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

Final Report for LS07-200

Project Type: Research and Education
Funds awarded in 2007: $200,000.00
Projected End Date: 12/31/2010
Region: Southern
State: North Carolina
Principal Investigator:
Dr. Michelle Schroeder-Moreno
North Carolina State University
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Project Information

Abstract:

Two separate studies were conducted to examine the effects of using summer cover crops as part of an integrated sustainable soil management approach for strawberry production in North Carolina that included a two-year field experiment and a one year on-farm trial. The field experiment was conducted at the Center for Environmental Farming Systems (CEFS) in Goldsboro, NC to examine the effects of eight cover crop treatments combined with two arbuscular mycorrhizal (AM) fungal inoculants on strawberry yields. Cover crop treatments included two grasses (Sudan grass and Pearl millet), two legumes (Soybean and Velvetbean), two grass/legume combinations (Sudangrass/Velvetbean and Pearl millet/Soybean), a non-AM host (Rape in year 1 and Buckwheat in year 2) and a control (no cover crop). Strawberry plugs were pre-inoculated with either a mixture of native AM fungal species or a single species derived from a commercially available inoculant. Sudan grass, Pearl millet and the Pearl millet/Soybean combination produced the highest aboveground biomass and the lowest weed biomass compared to the other treatments, although there were no significant differences among cover crop treatments for strawberry yields. Mycorrhizal treatments did not differ greatly, emphasizing the importance of the native AM fungal species.

A one-year on-farm study was additionally conducted on three separate farms to determine the effects of cover crop treatments on strawberry yields, weed biomass, and cover crop biomass, and to investigate the producer-perceived benefits and barriers to the adoption of cover crops in strawberry production. While cover crops reduced weed biomass at two of the farms, cover crops did not affect yields at one farm but reduced yields at another. Interviews with producers revealed they perceived the greatest barriers to adoption of cover crops in strawberry production are: 1) lack of information about how to integrate cover crops into a strawberry production schedule; 2) absence of practical guidance on how to increase cover crop biomass, 3) a need to evaluate cover crop benefits in strawberries over a longer time period, not just one season; and 4) an insufficient understanding of any potential interactions of cover crops with beneficial organisms or pests.

Project Objectives:
General Objective

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 below.

  1. Evaluate eight cover crop treatments that include 1) Sudan grass 2) Pearl millet, 3) Soybean 4) Velvetbean, 5) Pearl millet/Soybean combination, 6)Sudangrass/Velvetbean combination, 7) a non-AM cover crop host (Rape in year 1 and Buckwheat in year 2) and 8) control (no cover crop) for their impact on strawberry yields, growth, weeds, soil nutrients and impact on background native arbuscular mycorrhizal (AM) fungi.

    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 perceived 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.

Introduction:

Strawberries are a high-value crop and strawberry production has strong growth potential, especially in the Southeastern (SE) US where most producers sell directly to consumers through pick your-own operations and roadside stands. Unfortunately, SE strawberry growers operate in a hot, humid climate in poor soils that is often more favorable to fungi and other root diseases that can significantly reduce yields. Moreover, where strawberries are replanted year after year in the same location, such as near roadside stands, soil borne pathogens, root rot diseases, and weeds can significantly buildup, further diminishing yields and increasing management costs (Wing et al., 1995). Conventional producers have traditionally dealt with these pest problems by fumigating with methyl bromide, which is under restricted use for strawberry production. With restrictions on methyl bromide increasing, many producers are considering different synthetic alternatives, such as technical-grade 1,3-Dichloropropene (Telone II), but the health risks may be significant (National Toxicology Program, 1985). There is a critical need for sustainable approaches to pest and soil management for strawberry production in the SE, and especially for organic production. These alternatives should focus on promoting healthy plants and enhancing beneficial soil organisms, while reducing pests and diseases over the long term.

While not a common practice, summer cover crops can be integrated into strawberry production and may play a critical role in sustainable soil and pest management strategies for strawberry production in the SE. The incorporation of cover crops with annual crops is an fundamental practice, especially in organic production, that can help prevent erosion, increase soil organic matter and fertility (Sarrantonio, 2007), break up hard clay soils, disrupt pest cycles, and reduce weeds (Phatak and Diaz-Perez, 2007). Moreover, legume cover crops can fix atmospheric N, leading to increased N availability and yields of the subsequent crop. Cereal cover crops can produce large amounts of biomass, increasing overall soil organic matter (Snapp et al., 2005). Few studies have documented use of cover crops in strawberry production. Lamondia et al. (2002) found sorghum-sudangrass [Sorghum bicolor × S. sudanense (Piper) Stapf] and ‘Saia’ oat [Avena strigosa Schreb.] cover crops decreased pest populations and increased strawberry yield. Elmer and LaMondia (1999) additionally found oat cover crops combined with (NH4)2SO4 fertilizer reduced the incidence of strawberry black root rot. In general, these studies have demonstrated cover crops to benefit strawberries, but none have been conducted in the SE U.S., where climatic and growth conditions differ and higher pest pressures exist.

Selective cover crop species may also improve the arbuscular mycorrhizal (AM) fungal inoculum potential and subsequent crop benefit from AM. Arbuscular mycorrhizas are known to support healthier, higher-yielding crops through increased nutrient acquisition, specifically phosphorus (Smith and Read, 1997) but also K, S, Cu, Z, Fe (Koide, 1991) and N (Hodge, 2003). Extraradical AM hyphae act as extensions of plant roots, increasing the absorptive surface for nutrient uptake. Plant benefits from AM are diverse and include increased shoot and root biomass, higher tissue nutrient concentrations, greater tolerance for drought conditions (Augé, 2001), and greater resistance to soil borne pathogens (Linderman, 1995). Mycorrhizal fungi have been demonstrated to increase strawberry growth and nutrient acquisition (Taylor and Harrier, 2001) and decrease root damage caused by Phytophthora (Norman et al., 1996).

Commercial AM inoculants are available but they generally consist of only one or a few species that may or may not be well-adapted to the soil conditions where they are applied. Locally adapted AM fungal isolates can be produced on farm (Douds et al., 2008) and may be more effective than introduced species (Bull et al., 2005). Selection of cover crops that also function as good AM hosts may increase native AM populations, leading to increased overall belowground functioning (Gosling et al., 2006). Enhancing AM host diversity through crop and cover crop rotations is thought to play a key role in increasing AM inoculum potential and the growth of subsequent AM-dependent crops (Gosling et al., 2006).

There is a variety of summer cover crops species that can be grown in the SE U.S. (Creamer and Baldwin, 2000) and many of these would support AM fungi. Summer cover crops can be integrated into strawberry production in North Carolina where strawberries are harvested by early June and the fields are replanted with new plants in October. During the months of June through August, the fields typically remain fallow. No study that we are aware of has examined the integrated approach of using summer cover crops and beneficial AM inoculants for strawberry production in field conditions.

The primary objective of this study was to examine overall effects of cover crops and arbuscular mycorrhizal (AM) fungi as integrated parts of sustainable soil management practices for organic strawberry production in North Carolina. The first part of this study involves a two-year field study conducted at the Center for Environmental Farming Systems (CEFS) in Goldsboro, NC. In that field experiment, eight cover crop treatments paired with two mycorrhizal treatments (split plot factor) were examined for their effects on strawberries. Cover crop treatments were assessed for their aboveground biomass, impact on weed abundance and diversity, cover crop nutrients, soil nutrients, AM populations, parasitic nematode populations, and impact on subsequent strawberry growth and yields. Strawberry plants were sampled throughout the growing season for biomass responses, yield, and percent AM colonization of roots. The second part of the study was conducted jointly with three strawberry producers in NC (Buckwheat Farm, Iseley Farms, and Indigo Farms (see Fig 1 for location of farms and field research). On each farm, producers selected cover crop species and assisted in setting up a replicated field experiment and with data collection assessing the impact of two cover crop treatments compared to a bare ground control on strawberry yields. Each producer was additionally surveyed for their opinions on the barriers to cover crop adoption in strawberries, interest in adopting organic practices, their thoughts on phasing out methyl bromide, and suggestions for future on-farm research.

Cooperators

Click linked name(s) to expand
  • Sam Bellamy
  • Nancy Creamer
  • Gina Fernandez
  • Jane Iseley
  • Karma Lee
  • John Vollmer
  • Debby Wechsler

Research

Materials and methods:
2 Year Field Research Study (Objectives 1 and 2)

Experimental design. The 2 year field experiment was conducted at the Center for Environmental Farming Systems (CEFS) in Goldsboro, NC, U.S. between May 2007 and June 2009. The field study was designed as a split-plot randomized complete block design with four replications and two factors: cover crop as the main-plot factor (eight treatments) and arbuscular mycorrhizal (AM) inoculum as the sub-plot, split factor (two treatments).

The eight cover crop treatments consisted of two grasses grown alone: 1) sudangrass (SG) (Sorghum bicolor (L.) Moench. cv. Piper) and 2) pearl millet (PM) (Pennisetum glaucum (L.) R.Br. cv. 102 M Hybrid); two legumes grown alone: 3) soybean (SB) (Glycine max (L.) Merrill cv. Laredo) and 4) velvetbean (VB) (Mucuna deeringiana (Bort) Merr. cv. Georgia Bush), two grass / legume combinations: 5) sudangrass / velvetbean (SGVB) and 6) pearl millet / soybean (PMSB); 7) a non-mycorrhizal cover crop host (NONH) consisting of rape (Brassica napus L. var. napus cv. Dwarf Essex) and common buckwheat (Fagopyrum esculentum Moench) in 2007 and 2008, respectively; and 8) no cover crop control (NOCC) treatment. Mycorrhizal pre-inoculation treatments consisted of either a native AM fungal species mix (NAT) or a single AM fungal species, Glomus intraradices, from a commercially available inoculant (COM). The NAT AM fungal species from the baseline sampling and post treatments are listed in Table 1. Cover crop treatments were randomized into four replicated blocks each consisting of eight 6.4 m x 12 m plots for a total of 32 plots. Each cover crop main plot was split into two raised beds 0.91 m x 4.5 m which were spaced apart (2.44 m on center) to prevent mixing of AM sub-plot treatments. Location of cover crop and AM treatments were conserved both years. Soil samples were taken before cover crop and AM treatments were established as a baseline measurement and again after year 2 strawberry harvest. Soils had high phosphorus (437 mg P dm-3) and thus none was recommended for pre-plant fertilization.

Cover crop and field management. Cover crops were planted mid-June each year at the end of strawberry harvest in the piedmont region of North Carolina to correspond to realistic conditions of cover crop adoption. Cover crops were seeded fully across each plot and sudangrass was additionally seeded as a 3.6 m wide buffer between blocks. Legumes were pre-inoculated with either Bradyrhizobium japonicum for soybean or Bradyrhizobium sp. for velvetbean. Cover crops were cut with a 6 ft flail mower the first week of September each year and incorporated with a 21 ft disk. Soil fertility was managed based on initial soil analyses and nutrient recommendations for production in the SE U.S. (Poling and Monks, 2004). Organic pre-plant fertilizers, all OMRI-approved were applied each year after a second disk pass prior to bedding as follows: broadcasted limestone (Crop Production Services, Princeton, NC) at 1800 kg ha-1; sodium borate spray (Crop Production Services, Princeton, NC) at 5.6 kg ha-1; broadcasted potassium sulfate 0N–0P–50K (Coor Farm Supply, Smithfield, NC) at 112 kg ha-1; and broadcasted soybean meal 7N–1P–1K (J. Milo Pierce Farm Center, Pikeville, NC) at 800 kg ha-1. Soybean meal additions constituted 63 kg N ha-1, similar to the recommended 67 kg N ha-1.

Mycorrhizal inoculum. The COM inoculum contained a single AM fungal species (Glomus intraradices) found in commercially available AM inoculant. Only the pure Gl. intraradices spores were used for the COM treatment, rather than the off-the-shelf mycorrhizal inoculant, to separate the effects of the AM species from any additional materials commonly present in commercial inoculants, such as fertilizers and soil additives. The NAT mycorrhizal treatment consisted of a mixture of native AM fungal species isolated from the study site prior to the establishment of the treatments. The following fungal species were identified from the native (NAT) mycorrhizal inoculum: Acaulospora koskei, A. laevis, A. mellea, A. morrowiae, A. scrobiculata, Glomus clarum, Gl. etunicatum, Gl. intraradices, Gl. mosseae, Gl. tenue, two undescribed Glomus sp. (Gl. species 1 and Gl. species 2), Paraglomus occultum, and Scutellospora heterogamaTo develop the NAT mycorrhizal inoculum, twenty random soil samples were taken at a depth of 15 cm from each main plot on April 2, 2007, composited and established as AM trap cultures in greenhouses at North Carolina State University (NCSU). Trap cultures consisted of 300 g of each aggregate field plot soil sample mixed with steam-sterilized soil mix in a 1:4 volume ratio in 6-inch pots. A combination of corn (Zea mays), sudangrass (Sorghum bicolor), and prickly sida (Sida spinosa) were used as host plants and grown for 140 days. Each pot was fertilized with 1 tsp Osmocote 19N–6P– 12K and water was limited in the final days to induce AM fungal sporulation.

Strawberry pre-inoculation and management. Each year, new organic Chandler strawberry tips were purchased from a certified nursery. In 2007 Chandler tips were used, but due to severe disease problems (Phytophthora cactorum) observed in the 2008 Chandler tips, a new set of non-inoculated (without AM treatments), non-organic, Camarosa plugs were purchased. Due to the disease infestation in 2008, the methodology presented in the following paragraph applies to 2007 only. Since the disease took a few weeks to detect, the Camarosa plugs were field planted about one month late on November 13, 2008. After the tips were received, they spent one week in cold storage (1°C) and then were transferred to 50-cell trays and grown in the NCSU greenhouses for 3 weeks under misting benches. Tips were planted in OMRI-approved potting mix and were combined with either the NAT or COM mycorrhizal inoculant. Subsequent analysis revealed at least 40 AM spores per cell. Plants were misted with water 3 to 5 times per day for 15 seconds depending on conditions and fertilized once with organic fertilizers (5N–5P–5K) during the third week of greenhouse growth. Plants were placed outside under shade to acclimate one week prior to field planting.

Plasticulture beds were formed 2 weeks prior to planting and 26 strawberry plugs were planted in each AM treatment bed in 2 rows at 12-inch spacing within each row for a total of 52 plants per cover crop main plot. Only the center 12 plants in each bed were used for yield collection. From March 7 to April 7 2008, potash 0N–0P–60K and OMRI-approved fertilizers 7N–0P–0K were each applied separately via drip irrigation at the recommended rate of 67.25 kg ha-1each over five weeks. In 2009, fertilizers were applied during the same time and the potash rate remained the same, while sodium nitrate 16N–0P–0K comprised 20% of the total nitrogen applied.

Data collection. Soil fertility and nematode community structure were analyzed from composited soil samples collected in spring 2007 and summer 2008. Cover crop plots were evaluated for total weed aboveground biomass and weed diversity at 4 and 8 weeks after planting using 3 randomized 0.25 m2 quadrates per plot. Cover crop biomass was evaluated eight weeks after planting from 0.5 m2 quadrates randomly placed in each plot and all cover crop aboveground biomass within the quadrat was cut at ground level, collected, dried at 60°C for 96 hours, and weighed. Subsamples of this material were sent to the North Carolina Department of Agriculture (NCDA) Agronomic Services Lab for shoot nutrient analyses. In mixed cover crop treatments, the individual species were separated before analysis.

One representative strawberry plant per mycorrhizal treatment bed was collected at five time periods each year in 1) early January, 2) early March, 3) early April, 4) early May, and 5) late May (2008) or early June (2009). These dates were chosen based on key phenological stages of strawberry growth (Fernandez et al., 2001). Whole strawberry plants were removed from the field, washed thoroughly, and leaves, petioles, crowns, roots and fruits/flowers (if any) were separated, dried at 60°C for 96 hours, and weighed. Prior to drying, fresh leaf area was measured. Dried roots were later randomly sub-sampled for mycorrhizal colonization assessment, rehydrated, cleared, and stained. Percent mycorrhizal colonization of strawberry roots was assessed using a grid-line intersect method. Mycorrhizal fungal diversity was assessed through identification of fungal spores from trap cultures developed from five composited soil samples collected from each plot in May 2006 before the treatments were established and again in June 2009. During harvest, marketable yield, cull yield, and average berry weight data were collected on the inner 12 plants within each COM or NAT treatment beds. Average berry weight was calculated based on the number of berries harvested from the same 12 plants; if the number of berries exceeded 25, the calculation was based on a random sampling of 25 marketable berries. Culls were any berries deemed to be unmarketable due to size (<12 g), disease, or deformity.

On-farm Trials and Producer Surveys – Objective 3

Three strawberry growers in North Carolina that represented diverse locations, soil conditions, management practices, and differing experiences with strawberry production and the use of cover crops participated in on-farm trials from June 2008 through August 2009. The three farms were Indigo Farms in Calabash, NC, Buckwheat Farm in Apex, NC, and Iseley Farms in Burlington, NC. Indigo Farms and Iseley Farms grow a large variety of crops, operate diverse roadside stands and pick-your-own operations, and have been in operation for over 100 years. Buckwheat Farm, in
contrast, grows just three acres of strawberries for pick-your-own and farm stand sales and has been in operation for 13 years. All farms represent the diversity of typical strawberry growers and conditions in NC and the SE (Sydorovych et al., 2006) and produce strawberries using conventional practices including raised beds under black plastic and methyl bromide fumigation.
Project investigators met with each producer the year prior to beginning the on-farm research to understand the production and site challenges, to collectively select specific cover crop species to examine for the conditions on each farm, and to develop an agreement of shared responsibilities for managing the cover crops, strawberries, and data collection. Producers selected an appropriate site (average size: 1380 m2) for the on-farm research within the strawberry production area. On each farm two single cover crop treatments were compared to a control (no cover crop; NOCC) and each on-farm experimental site was set up as a randomized complete block design with three treatments and three replicates for nine total plots. Cover crops included cowpea (Vigna unguiculata . var. Iron Clay), foxtail millet (Setaria italic), pearl millet (Pennisetum glaucum cv. 102 M Hybrid), and
soybean (Glycine max cv. Laredo). Randomized soil samples (20 per plot) for soil nutrient analyses, nematode community evaluation, and mycorrhizal fungi assessment were taken from each treatment plot in early June 2008 when plots were established but before cover crops were planted.

Cover crops were seeded in late June 2008 for each farm via hand-held broadcast spreaders. Cover
crop biomass and weed diversity were assessed 8 weeks after planting in all treatment plots on each farm. Cover crop biomass was assessed by harvesting aboveground biomass from one randomly placed 0.5 m2 quadrat per plot. Weed species and abundance were measured by harvesting aboveground biomass from three randomly placed 0.25 m2 quadrats per plot. Cover crops were cut in late August at each farm and then incorporated after an additional two-week period needed for the cover crops to dry and decompose. The fields were then disked and pre-plant fertilizers were applied following typical fertilization practices on each farm (60 lbs N/acre and 50 lbs K/acre
depending on site needs). In mid-September, drip irrigation and plastic beds were formed and fumigated with methyl bromide on all farms. Deer fencing was installed after the bedding process was completed. Strawberry plugs were then planted 2–3 weeks later in early October. Strawberry harvest season typically begins mid-April and goes until early June, but this varied slightly between sites due to climactic conditions. Berries were harvested by the growers according to their own timetable, usually 2–3 times per week. Yield data were taken only from strawberry plants in a delineated center section (2 beds) of each plot to minimize any edge effects. Only the total end-of season harvest, calculated on a per-plant average basis, was used for comparison among cover crop treatments. The research plot at Iseley farms was destroyed by deer mid-season and therefore not included in the strawberry yield analysis.

At the conclusion of the study, the project investigators met individually with each producer to evaluate their experiences with cover crops and the on-farm study, describe the perceived benefits and challenges of using cover crops in strawberry production on their farm, and determine what other sustainable or organic management practices interest them.

Research results and discussion:
Cover crops and weeds- CEFS 2 yr Field Study

Cover crop biomass differed significantly in both years with treatments that included grasses generally being higher (Fig. 6). In both years, the fast-growing pearl millet and sudan grasses produced significantly more biomass than other cover crops. Across years, the pearl millet/soybean and sudan grass/velvet bean combination treatments contained significantly higher concentrations of all nutrients analyzed (results not shown). The average legume biomass component of the mixes was 9% for pearl millet/soybean mix and 16% for the sudan grass/velvet bean mix. After 8 weeks of growth, all cover crops had significantly less weed biomass than the control treatments in both years with the pearl millet and sudan grass treatments showing the most consistent weed reduction (Fig. 6). Treatments containing grasses significantly reduced weed biomass compared to legume species alone (P < 0.01) and all cover crop treatments significantly reduced weed biomass compared to the no cover crop treatment (P < 0.01).

Strawberry yields, growth, nutrients-CEFS Field study

Cover crop and mycorrhizal treatments did not significantly affect average berry weight, cull yield as a percent of total harvest, marketable yield, or total yield in 2008 or 2009 (Table 2), nor were there any interactions among treatments. Analyses of the root, shoot, crown, fruit, and flower weights and leaf area per plant across all sampling dates showed no significant effects from the cover crop or mycorrhizal treatments in either 2008 or 2009, although some of these biomass variables varied significantly between mycorrhizal treatments on individual dates(data not shown). Analysis of strawberry leaf nutrients showed no significant effects from cover crop treatments in either the April (Wilks’ Lambda P = 0.51) or May 2008 sampling periods (Wilks’ Lambda P = 0.87; data not shown). In 2009, cover crop treatment did affect Mg concentration during the April sampling period (the PMSB treatment had significantly lower Mg than all others, P = 0.02), but no differences were found in the June 2009 sample for any nutrient (Wilks’ Lambda P = 0.176; data not shown). Mycorrhizal treatments did significantly differ in their effect on overall nutrient analysis in April (Wilks’ Lambda P = 0.02) and late May 2008 (Wilks’ Lambda P < 0.01), as well as the following year in April 2009 (Wilks’ Lambda P < 0.01); data not shown). Mycorrhizal treatments did not significantly differ in their effect on the overall nutrient status of plants harvested in June 2009 (Wilks’ Lambda P = 0.25). When analyzed individually, in April 2008 the NAT mycorrhizal treatment had significantly higher levels of Ca, S, Cu, and Bo compared to the COM treatment. Additionally, the NAT mycorrhizal treatment had significantly higher levels of N, Fe, and Cu but lower levels of P, K, Mg, S, and Na when compared to the COM treatment in late May 2008 (data not shown). In 2009, many of these mycorrhizal treatment effects did not persist and only Cu levels were greater in the NAT mycorrhizal treatments in April 2009, while Mn and Zn levels were higher in COM treatments in June 2009.

Mycorrhizal Fungi Responses- CEFS Field Study

In both years, cover crop treatments did not significantly affect the percent mycorrhizal colonization in strawberry roots (2008 P = 0.47; 2009 P = 0.08; Fig. 7). The COM treatment had a significantly higher (P < 0.01) mean percent root colonization per strawberry plant in 2008 (37.8% vs. 26.3%), but this treatment effect did not carry over into 2009 when the plants were not pre-inoculated (P = 0.99). The collection date was significant (P < 0.001) across both years, with a general trend of the percent AM colonization increasing over time (Fig. 7).
In baseline measurements, 16 AM fungal species were identified and Gl. etunicatum was the dominant species found in 88% over all the plots (Table 3). A native Gl. intraradices was found in 32% of the plots in baseline measurements. After strawberry harvest in 2009, a total of 23 AM fungal species were identified and Gl. etunicatum again dominated and was found in 100% of NAT subplots and 97% of COM subplots. Gl. intraradices was not recovered in any of the COM subplots and was found in only 22% of NAT subplots.

Participation Summary

Educational & Outreach Activities

Participation Summary

Education/outreach description:
Workshops and Presentations
  • 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 United States.

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

    Dr. Schroeder-Moreno presented project results and general information on sustainable soil management to the Regional Vocational Agriculture Training for Teachers Workshop, CEFS, Goldsboro, NC, July 2007.”Soil Ecology and Sustainable Soil Management, Oral Presentation and field activity.

    Dr. Schroeder-Moreno presented project results and general information on sustainable soil management to the Natural Resources Conservation Service Grassland Ecology Conference Raleigh, NC. May 2007.”Soil biology, mycorrhizas and implications for sustainable soil management”.

Publications
  • Garland, B., M. Schroeder-Moreno, G. Fernandez, N. Creamer. 2010. Influence of summer cover crops and mycorrhizal fungi on strawberry production in the Southeastern United States. HortScience. Accepted for publication.

    B. Garland MS. Thesis Department of Crop Science, NCSU. Jan 2010. Enhancing Strawberry Production in the Southeastern U.S. through Summer Cover Crops, Beneficial Mycorrhizal Fungi, and On-Farm Participatory Research. Major advisor: M. Schroeder-Moreno

    Schroeder-Moreno, M.S., Fernandez, G., Creamer, N. “Cover crop management for strawberry production in the Southeast”. Conference proceedings, Southeast Strawberry Expo conference, Durham, NC, Nov 9 2009

Project Outcomes

Project outcomes:
  • More than 200 people attended presentations, workshops, tours, read conference proceedings across the Southeastern US that discussed the results of this project.

    Results from this preliminary research on cover crops and mycorrhizas are making both conventional and organic strawberry production in the SE more sustainable by enhancing soil health and biodiversity, increasing soil organic matter, breaking pest and weed cycles, and potentially reducing the amounts of extenrioanl synthetic fertilizers in drop irrigation when legumes are used.

    Evidence from this study demonstrates that native mycorrhizal fungi function equally to commercial mycorrhizal fungi as inoculants to strawberry plugs and will likely outcompete and persists in soils longer than commercial AM fungi. This demonstrates the importance of developing sustainable soil management practices without methyl bromide that enhance native mycorrhizal populations.

    From on-farm research and subsequent interviews with producers in this study, we identified farm-level benefits and potential management or other challenges to using summer cover crops and organic production practices in strawberry production systems. 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.

Farmer Adoption

  • All of the grower participants involved in this project are incorporating cover crops in thier strawberry production and one of the producers began organic strawberry production during the project.

    The majority of grower participants in the SE Strawberry Expo workshop were interested in starting cover crops and a few were already using them and exchanged ideas with other producers on ideas for choosing cover crops and management.

Recommendations:

Areas needing additional study

  1. Enhancing cover crop biomass. Strategies that enhance cover crop biomass production (e.g. enhanced seeding rates or an addition of compost), reduce fertilizers, especially nitrogen, and enhance soil biological activity are important priorities for both organic and conventional strawberry producers.

    Developing strategies to enhance native mycorrhizal populations and functions. Mycorrhizal functioning and benefits to crops can differ greatly between greenhouse and real-world field conditions. Our study was the first to evaluate the integrated effects of summer cover crops and inoculation with AM fungi on strawberry production in field conditions. The importance of investigating the effects of cover crops and AM together in field conditions cannot be overemphasized, as soil types, climate, fertility, weed pressures, and other variables can affect the outcome compared to greenhouse conditions where these factors are regulated. The complex functions of AM fungi in agroecosystems and the best management practices thereof are just beginning to be understood. The task remains to determine which cover crops and AM associations most benefit strawberries grown in the SE U.S., and how to package this information into systems-level practices that growers can adopt.

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.