Progress report for GNE24-332
Project Information
Forage growers in Pennsylvania and the northeastern US are facing
challenges due to climate change and may need to adapt management
practice to mitigate climate risks on forage productivity and
quality. Knowledge on how crop management practices will perform,
both in terms of productivity and quality, under future climatic
conditions will allow us to identify climate resilient management
practices. To address this knowledge gap, we are conducting a field
experiment examining how forage management practices (harvest
frequency and alfalfa variety) under normal or elevated
temperatures affect forage quality. Specifically, we will examine
how warmer temperatures and forage management affect protein and
fiber concentrations within forage tissue at critical harvest
timepoints likely to be responsible to both temperature and
management. We are using open-top chambers to increase temperature
within the field. We will also examine the effects of management
on forage productivity, but that is outside the scope of this
proposal. Maintaining forage quality is important because of its
economic significance to forage growers and dairy farmers. This
analysis will enable us to understand the dynamics of
environmental effects on forage quality and make better
recommendations to the farmers about how to maintain forage
quality in response to environmental variation. We plan to
disseminate our results through different scientific and
extension presentations and publications.
Objective 1
To quantify the effects of forage management (harvest frequency
and alfalfa fall dormancy levels) and temperature (ambient and
warming) on forage quality at different harvest time points in an
alfalfa and orchardgrass mixture.
Hypothesis 1: More frequent harvests and the
alfalfa variety with lower fall dormancy (FD5) will produce
higher protein (CP) and lower fiber (NDF, ADF, and ADL) content
(a better quality) in alfalfa and orchardgrass under warmer
growing conditions compared to ambient temperature.
Warmer temperatures are usually reported to decrease forage quality, but
we predict that increased temperature combined with five harvests
per year will have increased forage quality compared to when five
harvests per year is combined with ambient temperature. In
contrast, we predict that the four harvests per year and higher
fall dormancy (FD4) variety will have increased forage quality
under ambient compared to warmer temperatures.
Hypothesis 2: More frequent harvests will result
in better forage quality for orchardgrass under warmer growing
conditions.
Objective 2
Determine to what extent environmental factors (including soil
and air temperatures, and growing degree days (GDD)
measured/calculated at plot level) predict forage quality, and
whether this varies between different harvest time points.
Hypothesis 1: Higher temperatures and GDD
accumulation will be associated with higher fiber content and
lower protein content (a poorer quality) in both alfalfa and
orchardgrass.
The purpose of our proposed research is to identify climate resilient forage management practices by examining how harvest frequency and alfalfa variety affect forage quality under warmer temperatures.
Global climate change is challenging us to develop resilient cropping systems. Comparing the pre-industrial era (1850 - 1900 AD) to the last decade (2011 - 2020), estimated global temperature increase was 1.09 °C (0.95 to 1.2 °C) and is projected to reach 1.5 °C in the early 2030s (Arias et al., 2021). The northeastern US is experiencing warmer winters with greater temperature fluctuations throughout the season (Brown et al., 2010). Increased frequency of heavy rainfall, summer droughts, and heat stress are major vulnerabilities for cropping systems in the northeastern US (Wolfe et al., 2018). In the lieu of these challenges, agricultural research driven by farmers’ interests and needs can be effective in risk mitigation and adaptation to changing climate (Schattman et al., 2023)
Perennial forages face environmental variation year-round and are therefore, vulnerable to year-round temperature oscillations, especially during extreme winter weather fluctuations (Bélanger et al., 2002; Gu et al., 2008; Hristov et al., 2018). The warming temperature is predicted to increase perennial forage production (Rotz et al., 2016). However, the highly variable winter might decrease winter survival (Bélanger et al., 2002; Hristov et al., 2018) and reduce productivity. For cold-humid regions including northeastern US, studies have indicated a need for change in management practice to maintain resilience in forage production and quality (Thivierge et al., 2023).
Farmers in the Northeast are willing to shift management practices to adapt to climate change (Lane et al., 2018). Two perennial forage management practices that farmers are already adjusting to take advantage of warmer temperatures include increasing the number of harvests per year and changing their crop varieties. Switching to more frequent harvests and extending last harvest date further than the regular practice will theoretically allow us to utilize additional growing degree days (GDD) and thereby, harvest more biomass. Similarly, alfalfa varieties with a lower fall dormancy could continue growth late into fall, initiate regrowth earlier in spring, and have more rapid growth after harvest; enabling additional harvests and potentially increasing annual yields (Brummer et al., 2000, 2002; Undersander, 2017).
The frequency and timing of forage harvests are key factors in determining yield, forage nutritive value (Brink et al., 2010; Kallenbach et al., 2002; Rimi et al., 2014), and winter survival (Dhont et al., 2003; Ventroni et al., 2010). Early spring (first harvest) and late summer (third harvest) are likely when forage harvests will be most impacted by winter injury or heat stress, respectively (Wolfe et al., 2018). Shifting management practice to more frequent harvests and variety with lower fall dormancy level can increase winter injury and thereby negatively impact both the yield and quality of production (Dhont et al., 2002, 2003; Thivierge et al., 2023). Similarly, heat stress can reduce N and protein content, and increase non digestible fiber accumulation in plant tissues thus reducing forage quality (Buxton & Fales, 1994; Moore et al., 2020).
Alfalfa (Medicago sativa L.) or alfalfa-grass mixtures (such as orchardgrass (Dactylis glomerata L.)) are the most prominent forage systems for Pennsylvania (PA) as well as for the northeastern US and eastern Canada (Thivierge et al., 2023). Covering 23% of the area under hay production, alfalfa accounted for 40% of the value of production in the year 2022 in PA suggesting its importance in forage systems (USDA-NASS, 2023) with its higher protein content. Because alfalfa and alfalfa-grass mixtures are economically vital to our region, understanding how warmer temperatures and management may affect forage quality is critical to identifying climate resilient cropping systems.
To develop strategies for coping with climate change scenarios, climate manipulation experiments are often employed to understand how plants will respond to weather variation. However, warming effects on forage cropping system and especially forage quality parameters are less studied (Dumont et al., 2015) despite temperature affecting forage quality more than other environmental variables (Buxton & Fales, 1994; Moore et al., 2020). Our study tries to fill this knowledge gap and develop a management strategy that is well adapted to future warmer temperatures. This aligns with the Northeast SARE’s outcome statement of ensuring agricultural sustainability, resilience, and economic viability with the proper use of available resources.
Research
While increased temperatures may increase biomass production (Rotz et al., 2016), we also need to maintain the quality of forage produced, as it is of greater economic importance (Nelson & Moser, 1994). In general, forage quality is rated higher when there is lower complex fiber content and higher protein content. Forage quality could differ in terms of crude protein (CP) and cell wall (neutral detergent fiber, NDF) concentration due to differences in maturity levels regulated by both harvest frequency and forage genotype (Liu et al., 2024; Mitchell et al., 2020). In addition to CP and NDF, acid detergent fiber (ADF) and lignification are important quality parameters that are highly influenced by our management practices as well as environmental variability (especially temperature fluctuations) due to climate change (Buxton & Fales, 1994; Moore et al., 2020; Nelson & Moser, 1994).
This project will be conducted as a separate but integrated part of an ongoing forage management project, which investigates how warming and forage management influence forage productivity. The materials and methods associated with the proposed project will be discussed in this section, noted as the forage quality project. The forage management project, funded by a USDA NIFA AFRI grant, includes the warming impacts on forage productivity, winter survival, and carbohydrate metabolism throughout the cropping duration. We believe the proposed project will result in additional, yet essential knowledge and enable us to make better recommendations for a resilient forage cropping system, both in terms of productivity and quality, in future warmer conditions.
General experimental details (objectives 1 and 2)
Site characteristics: Our study site is located at the Pennsylvania State University R.E. Larson Research Center in Rock Springs, PA (40°43' N, 77°55' W, 350 m elevation). Soils are primarily comprised of Hagerstown silt loam (fine, mixed, mesic Typic Hapludalfs). The site is characterized by a cool temperate climate with a mean annual air temperature of 10 °C, mean monthly temperature range from -2.6 °C (January) to 22.3 °C (July), mean annual precipitation of 1055 mm, and mean annual snowfall of 1113 mm (30-year average from 1991-2000 for a nearby area (NCEI-NOAA, 2021).
Experimental design and field layout: To address our proposed research objectives, we have established a field experiment examining the effects of forage management (main plot) and temperature manipulation (split plot) in a split-plot randomized complete block design with four replicates (see the attached plot plan).
The forage management main plots include four treatment levels varying in their combination of harvest frequency and alfalfa variety differing in fall dormancy levels.
The four main plot treatments are:
- more dormant and four harvests (FD4×4), the current practice for our region;
- less dormant and four harvests (FD5×4), a climate transient practice;
- mix dormant and five harvests (FD4/5×5), a climate transient practice;
- less dormant and five harvests (FD5×5), a targeted future practice under warmer conditions.
The split-plot factor is temperature with two levels: 1) ambient control (Control) and 2) warmer temperature (Warming). For warming treatments, hexagonal open top chambers (OTCs) with ~2m top diameter (built based on modified International Tundra Experiment (ITEX) guidelines (ITEX, 1996; Marion et al., 1997)) were installed in November 2022. The area allocated for each experimental unit in the field is 6.4 × 15.24 m in order to do the mechanical harvests and fit the OTCs properly, but the actual plot size used for the experiment is 1 m2.
Crop management: The two varieties of alfalfa in our experiment are AFX 469 and AFX 579 with fall dormancy ratings 4 and 5 respectively (Alforex Seeds, La Crosse, WI), while a single genotype of orchardgrass was used (all seeds obtained in 2022). The alfalfa variety with a higher fall dormancy rating is less dormant in nature and it maintains a higher growth rate later into the fall and initiates regrowth earlier in the spring. The alfalfa and orchardgrass are grown as a 70/30 mix with 17.8 cm row spacing. Across all treatments, the seeding rate was 16.8 kg ha-1 alfalfa and 5.6 kg ha-1 orchardgrass.
Prior to planting in August 2022, the field was chisel plowed, disked, and cultipacked. The harvests are scheduled based on our crop management treatments.
Forage treatments will be harvested either four or five times per year (see treatment list above). In both four harvests per year treatments, harvesting is based off the recommended practice of waiting until alfalfa enters the bud to early flowering stage, and the last harvest occurs at the end of September. Within the five harvests per year treatment, harvest decisions are based on time intervals, such that the last harvest timepoint occur in mid-October, the first harvest timepoint is when alfalfa is in bud to early flowering stage (same as first harvest timepoint in four harvests per year treatments), and the three middle harvests are evenly spread temporally between those two timepoints (mimicking a farmer that bases their harvest schedule based on seasonal timing).
Thus far, we have conducted all four or five harvests (depending on treatments) throughout 2023 (already completed) and we will repeat throughout 2024. In 2025, we will only harvest the first timepoint from all treatments, after which the study will be concluded. Harvests are done mechanically using a flail harvester, with blades set to leave 10 cm residual stubble. Fertilizers were applied according to the soil test report before planting and after the first year of harvest was completed.
Data collection (objectives 1 and 2)
Field data: The hourly soil temperatures at 3 cm and 10 cm depth and air temperatures at 15 cm height are being measured from each plot after the installation of OTCs using HOBO Pendant® data loggers (Onset Computer Corporation, Bourne, MA). Ambient temperature and precipitation data for Rocksprings PA (study site) will be obtained using the air and water database public reports by National Water and Climate Center, USDA-Natural Resources Conservation Service.
Biomass data: Forage biomass samples will be harvested 1 day earlier to the mechanical harvest from 0.5 m2 area out of the 1 m2 plots using handheld electric shears, leaving behind 10cm stubble. The samples will be sorted into species (separating alfalfa, orchardgrass, and weeds), dried at ~60 °C for one week, and weighed.
Forage quality data: Due to the high cost of the forage quality analyses, we are unable to examine forage quality analysis at every harvest time point. Therefore, the forage quality analysis will be done on four harvest time points: the third harvest from 2023, first and third harvests from 2024, and first harvest from 2025. The reason these time points were selected is because, early spring (coinciding with our first harvest) and late summer (coinciding with our third harvest) are reported to be most impacted by winter injury or heat stress, respectively (Moore et al., 2020; Wolfe et al., 2018).
The samples for each of these harvest time points will be ground using a Wiley mill and stored in paper envelopes at room temperature until they are sent for the quality analysis. The alfalfa and orchardgrass samples will be shipped to the Custom Laboratory, Monnet, MO for the analysis of analytical dry matter, crude protein (CP), neutral detergent fiber (NDF), acid detergent fiber (ADF), and acid detergent lignin (ADL). All these analyses will be done using wet chemistry approach in the laboratory.
Finally, we will do a NIR spectroscopy forage quality analysis at our collaborating mentor – Guojie Wang’s lab to explore differences in quality parameters due to warming. The NIR spectroscopy will allow us to measure different nutrients and minerals from the forage samples. This analysis will not be done on the samples to be sent for analysis and the results will only serve as supportive information to our actual analysis results.
Statistical Analysis
The statistical analysis will be conducted using R. For objective 1, the analysis will be done separately for each quality parameter, plant species (alfalfa and orchardgrass), and time points. A two-way ANOVA with the specification of effect size will be conducted and interaction between factors will be assessed to test the hypothesis 1. The treatments FD4×4 & FD5×4, and FD45×5 & FD5×5 will be grouped and contrasted to test the hypothesis 2 if no interaction effect is observed. A linear mixed effects model will be used to analyze the fixed effects of forage management and climate manipulation on forage quality, and block will be included as a random factor.
For objective 2, linear mixed effects models will be used to determine to what extent environmental variation predicts forage quality. The fixed effects will include daily mean soil temperatures at 3 and 10 cm depth, air temperature at 15 cm height and growing degree days (GDD) averaged for each harvest interval (days between previous and the harvest of concern). Blocks will be included as a random factor.
So far, we do not have any results to present. We have concluded all the harvests from the year 2024. We have also ground the forage samples and stored them. We will send these samples for the quality analysis together with the samples from 2025 this summer.
Education & Outreach Activities and Participation Summary
Participation Summary:
So far, we have conducted an on-farm demonstration of our research field during the Pennsylvania Forage and Grassland Council's research tour on 14th August 2024. We explained our research objectives, treatments, and management practice to around 40 tour participants (comprising both forage growers and extension personnel). The participants were interested in learning more about the open-top chambers (OTCs) and the visible differences within our research field because of different harvest schedules. People asked questions about our choice of varieties and the quality metrics we intended to test. Overall, the demonstration tour was successful in reaching out to the forage-related personnel.
The original plan (from the proposal) was to present the results from this project to farmers, extension, personnel, students as well as other stakeholders through different meetings and outreach platforms described below:
Scientific community outreach
ASA, CSSA, SSSA Annual Meeting, November 2025: I will present our research findings to different personnel from academic, industry, non-profit, and government backgrounds at the tri-societies annual meeting. The audience will be from a larger demographics and diverse backgrounds. There will be professionals working on the sector of forage production systems as well as climate change.
Penn State Climate Solutions Symposium, May 2026: Penn State Climate Consortium, comprising numerous interdisciplinary Penn State Faculty and researchers working on the frontiers of climate change research, organizes the climate solutions symposium every year. I will present a poster with my results at this symposium. It would be interesting to present about developing a climate resilient management practice, as well as learn from other climate change researchers during this symposium.
Publication in a peer-reviewed journal, July 2026: A peer-reviewed article will include key findings and observations from our project. This will be useful to researchers as well as extension personnel working in the field of climate change and cropping systems.
Extension outreach
Pennsylvania Sustainable Agriculture (PASA) Conference, January 2026: The PASA conference is featured by the presence of a diverse audience including rural and urban farmers, educators, advocates, policymakers, entrepreneurs, and other stakeholders concerned about sustainable agriculture. We are hopeful that, through this conference, we will be able to reach more of the young and beginning farmers as these groups are especially more inclined towards sustainability. Our results would be very relevant to be presented at this conference as the avenues we are exploring (perennial forage systems and climate resilient agriculture) are important in terms of agricultural sustainability.
The Pennsylvania Forage Conference, February 2026: This conference is organized every year by the Pennsylvania Forage and Grassland Council in cooperation with Penn State Extension. With the help of our collaborating mentor Dr. Guojie Wang, I will present the results to the forage growers and related stakeholders in Pennsylvania.
Outreach through Penn State Extension: Our collaborating mentor Dr. Guojie Wang is a member of the Penn State Extension- Field and Forage Crops team. We will coordinate with Penn State Extension to present our results as well as in the preparation of extension articles, news, and video presentations related to our project. We will also try to do a demonstration of our research field and explain the management practices we are using to explore climate resilient practice during one of the related Extension field days. We will also post updates from our project on the Facebook page of Penn State Extension Field and Forage Crops which has over 1400 followers. We plan to reach out to forage, cover crops, and dairy farmers through this integrated extension approach.