Selecting cover crops for diverse functions: an integrated soil management approach for organic strawberry production in North Carolina

Selecting cover crops for diverse functions: an integrated soil management approach for organic strawberry production in North Carolina

Summary

We have conducted a two year field experiment (2008-2009) comparing seven summer cover crops and combinations (Sudan grass, Velvetbean, Sudangrass/Velvetbean, Pearl millet, Soybean, Pearl millet/Soybean, and Rape) to a control (no cover crop) for their effects in organic strawberry production in North Carolina. We also pre-inoculated strawberry plugs with either a native or commercial mycorrhizal fungal inoculum. Sudangrass, Pearl Millet and Pearl Millet in combination with Soybean produced the highest aboveground biomass and controlled the summer weeds most compared the control/no cover crop treatment, although there were no significant differences among cover crop treatments for strawberry total or marketable yields. Mycorrhizal inocula treatments did not differ greatly emphasizing the importance of the native species. We also performed three on-farm trials of selective cover crops where producers took part in selecting cover crops and evaluating them. Results of this two year field study and on-farm work were reported at the Southeast Strawberry Expo and the Carolina Farm Stewardship Conferences end of 2009. In this third year we initiated two new experiments – a field and greenhouse experiment to further investigate an integrated approach of using composts, selective cover crops planted at high densities, vermicomposts and native mycorrhizal incoulum for their effect on strawberry yields, nutrient uptake and suppressive effects on root rot pathogens.

• Weed suppression from cover crop treatments

Objectives/Performance Targets

• The overall objective of this study is to develop an integrated approach of cover crop rotations, compost applications, and beneficial mycorrhizal fungi management as sustainable soil and pest management practices for organic strawberry production in North Carolina. Importantly, these practices can also be used by conventional strawberry growers as they transition away from methyl bromide.

  Our specific objectives for this project are to:
  Evaluate seven cover crop species and combinations (Sudan grass, Velvetbean, Sudan grass/Velvetbean combination, Soybean, Pearl Millet, Soybean/Pearl Millet combination, and Dwarf essex rape) compared to a control (no cover crop) for their impact on strawberry yield and ability to enhance native arbuscular mycorrhizal (AM) fungi in organic strawberry production systems. This large research field study will occur over two strawberry seasons at the Center for Environmental Farming Systems in Goldsboro, NC.
  Evaluate strawberry yield benefit from native AM fungi and commercial AM fungi inoculum sources.
  Develop on-farm trials with three strawberry producers in North Carolina for evaluation of selected cover crop species on strawberry yields. Producers will also be interviewed for their perceptions of challenges and benefits of using cover crops.
  Promote technology and education transfer on cover crop and AM fungi management in organic and conventional strawberry production systems among farmers, extension agents, NRCS agents, the NC Strawberry Association, researchers and students.

Accomplishments/Milestones

• A field study at the Center for Environmental Farming Systems (CEFS) in Goldsboro, NC was initiated in June 2007 with the planting of seven summer cover crop that included Sudan grass, Velvet bean, Sudan grass/Velvet bean combination, Pearl Millet, Soybean, Pearl Millet/Soybean combination, Dwarf essex rape compared to a non-cover crop treatment (control). Organic strawberry (Chandler variety) plugs pre-inoculated with either a native or commercial beneficial arbuscular mycorrhizal fungal species mix were planted in early October this same year and strawberry biomass responses, total and marketable yields and nutrient uptake responses were monitored the following spring. In 2008, the same treatments were repeated and new strawberry plugs were planted following the same procedures to collect data over two years for this field experiment. Baseline soil fertility, nematodes and mycorrhizal fungal communities were sampled in May before cover crop treatments were established each year. Cover crops were assessed for their biomass responses, shoot nutrient response and effects on weed abundance. We found Sudangrass, Pearl Millet and Pearl Millet in combination with Soybean to produce the highest aboveground biomass responses and controlled the summer weeds the most compared to other cover crop treatments. All cover crop treatment significantly controlled weeds compared to the control/no cover crop treatment, although there were no significant differences among cover crop treatments for effects on strawberry total or marketable yields. Mycorrhizal inocula treatments did not differ greatly for their effects on strawberry yields or biomass responses, emphasizing the importance of the native mycorrhizal species mixture.
  Three on-farm research trials were established with producers in Calabash, Burlington, and Apex, NC from 2008-2009. The three farms represent different soil and climatic conditions for strawberry production and all the three producers have a strong interest in using and knowing more about management of summer cover crops for strawberries. The project coordinator and graduate student met with all three strawberry producers to discuss project details, responsibilities and together selected specific cover crops for each farm and specific conditions early 2008. On each farm trial, there were two cover treatments and a control (no cover crop) treatment with each treatment replicated three times for a total of nine plots. Specific cover crop species differed for each farm depending on the specific farm conditions and management considerations. Plots were established and cover crops planted mid June 2008 on all three farms. Prior to planting, baseline soil nutrients, nematodes and mycorrhizal fungi diversity were sampled at each farm. Cover crops were examined for their biomass, nutrient and weed control response prior to cutting and incorporation in preparation for strawberry planting in October 2008 and strawberry marketable yields were monitored .by producers in 2009. All of the three farms in this study are managed with conventional methods typically using methyl bromide but are interested in knowing more about cover crops and organic production and one of the farms has a new small area of certified organic strawberry production. Although cover crops did not increase strawberry yields on any of the farms after one season, the producers expressed their satisfaction with the study and their continued interest in using cover crops because of the long term benefits.

Impacts and Contributions/Outcomes

• Various summer cover crops and their combinations were evaluated for their effects on strawberry yields and nutrient uptake, weed management, soil nutrient properties, effects on the beneficial mycorrhizal fungal populations, and overall suitability in strawberry production systems for North Carolina. Results from this research on cover crops can be extended to producers throughout the Southeast US that are managing strawberries either organically or conventionally.
  From on-farm research and subsequent interviews with these producers, we identify farm-level benefits and potential management or other challenges to using summer cover crops and organic production practices in strawberry production systems in North Carolina. This information is extremely valuable to both encouraging more strawberry producers to use cover crops in rotation and to educate researchers to conduct future studies addressing specific farmers needs.
  Project leaders Michelle Schroeder-Moreno and Gina Fernandez and graduate student Ben Garland spoke to strawberry growers, the director of the NC Strawberry Association, and local Natural Resources and Conservation Services agents at a Strawberry Conservation Field Day on March 25 2009. This field day was organized by the NC Strawberry Association and occurred on the Apex farm (Buckwheat farms) one our on-farm trial of cover crops were. We discussed the project, answered questions about cover crop management and cover crops were discussed in context with other alternatives to methyl bromide. Evaluation of cover crop species for diverse functions, including enhancing AM fungi is a major advancement towards developing an integrated approach for sustainable soil and pest management in organic and conventional strawberry production in North Carolina and the Southeastern US.
  Project leaders Michelle Schroeder Moreno and Gina Fernandez co-presented project results with the three on-farm producers at the Southeast Strawberry Expo in Durham, NC on November 9 2009. The Wake County District Leader for the Natural Resources and Conservation Service followed the presentation with information about new cost share programs for strawberry producers to perform soil conservation strategies.

  Dr. Schroeder-Moreno also presented project results and general information on organic strawberry production practices and disease prevention together with Dr. Frank Louws (NCSU) at the Carolina Farm Stewardship Association in Black Mountain, NC on Dec 4 2009.

Collaborators: