1. Effects of genotypic diversity on forage stand productivity
I’m here to tell you a little bit about some research that we have been doing over at UNH related to the effects of genotypic diversity on forage stand productivity.
Dr. Richard Smith, Dr. Fred Pollnac, Nick Warren, Dept. of Natural Resources and the Environment

2. *Genotypic Diversity Pressing Issues
A recent needs assessment of organic dairy producers in the Northeast revealed a desire for research aimed at extending the grazing season (so as to ensure compliance with new NOP pasture rules)
Increasing variability in temperature and precipitation patterns associated with climate change presents additional challenges for maintaining high quality and productive pastures
*Genotypic Diversity
The two main issues that initiated this research were the results of a needs assessment, and potential for increased climatic variability in the future.
NOP Pasture rule = Access to pasture throughout the grazing season (specific to their geographical climate)
Diet consisting of at least 30% dry matter intake from pasture grazed during grazing
season, totaling at least 120 days.
Conventional farmers don’t need to deal with the NOP pasture rules, but may also benefit from extending grazing season
Climatic variability will be something that all farmers will have to deal with, regardless of their management strategy
One tool that is available and that can address both of these issues is the incorporation of genotypic diversity

3. Genotypic Diversity Defined Genotype = Cultivar (Perennial Ryegrass, Remington) Genotypic Diversity = Cultivar Diversity In Practice = Growing several cultivars in the same pasture together
A genotype is just another name for a single cultivar of a forage species
Genotypic diversity means growing several cultivars of a forage species in a forage stand at the same time

4. Single Cultivar Three Cultivars
Production
Environmental Conditions
Growing Season
(length of grazing season)
Duration of growth
Year
Three Cultivars
Production
Environmental Conditions
Growing Season
(length of grazing season)
Duration of growth
Year
The theory behind this research is that single cultivars have a zone of optimal performance or production during the growing season.
If conditions are optimal for that cultivar, production will be high. If conditions are not optimal for that cultivar, production will be lower.
Since environmental conditions aren’t stable during most growing seasons, or between years, productivity may be unstable throughout the growing season or between years if a single cultivar is used.
Adding more cultivars with different environmental tolerances may help to stabilize production over time, and may extend the growing season as well
***If conditions aren’t optimal for one cultivar, they may be optimal for another one in the mix, so performance is maintained under unstable environmental conditions
Extending grazing season/Increasing productivity
Dealing with environmental uncertainty
**Working with perennial ryegrass, but should be transferrable to other species
R. Smith

5. Genotypic Diversity Benefits Short Term: Increased forage productivity throughout the growing season Long Term: Stability of forage production from year to year
In the short term, genotypic diversity can potentially increase productivity throughout the growing season by including several different cultivars that are adapted to particular points in the growing season (early maturing, cold hardy, heat tolerant etc)
In the long term, inclusion of several cultivars is like an insurance policy guarding against climatic variability. i.e. if you have a particularly dry year, and you have a drought tolerant cultivar in your pasture, this will help to maintain productivity.

6. Establishing a pasture…
We established fields of perennial ryegrass on 2 of UNH’s research farms. At each site, we tilled and planted either plots of monocultures (single cultivars) or mixtures (several cultivars), at the recommended seeding rates. We spread seed either by hand when the plots are small, or as in the field pictured, we used a cone seeder, which works very well for evenly seeding large areas.
Monocultures and Mixtures of perennial ryegrass
2 Locations – UNH Kingman Farm, UNH Organic Dairy Research Farm (ODRF)
ODRF study is repeated in 4 states (NH, VT, ME, PA)

7. Once the fields are established, the process for gathering information is relatively straightforward. We measure the height of the ryegrass as it grows, and when the field reaches a certain height we harvest a small square (1/4 meter’s worth) from each one of our plots. The weeds are separated from the ryegrass and everything is then dried and weighed. Once we have harvested what we need from the field, we mow and bale everything that remains – this is an effort to simulate grazing cows, without the unpredictability of having animals on the field. Last year we repeated this 5 times before the growing season was over. The yield, or weight, and height from each of the plots is primarily how we compare each one of the treatments.

8. Three Measures of Forage Stand Productivity Dry Matter Yield Index
Response to Cutting
We are currently focusing on three main indicators of productivity:
Dry biomass taken per season
Yield index, compares relative productivity of monocultures and cultivar mixtures
Response to cutting, measures how quickly forage recovers from mowing (but we have very limited data for this at present)

9. Cultivar Diversity (no. of cultivars)
Results: Dry Matter
Ryegrass dry matter production vs cultivar diversity 1 3 6
Cultivar Diversity (no. of cultivars)
100
200
300
400
500
600
700
800
900
Dry Matter (grams per m2) b b a
This graph shows the average total dry biomass harvested from plots of 1, 3, and 6 cultivars over 2 years of the study.
The 1 cultivar plots have significantly lower dry matter than the 3 and 6 cultivar plots
However, there were 6 types of monocultures (not just the recommended cultivar) and the 3 cultivar mixtures were just random mixes from those 6. The 6 cultivar plots obviously contained all 6 cultivars

10. Ryegrass dry matter production vs treatment
Results: Dry Matter
Ryegrass dry matter production vs treatment T1 T2 T3 T4 T5 T6 T7
Treatment
440
480
520
560
600
640
680
720
760
800
Total Dry Matter (grams per m2)
This plot shows the dry matter harvested from the indicated treatments across the growing season of 2013.
The treatments were purposeful mixes, not just random like the last study
Each treatment included the recommended cultivar, but also included other cultivars to achieve the desired treatment (i.e. treatment 2 included other cultivars with earlier and later heading dates than remington)
Numbers after treatment represent the number of cultivars in the mix
There were no significant differences, although many of the treatments had higher mean yields than the monoculture
This is only one year of data, and it will be interesting to see if the mixtures have a more stable yield over the duration of this project (3 years) than the monoculture
It is important to note here that no significant differences means that the mixtures aren’t doing any worse than the recommended cultivar!
T1 = recommended cultivar (1)
T2 = earlier and later heading date (3)
T3 = even earlier and later heading date (5)
T4 = diversity within winter hardiness (5)
T5 = heading date within winter hardiness (5)
T6 = commercial blend (4)
T7 = winter hardiness within heading date (5)
P = 0.52
**Mixtures aren’t less productive than recommended cultivar

11. May Dry Matter (grams per m2)
Results: Dry Matter
Ryegrass dry matter production vs treatment T1 T2 T3 T4 T5 T6 T7
Treatment 40 80
120
160
200
May Dry Matter (grams per m2)
This is the same comparison, but just using data from the first harvest in May
Much closer to statistical significance, and the treatment with increased heading date range and the one with most winter hardiness range did the best as one would expect, since May is early in the growing season and can be a colder time of year.
T1 = recommended cultivar (1)
T2 = earlier and later heading date (3)
T3 = even earlier and later heading date (5)
T4 = diversity within winter hardiness (5)
T5 = heading date within winter hardiness (5)
T6 = commercial blend (4)
T7 = winter hardiness within heading date (5)
P = 0.15

12. What is a yield index? Results: Yield Index Monoculture Yield
Cultivar 1
Cultivar 2
Cultivar 3
Mixture Yield
Predicted
300g/m2
Observed
375g/m2
260g/m2
300g/m2
Another way to think about productivity is in terms of how the mixtures perform in comparison to some predicted yield based on their components.
If we know what the yields of 3 cultivars are in monoculture at a given seeding rate, and we plant a mixture with those three cultivars in equal proportion using the same overall seeding rate, then we can predict what the yield of that mixture will be in the absence of competition or facilitation
We then divide the observed yield by the predicted yield to determine if there is facilitation, competition, or neither, and this is called a yield index.
Observed/Predicted Yield = Yield Index
1 = predicted yield
>1 = over-yielding
<1 = under-yielding

13. What is a yield index? Results: Yield Index Monoculture Yield
Cultivar 1
Cultivar 2
Cultivar 3
Mixture Yield
Predicted
300g/m2
Observed
375g/m2
300g/m2
260g/m2
We saw significant over-yielding in our study (yield index significantly greater than 1) indicating some type of facilitation.
However, without further studies, we cannot be exactly sure why this happens.
One possible reason is that different genotypes utilize resources differently, so may be less competition between individual plants for:
Water
Light
nutrients
Observed/Predicted Yield = Yield Index
1 = predicted yield
>1 = over-yielding
<1 = under-yielding
**We saw significant over-yielding, why?

14. Fall Growth Rate vs Treatment
Results: Response to Cutting
Fall Growth Rate vs Treatment T1 T2 T3 T4 T5 T6 T7
Treatment
0.0
0.1
0.2
0.3
0.4
Growth Rate (cm/day) a* b* ab
This graph shows the fall growth rates of the different treatments, or there growth response immediately following the last harvest (period from november 14th to december 2nd)
This response will be monitored throughout the entire growing season next year
This particular graph shows that the treatment with the biggest range in heading dates has the largest growth rate late in the season.
This shows that combining cultivars may be an effective way to maintain productive pastures later into the growing season (thereby extending the growing season)
T1 = recommended cultivar (1)
T2 = earlier and later heading date (3)
T3 = even earlier and later heading date (5)
T4 = diversity within winter hardiness (5)
T5 = heading date within winter hardiness (5)
T6 = commercial blend (4)
T7 = winter hardiness within heading date (5)
* p = 0.056
**More productive late season pasture

15. Increasing the number of cultivars increased dry matter production
Summary
Increasing the number of cultivars increased dry matter production
Purposefully designed mixtures weren’t less productive than recommended cultivar monocultures (only first year of study)
Mixtures over-yielded, but need more time if we want to figure out exactly why
Purposefully designed mixture had better growth response than recommended cultivar late in growing season (grazing season extension?)

16. Stay tuned for information on yield stability over time
Conclusions
Genotypic diversity shows promise as a way to increase productivity and extend growing season
Stay tuned for information on yield stability over time
This study used perennial ryegrass, but the principles could be applied to other forage species

17. NH Agricultural Experiment Station
Acknowledgements
Assistance:
Liz Hodgdon, Kelsey Juntwait, Matt Morris, Nicole Guindon, Mark Dill, John Palmer, Devesh Singh (Barenbrug USA)
Funding:
NH Agricultural Experiment Station
This project is funded by the USDA Organic Research and Extension Initiative (OREI) Program and the NHAES