Progress report for LS23-376
Project Information
Alley cropping agroforestry systems are multifunctional land use systems that are well-established as effective systems for mitigating climate change and restoring essential ecosystem services. In alley cropping systems, herbaceous annual crops like vegetables are grown in wide alleys between rows of trees or large shrubs (typically leguminous, fruit, nut, or biomass tree species). Such systems are designed and managed to optimize resource-use efficiency and facilitative interactions between species. Given increasing frequency of extreme weather events induced by climate change in the southeastern USA, the ability of trees (with higher biomass and more spatially extensive aboveground and belowground structure than herbaceous species) to buffer many of these extremes is likely to increase resiliency of regional vegetable production. In particular, vegetable crops are especially susceptible to stress induced by heat extremes, which can significantly reduce yields and quality. Microclimate modification can effectively mitigate vegetable crop heat stress, but research on alley cropping systems as a microclimate modification strategy for vegetable production in the region is largely unexplored. Further, there are existing social and technical barriers that limit farmer adoption, including a lack of information on how to implement and integrate alley cropping systems into existing enterprises and a lack of information about the economic feasibility of adopting these systems. The overarching goal of this project is to establish alley cropping as a viable solution for organic and similarly managed vegetable production systems in the face of climate extremes in the southeastern USA. Our specific objectives are to 1) evaluate microclimate [e.g., soil, air, and crop canopy temperature, humidity, soil moisture, crop canopy light (PAR)], crop performance (growth, yield, quality and physiological parameters), vegetable crop mycorrhizal associations, and nutrient (carbon, nitrogen and phosphorus) cycling effects of leguminous tree alley cropping systems [nodulating black locust (Robinia psuedoacacia), or non-nodulating honey locust (Gleditsia triacanthos)] compared to open field systems on two model vegetable crops (winter squash and lettuce) at two soil nitrogen fertilization rates on an established alley cropping site in replicated research farm trials; 2) evaluate vegetable crop management on an established alley cropping site through deployment in a working university student farm; 3) assess the long-term profitability and risk of the leguminous tree alley cropping systems using capital budget valuation models and scenario analysis; 4) evaluate on-farm alley cropping system establishment and management and provide grower outreach through on-farm workshops in each cultural/geographic region of Tennessee (East, Middle, West), including rural and urban locations; and 5) extend knowledge through open-access data and open-access refereed journals, research station field days, and extension publications and videos. Our work will provide innovative research results related to vegetable crop microclimate, crop performance, nutrient cycling, and economic outcomes of leguminous tree alley cropping vegetable systems as compared to open-field systems and extend these results to researcher and grower communities. Our work involves farmers, as well as student farm interns, in the establishment, maintenance, and evaluation of alley cropping systems, and we will provide workshops for interested growers related to tree establishment and vegetable crop management in these systems.
Objective 1. Evaluate herbaceous crop microclimate [e.g., soil, air and crop canopy temperature, humidity, soil moisture, crop canopy light (PAR)], crop performance (growth, yield, quality & physiological parameters), vegetable crop mycorrhizal associations, and nutrient (carbon, nitrogen & phosphorus) cycling effects of leguminous tree alley cropping systems [nodulating black locust (Robinia psuedoacacia), or non-nodulating honey locust (Gleditsia triacanthos)] compared to open field systems on two model vegetable crops [winter squash (Cucurbita pepo var. turbinata) and lettuce (Lactuca sativa)] at two soil nitrogen fertilization rates on an established alley cropping site in replicated research farm trials.
Objective 2. Evaluate vegetable crop management on an established alley cropping site through deployment in a working university student farm. We will train student interns in alley cropping system vegetable production and management, and we will assess intern wellness, satisfaction, and productivity associated with alley cropping systems compared to open-field systems using semistructured interviews and follow up with a questionnaire interns will complete using TurningPoint Technologies.
Objective 3. Assess the long-term profitability and risk of the leguminous tree alley cropping systems evaluated in Obj. 1 using baseline capital budgeting valuation, scenario analysis, and stochastic simulation.
Objective 4. Evaluate on-farm alley cropping system establishment and management at four on-farm sites and provide grower outreach through on-farm workshops in each cultural/geographic region of Tennessee (East, Middle, West), including rural and urban locations.
Objective 5. Extend knowledge through open-access data and open-access refereed journals, research station field days, Extension agent in-service trainings, and Extension publications, webinars, and other forms of social media.
Cooperators
- (Educator)
- - Producer
- - Producer
- - Producer
- - Producer
Research
In spring 2020, we established an alley cropping research site at the University of Tennessee Organic Crops Unit, located in Knoxville, TN near UT’s campus. The site will be used for research in Obj. 1, 2 & 3, given that the trees are of adequate size. The site is a randomized complete block design with four replicates. The systems include a) black locust (Robinia psuedoacacia, a nodulating/nitrogen-fixing legume) alley cropping system, b) honey locust (Gleditsia triacanthos, a non-nodulating/non-nitrogen-fixing legume) alley cropping system, and c) an open field control (no trees). Each alley cropping plot contains three rows of trees (Fig. 1), 8-m (26-ft.) apart with 2-m (6.5-ft.) interrow spacing, with each plot sized 24 by 24-m (78 by 78-ft.).
For objective 1 (Butler, Shekoofa, Wszelaki), we will establish vegetable beds (five slightly raised beds, running parallel to the direction of the tree rows) in each system of warm- and cool-season vegetables and evaluate a model crop of each (winter squash and lettuce) (Fig. 1). A subplot treatment of two N fertilizer rates (40 and 80 kg N/ha using organic N fertilizer such as feather meal) will be established in each plot as a split-plot treatment. Butterhead lettuce (‘Harmony’) transplants will be planted as a double row in each outer bed (i.e., adjacent to the tree rows, Fig. 1), 30-cm (1-ft.) between rows and 20-cm (8-in.) between plants within the row. Beds will be covered with landscape fabric, and a single drip tape placed in the center of the bed for irrigation. To better evaluate microclimate effects, we will produce three lettuce crops throughout the growing season (in each of spring, fall, summer). At maturity, we will evaluate crop yield (number, weight) and quality (marketability using standard USDA grading categories, incidence of tip burn) of at least 16 consecutive plants per subplot. Recently expanded leaf tissues (at least 15 leaves per sub-plot) will be collected for evaluation of crop nutrient status (detailed below). Acorn squash (‘Tay Belle’) will be planted in each of the three center beds in a single row with 0.9-m (3-ft.) spacing between plants. One crop of winter squash will be produced each year (late spring to early fall). At maturity, we will evaluate squash yield (number, weight) and quality (marketability using standard USDA grading categories, incidence of physiological disorders and powdery mildew) from at least 8 plants per sub-plot. At early fruiting stages, recently matured leaves will be collected for evaluation of crop nutrient status (detailed below). Annual winter cover crops will be planted after the fall harvests in each year.
We will evaluate crop microclimate and physiological parameters through data logging/sensor technologies and pressure/photosynthesis chambers (Purdom et al., 2022). Advanced cloud data loggers (ZL6, METER Group, Inc., Pullman, WA) with soil sensors will be used to monitor soil environmental factors including soil water content and temperature, and photosynthetically active radiation (PAR) sensors (SQ-521, Apogee Instruments, Logan, UT) will be used to monitor PAR at crop canopy height in each plot for each crop (lettuce, winter squash). GO USB loggers (Emerson Electric Co., Ferguson, MO) with temperature and humidity sensors will be used to measure plant canopy temperature and relative humidity (RH%) during the growth season. Crop leaf transpiration rates (i.e., gas exchange/stomatal conductance) and quantum yield of fluorescence (as a measure of photosynthetic efficiency) will be measured using a LI-COR-600 Porometer or LI-COR 6400XT (LI-COR Biosciences, Lincoln, NE) to document the physiological response to high evaporative demand (i.e., vapor-pressure deficit, VPD), temperature, and moisture availability at canopy closure.
After canopy closure, physiological parameters including relative water content (RWC) and leaf water potential (LWP) will be measured periodically during the season. All RWC, LWP, and other samples will be collected between 1000 to 1200 EDST. The RWC will be measured on the youngest but fully expanded leaf from the middle part of the plant canopy (2 to 3 leaves per plot), which will be removed and placed in a sealed plastic bag (Gonzalez and Gonzalez-Vilar, 2001). Samples will be placed on ice in the field to ensure that the samples remain fresh and maintain turgidity. Samples will be taken back to the lab and fresh weight measured. The following day, leaf samples will be placed in deionized water for 6–8 h at 4 ⁰C and then weighed again for a turgid weight. Leaf dry weights will be measured after placing leaves in individual paper envelopes and placed in a drying oven at 80 ⁰C for 12 h. RWC will be calculated using the following equation:
RWC = [(Fresh weight – dry weight) / (saturated weight – dry weight)] × 100
For LWP, representative, healthy leaves will be identified (2 to 3 leaves/plot). Each sampled leaf will be covered using a polyethylene zip bag. Once the petiole is cut and the leaf blade is ready, the sample will be pressurized using a pressure chamber (PMS Instrument, Albany, OR) and leaf water potential will be measured (Shekoofa et al., 2020; Augé et al., 2008).
Soil carbon (C) and nutrient [N, phosphorus (P)] cycling will be evaluated through measures of soil (C, N, P) and crop nutrients (N, P), and nutrients in tree litterfall. We will evaluate soil nutrient changes over the course of the study in each treatment as related to soil profile depths with a standard push probe soil corer (1.75-cm internal diameter) to 30-cm depth, and at the beginning and end of the study using a deep hydraulic soil corer to 1-m profile depth. For the standard soil corer, soils will be sampled in fall and spring each year of crop production. Soils will be sampled to a depth of 30 cm, and each core divided into 0- to 5-, 5- to 15-, and 15- to 30-cm soil profile depths. Cores will be collected using a random sampling pattern within each production sub-plot (24 sub-plots). Each sub-plot sample will represent a composite sample of at least five soil profile cores. Soil samples will be evaluated for total soil C and N (by combustion; Flash EA 1112, CE Elantech, Lakewood, NJ), particulate organic matter C and N (POM-C and -N), inorganic N, and Mehlich I soil P as described in our previous work (e.g., Butler et al., 2016, Shrestha et al., 2021). POM-C and -N represent recently derived, relatively labile organic matter with potential for incorporation into more stable organic matter or organic-mineral complexes (a biotic and abiotic process that would largely occur outside the time-frame of this study). Further, we will evaluate C mineralization in a lab-based assay over a 24-hour period (Cmin-24), by capturing carbon dioxide evolved from a rewetted soil sample under laboratory conditions (Liptzin et al., 2022). The Cmin-24 measure largely represents carbon that is available for microbial respiration over a brief time period and is known to respond to changes in cropping systems that lead to longer-term changes in soil C storage. To further characterize soil chemical and physical properties potentially affecting soil C storage, we will measure soil pH and soil bulk density at each sampling time using standard methods. Deep soil core samples will be extracted using a hydraulic soil corer to 1-m depth, and samples divided into 0- to 5-, 5- to 15-, 15- to 30-, 30- to 60- and 60- to 100-cm soil profile depths. Samples will be evaluated as described above for total C & N, POM-C & N, Cmin-24, Mehlich soil P and soil pH.
Crop tissue (collection described previously) will be evaluated for total N and P, using combustion and colorimetric analysis following dry-ashing (e.g., Niklas and Cobb, 2006), respectively. Tree litter fall will be collected using litterfall traps (at least four in each plot) as described by Muller-Landau and Wright (2010). Tree litterfall samples will be weighed in order to calculate litter deposition rates, and samples dried and ground before analysis for total C, N, and P. For each crop, additional soil core samples taken from the crop root zone will be used to extract fresh roots (at least 3 g of fresh root segments) that will be collected for determination of hyphal, arbuscular, and vesicular colonization by mycorrhizae. Roots will be cut in 1-cm sections, rinsed with water, and placed in a cassette in 10% KOH. Roots will be boiled or autoclaved for 15 to 20 min, acidified with 2% HCl for 1.5 h, stained with 0.05% Trypan blue for 1 h, destained in lactoglycerol, and colonization quantified using the magnified intersections method (McGonigle et al., 1990). All data from Obj. 1 will be subjected to Mixed Models ANOVA using SAS 9.4 (Cary, NC) according to a split-plot design to determine differences among treatments.
In objective 2 (Wszelaki, Butler, Velandia), we will evaluate vegetable crop management in alley cropping systems through deployment in a working university student farm. Given alley crop plot size, there is considerable area for vegetable production outside of vegetable crop research plots. This area will also be used for organic vegetable production by interns in UT’s student organic farm internship program (“Vol Supported Ag”, a 100-member CSA program) each year. This will allow student intern training in alley cropping system vegetable production and management. We will assess intern wellness, satisfaction, and productivity associated with alley cropping systems compared to open-field using semistructured interviews and follow up with a questionnaire interns will complete using TurningPoint Technologies. We will conduct semi-structured interviews with all interns to gather information related to employee wellness, satisfaction, and productivity associated with the adoption of alley cropping systems. Key interview themes will be identified and used to develop a survey instrument that accurately captures interns’ perceptions of the topics mentioned above. The survey instrument will include questions from previous studies to assess general worker satisfaction, wellness and perceptions related to changes in productivity (Hobbs, et al., 2020; Krumbiegel et al., 2018; Schwabe and Castellaccil, 2020). A pretest of the survey instrument will be conducted. Then, following Hobbs et al. (2020), interns will complete a questionnaire in a group environment using TurningPoint Technologies. Interns participating in interviews and surveys will be paid their hourly rate while participating. Interviews and discussions associated with the TurningPoint Technologies’ survey will be transcribed, coded and analyzed by PI Velandia with NVivo qualitative analysis software (version 12; QSR International, Burlington, MA).
In objective 3 (Velandia, Trejo-Pech), we will develop capital budget valuation models and conduct financial analysis to evaluate the long-term profitability and risk of adopting alley cropping systems. Baseline capital budgeting valuation, scenario analysis, and stochastic simulation will be conducted to evaluate the profitability and risks of adopting the two alley cropping systems evaluated in Obj.1. We will use the discounted cash flow (DCF) method to build the capital budgeting model and evaluate the profitability of implementing these two alley cropping systems (Brigham and Houston, 2019). Financial metrics such as the net present value, the modified internal rate of return, and the payback period will be estimated for the alley cropping systems proposed in Obj. 1, thus providing profitability measures in terms of dollars, rate of return, and the number of years to recover the investment. Alternative scenarios to the baseline, constructed with sensitive parameters (e.g., yield, price, fertilizer use, and cost) will be evaluated. The rate of sensitivity to the risk of each variable/scenario will be evaluated to determine how influential each variable is (Clemen and Reilly, 2013; Yoe, 2019). Given that vegetable operations are subject to various sources of risk, including production and price risks, uncertainty will be incorporated into the analysis by performing a stochastic simulation with the software @RISK® (Palisade, 2018). The stochastic simulations will provide a distribution of profitability and risk outputs to enrich the economic analysis of alley cropping systems.
Baseline budgets to conduct the abovementioned analysis will be developed using data from field trials, Tennessee farmer survey information, current Tennessee/southeastern vegetable budgets, and focus group interviews with farmers and experts. Farmer surveys will also help determine relevant parameters for the scenario analysis. For alley cropping systems, establishment and maintenance costs will be determined from established field trials. Baseline budgets and assumptions related to changes in fruit yield and quality over time and prediction of heat stress events (assuming heat stress events from the past few years) will be validated using an expert focus group.
We will conduct a mixed-mode survey (i.e., paper/mail and Web) of Tennessee vegetable producers to gather general production and economics information from their farm businesses. Questions will be formulated in a way that could guarantee farmers’ privacy when summarizing survey results. Data collected from this survey include but are not limited to farm crop history, cultural practices, production costs, changes in production practices, input use due to specific weather events (e.g., heat stress), and the impact of weather events on the economics of the farm business.
The baseline costs estimated using survey data will be validated through farmer interviews and an online focus group with Extension personnel and other experts familiar with vegetable production and alley cropping systems. We will use a focus group approach similar to the one used by the Agri Benchmark network, a non-profit network of producers and agricultural experts that aims to analyze and understand the key drivers of current and future trends and developments in global agriculture (Chibanda et al., 2020). We will have a set of four to six participants per focus group. The focus group will be conducted via Zoom. A standard questionnaire will be used and filled in jointly with the focus group members. A moderator will moderate and direct the discussion around the typical farming situation in a typical year. The discussion aims at achieving a consensus for enterprise baseline budgets taking out extreme figures or particularities of these budgets (Chibanda et al., 2020). Additionally, during the focus group, we will gather information about reasonable assumptions related to specific parameters to be included in the sensitivity analysis and stochastic simulation. This information is important given that only two years of data will be obtained from field trials.
We will evaluate on-farm alley cropping system establishment and management through on-farm studies with cooperating farmers in objective 4 (Butler, Wszelaki, Velandia, Memphis Tilth). We will work with cooperating farmers to determine tree species (e.g., leguminous, fruit, or hazelnut based on discussions with cooperating farmers) and aspects of system design and management and assist with and monitor tree establishment (height, stem caliper) and management. Working with cooperating farmers and partner organizations, we will provide grower outreach through on-farm workshops (target of greater than 10 growers per workshop) on alley cropping system design and establishment, and economic considerations, in each cultural/geographic region of Tennessee (East, Middle, West). Grower experiences will be used to develop case studies of design and management considerations. More details of outreach activities associated with Obj. 4 are detailed in the Outreach section of the proposal that follows.
In objective 5 (all), we will extend knowledge gained through each objective to a larger audience through a) open access data and publications in open-access refereed journals, b) presenting results at two research farm field days at the research site (approximately 150 participants per event, primarily growers and other agricultural professionals), c) Extension agent in-service trainings targeted to fruit & vegetable production agents (~100 agents in Tennessee), and d) and prepare Extension publications, webinars, videos and podcasts related to system design, performance, and economics. For more details on this objective, please see the separate section on project outreach.
2024 Annual Report:
For Obj. 1/2, field trials with vegetable crops (acorn squash, lettuce) were established in summer 2023 soon after the project began in late spring 2023. Due to the late season start, the primary purpose of this season was to establish methodological and management details, and to begin to collect data on the vegetable crops, soil conditions, and microclimate variables. Due to difficulties with lettuce establishment, we decided to transition the lettuce crop to kale for the 2024 and 2025 seasons. For acorn squash, at maturity we measured squash yield (number, weight) and quality (marketability using standard USDA grading categories, incidence of physiological disorders and powdery mildew) from each sub-plot. At early fruiting stages, recently matured leaves were collected for evaluation of crop nutrient status. Crop microclimate and physiological parameters, including soil water content and temperature, photosynthetically active radiation (PAR), plant canopy temperature and relative humidity (RH%), crop leaf transpiration rates (i.e., gas exchange/stomatal conductance) and quantum yield of fluorescence (as a measure of photosynthetic efficiency) were measured in late summer 2024 as sensors and datalogging technologies were procured and methodological issues were resolved for the main seasons in 2024 and 2025. Soils were sampled in spring and fall 2023, and spring 2024, and are currently be analyzed for nutrient and quality parameters as described in our methodology. Tree litter fall was collected using litterfall traps (four in each plot) and nutrient analysis is currently in progress. Soil core samples taken from the crop root zone were collected and fresh roots (at least 3 g of fresh root segments) extracted, stained and mounted on slides to determine hyphal, arbuscular, and vesicular colonization by mycorrhizae.
For Obj. 3, we developed the Tennessee fruit and vegetable survey instrument in the fall of 2023. We conducted the survey between January and March of 2024 to assess farmers' use and willingness to use alley cropping systems, as well as the minimum amount they are willing to accept to implement alley cropping. We collected some baseline information that will help us develop our enterprise budgets to conduct the economic analysis. Farmers were surveyed using both web-based and mail versions of the survey. The survey was disseminated at the Pick Tennessee conference in February 2024 and was also advertised through the UT Crops Facebook page. On February 6, we sent the online version of the survey to the contact list of growers for whom we had e-mail addresses (839) and sent reminders on February 19 to those who had not responded to the survey by these dates. As of April 1, we have received 122 responses to the online version of the survey, which represents a response rate of 15%. We are in the process of collecting responses to the mail version of the survey. The mail version of the survey was sent at the end of February to 879 individuals for whom we had mail addresses. A second wave of surveys was sent the first week of March to those who had not responded to the mail version of the survey. Preliminary results suggest that about two-thirds of the respondents are slightly to not familiar at all with alley cropping. Nonetheless, about 60% of the respondents are willing and interested in adopting alley-cropping systems.
For Obj. 4, two on-farm demonstration sites were established. One with a hazelnut/mixed grain alley cropping system, and one with smooth alder (herbaceous crop TBD). Two additional sites are expected to be established during the next reporting period.
For Obj. 5, we began outreach activities. To growers, this included a "twilight tour" of the research farm site in summer 2023 attended by approximately 10 interested growers, two presentations at the Organic Association of Kentucky annual meeting in January 2024 (one by D. Butler, and one by D. Butler and farmer cooperator T. Malone) with over 100 total attendees. For researchers, one oral presentation was given by Ph.D. student G. Geetha at the North American Agroforestry Conference (CATIE, Costa Rica), and one poster presentation (G. Geetha) at the Forest Farming Conference (Roanoke, VA) both in winter 2024. Lastly, the research farm site was used for multiple educational activities for undergraduate and graduate students, including visits and laboratory activities from students in Plant Sciences 275 (Organic Production) and Plant Sciences 415 and 515 (Agroecology).
Educational & Outreach Activities
Participation Summary:
We will have education and outreach components throughout the project, and are primarily associated with Obj. 4 and 5. In year 1, we will use short videos promoted through social media to increase interest in our project among growers, agricultural professionals, and the general public, and to increase awareness of alley cropping systems and their design. Videos will be three minutes or less, and will be posted to YouTube and then distributed on our research farm site (https://easttn.tennessee.edu/), as well as social media posts on our internship Instagram site (https://www.instagram.com/ut_vsa/) and Facebook (https://www.facebook.com/UTProduce/), which have 1,088 and 3,700 followers, respectively. Posts/videos will include topics such as: what is alley cropping agroforestry?, an introduction to our research project, alley cropping tree species selection, and introductions to our project team and grower cooperators. We will also produce an Extension factsheet on “What is alley cropping?” targeted to growers. In year 2, we will continue with video/social media updates and begin on-farm workshops. In each geographic region of the state (East, Middle, West), we will work with our cooperating farmers and partner organizations (Appalachian Resource Conservation & Development Winter School and Memphis Tilth) to conduct on-farm workshops (target of > 10 growers per workshop) on alley cropping system design and establishment, and economic considerations. We will also include alley cropping agroforestry in our research farm field day in year 2 and 3, which will allow those attending (primarily agricultural professionals, organic growers, and university agriculture students) to visit the alley cropping site during the vegetable production phase. In year 3, we will publish trial results in Extension and open-access journal publications (target audience of agricultural professionals and growers), continue videos and social media posts, and create case studies of grower cooperator experiences to be published as an Extension publication. Also, in year 3, we will develop a K-12 hands-on workshop curriculum in agroforestry in conjunction with the STEM coordinator at Lone Oaks Farm, where they currently conduct a wide variety of programs for local public schools, homeschool groups, and 4-H (https://stem.loneoaksfarm.com/stem-programs/). In years 1 to 3, we will create two webinars (through Zoom) on the basics of alley cropping agroforestry (establishment and economics) and grower perspectives on agroforestry, as well as podcasts (e.g., https://utianews.tennessee.edu/articletype/podcast/) on these topics. Project results will be presented at on-farm and research farm field days, the state grower conference (https://www.picktnconference.com/, which had over 700 participants in 2022), scientific society professional meetings (e.g., American Society for Horticultural Science, Soil Science Society of America, American Society of Plant Biologists), and at Extension agent in-service training for Tennessee agents who deal with fruit and vegetable production (~ 100 agents). Our target audiences include growers across Tennessee and beyond, agriculture Extension professionals, NRCS professionals, agricultural researchers, and students (K-12, undergraduate, graduate).
2024 progress report: Outreach activities in the first year of our project were greater than we had anticipated. To growers, this included a "twilight tour" of the research farm site in summer 2023 attended by approximately 10 interested growers, two presentations at the Organic Association of Kentucky annual meeting in January 2024 (one by D. Butler, and one by D. Butler and farmer cooperator T. Malone) with over 100 total attendees. For researchers, one oral presentation was given by Ph.D. student G. Geetha at the North American Agroforestry Conference (CATIE, Costa Rica), and one poster presentation (G. Geetha) at the Forest Farming Conference (Roanoke, VA) both in winter 2024. Lastly, the research farm site was used for multiple educational activities for undergraduate and graduate students, including visits and laboratory activities from students in Plant Sciences 275 (Organic Production) and Plant Sciences 415 and 515 (Agroecology).