Cereal Rye Cover Crop Research Articles

Machine learning reveals dynamic controls of soil nitrous oxide emissions from diverse long-term cropping systems.

Soil nitrous oxide (N2O) emissions exhibit high variability in intensively managed cropping systems, which challenges our ability to understand their complex interactions with controlling factors. We leveraged 17 years (2003-2019) of measurements at the Kellogg Biological Station Long-Term Ecological Research (LTER)/Long-Term Agroecosystem Research (LTAR) site to better understand the controls of N2O emissions in four corn-soybean-winter wheat rotations employing conventional, no-till, reduced input, and biologically based/organic inputs. We used a random forest machine learning model to predict daily N2O fluxes, trained separately for each system with 70% of observations, using variables such as crop species, daily air temperature, cumulative 2-day precipitation, water-filled pore space, and soil nitrate and ammonium concentrations. The model explained 29%-42% of daily N2O flux variability in the test data, with greater predictability for the corn phase in each system. The long-term rotations showed different controlling factors and threshold conditions influencing N2O emissions. In the conventional system, the model identified ammonium (>15 kg N ha-1) and daily air temperature (>23°C) as the most influential variables; in the no-till system, climate variables such as precipitation and air temperature were important variables. In low-input and organic systems, where red clover (Trifolium repens L.; before corn) and cereal rye (Secale cereale L.; before soybean) cover crops were integrated, nitrate was the predominant predictor of N2O emissions, followed by precipitation and air temperature. In low-input and biologically based systems, red clover residues increased soil nitrogen availability to influence N2O emissions. Long-term data facilitated machine learning for predicting N2O emissions in response to differential controls and threshold responses to management, environmental, and biogeochemical drivers.

Planting soybean green: how cereal rye biomass and preemergence herbicides impact Amaranthus spp. management and soybean yield

Abstract Cereal rye (Secale cereale L.) cover crop and preemergence herbicides are important components of an integrated weed management program for waterhemp [Amaranthus tuberculatus (Moq.) Sauer] and Palmer amaranth (Amaranthus palmeri S. Watson) management in soybean [Glycine max (L.) Merr.]. Accumulating adequate cereal rye biomass for effective suppression of Amaranthus spp. can be challenging in the upper Midwest due to the short window for cereal rye growth in a corn–soybean rotation. Farmers are adopting the planting green system to optimize cereal rye biomass production and weed suppression. This study aimed to evaluate the feasibility of planting soybean green when integrated with preemergence herbicides for the control of Amaranthus spp. under two soybean planting time frames. The study was conducted across 19 site-years in the United States over the 2021 and 2022 growing seasons. Factors included cover crop management practices (“no-till,” “cereal rye early-term,” and “cereal rye plant-green”), soybean planting times (“early” and “late”), and use of preemergence herbicides (“NO PRE” and “YES PRE”). Planting soybean green increased cereal rye biomass production by 33% compared with early termination. Greater cereal rye biomass production when planting green provided a 44% reduction in Amaranthus spp. density compared with no-till. The use of preemergence herbicides also resulted in a 68% reduction in Amaranthus spp. density compared with NO PRE. Greater cereal rye biomass produced when planting green reduced soybean stand, which directly reduced soybean yield in some site-years. Planting soybean green is a feasible management practice to optimize cereal rye biomass production, which, combined with preemergence herbicides, provided effective Amaranthus spp. management. Soybean stand was a key factor in maintaining soybean yields compared with no-till when planting green. Farmers should follow best management recommendations for proper planter and equipment setup to ensure effective soybean establishment under high levels of cereal rye biomass when planting green.

Integrating fall‐planted cereal rye cover crop with herbicides for reducing Palmer amaranth seed production in soybean under planting green conditions

AbstractCover crops are usually terminated prior to planting the cash crop; however, “planting green” is an alternative approach that allows growers to plant cash crop into an actively growing, green cover crop, which is then terminated after the establishment of the cash crop. The objectives of this study were (1) to determine whether planting soybean (Glycine max L. Merr.) into a standing cereal rye (Secale cereale L.) cover crop provides superior weed suppression compared to terminating cereal rye 2 weeks before soybean planting and (2) to evaluate an integrated effect of herbicide programs and cereal rye termination timing on Palmer amaranth (Amaranthus palmeri S. Watson) control, biomass, seed production, soybean grain yield, and benefit/cost ratio. Field experiments were conducted in southcentral Nebraska from 2020 to 2022. Preemergence (PRE) herbicide with 2 weeks after planting (WAP) termination of cereal rye provided >95% Palmer amaranth control in 2021 and varied from 88% to 98% in 2022 at 28 days after PRE. A PRE herbicide followed by (fb) late‐postemergence (LPOST) herbicide with 2 WAP termination of cereal rye controlled Palmer amaranth 85%–92% in 2021 compared with 97%–99% control 28 days after LPOST herbicide application in 2022. Palmer amaranth density was higher with 2 WBP cereal rye termination compared with 2 WAP termination regardless of the herbicide program. PRE fb LPOST herbicide programs integrated with 2 WAP termination of cereal rye reduced Palmer amaranth seed production to less than 9100 seeds plant−1 in 2021 and no seed production in 2022. In 2021, terminating cereal rye 2 WAP played an integral role in controlling and reducing the density of Palmer amaranth; however, it had noticeable impact on soybean yield compared to terminating 2 WBP. In 2022, hail and windstorm had a confounding effect on soybean stand and yield.

Cereal rye cover crop termination at or before soybean planting has minimal effect on soybean yield across the midwestern US

ContextInterest is growing among farmers in the Midwestern US region in the potential benefits of establishing cereal rye (Secale cereale L.) as a cover crop. However, they are concerned about the implications and potential trade-offs due to this practice. ObjectiveWe aimed to evaluate the effects of cereal rye cover crop termination at or before soybean planting on soybean (Glycine max [L.] Merr.) seed yield. MethodsField experiments were conducted from 2019 to 2021 across 28 location-years in the Midwestern US. Treatments consisted of no cereal rye, cereal rye termination before soybean planting, and termination at planting. Cereal rye was chemically terminated at each termination timing. Cereal rye biomass and soybean yield were assessed. ResultsDelaying cereal rye termination in soybean systems increased rye biomass, but its impact on soybean yield was inconsistent. Results showed that delayed termination did not reduce soybean seed yield in 25 of 28 location-years compared to a no cover crop treatment. There was no clear evidence indicating that a threshold level of cereal rye biomass accumulation reduced soybean seed yield. ConclusionsOur results suggest that farmers who adopt cereal rye as a winter cover crop in the examined region have a flexible management window for terminating cereal rye, as the timing of termination had minimal effect on soybean seed yield. However, there were no significant soybean seed yield benefits that would justify the associated cost with the use of cover crops. Therefore, conducting long-term studies in the future is highly recommended to better understand how cereal rye cover crops can influence soybean seed yield and soil quality properties over time. Further studies should also investigate the aspect of non-chemical rye management to assess its potential cost-saving effects for farmers adopting this system. ImplicationsThese findings hold several implications for farmers, agronomists, and stakeholders. The increased cereal rye biomass due to delayed termination could offer greater soil benefits. While the inconsistent effects on soybean yield imply flexible termination options for cover crop adoption, the absence of substantial yield benefits underscores the importance of considering both short-term costs and long-term sustainability goals.

The effects of roller crimping direction for termination of fall sown cereal rye (Secale cereale L.)

Consensus around the optimal direction of roller crimping a row-planted cover crop has not been established. Several publications report crimping either parallel or perpendicular to the direction of cover crop planting with little to no justification apart from unpublished observations or hypotheses. This study explicitly compared the effects of roller crimping direction on crimping efficacy, weed suppression, and cash crop yield. At Elora, ON in 2020 and 2021, and Harrow, ON in 2021, a cereal rye ( Secale cereale L.) cover crop was planted in three orientations (north-south vs. east-west vs. no rye control) then terminated with a roller crimper parallel or perpendicular to the direction of planting. A sweet corn ( Zea mays L.) cash crop was planted either north–south or east–west in the same direction as roller crimping. A split plot treatment of weediness (weedy vs. weed-free) was applied. It was found that roller crimping direction did not have a consistent effect on rye mortality or number of upright tillers, nor did it affect weed control. However, total marketable sweet corn fresh weight decreased in perpendicular crimped rye compared to parallel crimping, despite equivalent cob counts. We did not find evidence in this study to suggest that perpendicular roller crimping improves ground cover and therefore weed suppression, contrary to other unpublished observations. Given the effect on sweet corn yield, roller crimping perpendicular to the direction of cover crop planting may not be a suitable practice. Alternative methods for improving cover crop-based weed control should be investigated.

Elucidating waterhemp (Amaranthus tuberculatus) suppression from cereal rye cover crop biomass

AbstractCereal rye (Secale cereale L.) as a cover crop can be an effective nonchemical tool for waterhemp [Amaranthus tuberculatus (Moq.) Sauer] suppression in crop production. Previous studies have evaluated A. tuberculatus suppression by cereal rye as part of weed management programs but have not investigated the underlying mechanism of suppression by the cover crop. This study aimed to investigate the effect of cereal rye biomass on A. tuberculatus emergence and development, and on soil environmental parameters (temperature, moisture, and light transmittance) that are key triggers of A. tuberculatus germination to elucidate the mechanism of suppression by the cover crop. A dose–response study was conducted under field conditions in Brooklyn and Janesville, WI, from 2021 to 2023. Cereal rye biomass from a fall-planted field was harvested at anthesis in the spring and dried to constant weight at 60 C to provide 0.0, 0.6, 1.2, 2.4, 4.8, 7.2, 9.6, and 12.0 Mg ha−1 of dry biomass that was evenly distributed over 1.9 m−2 plots. Increasing cereal rye biomass reduced A. tuberculatus height, biomass, and density. An average ED50 of 5.2 Mg ha−1 of biomass was needed to reduce A. tuberculatus density by 50%. Low levels of biomass (≤2.38 Mg ha−1) augmented A. tuberculatus density due to an increase in soil moisture underneath the mulch compared with bare soil. Cereal rye biomass decreased the amount of sunlight reaching the soil, which resulted in lower mean soil temperature and temperature amplitude throughout the day (9.3 and 2.7 C temperature amplitude at 0 and 12.0 Mg ha−1, respectively). Prevention of A. tuberculatus germination by this thermal effect is likely the main mechanism of A. tuberculatus suppression from the cereal rye cover crop. Our results support biomass from cereal rye cover crop effectively suppressing A. tuberculatus and contributing to the integrated management of A. tuberculatus.

Effect of ultra‐early, early, and normal soybean planting dates and rye cover crop on soybean grain yield

AbstractWith changes to climate and crop insurance, earlier soybean [Glycine max (L.) Merr.] planting dates need to be investigated. Additionally, the use of a cover crop prior to soybean is promoted as a sustainable practice though little is known about cover crop and ultra‐early soybean planting (prior to April 15). The objective was to evaluate soybean planting date and cereal rye (Secale cereale L.) cover crop termination timing on cover crop biomass, soybean plant population, and yield. The study was conducted in Northeast and West Central Ohio in 2021 and 2022. Treatments included three soybean planting dates (early April, late April, and late May) and three cover crop treatments (termination 1–2 weeks prior to planting or “early,” termination at or after planting or “late,” and no cover crop). Cover crop biomass increased as termination was delayed. Soybean planted in early April resulted in a yield reduction of 1.8 Mg ha−1 when planted into a cover crop compared to the no cover crop control. However, when soybean was planted in late April, grain yield was not different among cover crop treatments. Yield reduction associated with early April planting with a cover crop was likely due to low soybean plant population, especially in Northeast Ohio, where plant population was <55,000 plants ha−1 with a cover crop and >120,000 plants ha−1 without a cover crop. To maximize yield, soybean should be planted by the end of April in Northeast Ohio. In West Central Ohio, soybean can be planted in early April without a cover crop.

Early‐season biomass and weather enable robust cereal rye cover crop biomass predictions

AbstractFarmers need accurate estimates of winter cover crop biomass to make informed decisions on termination timing or to estimate potential release of nitrogen from cover crop residues to subsequent cash crops. Utilizing data from an extensive experiment across 11 states from 2016 to 2020, this study explores the most reliable predictors for determining cereal rye cover crop biomass at the time of termination. Our findings demonstrate a strong relationship between early‐season and late‐season cover crop biomass. Employing a random forest model, we predicted late‐season cereal rye biomass with a margin of error of approximately 1,000 kg ha−1 based on early‐season biomass, growing degree days, cereal rye planting and termination dates, photosynthetically active radiation, precipitation, and site coordinates as predictors. Our results suggest that similar modeling approaches could be combined with remotely sensed early‐season biomass estimations to improve the accuracy of predicting winter cover crop biomass at termination for decision support tools.Core Ideas Cereal rye winter cover crop biomass modeled on data from 35 site‐years. We found a strong relationship between early and late‐season biomass. Random forest model with early‐season biomass and weather data performed well. Similar approach could improve decision support tools for cover crop management.

Integrating cover crops and herbicides for weed control in soybean

Abstract In mid-southern, southeastern, and northeastern U.S. soybean production regions, the evolution of herbicide-resistant weeds has become a significant management challenge for growers. The rising herbicide costs for managing herbicide-resistant weeds are also a growing concern, leading to the utilization of cover crops as an integrated weed management strategy for addressing these challenges. Field experiments were conducted at two locations in Alabama in 2022 to evaluate winter cereal cover crops, including a mixture and herbicide system integration in soybean. Treatments included five cover crops: oats, cereal rye, crimson clover, radish, and a cover crop mixture. Cover crops were evaluated for their weed-suppressive characteristics compared to a winter fallow treatment. Additionally, four herbicide treatments were applied: a preemergence (PRE) herbicide, a postemergence (POST) herbicide, PRE plus POST herbicides, and a nontreated (NT) check. The PRE herbicide was S-metolachlor; the POST treatment contained a mixture of dicamba and glyphosate. The PRE plus POST system contained the PRE application followed by POST application. Results show that cereal rye and the cover crop mixture provided weed biomass reduction compared to all cover crop treatments across both locations. Furthermore, we observed greater soybean yield following the cereal rye cover crop than following the winter fallow treatment at one location. POST and PRE plus POST herbicide treatment resulted in greater weed biomass reduction and improved soybean yield than the PRE herbicide treatment alone and the NT check at both locations.

Split fertilizer nitrogen application with a cereal rye cover crop reduces tile nitrate loads in a corn-soybean rotation.

Splitting fertilizer nitrogen (N) applications and using cover crops are management strategies to reduce nitrate in tile drainage water. We investigated split fertilizer N applications to corn (Zea mays L.) on crop yields and tile nitrate loss in both corn and soybean (Glycine max L.) in rotation from 2016 through 2019. We evaluated the inclusion of cover crops in a split-N treatment. Fertilizer N treatments included 100% in the fall; 50% in the fall + 25% at planting + 25% at side-dress; 100% as spring preplant; 75% as spring preplant (reduced N rate); 50% as spring preplant + 50% at side-dress; and 50% as spring preplant + 50% at side-dress with a cover crop. We did not find significant differences between split and single full rate N application treatments for corn yields or tile nitrate loss; however, the reduced N rate treatment significantly decreased corn yield by 10%. Cumulative tile nitrate losses (over four seasons) ranged from 115kg ha-1 for all of the N in the fall to 65kg ha-1 for 50% as spring preplant + 50% at side-dress with a cover crop, a decrease of 43%. Tile nitrate loss responded similarly to (corn) N treatments under both corn and soybean, with 64% of the loss under corn and 36% under soybean. Our results suggest that decreasing the fertilizer N rate may impact corn yield more than nitrate loss, while split fertilizer N application with a cover crop has potential to reduce tile nitrate loss without decreasing crop yield.

Effect of Allelochemicals from Cereal Rye Cultivar and Pythium lutarium on Corn Growth and Disease

Allelopathic chemicals produced by a cereal rye (CR; Secale cereale L.) cover crop have been implicated in the negative effect of CR on corn planted into decomposing CR residue. Production of allelochemicals varies among CR cultivars. In the current study, the allelopathic effect of crude extracts from five CR cultivars (Elbon, Hazlet, Serafino, Tayo, and Yankee) was evaluated on corn seedling growth, mycelial growth of Pythium lutarium, and root rot of corn caused by P. lutarium using a plate assay. In general, crude extracts from all CR cultivars slowed pathogen growth and reduced corn coleoptile and radicle lengths. When corn was grown on media amended with crude extracts from the CR cultivars and colonized with P. lutarium, corn growth was reduced and root rot severity increased compared with the check (no extract with pathogen). Subsequently, a cup assay was used to further investigate the allelopathic effect of Elbon, Hazlet, and Serafino on corn seedling growth and root rot. Corn grown in cups into which each cultivar had been planted had shorter radicles and coleoptiles compared with the check (no CR), regardless of the CR cultivar. Results from this study suggest that allelochemicals released from decomposing CR vary among cultivars, and their interaction with Pythium spp. could affect seedling disease on corn. Consequently, choice of CR cultivar may be an important management decision to reduce the negative effects of CR on corn. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

Cover crop performance under a changing climate in continuous corn system over Nebraska.

Fall-planted cover crop (CC) within a continuous corn (Zea mays L.) system offers potential agroecosystem benefits, including mitigating the impacts of increased temperature and variability in precipitation patterns. A long-term simulation using the Decision Support System for Agrotechnology Transfer model was made to assess the effects of cereal rye (Secale cereale L.) on no-till continuous corn yield and soil properties under historical (1991-2020) and projected climate (2041-2070) in eastern Nebraska. Local weather data during the historical period were used, while climate change projections were based on the Canadian Earth System Model 2 dynamically downscaled using the Canadian Centre for Climate Modelling and Analysis Regional Climate Model 4 under two representative concentration pathways (RCP), namely, RCP4.5 and RCP8.5. Simulations results indicated that CC impacts on corn yield were nonsignificant under historical and climate change conditions. Climate change created favorable conditions for CC growth, resulting in an increase in biomass. CC reduced N leaching under climate change scenarios compared to an average reduction of 60% (7kg ha- 1 ) during the historical period. CC resulted in a 6% (27mm) reduction in total water in soil profile (140cm) and 22% (27mm) reduction in plant available water compared to no cover crop during historical period. CC reduced cumulative seasonal surface runoff/soil evaporation and increased the rate of soil organic carbon buildup. This research provides valuable information on how changes in climate can impact the performance of cereal rye CC in continuous corn production and should be scaled to wider locations and CC species.

Impact of cereal rye cover crop on the fate of preemergence herbicides flumioxazin and pyroxasulfone and control of Amaranthus spp. in soybean

AbstractPreemergence herbicides associated with cereal rye (Secale cereale L.) cover crop (hereafter “cereal rye”) can be an effective waterhemp [Amaranthus tuberculatus (Moq.) Sauer.] and Palmer amaranth (Amaranthus palmeri S. Watson) management strategy in soybean [Glycine max (L.) Merr.] production. Delaying cereal rye termination until soybean planting (planting green) optimizes biomass production and weed suppression but might further impact the fate of preemergence herbicides. Limited research is available on the fate of preemergence herbicides applied over living cereal rye in the planting green system. Field experiments were conducted in Illinois, Kansas, Pennsylvania, and Wisconsin to evaluate the fate of flumioxazin and pyroxasulfone and Amaranthus spp. residual control under different cover crop management practices in soybean in 2021 and 2022 (8 site-years). A flumioxazin + pyroxasulfone herbicide premix was applied preemergence at soybean planting under no-till without cereal rye, cereal rye early terminated before soybean planting, and cereal rye terminated at soybean planting. Flumioxazin and pyroxasulfone concentrations in the soil were quantified at 0, 7, and 21 d after treatment (DAT), and Amaranthus spp. density was determined at postemergence herbicide application. The presence of cereal rye biomass intercepted flumioxazin and pyroxasulfone at preemergence application and reduced concentration in the soil when compared with no-till, mainly at 0 DAT. Main differences in herbicide concentration were observed between no-till and cereal rye treatments rather than cereal rye termination times. Despite reducing herbicide concentration in the soil, the presence of the cereal rye biomass did not affect early-season residual Amaranthus spp. control. The adoption of effective preemergence herbicides associated with a properly managed cereal rye cover crop is an effective option for integrated Amaranthus spp. management programs in soybean production systems.

Managing herbicide‐resistant waterhemp (Amaranthus tuberculatus [Moq.] J.D. Sauer) seedbanks by integrating several management tactics

AbstractHerbicide‐resistant waterhemp (Amaranthus tuberculatus [Moq.] J.D. Sauer) continues to threaten the productivity of many US crops. Thus, integrating non‐herbicidal tactics with herbicides to reduce weed seedbanks is gaining popularity. A field study was conducted near Logan, IA from fall 2021 to fall 2022 to evaluate the impacts of cereal rye (Secale cereale L.) cover crop, herbicides, and harvest weed seed destruction on the waterhemp seedbank inputs. The cereal rye cover crop reduced waterhemp seed production by 90% compared to treatments without the cereal rye cover crop, while herbicides did not significantly affect waterhemp seed production. Furthermore, 96% of waterhemp seeds that entered the combine at harvest were destroyed and seed destruction effectiveness was not affected by cereal rye cover crop, herbicide program, or combine speed. Thus, cover crops and weed seed destruction are effective tactics to minimize waterhemp seedbank inputs. Waterhemp seed retention and combine header losses of waterhemp seeds were evaluated at harvest. Waterhemp seed retention was not affected by the cereal rye cover crop or herbicide programs. Only 30% of waterhemp seeds remained on the plant at harvest; the likely causes of seed shattering were late harvest and windy conditions prior to harvest. Waterhemp seed shattering from the combine header averaged 2.6% and was not affected by cover crop, herbicide program, or combine speed. These results support the inclusion of non‐herbicidal control tactics to reduce herbicide‐resistant waterhemp seedbanks and suggest the need for future research to optimize weed seed destruction.

The effects of cereal rye cover crop seeding rate, termination timing, and herbicide inputs on weed control and soybean yield

AbstractGrowers have been experimenting with cover crop termination timings to maximize weed suppression and potentially reduce herbicide inputs in soybean [Glycine max (L.) Merr.]. A field study was replicated three times from 2018 through 2021 in South Charleston, OH, to evaluate different management strategies involving a cereal rye (Secale cereale L.) cover crop. The objectives were to determine the effects of cereal rye seeding rate (0, 50, and 100 kg ha−1), management program (preplant, postplant, and delayed), and soybean residual herbicide (flumioxazin + chlorimuron ethyl and no herbicide) on cover crop, weed, and soybean parameters. The preplant program consisted of cereal rye terminated 7 d before planting (DBP) + a postemergence application. The postplant program consisted of cereal rye terminated 7 d after planting (DAP) + a postemergence application. In the delayed program, saflufenacil was applied in April and cereal rye was terminated 21 DAP, and there was no postemergence application. Giant foxtail (Setaria faberi Herrm.) density was reduced by the presence of cereal rye, averaged over other factors, regardless of seeding rate. Cereal rye seeding rate did not affect giant ragweed (Ambrosia trifida L.) density. The delayed management program was generally associated with the lowest weed density, but weed density was often similar in the postplant program. Setaria faberi density was lower in treatments that included a residual herbicide. Residual soybean herbicide use did not affect density of A. trifida. Terminating cereal rye after soybean planting resulted in increased soybean yield in 2019 and reduced yield in 2020, compared with preplant rye termination. These data suggest that adjusting the cereal rye management program may have a greater effect on weed suppression than adjustments to seeding rate. Delaying termination of cereal rye can aid in the suppression of weeds, but a comprehensive herbicide program was necessary to provide adequate (>85%) weed control.

Mechanisms of weed suppression by cereal rye cover crop: A review

AbstractCereal rye (Secale cereale L.) is an important cover crop species in the United States. It has the potential to minimize soil erosion, reduce nutrient leaching, decrease fertilizer inputs, improve soil water after termination, and enhance soil organic matter. Cereal rye is also an efficient tool for weed suppression (up to 100% under ideal conditions), which is achieved through several mechanisms. Reported biomass production estimates ranged from 0.9 to 20 ton ha−1 in different environments; weed suppression benefits were observed in all these scenarios, though the extent of suppression significantly differed across the studies, indicating the presence of multiple weed suppression mechanisms with cereal rye cover crops. These can be competitive (competition for space [i.e., mulching effect], water, nutrients, and light) or non‐competitive (allelopathy, reduction in soil temperature, and reduction in light quality). Such a variety of mechanisms make it an excellent tool for integrated weed management in both conventional and organic systems. In this review, we summarize and analyze published information on the mechanisms of weed suppression by cereal rye. First, we outline the physiological characteristics that make cereal rye an excellent cover crop species and the many benefits it can provide. Second, we review four competitive mechanisms of weed suppression, which are generally considered the leading ones. Third, we summarize three non‐competitive mechanisms, the applications of which are not yet fully understood in agricultural systems. Finally, we analyze the management implications of this information and identify knowledge gaps for directing future research on this topic.

Cereal rye cover crop seeding method, seeding rate, and termination timing effects corn development and seedling disease

AbstractCover crops decrease nutrient leaching from high‐input cropping systems and improve soil quality. In Iowa, cereal rye (CR, Secale cereale L.) is the most adopted species due to its winter hardiness, high biomass productivity, and low cost. Field management of CR is still not completely understood, and as its adoption brings more complexity to farmers, especially with the uncertain effects on corn (Zea mays L.) yields, adoption is slow. Additionally, cover crops immobilize N and increase the inoculum of pathogens such as Pythium spp. A 2‐year field experiment was conducted at three locations in Iowa investigating the effect of two seeding methods, three seeding rates, and two termination timings (one location only) of CR on CR biomass and corn growth, root disease, and yield. Cereal rye biomass and consequently corn growth and development were not affected by seeding rate but by seeding method and termination timing. Broadcast CR produced an average of 3.5 times more biomass but 7.2% less corn yield than the drilled CR. Cereal rye when terminated late (3 days before planting [DBP]) produced 2.1 times greater biomass but 4.1% less corn yield compared to early termination (14 DBP). In general, greater root rot incidence and more Pythium clade B were detected in corn seedlings sampled from broadcast CR than drilled CR. Radicle rot incidence of corn was also greater in the late‐terminated plots in 1 year. Farmers should be careful using broadcast seeding and later termination of CR cover crop when planted before corn.

Investigating tradeoffs in nitrogen loss pathways using an environmental damage cost framework

AbstractFew studies have addressed whether in‐field practices to reduce nitrate‐nitrogen (NO3‐N) leaching might increase nitrous oxide (N2O) emissions, which could undermine attempts to mitigate agricultural N pollution. Over a 3‐year period, we assessed the impacts of N application timing and cereal rye (Secale cereale L.) cover crop on subsurface drainage NO3‐N leaching and N2O emissions to quantify changes in total N loss and corresponding social and environmental damage costs under continuous corn (Zea mays L.). While NO3‐N losses were reduced by 37% with the combination of in‐season split N application and cereal rye cover crop relative to pre‐season N application, soil N2O emissions increased by 26%, highlighting a tradeoff between N loss pathways. As a result, total N losses and social and environmental damage costs from each system were not different. These results demonstrate the importance of addressing agricultural N pollution using a holistic framework accounting for the environmental and social risks of both NO3‐N losses and N2O emissions.

Evaluating the impact of at-plant termination of a cereal rye cover crop with different corn planting dates on arthropod activity.

Greater cover crop biomass is expected to result in a favorable microhabitat for beneficial arthropods. Natural Resources Conservation Service (NRCS) cover crop termination guidelines are based on the cash crop planting date. Therefore, a delay in cash crop planting could result in greater cover crop biomass. However, studies on delays in cash crop planting and greater cover crop biomass have led to a decrease in cash crop yield. Thus, a field study was conducted in eastern Nebraska over two years to evaluate the impact of early and late corn planting dates with at-plant cover crop terminations on pest potential, beneficial arthropod activity, and agronomic parameters. To measure arthropod activity and pests in the system, pitfall traps, and corn injury assessments were performed during the early stages of corn development. A total of 11,054 and 43,078 arthropods were collected in 2020 and 2021, respectively. The results have shown no impact of the corn planting dates with at-plant cover crop termination on arthropods but identified that cereal rye cover crop supports greater Araneae activity while its alternative prey varied when compared to the no-cover treatment. Significant yield penalties were observed when cover crop was used regardless of the corn planting dates. Pest pressure was not significant in any year, however, future research using cereal rye and different cover crop species should be used in this system with an artificial infestation of a pest to be able to evaluate the trade-offs between possible cash crop yield reductions and potential biological control of pests.

Multi-tactic strategies to manage herbicide-resistant waterhemp (Amaranthus tuberculatus) in corn–soybean rotations of the U.S. Midwest

AbstractField experiments were conducted over 2 yr (2019 to 2020) at two locations in Iowa to evaluate multi-tactic strategies for managing multiple herbicide–resistant (MHR) waterhemp [Amaranthus tuberculatus (Moq.) Sauer] in a corn (Zea mays L.)–soybean [Glycine max (L.) Merr.] rotation. The effect of three herbicide programs on A. tuberculatus control was tested in corn (2019). The effects of the prior year’s corn weed control, a cereal rye (Secale cereale L.) cover crop, and soybean row spacing (38-cm vs. 76-cm wide) on A. tuberculatus density, biomass, and seed production were tested in soybean (2020). A herbicide program used in corn with two sites of action provided only 35% control of MHR A. tuberculatus compared with ≥97% control by a herbicide program with three sites of action. In soybean, adequate control of A. tuberculatus (≥90%) in the prior year’s corn crop and use of a cover crop or narrow rows reduced A. tuberculatus density by more than 60% at 3 and 9 wk after planting (WAP) compared with inadequate control (30%) in the prior year’s corn and no cover crop. Cover crop and narrow-row soybean reduced A. tuberculatus density by 44% at 3 WAP compared with no cover crop and wide-row soybean. Inclusion of a single control tactic, adequate control (≥90%) with multiple herbicides in the prior year’s corn, use of a cover crop, or narrow-row soybean reduced A. tuberculatus biomass and seed production at soybean harvest by at least 24% compared with inadequate control (30%) in the prior year’s corn, no cover crop, and wide-row soybean. The combination of all three control tactics reduced A. tuberculatus biomass and seed production at soybean harvest by at least 80%. In conclusion, diverse control tactics targeting A. tuberculatus at multiple life-cycle stages can make substantial contributions to the management of MHR populations.