INCREASING RESILIENCE TO CHANGING WINTERS IN THE NORTHEAST: UNDERSTANDING EFFECTS ON PERENNIAL FORAGE AND WEED COMMUNITY DYNAMICS

• Sponsoring Institution: National Institute of Food and Agriculture
• Project Status: ACTIVE
• Funding Source: AFRI COMPETITIVE GRANT
• Reporting Frequency: Annual
• Accession No.: 1028090
• Grant No.: 2022-67013-36859
• Cumulative Award Amt.: $650,000.00
• Proposal No.: 2021-09936
• Project Start Date: Jan 15, 2022
• Project End Date: Jan 14, 2026
• Grant Year: 2022
• Program Code: [A1102]- Foundational Knowledge of Agricultural Production Systems

Recipient Organization
PENNSYLVANIA STATE UNIVERSITY
408 Old Main
UNIVERSITY PARK,PA 16802-1505

Performing Department
Plant Science

Non Technical Summary
Understanding the effects of weather variability on crop performance and agroecosystem processes is essential to assist farmers with adaptive management strategies. Perennial forage crops are especially vulnerable to year-round environmental variation, and the projected increase in winter weather variability will have profound effects on perennial forage productivity and resilience, and consequently, farm viability. Poor overwinter survival is one of the leading impediments to establishment and yield of perennial forage crops. Our proposed work will use both open-top chambers and snow removal to manipulate climate within the field and examine how warmer temperatures and increasing winter weather variability associated with climate change will affect perennial forage crops and their associated weedy plant communities. In Objective 1, we will determine the degree to which forage management practices (alfalfa variety and harvest frequency) may ameliorate or exacerbate climate effects on the persistence and performance of an alfalfa-orchardgrass mixture. In Objective 2, we will examine how warmer and more variable climates affect weed emergence timing and seed persistence in the soil seedbank, both of which are critical for effective weed management. Finally, we will use structural equation modeling to quantify the extent to which environmental variables within climate manipulation and forage management treatments predict forage and weed responses. Results from this work will provide essential information to growers in the Northeast on the effects that increasing weather variability may have on perennial forage systems, as well as the optimal management tactics to enhance farm resiliency in response to a changing climate.

Animal Health Component

70%

Research Effort Categories

Basic

30%

Applied

70%

Developmental

(N/A)

Classification

Knowledge Area (KA)	Subject of Investigation (SOI)	Field of Science (FOS)	Percent
132	1640	1070	40%
205	1640	1070	30%
213	2300	1140	30%

Knowledge Area
205 - Plant Management Systems; 132 - Weather and Climate; 213 - Weeds Affecting Plants;

Subject Of Investigation
1640 - Alfalfa; 2300 - Weeds;

Field Of Science
1070 - Ecology; 1140 - Weed science;

Keywords

alfalfa

climate change

forage

weed seedbank

winter survival

Goals / Objectives
Developing cropping systems resilient to weather variability will be a key challenge for the 21stcentury. Compared to annual crops, perennial forage crops are especially vulnerable to environmental variation year-round; hence, projected increases in both the mean temperature and temperature variability in the Northeast will have profound effects on perennial forage productivity and resilience, and consequently, farm viability. Our proposed research willinvestigate how changes in temperature associated with climate change affect the establishment, persistence, and performance of perennial forage crops and their associated weedy plant communities and determine the degree to which forage management practices (variety selection and harvest frequency) may ameliorate or exacerbate these effects.?Our long-term goal is to improve our understanding of the effects that changing winters will have on perennial forage production and weed communities in the northeastern US.To achieve this goal, we propose the following research objectives:Objective 1: Evaluate the effect that forage management (varieties varying in fall dormancy and forage harvest frequency) have on alfalfa (Medicago sativa L.) winter injury and survival, as well as forage yield, weed suppression, and community composition, in response to climate manipulations.Objective 2.Characterize the effect of climate manipulations on weed seedbank dynamics and emergence timing.Objective 3. Quantify the extent to which environmental variables within climate manipulations and forage management treatments predict forage and weed responses.We hypothesize that the 'climate risky' treatment, which includes a combination of greater harvesting frequency and lower fall dormancy (characterized by a higher fall dormancy or 'FD' rating) will reduce non-structural carbohydrate storage, rendering alfalfa more vulnerable to winter injury compared to the 'standard' and 'climate resilient' practice (see below for descriptions), ultimately decreasing yield in climate manipulation treatments without warming (control), with snow removal, and within the fluctuating warming (Figure 8). We further propose that lower winter survival and greater winter injury of alfalfa will lead to increased weed biomass.

Project Methods
Objective 1.We will establish field experiments ("Forage Management Experiment") in both PA and NH as a split-plot randomized complete block design with four replicates.Main Plot Alfalfa Variety and Harvest Frequency:1)Standard practice: dormant alfalfa (FD 4) + 4 harvests per year;2) Climate Risky: moderately dormant alfalfa (FD 5) + 5 harvests per year;3)Climate Resilient: dormant and moderately dormant (FD 4 + 5) alfalfa mixture + 4 harvests per year;4)Moderate Dormancy: moderately dormant alfalfa (FD 5) + 4 harvests per year ;5) Increased harvest frequency: FD 4 + 5 harvests/ year;6) Mix varieties + increased harvest: dormant and moderately dormant mixture (FD 4 + 5) + 5 harvests(a 4/5/5 system). Split-plot climate modifications. assign four climate manipulation subplots within each alfalfa main-plot, including: 1) Control: no warming, no snow removal; 2) Snow removal: we will carefully remove approximately 95% of all snow; 3) Constant warming: no snow removal, with constant, year-long warming; 4) Fluctuating warming: no snow removal, with year-long warming via an OTC, but which is periodically removed when weather forecasts predict a drop in maximum temperature from 1.5°C to under -1.5°C.To simulate warmer temperatures in the Constant Warming and Fluctuating Warming plots, hexagonal open-top chambers will be constructed from 1 mm thick Sun-Lite HP (Solar Components Corporation) attached to a wooden-frame, with a 2.65 m basal diameter, a top opening diameter of 1.75 m, and a height of 0.8 m.Agronomic Management: In both PA and NH, alfalfa-orchardgrass mixtures will be planted in early September 2022. Within each block, we will randomly assign the alfalfa genotypic composition and harvest frequency treatments to each main plot (13 × 13 m). The field will be tilled, and then alfalfa will be planted at the standard seeding rate of 16.8 kg ha-1 combined with a 5.6 kg ha-1 planting of orchardgrass.Forage yield, composition, and weed biomass. A herbage sample will be cut by hand 10 cm above the soil surface from the entire 1 m2 sampling area, separated to species, dried then weighed.Alfalfa winter survival and injury: 20 random plants per subplot will be marked with a 10 cm toothpick in the fall, then rated for winter injury on a 0 to 100% and monitored for signs of frost-heaving and disease.Alfalfa flowering time: We will monitor three times per week to assess budding and flowering.Alfalfa crown non-structural carbohydrate storage: Each year in November we will analyze alfalfa root crowns for for nonstructural carbohydrates.Analysis and interpretation of results. We will use repeated measures mixed models with year treated as a repeated measure, and alfalfa genotypic composition, harvest frequency, climate variation, and their interactions treated as fixed effects, and main plot nested within block treated as a random effect to account for the split-plot design.Objective 2.The experiment will be a randomized complete block design with four replicate blocks. Each block will consist of two randomized replicates of the four climate manipulation treatments (1. Control, 2. Snow Removal, 3. Constant Warming, 4. Fluctuating Warming).Weed propagule survival. In September 2022, approximately 2 weeks after alfalfa planting, we will install 24 cores, which will be grouped into three sets based on extraction year (removed after 1, 2, or 3 years). Within each extraction year, eight weed species (Amaranthus retroflexus, Abutilon theophrasti, Digitaria sanguinalis, Setaria faberi, Ambrosia artemisiifolia, Stellaria media, Thlaspi arvense, and Capsella bursa-pastoris).We will first use a bulk density corer (5 cm diameter × 15 cm depth) to remove 24 separate cores from the soil and soil will be mixed with 300 seeds from one of the eight weed species (only one species per core), then returned. Every week during the study period, cores will be checked for weed germination and any germinated individuals will be counted and removed. Cores will be extracted, seeds elutriated, and then assessed for viability with a TZ test. We will use nonlinear mixed-effects models to relate seed viability over time to an asymptotic exponential model that includes climate manipulation and time as fixed effects, and block as a random effect. We will use mixed models to examine the fixed effect of climate manipulation on seed half-life, with block nested within site as a random effect.Weed emergence timing. Within the climate manipulation subplots, we will establish permanent quadrats (0.75 m × 1 m) to monitor emergence of both summer and winter annual weeds throughout the course of the experiment. Quadrats will be divided into eight sections (0.25 × 0.25 m), in which we will sow 400 seeds of one of the eight weed species selected for the study (listed above). We will monitor, count, then remove weeds that have emerged within each sub-quadrat weekly throughout the entire spring, summer, and fall.Cumulative emergence of each weed species will be modeled using a Weibull function. We will use the model to extract time to 25%, 50%, and 75% emergence, and then examine whether the fixed effects of climate manipulation treatments affect the relative timing of emergence with block nested in year and site as random factors.Weed seed incorporation in the soil seedbank. Colored beads will include three size fractions (<1.4 mm, 1.4 to 2.4 mm, > 2.4 mm), and 300 beads from each size fraction will be spread on the soil surface in fall 2022 within two weeks of alfalfa planting. Then we will count the number of beads within each size-color fraction remaining on the soil surface in the spring and fall in each subsequent year. We will use repeated measure, mixed effects models to examine the fixed effects of climate manipulation treatment on seed incorporation (simulated via glass beads) in the soil, with year treated as a repeated measure, and block nested within year and site as a random effect.Objective 3. Both air and soil temperatures will be determined using HOBO Pendant® Temperature Data Loggers. Soil temperatures measurements will occur at both 3 and 10 cm depth, air temperature sensors will bemounted ~ 0.25 m aboveground. We will perform snow depth measurements weekly and determine volumetric water content from 0 to 12 cm using a handheld Campbell Scientific (CS, Logan, Utah, USA) HydroSense II handheld probe. Hourly ambient air temperatures and total precipitation inputs will be determined in NH using data from the NOAA Climate Reference Network Station co-located at the Kingman Farm research site (https://www.ncdc.noaa.gov/crn/data.html) and in PA from the NRCS National Water and Climate Center Station (https://www.wcc.nrcs.usda.gov/) in Rock Springs, PA.We will determine the integrated effects of the climate manipulations on the subplot environment by calculating: 1) seasonal and annual summary or air and soil temperatures and soil moisture; 2) daily snow depth and the area under the curve (AUC) of the depth and duration of snowpack; and 3) number of freeze-thaw cycles defined as the number of times soil temperature cycles from a ≤ -0.5°C to ≥ 0.5°C temperature. We will use structural equation models (SEM) to evaluate how variation in seasonal environmental variables and weed biomass interact to influence forage yields (alfalfa and orchardgrass biomass), winter injury, and alfalfa winter survival across forage management treatments. We will also use SEM to evaluate how variation in environmental variables affect weed seed persistence and timing of emergence.

Progress 01/15/23 to 01/14/24

Outputs
Target Audience:The Target Audience includes national and globalseed companies and dealers, as well as breeders that specialize in perennial forage crops. Additionally, we will target researchers, extension personnel, and farmers working with or growing forage crop. Finally, we will also target researchers at universities, government agencies, and within industry interested in climate adaptation strategies. Changes/Problems:The Objective 1 (warming and forage management effects on forage productivity)experiment was established at the UNH site in September of 2022. Replicate plots were sown with the two alfalfa cultivars (both alone and in combination) with orchardgrass on September 16, 2022, utilizing the same experimental design as was implemented at the PSU site. Unfortunately, alfalfa establishment across the treatments was poor due to a prolonged period of unfavorable weather that occurred soon after seeding. By the summer of 2023 it was apparent that the poor-quality alfalfa stand would undermine the integrity of any resulting data. Hence, rather than lose an entire study year and attempt to replant the alfalfa in another location in the fall, the decision was made to pivot at the UNH site from investigating the effects of winter warming on alfalfa/perennial forages to inter-seeded and fall-sown annual cover crops. Effects of winter warming on inter-seeded and fall-sown cover crops: While we were forced to make a modification to the project due to circumstances that were out of our control, we believe that our new experiment (described below) has the benefit of expanding the scope of our winter warming work to include an additional cropping system (annual row crops) and a cropping practice (use of annual cover crops), both of which have high regional and national importance. The degree to which anticipated winter warming may affect the establishment, overwintering survival, and subsequent spring growth of summer or fall-planted annual cover crops has important implications for the nature and magnitude of ecosystem services that cover crops provide. Reductions in cover crop survival over the winter or spring could reduce their ability to sequester soil nutrients, enhance soil organic matter, or suppress weeds. Conversely, warming winter temperatures could expand the growth window of cover crop species that typically do not overwinter reliably. Relatedly, warming winters may contribute to ecosystem disservices by changing the decomposition dynamics of cover crops and stimulating emissions of greenhouse gasses (GHG) during periods when such emissions tend to be minimal. What opportunities for training and professional development has the project provided?The PSU graduate student associated with the project presented research results at the 2024 annual meeting of the Northeastern Weed Science Society, as well as at an in-person project meeting help at UNH in 2024. He also has been analyzing data from the project and applying statistics he has learned in his PSU classes. How have the results been disseminated to communities of interest?Yes, research results were presented at: 1. The 2024 annual meeting of the Northeastern Weed Science Society 2. 2024 PSU Weed Science Field Day. What do you plan to do during the next reporting period to accomplish the goals?Pennsylvania State University In the upcoming year we will collect data for all three of our research objectives, which shall include: Objective 1: Forage biomass, as well as sugar accumulation in alfalfa root crowns, in all combinations of forage treatments that vary in variety and harvest timing within various climate manipulation treatments. Objective 2: Weed seed viability and emergence timing. Objective 3. We have temperature sensors set up in all plots to collect soil and air temperature sensors. We will also measure soil moisture frequently throughout the season. We will then analyze the collected data to summarize results to be disseminated to our target audience. Data will be analyzed by the graduate students associated with the project, with advice from the project mentors. The graduate students will present results at meetings over the course of the next year, which will also provide further training opportunities. Additionally, the graduate student will continue to analyze data from the project and begin manuscript preparation. University of New Hampshire Within the NH "Warming Effects on Cover Crops" (WECC) experiment, we will collect plant biomass and soil samples in each subplot in the spring of 2024 to determine the effects of winter warming conditions on cover crop and weed survival and biomass and soil biological and chemical parameters. Additionally, throughout the spring, within the OTC and ambient subplots we will quantify the effects of warming on greenhouse gas (N2O, CO2, CH4) emissions. Within Objective 2 (warming effects on weed emergence), weed emergence will be quantified in each plot on a weekly basis over the spring and early summer of 2024. The same experiment will be repeated in a new field the subsequent fall 2024 through spring/summer of 2025.

Impacts
What was accomplished under these goals? Pennsylvania State University Objective 1: In early Fall of 2022, we planted the alfalfa variety X harvest frequency experiment at both Rock Springs, PA and in Madbury, NH experiment. We also constructed OTCs for the experiment to initiate the climate manipulation treatments. The experimental design at both sites consisted of combination of alfalfa variety and harvests/year: 1) FD 4 (more dormant) X 4 harvests/year; 2) FD 5 (less dormant) X 4 harvests/year; 3) FD 4 + FD 5 (mix) X 5 harvests/year; 4) FD 5 (less dormant) X 5 harvests/year Throughout 2023, we collected the proposed data at the PA site: forage biomass throughout the summer (4 vs 5 harvest timepoints), periodic soil moisture readings, and soil temperature. We also collected alfalfa root crowns from each plot, and are in the process of analyzing them for soluble carbohydrate accumulation as a metric of winter hardiness. Objective 2: We established an experiment in Rock Springs, PA to examine the effects of climate manipulations and warming on weed emergence timing. We collected weed emergence data throughout the 2023 growing season, and we will repeat this experiment for one more year (2024). We are currently in the process of analyzing this data. We also continued to sample our experiment that examined the effect that warming temperatures had on the mortality rates of weed seeds in the soil seedbank. Thus far, we have found that warmer temperatures had varying effects on the mortality rate of weed seeds, with some species exhibiting greater mortality rates with warming (Redroot Pigweed), some species showing lower mortality with warmer temperatures (Large Crabgrass), and other species not affected (Velvetleaf and Common Ragweed). We are currently in the process of preparing this manuscript for publication, and hope to have it submitted in 2024. Now we are performing more controlled experiments examining warmer temperature effects seed mortality, both in the field and soon, we will also be conducting an experiment within growth chambers. Objective 3: We have installed soil temperature sensors in both Objective 1 and Objective 2 field experiments to quantify OTC effects on soil temperature, and we will do frequent soil moisture readings in both experiments. University of New Hampshire The "Warming Effects on Cover Crops" (WECC) field experiment was established in May 2023 in a field adjacent to the original alfalfa study plots at the UNH Kingman Research Farm in Madbury, NH. Soils at the site are Charlton fine sandy loams. The fall prior to establishing the experiment, the field was planted to winter rye. Prior to establishing the WECC experiment, the winter rye cover crop was terminated with glyphosate, flail mowed, and the field was moldboard plowed. Corn was then planted on May 30, 2023. Unfortunately, this initial corn crop suffered heavy crow damage, necessitating that the experiment be reestablished in June. Subsequently, corn (Red Tail Hybrid RT38T89-DI, Byron Seeds) was resown on June 21, 2023 with a Kinze 3000 four-row no-till planter at a rate of 30,000 seeds per acre on 30 inch (76 cm) rows. A post-emergence application of glyphosate was made to control weeds on July 14. Fertilizer was side dressed on July 19. On July 21 we established four cover crop treatments into the standing corn plots, each replicated four times across four adjacent blocks. Cover crop treatments were (T1) an interseeded mixture of annual ryegrass (50% of the mixture by weight), red clover (30%), crimson clover (10%), and tillage radish (10%); (T2) interseeded winter rye; (T3) winter rye sown in the fall after corn harvest; and (T4) a no cover crop control. The seeding rate for the cover crop mixture was 35 lbs/acre while the rate for both winter rye treatments was 150 lbs/acre. Interseeded cover crop treatments (T1 and T2) were sown with a Penn State Interseeder into corn on July 21 when the corn was at the V4 stage. Treatment T3 was sown on October 3, approximately one week after the corn was harvested from all plots. Cover crops were not sown into T4. To examine the effects of warming on our interseeded and post-harvest-seeded cover crop treatments we randomly assigned open-top chambers (OTCs) to one half of each treatment plot. The other half of each treatment plot (subplot) served as the ambient control. The OTCs were deployed on the plots on November 1, 2023. Each OTC consisted of the same design and materials as was used at the PSU site. Each OTC measured 2.65 (basal diameter) x 1.75 m (top opening diameter) x 0.8 m (height) and was securely anchored in each plot. Temperature and soil moisture loggers were installed in each OTC and ambient control subplot on October 26 and 27, 2023. Data collection: In addition to continuous measurements of soil and air temperatures and soil moisture, we quantified above ground biomass (cover crops and weeds) in each subplot on October 27, just prior to establishing the OTCs. At that time, we also collected soil samples (10 cm depth) in each subplot for analysis of soil variables. In addition, we installed PVC collars in the OTC and ambient subplots to quantify the effects of warming on greenhouse gas (N2O, CO2, CH4) emissions. Sampling for GHGs began February 27, 2024, and will continue on a bi-weekly basis throughout the spring until cover crop termination. We plan to quantify cover crop and weed biomass in the OTC and ambient subplots in late spring of 2024 and the experiment will be repeated in a new field beginning in the summer of 2024. Effects of warming on weed emergence dynamics: In addition to the cover crop experiment described above, the UNH site also established four OTCs in a separate nearby field that was fallow the year prior. Prior to OTC establishment, we removed all aboveground plant biomass by hand harrowing. The field was then divided into eight plots (two plots in each of four blocks). Plots within a block were randomly assigned to OTC or "ambient". The OTCs were deployed on November 21, 2023 and two temperature sensors (one buried 3 cm belowground and one 3 cm aboveground) were established in each plot.

Publications

• Type: Conference Papers and Presentations Status: Published Year Published: 2024 Citation: Koirala, N., Lowry,C., Smith, R., Contosta, A. WEED EMERGENCE TIMING IN A WARMER WORLD. 2024 Northeastern Weed Science Society Annual Meeting. Boston, MA.

Progress 01/15/22 to 01/14/23

Outputs
Target Audience:The target audience includes scientific colleagues, technical service providers, farmers, and the general public. Additionally, results will be relevant to breeders of perennial crops that strive to develop crop varieties that are more resilient to climate change and weather variability, Efforts include establishing research trials in both NH and PA which will be used to disseminate information to our target audience. Changes/Problems:Significant changes to the proposal: Because of increased cost of materials to build the open top chambers since the submission of the grant when the budget was made, we had to decrease the number of experimental units with an OTC within our experiments. Therefore, we devised a new experimental design that enabled us to fully address our research objective while also decreasing the experimental units. In doing so, we were able to improve the design of the OTCs so that they were more able to survive high wind conditions. Also, in year 1 of the experiment, we had very little snow so were unable to include the snow manipulation treatments in the experiment. What opportunities for training and professional development has the project provided?Currently, we have recruited 2 PhD students (one in PA and one in NH) for the project. These students are currently being trained in experimental design, statistics, ecology, agronomy and agricultural practices, and climate change. These graduate students are attending the lab meetings of our individual labs, as well as benefiting from one on one meetings with their advisors. They are both currently working on developing their dissertation research proposals and obtaining the training needed to complete their dissertation research, which includes taking multiple courses in statistics. How have the results been disseminated to communities of interest? Nothing Reported What do you plan to do during the next reporting period to accomplish the goals?In the upcoming year we will collect data for all three of our research objectives,which shall include: Objective 1:Forage biomass, as well as sugar accumulation in alfalfa root crowns,in all combinations of forage treatments that vary in variety and harvest timing within various climate manipulation treatments. Objective 2: Weed seed viability and emergence timing. Objective 3. We have temperature sensors set up in all plots to collect soil and air temperature sensors. We will also measure soil moisture frequently throughout the season. We will then analyze the collected data to summarize results to be disseminated to our target audience. Data will be analyzed by the graduate students associated with the project, with advise from the project mentors. The gradaute students will present results at meetings over the course of the next year, which will also provide further training opportunities.

Impacts
What was accomplished under these goals? Objective 1:In early Fall of 2022, we planted the alfalfa variety X harvest frequency experiment at both Rock Springs, PA and in Madbury, NH experiment. We also constructed OTCs for the experiment to intiate the climate manipulation treatments. The experimental design at both sites consisted of: varieties harvests/year FD 4 (more dormant) X 4 harvests/year FD 5 (less dormant) X 4 harvests/year FD 4 + FD 5 (mix)X 5 harvests/year FD 5 (less dormant) X 5 harvests/year Objective 2: We established an experiment in Rock Springs, PA to examine the effects of climate manipulations and warming on weed emergence timing. We also continued to sample our experiment that examined the effect that warming temperatures had on themortality rates of weed seeds in the soil seedbank. Thus far, we have found that warmer temperatures had varying effects on the mortality rate of weed seeds, with some species exhibiting greater mortality rates with warming (Redroot Pigweed and Common Ragweed), some species showing lower mortality with warmer temperatures (Large Crabgrass), and other species not affected (Velvetleaf). Objective 3: We have installed soil temperature sensors in both Objective 1 and Objective 2 experiments to quantify OTC effects on soil temperature, and we will do frequent soil moisture readings in both experiments.

Publications