Our long-term goal is to enhance the sustainability of dryland cropping systems in SW Colorado and SE Utah by growing cover crops during the fallow period between two cash crops. Our objectives are to: 1) evaluate the performance of several cover crop mixtures (CCMs); 2) assess the impacts of cover crops on soil health and quality, soil moisture, cash crop, and profitability; and 3) disseminate project results and contribute to improved soil health management in the region. To date, we conducted 10 field trials and tested 19 CCMs. These trials encompassed two crop rotations (winter wheat-fallow and winter wheat-safflower-fallow), two tillage practices (conventional tillage and no-till), and conventional and organic crop production. CCMs were planted in late summer or in the spring and consisted of three to ten species of legumes, grasses, brassicas, and other plants. Two of the three growing seasons had below average precipitation. The 2017-2018 season was especially dry (42% of normal) and resulted in crop failure at six of the nine sites that had a cover or cash crop. Hence, the results are not conclusive yet but some some trends have emerged.
Late summer-planted cover crops produced significantly more biomass than the spring-planted ones. However, in general, the greater the biomass, the less soil moisture and soil NO3-N was available to the cash crop. Moreover, when cover crops were planted too early after wheat harvest, volunteer wheat tended to dominate plant canopy and biomass. This can be mitigated somewhat with no-till and timely rainfall, and by minimizing wheat harvest losses. Some cover crop species performed poorly (e.g. teff, flax, sunn hemp, balansa clover) and the notion that the more species (i.e., greater diversity) in the mix, the better may not hold true in the project area due primarily to water limitations. Hence, the climate in the region (semi-arid with short growing season), in addition to seed cost and proper management (i.e., planting date, seeding depth, inoculation) are key considerations for developing high performance cover crop mixtures. Winter wheat yields were lower following cover crops than after fallow and this is likely due to temporary immobilization of soil nitrogen and reduced soil moisture at planting. No fertilizer was applied to the wheat crop and this will be reconsidered moving forward. Input costs were higher and the returns were lower for the cover crop treatments, but we feel that with continued management refinements and the expected benefits (e.g., reduced soil erosion and improved soil health and quality) from cover crops, the costs will go down in the medium to long-term. Further testing and analysis will be done in 2018-2021 thanks to continued funding by Western SARE–Project SW18-500.
Detailed results for 2015-2016 and 2016-2017 were published in CSU-AES Technical Bulletin TB18-1. Project concepts and highlights were presented at multiple events including: two field tours, one field day, and over 20 workshops, conferences, and meetings. Many of these presentations, along with project announcements, interviews, and useful links are available on the project website at http://drylandcovercrops.agsci.colostate.edu. Attendance to the outreach events was generally good. Moreover, the attendees appear to have gained knowledge on cover crops, soil health, and management practices. These and other indicators bode well for the adoption of cover crops and other soil health improvement practices in the region.
1. Evaluate the performance of cover crops and determine their effects on soil moisture, soil fertility, weed control, soil biology, soil erosion, and on the succeeding cash crop.
- Establish field trials on farmers’ fields and at the Southwestern Colorado Research Center (SWCRC).
- Collect baseline data at the start of each trial.
- Measure soil and plant characteristics annually to determine if and how cover crops affect dryland cropping systems in SW Colorado and SE Utah.
2. Assess the economic feasibility of cover crops in dryland cropping systems. Partial budget analysis was used to track changes in revenue that result from the operational and input costs associated with planting cover crops. Analysis includes measuring return on investment following cover crops, accounting for changes to yield or quality of cash crops. This will determine where a cover crop strategy produces a profit or loss to the operator. Indirect costs and benefits of cover crop management will be documented.
3. Educate farmers and others about cover crops and disseminate project results (all participants). This was achieved via:
- Yearly field tours and workshops
- CSU-AES Technical Bulletin
- Presentations at growers’ meetings, workshops, and other relevant events in Colorado and Utah
- The project website
4. Gauge the project’s impact by how well the outreach events are attended, feedback from each event, and the number of acres planted to cover crops since this project started. NRCS will continue to track the number of additional applications for cover crop grant assistance and will assist with long term monitoring of cover crop practice adoption.
Cover crops grown during the fallow period between two cash crops such as winter wheat and safflower will achieve one or more of the following benefits: (1) reduce soil erosion, (2) improve soil fertility and biological activity and/or (3) suppress weeds, without negatively impacting the profitability of the cropping system.
A total of 10 field trials were conducted on farmers’ fields and at the SWCRC in Montezuma and Dolores counties in Colorado and in San Juan County, UT. Most of these trials are still on-going and are located on fields that have been historically cultivated with non-irrigated (dryland) crops such as winter wheat, dry bean, and alfalfa. The trials included two crop rotations (winter wheat-fallow and winter wheat-safflower-fallow), two soil management practices (conventional tillage or CT and no-till or NT), and conventional and organic crop production systems. In the on-farm trials, cover crops were planted in either a large block or in large strips, with one or more control strips left fallow for comparison. The trials at the SWCRC were established on small plots with three replications.
Cover crop mixtures were developed with the participating farmer, NRCS staff, and research center staff. In 2015-2018, 19 summer/fall-planted cover crop mixes and five spring-planted cover crop mixes were tested. These mixes included legumes (e.g., pea, hairy vetch, clovers, sainfoin, dry bean, and sunn hemp–not to be confused with industrial hemp!), grasses (rye, ryegrass, triticale, barley, oat, corn, sorghum sudan grass, pearl millet, and teff), brassicas (canola, rapeseed, radishes, forage collards, and turnip) and other broadleaves (flax, safflower, sunflower, and buckwheat). The number of species in each mix varied from three to 10. The cover crop mixes (CCMs) were planted in fallow, in the summer or early fall after wheat harvest or in the spring after the snow melts and the soil is dry enough for field operations. The only test where a cover crop, namely yellow sweet clover, was interseeded with winter wheat was not successful due the slow and low growth of yellow sweet clover before it was terminated in the spring when winter wheat was sprayed to control weeds. Seeding dates varied from July 29th to December 6th and from April 2nd to April 22th. Terminations dates varied from June 10th in 2016 to June 24th in 2018. Seeding rates ranged from 10 to 43 lbs/acre and seed cost from $10/acre to $48/acre. The goal was to explore as many cover crop species and mixes as practical to determine their performance and their impacts on soil health and on the cash crop. We also wanted to test different management practices, so that we can narrow down the choice of species for the project area. This was important because of the lack of research-based information on cover crops in dryland cropping systems in the project area.
Soil mapping and baseline soil characterization was accomplished in the summer or early fall of 2015. Detailed soil and plant measurements were done each year to assess the impact of cover crops on soil quality and health and on the cash crop. They included:
- Gravimetric soil water content before planting cover crops and before planting the cash crop. Sampling depth varied from 2.0 to 4.0 feet, depending on the type of trial (on-farm vs. research center trials) and soil condition.
- Soil water infiltration rate with Cornell Sprinkle Infiltrometer. The infiltrometer was calibrated at each site to provide a rainfall rate of approximately 0.5 cm/min. Measurements were generally done in August or September.
- Soil test analysis to measure soil pH, organic matter, nutrient availability (major and some minor nutrients), and cation exchange capacity. Soil samples were taken at a depth of 0 to 6 inches prior to planting cover crops or the cash crop. The same soil samples were used to run the Haney soil health test, which provides an alternative method to assess soil nutrient (NPK) availability.
- Plant biomass and canopy cover: The Line-Point Intercept method was used to calculate canopy cover and ground cover prior to cover crop termination. Plant biomass was determined by clipping plant matter in a 1.24 ft.-radius range hoop, placed at the beginning of the Line-Point Intercept transect. A subsample was dried at the oven at 60 deg. C for 24 hours (plants were air-dried before we placed them in the oven) to determine dry matter.
- Cash crop yield and quality. Grain yields in the fallow and CCM treatments were provided by the cooperating farmer or we took several samples to come up with estimates. Grain protein (wheat) and oil (safflower) content were measured in the laboratory.
Results of the 2017-2018 cropping season:
Total precipitation from rain and snow in September 2017 through August 2018 at the SWCRC was 6.6 inches or 41.6% of the 1981-2010 normal. The whole project area experienced a severe drought in 2017-2018. The 2016-2017 precipitation was also below normal. The first year of the project (2015-2016) was slightly above normal.
Of the four trials/fields planted to cover crops in late summer 2017, only two (SWCRC#1 & Garchar) had enough canopy cover to terminate in June 2018. The other two (BEWW & BN) were terminated much earlier (March) due to poor cover crop stand or weed infestation. No cover crops were planted in the spring of 2018 due to drought.
Of the five field trials planted to winter wheat in 2017, only one (SWCRC#2) was harvested in 2018. The rest was terminated for crop insurance purposes, due to drought.
Cover crop biomass was much lower in 2018 than in 2016 or 2017. It averaged 1350 lbs TDM/acre at SWCRC#1 and 1354 lbs/acre at Garchar in 2018. Legumes represented only 13% of the total DM (TDM) in CCM#1 (winter pea, hairy vetch, yellow sweet clover) at SWCRC#1. The rest was mostly weeds, including volunteer wheat. CCM#2 (same as CCM#1 plus winter rye) and CCM#3 (same as CCM#2 + Winfred turnip + winter canola) had more legumes or rye (mostly rye), 57% and 72%, respectively, and fewer weeds (43% and 28% of TDM). There were no brassicas in the harvested biomass and no hits with the line-transect method. At Garchar (winter pea + hairy vetch + winter triticale + corn), 39% of the TDM was legumes (pea and hairy vetch), 40% cereals (winter triticale), and 21% weeds. No corn was present since it did not overwinter. The soil was fairly dry at planting and had low NO3-N content in 0-6” soil at SWCRC#1 (8 to 10 lbs/ac) and moderate (16 to 19 lbs/ac) at Garchar. It was extremely dry (wilting point) after cover crop termination, as measured in the fall of 2018 i.e., prior to winter wheat planting, particularly at Garchar. Nonetheless, the Fallow treatment had significantly more moisture in the top 3.0 ft of soil at Garchar. There was no significant difference between CCM and Fallow at SWCRC#1, probably because Fallow was weedy, and no weed control measures were taken, contrary to proper fallow management. NO3-N in 0-6” was significantly higher in Fallow (28.3 lbs/ac) than in CCM (6.0 lbs/ac) at Garchar. The same was true at SWCRC#1 but the difference between Fallow (17.0 lbs/ac) and CCM (11.4 lbs/ac) was smaller, likely because weeds were not controlled in Fallow.
In the two other fields that were planted to cover crops in late summer 2017, establishment was poor due to drought; hence the cooperator sprayed the two fields in the spring of 2018 to terminate whatever cover crops were up but primarily to control weeds such as goatgrass and cheatgrass. He sprayed them in March and again in April to terminate the peas that came up afterwards and to conserve moisture for the next cash crop. The cover crop mixes were (1) winter pea, hairy vetch, winter triticale, and nitro radish at Barry EWS, and (2) winter pea, hairy vetch, sorghum sudangrass, and sunflower at Barry North. They were planted on 9/16 and 9/17/2017, respectively. The reason cover crops did better at Garchar than at Barry was because there was a longer fallow period at Garchar (10/21/2016-08/26/2017) than at Barry (wheat was harvested on 7/19/2017 and cover crops were planted in mid-September). Moreover, no cash crop was planted at Garchar in 2015 or 2016. Instead two cover crop mixes were planted in succession in 2016 (Balansa clover, crimson clover, ryegrass, tillage radish on 4/22/16, and dry beans, maple peas, yellow peas, corn, barley, oats, sorghum sudangrass, and sunflower on 8/23/16). They performed poorly (50 and 230 lbs DM/ac, respectively) due to low soil moisture at planting, low precipitation, poor choice of cover crop species (e.g., including warm-season grasses in late-planted mixtures) or planting date, etc.
Summary of the project results to date:
1. Fall-planted cover crops produced more biomass than spring-planted cover crops, which can be expected due to the longer growing season for the fall-planted cover crops. Dry matter of spring planted cover crops were generally less than 1000 lbs (average of 713 lbs/acre at SWCRC#2, 692 lbs/acre at Barry Middle, 704 lbs/acre at Barry WSW, and 242 lbs/acre at Crowley). Summer or fall-planted cover crops averaged 4479 lbs/acre at SWCRC#1 in 2016 and 3438 lbs/acre at SWCRC#2 in 2017. The latter had a predominance of volunteer wheat. In 2018, cover crops plus weeds biomass only averaged 1350 lbs DM/ac at SWCRC#1 and about the same (1354 lbs/ac) at Garchar due to drought. In two other fields that were monitored in 2017 but were not part of this project, fall-planted cover crops averaged 3007 lbs/acre in one field and 1857 lbs/acre in the other field on May 16, 2017. Winter triticale or winter rye were the dominant species in these fields. In one of the project’s on-farm trials, cover crops were planted on July 29, 2015, approximately one week after winter wheat was harvested. They produced 400 lbs/acre of dry matter in one field and 968 lbs/acre in another field before they were killed by a hard freeze in late October. The cover crop mix included warm season species such as sunflower, sorghum sudangrass, and Proso millet. More biomass was produced in the spring by the species (e.g., purple top turnip and yellow sweet clover) that survived the winter.
2. The challenges of planting cover crops too early after wheat harvest are soil moisture availability and weed control, particularly volunteer wheat. Volunteer wheat was a major contributor to plant canopy and plant biomass in at least two trials. It can be considered a cover crop, except that it harbors diseases and insects (e.g., RWA, western bean cutworm) and will out compete other cover crop species and limit plant diversity. The time interval from wheat harvest until there is enough moisture to trigger seed germination varies from year to year and will determine how soon after wheat harvest one can control volunteer wheat and plant cover crops. That interval can be shortened with no-till management. No-till will also conserve moisture compared to conventional tillage. Volunteer wheat has not been much of an issue in spring-planted cover crops.
3. The more plant biomass is produced, the higher the uptake of soil moisture and nutrients. This was the case in eight field trials whereby the amount of available N and moisture was markedly higher in the fallow treatment than in the cover crop treatment(s) prior to wheat planting. In three of these trials where winter wheat was planted in 2016 and harvested in 2017, wheat yield was substantially lower in the cover crop treatment than where no cover crops were planted. The difference was highly significant at the SWCRC#1 trial which had three replications. The same was true in 2018 at SWCRC#2.
4. On the upside, there were fewer weeds in cover crop mixtures that had a good stand and produced a significant amount of biomass. In general, cereals (e.g., winter rye and winter triticale) contributed more to cover crop biomass than did legumes. Brassicas (e.g., Nitro radish or purple top turnip) also contributed significantly to the total ‘cover crops + weeds’ biomass in two fields, Barry North in 2016 and Barry WSW in 2017. Obviously, the contribution of each species in the mix will depend on its representation in the mix (e.g., % by weight or number of seeds), seeding and growing conditions, etc.
5. In the short-term, it appears that cover crops take up more nutrients than they contribute. This was certainly true for N. The question then is, “should there be restitution of the depleted nutrient e.g., by applying N fertilizer to the cash crop based on soil test recommendations?”. However, this may not make up for the loss of soil moisture and may even exacerbate it by promoting vegetative growth at the expense of grain production. Water in the project area is undoubtedly the most limiting factor to crop production and should be managed wisely. Nevertheless, in years with average or above average precipitation, applying fertilizer to the cash crop should be considered to enhance its performance and counteract nutrient uptake by cover crops. This would be particularly important if the goal is to increase soil C and produce as much biomass as would be tolerated by the soil-crop-climate system. Additional benefits would be greater erosion control and weed suppression. Reduced soil erosion will result in more nutrient and water retention than if no cover crops were planted during the fallow period. The effects of cover crops on soil erosion have not been measured or assessed yet.
6. It is expected that in the long term, cover crops will increase soil organic matter, which will enhance nutrient cycling and increase soil water holding capacity. Cover crops would also improve soil structure, increase soil cover and soil biological activity, and thus increase soil water infiltration and reduce soil evaporation. All these and other potential benefits discussed earlier (e.g., erosion control and weed suppression) would offset the cost of growing cover crops. However, in the short term (2015-2018), none of the cover crop treatments was profitable.
7. Microbial biomass was generally higher in the cover crop than in the fallow treatment, but the difference was either non-significant or its significance could not be established where there was no replication of the treatments. Water infiltration rate was significantly higher (P=87%) in the cover crop than in the fallow treatment at the SWCRC trial #1 in 2016 but there were no significant or apparent trends at the other test sites in 2016 or 2017.
8. The notion that the more species (diversity is important) in the cover crop mix, the better it is for soil health may be tough to achieve in the project area due to economic considerations and to limitations such as water scarcity and the relatively short growing season. Some species have not done well enough to warrant their inclusion in the cover crop mix in the future. They include teff, flax, sunn hemp, crimson clover, berseem clover, and Balansa clover. Hairy vetch shows promise but its contribution to plant canopy and biomass was negligible, except at Garchar in 2018. Yellow sweet clover did well in two fields in the fall of 2015 and spring of 2016 but at other fields its stand was poor or nonexistent. Among the legumes, peas did the best. Winter rye performed well as did winter triticale. Spring barley and oat get established easily if there is adequate moisture but in our tests, they did not produce much biomass, which has more to do with the length of the growing season than with the species themselves. Sorghum sudangrass, corn, sunflower, pearl millet, and possibly other warm season plants will put up significant growth if planted soon after wheat harvest. This was the case in only one test where cover crops were planted in late July and the first freeze did not occur until late October, which was two to four weeks later than normal. Among the brassicas, Winfred turnip did the best. Rapeseed and canola either did not get established or were planted too late to survive the winter. Both do well in monoculture in SW Colorado with best management practices and favorable weather conditions. Small-seeded cover crops such as canola, rapeseed, and yellow sweet clover present challenges due to their seed size. They cannot be planted deep (e.g., more than half an inch) or their emergence may suffer. This can be exacerbated by soil crusting after a rain event. A poor stand will diminish the small-seeded cover crops ability to compete with weeds and with other cover crop species, and to overwinter. Ideally, the smaller seeds should be placed in a separate drill box (small seed box) than the larger seeds but so far in this project, all the cover crop seeds were mixed before planting them, which may affect seed flow and distribution. Another consideration in selecting cover crop species and mixtures adapted to the project area is flowering and seed maturity. Cover crops are usually terminated before any of the species makes viable seeds. In 2016, cover crops were terminated around June 10th but in 2017, they were terminated around June 20th, which was late since some of the species (e.g., oats and barley) had already made seeds. Terminating cover crops earlier e.g., mid-May to early June may be advisable in our environment since it would reduce nutrient and water uptake and allow more time for recharge before winter wheat is planted. Summer- or fall-planted CCMs would be preferred to spring-planted CCMs in this scenario.
We used a participatory approach to conduct research and to educate agricultural producers and others about the potential benefits of cover crops in the project area. The approach consisted of having a select number of farmers test cover crops on their fields and share their findings with neighbors and other agricultural producers. These farmers decide what cover crop species to plant and when, with assistance from USDA-NRCS in their county. A large amount of data was collected and analyzed by the project staff to quantify the effects of these cover crops on the soil, cash crop, and the cropping system as a whole. The results were discussed by the project participants and presented to the larger community at meetings, tours of the test sites, workshops, conferences, etc. Information about the project, presentation excerpts, videos, and useful links were posted on the project’s website on a regular basis.
Educational & Outreach Activities
We organized several educational and outreach activities and participated to others.
- Field tours and field days:
- June 9, 2016: Cover crop field trials
- August 18, 2016- CSU-SWCRC Field Day: Cover crops, alternative crops, soil and water management and conservation, and orchard management
- May 30-31, 2017: Cover crop field trials
- Seminars & Workshops:
- Exploring Innovations and Efficiencies, SW Ag Seminar, 5-6 December 2015, Cortez, CO. The emphasis was on soil health and farming sustainability in Colorado, Utah, and New Mexico.
- Dryland Cover Crops and Soil Moisture Management, Four State Ag Expo, March 18, 2016, Cortez, CO. Presentations by Dr. Abdel Berrada, Dr. David Nelson, Dr, John Holman, and Kevin Larson; and panel discussion.
- Following in the Footsteps of Successful Farmers, SW Ag Seminar, October 22, 2016, Dolores, CO. Topics: soil health, cover crops, land conservation, weed control
- Soil Health Workshop, February 9, 2017, Dove Creek, CO. Updates on this project and a similar project in eastern Colorado and western Kansas, soil health assessment, panel discussion.
- Dryland Farming and Cover Crops in SW Colorado, August 24, 2016, Durango Colorado. Sponsored by the La Plata County Conservation District. Speaker: Dr. Abdel Berrada
- 2018 Soil Health & Crop Workshop in Monticello, UT on February 8, 2018.
- Presentations at the above seminars, plus the:
- Dove Creek Conservation District meeting on April 25, 2017.
- CSU-AES Research Center Conference in Ft, Collins in January 2016, 2017, and 2018.
- CSU-SWCRC Annual Advisory Meetings in 2016 and 2017.
- ASA-CSSA-SSSA Annual Meetings in Phoenix, AZ in 2016 and Tampa, FL in 2017.
- ASA-CSSA Annual Meetings in Baltimore, MD on Nov. 4-7, 2018.
- The New Mexico Sustainable Agriculture Conference in Los Lunas, NM on December 13, 2017.
- The Third Annual Southwest Agricultural Seminar in Lewis-Arriola, CO on November 18, 2017.
- Meetings: Several meetings were held in 2015-2018 to update the project participants about the project’s progress and discuss new developments and upcoming events. More meetings were held in 2017 and 2018 to plan for the continuation project and write the grant proposal.
- The Feasibility of Cover Crops in Dryland Cropping Systems in SW Colorado and SE Utah, CSU-AES Technical Bulletin TB 18-1, published in April 2018 https://webdoc.agsci.colostate.edu/aes/SWCRC/pdf/tb18-1.pdf
- Project website: The project’s website, http://drylandcovercrops.agsci.colostate.edu, is generating interest in cover crops and soil health from a broad audience (consumers, farmers, ag professionals, general public). After the release of the marketing flyer (e.g., flyer to advertise the project) in the community and local ag-related events, Google + reached almost 10,000 hits globally. The launch of project interview videos are increasing traffic 25% through YouTube and is expected to increase by the end of the year.
- At the 2017 Soil Health Workshop in Dove Creek, CO, surveys were provided to attendees. Four questions asked the attendees to rank their knowledge, interest, and willingness to try cover crops, before and after the workshop. By attending the Soil Health Workshop, attendees appear to have gained knowledge on cover crops, soil health, and management practices. Additionally, it appears that we are targeting the correct groups within our region, because participants had a strong interest in cover crops and a strong willingness to use cover crops, even at the beginning of the workshop. We feel the results of the survey are promising regarding the adoption of cover crops in the region.
- At the 2018 Soil Health & Crops Workshop in Monticello, UT, all the respondents gained knowledge about cover crops and soil health by attending the workshop. The gain was 62%, as measured on a scale of 1 to 10. 76% of the respondents stated that they would use the information learned at this workshop often, while 24% would do so occasionally. The information learned includes cover crops, nutrient cycling and management, compost, and herbicide drift management. Nine of the respondents or 53% would not consider growing cover crops after attending this workshop, although eight of them already had a strong interest in cover crops prior to this workshop. Three respondents were more willing and three were less willing to try cover crops after attending this workshop. The main reason was because in 2015-2018, cover crops reduced soil water and N availability and wheat yield. One respondent wrote that he ‘would hold off on using cover crops pending further information on long-term benefits’. Others suggested looking at forage-type cover crops, using compost or increasing residue cover to improve soil health.
- soil biology
- soil and water conservation
- soil quality
- cover crops
- farming sustainabilty
soil management, soil health and how to assess it and improve it, cover crops, nutrient management