Cultivating alfalfa with a spring-tooth harrow. Photo by Kyle Weber, YouTube.
Cultivating alfalfa with a spring-tooth harrow. Photo by Kyle Weber, YouTube.
I have noticed many farmers beginning their alfalfa field preparations this spring. Good cultural practices (proper stand establishment, irrigation, fertility, and harvest management) promote a dense, vigorous alfalfa stand that is able to suppress weeds and provides only minimal opportunity for weed encroachment during the growing season. Although a healthy alfalfa stand protects against most weed problems during the growing season, winter annual and perennial weeds can become established while the alfalfa crop is dormant. Winter annual weeds germinate in fall and late winter and become established before alfalfa growth resumes in early spring. Because competition from the alfalfa for moisture and light (shading) is minimal during dormancy, herbicides are usually needed to prevent weed establishment and assure a weed-free first cutting.

Some alfalfa growers also use cultivation or tillage of dormant alfalfa stands to control early weeds. Dormant-season tillage can provide control of winter annual weeds in established alfalfa but also may damage alfalfa crowns and predispose plants to diseases. Tillage of established alfalfa has been discouraged in higher-rainfall areas due to the increased risk of diseases.

According to Dr. Bruce Anderson, Extension Forage Specialist, University of Nebraska-Lincoln, there are advantages and disadvantages about this practice. Usually spring tillage of established alfalfa stands is done to control weeds like mustards and downy brome, but sometimes-light tillage is used to incorporate fertilizer, smooth rough spots, or lessen compaction.

In addition, some folks claim this tillage increases production by splitting crowns into two or more plants. Are these claims true or just old alfalfa grower’s tales? Well, tillage generally does stimulate early alfalfa growth by blackening the soil (thus, helping to increase soil temperatures).

However, most research shows that if spring tillage is aggressive enough to provide useful weed control, it also damages alfalfa stands and yields, by cutting open some of the crowns, allowing diseases to enter and start injuring the plant. These crown and root diseases usually take a while to show much damage, so if the field will be rotated to another crop in a year or two, losses will be slight if any. Furthermore, light tillage that does not harm stands usually fails to control many weeds. Apparently, you cannot have your cake and eat it, too.

The following is a quick summary of research conducted in Montana on the effects of Spring tillage on alfalfa production.

Montana Agricultural Experiment Station researchers compared three tillage methods and four tillage treatments:

• Deep tillage, (4 inches deep with a field cultivator containing multiple spring-loaded shanks (points);

• Shallow tillage, (2 inches deep) and

• Tandem disk tillage, (3 inches deep).

• The tillage levels were; 1) no tillage (control), 2) tilled once, 3) tilled twice (opposite directions) and 4) tilled three times (at right angles).

• Generally, deep tillage in one or two consecutive years stimulated alfalfa growth and vigor. Perennial rhizomatous grasses were also stimulated by a single deep tillage, but two consecutive years of deep tillage decreased grass yields. Shallow cultivator tillage and disk tillage did not greatly affect forage yield or weed populations. Alfalfa crowns were damaged more by shallow cultivator and disk tillage than by deep cultivator tillage. Shallow tillage detached alfalfa crowns, whereas deep tillage allowed shanks to slip around alfalfa crowns.

The final results showed that alfalfa yields from a single year, two-pass tillage were greater than a single year, three-pass tillage, but were not different than the control (no tillage). Two consecutive yearly spring tillages decreased alfalfa yields as compared to not tillage. Under no circumstances did tillage (1, 2 or 3 -pass) of a young vigorous stand significantly increase alfalfa yields as compared to the control (no tillage).

Nevertheless, if you want to keep that stand for a longer time, do not aggressively till or diseases might start to thin your stands earlier than normal. Bottom line – spring tillage, as long as it occurs before alfalfa greens up and when soils are dry, does little harm to alfalfa in low precipitation/humidity areas. However, it also does little good. Therefore, you may want to re-evaluate if it is worth the time, labor and cost to your operation.



Sources:

Response of Alfalfa to Three levels of Spring Tillage, Leon Welty, J.A. Hall, Ray Ditterline and L.S. Prestbye. Northwest Agricultural Research Center, Kalispell, MT.

Spring Cultivation of Established Alfalfa, Dr. Bruce Anderson, University of Nebraska-Lincoln.