Project Details:

Title:
Evaluating Deer Preferences for Soybean Varieties and Soybean Response to Deer Herbivory

Parent Project: This is the first year of this project.
Checkoff Organization:Delaware Soybean Board
Categories:Insects and pests, Environmental stress
Organization Project Code:65443
Project Year:2022
Lead Principal Investigator:Luke Macaulay (University of Maryland)
Co-Principal Investigators:
Nicole Fiorellino (University of Maryland)
James Lewis Jr (University of Maryland)
Keywords: deer, deer management

Contributing Organizations

Funding Institutions

Information and Results

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Project Summary

Deer are the leading cause of crop damage by wildlife in Maryland, with most recent government estimates showing approximately $10 million in losses annually, with 77% of those losses attributable to deer (USDA NASS 2011). Maryland in particular faces greater challenges than many other soybean growing areas in the country due to smaller field sizes that are more often interspersed with and bordered by forested areas that provide refuge for deer, which emerge to graze highly palatable and nutritious soybeans. Farmers have regularly identified deer and wildlife damage as one of their top concerns, and frustrations by farmers are well documented in news media articles. Soybean yields in 2020 in certain fields at the Wye Research & Education Center in Queenstown, MD, were reduced by 20-30 bushels per acre in a field bordering a forested area. While hunting and crop damage permits allow some farmers to reduce deer population densities, some locations are not amenable to this due to factors such as landowners or neighbors that do not allow hunting, nocturnal grazing activity, and time required to harvest sufficient numbers of deer.

In 2021, we engaged in research to better understand deer preferences and plant response in agricultural fields with forest edge and with consistent deer damage. The study found a surprising performance of a less expensive ($50/bag) Group 4.7 forage soybean, GT1 Brier Ridge from Lacrosse Seed as one of the higher performing varieties just after a Group 5.3 conventional soybean. These yields were considered by the farm manager as some of the best yields he’s observed out of these fields in many years.

A forage analysis of all the varieties in early September 2021 suggested that increased levels of crude protein and lower levels of dry matter may have driven preferences for a late maturing soybean variety. Camera trap data from 2021 also revealed that deer preferences may be tied to maturity group as data suggests a move from earlier varieties (Brier Ridge, Biologic, and conventional Pioneer Group 3.1 beans) to later varieties (Big Fellow, and Pioneer Group 5.3 beans) as the growing season progressed. In this proposal, we propose conducting more regular forage analysis (every 3-4 weeks during the growing season) to determine if forage quality changes with different varieties over time.

Past research suggests that timing of defoliation is important in effects of yield, with most significant effects on yield occurring at the full pod (R4) to full seed (R6) stages of development (Caviness & Thomas, 1980). We hypothesize that later maturing soybeans could serve to divert grazing off of earlier maturing varieties in their more vulnerable reproductive stages.

Project Objectives

Ongoing research has provided baseline information about the applicability of using various varieties of forage soybeans as a diversion crop around a field perimeter to reduce damage to core growing areas. This project seeks to continue that work and gain deeper understanding across a second growing season by continuing to assess 1) yield by different forage soybean varieties and 2) deer activity and preferences of these varieties. We seek to add to the project by 1) conducting regular forage analyses across the growing season to discern whether deer prefer certain varieties at certain times; 2) conducting a manual defoliation experiment to better understand soybean plant response to herbivory, and 3) providing a greater quantity of demonstration seeds to farmers and assessing their qualitative and quantitative observations about the practice.

Project Deliverables

We will focus the experimental effort at the Wye Research & Education Center, using a randomized complete block design on approximately five-seven soybean varieties in fields bordering forested areas with long-term historical deer grazing pressure. We will place a 5-10’ diameter hog-wire deer exclosure on each plot to asses yield potential in the absence of
grazing. We will expand the use of trail cameras to quantify deer grazing activity by different soybean varieties to gather improved information on deer preferences and activity across multiple replicates.

We propose planting the following varieties in a strip plot design:
1. Conventional Group 3.5 soybean - control
2. Group 4.7 forage soybean – GT1 Brier Ridge
3. Group 7 forage soybean – Big Fellow Eagle Seed brand
4. Group 6 forage soybean – Biologic
5. Conventional Group 5 soybean

To better understand soybean plant response to deer grazing, we plan to conduct a controlled herbivory simulation in a deer-proof fenced enclosure at the Wye Research & Education Center. We propose planting approximately 90 plants of each variety and leaving 30 without defoliation, 30 with weekly light defoliation (~33% defoliation), and 30 with weekly heavy defoliation (~66% defoliation). We will use weekly defoliation, which is consistent with observed deer grazing in 2021 that appeared to occur in heavy bouts approximately every 5-7 days. We plan to conduct this on the same five varieties that we will be testing in our strip plot design. We will sample a subset of plants for biomass at the R6 /R7 stage, when leaves begin to yellow, and harvest the rest of the plants for yield at normal harvest time.

We will use a thermal imaging camera mounted on a drone to test the applicability of using this approach to measure populations and quantify broader scale deer activity and populations in the area. We propose flying approximately 6-12 evening flights on a pre-determined survey path along field edges near forest cover to determine the applicability of using drone sampling as a method to detect deer populations and activity in agricultural fields. Multiple flight data will: Proposed strip plot layout with multiple replicates of varieties in a randomized complete block design, deer exclosures, and camera traps will be placed on each treatment for monitoring deer usage. provide us the opportunity to assess variability in deer activity and better understand the prerequisite number of flights needed to determine a deer population estimate for a given area.

Finally, we have reserved a large portion of the budget to provide demonstration seeds of forage varieties at a collaborating farmer’s fields on the Eastern Shore to evaluate performance of these varieties in different soil types and with different deer population characteristics. We will prioritize provision of demonstration seed to farmers who have a history of yield-monitor data on proposed fields of planting to compare before and after effects of buffer treatments.

Progress of Work

Updated July 19, 2022:
We have planted two fields with forage soybeans. Weeds have been sprayed. ~32 cameras are monitoring deer use of each variety. Experimental clipping to simulate deer grazing is underway. We are clipping biomass every 1-2 weeks, and taking forage samples every other clipping.

Updated December 19, 2022:
We completed the growing season and the manual clipping experiment. We have completed harvest on all plots. We have gathered forage analysis data. We have reviewed thousands of wildlife photos. Analysis and writeup is next up on our plate! Happy to share additional details if desired! Luke Macaulay c: 703-798-8459.

Final Project Results

Updated November 18, 2023:
See attached report. Thank you for your support!

View uploaded report PDF file

In summarizing the multi-year forage soybean research supported by the Maryland Soybean Board, the effectiveness of forage soybeans as an effective buffer to deter deer damage remains tentative. Although methods are limited in our study to the use of trail cameras that may not accurately capture deer activity in different plots, clear preferences by deer for specific soybean varieties have not been established, suggesting that factors such as proximity to cover may play a more significant role in deer grazing habits.

Biomass measurements from different field seasons have provided insights into grazing and plant vigor. We found evidence to suggest that moderate deer grazing could potentially lead to compensatory growth in soybeans. We also found that protecting soybeans early in the growing season from heavy grazing can result in the later growth of much more biomass in mid-summer, which can outgrow deer appetites. Interestingly, we found in 2023 that the biomass of a conventional Pioneer group 5.3 soybean matched that of Eagle Seed Big Fellow variety.

Forage analyses and yield results also offer a mixed picture. While there may be minor increases in sugar content and crude protein for certain forage soybean varieties, the differences seemed relatively minor and cast doubt on significant preferences that can be revealed through forage analyses. Yield data indicates that some forage varieties can maintain production under high grazing pressure; however, concerns about the replicability of these findings and the potential for measurement errors must temper any conclusions drawn.

Yield analyses from previous years indicate that while some forage soybean varieties can perform comparably to conventional ones under grazing pressure, variations in yield and the complex nature of deer grazing effects on soybeans highlight the need for further research.

Farmers had an overall positive perception of forage soybeans' utility ranking as a 7 on a scale of 0-10, which does provide some encouragement for their future application. Still, the survey results should be interpreted with caution due to the subjective nature of such assessments, low sample size, and confirmation bias.

One component of forage soybeans that may warrant further study or explain the efficacy that farmers see is the role of later maturity group soybeans to draw deer away from earlier maturing varieties even in the middle of summer. Our methods were limited in their ability to detect this behavior, but it could very well be occurring outside our ability to measure it using the methods available. A future study could place GPS collars on a large number of deer and then track with much greater precision where each deer is spending its time, which may reveal preferences we were not able to do using trail cameras.

A final note about the use of the term “forage soybean.” In most cases we found differences in the characteristics of forage soybeans to conventional soybeans. Usually, they are characterized by long viney growth patterns that often lodge in mid-summer. However, some soybeans marketed as “forage soybeans” sometimes appear to simply be conventional soybeans marketed as forage soybeans.

Preliminary Conclusions and Recommendations

After 3 years of work on forage soybeans, I would recommend different approaches to using soybean buffers depending on a few factors, especially focused on herbicide traits, and timing of hunting programs:

Because deer did not appear to prefer any soybeans over another, my recommendation is to focus on high-biomass producing soybeans that will feed a greater number of deer. In 2023, we found that a conventional Pioneer group 5.3 soybean, was able to match Eagle Seed’s Big Fellow forage soybeans in biomass production

If a farmer has weed issues that require herbicides beyond glyphosate, I would recommend a conventional group 5 soybean, which can produce high biomass, be resistant to additional herbicides, and produce a high yield.

If a farmer is interested in using a soybean buffer as part of a lethal control or hunting program that includes a heavy focus on early hunting in September, I would recommend the latest maturity group variety available. In the soybeans we studied, Eagle Seed has a high biomass producing forage soybeans that will stay green partway into the second half of September which aligns with the early archery hunting season in many places, and may draw deer into the field for that. Note: other food plot species stay green later into the season, including cowpeas and lablab, but I am not aware of any commercially available varieties with herbicide resistant traits, limiting farmers to grass-selective herbicides for weed control.

If farmers want to use an unharvested soybean buffer as a food-plot attractant for a lethal control or hunting program later in wintertime and are not interested in early season hunting, I would recommend a group 5 high-yielding and high-biomass-producing conventional soybean.

If a farmer is interested in hunting in both early season and late season, and glyphosate tolerant varieties are sufficient, I would consider a mix of conventional and forage soybeans to achieve green forage in the early season, and a good yield of soybeans in winter.

Benefit to Soybean Farmers

Performance Metrics

Project Years