Source: UNIVERSITY OF GEORGIA submitted to NRP
FERTILIZER FOLLY: INVESTIGATING THE EFFECTS OF EXCESS PHOSPHORUS ON MICROBE-PLANT-INSECT INTERACTIONS IN ORGANIC CROPPING SYSTEMS
Sponsoring Institution
National Institute of Food and Agriculture
Project Status
ACTIVE
Funding Source
AFRI COMPETITIVE GRANT
Reporting Frequency
Annual
Accession No.
1032631
Grant No.
2024-67011-42899
Cumulative Award Amt.
$179,304.00
Proposal No.
2023-11466
Multistate No.
(N/A)
Project Start Date
Aug 15, 2024
Project End Date
Aug 14, 2027
Grant Year
2024
Program Code
[A7101]- AFRI Predoctoral Fellowships
Recipient Organization
UNIVERSITY OF GEORGIA
200 D.W. BROOKS DR
ATHENS,GA 30602-5016
Performing Department
(N/A)
Non Technical Summary
Phosphorus is an essential nutrient for crop growth and development, but in excess may exacerbate insect pest pressure in agroecosystems. While high levels of phosphorus is a soil characteristic of the vast majority of cropping systems, remarkably little is known about how surplus phosphorus alters agroecological communities via both bottom-up forces, such as plant defenses, and top-down forces, such as predation of insect herbivores. Filling this knowledge gap is critical for farmers to develop sustainable fertility management strategies while mitigating the environmental harms of phosphorus runoff into water bodies. This predoctoral integrated research and extension project includes two objectives to address agroecological consequences of surplus phosphorus: 1a) conduct a manipulative paired comparison of high and low phosphorus on four collaborating farms, measuring effects of phosphorus on top-down predation of herbivores, 1b) characterize how changes in soil quality and microbial diversity due to excess phosphorus application impact the bottom-up suppression of herbivores, and 2) engage and educate regional farmers about fertility and pest management with an on-farm field day and by developing a guidebook to common agricultural arthropods in the Southeast. Understanding the role of phosphorus in microbe-plant-insect interactions is crucial to both crop production and the development of sustainable agroecosystems. The outcomes of this project will help us identify pratical, organic fertility-management strategies that reduce phosphorus applications and enhance insect pest management while providing a hands-on educational environment for farmers.
Animal Health Component
50%
Research Effort Categories
Basic
50%
Applied
50%
Developmental
0%
Classification

Knowledge Area (KA)Subject of Investigation (SOI)Field of Science (FOS)Percent
1020110101040%
1024099107030%
2151429113030%
Knowledge Area
102 - Soil, Plant, Water, Nutrient Relationships; 215 - Biological Control of Pests Affecting Plants;

Subject Of Investigation
4099 - Microorganisms, general/other; 0110 - Soil; 1429 - Cucurbits, other;

Field Of Science
1130 - Entomology and acarology; 1070 - Ecology; 1010 - Nutrition and metabolism;
Goals / Objectives
The long-term goals of this project are to improve crop production while reducing the environmental and human harms of agriculture by promoting fertility management strategies that enhance biocontrol, while expanding our basic knowledge of how soil nutrients mediate microbe-plant-insect interactions. This project was inspired by the insights and concerns of farmers in the southeastern U.S. with high soil phosphorus levels on their farms. The two main objectives of this project aim to provide farmers with evidence-based scientific information on how fertility strategies affect crop productivity and pest management:Objective 1a: Conduct a manipulative paired comparison of high and low phosphorus on four collaborating farms to determine the effects of phosphorus on top-down predation of herbivores.Objective 1b: Characterize how changes in soil quality and microbial diversity due to excess phosphorus application impact the bottom-up suppression of insect pests.Objective 2: Engage and educatefarmers about fertility and pest management with an on-farm field day, and by developing a guidebook to common cucurbit crop arthropods in Georgia.
Project Methods
During the proposed project, two major objectives will examine how surplus phosphorus impacts agroecological communities via both bottom-up forces such as plant defenses, and top-down forces, such as insect predators.Obj. 1a: Conduct a manipulative paired comparison of high and low phosphorus (P) on four collaborating farms, measuring effects of phosphorus on top-down predation of herbivores. Methods: PD Sharp will perform a randomized complete block design experiment on four organically-managed farms in Georgia. Three treatments will be applied: high P, low P, and a control (no fertilizer). Treatments will be applied across 30m rows with three replicates of each treatment. Ten zucchini plants, C. pepo, will be seeded in each plot. Before treatments are applied, soil will be tested to determine pre-existing N, P, and K nutrient levels. Visual arthropod surveys will be conducted biweekly with herbivores and natural enemies counted and identified to the family level. Fruit will be harvested four times per week and separated into two categories based on USDA standards, marketable and unmarketable. Two random zucchini plants from each plot will be destructively harvested (cut at the base of the stem) for analysis of plant biomass and nutrient content. Briefly, subsamples from each plot will be homogenized, dried, and milled to a fine powder. The samples will then be submitted for estimates of foliar nutrients. Analysis: PD Sharp will use structural equation models (SEMs) to map out interactions between the many covariates measured in this experiment. SEMs combine a series of linear regressions to test a web of hypothesized causal relationships. The "PiecewiseSEM" package in R will be used to determine best-fit combinations of these generalized linear mixed models, providing explanatory links between fixed effects (e.g., soil P, foliar nutrients, herbivore and predator abundance, crop biomass, and yield), while accounting for random effects of spatiotemporal variation. The best-fit combination will be determined using directed separation tests and Akaike Information Criteria (AICc).Obj. 1b: Characterize how changes in soil quality and microbial diversity due to excess phosphorus (P) application impact the bottom-up suppression of insect pests. Methods: PD Sharp will randomly collect three soil samples for each replicate noted in Obj. 1a from the 0-15 cm profile twice throughout the growing season. These three subsamples will be homogenized for each plot and microbial DNA will be extracted using the Qiagen MagAttract PowerSoil Pro DNA Kit for KingFisher (Qiagen, Carlsbad, CA). DNA concentration will be quantified using Qubit assay (Invitrogen, Carlsbad, CA) before samples are sent to Novogene (Sacramento, CA) for library preparation and sequencing on an Illumina MiSeq. DNA samples will be divided into two aliquots, one used for bacterial sequencing and one used for fungal sequencing. The remaining soil will be submitted to the UGA Agricultural & Environmental Services Laboratories for analysis of micronutrients, macronutrients and percent organic matter. In addition, we will collect leaf tissue to measure concentrations of cucurbitacins, the main defensive compounds in cucurbit plants. Samples will then be analyzed by liquid chromatography mass spectrometry (HPLC-MS/MS) at the following the methods of Theis et al. (2014). In brief, PD Sharp will lyophilize and grind leaf tissue, extract metabolites, separate them by liquid chromatography and identify compounds by mass spectrometry. Analysis: PD Sharp will normalize differences in sample sequencing depth and assess alpha diversity using diversity indices. PD Sharp will then use Principal Coordinates Analysis to examine sample dissimilarity according to treatment with Bray-Curtis distances. Functional diversity will be inferred using PICRUSt and FUNGuild. Also, PD Sharp will use permutational multivariate ANOVA (PERMANOVA) with farm and treatment as predictor variables to evaluate soil P effects on bacterial and fungal identity and function. In addition, PD Sharp will use generalized linear mixed models to evaluate effects of soil P on cucurbitacin concentration, herbivore performance, microbial biodiversity and plant biomass. Best-fit models will be chosen using an information theoretic approach, selecting models that include the fewest variables within 2 corrected AICc values.Obj. 2: Engage and educate farmers about fertility and pest management with an on-farm field day, and by developing a guidebook to common cucurbit crop arthropods in Georgia. Methods: PD Sharp will collaborate with four organically-managed farms, UGA Extension and Georgia Organics for engage and educate farmers. First, by participating in the on-farm experiment themselves, collaborating farmers will be able to spread the word about the results within their networks. Second, in collaboration with UGA Extension and Georgia Organics, PD Sharp will organize an on-farm field day during the growing season. The field day will be open to all farmers in the region, and the content of the field day will include education on soil health, fertility management strategies for reducing soil P, and conservation strategies to promote beneficial arthropods. Third, PD Sharp will co-present with collaborating farmer(s) on approaches to organic fertility management and pest-management at regional grower-focused conferences. Co-presenting will give collaborating farmers agency over the research and provide an opportunity for them to network with other farmers in the region. Lastly, PD Sharp will develop a guidebook to common cucurbit crop pests and natural enemies specific to Georgiawith pictures for identification, host plant information, life cycle information, scouting strategies, and conservation strategies for beneficial insects. This guidebook will tie this project together with a section on nutrient management strategies for enhancing crop productivity and pest management, while reaching growers that cannot attend the in-person field day.Evaluation: PD Sharp will present results of the project at the annual National Entomological Society of America meetings, and at the USDA NIFA EWD Project Directors Meeting. PD Sharp will co-present with collaborating farmers at regional grower-focused conferences. PD Sharp will evaluate the success of these presentations through attendance and feedback forms. PD Sharp will synthesize and share applied knowledge from this research through a field day and a guidebook (see 'Obj. 2') that will be published through the UGA Extension peer review system. The success of the field day will be evaluated via public interest, attendance, questions, and feedback at the conclusion of the field day. The influence of the guidebook will be assessed based on frequency of use and farmer evaluations. Finally, PD Sharp will submit three manuscripts to peer-reviewed journals at the end of the third year that will demonstrate my successful research training: (1) a review on managing soil phosphorus to promote arthropod pest suppression that will be submitted to Frontiers in Sustainable Food Systems; (2) a research paper on the effects of soil phosphorus on top-down predation of herbivores that will be submitted to Biological Control, and (3) a research paper on the effects of soil phosphorus on herbivore performance via altering plant chemical defenses that will be submitted to the Journal of Chemical Ecology.

Progress 08/15/24 to 08/14/25

Outputs
Target Audience:The target audience for thisproject consists of three core groups: the project team, the stakeholders, and the advisory committee. These groupsinteract throughout the course of the project to meet project goals, improve project direction, and evaluate progress. Stakeholders in this project include Georgiafarmers and UGA Extension. During this reporting period, an advisory panel with representatives from the collaborating farms, UGA county extension coordinators, and PD Sharp's primary mentor, Dr. William E. Snyder, wasestablishedto advise the research and content of outreach activities. PD Sharp presented preliminary dataupdates to the stakeholders via a meetingand provided a written report.The project team consists of the sole PD on the project, Carly Sharp. PD Sharp isresponsible for completion of project goals including conducting research, analyzing results, developing a guidebook, and participating in education and outreach activities. During this reporting period, PD Sharp completed: a manipulative paired comparison experiment of high and low phosphorus (P) on four collaborating farms; mentored three undergraduate students as field and laboratory technicians; mentored a high school student on an independent project; attended the annual Entomological Society of America National Meeting 2024 to present preliminary results; collaborated with UGA Extension and Georgia Organics to host an educationalfield day for local farmers; and began evaluating microbial and fungal diversity from experimental soilsamples. These deliverables have beencommunicated back to the advisory committee and stakeholders through meetings and reports. The advisory committee for this projectprovides guidance on project direction, goals, and initiatives. The advisory committee consists of PD Sharp's doctoral committee at the University of Georgia, which includes Dr. William E. Snyder (primary advisor and insect ecologist), Dr. Kate Cassity-Duffey (horticulturist), Dr. Carmen Blubaugh (insect ecologist), and Dr. Anny Chung (plant biologist). These four people were selected due to their expertise and ability to provide advice and guidance related to the project goals. During this reporting period,PD Sharp metwith this committeeto review project methods and accomplishments. During advisory committee meetings, preliminary methodologies and data werepresented for review, feedback, and adjustments. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?During the current reporting period, the project has provided multiple opportunities for training and professional development to improve PD Sharp'steaching, research, and extension abilities. PD Sharp began theGradTeach Certificate program at the University of Georgia to expand her skills as an effective and engaging educator. She has also hadopportunitiestoimprove her communication skills to better convey evidence-based scientific concepts to diverse audiences by presenting her work at a national scientific conference (Entomological Society of America National Meeting 2024) and bycollaboratingwith the University of Georgia Extensionand a local non-profit, Georgia Organics, toprovide an on-farm educational field day for farmers. In addition,PD Sharp wasmentored by her primary mentor, advisory committee and lab group. During the reporting period, PD Sharp maintainedweekly one-on-one meetings with her primary mentor, monthly lab group meetings, and semiannual advisory committee meetings. Through these meetings, PD Sharp receivedfeedback on all aspects of her project, including experimental design, research methodologies, scholarly writing, and statistical analyses. How have the results been disseminated to communities of interest?Theresults from the current reporting period of the projecthave been disseminated by PD Sharp to farmers and fellow scientists via the following activities: Collaborating with local farmers to conduct on-farm experiment outlined in Objective 1a - by participating in the on-farm experiment, four Georgiafarmers were able to gain first-hand knowledgeon fertility management andspread the word about the results within their networks. Hosting a farmer field day - 40Certified Organic Farmers in the Georgia community gained knowledge onfertility management strategies toimprove pest control and reduce the environmental consequences of agricultural runoff. Presentating data at a scientific conference - fellow scientists gained knowledge onphosphorus-mediated effects on natural enemies and predation of herbivores. Presenting data tostakeholders via a meeting and written report - collaborating farmersgained knowledge onphosphorus-mediated effects on natural enemies and predation of herbivores specific to their farms. What do you plan to do during the next reporting period to accomplish the goals?During the next reporting period, PD Sharp will focus on the following goals for each objective: Objective 1a: PD Sharp will work on disseminating results to communities of interest via (1) a research paper on the effects of soil phosphorus on top-down predation of herbivores that will be submitted to the Journal of Applied Ecology,(2) presentingat a scientific conference (Entomological Society of America National Meeting 2025), and (3) presenting tostakeholders and advisory committee viameetings and written reports. Objective 1b: PD Sharp will work on analyzing data from collected samples and disseminating preliminary results to communities of interest via(1) presentingat a scientific conference(Entomological Society of America National Meeting 2025)and (2) presenting tostakeholders and advisory committee viameetings and written reports. Objective 2: PD Sharp will work on creating theguidebook for stakeholders and the publicon common cucurbit crop pests andnatural enemies with an emphasis on fertility and pest management that will be published through the UGA Extension peer review system and made publicly available as a UGA Extension publication. In addition, PD Sharp will complete the GradTeach Certificate program at the University of Georgia to expand her skills as an effective and engaging educator.

Impacts
What was accomplished under these goals? Phosphorus is an essential nutrient for crop growth and development, but in excess may exacerbate weed and insect pest pressure in agroecosystems. While a high level of phosphorus is a soil characteristic of the vast majority of cropping systems, remarkably little is known about how surplus phosphorus alters agroecological communities. Understanding phosphorus-mediated microbe-plant-insect interactions could be critical for farmers to develop sustainable fertility management plans while promoting biological control of weeds and insect pests. During the current reporting period, several accomplishments were achieved for each objective. Objective 1a: PD Sharp completed a manipulative paired comparison experiment of high and low phosphorus across four collaborating farms in Georgia. During the experiment, PD Sharp collected data on soil nutrients, foliar nutrients of the crop, crop yields, crop biomass, weed biomass, insect-pest abundance, and beneficial insect abundance. A preliminary analysis of this data via a structural equation model indicates that soil phosphorus is an important mediator of predation of herbivorous insects and, in excess, leads to a net decrease in yields. Additionally, fire ants seem to provide biological control in cropping systems where they are a key predator of pests. However, the overall effects of surplus phosphorus may be context-dependent due to the wide range of environmental variables faced by different farms. Accomplishments: 1 graduate student (PD Sharp) made progress towards completing her dissertation and a scientific publication by designing, conducting, and analyzing research, which will ultimately be published and contribute towards new knowledge of phosphorus-mediated effects on natural enemies and predation of herbivores for fellow scientists, farmers, and the public. 1 graduate student (PD Sharp) gained experience presenting results from experiment at a scientific conference (Entomological Society of America National Meeting 2024), contributing towards new knowledge of phosphorus-mediated effects on natural enemies and predation of herbivores for fellow scientists. 3 undergraduate students were mentored on the basics of conducting field and laboratory research in an agroecology setting and supervised on individual research projects, which will contribute to an Extension publication on fertility management strategies that farmers can utilize to reduce phosphorus inputs and improve pest control. 1 local high school student was mentored on the basics of experimental design and sampling. This student conducted an independent project leading to presentations at the Georgia Science and Engineering Fair. Objective 1b: From the experiment outlined in Objective 1a, PD Sharp collected soil samples to determine how changes in soil quality and microbial diversity due to surplus phosphorus impact biological control of pests. PD Sharp finished processing the samples and is currently analyzing the data (soil microbial community, foliar defensive chemistry, and soil nutrient levels), so there are not preliminary results yet. Accomplishments: 1 graduate student (PD Sharp) made progress towards completing her dissertation and a scientific publication by designing, conducting, and analyzing research, which will ultimately be published and contribute towards new knowledge of: (1) phosphorus-mediated effects on soil microbial community composition and functionality, and (2) phosphorus-mediated effects on plant defensive chemistry and herbivore suppression for fellow scientists, farmers, and the public. Objective 2: PD Sharp collaborated with the four organically-managed farms outlined in Objective 1a, the University of Georgia Extension, and a local non-profit, Georgia Organics, to educate and engage farmers about fertility and pest management via three major activities: (1) participation in the on-farm experiment, (2) organizing a farmer field day, and (3) presentation of preliminary data analyses. Accomplishments: 4 collaborating farmers participated in on-farm experiment outlined in Objective 1a, contributing towards the establishment of a network of local mixed-vegetable farmers for support and advice. Hosted farmer field day for 40 Certified Organic Farmers in the Georgia community on the topic of "Balancing Soil Fertility and Organic Pesticide Management." This field day led to: (1) better fertility management decision-making ability of farmers to improve pest control and reduce the environmental consequences of agricultural runoff, and (2) the establishment of a network of local mixed-vegetable farmers for support and advice. 1 graduate student (PD Sharp) gained experience presenting data from experiment to collaborating farmers in a meeting and as a written report, resulting in the application of fundamental knowledge on phosphorus-mediated plant-insect interactions to enhance pest control.

Publications