By the OMAFRA Field Crop Team
With the recent rains, many hay fields have seen significant growth in the last two weeks and this has producers wondering if they should be taking a fall cutting of alfalfa this year. The decision needs to balance the needs of the farm for immediate forages, with the increased risk of winterkill and potential yield reductions the following year.
This year, plants have been stressed from the dry weather and now we are contemplating stressing them further by taking a fall cutting. Even if there is no winterkill, the added stress typically results in the delay of first cut in the spring with yields being reduced by roughly the same tonnage that would be harvested in the fall. The Critical Fall Harvest Period for alfalfa is the 6 week period preceding a killing frost and the starting date ranges from August 10 in Northern Ontario to September 4th in Southwestern Ontario. To see when the start of the critical fall harvest period is in your region, Refer to Figure 1. After the last cutting of alfalfa, it will utilize the root reserves for plant regrowth. It takes 2-3 weeks for the plant to have enough regrowth to be able to use photosynthesis to start to rebuild the root reserves. It is most damaging to the plants if they are cut in the middle of the critical harvest period compared to the start or end, because at this point, they will have drained their root reserves and will not be able to regrow quickly.
Cutting alfalfa close to a killing frost can minimize the risk of winterkill. The alfalfa can be cut before or after the frost. If it is cut before a frost there will be little regrowth to deplete nutrient reserves. After a frost, alfalfa leaves will start to drop and nutrients will leach out of the plant. A killing frost for alfalfa occurs when the temperature reaches -4 °C for several hours. With a late fall cutting of alfalfa, insufficient plant growth may be a contributing factor to winterkill. The top growth will help hold snow in place and protrude through winter ice sheets allowing oxygen to enter. Since the top growth is being removed, it is recommended to set the cutter bar at a minimum height of 4” and preferably at 6” to increase the snow holding capacity of the stubble, keep in mind that raising the cutter bar will reduce tonnage. If there are heavy stands of forages or clovers going into winter, they pose a risk of smothering because the top growth will form a dense mat. Heavy stands of alfalfa do not pose that same risk because alfalfa loses its leaves following a fall frost and the stems stand upright.
When considering fall cuttings, certain fields are at higher risk of winterkill. First year stands of alfalfa should not be cut in the fall harvest period as these fields are still establishing their root system and it is not a good idea to put any additional stresses on them. Older stands, stands with low pH, low potassium, poor drainage or insect or disease pressure are at increased risk of winterkill, and compounding that with fall harvest will increase the risks. Aggressive cutting schedules of less than 30 days will increase the risk while allowing alfalfa to flower and harvesting at intervals of 40 days will decrease the risk of winterkill.
Managing Forage Fertility
After the stress that forage stands have been through this year, managing soil fertility this fall can help with overwintering and give plants a head start on next year. Fall is an excellent time of year to supply fertilizer to hay crops, either through manure or commercial fertilizer. Some phosphorus and potassium will be taken up by the crop this fall and produce a healthier plant going into winter, while most of the nutrients will work their way into the ground over the winter to be readily available for next year’s crop. Grass pastures, especially those with a lot of fescue, can benefit from adding nitrogen early in September. The nitrogen will promote grass growth, and tillering which will result in additional fall forage. The added nitrogen, also produces healthier plants which start to grow earlier in the spring and can produce an extra 2 weeks of early spring pasture. Adding fall nitrogen to a pasture will not affect the legume content of the pasture. Fall fertilizer is most advantageous if it is applied directly after the final cut of the season, near the start of the critical fall harvest period. This will allow the plants to have time to utilize the nutrients before winter. The best way to determine phosphorus and potassium requirements is by conducting a soil test.
Alternative for Fall Forages
Fall forages such as oats typically require 60 days to reach boot stage, and with shorter fall days and the cooler weather, that may stretch to 70. While it is still possible to plant a cover crop for fall pasture or forage, the yield is going to be reduced. It is more beneficial to look at planting a crop, such as winter rye, or winter triticale for early spring forage. Fall rye is generally ready to be pastured in the mid-late April which makes it ideally suited for early season pasture. It can also be utilized for early season forage, as it typically reaches boot stage mid-May, but loses quality quickly after that. Fall rye should be planted as early as possible in September for spring forage, but it can also be planted following corn silage or soybeans in October. Early plantings of fall rye can be seeded at 110kg/ha (100lbs/acre) while later plantings can be increased to 190kg/ha (168lbs/acre, 3bu/acre) for later plantings, or if the seed is broadcast. Fall rye is more winter hardy than wheat and will out yield wheat, while winter triticale is a cross between rye and wheat. Fall rye should receive 55-80kg/ha (50-70lbs/acre) of nitrogen in the spring at green up. The early harvest allows another crop to be planted next spring, such as soybeans or corn silage.
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This Report includes data from WIN and Environment Canada.