Optimizing Nutrient and Water Management for Organic Mixed Vegetable Production Systems

Progress report for LS20-334

Project Type: Research and Education
Funds awarded in 2020: $299,116.00
Projected End Date: 03/31/2023
Grant Recipient: University of Florida
Region: Southern
State: Florida
Principal Investigator:
Gabriel Maltais-Landry
University of Florida
Co-Investigators:
Kevin Athearn
University of Florida
Eban Bean
Agricultural and Biological Engineering, UF/IFAS
Dr. Carlene Chase
University of Florida
Tatiana Sanchez
UF/IFAS Extension Alachua County
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Project Information

Abstract:

Optimal nutrient and water management are critical to sustainable farming and its goals of maximizing yield, food quality and profitability while maintaining soil fertility and soil health and minimizing environmental impacts. Certified organic growers must rely on non-synthetic amendments (e.g., compost, manure) and nitrogen fixation from legumes to meet crop nutrient demand. However, relying on these fertility sources poses several challenges in terms of balancing inputs and outputs for different nutrients (e.g., nitrogen, phosphorus) and synchronizing nutrient release in sufficient quantity to satisfy crop demand. Resulting organic amendments inputs are typically high to meet crop nitrogen demand and build soil organic matter but can result in phosphorus over-fertilization. Increasing nitrogen inputs via nitrogen fixation can also increase soil fertility, but without proper synchronization of nutrient release, nitrogen transfer to subsequent crops can be low (20-30%), which may increase losses via leaching, especially for sandy soils. Water management will also affect nutrient cycling, with potential impacts on nutrient inputs, yields, crop nutrient uptake, nutrient-use efficiency, and ultimately losses to the environment. Conversely, nutrient and water management affect weed and plant-parasitic nematode abundance, affecting the overall benefits of different nutrient and water management approaches. Ultimately, potential synergies and trade-offs among different nutrient and water management approaches will be site-specific and driven by practical considerations and constraints, affecting economic returns and the likelihood of grower adoption.

The proposed research will combine on-farm trials and a trial on a research station to better understand the linkages between nutrient and water management in organic mixed vegetable production systems in Florida. The ultimate goal is to determine how nutrient and water management can be improved in these systems. Our first objective is to evaluate current nutrient and water management practices of three farms to compute nutrient and water budgets and identify how nutrient and water management can be improved in these systems. In collaboration with these growers, we will develop on-farm field experiments to evaluate the effects of changes in management practices, such as using rainfed cover crop polycultures, different processed organic fertilizers, and/or sensor-controlled irrigation systems. Growers will also provide input as we design the replicated four-system experiment that will compare different nutrient and water management approaches at a research station site, which has similar soil and climatic conditions as participating farms. Finally, we will quantify economic costs and returns for all systems under study to determine their economic viability.

Both sets of experiments will be conducted for two years, focusing on crop productivity, nutrient cycling and soil fertility, soil health, water use, weed and nematode abundance, and economic costs and returns. Research results will be shared with individual growers to identify the most beneficial practices for their operation. We will develop extension materials and hold field days to share our results with the broader farming community. Ultimately, this project will identify how organic vegetable production in Florida and the Southeastern US can become more sustainable by identifying the most beneficial and profitable nutrient and water management approaches.

Project Objectives:

Objective 1: Build nutrient and water budgets with grower participation, using ancillary data and limited sampling, to identify leverage points to improve on-farm nutrient and water management;

Objective 2: Conduct on-farm trials to determine how different systems aimed at improving nutrient and water management affect yields, soil fertility and soil health, water application, and the abundance of weeds and plant-pathogenic nematodes;

Objective 3: Conduct a parallel trial in controlled conditions at UF’s Plant Science Research and Education Unit (PSREU) comparing how different systems developed with grower participation affect the impact of nutrient and water management on the same indicators as objective 2;

Objective 4: Compare the economic costs and returns of alternative nutrient and water management strategies;

Objective 5: Synthesize information and communicate key outcomes to cooperating growers, Extension agents and the farming community via field days, Extension documents, and professional development workshops.

Cooperators

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Research

Materials and methods:

Objective 1

Completed as of 3/2021: Before objective 1 was initiated, we submitted our project to the Institutional Review Board (IRB), including the survey we will use to collect information from growers, and we were approved as exempt. We ensured every member of the team completed the necessary trainings before starting the work. We initiated contact with growers during the summer of 2020 to discuss the project, especially the details of on-farm trials (e.g., factors/treatments to compare, timeline, crops to grow - see objective 2 for details), and two were very responsive (Charley Andrews, John Bitter), participating in many phone calls and email conversations. The third grower was not responsive, and after several emails and phone calls placed between August and November, the decision was made to look for a new cooperator (Cody Galligan, from Siembra Farm) who agreed to join the project. After delays due first to COVID (which prevented face-to-face interactions), then the non-responsive grower, and finally finalizing contracts between growers and UF, in-person interviews are now scheduled to happen in April 2021. While this has delayed our timeline relative to original plans, it allowed us to hire the postdoctoral fellow, who will now participate to all activities.

Completed between 4/2021 and 3/2022: Following Covid-19 protocols, 2h in-person interviews were conducted at each of the participating farms in April and May 2021. Farmers responded to a set of questions describing soil preparation, crop rotations, cover crop practices, irrigation capabilities and set up, nutrient management, and pest management. We reached out to farmers to collect additional information and they responded accordingly. Farmer feedback was considered in the experimental setup at their farm. Their experiences and recommendation also served as a point of reference for the research plots set up at the research farm. 

To be completed in the remaining duration of the project: We will continue collecting the information necessary to compute nutrient, water, and financial budgets, and we will identify leverage points to improve nutrient and water management. 

 Objective 2

Completed as of 3/2022: The original goal of this objective was to compare three systems per farm (two plots per system), on a 0.25-acre field. After discussing with growers and realizing that the systems compared would vary among farms, the research team and growers agreed that it would be more relevant to compare two to three systems using four plots per farm, in order to get the adequate replication on each farm to conduct statistical analyses. In addition, because one cooperator changed, the systems to be compared for that farm changed as well. In collaboration with growers, we established the following treatments to compare:

1. Hammock Hollow Farms: System 1 will consist of a sunn hemp (Crotalaria juncea) summer cover crop vs. sesbania (Sesbania exaltata) for system 2. All other practices are identical between systems, including the cash crops - cauliflower and Romanesco (Brassica oleracea var. botrytis).

2. Frog Song Organics: Both systems will use a millet (Pennisetum glaucum) cover crop in the summer but system 1 will terminate it by mowing and disking vs. grazing by pigs for system 2. All other practices are identical between systems and a cabbage (Brassica oleracea var. capitata) crop was grown.

3. Siembra Farm: All three systems use a sunn hemp (Crotalaria juncea) and sorghum sudangrass (Sorghum × drummondii) summer cover crop but differ in terms of clay amendments: none (system 1), a local on-farm clay source (system 2), or a sand mining byproduct (system 3). All other practices are identical between systems and a cabbage (Brassica oleracea var. capitata) crop was grown.

After establishing systems at each site, the following data were collected:

  • Soil moisture sensors and irrigation flowmeters were deployed (except at Frog Song Organics), with data collection every 15 minutes. Soil moisture sensors were installed in each plot of each site at a depth of 15 cm, and some plots had an additional sensor installed at 30 cm. Data have been recorded but not yet analyzed.
  • Weeds and soil nematode presence were assessed at cover crop termination and during cash crop season in all farms. In all cases, preliminary results showed no difference in weed biomass between treatments for both sampling dates. For soil nematodes, the analysis showed that all farms had negligible soil nematode count prior to CC, at CC termination, and at cash crop season, indicating no potential damage by soil nematodes.
  • Surface soils were collected before and after cover cropping, after system establishment, during the growing season, and/or after harvest at all sites. Additional deep soil sampling was conducted as needed, and intact soil cores were collected from Siembra Farm to determine water release curves in addition to bulk density.
  • Soils were analyzed in the laboratory for inorganic N, potential net mineralization (PNM) as well as some soil health indicators (permanganate oxidizable carbon). Soils for other nutrient analyses were sent to an external lab. Data analysis is ongoing but not yet completed.
  • Cover crops and cash crops (marketable and total aboveground) were harvested and analyzed for nutrient concentrations.

To be completed in the remaining duration of the project: 

  • After preliminary analysis of results from the first year of trials, we will reach out to growers to share results and hear their thoughts.
  • At each location, another round of experiments is planned to start in summer 2022, where the current plan is to replicate the same experiment as in 2021 with a squash crop.
  • A similar sampling scheme will be used for water monitoring (sensors, flowmeters), weeds and nematodes, and soil analyses, along with sampling for cover crops and cash crops. Deep soil coring will be conducted three times per growing season (pre-plant, mid-season, post-harvest) to measure nutrient movement.
  • Lab analyses will be completed for the first year of data for additional indicators (e.g., soil texture, total C and N, loss on ignition, water release curves) and for samples collected during the second year of experiments.
  • Statistical analyses and manuscript writing is planned to be completed for all sites and indicators during winter 2023, before submission to scientific journals in spring 2023.

Objective 3 

Completed as of 3/2022:

Based on grower feedback, we established a six-system comparison at the PSREU in early summer 2021, a change from the original plan of four systems. Each system is replicated four times in a randomized complete block design. There is a business as usual (BAU) system compared to three main alternative systems: a “nutrient-only” improvement, a “water-only” improvement, and a “water and nutrient” improvement. Two additional systems consist of a system where cover crops are rolled and crimped rather than mowed and incorporated, and a system where beds are covered with plastic much (all other systems do not use plastic mulch).

The BAU system uses sunn hemp as a summer cover crop followed by cabbage production in the fall. Fertilization was made with poultry manure exclusively. Drip irrigation was used on a fixed schedule. The "nutrient only" improvement added sorghum sudangrass in the cover crop mixture and split fertilization between manure and NatureSafeTM 10-2-8, the “water-only” improvement consisted of drip irrigation made based on soil moisture sensors, and the "Water and nutrient" improvement combined the other two systems.

After establishing systems, the following data were collected:

  • Soil moisture sensors and irrigation flowmeters were deployed, with data collection every 15 minutes. Soil moisture sensors were installed in each plot of each site at 15 cm, and some plots had an additional sensor installed at 30 cm. Data have been recorded but not yet analyzed.
  • Weeds and soil nematode presence were assessed at cover crop termination and during cash crop season. Preliminary results showed no difference in weed biomass between treatments in both sampling dates. For soil nematodes, the analysis showed that all farms had negligible soil nematode count prior to CC, at CC termination, and at cash crop season, indicating no potential damage by soil nematodes.
  • Surface soils were collected before and after cover cropping, after system establishment, during the growing season, and/or after harvest at all sites. Additional deep soil sampling was conducted. In addition, intact soil cores were collected to determine water release curves in addition to bulk density.
  • Soils were analyzed in the laboratory for inorganic N, potential net mineralization (PNM) as well as some soil health indicators (permanganate oxidizable carbon). Soils for other nutrient analyses were sent to an external lab. Data analysis is ongoing but not yet completed.
  • Cover crops and cash crops (marketable and total aboveground) were harvested and analyzed for nutrient concentrations.

To be completed in the remaining duration of the project: 

  • A spring crop (Swiss chard) was planted in mid-March and will be harvested in May, followed by another round of cover crops and cash crop (squash) in summer 2022. 
  • The implementation of water treatments has been difficult and a new approach will be used starting in April 2022, with the use of timer irrigation to achieve different levels of soil moisture content (verified by soil moisture sensors), as opposed to being controlled directly by soil moisture sensors.
  • A similar sampling scheme will be used for water monitoring (sensors, flowmeters), weeds and nematodes, and soil analyses, along with sampling for cover crops and cash crops. Deep soil coring will be conducted three times per growing season (pre-plant, mid-season, post-harvest) to measure nutrient movement.
  • Lab analyses will be completed for the first year of data for additional indicators (e.g., soil texture, total C and N, loss on ignition, water release curves) and for samples collected during the second year of experiments.
  • Statistical analyses and manuscript writing is planned to be completed for all sites and indicators during winter 2023, before submission to scientific journals in spring 2023.

Objective 4 (to be completed in the next two years) 

Completed as of 3/2022: We did not establish a recordkeeping system to track material costs, labor hours, use of equipment and durable supplies, and marketable yields for the different systems due to resistance from growers to share sensitive information in writing. As an alternative, we have been in constant communication with growers and have collected the necessary information this way, focusing on differences between systems for management and costs.

To be completed in the remaining duration of the project: Continue data collection through communications with growers, and analyze differences between systems, including additional costs for growers (e.g., electric fencing and labor for managing livestock; costs of purchasing, preparing and applying clay).

Objective 5

To be completed in the remaining duration of the project: Research is still ongoing and outreach activities are planned in Fall 2022 as a field day highlighting the similarities and differences of each of the systems considered in this study. Detailed activities for Objective 5 are detailed below. Briefly, we will:

  • Share results with participating growers in spring 2022 and 2023 to receive their feedback on experiments and extension/outreach programs, with  interviews conducted in 2023 being "end-of-project" interviews;
  • Organize a field day at the research station in fall 2022 (with pre- and post-test surveys to assess knowledge gain, aspirations to adopt the recommended practices, level of confidence in practicing a new skill, and changes in attitudes toward the research subject), which should be combined with a virtual field day to present the results from each individual on-farm trial;
  • Produce extension fact sheets, blogs and videos in Winter and Spring 2023, including sharing materials through social media (e.g., Facebook pages, blog posts, YouTube, etc.);
  • Develop a presentation that summarizes key outcomes from the research that several members of the team could present at field days, extension events and/or at the Organic Food and Farming Summit, with a version adapted to be included in guest lectures teaching faculty from the project could share with students in classes;
  • Create an article to be submitted to the Florida State Horticultural Society proceedings, paired with a presentation at that meeting.
Research results and discussion:

After delays due to COVID-19, the project finally ramped up in spring and summer 2021. Sites were setup, samples were collected and processed, and data is being compiled and analyzed. A few unexpected events occurred, most importantly difficulties in setting up the irrigation treatments at the research station, which triggered a change in the approach to define these treatments. A minor related issue was the diagnostic of diseases at the research station (rhizoctonia, fusarium, pythium) which affected growth and may have been caused by difficulties encountered with irrigation.

Preliminary analysis of results so far indicates few significant differences among systems, although non-significant trends (p<0.1) have been noted for some indicators at some sites. A more thorough analysis of results combined with an additional year of data collection will allow us to better determine the effects of the systems on crops, soils and water, if any.

Participation Summary
3 Farmers participating in research

Education

Educational approach:

The educational approach and timeline is described in objective 5 of the research. Most educational and outreach activities will take place in year 3 of the project.

Educational & Outreach Activities

3 Consultations

Participation Summary:

Education/outreach description:

As most educational and outreach activities will take place during year 3 of the project, there is little to report for this year. However, we did have extensive communication and collaboration (interviews, on-farm trials) with the three growers that are participating in the project, even though they are listed above as only 3 consultations.

Participants

No participants
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.