What is in this article?:
- The ‘summer slump’ period is a decline in alfalfa growth in the low desert areas of the West.
- The summer slump is tied to high temperatures.
- Increased humidity and high nighttime temperatures are other culprits.
Although eliminating alfalfa’s summer slump is impossible under the severe summer climate conditions, some factors can reduce the impact.
Alfalfa varieties grown in the Arizona low desert are non-dormant in the fall and have smaller crowns and taproots compared to more dormant varieties.
This indeed may be true if the cause of summer slump is reduced root carbohydrates, and the relatively larger roots of these varieties are able to avoid critically low levels of carbohydrates in the roots.
However, growing semi-dormant alfalfa varieties in the Arizona low desert is generally not recommended since yield gain during the summer may be small and variety dependent, and is often offset by a loss of yield during the fall and early spring, compared to non-dormant varieties.
Water stress can worsen the effects of the summer slump, and even cause the plant to flower prematurely as mentioned above. Keeping the crop well watered is among several management practices a grower can utilize to delay or lessen the effects of the slump.
Remember that alfalfa water use slows during the summer slump due to decreased growth. Also, water standing for more than 24 hours when the high air temperature is above 100 degrees can lead to scald injury.
Nutrient deficiencies theoretically contribute to the effects of the slump since anything which reduces crop growth and vigor can intensify the effects of summer slump. However, applications of plant nutrients not needed for crop growth is not expected to reduce the impact of summer slump.
It has been suggested that high soil temperature reduces the effectiveness of the nitrogen-fixing root nodules in alfalfa, and the application of nitrogen fertilizer could reduce the effects of summer slump.
Yet, most of the nodules are found in the 4-12-inch depth where soil temperatures are optimal for nodule functioning and the response to nitrogen during the summer slump has been mixed.
Alfalfa is less competitive with weeds during the summer slump due to the relative growth of the crop compared to weeds. Summer annual grasses, including Bermudagrass and nutsedge, can be particularly competitive with alfalfa.
Herbicides are available to control these weeds, yet are not as effective compared to when alfalfa is more vigorous.
The most effective weed control in alfalfa is a healthy stand. Before the advent of selective herbicides in alfalfa, non irrigation during the summer slump was a weed control strategy.