Sustainable Vegetable Production: Screening Cover Crops for Water Use Efficiency

Final Report for SW07-014

Project Type: Research and Education
Funds awarded in 2007: $118,411.00
Projected End Date: 12/31/2010
Region: Western
State: Utah
Principal Investigator:
Dr. Daniel Drost
Utah State University
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Project Information


Due to unexpected circumstances and personnel problems, much of the data was lost, and the data collected was of little value. Based on ancillary observations, there appears to be differences in drought tolerance within the different cover crops evaluated. We are continuing to investigate the central hypotheses that “winter and summer cover crops enhance nutrient cycling, reduce weed pressure and improve soil quality.” Grower cooperators note fall-seeded cover crop (wheat, barley) establishment is difficult under dry conditions. Growers continue to use cover crops and are interested in cover crops to take advantage of the known benefits.

Project Objectives:
  1. To identify and evaluate winter cover crops that can help improve early plant establishment (reducing wind erosion effects and soil crusting) while minimizing interference with plant growth and soil water storage and while contributing to better farm nutrient management and soil quality;
  2. To identify and evaluate summer cover crops that can help improve nutrient cycling and late season weed management while minimizing water establishment requirements;
  3. To conduct these studies in a variety of different climatic conditions (regional within Utah), with different vegetable crops (cucurbits, tomatoes, corn, other crops) and cropping systems (organic and non-organic);
  4. To disseminate this information to Utah’s farmers, service agencies and other potential user groups at farm field days, through print and electronic media and at state, regional and national meetings.

Vegetable growers throughout Utah have requested more information about how to identify useful cover crops, how to incorporate them into their production systems, and how they may interfere with water management, crop performance and nutrient cycling. Cover crops are known to reduce nutrient leaching, improve to nitrogen cycling, decrease the need for additional fertilizers and minimize ground water pollution, thereby enhancing crop productivity (Abdul-Baki and Teasdale, 1997; Drinkwater et al., 2000; Sainju and Singh, 1997; Yaffa et al., 2000). Mulches also reduce evaporative demand (Hutchinson and McGriffen, 2000; Madden et al., 2004), and thereby increase water use efficiencies (Morse, 1993) while stabilizing the soil, which reduces soil erosion (Shennan, 1992). Vegetable crop rotations can benefit from the inclusion of soil-improving cover crops. Cover crop selection is important in reduced tillage, no-tillage or organic cropping systems, as each has quite different cover needs (Carrera et al., 2004; Creamer and Dabney, 2002; Harrison et al., 2004; Luna and Stabe, 2002; Stevens et al., 2005). In reduced and no-tillage systems, much of the plant residue remains on the soil surface. Often times, the residue interferes with planting, limits irrigation movement through the field and might not contribute to soil fertility since tissue breakdown and nutrient release requires incorporation into the soil (Shennan, 1992). Cover crops are very important in erosion control and weed management (Creamer et al., 1995), but one has to decide whether to incorporate the cover crop to improve fertility or leave it on the surface for better weed control (Hoyt et al., 1994; Nelson et al., 1991; Sainju and Singh, 1997).

In the drier western U.S., growers are worried that cover crops may extract to much soil moisture and that this may interfere with the desired crop’s establishment if late winter or spring conditions are dry and irrigation is not yet available (Madden et al., 2004; Uri, 2001). In addition, if summer cover crops are planted, they often require water to establish (Hutchinson and McGriffen, 2000) and may not produce sufficient biomass if not irrigated regularly. Furthermore, in short water years, it would be uneconomical and unwise to dedicate limited water resources to establish and maintain a cover crop. Therefore, growers are wary of incorporating cover crops into their farming operations unless more is known about the water use and general growth characteristics of the plants. Our research focus was determining which covers have better water use while still helping improve fertility, weed management and plant protection. Moreover, the selection of the cover crop and desired cash crop should complement each other, especially if growing seasons are short or water resources are limited.

Literature Cited

Abdul-Baki, A.A. and J.R. Teasdale. 1993. A no-tillage tomato production system using hairy vetch and subterranean clover mulches. HortScience 28:106-108.

Carrera, L.M., A.A. Abdul-Baki, and J.R. Teasdale. 2004. Cover crop management and weed suppression in no-tillage sweet corn production. HortScience 39(6):1262-1266.

Creamer, N.G. and Dabney, S.M. 2002. Killing cover crops mechanically: Review of recent literature and assessment of new research results. American Journal of Alternative Agriculture 17:32–40.

Drinkwater, L.E., R.R. Janke, and L. Rossoni-Longnecker. 2000. Effects of tillage intensity on nitrogen dynamics and productivity in legume-based grain systems. Plant and Soil 227:99–113.

Drost, D.T., G.A. Long, and K. Hales. 1998. Targeting extension efforts needed for adoption of sustainable farming practices. Journal of Extension 36(5) October 1998. (

Drost, D., G. Long, and K. Hales. 1997. Utah’s vegetable growers: Assessing sustainable agriculture. HortTechnology 7(4):445-450.

Harrison, H.F., D. M. Jackson, A.P. Keinath, P.C. Marino, and T. Pullaro. 2004. Broccoli production in cowpea, soybean, and velvetbean cover crop mulches. HortTechnology 14(4):484-489.

Hoyt, G.D., D.W. Monks, and T.J. Monaco. 1994. Conservation tillage for vegetable production. HortTechnology 4:129–135.

Hutchinson, C.M. and M.E. McGiffen, Jr. 2000. Cowpea cover crop mulch for weed control in desert pepper production. HortScience 35(2):196-198.

Luna, J.M. and M.L. Staben. 2002. Strip tillage for sweet corn production: yield and economic return. HortScience 37(7):1040-1044.

Madden, N.M., J.P. Mitchell, W.T. Lanini, M.D. Cahn, E.V. Herrero, S. Park, S.R. Temple, and M. Van Horn. 2004. Evaluation of conservation tillage and cover crop systems for organic processing tomato production. HortTechnology 14(2):243-247.

Morse, R.D. 1993. Components of sustainable production systems for vegetables: Conserving soil moisture. HortTechnology 3(2):211–214.

Nelson, W.A., B.A. Kahn, and B.W. Roberts. 1991. Screening cover crops for conservation tillage systems for vegetables following spring plowing. HortScience 26:860–862.

Sainju, U.M. and B.P Singh. 1997. Winter cover crops for sustainable agricultural systems: Influence on soil properties, water quality, and crop yields. HortScience 32(1):21-28.

Shennan, C. 1992. Cover crops, nitrogen cycling, and soil properties in semi-irrigated vegetable production systems. HortScience 27(7):749–754.

Steven V., H.C. Wien, and A. Rangarajan. 2005. Time of interseeding of lana vetch and winter rye cover strips determines competitive impact on pumpkins grown using organic practices. HortScience 40(6):1716-1722.

Sustainable Agriculture Network (SAN). 1998. Managing cover crops profitably. 2nd ed. Sustainable Agr. Network Natl. Agr. Library, Beltsville, Md.

Uri, N.D. 2001. The potential impact of conservation practices in US agriculture on global climate change. Journal of Sustainable Agriculture 18(1):109–131.

Vigil, M.F. and D.E. Kissel. 1991. Equations for estimating the amount of nitrogen mineralized from crop residues. Journal of Soil Science Society of America 55(3):757–761.

Yaffa, S., U.M. Sainju, and B.P. Singh. 2000. Fresh market tomato yield and soil nitrogen as affected by tillage, cover cropping, and nitrogen fertilization. HortScience 35:1258–1262.


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Materials and methods:

Yearly replicated experiments featuring a variety of winter and summer cover crops were planted in 2008 and 2009 at the Greenville Farm in Logan, Utah. Commonly grown and novel cover crops were to be evaluated for biomass accumulation, nutrient content, soil quality improvement, water use efficiency and soil water depletion, and crop production performance. Cover crops of interest include pure and mixed stands of a variety of small grains, legumes, non-legume broadleaf plants and various grasses widely used around the U.S. but generally unused or deemed unsuitable for Utah (SAN, 1998). The cover crops were reportedly sown at recommended rates for the different species and were planted in the late spring, depending on the species (Table 1). Cover crops were to be incorporated (mowed, chopped and incorporated) or mowed and left on the soil surface depending on if nutrient cycling, better weed management, erosion protection or other crop production strategies were to be assessed. Each cover crop was replicated at least three times.

Cover crop growth (leaf area, crop cover, plant height) and yield (size, weight, quality, plant nutrient status) were to be assessed throughout the year.

Soil Quality: Percent soil cover and leaf biomass production from the different cover crops were to be used to calculate amount of dry matter production, the amount of expected fertility (N,P,K), a soil conditioning index (Vigil and Kissel, 1991), and generate an estimate of organic matter change.

Soil moisture levels were to be assessed gravimetrically at weekly intervals throughout a dry down period in the different cover crops, and penetrometer values used to understand the influence of cover crops on possible changes in soil compaction. Irrigation durations (sprinkler) were to be recorded and periodically, catch cups were to be used to determine the amount of water applied during an irrigation event to the cover crops and vegetable crops. Since the timing of cover crop growth relative to the season of the year differs greatly, soil moisture dynamics may influence stand establishment in the following spring.

Crop production systems using cover crops (CCs) for nutrient cycling requires some understanding of water use and level of biomass generation. After the departure of the PhD student assigned to the study, and due to the lack of good records from earlier years, we modified the project in 2010. Our goal was to explore modifications to local seeding rates as a way to increase stand establishment, cover crop density and weed suppression for spring/summer-seeded grass (annual rye, millet, barley, sorghum), broadleaf (buckwheat, rape) and legume (chickling vetch, soybean, hairy vetch, lentil, adzuki bean, lab lab and lupine)cover crops (Table 2).

Many of these CCs had been noted to performed well in the past, show some drought tolerance and have been reported to produce reasonable amounts of biomass. Crops were seeded at the standard rate and at a 2x rate on June 21 to ensure high densities and better cover. Plots were irrigated and stand counts taken on July 7, and fresh and dry weights measured on July 28. To assess drought tolerance, irrigation was stopped, and the diurnal change in leaf water potential measured two weeks later.

Research results and discussion:

Cover crops that show potential adaptation to the intermountain west include annual rye, barley, millet, hairy vetch, buckwheat, rape and sorghum (Table 2). Less adapted CCs included soybean, adzuki bean, lentil, lab lab and chickling vetch, which had weaker stands, slow growth/cover and less biomass when planted at lower seeding rates. As seeding rates increased, biomass production increased, greater crop densities were noted and weed control ratings improved. While the amount of data collected does not allow solid conclusions, growers wanting to use cover crops should increase the seeding rates to ensure better plant densities, more biomass and thus achieve improved weed control. At lower densities, too many weeds grow and fill in the open areas of the field. These types also allowed more weed growth due to lower density and more open stands.

After a two week dry-down period, leaf water potential measurements taken on the 12 different cover crops show there is large differences between crops (Table 3). Grass cover crops (sorghum, barley, rye and millet) had lower morning water potentials than broadleaf (rape, buckwheat) and legume cover crops (beans, and vetches). Leaf water potential in grasses dropped rapid around noon (range -1.1 to -1.9 MPa) and stayed at low levels through the remainder of the day. Broadleaf cover crops stayed fairly constant over the same period. Legume cover crops dropped to about -0.5 Mpa and then remained steady over the day. Very low water potentials like those measured in the grasses suggests less tolerance to water stress while higher values suggest more stress tolerance.

Some additional work is needed to correlate leaf water potentials to soil water content to assess the degree of tolerance and how changing soil moisture content may impact productivity aspects of the more drought tolerant cover crops.

Research conclusions:

While there were problems with data collection encountered over the course of this study and much of the first two years of data was lost or deemed unusable (for a number of reasons), there appears to be large differences in cover crops adaptation to local conditions. Cover crops that show promise for use in the intermountain west are annual rye, birdsfoot trefoil, millet, mammoth red clover, lana vetch, buckwheat, rape, hairy vetch and sunflower. All performed well in forced dry downs over a thirty day period. Hairy and lana vetch had superior ground cover and biomass. Birdsfoot trefoil and mammoth red clover had good ground cover, but above ground biomass was lower (unconfirmed in later studies). Sunflower was drought tolerant but may need to be seeded at a higher rate to reach adequate ground cover (no further testing). Other cover crops that were reported to be drought tolerant did not establish well by thirty days. These included cowpea, adzuki bean and lab lab bean. Higher seeding rates than those recommended suggest some improvement, and cowpea established better in a separate study. Oats and barley were also analyzed but died during the forced dry down and were determined to not be drought tolerant. Lentil and white lupin performed very poor in this study and failed to grow or thrive. Students reported that samples were disposed of by unknown person before all data collected.

More effort is needed to screen these cover crops for adaptation and, work on over-wintering cover crops is sorely needed.

In cooperation with Greg and Tim Vetere (Green River, UT), we evaluated winter wheat cover crops for weed management and soil stabilization (Photo 1 & 2). The Veteres grow a range of vegetables (various types of melons, sweet corn and potato) and do this on more than 100 acres. They use fall-seeded wheat to hold sandy soils in place and provide wind protection for early seeded and transplanted melons in particular. Because they have irrigation, stand establishment of the CCs is good, but since the water is pumped, it can be costly. Fields are generally sprayed out in the spring and strip tilled before laying black plastic, drip and planting. In the previous three years, dry winter conditions (limited snow cover and moisture) affected survival and spring growth. Poor spring stands and low stature of the CC limited the amount of wind protection and weed control achieved. Growers, however, are pleased with the results as melon plant damage is greater without the CC than the impact of weeds on melon crop performance. Growers report that any protection is better than what they had prior to using CCs. Growers want to continue evaluating different CC blends (adding in a legume) and assessing the timing of cover removal and how density impacts melon establishment and growth.

Cooperators David Sterling (Leeds, UT) and Tim Thompson (Hurricane, UT), continue to use cover crops for weed and wind management for seeded and transplanted melons (watermelon and cantaloupe). Both growers note that that dry winters (limited snow or open fields) create CC stand losses that then provide limited biomass in the spring needed for protection. This seems to be a common problem in the dryer areas of eastern and southern Utah (Grand and Washington Co.). While these growers use plastic mulches and drip or center pivot (drop nozzles) irrigation for their crops if winter CC growth is inadequate, the between row area with the cover crop does not provide sufficient wind protection for young plants in the spring. Regardless of the amount of CC growth, all growers continue to say that fruit yields and quality (size, shape, etc) is improved using this system. We continue to ask about trying to establish mixed cover crop systems (with legumes) to improve soil nutrition re-cycling, but growers are not that interested in the nutrient aspects of the CC system.

Grower Cooperator Randy Ramsley (Caneville, UT) did not want to continue due to other commitments and the difficulty of getting any of the crops to establish in his area.

In cooperation with Utah onion growers, we evaluated if inter-cropping of carrot, buckwheat and phacelia altered the feeding preferences of onion thrips. These crop plants are all known to be very attractive to onion thrips. We periodically sampled the cover crops and onions in proximity to the CCs for thrips and their impact on onion productivity. Research findings showed that thrips were attracted to phacelia and buckwheat CC when the CCs were young but less attracted as the CCs matured. While growers may not use this approach to managing onion thrips, the research suggests it could be a viable approach to creating a systems method for concentrating thrips and targeting sprays. Additional testing on multi-CC species, border field plantings, strip plantings and extending planting date studies are needed to design a CC strategy to help manage onion thrips. Since there are ready markets for buckwheat and phacelia, these CCs are more likely to be adopted by local onion growers. Having thrips-attracting CCs may allow reduced pesticide applications to onions without sacrificing onion productivity or quality.

Participation Summary

Educational & Outreach Activities

Participation Summary

Education/outreach description:

August 2007

PhD student hired to conduct research on Cover Crop (CC) assessment for drought tolerance and water use efficiency. Student organized research protocols (in line with research objectives listed above) and secured various grasses, broadleaf and legume covers reported to have some drought tolerance and be used to evaluate growth, biomass generation, water use and adaption to local conditions during fall 2007 and spring 2008. Crops plant in June 2008. Student used data from 2008 to establish 2009 plantings. Student was responsible for planting, plot management and data collection. Much of the findings were lost or deemed unusable due to poor record keeping. Student left the program in April 2010. Tried to re-create plantings in 2010 from provided records but was unable to due to limited information and records.

Field Days

August 12, 2008 – Utah Onion Field Tour. Box Elder Co, UT. Sixty-three onion growers and industry persons observed buckwheat, phacelia and carrot CCs inter-seeded with onions. Discussion centered on if CCs are attractive to onion thrips, how the CCs may fit into onion production system and limitations for use on-farm.

August 14, 2008 – Kaysville Field Day. Kaysville, UT. One hundred-three fruit and vegetable growers, industry persons and extension educators viewed the USU organic vegetable trials. Attendees saw various fall- and spring-planted CC combinations, assessed growth of vegetable crops grown in these CCs and evaluated their impact on nutrient cycling and weed control. Growers discussed pros and cons to using cover crops on their farms and possible solutions to problems identified in research trials.

September 1, 2009 – Evening Farm Tour. Green River, UT. Six vegetable growers. Gathered to discuss watermelon and cantaloupe production issues. Led discussion on windbreaks, ground covers and plant performance.

June 30, 2010 – Summer Evening Onion Growers Field Tour. Norman Farms. Corinne, UT. Ten onion growers and industry persons observed how buckwheat, phacelia and carrot cover crops could be used on-farm to attract onion thrips. Discussion centered on attractiveness, establishment issues, integration of CCs into the farming system, marketing and usefulness of products, and cost.

August 17, 2010 – Kaysville Field Day. Kaysville, UT. Fifty-six fruit and vegetable growers, industry persons and extension educators toured the USU organic vegetable trials that are using various cover crop combinations (fall- and summer-planted) to cycle nutrients and support vegetable growth.

Extension Presentations:

November 7, 2007. Dan Drost was an invited speaker at the Utah Association of Conservation Districts on in St. George, UT. Provided the attendees with a variety of information on Utah State University’s research effort cover crop management. Title “Finding Ways to Increase Farm Productivity: High Tunnels and Cover Crops.”

Research Presentations:

March 31, 2009. Ragland, A. and D. Drost. Regenerative Organic Agriculture Systems Using Cover Crops. Intermountain Graduate Research Symposium. Logan, Utah.

April 5 2010 – PhD student presented 2008-09 research findings to the department of Plants, Soils and Climate as part of the weekly seminar series at Utah State University.

August 2-5, 2010 – Buckland, K., J. Reeve, D. Alston, and D. Drost. Evaluating the Effects of Nitrogen, Crop Rotation, and Trap Crops on Onion Thrips, Iris Yellow Spot Virus, and Crop Yield. HortScience 45(8): S212-213. (abstract) Palm Desert, CA.

September 25-28, 2011 – Drost, D. Unique Winter and Summer Cover Crop Combinations Improve Bean, Broccoli, and Sweet Corn Productivity. HortScience 46(9): S257. (abstract) Waikoloa Village, Hawaii.

Project Outcomes

Project outcomes:

We were unable to conduct any detailed analysis due to the lack of useful data. However, grower-cooperators using cover crops report that they help ensure crops establish and grow early in the production season when winds can seriously damage crops. Many melon growers in Utah are using cover crops, strip tillage, and are doing it successfully. Without the use of a cover crop, stand reduction would occur that compromises yield potential particularly with melons.

Farmer Adoption

We estimate that about 250 growers, industry leaders and extension personnel have visited, heard or participated in field days, workshops, and grower meetings associated with cover crop use. Our grower cooperators continue to use cover crops on their farms. Greg Vetere (Green River, UT) said “We would never be able to grow watermelons on our sandy soils if we didn’t have some way to keep the sand from blasting the plants. We could continue to irrigate during establishment, but this is really expensive. Cover crops help solve this problem. We still need to get more growth (taller and more density) from the cover crops. It blows so much on this farm that without protection from the wind, our crops would never grow.” Dave Sterling stated “It only takes one big wind storm to ruin a crop. Having good wind breaks makes a big difference.”

While adoption of cover crops use is occurring, growers are still reluctant to incorporate them into their production systems. Growers worry about competitiveness, water loss to the cover crop and re-growth issues. One onion grower stated “Cover crops will never work for us. They are just too competitive.”


Areas needing additional study

Working with our cooperators and with the limited findings of our research studies further reinforce the need to know and focus on the identification of cover crops with different plant growth characteristics including: rapid establishment, cold and heat tolerance, water use efficiency and a non-competitive nature. In production areas with short growing seasons like the intermountain west, direct transfer of cover crops use information from production areas with long growing seasons (like California) just does not seem to work. Cover crops interfering with production schedules remains a serious problem. Cover crop establishment has to occur early enough in the fall to get some growth, but this interferes with existing crop production cycles. Therefore, some additional thought on cover crop selection, cover crop use practices and production approaches that make growers less hesitant to adopt them is really needed. Unless there is good sound economic or production reasons for growing the cover crops, growers will not adopt their use. Therefore, more effort is needed, particularly in looking for fall-planted covers that do not interfere with spring farm activities, and for spring summer crops that establish quickly and then can be used in a limited or no-till type of system.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.