Identifying Alfalfa Varieties Best Suited to Pasture Rejuvenation
Project Title
Identifying Alfalfa Varieties Best Suited to Pasture Rejuvenation
Researchers
Jonathan Bennett (USask) jon.bennett@usask.ca
| Status | Project Code |
|---|---|
| Completed April, 2023 | POC.17.21 |
Background
Pasture productivity can decrease over time, particularly the legume component, which negatively impacts forage and animal performance. Instead of replacing a forage stand, which costs a considerable amount of time and money, 2/3 of Canadian producers opt for pasture rejuvenation. While there are many pasture rejuvenation strategies, a common practice is to over-seed or sod-seed alfalfa with the goal of restoring the productivity of the perennial pasture. However, the soil microbial community of the existing/older pasture plays a key role as to how successful rejuvenation can be and can even inhibit future plant growth. Some soil microbes can reduce plant growth (e.g., pathogens) whereas others can increase it (e.g., Rhizobia). Responses to these microbes is dependent on alfalfa varieties with some cultivars showing a 25% reduction in production and others increasing their production by 90% when planted in soil from the same existing pasture. Identifying cultivars that benefit more from the microbes in existing and older pasture stands should increase the potential success of pasture rejuvenation.
Objectives
- Determine which alfalfa varieties respond positively to soil microbes from older alfalfa fields and can thus be recommended for pasture rejuvenation.
What they Did
This team tested 20 different alfalfa seed varieties (table 1.) to see which may be best suited for rejuvenation. Soil samples (which contained different soil microbes) were collected from 12 producer farms spanning four soil zones that have declining alfalfa stands and varied in age from 4 to 60 years. They also collected data from each site on soil characteristics (texture, pH, salinity), climate (temperature and precipitation), and which plants were there. In the greenhouse they grew each alfalfa cultivar in three different soil samples from each site as well as in sterilized soil. After two months alfalfa was harvested, and forage productivity and root biomass were measured. To determine the effects of the microbes, growth in the field-collected soil was compared to growth in sterile soil. They used statistical analyses to determine which alfalfa cultivars do best in pasture soil while accounting for differences in soils, climate, and plants among sites.
Alfalfa seed sources used in the study:
| Provider | Cultivar | Root Structure | Fall Dormancy | Winter Hardiness |
|---|---|---|---|---|
| Unknown | Beaver | Tap | 2 | 2.1 |
| Brett Young | 2010 | Branching | 2 | 2 |
| Brett Young | 3010 | Deep-set crown | 2.5 | 1.8 |
| Brett Young | Foothold | Spreader | 2 | 1.7 |
| Brett Young | Spyder | Creeping | 1 | 1.0 |
| DLF Pickseed | Assalt ST | Tap | 4 | — |
| DLF Pickseed | Vision | Tap | 4.4 | 1.5 |
| AAFC | AC Bridgeview | Deep-set crown | — | — |
| NorthStar | TH2 | Tap | 4 | 2.5 |
| NorthStar | Haygrazer | Fibrous | 4 | 2 |
| NorthStar | Perfection | Tap | 4 | 2 |
| NorthStar | Response WT | Branching | 3.6 | 2 |
| NorthStar | Revolution MD | Tap | 3.7 | 1.7 |
| NorthStar | Robust | Tap | 2 | 1.5 |
| NorthStar | Rugged ST | Tap | 3 | 2 |
| NorthStar | Sidewinder | Creeping | 2 | 1.6 |
| Early’s F & G | Algonquin | Tap | 2 | 2.1 |
| Early’s F & G | Rambler | Creeping | 1 | — |
| Early’s F & G | Common | Creeping | — | — |
| Early’s F & G | Common | Tap | — | — |
What They Learned
Alfalfa cultivars differ greatly in their responses to soil microbes. Five cultivars produced more forage when grown with pasture microbes (Assalt ST, Rambler, Spyder, TH2, Vision), with an average 20% increase in forage produced. Seven cultivars (Beaver, AC Bridgeview, Foothold, Haygrazer, Response WT, Revolution MD, Robust) and the tap-rooted common seed produced less forage, with cultivars AC Bridgeview, Haygrazer, and Robust producing more than 30% less. The other six cultivars (2010, 3010, Perfection, Rugged ST, Sidewinder, and Algonquin) and the creeping rooted common seed did not show any consistent responses to the microbes.
When considering root production, only the tap-rooted common seed and Robust alfalfa produced more root mass when growing with microbes, but both had reduced forage production, suggesting benefits may be limited. Many of the cultivars produced less root with microbes while others showed no change. Importantly, TH2, one of the cultivars that increased shoot production, produced 30% less root when grown in the soil containing microbes, suggesting that it might not continue to produce more forage long-term. Cultivars Assalt ST, Rambler, and Vision showed no change in root production, whereas Spyder had a small reduction (~10%) in root production. Some of the responses to pasture microbes did depend on certain qualities of the pasture which was considered.
Among the five cultivars that increased forage production, Vision generally produced fewer roots when inoculated with soils from older stands, while TH2 performed the best in those conditions. Root production responses to the microbes also generally increased with average temperature of the site sampled for all the highest producing cultivars, except Vision.
What It Means
The alfalfa cultivar you pick for your pasture will likely affect the success of rejuvenation. Selecting cultivars that respond positively to soil microbes in existing and older pastures can increase the chances of successful establishment and longevity of the newly introduced legume.
This study identified five cultivars (Assalt, Rambler, Spyder, TH2, Vision) that can benefit from the microbiome of old pasture soils by producing increased forage. Although, TH2 may decline over time if it root production continues to decline. These identified cultivars remain successful across all pastures tested. Specifically, Vision would perform better in newer pastures and colder environments while TH2 would be better suited to older pastures. It is important to note that the soil microbes inhibited the productivity of some alfalfa cultivars which means they should be avoided when selecting a variety for rejuvenation. While the study was essential to prove the hypothesis that some alfalfa cultivars are better suited for pasture rejuvenation than others, field trials are required to fully answer this question and identify recommendations of cultivar selection dependent on soil type, environment, region, and age of the pasture stand.