Progress 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 is included to evaluate weed suppression and dry bean response to cereal cover crops in an organic production system. All experiments are proposed as randomized complete block designs, with location in the field as a blocking factor accounting for field variability. For the conventional system, both cover crops and dry beans were grown under sprinkler irrigation. Gravity (furrow) irrigation was used in the organic system. 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) As part of Graduate Student Prayusha Bhattarai’s master's research, we received funding from the Idaho Department of Agriculture through the Idaho Bean Commission to evaluate cereal cover crops and herbicides for weed control in conventional dry beans. The proposed study will impose termination treatments (haying vs chemical termination) and evaluate the impact on weed control, soil health, and dry bean response. We established a 12-month experiment beginning in the fall of 2022 (cereal cover crops planted October 6, 2022), which was repeated in the fall of 2023 (cereal cover crops planted October 5, 2023). The study is designed as a split-split-plot randomized complete block design with 4 replicates. We chose cereal monocultures (barley, wheat, and triticale) instead of mixtures as cover crops because research shows that if weed suppression is the primary objective, choosing the most weed-suppressive crop and planting it in monoculture is likely to provide better results compared to planting cover crop mixtures (Baraibar et al. 2018, Smith et al. 2020). A meta-analysis involving 26 cover crop species demonstrated four cereal crops (rye, oat, triticale, and wheat) were the most effective at suppressing weeds (Osipitan et al. 2019). We chose wheat, barley, and triticale as our cover crop species because they are well-adapted to our growing region, easy to find, and many growers are familiar with these crops. Cereal rye is not included in this trial because small grain producers in our region are becoming increasingly concerned about the weed potential of rye, as many annual ryegrass biotypes have evolved resistance to herbicides.
Main plot (Fall planted cereal cover crop): Main plots were approximately 13 by 9 m and consisted of three winter cereals: barley, wheat, and triticale, and a no-cover crop treatment. The no-cover crop treatment was tilled (disked) to mimic the standard local practice of field preparation. Barley, wheat, and triticale were planted at rates of ~112 kg/ ha (1.5 million seeds/ha) on October 6, 2022, and October 5, 2023. Cover crops were allowed to grow until early May 2023. Cover crop biomass and weed density were collected before terminating the cover crop. Second biomass and weed density counts were done before planting dry beans to measure any regrowth from haying treatment at the time of dry bean planting. Glyphosate was applied over all cover crop treatments to ensure all plots were weed-free at the time of planting dry bean.
Split-plot (termination): Split-plots measuring about 6.5 by 9 m were established within each main plot (cover crop). There were two termination treatments: 1) chemical termination (using glyphosate) 14 days before planting and 2) haying 14 days before planting. The chemical termination ensured maximum cover crop biomass for weed suppression. The haying treatment enabled us to determine whether growers can utilize fall-planted cereals as a dual-purpose crop (weed suppression and forage).
Split-split-plot (herbicide): Split-plots measuring about 2.2 by 9 m were established within each split-plot (termination). Split plots consisted of five herbicidal treatments; three pre-emergence herbicides (pendimethalin + EPTC, dimethenamid-p + EPTC, and pendimethalin), one post-emergence herbicide (bentazon + imazamox), and one nontreated check where no herbicides were sprayed. The use of herbicides enabled us to determine the effects of cover crop biomass and herbicides on season-long weed control whereas nontreated checks enabled us to determine the effect of cover crops on weed suppression.
Data collection (Specific Objectives #1)
At each termination event and at dry bean planting, weed density (by species), weed biomass, and cover crop biomass were collected. Weed density was measured by counting weeds within a 1 m2 area in the plots. Cover crop and weed above-ground biomass were harvested in 1 m2 area per plot. Cover crop biomass from the haying treatments were dried, weighed, ground, and analyzed for nutritional composition using Near-Infrared Reflectance Spectroscopy (NIRS).
Two weeks after dry bean planting and application of preemergence herbicides, dry bean plant density, weed density (by species), weed biomass, and visible weed control (0 to 100%, 0 being no weed control and 100% being complete weed control) were measured 3 to 5 times. The final dry bean stand count was done before canopy closure to enable us to relate stand density to dry bean yield. Photosynthetically active radiation (PAR) was measured at the soil surface using an AccuPAR Ceptometer (Meter Environment, Pullman, WA, USA), to quantify light blocked by the cover crop residue. Cover crop biomass affects soil temperature and moisture, which may influence dry bean emergence. Therefore, a soil profile moisture and temperature sensor (GroPoint Profile, RioT Technology Corp., North Saanich, BC, Canada) was installed within each split plot (cover crop x termination) in the first block. The sensors will enable us to monitor soil moisture and temperature at multiple depths (0 to 15, 14 to 30, and 30 to 45 cm) and determine how cover crop biomass may impact dry bean emergence through changes in soil moisture and temperature. Dry bean yield was taken at season’s end 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 will be terminated in mid to late 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 will be planted in late May or early June, and plots will be managed according to the farmer’s standard practice throughout the season. The record of production practices will be obtained from the farmer at the end of the season.
Data collection (Specific Objectives #2)
At the time of cover crop termination and at dry bean planting, weed density (by species), weed biomass, and cover crop biomass will be collected. Weed density will be measured by counting weeds within a 1 m2 area in the plots. Cover crop and weed above-ground biomass will be harvested in 1 m2 area per plot. Beginning two weeks after dry bean planting, dry bean plant density, weed density (by species), and weed biomass will be measured 3 to 5 times. A final dry bean stand count will be completed right before canopy closure that will enable us to relate stand density to dry bean yield. Soil profile moisture and temperature sensors (GroPoint Profile, RioT Technology Corp., North Saanich, BC, Canada) will be installed within the first block. Sensors will enable us to monitor soil moisture and temperature at multiple depths (0 to 15, 14 to 30, and 30 to 45 cm) and determine how cover crop biomass impacts dry bean emergence through changes in soil moisture and temperature. The collaborating producer will harvest the dry bean for yield using standard farm equipment and data obtained will enable us to assess the impact of treatments on dry bean 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.) will be recorded and used in the economic analysis. The economic benefit of each treatment will be 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. First-year data will involve random measurements from unreplicated strips of cover crops, and a random effects model will be used to evaluate the contribution of each cover crop to the total variation observed in response variables.
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
Research Outcomes
Research outcomes from Field Study #1:
- In both locations, triticale had greater height (74 cm in Kimberly and 62 cm in Parma) and biomass (1669 kg ha-1 in Kimberly and 3128 kg ha-1 in Parma) among the three cereals. The biomass of cereals was almost double in Parma as compared to Kimberly. The cold spring in Kimberly may have slowed down the growth of cereal cover crops.
- In Parma, cover crops reduced weed biomass by 52% to 79% mostly by outcompeting glyphosate-resistant kochia, while most herbicide treatments reduced weed biomass by 41 to 83%. In Kimberly, herbicide treatments reduced weed biomass by 17 to 66%.
- Terminating cereal cover crops by haying before planting dry beans reduced stand density across all three cereal cover crops in Parma but had no such effect in Kimberly. The reduced stand density in Parma could be attributed to the planter issue; stem pieces of cereals in the hayed plot may have reduced seed-soil contact.
- Seed yield was primarily influenced by herbicide treatments and was reduced by 40 to 64% in Kimberly and 23 to 30% in Parma in untreated check.
- Dry bean stand count from the organic farm showed that dry bean density was numerically greater in the winter wheat + spring barley + peas cover crop compared to the spring barley + brassicas + peas cover crop. The slight differences in stand density could not be attributable to allelopathy because both fields had small grains in the cover crop mix and the fields were not replicated.
- Weed density assessments showed that common lambsquarters was the most dominant weed, followed by green foxtail. These trends in weed density could not be attributable to allelopathy because both fields had small grains in the cover crop mix and the fields were not replicated.
Integrating cover crops with herbicides seems to be a promising strategy for effective weed control in dry beans, as well as a sustainable approach to reducing over-reliance on herbicides and managing difficult herbicide-resistant weeds.
Education and Outreach
Participation Summary:
Field trials were shown to farmers and stakeholders at Field Days and Tours In Kimberly and Parma, Idaho. In addition, results were presented at stakeholder meetings and scientific conferences.
Results from this project have been presented at the following events:
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 IAPP conference: 45 attendees
Poster presentation at the 2024 Western Society of Weed Science conference.
Oral presentation at the 2024 Weed Science Society of America conference.
University of Idaho Department of Plant Science seminar: