Alfalfa Management Under Moisture Stress

Scott Hendrickson, Ag Exten. Educator, Manitowoc Co.
Dan Undersander, Forage Agronomist

Moisture swings during growing season 2001 have been significant to say the least. Although the current round of dry weather may not rival the memorable droughts of prior years, it is raising management concerns. thresholds at various stem heights are as follows: 3 inches (.2 adult leafhoppers per net sweep); 6 inches (.5 adult leafhoppers); 8-11 inches (1.0 adult or nymph); and 12-14 inches (2.0 adults or nymphs).

As we relate current dry weather conditions to alfalfa management, several things should be kept in mind. Although most second crop alfalfa has been harvested, the wide variation in first crop harvest dates will stretch remaining second and third crop harvests beyond the norm for many.

As you watch alfalfa under drought stress, it is obviously shorter. Flowering typically indicates that additional top growth has ceased. New growth will be triggered from sunlight reaching the crown buds at the base of the plant. If the plants are so short that you can still see the crowns, there is little value in taking a cutting. Simply skip the cutting and allow the new growth to thicken the stand and cut when mid-bud to early flower is reached.

If the crop is thin, yet sufficient in yield, and canopied to the point where you can’t see the crowns, harvest on schedule. Research from the University of Minnesota suggests that cutting drought stressed alfalfa stands simply to stimulate growth may actually reduce yield.

To give additional cuttings a boost, monitor potato leafhopper pressure and treat if necessary. Economic

Fertilize if needed. Alfalfa’s fertility demand is substantial. Each ton of alfalfa dry matter harvested removes about 14 pounds of phosphate and 58 pounds of potash. Consult current soil test recommendations to target fields that can benefit most. Fertility adjustments can be made based on reduced yields due to drought stress.

Drought stressed alfalfa in dairy rations may also be a point for attention. Leaf-to-stem ratios are usually high resulting in higher than would be expected relative feed values. Under drought stress, however, alfalfa does release alkaloid like compounds that can reduce palatability. Monitor feed intake and adjust the forage mix in the ration accordingly.

As we look toward the next cutting, yield will be determined largely by rainfall within the first two weeks of regrowth.

For those thinking about late summer alfalfa seeding, seed only under conditions of adequate soil moisture. Seeding into dry soil may mean that the seed will not germinate for some time and emerge too late to get sufficiently established to survive the winter. Moisture in the top 3 to 4 inches of the soil surface is needed. As a general thumb rule, 1 to 2 inches of rain in close proximity to seeding should suffice on most soil types.