Final report for GNC18-270
High tunnels are protected production systems that offer many benefits: disease and pest exclusion, crop season extension, and increase in crop yields and quality. Despite the many benefits high tunnels offer, soils are frequently degraded by intensive production in these systems. This study builds on a current OREI project “A multi-regional approach for sustained soil health in organic high tunnels: nutrient management, economics, and educational programming” that investigates the use of cover crops in high tunnels in regard to agronomic and soils data. We propose to expand this two-year study to include a larger group of cover crop species mixtures in addition to an investigation of belowground arthropods that are involved in high tunnel cover cropping systems. Cover crop plots will be grown in a high tunnel during three growing seasons: over-winter, summer, and fall. Three non-leguminous species will be evaluated with and without hairy vetch (Vicia villosa) or cowepea (Vigna unguiculate). Belowground arthropods (insects and mites) will be isolated using sieve and a lighted berlese funnel system. This work will expand the body of knowledge of high tunnel production and cover cropping by discovering their interplay in affecting belowground arthropod species and abundance.
This study is the first to investigate belowground arthropod abundance in a high tunnel production system and determine the effect of cover crop species. In the study, mites were the most abundant arthropods. In the summer cover crop experiments, more mites were recovered from the buckwheat and cowpea treatment than the other treatments. In the winter cover crop experiments, wheat and vetch, triticale, wheat, and triticale and vetch treatments resulted in fewer mites, indicating that cover crop type may influence mite abundance. In the summer experiment, as soil organic matter increased, mite abundance also increased. However, in the winter experiment, as soil organic matter increased, mite abundance decreased. Therefore, the effects of organic matter on soil arthropod abundance is not clear. As such, more studies are needed to understand why decreases in mite abundance occur with increases in soil organic matter.
Despite studies in open field systems showing a positive correlation between soil water content and arthropod abundance, this was not the case in high tunnels when dry soil conditions occur. Dry soil conditions at the start of the experiments may have resulted in unfavorable conditions for survival. We did not classify belowground arthropod families based on function or measure the impact of arthropods on cover crop decomposition. Therefore, we were not able to assess whether the mites were predators or fungivores, which may have indicated their function in the soil ecosystem. In the study, we did see low diversity of arthropod families in high tunnel systems which may affect soil ecosystem services. This study assessed the relationship between production practices and changes in arthropod abundance. In conclusion, soil management practices in high tunnels can affect arthropod abundance by cover crop type, soil carbon, and organic matter. Understanding how production practices in high tunnels can affect belowground arthropods will help develop best management practices for soil health in high tunnels.
This research project seeks to develop adaptable cover cropping methods in high tunnels and increase our understanding of the belowground arthropod communities. Learning outcomes include: -
- Knowledge regarding soil food web community within high tunnel systems
- Flexible and adaptable cover crop recommendations for growers
- Interaction between cover crop species mixtures and below ground arthropods
- Functional high tunnel crop rotations that include cover crops
This research will influence farmer’s soil nutrient management and production planning in high tunnels in the North Central Region and beyond. Specific behavior changes could include:
- Implementation of season-appropriate cover crops and functional crop rotations in high tunnels
- Adoption of cover crops in high tunnels that promote soil food web activity
- Higher adoption of high tunnels to support local food production using practices that promote soil health
- Extension and other educators provide research-based knowledge to growers that support environmental, social, and economic sustainability
The study site for this project is located in Olathe, Kansas at Olathe Horticultural Research and Extension Center, a research site for Kansas State University. The two-year study took place in a 200 ft. high tunnel that has been used for vegetable research for the past 8+ years. The high tunnel is managed organically and is currently in transition to certified organic status. Three seasons were studied in the project the summer (June-August), winter-killed (August-October), and overwintering (October-April). The 200’ high tunnel includes three 51’ x 24’ experiments and each trial was managed independently. The plot design for the three seasons is split-plot design with the presence or absence of legumes being the main plot factor and the sub-plot factor is the variety of non-leguminous crops used within the treatments. There were 8 treatments and 4 replications per season. Season specific cover crop (CC) species and legumes will be used in each season. Each replication included a bare (weed-free) control as well as a legume-only control. The size of each treatment was 5x4 ft. After each cover cropping season, a cash crop was planted directly into the CC residues to mimic a farmer’s production schedule. The cash crops that were included in the study are listed below:
• Tomatoes- after overwinter CC
• Peppers- after overwinter CC
• Spinach- after summer CC
• Lettuce- after winter-killed CC
Baseline soil parameters such as soil organic matter (OM), available nitrogen (N), water infiltration, soil electrical conductivity (EC), and cation exchange capacity (CEC) were measured at the start of each season. Subsequently, five other soil samples were taken:
1. CC termination
2. 0 weeks after CC termination (when cash crop is planted)
3. 2 weeks after CC termination
4. 4 weeks after CC termination
5. End of cash crop growth
OM, N, EC, and CEC were measured by submitting soil samples to a local soil testing lab for assay. Soil water infiltration will be tested on-site using the protocol outlined by the National Resource and Conservation Service.
Identifying Soil Communities
To characterize soil communities, arthropod soil sampling took place as the cover crop soil sampling occurs. Soil samples taken after CC termination will be important so the belowground arthropod activity can be monitored during CC decomposition. To measure trends in belowground arthropod communities, soil sampling took place during the cash crop growing season and at termination of the cash crop. Soil sampling involved taking twelve to fifteen 5-cm diameter soil core samples from random locations in each plot. The samples were taken from the organic layer (within 10 cm of depth) of the soil (Gorman, 2013) and stored in a cooler until transported to the on-site research lab for further assay. Samples were sieved using a brass soil sieve from BioQuip Products. Insects isolated using the brass sieve were identified to family using a dissection microscope. Smaller insects were identified using a lamp-lighted Berlese funnel system that stimulates extraction of smaller arthropods into 2-ounce vials containing ethyl acetate (Macfadyen, 1961). These smaller arthropods were then identified to family using a microscope (Gorman, 2013). The abundance and families of belowground arthropod species was recorded throughout the experiment at the soil sampling time points discussed earlier. This data was then subjected to statistical analysis using JMP.
Educational & Outreach Activities
This data has been disseminated to growers, educators, and the general public in numerous ways. Ms. Skinner delivered the results of her study at the Great Plains Growers Conference in St. Joseph, MO. She also set up a table and discussed the work with numerous growers at the SAWG conference in Little Rock, AR and the Practical Farmers of Iowa Conference. Ms. Skinner was also proactive in developing curricula on "Identifying Belowground Arthropods", "Soil Compaction and Water Infiltration", and "High Tunnel Production" that she delivered to middle school and high school students through collaborative field days with nearby school districts.
In addition to Ashlee's work, the data that this project has generated has also been incorporated into Dr. Rivard's national extension program. Data as well as general findings from this project make a significant contribution to a presentation titled "Diversifying High Tunnel Production Systems" that has been delivered to growers in KS, MO, IA, WI, PA, and through an eOrganic webinar. Dr. Rivard was also invited to present the results of the project at the American Society of Horticulture Science Conference in 2019 and at grower meeting in Hershey, PA.
Two journal articles have been prepared as a part of Ms. Skinner's thesis, but have not been submitted yet. The thesis can be found at https://krex.k-state.edu/dspace/handle/2097/40667
High tunnel production systems contribute significantly to local food production in nearly all areas of the US and globally. One of the major barriers to the sustainability of high tunnel systems is their (negative) impact on soil health. This project and the data that was collected will directly contribute to better management of soils by high tunnel growers as well as recommendations by educators and/or consultants.
This project added knowledge through data collection related to microclimate, soil physical and chemical properties, and crop yield as they relate to the integration of winter, summer, and fall cover crops. For each season, we were able to identify high-performing cover crops (alone and in mixtures) for maximizing biomass production and subsequent impact on soil. We also found some interesting trends within the data that may be important for moving forward. Nutrient mineralization from cover crop biomass tended to work faster (14 days) during the summer in the high tunnels as compared to the standard 28-30 days that is recommended for open-field systems. Our data also showed that this trend was less dramatic during the spring when soils were cooler. We also found that even in the short time that this study took place (2 years), significant effects on soil OM and other characteristics were found, which is very fast compared to open-field systems. Both of these observations contributed to new knowledge within the research community and help to elucidate the differences between open-field and high tunnel systems. Lastly, this project identified to the research team the drastic differences that below ground arthropod populations have in high tunnels soils as compared to the open-field. In our first sampling, we found almost zero arthropods and found out over time that we would need to water the soil to help promote arthropod activity. Many high tunnel growers have observed that soils can become highly compacted and typically attribute this to intensive production. However, our data indicates that the low soil moisture conditions are likely leading to reduced arthropod populations and these organisms play a critical role in alleviating compaction. These trends are anecdotal due to the way our experiments were designed, and more research is needed to confirm this theory, but it is likely that we have found an important piece to the puzzle of maintaining soil health in high tunnel systems.
A high tunnel tomato grower in Kansas said "I have to learn how to incorporate rotation into my system. The soil in my tunnels is terrible and I need to find a way to fix that."
The biggest success story is one of collaborative research. This project is the first that included Dr. Cloyd and Dr. Rivard working together on high tunnel production systems and this partnership was initiated by Ms. Skinner. By utilizing Dr. Cloyd's expertise in below ground arthropods, we were able to identify some very exciting areas of research. We expect that this partnership will help to develop more grant projects in the future.