Weeds, Nitrogen, and Yield: Measuring the Effectiveness of an Organic No-Till System

Project Overview

Project Type: Graduate Student
Funds awarded in 2013: $10,927.00
Projected End Date: 12/31/2015
Grant Recipient: Clemson University
Region: Southern
State: South Carolina
Graduate Student:
Major Professor:
Dr. Geoff Zehnder
Clemson University

Annual Reports


  • Vegetables: cucurbits, tomatoes


  • Crop Production: application rate management, conservation tillage, cover crops, no-till, organic fertilizers, tissue analysis
  • Production Systems: general crop production
  • Soil Management: organic matter, soil analysis


    Mulches of mechanically terminated winter annual cover crops such as cereal rye (Secale cereale L.) and crimson clover (Trifolium incarnatum L.) can be used as an effective early-season weed management tool in reduced tillage organic vegetable cropping. Previous research in the mid-Atlantic and midwestern USA has identified advantages and drawbacks of “organic no-till” vegetable production, but few studies have been conducted in the warmer southeastern region. The purpose of this study was to examine the effects of tillage [no-till (NT) vs. conventional tillage (CT) of a cereal rye/crimson clover cover crop] and three N fertilization levels on organic tomato (Solanum lycopersicum L.) and summer squash (Cucurbita pepo L.) yield and soil N in two years at the Clemson University Student Organic Farm in Clemson, SC. Squash yields were comparable among tillage treatments in both years. NT tomato yields were 43% greater than CT yields in 2014, whereas CT tomatoes yields were 46% greater than NT yields in 2015. Squash and tomato yields per unit of management labor (time) were significantly greater in NT compared to CT treatments for both years. There were no statistical differences in squash and tomato yields among N fertilization treatments in either year, nor were there significant tillage x N fertilization interactions. 


    Weed management and the associated labor inputs are consistently some of the biggest challenges to organic crop production (Riemens et al., 2007; Sooby et al., 2007). Organic farmers, out of necessity, rely heavily on soil tillage and other forms of labor-intensive soil cultivation for weed management despite the well-known disadvantages to soil health associated with intensive soil disturbance (Schonbeck and Morse, 2007; Morse and Creamer, 2006).

    A small but growing number of organic farmers have begun adopting reduce tillage techniques, which blend the soil-conserving and labor-saving methods of conventional no-till systems with traditional soil building practices (i.e. cover cropping) used in organic production (Leavitt et al., 2011; Mirsky et al., 2013). In organic no-till, an in situ mulch is created by mechanically terminating mature cover crops. Subsequent cash crops are direct seeded or transplanted into the mulch-covered soil. The cover crop mulch manages weeds in place of mechanical cultivation through physical impedance, light interception, and allelopathy (Mohler and Teasdale, 1993; Teasdale and Mohler, 1993; Teasdale and Mohler, 2000).

    Despite the demonstrated weed suppression of no-till mulches, organic no-till vegetable production systems have produced mixed results (Delate et al., 2012). Yield reductions associated with no-till mulches were documented in squash (Leavitt et al., 2011), bell pepper (Diaz-Perez et al., 2008; Leavitt et al., 2011), and tomato production (Leavitt et al., 2011). On the contrary, comparable or positive yield responses in organic no-till systems compared to conventionally tilled systems were reported in tomatoes (Abdul-Baki et al., 1996; Madden et al., 2004; Delate et al., 2012).

    Common problems researchers have identified regarding organic no-till production include: sub-optimal soil temperatures early in the season and shortened degree growing days caused by the cooling effect of cover crop mulches; loss of earliness due to a lack of synchrony between cover crop maturity and optimal cash crop planting dates; N immobilization when using high C/N cover crops (i.e. rye); increased weed pressure particularly when cover crop stands are inadequate; and reduced N mineralization and poor N synchrony due to a lack of cover crop incorporation (Leavitt et al., 2011; Schonbeck and Morse, 2007; Schonbeck, 2015; Moyer, 2011; Creamer et al., 1997; Morse, 1999; Mirsky et al., 2011; Parr, et al., 2014).

    Given the pitfalls and mixed results associated with organic no-till systems, we sought to evaluate an organic no-till system for vegetable production compared to a conventionally tilled system along the following parameters: vegetable yield, soil N, and weed management inputs.

    Literature Cited

    Abdul-Baki, A., Stommel, J., Watada, A., Teasdale, J., and Morse, R. (1996). Hairy vetch mulch favorably impacts yield of processing tomato. HortScience, 31(338), 340.

    Creamer, N. G., Bennett, M. A., and Stinner, B. R. (1997). Evaluation of cover crop mixtures for use in vegetable production systems. HortScience, 32(5), 866-870.

    Delate, K., Cwach, D., and Chase, C. (2012). Organic no-tillage system effects on soybean, corn and irrigated tomato production and economic performance in Iowa, USA. Renewable Agriculture and Food Systems, 27, 49-59.

    Diaz-Perez, J., Silvoy, J., Phatak, S., Ruberson, J., and Morse, R. (2008). Effect of winter cover crops and no-till on the yield of organically grown bell pepper (Capsicum annuum L.). In R. Prange and S. Bishop (eds.). (Ed.), Proc. XXVII IHC-S11 Sustainability through integrated and organic horticulture. pp. 767.

    Leavitt, M. J., Sheaffer, C. C., Wyse, D. L., and Allan, D. L. (2011). Rolled winter rye and hairy vetch cover crops lower weed density but reduce vegetable yields in no-tillage organic production. HortScience, 46(3), 387-395.

    Madden, N. M. et al. (2004). Evaluation of conservation tillage and cover crop systems for organic processing tomato production. Horttechnology, 14(2), 243-250.

    Mirsky, S. B. et al. (2013). Overcoming weed management challenges in cover crop-based organic rotational no-till soybean production in the eastern United States. Weed Technology, 27(1), 193-203.

    Mirsky, S. B., Curran, W. S., Mortensen, D. M., Ryan, M. R., and Shumway, D. L. (2011). Timing of cover-crop management effects on weed suppression in no-till planted soybean using a roller-crimper. Weed Science, 59(3), 380-389.

    Mohler, C. L. and Teasdale, J. R. (1993). Response of weed emergence to rate of Vicia villosa Roth and Secale cereale L. residue. Weed Research, 33(6), 487-499.

    Morse, R. D. (1999). No-till vegetable production – its time is now. Horttechnology, 9(3), 373-379.

    Moyer, J. (2011). Organic no-till farming. Austin, TX: Acres U.S.A.

    Parr, M., Grossman, J. M., Reberg-Horton, S. C., Brinton, C., and Crozier, C. (2014). Roller-crimper termination for legume cover crops in North Carolina: impacts on nutrient availability to a succeeding corn crop. Communications in Soil Science and Plant Analysis, 45(8), 1106-1119.

    Riemens, M., Groeneveld, R., Lotz, L., and Kropff, M. (2007). Effects of three management strategies on the seedbank, emergence and the need for hand weeding in an organic system. Weed Research, 47, 442-451. 

    Schonbeck, M. W. (2015). What is "organic no-till," and is it pratical? Extension Foundation, eOrganic Community of Practice. Retrieved from https://www.extension.org/pages/18526/what-is-organic-no-till-and-is-it-practical#.VAuqLhar_No

    Schonbeck, M. W. and Morse, R. D. (2007). Reduced tillage and cover cropping systems for organic vegetable production. Virginia Association of Biological Farming Info Sheet, 9-07. Retrieved from: http://www.sare.org/Learning-Center/SARE-Project-Products/Southern-SARE-Project-Products/Reduced-Tillage-and-Cover-Cropping-Systems-for-Organic-Vegetable-Production

    Sooby, J., Landeck, J., and Lipson, M. (2007). 2007 National Organic Research Agenda. Santa Cruz, CA.: Organic Farming Research Foundation. Retrieved from: http://ofrf.org/sites/ofrf.org/files/docs/pdf/nora2007.pdf

    Teasdale, J.R. and Mohler, C. L. (1993). Light transmittance, soil temperature, and soil moisture under residue of hairy vetch and rye. Agronomy Journal, 85(3), 673-680.

    Teasdale, J.R. and Mohler, C. L. (2000). The quantitative relationship between weed emergence and the physical properties of mulches. Weed Science, 48(3), 385-392.


    Project objectives:

    The objectives of our experiment are: 

    1. To assess two tillage treatments (no-till and tilled) of a rye and crimson clover cover crop for organic tomato and summer squash production; 

    2. To determine the interactions between two tillage treatments and three fertilization treatments (no nitrogen fertilizer, half the recommended rate of nitrogen fertilizer, and full recommended rate of nitrogen fertilizer) as they correspond to tomato and squash yields; and 

    3. To evaluate the management costs of a no-till system compared to that of a tilled 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.