weed suppression.
Cover crop bounce-back was relatively low across all treatments with less than 20% of the barley plants “standing back up” after rolling-crimping, and less than 15% of the triticale and 10% of the rye plants doing the same. It is unlikely that the incompletely-terminated cover crops—most of which stood at a 45° angle and simply died at a slower rate than their flattened counterparts—impacted soybean yield. However, the resulting seed some cover crop plants produced might have resulted in volunteer cover crops in the following year.
It is worth noting that no-till drilling soybean seed into rolled cover crop mulch is not the recommended practice for most situations (Mirsky et al., 2013). Drilling can require adding a considerable amount of additional weight to the drill units to achieve acceptable, uniform planting depth if soil conditions are dry. Instead, a no-till planter set at 15- or 30-inch rows tends to perform better over a wider variety of soil conditions and biomass levels. We used a drill for the on-farm trial because it was the only no-till equipment available. Similarly, rolling-crimping and no-till drilling would ideally be completed in a single pass, but two operations were required in this experiment because the no-till drill width did not match the width of the roller-crimper.
Weed biomass. Across all treatments, weed biomass in early fall (September 15) tended to be lower in plots with greater cover crop biomass (measured before rolling-crimping). We observed lower weed biomass in late-terminated rye and triticale compared with early-terminated barley (P < 0.05), but weed biomass was not statistically different between the two termination dates within each species (Figure 5).
Figure 5. Weed biomass in early fall for two cover crop termination dates in 2014. Error bars represent the standard error of the mean, and bars with the same letters represent values that are not significantly different at P < 0.05.
The perennial weed quackgrass (Elymus repens [L.] Gould) comprised 44% of the total weed biomass across all treatments. Across all species, mean quackgrass biomass was 512 lb/acre at the early termination date and 294 lb/acre at the late termination date (P = 0.08). This is an important consideration, since perennial weeds tend to proliferate in the absence of tillage. Common ragweed was the other dominant weed species in the experiment at 42% of the total weed biomass across all treatments. Similarly, mean common ragweed biomass was lower (P = 0.09) in the cover crop treatments terminated later (220 lb/acre) compared with the earlier termination date (541 lb/acre).
Soybean yield. Soybean yield was relatively high across all treatments, averaging 40 bu/acre (Figure 6). Even if weeds do not reduce crop yield, they can produce seeds and cause problems for future crops in the rotation. In this trial, late-terminated rye and triticale produced similar results, with high cover crop biomass, minimal cover crop bounce-back, low weed biomass, and relatively high soybean yields. Although soybean yield was not statistically different, early-terminated barley had the lowest cover crop biomass and greatest weed biomass (Figures 3 and 5). Thus, our results indicate that rye or triticale perform better than barley in this system, and terminating the cover crops at a slightly later date can be advantageous for reducing weeds (especially quackgrass and common ragweed) without sacrificing soybean yield.
Watching the weather. Soil moisture conditions are also very important to consider. In an extremely dry spring, such as in 2016, transpiration from a dense cover crop stand can reduce soil moisture, which can inhibit soybean seed germination and reduce yield potential. When the soil is this dry, the best option might be to forgo planting soybean entirely. Instead, it might be advisable to allow the cover crop to grow to maturity, harvest it, and plant a different crop afterwards. In most years in New York, however, limited spring rainfall is not a problem. Still, winter cereal cover crops can dry out the surface of the soil, making seed placement difficult. In this situation, we have found that adjusting planting dates based on rain events can be helpful to ensure the planter can penetrate the soil and achieve good seed-to-soil contact. In addition to no-till planting right after a rain, another trick that we have used is to add weight to the planter to increase the down pressure on the front coulters.
Figure 6. No-till planted soybean yields in rolled-crimped cover crops at the Martens Farm in 2104. Yields were not significantly different (P < 0.05) across all treatments.
Conclusions. This on-farm trial augmented our research farm experiments in several ways. We had high cover crop biomass production at this site, and we were able to observe the results from different types of equipment than were used at the Musgrave Research Farm or Beltsville Agricultural Research Center. Perhaps most importantly, the good yields on this small field gave the farmer confidence in using this method on more soybean acres, and he has since advocated this approach at farmer meetings. However, our on-farm results were only from one year, so trials on more sites and over more seasons are needed to refine our management recommendations.
This work was supported by a joint research and extension program funded by the Cornell University Agricultural Experiment Station (Hatch funds) and Cornell Cooperative Extension (Smith Lever funds) received from the National Institutes for Food and Agriculture (NIFA) U.S. Department of Agriculture (Project: 2013-14-425). Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the authors and do not necessarily reflect the view of the U.S. Department of Agriculture.
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However, there has been less documentation of conservation and soil health benefits associated with early interseeding compared to either winter fallow or post-harvest cover crop seeding. Understanding these benefits, and potential management tradeoffs, will help understand the return-on-investment of this practice. Finally, there is a general consensus that early cover crop interseeding works better in certain growing regions and production systems than others. Defining the geographic and agronomic fit for cover crop interseeding is one of our project objectives.
