Over the last three years, Montana State University’s Northwestern Ag Research Center (NWARC) has been growing less dormant alfalfa as part of their alfalfa trials with more dormant varieties.
“Alfalfa is a very important forage for Montana, a preferred forage as it gives high yield,” said Jessica Torrion, associate professor in crop physiology and superintendent at NWARC, who is conducting the trials with Eeusha Nafi, postdoctoral researcher at NWARC. “Over the past three years, we have been trying less dormant alfalfa in the valley.”
One of the reasons she said they are growing the “less dormant alfalfa variety” is the discovery by MSU faculty that the ag growing season seems to be extending in the fall.
“The evidence is showing our fall has been extending a little. There might be opportunities to plant alfalfa with less fall dormancy compared to more dormant alfalfa varieties we normally plant,” she said.
Less dormant varieties grow slightly faster in the spring than more dormant varieties.
At NWARC, the scientists planted fall dormancy number two, number three, and number six and grew them under varying irrigation levels.
“It is important for us to test fall dormancy number six because this is outside of our usual choice for alfalfa genetics,” Torrion said. “We want to document the performance of more dormant to less dormant genetics under water and nutrient levels, as well as persistence of these genetics.”
Torrion talked about a two-year irrigated trial (from 2018-19) with alfalfa dormancy number three, Rugged Alfalfa, and dormancy number six, Cisco II, planted under extreme conditions in Tucson, Ariz., and Creston, Mont., for comparison purposes.
“We sampled a small area during the season to monitor why fall dormancy six, which is less dormant, would be advantageous in some areas, while fall dormancy three, which is more dormant, would not be,” Torrion said.
In Arizona, fall dormancy six is often grown.
“We heard Arizona farmers want to try fall dormancy three to have more quality over yield. Yield is not so much a hindrance there under irrigation,” she said.
In Montana, and especially in northwestern Montana, producers usually don’t have problems achieving high forage quality.
In Arizona, the fall dormancy number six variety over two years had greater yield than number three.
“You’d be surprised how similar Montana was, with fall dormancy six having slightly higher yields than number three, especially in the second year,” Torrion said.
In the fall of the first year of planting at Creston, the fall dormancy number six (Cisco II) variety started to have faster regrowth than the fall dormancy number three variety.
“This advantageous fast regrowth in fall dormancy number six continued in the spring, and then nothing. So there is just a small window in the fall and in the spring that shows an advantage,” she said. “After cutting, fall dormancy number six seems to grow faster.”
Accumulated biomass is due to extension of different tissues like leaves and stems.
There was fall regrowth some 319 days after planting in Montana. Yields were lower in Montana than Arizona.
In the establishment year of 2018, irrigation was scheduled with three moisture regimes: one, all rain-fed; two, 100 percent evapotranspiration (ET) irrigated at 10 inches, or irrigation where the plants don’t feel stress; and three, 50 percent ET where it was the 100 percent irrigation schedule cut in half at 5 inches.
“Even though there were not significant differences in the first year of establishment, fall dormancy six is in the higher range, numerically speaking, and is consistent across moisture regimes,” Torrion said.
A summary of the response to the irrigation in 2018 showed at 50 percent ET there was .22 tons per inch and at 100 percent ET, there was .17 tons per inch.
The first cutting at 100 ET yielded 1.4 tons per acre, while the 50 ET yielded 1.2 tons per acre and the rain-fed yielded 1 ton per acre.
“Our results are showing the fall dormancy six has the best yield overall,” Torrion said.
They also found that irrigating more was not necessarily advantageous.
The second cutting at 100 ET yielded 1.8 tons per acre, while the 50 ET yielded 1.4 tons per acre and the rain-fed yielded one-half ton per acre.
In 2019, fall dormancy number six, Cisco II, was beginning to show an advantage.
“Cisco II was beginning to show an advantage, especially under irrigation,” Torrion said. “It is also important to note that the 50 ET productivity is .6 ton per inch, with only 6.4 inches applied this year.”
However, the 100 ET only had .4 ton per inch yield response, even if the total irrigation was increased up to 12.7 inches.
“The deficit irrigation is definitely advantageous in terms of water and energy savings,” she added.
In 2020, the varieties and yields were: fall dormancy two, FSG229CR variety, 7.4 tons per acre; fall dormancy two, Maxi Graze variety, 7.3 tons per acre; fall dormancy three, Rugged variety, 7.2 tons per acre; fall dormancy three, Big Sky Ladak variety, 7.5 tons per acre; fall dormancy six, Cisco II variety, 7.5 tons per acre; and dormancy six, Hi Gest 660 variety, at 6.3 tons per bushel.
“Hi Gest alfalfa, a fall dormancy six with low lignin content, was consistently lower in yield, probably because the variety was developed for quality,” Torrion said.
The three watering treatments were: 100 ET, 9.8 plus inches irrigation and 8 tons per acre; 50 ET, 4.8 plus inches irrigation and 8.2 tons per acre; and rain-fed, 9.7 inches rain and 5.3 tons per bushel.
“Similarly, in 2019, the deficit irrigation (50 ET) is a better strategy than irrigation at the full amount (100 ET),” she said.
Fall dormancy number two was slightly more advantageous under the rain-fed ground.
Another study containing six varieties of more dormant to less dormant alfalfa varieties (dormancy two through dormancy seven) involving the usage of five fertilizer (phosphorus and potassium) rates was conducted under irrigation.
“This was a large study at Creston with three cuttings, so I have to thank the staff for all their hard work on it,” Torrion said.
In the first year, there were lower yields and no significant impact from the fertilizer rates.
“In 2020, we began to see an effect from the fertilized acres,” she said.
In 2020, fall dormancy six had the highest yields.
The takeaways from the study are as follows:
- Fall dormancy six, Cisco II, showed a competitive yield advantage in the three-year study.
- Fall dormancy six, a low lignin type, Hi-Gest 660, was the least competitive for yield, but should be used for special purposes, such as quality.
- For two years of the study, fall dormancy seven persisted with similar yields to most of the fall dormancy entries.
- In general, irrigation using a deficit approach, with less water application per irrigation even, showed greater irrigation productivity.
- In the second year, rain-fed is more negatively impacted with reduced P and K rates.
“Irrigation tends to make these nutrients available,” Torrion said.
This year will be the last year of the study.
In collaboration with the University of Arizona, the University of California-Davis, and the University of Florida, the trials are being supported by the USDA-National Institute of Food and Agriculture (NIFA) and the Montana Fertilizer Advisory Committee.
At field days this summer, Torrion talked about the alfalfa trials and the implications for Montana producers.