Progress report for SW18-500
Cover crops have gained considerable attention in recent years as an important option for improving soil health and productivity on farms around the US. However, dryland agricultural systems in the western part of the country present a unique set of opportunities and challenges for cover crops. The Colorado Plateau, in particular, has a relatively short growing season along with low and erratic precipitation. Wheat-based cropping systems in the region rely on tillage and herbicide applications to keep soils bare for much of the year, and this has resulted in widespread soil degradation due to low organic matter inputs and erosion. Cover crops can help to counteract such losses in soil fertility and long-term productivity, but may also compete for water with cash crops and their net benefit remains largely unstudied in the Colorado Plateau.
Given the lack of research on cover crops in the high desert region, this project seeks to fill a critical information gap for local dryland producers. The proposed work will build on research conducted in the first phase of this project and assess the on-farm performance of different cover crop mixtures as well as the medium-term impact of cover crops on crop yields, overall farm profits, soil health, and a range of ecosystem services (e.g. soil water capture, erosion control, carbon sequestration, forage provision, weed control). Additionally, we will incorporate new research elements that emerged from Phase I (Western SARE Project SW15-008), including the testing of soil inoculants and alternative termination strategies of cover crops to minimize tillage. This project and the evolving directions of this research have grown directly out of local producer and stakeholder discussions, and represent a truly collaborative effort to understand the potential of cover crops to enhance long-term profitability and environmental quality of the region.
- Evaluate the growth and performance of different cover crop mixtures within different environmental and rotational contexts in multiple producers’ fields and at the Southwest Colorado Research Center (SWCRC) (Fonte, Russell, Schipanski, Berrada, Eash, Lockard, participating farmers). Mixtures will be comprised of functionally similar species combinations (considering legumes vs. grasses, fibrous vs. tap roots, warm vs. cool season, etc.) across fields/farms and rely largely on locally available seed.
- Assess medium-term (4-6 yr) impacts of cover crops on soil health and soil-based ecosystem services. Ecosystem services of interest include water capture and storage, crop production, erosion control, potential forage provision, and weed control. Additional soil health parameters include the maintenance of soil structure, soil C dynamics, and soil microbial diversity and activity (Fonte, Trivedi, Schipanski, Parslow, Eash, Lockard).
- Conduct economic analysis of cover crops to understand the net balance of establishment costs, differences in weed management and labor expenditures, and subsequent impacts on crop yields (Beiermann, participating farmers).
- Understand the potential of perennial species mixtures to contribute towards longer-term soil restoration on low productivity and/or degraded soils. This objective also seeks to establish a reference against which annual cover crop mixtures can be compared in terms of their potential to support soil health and ecosystem services (Fonte, Russell, Eash, Lockard).
- Examine alternative management techniques to address emerging grower concerns (Russell, Trivedi, Fonte, Eash, Lockard). Specifically, these will include testing effectiveness of different legume inoculation techniques within cover crop mixtures as well as alternative termination methods (e.g. crimping – for application in organic systems) to foster the development of reduced tillage practices.
- Engagement with producers, community members, and other stakeholders to share project results and discuss the benefits and challenges associated with cover crops (Russell, Fonte, Eash, Lockard, and all participants). This will be achieved via:
- Annual workshops and field days with local stakeholders in Montezuma and Dolores Counties, CO, and San Juan County, UT.
- CSU/AES technical bulletins, factsheets, and peer-reviewed journal articles.
- Presentations of project results at regional conferences, workshops, and extension events in other parts of Colorado, Utah and the broader Western SARE region.
- Project videos (interviews, presentations, etc.).
- Regular updates and posting of materials (e.g. videos, presentations, technical bulletins) on project website (http://drylandcovercrops.agsci.colostate.edu/).
- Outreach to local schools to engage next generation farmers and agricultural researchers.
- Evaluate the project’s impact and reach (Westerman, Boswell). This will be achieved by documenting how well the outreach events are attended and obtaining feedback from each event. Additionally, we will track the number of acres planted to cover crops in the region since the start of the project. NRCS will continue to provide information on the number of additional applications for cover crop grant assistance, and will assist with long term monitoring of cover crop practice adoption.
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Replacing fallow periods between cash crops with a cover crop mixture will result in one or more of the following benefits: (1) reduction in soil erosion potential, (2) improved soil fertility, (3) weed suppression, and (4) enhanced overall profitability of the cropping system.
Cover crop evaluation at the Southwestern Colorado Research Station
This project is a continuation of Western SARE Project SW15-008, in which two field trials were established on the Southwestern Colorado Research Station (SWCRC) to evaluate various cover crop mixtures. These trials were continued with the aim of assessing the effect of different mixtures (varying in legume vs grass proportion, cool vs warm season species, etc.) on biomass accumulation, soil health and ecosystem services. Cover crop mixtures were chosen in collaboration with participating farmers, NRCS staff, and research center staff. Mixtures include varying proportions of legumes, grasses, brassicas, and other broadleaves.
The first field trial was established in Fall of 2015 (Experiment 1) and compared three mixtures vs. a fallow control in a randomized complete block (RCB) design with three replicate plots. All were managed under no-till and planted to wheat in Fall of 2016. The same cover crop mixture was re-planted in September 2017, followed by wheat planting in Fall 2018.
In Fall of 2016 a second replicated trial (Experiment 2) was established with nine cover crop treatments including both spring- and fall- planted mixtures (planting windows). The experiment also examined these cover crop treatments within two-tillage regimes (no-till vs. conventional tillage) and employs a RCB design. All plots within this second experiment were seeded to wheat in September 2017, followed by cover crop planting in Fall 2018.
In Fall of 2018 a third trial was established at the SWCRC to evaluate the potential of perennial grasses and legumes for soil health restoration. Eight treatments were established, including a wheat fallow control and a wheat-annual cover crop treatment. Perennial treatments varied from dryland alfalfa (a practice already used by organic wheat farmers in the region) to mixtures of ryegrass, wheatgrass, alfalfa and sanfoin. The trial follows a randomized complete block design with four replicates per treatment. Treatments will be maintained for the remainder of the project to observe productivity, soil cover, and changes in soil quality over a three-year period. Due to extremely dry conditions in Fall 2018, germination was low and stand establishment was poor. The trial was replanted in Spring 2020 and will be evaluated again in Spring 2021 for stand establishment.
In the Fall of 2019 an inoculant trial was planted at the SWCRC to evaluate different types of rhizobium inoculants (liquid, peat, and granular) compared to a no inoculant control. Additionally, this trial had a termination treatment component blocked by tillage, chemical and crimping termination methods. The trial used the main cover crop mixture used in the on-farm trials (see below) and was terminated in the Spring of 2020.
On-farm trials to evaluate cover crop mixtures
In order to assess performance of cover crop mixtures, medium-term impacts of cover crops on soil health, and evaluate profitability of cover crop implementation, field trials of annual cover crop mixtures, which were established in Project SW15-008 as early as 2015, continued in dryland production fields of participating farmers in Colorado and Utah. Farmer fields are divided into cover crop treatments and control treatments. The control treatment is managed according to usual farmer practices, usually a cash crop followed by a fallow period. Plots under cover crop management will be planted to a cover crop when the farmer would typically leave his or her land fallow. Four local producers are continuing their participation in the project (planted to either cover crop or winter wheat in Fall 2020), and one new field in Colorado was planted to cover crop in Fall 2018 and continued for a second cover crop cycle in Fall 2020.
The cover crop mixture evaluated on-farm is consistent across all participating farms and includes winter pea, hairy vetch, winter triticale, oats, nitro radish, and rapeseed. This mixture was selected based on farmer feedback and production data collected in Project SW15-008, taking into consideration both biomass production as well as cost minimization. It includes a significant proportion of both legumes and grasses, to gain the benefits of both nitrogen fixation as well as biomass accumulation.
Field Measurements/Data Collection
The following measurements are being taken to assess cover crop benefits:
- Cover crop biomass. Collected using four sub-samples per replicate in each field using a 75-cm dia. range hoop), with all vegetation cut to a height of 1-2 cm and returned to the lab for sorting, oven-drying, and weighing.
- Soil cover. Measured using quadrats and a transect and line-point intercept method.
- Forage quality. Evaluated using near infrared reflectance spectroscopy (NIRS) to determine nitrogen content and decomposition dynamics of the residues.
- Soil moisture. Evaluated using soil cores, taken to a depth of 1.0 m with a Giddings probe at cash crop planting.
- Potential water capture and erosion control. Assessed immediately following cover crop termination using a Cornell Sprinkle Infiltrometer, which estimates relative infiltration and runoff volume.
- Bulk density and aggregate stability. Measured in top layer (0-15 cm) of soil to evaluate soil compaction and structure.
- Soil fertility. Assessed at CSU for total organic C and N, available P, pH, and electrical conductivity. We will also measure permanganate oxidizable C (POXC), an active fraction of soil organic matter that may provide an indicator of organic C accumulation in soils. Potentially mineralizable N will be assessed via short-term laboratory incubations, to understand potential microbial activity, and release and availability of N for the subsequent crop.
- Crop yields. Production data for cash crops will be collected to understand economic impacts of cover crop implementation. This will be done at both on-farm and on-station trials.
- Cost analysis. Through farmer surveys and interviews, field operations and associated costs will be estimated to understand the cost of cover crop implementation.
Data from 2015 to 2020 were analyzed to produce preliminary results and conclusions.
Experiment 2: On-station experiment started in 2016
Total cover crop biomass produced in 2018-2019 differed between planting windows. As seen in Figure 1, the fall-planted mixes (1 through 5) produced significantly more biomass than the spring-planted mixes (6 through 8) (p<0.001). Treatments in the fall-planted window were dominated by volunteer wheat, but to a lesser extent than previous years. Within each planting window, the different treatments/mixes did not significantly differ in terms of total biomass produced (p>0.05).
Figure 1. Biomass sampled in June 2019 in Experiment 2, grouped by plant type. Cover crop mixes 1 through 5 (CCM1 – CCM5) were planted in Fall 2018, while CCM6 through CCM8 were planted in Spring 2019.
Wheat was planted in September 2019 following cover crop termination (in June 2019) and harvested in August 2020. Significant differences were again observed between plots that had a fall-planted cover crop and plots that had a spring-planted cover crop, with spring-planted cover crop plots experiencing a higher average wheat yield the year after cover crop termination (Fig. 2). The fallow treatment had the highest average yield, which significantly differed from the fall- and spring-planted treatments (p<0.05). This difference in wheat yields between planting windows was correlated with amount of biomass produced among treatments, as evidence by the linear regression between 2019 cover crop biomass and 2020 wheat yields (Fig. 3; R2=0.555; p<0.001).
Figure 2. 2020 wheat yields in Experiment 2 for cover crop mixes (CCM) 1 through 8 and the fallow treatment (F).
Figure 3. Correlation between 2019 cover crop biomass and 2020 wheat yields in Experiment 2 (R2=0.555). Data points color coded by cover crop planting window.
Soil moisture (Fig. 4), measured at wheat planting in 2019, was lowest in fall-planted cover crop treatments, highest in the fallow, and intermediate for the spring-planted treatments. Moisture levels were significantly different between the fallow and the fall-planted treatments, but not between the spring-planted treatments and neither the fallow nor the fall-planted treatments. The lower soil moisture at wheat planting could explain the low wheat yields in fall-planted treatments. These trends follow results seen in previous years of this trial.
Figure 4. Soil moisture down to 6 ft in Experiment 2 for fall-planted cover crop mixes (CCM)2, 3 and 5, spring-planted CCM 6, and the fallow treatment (F).
Experiment 1: On-station experiment started in 2015
In experiment 1, trends in 2017 wheat yields, soil moisture, and soil nitrate levels followed those observed in Experiment 2 (described above), as wheat yields in the fallow treatment were on average 36% greater than the wheat yields in the cover crop treatments (Fig. 5). This could be due to lower soil moisture and lower soil nitrate levels observed in the cover crop treatments relative to the fallow (p<0.05). In 2018, however, cover crop stands were poorly established due to drought conditions, and thus wheat yields in 2019 were not significantly different between treatments (p>0.05).
Figure 5. 2017 and 2019 wheat yields in Experiment 1 for cover crop mixes (CCM) 1 through 3 and the fallow treatment (F).
In 2020, total cover crop biomass among treatments did not significantly differ in 2020 (p=0.32; Fig. 6). Biomass of cover crop legume species did differ significantly among treatments, with CCM1 having greater legume biomass than CCM2 and CCM3 (p=0.02).
Figure 6. Biomass sampled in June 2020 in Experiment 1, grouped by plant type. Cover crop mixes 1 through 3 (CCM1 – CCM3) were planted in Fall 2019.
Soil moisture measured at 2020 wheat planting (Fig. 7) was significantly lower in the cover crop plots as compared to the fallow at depths 6-12 in, 12-24 in, and 24-36 in.
Figure 7. Soil moisture sampled at wheat planting (Sept 2020) down to 6 ft in Experiment 1 for fall-planted cover crop mixes (CCM)1, 2 and 3, and the fallow treatment (F).
Similar trends have been observed on plots located in participating farms. Biomass produced in cover crop plots on-farms has been highly variable, depending on precipitation, planting window and cover crop mix. 2017 wheat yields following a cover crop were on average 21% less than following a fallow period. However, this trend was not as pronounced in 2019 due to poor cover crop stand establishment in 2018 (Fig. 8).
Figure 8. 2017 and 2019 wheat yields in fields of participating farmers for cover crop and fallow plots.
Soil health metrics such as total C and aggregate stability were measured in Experiment 1 in July 2018 after two full cover crop cycles. Though not significantly different (P > 0.05), cover crop treatments show a higher average total soil C content (0.76 % total C ± 0.02) relative to the fallow treatment (0.72% total C ± 0.03). Mean weight diameter of aggregates in cover crop treatments (399 um ± 67) is also slightly greater than that of the fallow treatment (374 um ± 100). These metrics typically take some time to show up. We sampled them again in July 2020 and will perform the analysis in Spring 2021.
Inoculation and Termination Trial
A cover crop mixture of winter pea, hairy vetch, winter barley, forage radish, and rapeseed was inoculated with either a peat-based, granular, or liquid rhizobia inoculant before planting in Fall 2019. A control with no inoculant was also included. Root nodulation and plant biomass was measured in June 2020. There were no root nodules observed, possibly due to dry conditions. While there were no significant differences in total biomass among inoculation treatments (p=0.09), significant differences were detected (p = 0.02) using orthogonal contrast analyses to compare the group of inoculation treatments (peat-based, granular, and liquid) vs. the control treatment. On average the inoculated treatments produced more biomass than the control (non-inoculated) treatment (Fig. 9).
Figure 9. Biomass sampled in June 2020 in the inoculation trial, grouped by plant type [cover crop (CC) legume, CC grass, CC brassica, or weeds]. Cover crop was planted in Fall 2019 and treated with either a liquid, granular, or peat-based inoculant. The control was not treated with inoculant.
We used a strip-plot design to also examine the success rate of different cover crop termination methods, specifically roller crimping, herbicide (40 oz/acre of glyphosate), and tillage (using a field cultivator). Two weeks after termination, percent cover of bare soil, brown vegetation, and green vegetation was noted within a 0.25 m2 quadrant, taking in 3 locations per plot (Fig. 10). A visual termination rating scale of 0 to 10 was assigned to each quadrant, with 0 being no kill and maximum greenness and 10 being complete kill (Fig. 11). This method follows procedures outlined in Ashford & Reeves (2003).
The roller crimper was the least effective termination method, with an average termination rating of 4.29 ± 0.32. This may be due to a dry soil surface that did not mold to the form of the roller crimper and effectively break cover crop stems. The most effective termination method was tillage, with an average termination rating scale 9.96 ± 0.04. Herbicides were moderately effective in comparison, which again may have been due to dry conditions that limited plant uptake.
Figure 10. Percent cover of bare soil, brown vegetation, and green vegetation in plots examining different cover crop termination methods. Measurements were taken 2 weeks after termination.
Figure 11. Visual termination rating scale of 0 to 10 assigned in plots examining different cover crop termination methods. A rating of 0 indicates no kill and maximum greenness and 10 indicates complete kill. Measurements were taken 2 weeks after termination.
In dryland systems such as on the Colorado Plateau, cover crops present a trade-off in terms of subsequent cash crop productivity. In the first few years of the on-station trials, this trade-off has been observed, particularly following fall-planted cover crops which tend to produce the most biomass (and thus use the most water). As precipitation is extremely low in the region and water is considered to be a major limitation to production, this cash crop penalty is likely due to lower soil moisture observed in cover crop plots. However, lower available N following cover crops (potentially associated with immobilization of soil N by decomposing cover crop residues) could also be limiting wheat yields.
Nonetheless, soil health benefits could justify this decrease in cash crop productivity, particularly as soil degradation becomes a greater concern in the region and farm longevity is threatened. After only two cover crop cycles, there are promising trends in soil health metrics such as aggregation and total soil C. These metrics will continue to be monitored for the duration of the project (and hopefully beyond) to assess the potential for cover crops to improve soil health in the long-term.
A participatory research approach is being implemented to achieve the research and educational objectives of the project. We view effective outreach and demonstration as essential to introducing findings of the project to the local community and ensuring that findings are applicable to local production systems. Formal outreach and demonstration activities will include:
- Field tours – Field tours held yearly to allow community members the opportunity to interact and ask questions about cover crop management.
- Workshops – Each year, a workshop held in one of the participating counties to discuss educational themes related to the project. Feedback to be collected from attendees to guide future outreach efforts. A workshop was held in February 2020 and included presentations on cover crops and soil health and a Q&A panel of participating farmers.
- Local Presentations – Up-to-date results are presented at relevant local events, including the SWCRC advisory board meetings, Conservation District meetings, etc..
- A dedicated listserv to facilitate the sharing of project information and outreach events.
- Presentations at the state and regional level – PIs of the project and/or extension team members to relay project information at state and regional meetings.
Educational & Outreach Activities
- Annual field tours – A cover crop specific field tour was held on June 3, 2019 with approximately 40 participants. An additional research center Field Day was held on August 14, 2019 with cover crop resources presented to 50 area participants including farmers, ranchers, Extension personnel, and community members. A 2020 field tour was originally planned but was not held due to COVID-19.
- Local Presentations – Local presentations were limited in 2020 due to COVID-19.
- Soil moisture and fertility sampling demonstration at Fozzie’s Farm, June 2020, Lewis, CO. ~15 attendees.
- Winter Workshop, covering cover crops, soil health, and project results, February 2020, Dove Creek, CO. ~30 attendees.
- Soil Sampling Demonstration, Veteran’s Homestead Project, April 2019, Hesperus, CO.
- Provided demonstration cover crop plantings for NRCS “demo box” for area elementary educational programming.
- Plant ID workshop, Montezuma Land Conservancy Fozzie’s Farm, June 15, 2019, Lewis CO. Community Event, ~15 participants
- Research Update, Southwestern Colorado Research Center 2019 Advisory Committee Meeting, Yellow Jacket, CO.
- Aggregate stability demonstration, Chuck McAfee-local rancher, June 2019.
- Soil Infiltrometer Demonstration, Veteran’s Homestead Project, April 2018, Hesperus, CO.
- Soil Infiltrometer Demonstration and Soil Health Presentation, Montezuma Land Conservancy Fozzie’s Farm, September 2018, Lewis CO. Dolores Elementary School 6th grade class, ~40 students.
- Research Update, Southwestern Colorado Research Center Advisory Committee Meeting, November 2018, Yellow Jacket, CO, ~20 attendees.
- Continual communication through text, phone calls, and emails has been maintained with participating farmers. This provides a means to gather farmer feedback and planning for project activities.
- Presentations at the state and regional level
- Presentation at USU Field Day, June 2020, virtual, ~50 attendees.
- Research Update, CSU Agricultural Experiment Station Conference, January 2020, Fort Collins, CO, ~60 attendees.
- Research Update, CSU Agricultural Experiment Station Conference, January 2019, Fort Collins, CO, ~60 attendees.
- Video presentation with CSU Extension published to the project website, in which Steve Fonte, Katie Russell and Gus Westerman gave an overview of the project objectives and methodology. (https://www.youtube.com/watch?v=7eOTuFzfeBI&feature=youtu.be)
- Cover crop management
- Soil health
- Soil conservation concepts
Cover crop management
Considerable research has been done regarding cover crops as a viable option to aid in soil and nutrient conservation in farms around the United States. Numerous benefits have been proven, including improvements to soil fertility and sustainability and profitability of farming systems. However, the extent to which these benefits are expressed is context-dependent and depends on climatic conditions as well as management practices that vary by region. The overall goal of this project is to evaluate the long-term impact and economic viability of cover crops in the high desert region of the Colorado Plateau, thereby contributing to agricultural sustainability in the region. The participation of farmers in each step of the research process will ensure that these findings are pertinent in local production systems and will aid in the dissemination of these findings throughout the community.
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