Managing alfalfa during drought
As our area continues to experience drought conditions, many alfalfa producers may be asking, “How is the drought affecting my alfalfa stands?” And “Should I continue to harvest my alfalfa?”
Alfalfa is a deep-rooted plant, allowing it to find water longer than some other forages.
It also has the ability to go dormant and wait out more severe droughts, making it well-adapted to survive drought when managed appropriately to keep other stresses to a minimum.
Whenever plants are stressed, it becomes especially important to make sure they are allowed to replenish the energy and protein stores in the roots, because these are vital to support new growth from buds in the crown once conditions improve.
Failure to allow alfalfa to recharge root reserves greatly increases the odds that plants may not survive adversity.
We generally accept that root reserves are fully recharged when plants have reached full flower stage. Full flower occurs when every full-height stem has at least one open flower.
Drought-stressed alfalfa will accelerate its maturation process in an attempt to complete its seed production cycle as quickly as possible.
Stem internode growth is suppressed, resulting in a greater proportion of leaves on shorter stems.
Flowers will develop more quickly than in a normal growth cycle and may appear on stems that are only four to six inches tall in as few as 14 days after the last cutting. Once a stem has flowered, there will be little additional growth in that stem.
In the short term, the greater proportion of leaves in the drought-stressed forage improves feed quality and digestibility, but yield is reduced because of the short stems.
If drought continues long term, both yield and quality will decline because alfalfa will drop its leaves as it goes completely dormant.
The decision whether or not to harvest a droughty alfalfa crop is whether or not enough yield exists to cover the cost of harvest. A general rule of thumb is that you need to harvest over ½ ton per acre to cover harvest expenses. Keep in mind that the breakeven tons per acre harvested will vary per operation, depending on individual operating costs.
However, value per ton of forage may increase when supplies are short and allow a profitable harvest at yields lower than the normal break-even yield. If the decision is made to cut, use the normal recommended cutting height of two inches for pure alfalfa stands.
There is no advantage to the alfalfa plant of leaving higher stubble during drought. Greater stubble heights encourage regrowth from axillary buds at the base of cut stems, which are lower yielding growth points than the crown buds which are encouraged by close cutting.
If an economical mechanical harvest is not feasible, it is possible to salvage some value from the crop by grazing it. Alfalfa makes excellent pasture for all types of grazing livestock, but it can cause bloat, especially in animals that aren’t used to grazing it.
To reduce bloat risk, let animals take the edge off their hunger by feeding hay before turning onto alfalfa pasture, avoid grazing alfalfa wet with dew or rain, use a heavy stocking rate to discourage animals from eating only the leaves, and consider feeding a bloat preventative.
If stands will not yield enough hay to cover the cost of harvest, and grazing is not feasible, then it will not harm the alfalfa to leave it uncut until the drought breaks and dormancy is broken.
It is not necessary for health of the stand to clip off the old droughty stems before the next harvest. However, the old stems will decrease forage quality of the new harvest to an extent proportional to the amount present.
Such hay should not be marketed for animals such as high-producing dairy cows, but it is suitable for most other classes of animals.
Regardless of harvest management, stands should continue to be monitored for insect problems through the drought and treated if necessary, especially for insect pests. Scheduled fertilizer applications should continue as indicated by soil test. Plentiful potash (potassium) is particularly important in helping plants tolerate drought stress, and drought is not the time to skimp on this nutrient.
Drought in late summer and early fall certainly reduces the carbohydrates stored in the roots for winter survival and spring growth.
Whether this will be significant will depend on the winter: if the stands encounter warm periods so that they begin to green up and are frozen back, this pattern will be more detrimental than if plants are healthy. Thus, good snow cover will minimize the weak stand effects and a warm, open winter will exacerbate the weakness of the stands.
Dry soils going into the winter enhance alfalfa survival since dry soils insulate the crown better from air temperatures and result in less disease in the alfalfa roots.
Contrary to some popular views, alfalfa has a range of positive biological characteristics that should be quite useful when facing water-short conditions. These characteristics include a high degree of flexibility to ‘deficit irrigate’ the crop, ability to survive drought periods, high water-use efficiency, deep rootedness, salinity tolerance, and the ability to utilize degraded water. It is additionally very valuable to wildlife, which also suffers during a drought.
Oh, and by the way, it is also very valuable to the millions of consumers who depend upon the milk, cheese, yogurt, and yes ice cream, produced from alfalfa.
Sources:
Adjusting Harvest Management During Drought May Salvage Some Yield and Aid Alfalfa Recovery, by Kim Cassida, Michigan State University Extension
Effect of Drought on Alfalfa and Managing for Next Growing Season, by Dr. Dan Undersander, Agronomy, University of Wisconsin