One of the things we have learned over the years is that new alfalfa seedings that have good growing conditions yield much better in future years. Said another way – seeding year stress lowers yield potential of alfalfa in future years.
We have seen this with seeding year insect infestations where, for example, uncontrolled potato leafhopper infestations in the seeding year reduced alfalfa yield the next year even if the potato leafhopper was controlled. The seedling plants with infestation had less of a taproot than plants where the insect had been controlled.
Diseases in the seeding year can also reduce future yield of alfalfa. The most common is aphanomyces, which can kill seedlings but more commonly reduces root growth and stunts growing plants. These plants may appear yellow and have reduced height (and yield). This disease occurs in oval spots in the field that will often become weedy over time. If seeing this in some fields, the best recommendation is to plant aphanomyces-resistant varieties where the seed is coated with Stamina seed treatment next time.
Other diseases (phytophthora, rhizoctonia, verticillium, anthracnose) can cause reduced stand and weaken plants that will yield less in the future. It is best to plant alfalfa varieties with the greatest disease resistance and use seed that is coated with Apron and Stamina fungicides.
Lack of nutrients in the seeding year can also cause plants to grow less vigorously. High-yielding alfalfa is most likely to occur on fields that have been soil tested and fertilized according to recommendations. For example, phosphorus stimulates root growth and sulfur is necessary for chlorophyll formation and promotes nodulation. Lack of a needed nutrient will stunt the plant.
Stunted seedlings, either because of weather or any of the above factors will also allow weeds to be more competitive. Weed competition can stunt plants and result in reduced yields in future years. Weed control is crucial in the first 60 days after planting. However, weed competition can stress the alfalfa seedlings at any time in the seeding year.
Drought stress can also reduce plant growth in the seeding year and cause low-yielding plants in future years even if rainfall or irrigation is adequate. This will be a particular problem next year as about 40% of the U.S. alfalfa-growing region was in a drought in 2023.
It will be crucial to carefully monitor the first-year yields of fields planted in 2023. If they yield well, then all is well; however, if the yield is low, one must recognize that the field was damaged in the seeding year and will likely never yield well. Rather than maintaining these low-yielding alfalfa stands, they should be considered for a shortened stand life.
Short rotations can be beneficial in several ways:
- Seeding new stands will result in stands with greater yield potential.
- The turned-down stand (after two years) will provide sufficient nitrogen for one or two years of a succeeding crop.
- For corn or sorghum (assuming legume credits meet total nitrogen need of 175 pounds per acre), this is $110 for urea fertilizer or $74 for anhydrous ammonia.
- For wheat (assuming legume credits meet total nitrogen need of 120 pounds per acre), this is $76 for urea fertilizer for each of two crop years.
- Each crop has a rotational benefit of 20% yield increase when following alfalfa. This can be approximately $150 per acre additional value for corn, $250 additional value for sorghum or $72 additional value for wheat for each of two years. (Note that wheat has also been shown to have increased protein by 1% following alfalfa).
Thus, turning over a low-yielding alfalfa field may be more profitable than keeping the stand.
A major consideration is to pay attention to herbicides used on other crops so that alfalfa could be seeded into the field in 2025. A number of herbicides for corn and wheat have no-plant recommendations of 18 to 24 months, which would prohibit seeding alfalfa into the field until 2026 if the herbicide was used in 2024. However, herbicides can be chosen that could be used on crops next year and still allow alfalfa planting in 2025.
In summary, we hope that new seedings of alfalfa established well in 2023. However, we should watch yield carefully in 2024 and be prepared to shorten stand life if yield is low. Consider that a low-yielding alfalfa stand the first year after seeding will likely not yield any better in succeeding years. There are economic benefits to turning over low-yielding stands and taking legume credits and rotational benefits rather than keeping the low-yielding field.
