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

Organic strawberry production is a growing market and can offer alternatives for the loss of methyl bromide in conventional strawberry systems and transition from tobacco in North Carolina. Soil borne pathogens, root rot diseases, weeds, and nematodes can considerably reduce strawberry yields, especially when strawberries are replanted in the same site. The majority of organic strawberry production research, however, has been conducted in California where climate, soils, production practices and pest pressures differ vastly from the Southeastern United States. It is imperative to investigate sustainable practices specific for organic strawberry producers in this region that improve soil fertility, minimize disease and weed incidence and enhance soil biological activity.

In this study, we will examine the use of summer cover crops as an integrated soil and pest management approach for a transition to more sustainable strawberry production in North Carolina. Thus, these practices can be both used in organic or conventional production systems. Using cover crops in rotation is an important strategy for many sustainable and organic systems to prevent erosion, increase soil organic matter and fertility, enhance biological activity, and break up pest cycles. The use of cover crops is relatively unexplored in practice in strawberry production. Selective cover crop species may also improve the arbuscular mycorrhizal (AM) fungal inoculum potential and subsequent crop benefit from mycorrhizas. Arbuscular mycorrhizas have been demonstrated to benefit strawberry growth by increasing nutrient acquisition and decreasing damage caused by Phytophthora root rot. Many commercial AM inoculants are available with variable success. Locally adapted AM fungal isolates, however, can be produced on farm and may be more effective than introduced species. Selection of cover crops that also function as good AM hosts can increase the activity of indigenous AM fungi, strawberry growth and overall soil community sustainability.

We will carry out this study with three approaches: a field experiment at the Center for Environmental Farming Systems (CEFS) in Goldsboro, NC, greenhouse experiments and on-farm research trials. The on-farm trials will be done in collaboration with three strawberry producers throughout North Carolina and the cover crops will be selected on a site specific basis. Results from this study will be shared with the NC Strawberry Association, farmers, researchers, extension personal and students through formal and informal presentations and publications. 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 strawberry production in North Carolina and the Southeastern United States.

Objectives/Performance Targets

1. Advertise and select a graduate student to conduct their master thesis on this project under the direction of project coordinator, Dr. Michelle Schroeder-Moreno.

   Initiate field research study at the Center for Environmental Farming Systems (CEFS) in Goldsboro, NC. Cover crop treatments will be planted in mid summer 2007, monitored, harvested and plant subsequent strawberries in October 2007.

   Develop on-farm research collaborations with three strawberry producers in North Carolina. On-farm research would not begin until summer 2008 but the initial design considerations, responsibilities, land requirement, etc. would be planned late 2007 and early 2008.

Accomplishments/Milestones

1. A graduate student was advertised for and selected for this project. Ben Garland, a University of Georgia Horticulture major, was chosen and accepted for admission to the masters program in Crop Science at NC State University beginning fall 2007. Ben will be co-advised by Dr. Schroeder and Dr. Fernandez, (project coordinators) and the project described here will serve as Ben’s masters thesis.

   The field study at the Center for Environmental Farming Systems (CEFS) in Goldsboro, NC was initiated in June 2007. This research study will be 2 years long and examine seven different summer cover crop treatments consisting of sudan grass, velvet bean, sudan grass and velvet bean combination, pearl millet, soybean, pearl millet and soybean combination, dwarf essex rape and a non-cover crop treatment (control) for their subsequent effects on strawberry yields and the benefiical arbuscular mycorrhizal fungi community. Soil samples were collected for baseline soil fertility, nematode and native mycorrhizal fungal species diversity measurements. All cover crops were planted on June 11 2007 and weed diversity and cover crop growth were measured continuously throughout the summer. Summer cover crops were harvested early September 2007 and strawberries were planted ealry October 2007 (typical planting schedule for North Carolina). Starwberries were purchased loally and were inoculated in the greenhouse at NC State University with either the native mycorrhizal fungi from CEFS or a comercial mycorrhizal inoculant 4 weeks prior to planting in the field.

   Three commercial sources of mycorrhizal fungal inoculum were examined for their root colonization potential and growth effects on strawberry plants in the greenhouse. The commercial mycorrhizal inoculum with the highest root colonization (approx 20%) was chosen for the field experiment at CEFS. Dr. Schroeder has contacted the company for approval of use in this experiment.

   Project coordiantors, Michelle Schroeder-Moreno and Gina Fernandez, met with all three strawberry producers involved in the on-farm research trials late summer 2007. All producers have agreed to be part of the research. Dr. Schroeder-Moreno and Ben Garland (graduate student on this project) met again with the three producers a second time early 2008 to confirm the project design, land selection, cover crop selection and project responsibilities with each producer. Soil samples were taken at each farm to examine the baseline mycorrhizal fungi community.

   Project leaders Gina Fernandez and Ben Garland and the majority of the on-farm research collaborators/prodcuers additionally attended the Southeast Strawberry Expo in Novmember 2008.

Impacts and Contributions/Outcomes

Field-scale examination of selective cover crop species and combinations for their effects on strawberry yields in an organic production system.

Evaluate selective cover crop species and combinations for their effects on native mycorrhizal fungi community and subsequent growth effects on strawberry plants in the field.

Evaluate of strawberry yield benefit from indigenous AM fungi compared to various commercial AM fungi inoculants in field conditions.

Assess the number of effective mycorrhizal fungal propagules per unit of inoculum for each AM fungal inoculum source (native or commerical).

Identify farm-level benefits and potential challenges to using summer cover crops in organic strawberry production.

Educate researchers, extension agents, producers and students about summer cover crop practices and beneficial mycorrhizal fungal management in strawberry production systems

Collaborators: