Recipient Organization
PENNSYLVANIA STATE UNIVERSITY
408 Old Main
UNIVERSITY PARK,PA 16802-1505
Performing Department
(N/A)
Non Technical Summary
Weed management is one of, if not the, greatest challenge for organic crop production. Organic farmers rely on tillage for weed control; however, tillage is often less effective than conventional forms of weed management (e.g. herbicides) and therefore weeds can reduce yields in organic systems. Additionally, interest in ecologically produced food is increasing among the public. Soil microbes can infect and kill weed seeds, thereby reducing populations of problematic weed species. Determining what crop management approaches can increase microbially-mediated mortality of weed seeds in the soil could greatly improve the ability or organic farmers to control weeds. However, research has been limited on which microbial taxa can increase weed seed mortality, and what management factors promote those microbial populations.To address this knowledge gap, we will conduct complementary field experiments. First (Obj. 1), we will conduct two complementary experiments (one in field crops and one in vegetables) examining how organic soil amendments influence both weed seed mortality and microbiome, as well as the soil microbiome. To do this, we will compare organic soil fertility amendments that vary in chemical and nutrient quantities. Second (Obj. 2), we will leverage a long-term organic experiment at PSU to evaluate how distinct perennial forage crops (compared to a standard organic annual crop rotation) influence weed seed mortality and microbiomes, as well as the soil microbiome. For both experiments, we will use amplicon sequencing to characterize the bacterial and funal communities within weed seeds, and tetrazolium tests to assess seed viability. Additionally (Onj. 3), using a series of on-farm trials as well as our on-station trials, we will determine the drivers (e.g. soil abiotic factors and soil microbiome) of weed seed mortality and microbiomes. Finally in collaboration with organic farmers, (Obj. 4) we will use our farmer advisory panel, on-farm trials, and other extension events to develop a mutual understanding of how soil fertility and crop rotations can be leveraged within organic systems to enhance weed seed mortality in the soil seedbank.We expect the proposed research to identify specific microbial taxa that are associated with greater mortality of weed seeds. The integrated research and extension publications and events (such as field days at on-farm sites, study circles, and presentations at grower meetings) will provide valuable information to organic farmers in how to manage the soil in ways that promote microbially mediated weed seed mortality. Ultimately, our proposed research will result in a greater understanding of how to use ecological approaches to manage weeds in organic systems. This proposed project aligns with the priorities in the Organic Transitions program by focusing on understanding the effects of organic management on populations of problematic weeds.
Animal Health Component
40%
Research Effort Categories
Basic
50%
Applied
40%
Developmental
10%
Goals / Objectives
Our long-term goal is to develop more ecologically based farming systems, with a greater ability to regulate weed populations through biotic interactions.Ultimately, this will help increase the long-term profitability of organic farms by decreasing the time and financial investment required for effective weed management. To accomplish this goal, we need to determine how crop management influences weed seed mortality, the soil and weed seed microbiome, and ultimately determine which microbial taxa are associated with seed mortality.To address these knowledge gaps, our proposed research will address the following research questions:1. How does soil fertility management influence weed seed mortality and seed microbiomes?2. How do crop species and rotation affect weed seed mortality and seed microbiomes?3. To what extent does the soil microbiome and soil abiotic factors predict the weed seed microbiome, and does the seed microbiome predict seed mortality?To disseminate project results and create a greater understanding about how soil microbes contribute to weed seed biocontrol, we will also:1. Extension objective: Disseminate project results to a broad range of organic farmers, and work with them to develop a mutual understanding of the potential for soil management to influence the soil and seed microbiome to enhance weed seed mortality in the soil seedbank.2. Education objective: Develop a learning module focused on the biological control of weed seeds via the soil microbial community.
Project Methods
Objective 1.Experimental design. We will apply seven different soil fertility treatmetns in two complementary field experiments: one in field crops and one in vegetables. Two weeks after applying soil fertility amendments, we will bury weed seed bags of three target weed species within the field to characterize treatment effects on seed mortality and microbiome.Objectives 1 (methods same for Obj 2 and 3) Weed Seed Mortality Assessment.Seeds of our three model weed species will be collected in Fall of each year, cleaned, and buried in bags in the soil. Seeds will be excavated at harvest, washed through a series of sieves, and separated into two submsamples: half for viability assessments and half for microbiome characterization. We will use tetrazolium tests to determine viability.To characterize the microbial endophytic community within seeds of our three weed species, seeds will be freeze-dried, then homogenized with a bead mill. We will then use the Qiagen DNeasy Plant Kit to extract DNA, which will be quantified using a Qubit Fluorometer.We willuse amplicon sequencing of the ITS marker region for fungal taxonomic composition and 16S rRNA gene marker gene for bacterial taxonomic composition.Objective 2: How does crop species and rotation influence weed seed mortality and seed microbiomes?Experimental Design:We will leverage an existing ORG funded project to examine how functionally distinct crop species influence weed seed and soil microbiomes and weed seed mortality. This previously funded experiment, of which PD Lowry is also a coPI, examines how perennial forage monocultures and mixtures influence forage yield, weed suppression, soil health, and farm profitability. We can leverage this existing experiment to examine whether functionally distinct perennial forages influence seed mortality. While the larger experiment consists of six perennial forage species that were selected because they have similar phenology, and six combinations of these species grown in mixtures, for our work we will only utilize three monocultures, which includes two grasses and two legumes, and two grass-legume mixture combinations. We selected alfalfa, orchardgrass, and tall fescue because they are the three most commonly grown forage species within our region. We also included birdsfoot trefoil because we wanted to see if perennial legumes other than alfalfa also promoted weed seed mortality, and also because birdsfoot trefoil has a similar phenology as alfalfa, which means they can be managed similarly. The alfalfa-orchardgrass mixture is the dominant forage mixture grown within our region, and we included the birdsfoot trefoil-alfalfa-orchardgrass mixtures because we wanted to evaluate if increasing the number and proportion of legumes within a forage mixture can accelerate weed seed mortality and affect seed microbiomes. The perennial forage phase of the crop rotation will be in place for two years, Spring 2025 to Spring 2027. While most perennial phases of crop rotations are three years or longer, maintaining a two-year rotation enables us to ask whether we can realize seed mortality benefits even with a short perennial phase in case stand failures or market demands necessitate returning to corn earlier in the crop rotation. In the final year of the crop rotation (Spring to Fall 2027), all treatments will return to corn so we can then assess whether the rotation treatments created a legacy in the soil that affected weed seed mortality and microbiome during the subsequent crop rotation phase. During the corn crop phase of the rotation, we will compare the perennial forages to an annual soybean-wheat-corn rotation control, which is a common crop rotation for organic field crop farmers that are not growing perennial forages. Plot sizes will be 6 m X 24m.Weed seed mortality and microbiome assessments: Weed seed burial bags will be prepared and processed for microbiome and mortality analyses as detailed in Objective 1. However, we will use two phases of the crop rotation to examine how crop species and rotations influence seed mortality and the microbiome: 1) during the phase of the perennial forages growth; and 2) during the phase of the subsequent corn cash crop after the perennial forages have been incorporated and are decomposing in the soil.Objective 3: To what extent does the soil microbiome and soil abiotic factors predict the weed seed microbiome, and does the seed microbiome predict seed mortality?On-farm Trial Descriptions:Using our on-farm and on-station trials, we will examine how the soil microbiome composition influences the seed microbiome and mortality. In Years 2 and 3, we will initiate 10 on-farm trials per year for two years to improve our understanding of how soil microbiome management influences weed seed mortality. To do this, we will first share the results of Year 1 from Objective 1 (soil fertility management) with farmer participants, and farmers will be asked to pick one or two soil fertility amendments based on Year 1 results and we will compare these amendments with their current soil fertility practice.Therefore, for each on-farm site, we will include a minimum of two treatments to quantify weed seed mortality and microbiomes within a crop and organic amendment of their choice: 1) standard farmer practice, and 2) farmer-selected organic amendment and rate. If farmers are interested and have space, they can select other organic amendments and rates to trial.Farmers will also get to pick which crop they would like to conduct the study within, with the one exception that it must be a longer duration crop (at least a 75-days) to allow time to see effects.Integrating on-farm and on-station trials to understand the predictors of weed seed mortality:Structural Equation Modeling (SEM) is a powerful empirical modeling approach that visualizes and detects relationships among multiple and correlated variables. SEMs are useful because they: (1) specify direct or indirect relationships between variables; (2) tease apart important interactions rather than analyzing variables independently (versus multiple linear regressions); (3) generate important hypotheses and provide a common framework to test and refine hypotheses. Finally, the output can be drawn visually, which is a clear and intuitive way to present our results to growers and other stakeholders.Using SEM, we will be able to determine the relative contribution of the soil abiotic conditions and the soil microbiome, and whether they can directly or indirectly influence or interact to influence weed seed mortality.Additional data collection for our SEM model.Soil temperature, moisture, and nitrogen availability can influence the soil microbiome composition (e.g., bacterial and fungal communities), presumably by affecting the growth rate and metabolic activity of some but not all soil microbial populations. As potential predictors in our SEM, we will repeatedly measure soil abiotic factors and characterize the soil microbiome in each of the proposed on-station and on-farm field experiments. In addition to other data collection previously mentioned above, we will collect the following data in each experimental plot:Soil plant available nitrogenSoil volumetric water contentSoil temperature Soil microbiome.