Final report for GW23-250
Project Information
There has been substantial interest in cover crops in our region, especially from farmers who grow specialty and small-acreage crops like dry bean. This has been driven primarily by goals of weed suppression, erosion control, and protecting crops from wind damage. Despite the profound interest, the adoption of cover crops in Idaho remains one of the lowest in the United States. Demonstrating the short-term weed suppression and potential economic benefits may increase the adoption and integration of cover crops into cropping systems. Cereal cover crops can be effective at suppressing weeds, however, maximizing suppressive ability is dependent on management practices that promote biomass production at the time of cash crop planting. Cover crops (wheat, barley, and triticale) were planted in the fall of 2022. Cereal cover crops were either terminated with herbicide (glyphosate) or harvested for forage. In an organic system cover crops will be tilled. In the conventional system, there were five herbicide treatments; three preemergence, one postemergence herbicide treatment, and one nontreated check where there was no herbicide spraying. Data were collected on soil moisture, soil temperature, soil health, dry bean stand density, weed control, crop yield, as well as economic analysis. It is expected that cover crops will increase labile carbon, suppress weeds, and not negatively impact bean yield. Results will be disseminated to stakeholders through field days, bean school presentations, extension publications, and peer-reviewed publications. Results from this project will provide the foundational knowledge needed by stakeholders to adopt and integrate cover crops to maximize weed suppressive benefit, reduce reliance on herbicides, and minimize the potential for negative yield impacts.
Research Objectives:
- Quantify biomass production and weed suppression of fall-planted cover crops
- Evaluate how termination practice (chemical termination vs haying) affects weed suppression ability of fall-planted cereal cover crops in dry bean.
- Evaluate weed suppression and dry bean response to cereal cover crops in an organic production system.
- Evaluate changes in soil labile carbon in cereal cover crop – dry bean production systems.
- Use crop yield and input cost to quantify the economic impact of integrating cereal cover crops and herbicides for weed control in dry bean.
Educational objective(s):
- Educate producers and stakeholders on cover crops and management practices that optimize weed suppression and soil health benefits, and profitability
Cooperators
- - Producer
Research
Objective(s):
Our long-term goal is to provide the foundational knowledge needed by stakeholders to adopt and integrate fall-planted cover crops into their operations for improved weed control, reduced herbicide applications, soil health, and profitability. Specifically, we are proposing to:
- Quantify biomass production and weed suppression of fall-planted cover crops
- Evaluate how termination practice (chemical termination vs haying) affects weed suppression ability of fall-planted cereal cover crops in dry bean.
- Evaluate weed suppression and dry bean response to cereal cover crops in an organic production system.
- Evaluate changes in soil labile carbon in cereal cover crop–dry bean production systems.
- Use crop yield and input cost to quantify the economic impact of integrating cereal cover crops and herbicides for weed control in dry bean.
Research Methods:
We propose answering the following questions:
- Do fall-planted cover crops produce enough biomass to suppress weeds and how does this impact the efficacy of soil-applied herbicides?
- What are the short-term impacts of cereal cover crops on soil active carbon and soil moisture?
- How do cereal cover crops and herbicide programs affect weed control, crop yield, and profitability?
Field studies were established in Kimberly, ID (University of Idaho Kimberly Research and Extension Center) and Parma, ID (University of Idaho Parma Research and Extension Center) as well as a third on-farm site located in Shoshone, ID was included to evaluate weed suppression and dry bean response to cereal cover crops in an organic production system. All experiments were arranged as a randomized complete block design, with location in the field as a blocking factor accounting for field variability. Both cover crops and dry beans were grown under sprinkler irrigation. Dry beans were planted at a rate of about 280, 000 to 350,000 seeds/ha in 56 cm rows in early June 2023.
Field study #1 (Conventional dry bean): Fall planted cover crop biomass production and weed suppression
(Specific Objective 1)
The experimental fields were designed as a split-plot randomized complete block with 35 treatments and four replications. The main plots comprised three fall-planted cereal cover crops: barley, triticale, and wheat, along with a no-cover crop treatment. The cereals were planted with a seeding rate of 112 kg ha-1 in both locations. Each of the cereals was terminated by two termination treatments: chemical termination using glyphosate (at 1261 g ai ha-1) and haying termination using a Wintersteiger Cibus F forage harvester (Wintersteiger AG., Ried, Austria). Dry beans (“Othello” pinto beans) were planted within 2 weeks after cover crop termination in the years 2023 and 2024 at both locations. The dry beans were planted at the rate of 230,000 seeds ha-1 in Parma, whereas in Kimberly, they were planted at the rate of 290,000 seeds ha-1. The seeding rate was different because of the different types of planters used in the study at each location. The planter used in Parma was a custom-built unit with a heath planter attached to a John Deere frame. In Kimberly, a Monosem row planter (Monosem Inc., Kansas City, KS) was used. The spacing between the rows was 56 cm (four crop rows per plot). Glyphosate was applied at 1261 g ai ha-1 to all plots at dry bean planting to ensure all plots were weed-free at the time of dry bean emergence.
The seven main plots based on cover crop and termination treatments including control were treated with five herbicide treatments: no herbicide, pre-emergence application of pendimethalin, pendimethalin + EPTC, dimethenamid-p + EPTC, and post-emergence application of imazamox + bentazon. These herbicides are considered safe for use in dry beans (Pacific Northwest Pest Management Handbooks, 2022). Pre-emergence herbicides were applied within 48 hours after dry bean planting and incorporated with 2.5 cm of overhead irrigation water. Post-emergence herbicides were applied when the first trifoliate leaves of dry beans fully emerged. Herbicide applications were made using a CO2-pressurized bicycle sprayer delivering 144 L ha-1 at 207 kPa with TeeJet 11002DG nozzles.
Data collection (Specific Objectives #1)
At cover crop termination, cover crop and weed above-ground biomass, and cover crop height were measured. Cover crops and weed biomass were harvested in 1 m2 area per plot. Cover crop biomasses from the haying treatments were dried, weighed, and sent to Ward Laboratories (Kearney, Nebraska, USA) for wet chemistry analysis of forage nutritional value. The specific nutrients quantified in the forage samples included crude protein (CP), acid detergent fiber (ADF), neutral detergent fiber (NDF) and relative feed value (RFV). Dry beans stand density was measured four weeks after dry bean planting to enable us to assess the association of stand density to dry bean yield. Weed above-ground biomass was collected after five weeks of post-emergence herbicide application to determine the impact of treatment on weed control. Dry bean yield was taken at the end of the season by harvesting the two center rows in each plot to assess the impact of treatments on crop yield.
Field study #2 (Organic dry bean): Weed suppression and dry bean response to cereal cover crops
(Specific Objective 2) The collaborating organic farmer observed that although cereal cover crops fit into their operations for weed suppression and soil health, some cereal cover crops such as wheat and triticale tend to reduce dry bean density. This confirms findings from a controlled environment experiment that observed a 58% reduction in dry bean germination when watered with winter wheat extract (Flood and Entz 2009). Triticale extract also reduced dry bean germination by 21 to 40% (Flood and Entz 2009). The primary objective of the on-farm experiment is a better understanding of weed suppression and any possible allelopathic effect (dry bean response) of cereal cover crops. The collaborating farmer had already planted winter spelt, spring barley, and winter wheat. Although not a replicated study, data were collected in transects in the summer of 2023 to serve as baseline data for the on-farm trial. We then established a 12-month experiment beginning in fall 2023. The study comprised four treatments arranged in a randomized complete block design with 4 replicates.
Treatments comprised fall-planted wheat, triticale, and barley, in addition to a no cereal cover crop treatment. Cereal cover crops were planted at a rate of about 2 million seeds/ha in October of 2023, the typical time for our region. Winter peas were planted in the no cereal cover crop treatment as the collaborating farmer preferred to have ground cover to prevent erosion. Cover crops were terminated in mid May by mowing, followed by disking and roller-harrowing to ensure plant biomass is well incorporated within the rooting zone of the dry bean crop. Dry beans were planted in early June, and plots were managed according to the farmer’s standard practice throughout the season.
Data collection (Specific Objectives #2)
At the time of cover crop termination, the height and above-ground biomass of the cover crops and weeds were measured. Cover crops and weed biomass were measured by placing a m2 quadrat randomly per plot. The biomasses were then oven-dried at 60 °C until completely dry to determine biomass yield. Beginning one week after the dry bean planting, dry bean stand counts were measured 3 to 4 times by counting bean plants within the five center rows of each plot. The final weed count was measured four weeks after planting dry beans. Dry bean yield was taken at the end of the season by harvesting four rows (3m by 4 rows) in each plot to assess the impact of treatments on crop yield.
Specific objective #3 (Conventional and organic dry bean): Soil health
Soil samples were collected before planting cover crops for both conventional and organic production systems. In the conventional system, soil sampling was also done after dry bean harvest and sent to a commercial lab to determine any changes in soil labile carbon, Haney test, and PFLA test. Soil samples will be analyzed following standard laboratory protocols.
Specific objective #4 (Conventional dry bean): Economic impact of integrating cereal cover crops and herbicides
Crop yield and all inputs (fertilizer, fuel, herbicide, labor, seed, etc.) were recorded and used in the economic analysis. The economic benefit of each treatment was determined using partial budgeting.
Statistical procedures
A linear mixed-effects ANOVA was performed in R statistical language using the lmer function of the lme4 package and convenience functions from the lmerTest package. Cover crop, termination practice, and herbicide treatments were considered fixed effects, and block and year were considered random effects. The relationship between cover crop biomass vs dry bean stand count and cover crop biomass vs weed density and weed biomass will be analyzed using regression techniques; either linear regression or nonlinear regression. For the organic dry bean experiment, one-way ANOVA will be used to determine the effect of cover crop treatments on dry bean stand density, weed density, yield, soil moisture, and labile carbon concentration.
References:
- Baraibar B, Hunter MC, Schipanski ME, Hamilton A, Mortensen DA (2018) Weed Suppression in Cover Crop Monocultures and Mixtures. Weed Science 66:121–133
- Flood H, Entz M (2009) Effects of wheat, triticale and rye plant extracts on germination of navy bean (Phaseolus vulgaris) and selected weed species. Canadian Journal of Plant Science 89:999-1102
- Osipitan OA, Dille JA, Assefa Y, Radicetti E, Ayeni A, Knezevic SZ (2019) Impact of Cover Crop Management on Level of Weed Suppression: A Meta-Analysis. Crop Science 59:833–842
- Smith RG, Warren ND, Cordeau S (2020) Are Cover Crop Mixtures Better at Suppressing Weeds than Cover Crop Monocultures? Weed Science:1–33
Objective #1: Conventional study: Weed suppression, dry bean stand density and yield impacts
Cover crop height and biomass
Triticale had significantly greater height (63 cm in Parma and 95 cm in Kimberly) than barley and wheat in both locations . In Parma, triticale was the most productive cover crop in terms of biomass production (3540 kg ha-1), which significantly differed from wheat that produced the least biomass (2753 kg ha-1). In contrast, barley produced the highest regrowth biomass (867 kg ha-1), while triticale produced the least regrowth biomass (512 kg ha-1). In Kimberly, however, there were no significant differences in biomass among the cereal cover crops.
Dry bean stand density
In Parma, dry bean stand count was significantly influenced by cover crops and herbicide treatments . All three cover crops, when terminated by haying, reduced the stand density of the bean crop up to 38 % compared to chemically terminated barley plots. The highest dry bean stand count (193,008 plants ha-1) was recorded in chemically terminated barley plots, while the lowest (119,795 plants ha-1) was recorded in hayed-triticale plots.
In Kimberly, dry bean stand count was significantly influenced by both cover crop and herbicide treatments, as well as their interaction. Chemically terminated cover crop treatments had significantly lower dry bean stand density compared to no cover crop treatments and hayed cover crop treatments. The highest dry bean stand count (191,760 plants ha-1) was recorded in hayed-wheat plots, while the lowest (121,482 plants ha-1) was recorded in chemically terminated barley plots.
Weed biomass
In Parma, total weed biomass was significantly influenced by cover crop treatments. The no cover crop treatment had the highest weed biomass (198 g m-2), dominated by kochia (168 g m-2). All three cover crops, either chemically terminated or hayed, reduced kochia biomass by up to 91%, with the total weed biomass reduced by 65-80%. Among the cover crops, triticale and barley treatments showed substantial suppression of kochia, resulting in significantly lower kochia biomass of around 15-17 g m-2 in the chemically terminated treatments These cover crops also suppressed other weed species, such as green foxtail and red-root pigweed, but to a lower extent than kochia. In addition, cover crops had varying effects on weed species like yellow nutsedge and common purslane, where their biomass was significantly greater in hayed-cover crop treatments compared to chemically terminated cover crop treatment and no cover crop treatment.
Herbicide treatments varied significantly in their effectiveness against different weed species. The combination of bentazon + imazamox was the most effective in controlling kochia, reducing its biomass by 82% compared to the nontreated control. This combination also effectively reduced the biomass of yellow nutsedge, green foxtail, and common purslane, demonstrating its broad-spectrum efficacy. In contrast, dimethenamid-p + EPTC treatment was not effective on kochia but was effective on controlling yellow nutsedge, green foxtail, and common purslane. This resulted in the highest total weed biomass of 107 g m-2, even more than the nontreated control. The pendimethalin-based treatments were observed effective on common purslane and moderately controlled kochia and green foxtail but these were less effective against yellow nutsedge.
In Kimberly, cover crop treatments had a significant influence on total weed biomass, with the highest weed biomass (224 g m-2) observed in plots with no cover crops. Common lambsquarters, redroot pigweed, and green foxtail were the common weeds found in Kimberly. Among these weeds, cover crops that were chemically terminated significantly suppressed redroot pigweed biomass (7 g m-2), followed by cover crops that were hayed, and the highest weed biomass was recorded in the absence of cover crops (57 g m-2).
The nontreated plot had significantly greater biomass of common lambsquarters, redroot pigweed, and green foxtail than the treated ones, demonstrating poor weed control in the absence of herbicide application. The herbicide treatment, dimethenamid-p + EPTC showed the most effective weed suppression, resulting in the lowest total weed biomass (69 g m-2) and the least biomass across individual weed species. The pendimethalin + EPTC treatment also showed strong weed control with significantly lower biomass (108 g m-2), particularly for common lambsquarters and redroot pigweed. The treatment bentazon + imazamox provided moderate weed control (119 g m-2), with weed control comparable to pendimethalin + EPTC. Overall, in Kimberly, pre-emergence herbicides worked better in controlling weeds than post-emergence herbicides.
Dry bean seed yield
In Parma, dry bean seed yield was primarily influenced by herbicide treatments, where the seed yield was significantly reduced by 31% in nontreated control. Although the dry bean density was reduced in hayed cover crop treatments, it did not result in significant yield loss, which showed that bean plants compensate stand reductions with yields.
In Kimberly, dry bean seed yield was influenced by cover crops and herbicide treatments. Barley hayed treatment had the greatest seed yield (2,556 kg ha-1) that was statistically comparable to seed yields from triticale hayed and no cover crop treatment. Seed yield was reduced by 38 to 49% in chemically terminated cover crop treatments compared to barely hayed treatment. The reduced seed yield in chemical termination treatments was a result of reduced dry bean stand densities in those treatments due to high forage biomass production in 2024 in Kimberly.
Objective #2: Organic on-farm study: Weed suppression and dry bean stand density impacts
Results showed that cereal cover crops reduced weed biomass by 60 to 74% compared to winter peas at the time of termination. However, weed suppression was similar among the treatments after they were incorporated into the soil. Similarly, there were no differences in dry bean stand density and seed yield among the cover crop treatments. The study demonstrated that cereal crops could be used as cover crops in dry bean production without concerns regarding their negative impacts on stand densities and seed yield.
Objective #3: Soil health
Post-cover crop active carbon increased in all cover crops and herbicide treatments in Parma, with the highest increase observed in the ‘no cover crop, dimethenamid-p + EPTC’ treatment (up to 39 %). In contrast, post-cover crop active carbon in Kimberly decreased across all treatments (up to 43 % less). Similarly, post-cover crop total microbial biomass increased in all cover crop treatments by 68 % in Parma, while in Kimberly, only barley increased microbial biomass by 14%. These factors suggest that short-term changes in soil health might depend on site-specific factors and might not be achieved in most cases.
In the organic on-farm study, soil tests showed that post-cover crop active carbon decreased in all cover crop treatments by 43 to 61 %. Total microbial biomass increased in wheat (by 18 %) and triticale (by 16%), while it decreased in barley (by 31 %) and winter peas treatment (by 23 %).
Objective #4: Economic implications
Estimated net return (revenue minus production costs) values that were calculated for each cover crop termination type and herbicidal treatment combination, excluding the no-herbicide treatment. The net returns obtained from the no herbicide treatment were consistently negative for all cover crop treatments. Therefore, this treatment was excluded from this discussion to prevent the negative net returns from skewing the profitability estimates obtained from cover crop use when integrated with herbicides.
The profitability estimates based on field trial results from Parma indicated that a positive net return would be expected for the cover crops triticale and barley when both chemically terminated and hayed. The positive net return ranged between 260.75 to 1024.5 US$ ha⁻¹ for these cover crop treatments. Among these, hayed barley yielded the highest estimated profit (1025 US$ ha⁻¹) followed by hayed triticale (841 US$ ha⁻¹). However, chemically terminated and hayed wheat treatments were estimated to have a negative net return (-34 and –61.75 US$ ha⁻¹ respectively). This was similar to what Reddy (2001) found where chemically terminated wheat in combination with herbicides resulted in negative net returns. This was primarily due to lower revenue in herbicide treatments involving dimethenamid-p + EPTC and pendimethalin, as dimethenamid-p + EPTC led to higher weed pressure in Parma, reducing seed yield and estimated revenue. Additionally, biomass production in the wheat cover crop treatment was less in Parma compared to triticale and barley, which contributed to its lower estimated revenue in the haying treatment.
In Kimberly, all the cover crop treatments were estimated to have positive net returns ranging from 433.75 to 2971 US$ ha⁻¹, except for chemically terminated barley (-313 US$ ha⁻¹). The significant biomass production of cover crops in Kimberly in 2024 interfered with the germination of dry bean crops in the treatments where cover crops were chemically terminated. This led to reduced dry bean stand count and seed yields, and, thus, lower estimated revenues. The hayed barley was the most profitable with a gain of 2971 US$ ha-1 in Kimberly, followed by triticale when hayed with a gain of 2042 US$ ha-1. Profits were generally higher when cover crops were hayed rather than chemically terminated at both locations.
Research Outcomes
The field studies conducted have demonstrated that cereal cover crops provide a sustainable approach to weed management in dry beans, when combined with herbicides and when used alone. Cover crops along with providing immediate weed suppression, aid in managing problematic herbicide-resistant weeds. Field study #1 (conventional dry bean) results showed that the combination of fall-planted cereal cover crops and herbicides can be a promising strategy for effective weed control in dry beans. However, careful management of cover crops is important, particularly in high biomass situations, to prevent negative impacts on the subsequent dry bean crops.
In Field study #2 (organic dry bean), results showed that cereal cover crops perform better than legume cover crops in suppressing weeds at the time of termination mainly by producing more biomass. Cereal cover crops showed promise for weed control without negatively impacting dry bean stand density and yield in an organic system. Overall, the projects carried out provided valuable insights into sustainable weed management strategies for dry bean production, offering a foundation for future studies and practical applications in both conventional and organic farming systems.
Soil health study showed that soil health benefits by planting cover crops, particularly active carbon and microbial biomass, may not be achieved in most cases in short-term studies. Soil health improvement is a gradual process and requires a longer period to show changes. Growers who want to incorporate cover crops into their cropping systems should consider other short-term benefits of cover crops such as weed suppression, erosion control,
and protection of the crop from early-season wind damage when assessing the value of cover crops.
Economic analysis revealed that combination of cover crops and herbicides is profitable if proper management practices are followed to maintain crop yield. It also showed that farmers might lose a considerable amount of money if none of the weed management practices are followed.
Education and Outreach
Participation Summary:
Field trials were shown to farmers and stakeholders at Field Days and Tours in Kimberly and Parma, Idaho. These events included guided plot visits and presentations about cover crop selection, termination methods, weed suppression results, and early observations on crop response. In addition to field-based events, results were presented at stakeholder meetings, university's seminars and scientific conferences. These events allowed us to reach both local and regional stakeholders, including producers, extension personnel, and researchers.
As of now, following education activities were achieved:
- 3 field days/tours (2023 and 2024)
- 1 regional meeting presentation (2023)
- 3 conference presentations (2024 and 2025)
- 2 departmental seminar presentations (2023 and 2024)
- 2 bean school presentations (2025)
Results from this project have been presented at the following events to engage producers, agricultural professionals, researchers, and other stakeholders:
- 2023 University of Idaho Parma Research & Extension Center Field Day: 50 attendees
- 2023 University of Idaho Kimberly Research & Extension Center weed tour & field day: 85 attendees
- 2023 Idaho Association of Plant Protection Conference, Rupert, ID: 45 attendees
- Poster presentation at the 2024 Western Society of Weed Science conference, Denver, CO.
- Oral presentation at the 2024 Weed Science Society of America conference, San Antonio, TX.
- University of Idaho Department of Plant Science seminar: 21 attendees
- 2024 University of Idaho Kimberly Research & Extension Center weed tour & field day: 82 attendees
- 2025 Idaho Bean School, Twin Falls, ID: 125 attendees
- 2025 Idaho Bean School, Caldwell, ID: 82 attendees
- Poster presentation at the 2025 Western Society of Weed Science conference, Seattle, WA
Through these outreach events, we engaged a wide range of farmers, researchers and agricultural professionals through in-person participation. Presentations at field days allowed for direct interaction with farmers and stakeholders, where project methods and results were discussed on-site. This approach helped growers better understand how cover crop management can affect weed suppression and crop performance.
At scientific meetings and conferences, we shared findings with researchers, students, and industry representatives. The posters and presentations generated valuable discussions and allowed us to answer questions about practical cover crop management strategies.
Effective strategies included presenting research in simple visual formats (graphs, photos, summaries), providing printed handouts during field tours, and encouraging one-on-one conversations.