Final report for LS20-334
Project Information
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. Growers will also provide input as we design the replicated 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.
Objective 1: Build nutrient and water budgets with grower participation, using ancillary data and limited sampling, 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
- - Producer
- - Producer
- - Producer
Research
Objective 1
After getting approval from the Institutional Review Board (IRB), we contacted growers during the summer of 2020 to discuss the project, especially the details of on-farm trials (see objective 2 for details). Two were very responsive (Charley Andrews, John Bitter), but the third grower was not responsive. After several emails and phone calls placed between August and November, we looked for a new cooperator (Cody Galligan, from Siembra Farm) who agreed to join the project.
After several delays (COVID-19, non-responsive grower, etc.), 2h-long in-person interviews were conducted at each farm in April and May 2021. Growers responded to questions describing soil preparation, crop rotations, cover crop practices, irrigation capabilities and set up, nutrient management, and pest management. We also collected additional information during follow-up communications. Grower feedback was considered in the experimental setup of on-farm trials, and their experiences and recommendations were used to design research plots at UF's research farm. However, because practices vary tremendously among fields and crops in these highly-diverse operations, it was not feasible to establish consistent nutrient and water budgets for each farm. Instead, we focused on the on-farm trials (i.e., objective 2), which were more elaborate than originally planned and driven by each grower's main research question, which both researchers and growers thought would generate more useful outcomes.
Objective 2
The original goal was to compare three systems per farm (two plots per system). 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 system on each 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 systems:
1. Hammock Hollow Farms: System 1 consisted of a sunn hemp summer cover crop vs. a sesbania cover crop for system 2; all other practices were identical between systems, including the cash crops (cauliflower and Romanesco).
2. Frog Song Organics: Both systems used a millet summer cover crop but system 1 was terminated by disking whereas grazing by pigs was used for system 2; all other practices were identical between systems and a cabbage cash crop was grown.
3. Siembra Farm: Three systems were established that differed in terms of clay amendments: none (system 1), a local on-farm clay source (system 2), or a clay derived from dredging a nearby water retention pond (system 3); all other practices were identical between systems and a cabbage cash 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 that irrigates with a water gun), 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.
- Weeds and soil nematode presence were assessed at cover crop termination and during cash crop seasons in all farms.
- Surface soils were collected before and after cover cropping, after system establishment, during the growing season, and/or after harvest at all sites. Deep soil coring was conducted after the harvest of each cash crop. 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 (e.g., permanganate oxidizable carbon). Soils for other nutrient analyses were sent to an external lab.
- Cover crops and cash crops (marketable and total aboveground) were harvested and analyzed for nutrient concentrations.
After preliminary analysis of first year results, we reached out to growers to share results. After this discussion, Hammock Hollow decided not to continue for a second year, given issues in growing sesbania and limited personnel to maintain the experiment. In contrast, Siembra Farm and Frog Song decided to replicate the first year of trials, using cabbage as a cash crop again - the original plan was to use squash, but both farmers thought growing cabbage again would provide more meaningful results. Hence, we completed another round of trials using the same plots as before (Siembra) or new plots (Frog Song). At both locations, a similar sampling scheme was used for water monitoring (sensors, flowmeters), weeds and nematodes, and soil analyses, along with sampling for cover crops and cash crops. Deep soil coring was conducted after harvest in winter/spring of 2023.
At the end of the project (i.e., as of 5/15/2024), the following activities were completed and/or in progress:
- Lab analyses were completed for all indicators, including crops, soils, and water indicators.
- Statistical analyses and manuscript writing is ongoing, with the following progress made for individual sites:
- A complete manuscript draft for the Siembra site is complete, and journal submission should take place by the end of June 2024.
- Data analysis is still ongoing for the Frog Song site, which will be followed by manuscript writing during the summer of 2024. The target journal submission date is the end of September 2024.
- Because the field trial was not replicated for a second year at Hammock Hollow, data collected at that site is insufficient to generate a peer-reviewed publication.
- As final data analysis and manuscript writing is still ongoing for both sites, we will reach out to growers to share results and outcomes from the full experiment once data analysis and writing is completed, during the summer of 2024.
Objective 3
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 was replicated four times in a randomized complete block design. Four systems grew crops on the flat, with regular tillage and no plastic mulch. Among those four systems, there was a system using common practices compared to three alternative systems: a “nutrient-only” improvement, a “water-only” improvement, and a “water and nutrient” improvement. Two additional systems consisted of 1) a system where cover crops were rolled and crimped rather than mowed and disked and 2) a system where beds were formed and then covered with plastic much.
The system with common practices used sunn hemp as a summer cover crop followed by cabbage production in the fall. Fertilization was made with poultry manure exclusively and 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 fertilizer, the “water-only” improvement consisted of drip irrigation made based on soil moisture sensors and reduced irrigation, and the "water and nutrient" improvement combined the other two systems. The rolled-crimped and plasticulture systems received some of their fertility through the drip tape, as in-season solid fertilization (i.e., manure or fertizer) could not be incorporated in the soil for these two systems.
After the original round of cabbage in fall 2021 to spring 2022, a spring crop (Swiss chard) was planted in mid-March 2022 and harvested in May; all systems used plastic mulch in an effort to reduce weed pressure for the subsequent fall cash crop. Another round of cover cropping took place in summer 2022, and a fall cash crop (squash) was planted in early fall, with harvest completed by late November 2022. In spring 2022, we implemented 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. Despite these improvements, water delivery among the systems was variable, hence final sensor irrigation data analysis will be required to determine the efficacy of the different irrigation 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.
- Weeds and soil nematode presence were assessed at cover crop termination and during cash crop seasons.
- Surface soils were collected before and after cover cropping, after system establishment, during the growing season, and/or after harvest at all sites. Deep soil coring was conducted after the harvest of each cash crop. 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.
- Cover crops and cash crops (marketable and total aboveground) were harvested and analyzed for nutrient concentrations.
At the end of the project (i.e., as of 5/15/2024), the following activities were completed and/or in progress:
- Lab analyses were completed for all indicators, including crops, soils, and water variables.
- A thorough analysis of the soil water and irrigation data will be required to determine the extent to which each water system was implemented successfully or not. If irrigation treatments were not implemented successfully, data analysis and writing will focus on the four systems that were irrigated using common practices.
- Statistical analyses are ongoing and manuscript writing will follow, with a goal of journal submission by end of December 2024. Data analysis and writing for this objective were delayed because growers were not included directly, and we prioritized providing results and outcomes to growers for trials taking place on their farm first.
Objective 4
Throughout the project, we were in constant communication with growers to collect the necessary information, focusing on differences between systems for management and costs, to develop partial budgets.
At the end of the project (i.e., as of 5/15/2024), the following activities were completed and/or in progress:
- Data collection was completed through communications with growers, and data analysis focusing on differences between systems, including additional costs for growers (e.g., electric fencing and labor for managing livestock; costs of purchasing, preparing and applying clay) were computed. The outcomes of these analyses will be included in the papers focusing on individual farms.
- Data collection and analysis for the research conducted at PSREU will continue, and the outcomes of these analyses will be included in the paper focusing on the PSREU site.
Objective 5
As data analysis was progressing, different outreach activities were prepared.
At the end of the project (i.e., as of 5/15/2024), the following activities were completed and/or in progress:
- We shared results from the first year of the experiments with participating growers in spring and summer 2022 to receive their feedback on experiments and extension/outreach programs.
- "End-of-project" interviews conducted with participating growers are planned for summer 2024.
- We organized a field day at the PSREU research station on September 20, 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).
- We will create a virtual field day to present the final results of the project, invite attendees to the original field day, and conduct a follow-up survey.
- Two videos were produced (one per on-farm trial) and posted on UF/IFAS's YouTube channel,
- One blog was completed, focusing on the trial conducted at Siembra Farm.
- Another blog will be completed, focusing on the Frog Song Organics research.
- As data analysis and manuscript writing are completed, we will produce additional outputs:
- Additional blogs and social media communications;
- Formal extension publications (e.g., EDIS).
After delays due to COVID-19, experimental plots were established in Summer 2021, followed by sample collection and analysis. Most on-farm trials changed from the original proposal, and for the most part on-farm trials progressed with limited issues, especially at Siembra Farms and Frog Song Organics. Unfortunately, the on-farm trial at Hammock Hollow Farms stopped after one year.
We experienced more issues at the PSREU research station. Most importantly, difficulties in setting up the irrigation treatments triggered a change in the approach to define these treatments (i.e., from using soil moisture sensor to using timers). We also experienced issues with diseases (rhizoctonia, fusarium, pythium) which affected growth and may have been caused by excessive irrigation. Finally, weed management was challenging due to the use of PVC pipes to protect soil moisture sensor cables, which limited our ability to cultivate and control weeds effectively, except for the plasticulture system that did not rely on cultivation for weed control.
At the end of the project (i.e., as of 5/15/2024), the following conclusions can be made:
- At Siembra Farm, the addition of two different types of clays (dug on site or imported as dredged sediments from a nearby water retention pond) had small or no effect on cover crop biomass production, cabbage yield, soil properties, weed pressure, and nematodes.
- There was a trend of slightly higher yields in the first year with both clays, but it was non-significant, and there was no similar trend in year 2.
- There was a small but significant increase in volumetric water content in plots that received clays, suggesting a greater water retention capacity with clays that could potentially be translated in reduced irrigation.
- Due to the lack of significant differences in yield, the economic analysis showed higher costs for the clay treatments without statistically significant gains in yields and economic returns.
- The small effect of clays at this site could be due to the unusually high levels of soil organic matter (SOM) at this site compared to most other farms in the area, which would reduce the potential benefits of increasing clay content in the very sandy soils of North Central Florida. Indeed, we conducted a parallel greenhouse experiment using a soil with much lower SOM and different levels of clay inputs, and observed greater benefits in this context as compared to the field trial.
- At Frog Song Organics, cover crop grazing by pigs had a small but positive effect on cabbage yield, with important impacts on soil nutrients.
- In both years, cabbage yields were higher when cover crops were grazed as compared to being disked. This was restricted to the general area of grazed plots, with no such benefits in the area where pigs sleep/rest under a shade structure ("housing") or in the area where they defecate. In year 2, when multiple harvests were conducted, there were yield benefits of grazing only for the first two (out of four) harvests.
- Grazing had no impact on weed pressure, but weed pressure increased during the growing season. Root-knot nematodes were in greater abundance at cover crop termination for the grazed plots, although there was no significant difference in nematodes at cabbage harvest.
- We observed nutrient accumulation within the grazed plots, with much higher soil P and K accumulation in the defecation area as opposed to other areas in the grazed plots. This was only observed immediately after grazing, with no differences in nutrients at cabbage harvest. In contrast, there were small differences between the general/housing area of grazed plots and non-grazed plots, at either sampling times.
- Economic analyses indicated that grazing increased net returns in these systems, due to the higher yields and limited increases in costs. However, these partial budgets were made assuming that a grower already had animals on the farm and that no/small additional costs were associated with grazing a millet cover crop; economic outcomes would differ in the case where a grower would not already have animals available for grazing, which would likely increase costs to implement grazing.
- At the research station, as noted above, there were issues with implementing different irrigation systems. As a result, we focus here on the four systems that did not differ in their irrigation practices.
- Summer cover crops produced a larger amount of biomass in summer 2022 vs. 2021, with no differences in biomass produced among systems. The sorghum sudangrass dominated the mixture with sunn hemp in systems where mixtures were grown, resulting in much larger N accumulation in cover crop biomass for systems where a monoculture of sunn hemp was planted.
- Squash yields were much higher in the plasticulture system, with slightly higher yields in the system fertilized with manure and fertilizer as opposed to the system fertilized only with manure. Squash P and K were highest in the system fertilized only with manure.
- Soil nutrient analyses indicate a substantial build-up of soil P and K in the system relying on manure for fertility. Soil pH and CEC were also higher in the manure-only system.
- Weed biomass recorded mid-season was lowest with the plasticulture system, and highest in the systems with no rolling-crimping of cover crop biomass. The rolling-crimping system was not effective with sorghum sudangrass because of regrowth during the growing season; pearl millet might be a more promising grass cover crop in these systems. Nematode populations were low overall.
- Partial economic analysis indicates that the plasticulture system was most profitable, given the higher yields.
Education
The educational approach and timeline are described in objective 5 of the research section. Educational and outreach activities conducted so far include follow-up meetings with growers to share results from on-farm trials, a field day, two videos, and a blog. Additional activities (e.g., virtual field day, additional blogs, official extension publications) will be conducted once data analysis and interpretation are completed.
Educational & Outreach Activities
A blog was produced by UF/IFAS communication.
Participation Summary:
In 2022-2023, We organized one field day at the research station (Sept. 2022) which was attended by 50 people, half of which were growers. This field day consisted in a series of talks, in addition to a visit to research plots where squash had just been planted. The research plot visit included a demonstration of soil moisture sensors, and how to use them. We also held follow-up meetings with the three participating growers, to share results from their on-farm trials and plan the next season.
In 2023-2024, we published two outreach videos (one per on-farm trial) and one blog summarizing the main outcomes at Siembra farm. While people accessed these resources, it's unclear how many of them were growers or agricultural professionals; as a result, the number of participants listed above does not include access to these resources.
As data analysis continues to progress and conclusions become clearer, educational and outreach activities will be completed. These will include a virtual field day focusing on results from the research station, follow-up interviews with growers to present the final results from the project, and dissemination of results through blogs and official extension publications.
A more detailed description of outreach and educational activities is presented in objective 5 of the research section.
Learning Outcomes
During the field day, 79-81% of participants indicated a knowledge gain on 1) how to place a soil moisture sensor in their field and 2) factors that affect how a soil moisture sensor represents the moisture content of a field, based on a pre/post assessment of 42 participants.
During the field day, 74-79% of participants indicated a knowledge gain on 1) the effects of cover crops on nitrogen cycling and 2) the impacts of soil fertility management on vegetable attributes, based on a pre/post assessment of 42 participants.
During the field day, 76% of participants indicated a knowledge gain on soil microbiology, based on a pre/post assessment of 42 participants.
Project Outcomes
For the Siembra Farm project (clay amendments), we found no strong effects of adding clays, suggesting limited benefits. However, this could be driven by the already high soil organic matter (SOM) at this site, which may have masked clay benefits. Additional research conducted with soils poorer in SOM, and with higher clay inputs, could lead to different results, as clays could potentially be more beneficial for soils in poorer condition than those found at Siembra Farm.
For the Frog Song Organics project (cover crop grazing), we found yield benefits for cabbage grown after cover crops were grazed instead of disked. In contrast, nutrient accumulation in some areas of the grazed plots could lead to negative environmental impacts. In addition, although economic analyses indicated benefits of grazing, this partial budget analysis assumed that growers already owned animals; economic outcomes might differ for growers that do not already own animals. Given the promising results obtained with this approach, discussions have been started with both Siembra Farm and Frog Song Organics to develop future proposals focusing on the grazing of cover crops in Florida organic vegetable systems.
For the research station trial, a major conclusion was the lack of suitability of sorghum sudangrass in roll-crimped systems; alternatives (e.g., pearl millet) might be more promising. The plasticulture system was by far the most productive, due to better weed control. Among the other systems, the lack of efficient weed control was a limitation, and determining how to improve yields in non-plasticulture systems remains a critical need for organic agriculture. Similarly, managing the high nutrient surpluses observed when relying on manures for fertility is another concern that remains for organic vegetable production.