Organic No-till Soybean Production in Pennsylvania: Is It for You?

Part 1: IWM for organic no-till soybean production

There are many management decisions to make in this system, and each can affect the success of your cover crop, soybean crop, and short- and long-term management factors such as your weed seed bank, nitrogen availability, and soil health.

Introduction

Pennsylvania grain growers are well-positioned to take advantage of demand for organic soybean by poultry and dairy producers in the Mid-Atlantic and northeastern U.S. The region's many no-till farmers have been working to reduce their pesticide inputs, and transitioning to organic may be a viable way to diversify their farming operation. Interest is growing around farming practices that minimize both soil disturbance and synthetic chemical inputs.

A 2020 survey of Pennsylvania's organic grain farmers (n=102) found that thirty-six of the responders grew soybean, yet only five (14 percent) were using no-till techniques to do so.¹ While continuous no-till organic field crop production remains elusive, there are opportunities for using no-till practices for grain crop production in certain phases of an organic rotation. This guide discusses opportunities to reduce tillage in organic soybean production.

Producing soybean organically and with reduced tillage can enable farmers to minimize inputs, improve soil health, and capitalize on organic price premiums (Figure 1). Regardless of whether you currently have certified organic land or are thinking about transitioning land, this guide will provide you with important points to consider before managing organic no-till soybean.

This guide is a result of over two decades of research within the Mid-Atlantic region by land-grant universities (The Pennsylvania State University, Cornell University, University of Delaware), the USDA-ARS (Beltsville, MD), and participating farms. The body of work that we share spans fundamental studies of cover crop and weed interactions, integrated crop management experiments, and longer-term cropping system studies.

As you read this guide, you will not find a prescriptive management plan. Rather, we aim to share what we have learned about the ecology and management of cover-crop-based, rotational no-till organic systems. We hope this helps you decide whether to give it a try, and if so, what you might need to do in order to adapt rotational no-till practices for your particular crop rotation, farming system, and region.

What organic rotational no-till soybean production looks like

No-till organic production of soybean is primarily accomplished by using a roller-crimper to mechanically terminate a fall-sown cover crop in late spring, and then no-till planting into the cover crop mulch. The approach is often referred to as "cover crop-based, rotational no-till organic" production because, although there is minimal soil disturbance during soybean planting, tillage is likely necessary to create a weed-free seedbed for sowing cereal rye in early fall.

Weeds are the greatest threat to a successful organic no-till soybean crop. Successful organic no-till soybean production must rely on integrated weed management (IWM), the process of using multiple tactics to optimize weed control. IWM is a major focus of this guide because, since synthetic herbicides are not allowed and tillage is minimized in this system, the primary tool for weed suppression is a dense, high-biomass cover crop mulch and successful soybean emergence and establishment. It's important to have other weed control strategies in the toolbox, too.

Which cover crop, and why roller-crimping? Winter cereals are appropriate cover crops for this system, and we believe cereal rye is the best one. Cereal rye grows aggressively, accumulates abundant biomass (above-ground dry matter), matures earlier than other winter cereals, and its residue persists longer than legumes or legume-grass mixtures, which have a lower carbon to nitrogen (C:N) ratio and therefore break down faster. In this guide, whenever we refer to the cover crop, we are referring to cereal rye, although we'll briefly discuss alternatives in the "Rye management tactics" section.

We recommend terminating your cover crop by roller-crimping because it leaves the residue intact and thus slows its decomposition more than if it were mowed. This combination of cover crop species and termination method has the greatest potential to produce a thick and long-lasting mulch that suppresses weeds well into the soybean crop's development.

No-till yields and net returns are comparable to tilled soybean

The performance and profitability of organic no-till soybean production can vary when compared to tillage-based production. Although the no-till system can cut production costs, small reductions in yield can result in lower profit margins. When organic price premiums are high, they can compound the financial impacts of even minor yield losses.

No-till soybean averaged 41 bushels per acre across five years of side-by-side comparisons (2015-2022) at Penn State's research station in Rock Springs, Pennsylvania. Tilled soybean averaged 43 bushels per acre. In one of five years, no-till soybean significantly outyielded its tilled counterpart. In three of those five years, no-till soybean outperformed tilled soybean in net returns. From 2015-2017, no-till soybean netted an average of $473 per acre. In 2021 and 2022, with substantially higher soybean prices, they netted $1,183 per acre (Table 1).

Within Penn State's experiments, organic no-till production saved an average of 2.6 equipment passes through the field per year compared to tilled soybeans and therefore reduced labor, fuel, and repair costs – particularly those associated with cultivation events.⁴ Seed costs varied across years due to price fluctuations and seeding rate decisions, but generally, higher seeding rates are used for both rye and soybean in organic no-till production. Increasing seeding rates can help control weeds but can increase input costs compared to tillage-based production practices (see "Seeding rate" sections for rye and soybean).

If you're already certified organic and transitioning to no-till organic soybean production, your short-term return on investments will be a function of changes in seed, fuel, and labor inputs and soybean yield performance. Organic soybean price premiums can compound the profit losses associated with even a small yield drag relative to tillage-based yields.

Table 1. A partial budget comparison between organic soybean production using no-till and inversion-tillage (e.g., moldboard plow) practices in Penn State cropping system experiments (2015-2017 and 2021-2022). (John Wallace/Abbe Hamilton, adapted from Rebecca Champagne)

Consider both short- and long-term returns on investment

Here is a scenario drawn from our own research over a three-year period (2015-2017): As compared to tilled soybean, our no-till system cost about 26 percent more in soybean seed, 23 percent less in labor, 22 percent less in fuel, and 25 percent less in repairs and maintenance.⁴ Overall, the no-till system's production costs were 10 percent less than the tilled system. However, grain yields were 10 percent lower, and the high price premiums meant that these losses outweighed the savings in production costs. The no-till beans earned 3 percent less in net returns than the tilled beans.

However, it is also worth considering the potential longer-term soil health benefits gained from including a no-till phase in your crop rotation (see "Soil health" section). Given the potential trade-offs in production costs and potential yield reductions, it's up to you to decide whether the potential risks versus returns of organic no-till soybean are right for your operation.

Cereal Rye Management Practices that Optimize Weed Suppression Potential

In the Mid-Atlantic, if your rye stand is dense enough to completely cover the ground by early April, it is likely to yield enough dry matter by its flowering stage (5,000 lb./A or more) to suppress weeds in the no-till soybean crop. (John Wallace, personal communication.)

Growing season window

Cereal rye growth stage development and biomass production are regulated by the accumulation of heat units (growing degree days, or GDDs) as well as nitrogen availability. Cereal rye needs a long growing season window to produce enough biomass to suppress weeds during the soybean growing season. Lengthening the cereal rye growing season window by planting earlier in the fall is critical for optimizing biomass potential (see "Making room in the crop rotation").

It's difficult to lengthen the cereal rye growing season in regions with shorter overall growing seasons (USDA plant hardiness zones 4-6). Experiments conducted in Rock Springs, Pennsylvania (Zone 6b) show that delaying termination of cereal rye in the spring results in more biomass than sowing earlier in the fall (Figure 4). Delaying termination of cereal rye by ten days in the spring resulted in as much additional biomass as planting fifty days earlier in the fall.⁵ However, spring termination must occur at the right cereal rye growth stage to optimize cover crop control.

Termination timing

Terminating cereal rye in its flowering (or anthesis) stage is critical to effective control with the roller-crimper. Research suggests that approximately 90 percent control of cereal rye can be achieved when roll-crimping is delayed to this growth stage (Zadoks 68, Feekes 65, or when the male flower parts [anthers] are clearly visible). Roll-crimping at an earlier stage risks incomplete termination and subsequent regrowth, and any further delay risks viable rye seed production. Consequently, roll-crimping too early or too late can lead to volunteer rye becoming a weed in later phases of your crop rotation (see "Volunteer rye weed pressure").

The optimal time for roll-crimping is when anthers, which contain a yellow-colored pollen, are visible up and down the seedhead (Figure 5a). The optimal termination timing coincides with maximum rye biomass, which optimizes weed suppression potential. The drawback is that terminating rye at anthesis may not align with optimal timing for soybean planting. Cereal rye often reaches anthesis approximately ten to fourteen days later than average regional soybean planting dates.

Fertilization

Along with the accumulation of growing degree days, nitrogen fertility is very important for maximizing cereal rye biomass. Although some fields may have enough residual nitrogen to maximize rye biomass if there is high soil organic matter content and a history of manure and legume cover crop use, this isn't always the case. A study conducted across the Mid-Atlantic region found that cereal rye required an additional 65 pounds per acre of added nitrogen beyond typical residual fall fertility levels in soil to maximize biomass production (8,000 lb./A).⁶

It may be tempting to supply additional nitrogen during the cereal rye growing season to maximize biomass potential, but there are some drawbacks. The total amount of nitrogen and the timing of its availability is difficult to fine-tune with organic nitrogen sources, particularly during a winter grain growing season. Consequently, there are few recommendations for starter or topdressing application rates for organic winter grain production in the Mid-Atlantic region.

Field experiments conducted in Pennsylvania and Maryland showed that spring topdressing poultry litter [4-2-3] at a rate of 70 lb. N/A increased rye biomass production by 14 percent but did not affect weed suppression.⁷ For this type of fertilizer application, it is assumed that only half of the applied nitrogen is available to the rye cover crop, with the other half available later during the soybean growing season, when it might aid weeds more than the crop. Nitrogen immobilization by a cereal rye cover crop is an important weed suppression mechanism, so it may be better to not fertilize the rye and give up some biomass potential in order to put weeds at a competitive disadvantage during the soybean growing season.

A second unintended consequence of fertilizing the rye cover crop is the increased potential for lodging, which is associated with excess nitrogen in the soil. Lodging can significantly decrease roll-crimping efficacy. As a rye cover crop nears anthesis and growers monitor soil conditions for planting, many growers also monitor the weather forecast for high winds and will proactively roll-crimp the rye ahead of windy conditions that may result in lodging. Lodged cereal rye is more difficult to plant into, as it lies in multiple directions and makes it harder for the soybean planter to cut through.⁸ You may need to weigh the risks associated with fertilizing against the benefits of additional rye biomass.

Cereal rye seeding rate

We recommend sowing cereal rye at 120 to 165 lb./A for organic no-till soybean production. When cereal rye is sown in early fall into soil with high nitrogen fertility, a lower seeding rate (e.g., 60 lb./A) can often produce similar total biomass by the anthesis growth stage in late spring. However, higher seeding rates (120-165 lb./A) can increase early spring ground cover, which may increase suppression of some early-emerging summer annual weed species. For example, a multi-year study conducted in Pennsylvania and Maryland found no difference in total rye biomass production when increasing cereal rye seeding rates from 80 to 186 pounds per acre, but the highest seeding rate did reduce total weed biomass by 33 percent compared to the lowest rate when measured four weeks after rye termination.⁹ Higher seeding rates caused denser ground cover, which suppressed early-season weed growth even though the denser seeding rate didn't lead to higher rye biomass at anthesis as compared to lower seeding rates.

To determine if the benefit of higher seeding rates (120-165 lb./A) justifies the marginal increase in production costs (Table 2), we suggest considering two criteria. First, what is the preceding crop? If it is harvested late in the fall or doesn't leave much residual nitrogen in the soil, consider seeding rye at a higher rate to help it cover the ground faster.

Second, what are your problem weeds? If there are a lot of winter annuals like common chickweed, purple deadnettle, or other common fall and spring emerging species, then increasing seeding rates may improve weed suppression and ensure that cereal rye reaches its full biomass potential. Early-emerging summer annual weeds like common ragweed and lambsquarter can cause problems in roll-crimped cereal rye systems, and a higher cereal rye seeding rate can help manage those problem species, too. See "Problematic weed species" for more discussion.

We typically establish rye with a drill-seeder in 7.5-inch rows. Some commercially available grain drills in the Northeast (Esch Manufacturing) are designed with narrower row spacing (5.5 inches), which can improve weed suppression during establishment by increasing ground cover and competition for light.

Cultivar selection

The best cereal rye cultivar for an organic no-till soybean system is one that has high biomass potential, matures early, and has high-quality seed with uniform seed size. These traits help to produce a more uniform stand, which increases the potential for successful roll-crimping. Purchase certified varieties from a reputable seed dealer to maximize the likelihood of producing a uniform stand. In general, "variety not stated" (VNS) varieties are often lower-yielding and produce a more variable stand. Bin-run rye may perform well, but you should ensure that weed seed contamination is minimal and the seed is stored in a way that doesn't compromise its viability. If you're considering seed saving, follow any relevant regulations related to seed sales and crops with protected genetics. Aroostook, Elbon, Rymin, and Wheeler are four rye varieties that are not patent-protected¹⁰ and have performed well in the Mid-Atlantic region.

In an experiment comparing Aroostook and Wheeler rye varieties for roll-crimping in the Mid-Atlantic,¹¹ researchers determined that Aroostook rye is more suitable than Wheeler for the Mid-Atlantic region. The Aroostook variety matured earlier and was terminated more effectively in early May, though both varieties were terminated equally well with a roller-crimper by the end of the month.

Different rye varieties can have extremely different seed counts per bushel. The seed size of a given variety is also likely to vary from year to year as the weather fluctuates. Researchers recently compared twenty-seven commercially available varieties and determined that some varieties could contain almost twice the number of seeds per bushel.¹² While the researchers emphasized the importance of seeking out density-based seeding rate information, they did not recommend one variety over another: smaller-seeded varieties may germinate faster¹³ and could provide more plants per acre if seeding by bushel per acre, but larger-seeded varieties may have a greater emergence rate.¹⁴

Alternate establishment methods

Although you can broadcast seed rye, we recommend drill seeding to improve rye establishment and stand uniformity. Research on seeding rye in a grid pattern (i.e., sowing in two directions) is in progress at Penn State to determine if the weed suppression benefit outweighs the cost of an additional drill pass.

Alternate cover crop species

Although we recommend rye for use in this system, other winter cereals might fit when timely soybean planting outweighs the need to maximize biomass potential. Earlier-maturing varieties of barley, for example, could allow for earlier termination and therefore earlier soybean planting as compared to rye. In a western New York study, fall-sown barley produced less biomass than rye but suppressed weeds and sustained soybean yields to the same extent.¹⁵ Triticale performs less consistently than cereal rye in terms of winter survival and maximum biomass.^{16, 17}

Roll-Crimping Techniques that Minimize Rye Regrowth, Seed Production, and Spread

The roller-crimper has revolutionized high-residue cover crop management. This implement was developed in South America and studied by USDA-ARS researchers in Auburn, Alabama¹⁸ before the Rodale Institute and Pennsylvania manufacturers popularized it.

Front- or rear-mounted roller-crimpers (Figure 6a) are characterized by a steel cylinder with metal slats welded perpendicular to the cylinder and arranged in a chevron pattern, which reduces vibration and allows for operation at faster speeds. Front-and rear-mounted roller-crimper blueprints are available through the Rodale Institute, and roller-crimpers are commercially available through I&J Manufacturing in Pennsylvania.

One notable difference in design is found in the integrated roller-crimper system (Figure 6b), which was developed by Pennsylvania no-till farmer and machinist Charlie Martin and is now manufactured by Dawn Biologic. This system has small-diameter cylinders containing the chevron pattern that operate independently and in tandem with row-cleaners and is designed to be mounted on a planter frame.

Several variations of roller-crimpers are now sold commercially. Organic no-till research experiments conducted at Penn State have used both integrated and front-mounted designs. In Table 4, we highlight the key tradeoffs between these roller-crimper technologies, including some designs we haven't used ourselves. Watch the market for new designs with better cover crop termination efficacy. Although a cultipacker will roll down a stand of rye, it won't crimp it, which is essential to preventing regrowth.¹⁹

Effective cereal rye termination is critical for success of organic no-till soybean production: A termination rate less than 90 percent jeopardizes successful cash crop growth as surviving rye competes for resources.²⁰ Making two or more passes over a field with a roller-crimper may improve termination efficacy ^{20, 21} The design of the roller-crimper, its maximum operating speed, and the feasibility of making multiple passes are all factors that will determine the best setup for your operation. You'll also need to consider how soybean planting fits into your roll-crimping operation, as illustrated in Table 5.

Suppressing Weeds with Rye Mulch

Cereal rye mulch can suppress weeds at nearly every stage in their life cycle (Figure 7 ). Two points are worth considering: First, greater biomass production generally leads to greater weed suppression. Second, the level of biomass production needed to achieve season-long weed suppression will depend on environmental conditions, soil conditions, and the number and species of weeds in the seedbank at your location. Although every field's individual conditions will make for slightly different requirements, research in our region suggests you need at least 5,000 pounds (dry matter) of cereal rye per acre to make this practice viable. Here, we briefly describe the primary ways in which cereal rye mulch suppresses annual weeds.

Light

Rye mulch reduces the amount of light that reaches the soil. Some weed species have evolved a light requirement to germinate, while other species are capable of germination in the absence of light. Once germinated, the growth of weed seedlings will be affected by reduced amounts of light as they emerge through the mulch layer using energy stored in the seed.²⁵

Soil moisture

Cereal rye growth throughout spring can reduce soil moisture compared to tillage-based production by soybean planting, but the surface mulch created by roll-crimping can also conserve soil moisture in the upper soil profile during the soybean growing season.²⁴ Changes in soil moisture conditions affect the timing of weed germination and emergence and can also impact soybean performance.²⁵

Soil temperature

A thick cover crop mulch tends to lower the average soil temperature and reduces daily temperature fluctuations.²⁵ Lower and less variable soil temperatures may result in delayed germination of some weed species and may also reduce growth rates of weed species as they establish within surface mulch. There is also potential for lower soil temperatures to negatively impact soybean emergence and early-season growth.

Soil nitrate levels

Prior to termination, cereal rye growth takes up nitrogen from the soil, which reduces the amount available to weeds attempting to emerge through the mulch. Even after the rye is roll-crimped, it immobilizes the nitrogen it collected and releases it back to the soil at a slower rate.

As a result, many summer annual weed species that have evolved to take advantage of a pulse of available nitrogen become less competitive with soybean in early growth stages. Although this also reduces available soil nitrogen for soybeans, studies suggest that soybeans can rebound from early nitrogen deficiencies when they nodulate and begin to produce their own nitrogen.²⁶

Allelopathy

Although cereal rye produces secondary compounds that can be toxic to other plant species (i.e., allelopathy), this effect likely plays a minor role in the weed suppression potential of cereal rye.²⁷ One recent experiment found that 65 to 90 percent of rye's allelopathic chemicals degraded within one week following termination by roll-crimping.²⁸

Soybean Management Practices to Enhance Crop Competition

Variety selection

Organic soybean varieties that have good seedling vigor, particularly under cooler temperatures, and that have good branching characteristics (i.e., bushy) are ideal for the organic no-till system. If you plan to grow certified organic soybean, make sure your variety is non-GMO. You must use organically grown seed unless no adapted lines are available, and no transgenic varieties are allowed. Check with your certifier for a list of organic seed suppliers that can help you find lines suitable for your operation.

Soybean seeding rate

It's common in organic crop production to seed soybean at a higher rate than used in non-organic production to ensure a good stand. While soybean seeding rates in conventional production systems may be as low as 125,000 seeds per acre, organic soybean seeding rates often exceed 200,000 seeds per acre. Higher seeding rates hedge against potential stand loss due to cultivation or early-season insect damage. Higher seeding rates can also increase suppression of weeds that emerge within the crop row, and may lead to quicker soybean canopy closure, which can improve between-row weed suppression in combination with cereal rye surface mulch.²⁹ However, some studies suggest that higher soybean seeding rates can lead to greater risk of soybean diseases.^{30, 31, 32}

The combined use of cereal rye surface mulch and high soybean seeding rates can be an effective IWM approach. An experiment conducted in Pennsylvania and Maryland from 2007-2009 determined that increasing soybean seeding rates reduced weed pressure in only half of the field experiments when used as the sole management tactic, but reduced weed pressure across all experiments when used in combination with cereal rye residue.⁹

Establishment method

We recommend planting soybean using 15- or 30-inch row spacing. If cereal rye biomass is sufficient to serve as a weed suppressive mulch (greater than 5,000 lb./A), use of a no-till grain drill and 7.5-inch row spacing will likely result in sub-optimal seed placement and stand issues. Drilling soybean also prevents the use of between-row cultivation or other weed control practices.

In comparison to grain drills, planters exert higher down-pressure per row, allow greater precision in seed metering and depth control, and allow greater flexibility for using additional residue management tools such as coulters and row cleaners.

We recommend planting soybean as close to roll-crimping as possible since growing or fresh residues are easier to cut with no-till coulters than terminated mulch that has begun to dry. Soil moisture conditions just before or after roll-crimping are also typically more suitable for planting as compared to later dates. This is because less evaporation occurs after roll-crimping, which can lead to seed placement and side-wall compaction issues.⁸

Row spacing

The width of soybean rows and the limitations of planting equipment have some inherent trade-offs, particularly between optimal weed suppression and optimal soybean seed placement.

Using split-row units to plant on fifteen-inch row spacing can potentially combine the benefits of faster canopy closure and optimal seed placement, but row spacing narrower than thirty inches will increase the difficulty of cultivating between rows and will likely require investment in precision-cultivation technologies.

We compared organic no-till soybean planted on thirty-inch row spacing followed by one to two high-residue cultivation passes to soybean planted on fifteen-inch row spacing and no between-row cultivation, and found that uncultivated, fifteen-inch row soybean production resulted in higher yield but greater weed pressure compared to thirty-inch spacing combined with high-residue cultivation.³³ These results were not surprising as neither treatment resulted in late-season weed biomass that exceeded 300 pounds per acre, a threshold recognized by many weed scientists as the minimum necessary to cause grain yield suppression. (Bill Curran, personal communication.)

Integrating Weed Control Tactics during Soybean Growing Season

Our research suggests that when annual weed seedbanks are relatively low, which can occur during the organic transition period, cereal rye surface mulch alone can achieve acceptable levels of weed control.

When annual weed seedbanks increase, additional tactics are necessary to achieve acceptable levels of weed control even with ample cereal rye biomass.³⁴ The performance of cereal rye residue will vary based on weather, soil conditions, and other management factors, so it's important to have additional weed control tools as a backup option.

If you have high weed pressure after soybean planting, weed control options that can be applied in combination with surface mulch include high-residue cultivation, electric weed control, and inter-row mowing. Each of these tools has limitations, including management windows during which they can be used.

High-residue cultivation and inter-row mowing can be accomplished earlier in the soybean growing season than electric weeding. They are thus likelier to reduce soybean yield loss by reducing early-season competition.

Electric weed control is currently only a viable approach after weeds have grown above the soybean canopy. It can reduce weed seed return to the seedbank, but it may be too late to make a difference in soybean yields if they've already been compromised by early-season weed competition.

High-residue cultivators

High-residue cultivators work by severing weed shoots from roots while minimizing disturbance to surface residues. Field experiments conducted in Pennsylvania found that it's best to do the first pass several weeks after soybean planting, at approximately the V4 growth stage, and cultivate the second time two weeks later at the V6 growth stage.

The first pass may kill early-emerging or fast-growing species, while the second controls later-emerging species and weeds that were too small to be controlled with the first pass. Two passes with a high-residue cultivator were needed to optimize weed control and minimize yield loss to weed competition.²¹ Cultivating too early risks leaving weeds intact and capable of reestablishing.

Under wet soil conditions, high-residue cultivation may not always kill weeds, but it can still slow weed growth and reduce competition with soybeans. Other Mid-Atlantic field experiments found that high-residue cultivation reduced weed biomass by 18 to 39 percent but didn't always improve soybean yield.⁸

While high-residue cultivation is designed to minimize soil disturbance, cereal rye residues may degrade more quickly following multiple cultivation passes. Also, surface residues will be less uniform following cultivation due to the action of shanks that part the residue in the middle of row, potentially leaving soil exposed while pushing residues closer to the soybeans. This can change weed populations and soil moisture levels compared to a more even distribution of mulch.

The cost associated with high-residue cultivation can be prohibitive. A partial budget analysis conducted for organic no-till soybean production found that although there were no yield losses associated with high-residue cultivation, yields failed to increase enough to cover the additional cost.³⁵ However, those weed population reductions can reduce weed seedbanks and the magnitude of future weed problems.

Inter-row mowing

Inter-row mowing³⁶ can protect yields in organic no-till soybeans and reduce weed biomass by 60 percent as compared to no secondary weed management tactics, according to research from Cornell University. Inter-row mowers are currently designed as front-mounted units with individual mowers positioned between crop rows with crop-protecting shields (Figure 10). Mowers can be adjusted to cut between two and seven inches above the soil surface. Currently, commercially available units are only compatible with soybean planted in thirty-inch rows.

In the Cornell experiment, mowing was implemented twice, two to three weeks apart, before the soybean canopy formed. Mowers can disturb heavy rye mulch, but mulch does not impact mowing operations. Results suggest inter-row mowing may select for perennial species over time, particularly those with prostrate growth forms.³⁷

Electric weed control

Electric weed control is an emerging technology for managing weeds growing above the soybean canopy. Current research suggests that electrical weeding can serve as an important seedbank management tool by managing weed escapes. Depending on the level of infestation, it may also reduce crop yield loss.

An electronic discharge system (EDS), like the commercially available Weed Zapper, works by delivering a strong electrical impulse to any plant it contacts. Operators set the boom height to just above the cash crop height. Recent research conducted in Missouri suggests the technology is most effective on weeds that have reached their pollination and seed-setting growth stages. It may work better for broadleaf weeds than grasses. There's a risk of damaging soybeans and losing yield if the crop is electrocuted in later growth stages.³⁸ This technology requires a tractor with at least seventy-five horsepower for the PTO-driven generator.³⁹

Part 2: Implications for cropping system design

Problematic Weed Species

Our cropping system research has shown that the use of heavy rye mulch quickly selects for well-adapted weed species, which become a more significant management problem over time. In general, rye mulch residues are more effective at suppressing annual weed species with relatively small seed size in comparison to larger-seeded annual weed species (Figure 11) and perennial weeds. Rye mulch is also more likely to effectively suppress annual broadleaf species compared to annual grass species. Finally, roll-crimped rye mulch is less effective at suppressing early-emerging summer annual weed species that establish prior to roll-crimping.

Common ragweed and giant foxtail are two well-adapted species that can become problematic in organic no-till soybean production. Common ragweed germinates at lower temperatures than other summer annual weeds, so it often establishes in early May before roll-crimping occurs and survives the roll-crimping.

Giant foxtail can also emerge before and survive roll-crimping, but has a longer emergence window than common ragweed. Compared to other weed species, it's less affected by the low light conditions under growing or roll-crimped cereal rye.

Our research has shown that common ragweed is more competitive and dominant in organic no-till soybean production compared to no-till corn, whereas giant foxtail is competitive in both crops (Table 7).

It's critical to integrate fall-sown winter grains or perennials into the crop rotation post no-till soybean to manage weed species like foxtails and ragweed. A well-established winter cereal crop, such as wheat or spelt, can outcompete emerging summer annual species. The emergence of these weed species in winter cereals is often delayed, but they remain present in the understory in mid-summer, at the time of winter cereal grain harvest. Grain harvest presents an opportunity to control this flush of weeds with shallow tillage passes. Perennial forages also help to draw down the annual weed seedbank, particularly after the establishment year when multiple harvests can be achieved throughout the growing season. Longer-lived perennial stands (three years or more) also encourage seed decay, or loss of viability, of annual weed species, particularly annual grasses that have a soft seed coat.

Volunteer cover crops are a weed management challenge

Incomplete control of cereal rye with roller-crimpers can produce a significant weed management challenge in some scenarios. Roll-crimping cereal rye too early or too late, based on its growth stage, can result in viable seed production. Consequently, cereal rye can become a winter annual weed in subsequent phases of the rotation. This is particularly problematic when a winter grain cash crop, like winter wheat or spelt, follows soybean in the rotation. Our research showed that cereal rye comprised 3 to 11 percent of the harvested grain in a subsequent winter wheat cash crop, which can result in dockage at grain elevators depending on the acceptable level of contamination⁴¹.

There are a couple of ways to minimize volunteer rye in your rotation. As discussed in the "Cereal rye management tactics" section, prioritize timing your termination to the optimal rye growth stage: Zadoks stage 65 to 73, or 50 percent anthesis to early milk. This stage balances effective termination with minimizing rye seed production. But if viable seed is produced, rotating to a spring-sown crop (e.g., oats) or back to a summer annual cash crop provides opportunities to kill fall-emerging cereal rye. Most of the viable seed produced and left on the soil surface is likely to either germinate, decay, or be eaten by insects or mice in fall. In locations with a longer fall, creating a false seedbed (allowing weeds to grow in a cultivated bed for a couple of weeks before cultivating again and sowing a winter grain) may also be effective for controlling volunteer cereal rye. A drawback of these approaches is that this costs you and your soil an extra tillage event. Finally, adding a perennial forage crop to your rotation is one way of disrupting a volunteer rye population, as it is less likely that cereal rye will have a negative impact on forage quality if the perennial crop is well established⁴⁰.

Insect pests in organic soybean

Soybeans are usually relatively free of economically significant insect pest populations in the northeastern United States. This is partly because soybeans have great capacity to compensate for insect damage. Pre-bloom, soybean plants can tolerate up to 35 percent defoliation. While pods are small and soft, they can tolerate 15 percent defoliation, and at pod hardening, 35 percent⁴².

Key early-season pests (May-June) of soybean include seed corn maggot, green cloverworm, bean leaf beetle, and slugs. Mid-season (June-July) pests include green cloverworm, potato leafhopper, grasshoppers, stinkbugs, soybean aphid, brown marmorated stink bug, and slugs. Late-season (mid-July–September) pests include two-spotted spider mite, potato leafhopper, Japanese beetle, Mexican bean beetle, grasshoppers, soybean aphid, stink bugs, and brown marmorated stink bug.⁴³

Insect damage has not negatively impacted soybean yield in Penn State's organic no-till soybean experiments. In part, this is because the system supports abundant predatory arthropods, especially carabid (ground and tiger) beetles and spiders, which control pest populations.

Ground beetles play a major role in organic agroecosystems by eating weed seeds, insects, and slugs; they can consume up to their body weight daily⁴⁴. Ground beetles and other soil-associated predators are more likely to survive in fields where no-till or non-inversion tillage is used. In comparison with inversion tillage, non-inversion tillage causes less soil disturbance and kills fewer eggs, larvae, and adults of soil-associated predators. Ground beetle larvae in the soil have soft bodies and are especially sensitive to tillage and cultivation. Minimum-tillage systems also preserve surface vegetation and mulch, which can provide microhabitats for ground beetles and other predatory arthropods as well as protection from environmental conditions and other predators. You can support beneficial predatory insects in your fields by providing refuges from disturbance and other attractive resources. This can be accomplished by reducing inversion tillage and maintaining surface residues, providing undisturbed habitats of annual (e.g., cover crops) or perennial vegetation (e.g., beetle banks, perennial forages) within or on field edges (e.g., hedgerows, permanent grassed driveways, conservation plantings)^{45, 46}.

Soil health

Reduced tillage is generally linked to improvements in soil health on organic farms⁴⁷. Soil organic matter is an important indicator of soil health because it serves as an important resource for soil organisms at the base of the food web and benefits the physical and chemical properties of soil⁴⁸. The number of soil disturbances from tillage and cultivation did not impact the concentration of total organic matter in the top six inches of soil in organic no-till soybean trials run at Penn State in 2021 and 2022. The number of tillage events also did not affect the treatments' Cornell Soil Health Assessment overall soil health scores (unpublished).

However, soil organic matter concentrations were greater in soybeans managed with shallow tillage (2.25 percent) and no-till (2.24 percent) compared to full inversion tillage (2.04 percent), and treatments' overall soil health scores were affected by differences in percent soil moisture, percent silt, and the prevalence of a beneficial soil fungus.

High-residue cultivators are designed to minimize soil disturbance in mulch-based production. Our research shows that one to two passes in organic no-till soybean production doesn't appear to have a significant detrimental effect on soil health over time. We measured differences between an organic no-till system that received high-residue cultivation versus no-till production without cultivation and found no significant difference in three indicators of soil health: permanganate oxidizable carbon (POX-C), aggregate stability, and entomopathogenic fungi⁴⁹.

Making room in the crop rotation

In general, the transition to organic no-till soybean production requires prioritizing adequate seedbed preparation and early fall rye sowing dates to ensure a successful organic no-till soybean crop. It may be difficult to fit this practice into your existing rotation, since in cooler regions, grain corn may be harvested too late to establish a good rye stand, and even corn silage harvest time may result in a shortfall growing season. Ideally, cereal rye should be sown after a small grain or summer annual forage that provides a sowing window in September or early October.

In the spring, organic no-till soybean planting dates may be later than the average for non-organic soybean, depending on cereal rye development, and as a result, soybean harvests may be pushed into later fall, which creates challenges for establishing a good winter cover or cash crop. As a result, adoption of organic no-till practices may require a redesign of your cropping system, or a switch to shorter-season varieties.

Finding marketable and productive crops that can be integrated into organic crop rotations to facilitate no-till production practices remains a significant challenge. Grower ingenuity and adaptations will be needed to make this important advancement in sustainable organic grain production.

Resources

Several resources are available that provide additional insight into organic production practices and ecologically based pest management strategies. We recommend:

Mohler, C.L., S.E. Johnson. (2009) Crop rotation on organic farms: a planning manual. Sustainable Agricultural Research and Education (SARE) NRAES Series.

Mohler, C.L., J.R. Teasdale, A. DiTomasso. (2021) Managing weeds on your farm: a guide to ecological strategies. Sustainable Agricultural Research and Education (SARE). Handbook 16. 

Ryan, M.R. B.A. Caldwell, K. Crowley, J.A. Liebert, U. Menalled, C.J. Pelzer, L. Pickard, and S. Wayman. 2021. Organic No-Till Planted Soybean Production. Sustainable Cropping Systems Lab. Cornell University, Ithaca, NY.

Literature cited 

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Acknowledgements

The insights shared in this guide result from a shared and sustained vision among growers and researchers for advancing the sustainability of organic cropping systems. It is particularly noteworthy that this management guide could draw almost exclusively from research conducted in the northern Mid-Atlantic region.

Lead researchers who have made a significant contribution to our understanding of these practices include Bill Curran, Mary Barbercheck, Dave Mortensen, Matt Ryan, Steven Mirsky, Kristy Borrelli, and Mark VanGessel.

Technical staff who have been instrumental in this research include Dave Sandy, Christy Voortman, Mark Dempsey, Dayton Spackman, and Tosh Mazzone.

Graduate students and post-doctoral research associates who have produced important scholarship include Ruth Mischler, Randa Jabbour, Ariel Rivers, Clair Keene, Karly Regan, Rebecca Champagne, Barbara Baraibar, Moriah Bilenky, and Laurel Wellman.

The research that produced these insights have been supported by several sources, including the USDA's Organic Research & Extension Initiative (OREI) and Sustainable Agricultural Research & Education (SARE), the Northeast IPM Center, and Penn State's College of Agricultural Sciences.