Seeding perennial forage species in the Northern Great Plains
Spring is often thought of as the most common time to establish alfalfa and many other perennial species in Montana. However, there are opportunities at other times of the year to achieve high success rates.
Recent research, conducted by Extension Forage Specialist Emily Glunk at the Plant Materials Center in Bridger, Mont., found that a late-summer seeding had similar germination rates and production rates compared to a spring seeding under flood irrigation. But what about in water-limited, dryland areas around Montana?
Often, in the summer months, there is limited water availability for seed germination. A seed will require approximately twice its weight in water in order to begin the imbibition process. In the heat of the summer, that small amount can be hard to come by, particularly if any sun-baking of the surface soil has occurred, making seedling establishment difficult.
Sun-baking refers to surface soil temperatures exceeding ambient air temperatures, mainly due to radiant heat from solar energy that has been absorbed by the soil. Sun-baking can occur to depths of 3 inches or more, challenging even the hardiest of seeds. Depth of sun-baking increases in the absence of surface residue to provide insulation and to reflect sun rays.
Sun-baking becomes especially important in areas of saline seeps, an area where alkali salt crystals form due to salty water evaporating from the surface. Many times we see these areas occur in fields that use fallow consistently, or areas where there are high water tables close to the soil surface. If these areas are seeded in the summer, then the seed will likely not germinate until fall, when sufficient moisture has accumulated and evaporative demand is lower due to cooler temperatures.
Most times, alfalfa is recommended for planting in the recharge areas, up slope from the seeps, to help with drawing the water source down and decreasing the spread of the seeps. More salt tolerant species, such as AC Saltlander wheatgrass and western wheatgrass are planted into the seep area.
If summer seeding into a seep or dryland area that does have sufficient soil moisture, it's ideal to use a drill that uses press wheels and gently moves the surface soil. Moving the surface soil slightly to the side reduces the salt concentration around the seed. The operator should move at slower speeds, to avoid moving soil from one furrow into the next. Sun-baking post-seeding can occur to the exposed soil if high temperatures persist, although cooler night temperatures can help limit the depth of the sun-baking.
In areas where seeps are present, or a significant amount of sun-baking has occurred, summer seeding may not be viable. In this case, fall seeding or even dormant season seeding may be advised, if there is a high potential for spring conditions to be too wet and soggy for seeding. With a fall seeding, you are expecting the plant to germinate and grow prior to winter. In dormant seeding, the seed is placed in the soil, but not expected to germinate until the following spring. Fall and dormant season seeding avoids conflicts with other spring work.
The key to fall seeding is that enough time must be provided between germination and the first killing frost. An alfalfa plant is considered to be "established" once it has three trifoliates present. After the plant has five trifoliates present, it can begin to store energy in the form of root carbohydrates. Approximately 6-8 weeks, depending on available moisture and temperatures, are often necessary for germination and adequate alfalfa seedling growth to endure a cold winter dormant period.
The other difficulty is that freezing temperatures can prove fatal to the new seedlings. In the fall, days are usually warm, while the nights may or may not be cold. For seedlings that initially experienced continuous warm to hot growing conditions, a sudden drop in temperatures to 27 degrees F or colder could be fatal. However, seedlings that germinated and emerged during cooler conditions and experienced light frosts over an extended period of time will have hardened against freezing and will tolerate colder temperatures. Alfalfa seedlings from early spring and dormant season seedings typically exhibit this greater cold tolerance as a result of germinating in cooler soils and emerging at cooler temperatures.
Dormant seeding, planting after the soil has cooled much below optimum germination temperatures, is another option for producers in dryland environments. There are some disadvantages to this strategy. In Chinook zone, the frequent winter freezing and thawing, wetting and drying can cause seed decay and mortality, namely that there is typically lower seed survivability compared to a spring seeding. But it helps to break up the heavy workload of spring, as well as ensure that you are not dealing with muddy fields again. Ideal dormant seeding temperatures are when it is colder than 37 degrees F. Alfalfa can initiate germination even at 37 degrees, so care must be taken to avoid that. Additionally, soil water moves fairly slowly at colder temperatures, increasing the time for the seed to sufficiently imbibe to initiate germination reducing the risk of seed imbibition too early.
Germination and seedling growth is very slow at colder temperatures so it may take a month for the seedling to push to the surface, from a half inch depth. It is also advised to try to use natural freeze-thaw cycles to help incorporate the seed into the ground. Broadcast seeding on top of a layer of snow has worked for some, as when the snow melts, the seed will be placed closer to the soil surface. However, there are several research projects that have found overall germination rates for many species are lower than that of spring or fall seeding, mainly due to seed drying, as well as seed being removed from the field due to wind or birds or other animals. Harrowing before or after broadcasting may help to reduce these losses.
There are several options for timing of seeding throughout the year. Care must be taken to evaluate which situation will work best for your own farm or ranch. Careful evaluation of precipitation and temperature patterns will help in deciding what may or may not work for you. If you have any questions, please feel free to contact Emily Glunk at firstname.lastname@example.org; 406-994-5688, or Dave Wichman at email@example.com.