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Nutrient Management Program

Nutrient Management Program

Continuing research from 2022-23 and new studies starting in 2023-24

2023-24 Statewide General Plan of Work

  • Funding provided by SB 2500, Specific Appropriation 1510A will support 14 continuing projects started in FY 2022-23 and 5 new projects starting in FY 2023-24.
    • Continuing projects involve corn, cotton, citrus, potato, watermelon, snap beans, tomato, peaches, limpograss, and hemp, plus soil testing and artificial intelligence.
    • New projects involve sod production, blueberry, bahiagrass, and lettuce, plus an effort focusing on site-specific recommendations.
  • Nitrogen and phosphorus continue as the primary nutrients studied.
  • Fertilizer management research is concentrating on the 5Rs of nutrient management: Right Rate, Right Place, Right Source, Right Timing, and Right Water.
  • Most of the research will be done in partnership with grower-cooperators on their fields. Some studies will occur at UF/IFAS facilities.
  • Agronomic and horticultural yield and quality continue as the major foci in fertilizer response research, but most projects have aspects pertaining to the environmental fate of N and/or P. These projects will also increase our understanding of how UF/IFAS will derive site-specific nutrient management recommendations.
  • Most projects include economic analyses.
  • Investigators will share research outcomes and implications for future recommendations with producers, agencies, grower organizations, and other interested parties through a variety of extension activities and products. Project reports and updates will be published on this website.
  • Optimizing N Management for Agronomic Crops

    Optimizing Nitrogen Management by Improved Fertilizer Placement and Utilizing Enhanced Efficiency Fertilizers

    Lead Investigator: Hardeep Singh, Assistant Professor, WFREC-Jay

    Team: Lakesh Sharma (Soil, Water, and Ecosystem Sciences-GNV), Zachary Brym (TREC-Homestead), Sudeep Sidhu (NFREC-Live Oak), Madelyn Grant (Escambia County Extension), Ethan Carter (Jackson County Extension)

    This project addresses BMPs for N fertilizer application in corn, cotton, and hemp (fiber production) in the Florida panhandle. In addition to determining the appropriate fertilizer rate, the right placement and right source of fertilizer are also important for increased fertilizer use efficiency. While broadcasting fertilizer is the most common method for corn and cotton, banding the fertilizer, placing it into the soil, and using enhanced-efficiency materials helps reduce N losses to the environment. The investigators hypothesize that banding N fertilizer and using enhanced-efficiency fertilizers (EEF) for cotton, corn, and industrial hemp will simultaneously increase N use efficiency and crop yield. The findings from this project will help develop recommendations for maximum yield and quality while minimizing nutrient inefficiencies to the environment.

    Expected outcomes: We will gain an in-depth understanding of EEFs and band application of N fertilizers for efficient N management and yield optimization for corn, cotton, and hemp production in the Florida panhandle. We expect to publish up to three peer reviewed articles from this project that will form the basis of improved IFAS nutrient management recommendations.

  • N Rates and Timing for Cold-Hardy Citrus

    Developing Site-Specific Recommendations on Nitrogen Application Rates and Timing for Cold Hardy Citrus Production in North Florida

    Lead Investigator: Muhammad Shahid, Assistant Professor, NFREC-Quincy

    Team: Davie Kadyampakeni (CREC-Lake Alfred), Cheryl Mackowiak (NFREC-Quincy), Danielle Williams (Gadsden County Extension), Sudeep Sidhu (NFREC-Suwannee Valley), Kevin Athearn (NFREC-Suwannee Valley), Ali Sarkhosh (Hort Science-GNV), Jeffrey Brecht (Hort Science-GNV), Mark Ritenour (IRREC-Ft. Pierce)

    Cold hardy citrus (CHC) production is a newly emerging industry in north Florida. Most orchards are 6 to 8 years old or less. UF/IFAS lacks research-based N management guidelines for early maturing CHC grown for the fresh market. North Florida soils are more fertile compared with the south, which translates into potentially lower annual fertilizer requirements compared with traditional citrus-growing areas.

    Due to a lack of site-specific recommendations for N, CHC growers are applying a wide range of N. Growers require customized N recommendations to produce optimum yield and fruit quality. This project is identifying optimum N fertilizer rate and application timing in nonbearing, young, and mature CHC. We are determining optimal horticultural attributes, tree performance, physiological/biochemical attributes, yield, fruit quality, and postharvest life as a function of N rates and application timing. We are also evaluating N rates and application timing in terms of cost and revenues.

    Expected outcomes: 

    • New UF/IFAS N fertilizer application rate and timing recommendations for CHC production in north Florida.
    • Site-specific guidelines on N fertilization and BMPs for CHC production.
    • New IFAS Extension publications describing N management for CHC production in north Florida.
    • Up to three refereed journal articles describing response of young and mature citrus to N fertilizer rates and timing.
    • Improved adoption and awareness of BMPs among CHC growers in north Florida
    • Economic feasibility and potential profitability of using different N fertilizer rates and associated application timing in north Florida CHC production.
  • Precision Ag Research in North Florida

    Precision Ag Research to Fill Knowledge Gaps and Increase Adoption in North Florida Nutrient Best Management Practices

    Lead Investigator: Robert C. Hochmuth, Regional Specialized Extension Agent IV, NFREC-Suwannee Valley

    Team: Sudeep Sidhu (NFREC-SV), Vivek Sharma (Ag and Bio Engineering, GNV), Lakesh Sharma (Soil, Water, and Ecosystem Sciences-GNV)

    Collaborating Extension Faculty: Shivendra Kumar, Kevin Athearn, Mark Warren, Tatiana Sanchez-Jones, Jay Capasso, Emily Beach, Tyler Pittman, Dan Fenneman, Jim DeValerio, Keith Wynn

    Agronomic row crop and vegetable water and nutrient management are top priorities in the heavily agricultural Suwannee Valley, as this region’s soils are vulnerable to nutrient loss. The current BMAP requires a reduction in N load to the basin by 4.2 million lbs. Current work by the investigators focuses on developing site-specific corn, potato, snap bean, carrot, and watermelon N rates, optimizing nutrient application methods, and testing high-technology N sources like controlled-release fertilizers (CRFs) for optimum rates and application timing. Site-specific nutrient management is incomplete without proper irrigation scheduling and variable rate irrigation technology. Last year, we acquired specialized equipment to support current FDACS-funded projects and to increase the capacity of NFREC-SV to conduct site-specific N and BMP research at the Center and on cooperating farms.

    Goals and objectives:

    • Demonstrate and evaluate the 5Rs concept of nutrient management on various crops that will lead to updated IFAS recommendations and grower adoption of same.
    • Summarize the ongoing research and extension activities being conducted in the Suwannee Valley, both at NFREC-SV and on cooperating farms.
    • Document progress toward adoption of BMPs and N load reductions on farms in the region.
    • Provide regional level activity coordination and communications between BMP project leaders and stakeholders in the Suwannee Valley.

    Expected outcomes: We will improve our capacity to integrate precision agricultural techniques and BMPs that will generate site-specific nutrient and water management recommendations. This project will result in research findings on which N rates, including specific nutrient and irrigation management systems, can be used to update UF/IFAS recommendations on key agronomic and vegetable crops grown in the Suwannee Valley. We plan to begin to document adoption of specific BMPs on targeted crops in the region.

  • Advanced Tools to Estimate Crop N and P Requirements

    Quantifying Nitrogen and Phosphorus Losses Using Advanced Tools to Estimate Nitrogen and Phosphorus Requirements

    Lead Investigator: Lakesh Sharma, Assistant Professor, Soil, Water, and Ecosystem Sciences

    Team: Sudeep Sidhu (NFREC-Live Oak), Hardeep Singh (WFREC-Jay), Diego Leitao

    FDACS and FDEP have funded N and P fertilizer rate/nutrient management studies for corn and potatoes from 2022 to 2025. The only research gap in the project scope is measuring nutrient stress using advanced agricultural tools to develop site-specific nutrient recommendations. This project will further improve N and P recommendations for these crops. The investigators propose to acquire powerful plant canopy analyzer instrumentation to detect the non-destructive stress of N and P in corn and potato, respectively, by measuring photosynthesis, respiration, chlorophyll fluorescence, hyperspectral, and phenotypic measurements. The project objective is to determine phenotypic parameters to detect N and P stress from rate studies to develop BMPs to improve N and P fertilizer use efficiency.

    Expected outcomes: We will determine plant stress due to N and P that cannot be detected with the naked eye or under destructive lab analysis. The project will fill the gap in the ongoing projects to understand nutrient uptake behaviors of Florida crops using advanced agricultural tools. Peer-reviewed articles will be published that will serve the basis for refining corn and potato nutrient management recommendations.

  • Optimizing P Management for North Florida Snap Bean Production

    Optimizing Phosphorus Management for Snap Bean Production in North Florida

    Lead Investigator: Guodong (David) Liu, Associate Professor, Horticultural Sciences-GNV

    About 27,000 acres of snap beans are harvested annually in Florida. Florida soils require site-specific phosphorus (P) management practices. One P fertilizer recommendation for the entire state is insufficient due to widely ranging production conditions. There is an urgent need for bean growers to have site-specific P recommendations. The combination of the optimal P rate and an efficient method of P application is essential for maximizing the P use efficiency when growing snap beans. To achieve this, it is crucial to understand P dynamics in soil and quantify bean yield response to P fertilizer rates and application methods. Increasing P use efficiency will reduce production costs and will achieve the utmost output of bean yield and quality, which in turn will lead to maximum profitability for growers.

    The research and extension goals and objectives of this proposed project are to maximize the P use efficiency for snap bean production via optimizing P rates and identifying the optimal P application method. The specific objectives:

    • Conduct soil testing and calibration with seven P rates through applying dry granular P fertilizer at the Hastings Agricultural Education Center.
    • Compare P application methods with the same seven P rates via dry granular fertilization and fertigation by drip irrigation at PSREU-Citra for snap bean production.

    Disseminate the new findings to current and potential snap bean growers and other professionals via in-person or virtual field demonstrations, workshops, factsheets, and peer-reviewed publications.

    Expected outcomes: 

    We expect to produce practical information on sustainable P fertilizer application rates for snap bean production on sandy soil in north Florida. Specific project outcomes include:

    • Best snap bean P rate specific for sandy soil in north Florida.
    • One refereed journal publication.
    • One EDIS publication.
    • One in-person field day demonstration at HAEC.
  • P Fertilizer Source and Application Timing for NE Florida Potato Production

    Phosphorus Fertilizer Application Timing and Source Study for Potato in NE Florida

    Lead Investigator: Christian Christensen, Regional Specialized Extension Agent II and Hastings Agricultural Extension Center Director

    Team: Lincoln Zotarelli (Horticultural Sciences-GNV), Lakesh Sharma and Kelly Morgan (Soil, Water, and Ecosystem Sciences-GNV)

    Florida’s potato growers are required by law to enroll in the State Best Management Practices (BMP) Program and implement applicable BMPs or conduct water quality monitoring to demonstrate that total maximum daily loads for N and P comply with water quality standards.

    This proposal will advance studies on P fertilizer rate by evaluating P fertilizer application timing and source on chip potato yield and quality. These efforts will support and refine an interim IFAS P fertilizer recommendation that considers commercial production practices, weather, growing season, and soil conditions. These efforts will support future implementations of site-specific nutrient management plans that are better aligned with BMPs for the TCAA by identifying optimum application timing and source of P fertilizer to achieve maximum yield and quality goals of the grower and minimize nutrient inefficiencies to the environment.

    The objective of this project is to determine the optimum phosphorus fertilizer source and timing of application for potato production in northeast Florida considering soil P availability using either Mehlich-1 (M1) or Mehlich-3 (M3) soil testing (contingent on 2022 and 2023 season findings), total and marketable tuber yield, plant biomass and P uptake accumulation, and P-fertilizer use efficiency to support an update of the current UF/IFAS P fertilizer recommendation rate.

    Expected outcomes: Barring weather issues like the hail damage we experienced in 2023, this project will yield peer-reviewed, published manuscripts that clearly demonstrate the evaluation of current IFAS-recommended fertilizer/nutrient management practices and justify updating and modernizing these recommendations and BMPs to maximize yield and quality goals of growers and minimize nutrient inefficiencies to the environment.

  • Benchmarking Site-Specific Nutrient Management Practices

    Benchmarking Site-Specific Nutrient Management Practices in Florida Cropping Systems

    Lead Investigator: Emma Matcham, Assistant Professor, Agronomy-GNV

    Team: Kelly Morgan (Soil, Water, and Ecosystem Sciences-GNV), Michael Dukes (Center for Land Use Efficiency-GNV), Lincoln Zotarelli (Horticultural Sciences-GNV), Lauri Baker and Ricky Telg (Center for Public Issues Education-GNV)

    This project will directly address SB 1000 from the 2022 legislative session. The goals and objectives are:

    1. Benchmark current methods used by certified crop advisors (CCAs) to make site specific nutrient management recommendations.
    2. Develop a minimum data set for future site-specific nutrient management trials.
    3. Generate a glossary of terms relevant to site-specific nutrient management.
    4. Develop a generic nutrient management decision matrix based on the minimum data set and 5Rs stewardship concepts to serve as a basis for commodity-specific, site-specific recommendations.

    Expected outcomes: 

    Research deliverables:

    • A report on the results of the CCA survey, indicating which site characteristics and information sources are currently being used by crop advisors for site-specific nutrient management recommendations in the state of FL. Responses will be organized by 4/5R categories to ensure that these fundamental concepts of crop production are being used.
    • A minimum data set protocol and associated fillable data sheets for use in future UF/IFAS nutrient management trials and modeling (including AI). Protocols will include definitions from the glossary of terms for site-specific nutrient management.
    • Report to Plant Nutrient Oversight Committee (PNOC) on nutrient management decision matrix for input and suggestions for next steps. Once approved by PNOC, the matrix will be disseminated to UF/IFAS, and those involved in production agriculture.

    Extension deliverables:

    • Meetings with farmers and crop advisors about their site-specific nutrient management needs and to encourage their participation in future precision nutrient stewardship programs.
    • An EDIS publication clarifying important site-specific nutrient management terms.
  • Artificial Intelligence for Improved Crop Nutrient Management

    Using Artificial Intelligence for Improved Crop Nutrient Management

    Lead Investigator: Lincoln Zotarelli, Professor, Horticultural Sciences-GNV

    Team: Joel Harley and Alina Zare (Electrical/Computer Engineering-GNV), Carlos Messina (Horticultural Sciences-GNV), Kelly Morgan and Lakesh Sharma (Soil, Water, and Ecosystem Sciences-GNV)

    The fact that Florida grows more than 300 agricultural and horticultural commodities leads to a fragile balance between agricultural sustainability and natural resources. Recent advances in agricultural techniques (e.g., new cultivars, precision ag, etc.) are leading to an overall increase in crop yield. It will be impossible to determine site-specific fertilizer recommendations for all crops using traditional field trials in multiple locations to keep IFAS recommendations up to date. Furthermore, agricultural practices have evolved and are rapidly improving to balance producer needs and environmental impacts. To address this quandary, we propose to use available data collected from several data sources evaluating crop nutrient requirements (e.g., traditional academic research plots and on-farm trials) to train an artificial intelligence (AI) model (specifically, a multi-layer perceptron) and a Decision Support System for Agrotechnology Transfer (DSSAT) crop model using field data from potato N and P fertilizer rate and application timing studies to predict tuber yield, soil measured mineral N and P, and potential leaching. We will use these sources to build a database that can be continually updated and used to provide optimized crop nutrient recommendations and develop recommendations for new crops. The fundamental change we proposed in this funding cycle is the merging of AI models to support further development of DSSAT models and vice-versa.

    The AI effort started in 2021 (LBR – Phosphorus calibration project) led by Dr. Kelly Morgan and Dr. Zotarelli. Currently, the AI team of graduate students, undergrads, and a postdoc is working to develop a hybrid model comprised of a process-based crop model (DSSAT) and a machine learning (ML) model to estimate the soil mineral N concentration and fate. The work is based on the previous efforts of the team to organize the field data of several potato trails conducted between 2010 and 2014 by collaborating with Dr. Zotarelli’s group. Amid limited field sampled observations for the ML modeling training, the team used DSSAT to replicate the observed data. The team was able to simulate the daily time series of soil mineral N and potato growth (tuber dry weight, plant dry weight, tuber N uptake, plant N uptake, and tuber yield) under varied applied N fertilizer rates and timings using a calibrated DSSAT model. So far, we have developed a ML model based on a long-short term memory (LSTM) method to estimate the soil mineral N. In the new funding cycle, we will use these DSSAT simulated results and ML model estimated soil mineral N to develop another ML model to estimate plant growth (tuber dry weight, plant dry weight, tuber N uptake, plant N uptake, and tuber yield). The combined ML model (both for soil N and plant growth) would aid in establishing a crop nutrient recommendation system considering the variations of site-specific and weather patterns as an ultimate goal of this project.

    The use of AI to improve crop nutrient recommendation is a long-term project that consists of three primary thrusts: 1) the development of a consistent data collection framework for agricultural field trials to ensure collected data is compatible with current and future AI efforts; 2) development of statistical machine learning models to aid in crop nutrient recommendations; and 3) development of hybrid AI modeling approaches for nutrient recommendations focusing on N initially, and later P. Dr. Joel Harley, Dr. Alina Zare, and Dr. Carlos Messina specialize in AI, ML, and predictive algorithms and directly support the development of AI and crop modeling.

    Thrust 1: Statistical machine learning (ML) models, a subset of artificial intelligence (AI) based methods, are trained in a primarily data-driven manner. Thus, the mechanism and organization of data collected play a significant role in developing approaches’ resulting performance and success.  We will continue developing a data collection framework to share with field teams to ensure data consistency, completeness, and quality across the sites.  The scope and complexity of the analyses will continue to develop as more datasets are contributed to the AI project. Based on the experiences and feedback from field teams, this framework will be adjusted.

    Thrust 2: In addition to designing a data collection framework, we will continue training our current ML model using additional field data from ongoing potato N fertilizer rate studies and published data to predict tuber yield, soil-measured mineral N, and plant N accumulation. We will also conduct ablation studies to determine features that are most critical in predicting yield. 

    Thrust 3: We will develop a hybrid ML modeling approach to support nutrient recommendations associated with DSSAT. The objective is to develop robust approaches to incorporate DSSAT results in the ML model and fine tune the ML model using observations. This approach would improve our understanding of the potato-agroecosystem to develop a crop nutrient recommendation system.

    Expected outcomes: 

    • A data collection framework for agricultural field trials, identifying the required dataset compatible with current and future AI efforts that will be made available to collaborators.
    • The statistical ML models developed in the project will be used to further refine crop nutrient recommendations for N (primary) and P (future), and to predict yield and crop nutrient removal.
    • The capabilities of DSSAT will improve by calibrating the ML model alongside DSSAT. Outputs can be used to improve AI models to further refine nutrient recommendations focusing on N.
    • The results from these project will be used to further leverage funds from Federal Funding Agencies (e.g., NIFA, NSF, etc).
  • Evaluating Site-Specific Plant P Bioavailability and Soil Testing Accuracy

    Evaluation of Site-Specific Plant Phosphorus Bioavailability and Lab Accuracy on Mehlich-3 P Fertilizer Recommendations

    Lead Investigator: Vimala Nair, Research Professor, Soil, Water, and Ecosystem Sciences-GNV

    Team: Kelly Morgan (Soil, Water, and Ecosystem Sciences-GNV)

    The basic assumption of current UF/IFAS recommendations is that Mehlich 3 (M3) soil test results are consistent from site-to-site and from lab-to-lab. Data from the 1st and 2nd years of legislative supported crop nutrient studies indicate various problems associated with M3-P determinations that include: 1) M3-P results compared with Mehlich 1 (M1)-P vary from site-to-site, 2) M3-P determination for the same soil sample varies substantially across different commercial labs, and 3) variation in M3-P values depends on method of analysis (colorimetry vs. ICP). Since the relationship of M3-P or M1-P to yield will also vary from site-to-site, recommendations may vary because of differing soil characteristics found in different parts of Florida.

    The objectives for our 3rd year of work are:

    1. Develop and refine M3-P recommendations across all locations in Florida.
    2. Identify additional site-specific components for locations that do not follow the expected trend.

    The intent of this work is to evaluate the influence of the various soil parameters that are site-specific, particularly above the change point (Soil Phosphorus Storage Capacity; the threshold P saturation ratio, PSR = 0.1 identified for Florida soils), on M3-P recommendations. When the SPSC is positive, P is expected to be associated primarily with Fe and Al. We would also confirm any P in the solid state below the change point via X-ray diffraction on representative soil samples, especially when there is underlying calcareous material below a thin surface soil layer.

    Expected outcomes:

    • Obtain a M3-P recommendation for Florida soils corresponding to the “high” of 30 mg/kg M1-P applicable over a range of soils.
    • Suggest alternate M3-P recommendations (e.g., use of other extractants) for those soils that are outliers from the M3-P recommendation above.
    • Obtain the relationship of M3-P with other soil components (pH, elemental content, organic matter etc.), before and after the change point to evaluate the potential to address variability under site-specific conditions.
    • Identify the period within which M3-P should be analyzed after soil collection to obtain consistent values.
    • Document changes in M3-P values if the ratio of soil to extraction solution changes.
    • Document site-specific variation in M3-P when determined using the colorimetric and ICP methods.
  • N Fertilizer Recommendations for Sod Production

    Developing Optimal Nitrogen Fertilizer Recommendations for Sod Producers in Florida

    Lead Investigator: A.J. Lindsey, Environmental Horticulture-GNV

    Team: Bryan Unruh (WFREC-Jay), Emma Matcham (Agronomy-GNV), Prissy Fletcher (St. Johns County Extension)

    This project is focused on improving nutrient management recommendations for sod producers as part of Florida’s best management practices (BMPs) program. This project will evaluate the current UF/IFAS N fertilizer recommendations for Florida sod producers that are based on a 1988 Electronic Data Information Source (EDIS) publication that was last revised in 2016. The origin of these nutrient recommendations is unknown, but it is likely based on legacy input from former UF/IFAS faculty. There are essentially no published research results on Florida sod production. The time it takes to harvest sod is a result of nutrient inputs (among other things). Stakeholders recognize the need to update N management recommendations to shorten the length of time to harvest while also considering water quality impacts.

    The goal of this project is to evaluate N fertilizer rate recommendations for Florida sod growers to achieve yield goals (shorten time to harvest) without negatively impacting water quality. The objectives include:

      1. Quantify yield (time to harvest) and N and P leaching from different N fertilizer rates during Florida sod production.
      2. From the data collected, provide justification to update and optimize N fertilizer management recommendations for Florida sod production that will shorten the sod harvest time while reducing water quality impacts.

    Expected outcomes: The expected outcomes are the optimization of N fertilizer management recommendations for Florida sod producers that reduce the time it takes to harvest a crop while minimizing potential N losses through leaching. The results will be used to validate or update UF/IFAS N fertilization recommendations to aid Florida sod producers across the state.

  • N-P-K Application Rates for Low-Chill Peaches

    Developing a Guideline on Nitrogen-Phosphorus-Potassium Application Rates and Timing for Low-Chill Peaches Grown in Florida

    Lead Investigator: Ali Sarkhosh, Associate Professor, Horticultural Sciences-GNV

    This project is currently funded by FDACS/SCBG. There are more 2,000 acres in Florida peach production, but no Florida-based NPK fertilizer recommendations are available to commercial growers. The current work is aimed at developing guidelines to adjust NPK fertilizer application source and rate for growing Florida peaches. The results of this study will improve BMPs for environmental sustainability while optimizing tree growth, fruit quality, and fruit yield. This information is essential to industry expansion, profitability, and environmental sustainability leading to a strong Florida peach industry.

    The objectives of this project are to 1) determine the influence of NPK application rates, splitting the applications among four phenological stages; 2) determine the fate of NPK nutrients applied at different application rates, as fertilizer application is split to coincide with four different phenological stages; and 3) provide extension resources for grower training and education and develop a statewide roadshow to extend project lessons to growers. As the science develops, recommendations for optimum NPK rates for Florida peach production will be released to the industry.

    Expected outcomes: We expect to develop an NPK application guideline for Florida peaches that will improve fruit quality and tree growth while reducing fertilizer loss. This project will improve grower returns by increasing fertilizer use efficiency. We expect that new peach fertilizer recommendations will be adopted by Florida growers as a result of a rigorous extension education program.


  • N Fertilization Requirements for Blueberry Production

    Determining Nitrogen Fertilization Requirements for Commercial Blueberry Production in Florida

    Lead Investigator: Jeff Williamson, Professor, Horticultural Sciences-GNV

    Team: Gerardo Nunez (Horticultural Sciences-GNV)

    Currently there are no research-based N fertilizer recommendations for commercial blueberry production in Florida. Blueberry fertilization, particularly N, is complicated by commercial farming practices. Growers use pine bark as a soil amendment. Pine bark can affect the availability of N fertilizer, depending on its age, level of decomposition, and amount used. Pine bark can also increase soil porosity and lead to more nutrient leaching.  Pine bark use is not standardized among growers; some use more and others use less. We have identified two commercial blueberry farms where we can apply contrasting N fertilization rates at the time we monitor pine bark decomposition. These farms (Straughn Farms in Alachua County and Wild Goose Farms in Lake County) have agreed to participate in the project, and each has a strong history of collaboration with UF/IFAS Research and Extension programs.

    The project goal is to determine N fertilization needs for bearing southern highbush blueberry plants grown in pine bark production systems. With multiple years of funding and research, the overall objective is to establish N fertilizer guidelines for maximum berry yield and high fruit quality while minimizing nutrient inefficiencies. Specific objectives for FY 2023-24 include:

    • Evaluate southern highbush blueberry yield responses to five N fertilizer rates at two commercial farms.
    • Share information on southern highbush blueberry fertilization practices that maximize agronomic productivity while minimizing nutrient losses.

    Expected outcomes: At the end of FY 2023-2024, we expect to have first year data about the impact of N fertilizer rates on blueberry fruit yield and quality. Additionally, we expect to have a detailed look at the impact of fertilization rates on leaf N concentrations. As stated previously, blueberry is a woody perennial plant with significant carryover affects from one year to the next. Therefore, while we do not expect to be able to make nutrient recommendations for blueberry, we expect to have started to build the experimental site and data set required for this purpose. However, additional years of fertilizer treatments and data collection will likely be needed to understand the effects of different N fertilizer rates on blueberry growth, yield, and overall productivity across seasons.

  • Site-Specific N and P Fertilizer Rates for Florida Citrus

    Developing Site-Specific Nitrogen and Phosphorus Rates for Young and Mature Sweet Oranges, Grapefruits, and Mandarins in Florida

    Lead Investigator: Davie Kadyampakeni, Associate Professor, CREC-Lake Alfred

    Team: Kelly Morgan (Soil, Water, and Ecosystem Sciences-GNV), Alan Wright (IRREC-Ft. Pierce), Muhammad Shahid (NFREC-Quincy), Mark Ritenour (IRREC-Ft. Pierce), Lorenzo Rossi (IRREC-Ft. Pierce), Kimberly Morgan (SWFREC-Immokalee), Danielle Williams (Gadsden County Extension), Mongi Zekri (Hendry County Extension), Chris Oswalt (Polk County Extension)

    Current citrus nutrient guidelines based on studies of healthy citrus trees conducted in the pre-Huanglongbing (HLB) era may no longer be valid for the present situation where 100% of mature citrus trees in Florida are HLB-affected. We are conducting research on N and P fertilizer effects on young/mature citrus cultivars including sweet oranges, grapefruits, and mandarins. Our project is evaluating five N rates and five P rates.

    Fertilizer rates address the objective of evaluating different levels of N and P in identifying the appropriate site-specific rate of N and P for HLB-affected citrus using site soil characteristics and production practices to determine if we need to increase or decrease current guidelines for N (200 lbs/acre) or P2O5 (15 lbs/acre). Using fertigation and controlled release fertilizer (CRF) fertilization sources, we should be able to develop and provide site-specific N and P guidelines for young and mature citrus trees of sweet oranges in central and southwest Florida, grapefruits in the Indian River district, and Satsuma mandarins in north Florida.

    The objectives of this study are:

    1. Evaluate the impact of two forms of N and P fertilizer on yield (including size distribution and percentage of healthy vs. HLB symptomatic fruit), juice quality, fruit shelf-life, tree growth, physiology, and environmental quality.
    2. Determine the optimal N and P rate for young and mature citrus trees at different citrus growing zones (south, central, and north) in Florida based on soil characteristics.
    3. Assess nitrate and orthophosphate leaching as a function of fertilization rate and fertilizer source/form.
    4. Determine optimal horticultural, tree performance, physiological and biochemical variables as result of fertilization rate and fertilizer form.
    5. Conduct an economic analysis of profitability estimates based on underlying cost and revenue estimates specific to varying fertilization rates and sources.

    Expected outcomes: 

    • Site-specific updates and guidelines on N and P fertilization and BMPs.
    • Refereed journal articles and extension bulletins showing response of young and mature citrus to different N and P rates in different growing regions.
    • Changes to UF/IFAS N and P recommendations for citrus trees affected with HLB through PNOC if the project determines this is needed. Revision of the Florida Citrus Production Guide will follow.
    • Revised SL253 (the “Nutrition of Florida Citrus Trees” EDIS publication) in the long-term based on the results of this work.
    • Improved adoption citrus BMPs by growers.
    • Document economic feasibility of costs and benefits of using selected fertilization rates and sources. Assess adoption of recommended production practices and potential for improved profitability using NPV scenario analysis.
  • Refining P Fertilization Recommendations for Limpograss

    Refining Phosphorus Fertilization Recommendations for Limpograss in South Florida

    Investigator: Joao Vendramini, Professor, RCREC-Ona

    Team: Maria Silveira (RCREC-Ona), Lauren Butler (Okeechobee County Extension), Colleen Larson (SE District Regional Specialized Agent)

    Limpograss (Hemarthria altissima) is the second most used forage species for livestock production in South Florida. Limpograss can withstand seasonal flooding and grows best in areas of heavier soil that retain moisture. It is commonly cultivated in sensitive areas around water bodies.

    Due to the high importance of limpograss to Florida’s livestock producers, UF/IFAS developed two new cultivars, Gibtuck and Kenhy, which were the first limpograss hybrids (Floralta x Bigalta) ever released in the world. It has been observed that Gibtuck and Kenhy have greater forage production and persistence than Floralta in south Florida. However, the fertilizer recommendation in place is still based on the production and nutritive value of Floralta.

    Fertilization is one of the most-costly inputs in Florida livestock production systems. However, fertilization is essential to enhance production, nutritive value, and persistence of warm-season forages. Phosphorus fertilizer has been cited as a major contributor to eutrophication in Lake Okeechobee. Despite a significant reduction in P fertilizer use due to the implementation of BMPs, it is necessary to evaluate P fertilizer rates that will optimize limpograss production and persistence without impacting water quality.

    The objective of this proposal is to evaluate forage production, nutritive value, and persistence of two limpograss cultivars to P fertilizer rates and quantify the impacts of these treatments on soil, plant, and water P concentration. This project was partially funded by The Florida Cattlemen’s Enhancement Board. Additional funding for personnel and equipment will leverage continuation of the project in 2023-2024. In addition, this project has the objective to change the limpograss P fertilization recommendation in south Florida and incorporate tissue P concentration as a tool to increase the accuracy of P fertilizer recommendations.

    Expected outcomes: We expected to evaluate the effect of P fertilizer application rate on performance of the new limpograss cultivar, Gibtuck, and evaluate the effects of these limited P levels on soil health. In addition, we expect to create a minimum tissue P concentration for limpograss that could be used in the future to refine limpograss P fertilization recommendations. It is estimates that limpograss covers about 300,000 acres in south Florida. If producers could save $20/acre in P fertilizer cost, it would result in approximate $6,000,000 savings for livestock producers.

  • Agronomic P Recommendations for Bahiagrass Pasture

    Agronomic P Recommendation for Bahiagrass Pastures Fertilized with Biosolids

    Investigator: Maria Silveira, Professor, RCREC-Ona

    Team: Joao Vendramini (RCREC-Ona)

    Biosolids are an effective source of crop nutrients and organic matter. However, public pressure has led to stricter land application policies in Florida. Based on the new FDEP Rule 62-640, Florida Administrative Code effective June 21, 2021, biosolids must be applied at reduced rates to meet crop P requirements. This approach significantly limits the biosolids application rate that can be recycled in pastures in central and south Florida. Although limited information currently exists regarding forage production and nutritive value responses when biosolids are applied at reduced (P-based) rates, our preliminary data demonstrated that such low rates are unable to supply enough N and other essential nutrients to sustain adequate forage production. In addition, the new rule also requires water quality monitoring when the annual P application rate exceeds 40 lbs P2O5/acre. Our previously published data indicated no detrimental impact of biosolids on water quality even when biosolids was applied at a N-based rate. Reduced (P-based) biosolids application rates may not be practical or economically feasible for farmers, which will result in the loss of a valuable resource that can have many agronomic and environmental benefits.

    Nutrients in biosolids cannot be substituted for those in commercial fertilizer on a pound-for-pound basis because not all biosolids-derived nutrients are readily available to a crop in the year of application. Although IFAS currently has no specific nutrient recommendations for crops fertilized with biosolids, the revised FDEP 62-640 contains specific information about N and P requirements for bahiagrass and other major forage crops. The FDACS Cow/Calf BMP manual requires that land application of biosolids abides by all applicable regulations in the rule, however limited information is available to support the rule.

    The main objectives of this study are:

    • Evaluate the relative availability of biosolids-P compared with inorganic P fertilizer.
    • Investigate the agronomic impacts of P recommendations in the revised 62-640 rule.

    Expected outcomes: Previous biosolids research in Florida consisted of short-term characterizations and/or conducted under controlled laboratory or greenhouse conditions. These research efforts were instrumental in developing guidelines for safe land application of biosolids in many areas of Florida and nationally, but they are not universally applicable. Field-scale trials are essential to accurately assess the risks and benefits of land application of biosolids to Florida pastures. The current experimental area offers a unique scenario where science-based information regarding the benefits of land application of biosolids will be generated and shared. Below are the timeline and expected outcomes.

  • P Fertilizer and Site-Specific Recommendations for Tomato, Potato, and Snap Beans

    Developing Phosphorus Recommendations and Site-Specific Management for Tomato, Potato, and Green Beans through Large-Scale Participatory Research with Stakeholders

    Investigator: Sanjay Shukla, Professor, SWFREC-Immokalee

    Team: Shinsuke Agehara (GCREC-Balm), Nikolay Bliznyuk (Ag/Bio Engineering-GNV) , Johan Desaeger (GCREC-Balm), Craig Frey (Hendry County Extension), Lisa Hickey (Manatee County Extension), Anna Mészáros (Palm Beach County Extension), Kimberly L. Morgan (SWFREC-Immokalee), Rao Mylavarapu and Vimala Nair (Soil, Water, and Ecosystem Sciences-GNV), Pamela Roberts (SWFREC-GNV), and Gary Vallad (GCREC-Balm)

    This project continues the 2021-22 LBR P rate study for tomato and potato and the bean experiments started in 2022-23. It is evaluating yield response and water and nutrient use efficiencies associated with four to six P rates for tomato, potato, and beans. The 2022-2023 was a challenging year considering the effects of hurricanes Ian and Nicole that directly affected the fall experiments. The hurricanes affected experiments where harvests overlapped combined with a personnel shortage and delays in instrument and equipment acquisition. Thus, accomplishing project objectives will be delayed into the next fiscal year (2023-2024). Completing the processing and analyses of past data including modeling and conducting experiments to collect third year data for potato and tomato and second year data for bean in central and south Florida (CSFL) will be the focus for the next fiscal year.

    Goals and Objectives:

    • Evaluate the Mehlich-3 (M-3) based P fertilizer recommendations for tomato, potato, and snap beans with regard to plant growth and yield, produce quality, profitability, and environmental losses at commercial farms in central and south Florida.
    • Compare the applicability of M-3 and other soil P tests as indicators of bioavailable P.
    • Determine optimum P fertilizer rates considering both economic and environmental factors.
    • Identify site-specific factors for variable yield responses to develop variable rates and management guidelines using linkages of yields with biotic and abiotic factors including irrigation.
    • Disseminate the results to participating producers and select stakeholders and collect feedback to inform the applicability and potential changes in the current P recommendations.

    Expected outcomes:

    • Completion of processing and analyses of 2021-2023 data to evaluate the current recommendations.
    • Presentation of interim results to PNOC to explore provisional changes in recommendation for tomato.
    • Completion of hydrologic modeling using past data and integration of model results with field data to explain variable yield response by regions, seasons, hydrology, and management.
    • Identification of site-specific factors affecting yield and their use in revising the current recommendations considering economic, management, and environmental factors.
    • Suitability of the Mehlich 3 soil test to guide P fertilizer application for different regions and environments.
    • Reestablishment of growth stage-specific optimum ranges for leaf tissue P concentration.
    • Development of a decision support system framework for site-specific recommendations including economic analysis.
    • Greater likelihood of future adoption of IFAS P fertilizer recommendations due to an engaged industry.
  • P Fertilizer Recommendations for Lettuce on Muck Soils

    Phosphorus Recommendations for Lettuce Grown on Muck Soils

    Lead Investigator: Germán Sandoya Miranda, Professor, EREC-Belle Glade

    Team: Jehangir Bhadha (EREC-Belle Glade), Steven Sargent (Horticultural Sciences-GNV)

    Current commercial lettuce varieties require phosphorus fertilizer to maintain economically viable production in Florida, the third largest producer of this vegetable in the United States. Fertilizer rate recommendations need to be developed and refined for commonly produced lettuce cultivars in Florida. Around 10,000 acres of lettuce are planted in the Everglades Agricultural Area (EAA).

    The IFAS fertilizer recommendations in place today were released in the 1990s and were developed for iceberg lettuce. Fertilizer needs are type-dependent based on morphology. In addition, soil chemistry in the EAA is changing due to subsidence of the muck. When soil is lost, lime rock becomes mixed with the surface muck, increasing soil pH and rendering soil P less available.

    The proposed research will help us understand how new germplasm responds to P fertilizer rates in romaine, iceberg, butterhead, and leaf lettuce. Phosphorus is a key component of the cell structure and metabolism in plants. For example, chlorophyll content and can affect plant metabolism. In this research, we will study the effects of reduced or increased P soil conditions on horticultural traits, postharvest characteristics (shelf life), resistance to diseases, and physiological disorders.

    With the goal of proposing revised P fertilizer recommendations for production of lettuce on muck soils, our objectives are:

    1. Evaluate lettuce yield response to P fertilizer rate under field production conditions.
    2. Determine if lettuce quality is affected by P fertilizer management.

    Expected outcomes:

    • Initial (year 1) results on yield of lettuce at different P rates. Therefore, these results will suggest continuation for following years.
    • Information on postharvest quality and shelf life will indicate consequences of the newly proposed recommendations on quality of these lettuce types.
  • P Management for Snap Bean on South Florida Calcareous Soils

    Miami-Dade County is a major green bean production region in Florida. The Homestead area is known for its calcareous soils that require soil-specific phosphorus (P) management practices. One P fertilizer recommendation for the entire state is insufficient due to widely ranging production conditions. There is an urgent need for bean growers to have a P fertilizer recommendation specific for calcareous soil. The combination of the optimal P rate and the efficient method of P application is essential for maximizing the phosphorus use efficiency of snap bean production. To achieve this, it is crucial to understand P dynamics in soil and quantify green bean yield response to different P rates and application methods. Increasing P fertilizer use efficiency will reduce production costs and will achieve the utmost output of bean yield and quality, which in turn will lead to maximum profitability for growers.


    The goal of this project is to maximize P fertilizer use efficiency of snap beans by optimizing P rates for calcareous soil (Krome series). This goal will be achieved by pursuing the following specific objectives:

    1. Conduct soil testing and calibration for six P fertilizer rates at the TREC Research Farm.
    2. Investigate snap bean response to P fertilizer application rates with two irrigation regimes at the TREC Research Farm.
    3. Optimize P fertilizer application rates to snap bean on a cooperating commercial farm.
    4. Share new findings with current and potential snap bean growers and other professionals via in-person or virtual field demonstrations, workshops, factsheets, and peer-reviewed publications.

    Expected outcomes:

    We expect outcomes from this project to include well-established and actionable information about the optimal P fertilizer application rate for snap bean production on calcareous Krome soil in South Florida. Specific project outcomes include:

    • Best snap bean P rate specific for calcareous Krome soil in the Homestead area.
    • At least one refereed journal publication.
    • Two EDIS publications.
    • One in-person field day demonstration.
    • At least one conference presentation at the 137th FSHS Annual Meeting.
  • Hemp Fertilization Research and BMP Development

    Visibility for Hemp Fertilizer Research and BMP Development

    Investigator: Zachary Brym, Assistant Professor, TREC-Homestead

    Team: Lakesh Sharma (Soil, Water, and Ecosystem Sciences-GNV), Hardeep Singh (WFREC-Jay), Jehangir Bhadha (EREC-Belle Glade)

    Hemp has recently been introduced to Florida. New hemp farms are expected to adopt BMPs developed from research. While there are established BMPs for other agronomic crops, hemp BMP research is just starting. Such research is also limited nationally and only marginally useful given Florida’s unique and diverse environments.

    The goal of the project is to continue nutrient management research resulting in maximum yield and quality targets for hemp growers in a manner that minimizes nutrient loss to the environment. The objective is to support visibility of nutrient rate research and development of guidelines for hemp nutrient rate, timing, source, and site-specific management practices.

    Expected outcomes:

    • Professional presentations about hemp nutrient management at a national horticulture conference in Orlando.
    • Hemp nutrient management education at various extension events including the BMP Summit and Hemp Field Day at PSREU in Citra.
    • Presentation of research to the Plant Nutrient Oversight Committee.
    • Integration of ongoing work with minimum data standards.