Pitfalls of Thickening Old Alfalfa Stands April 13, 2016
If your alfalfa is looking a little thin, you may be tempted to add alfalfa to thicken the stand. Before you do, consider:
Is this stand performing up to what can be expected? Alfalfa needs only two to three healthy plants with 25 to 35 shoots per square foot for older, dryland stands to achieve top production. Adding more plants won't increase yield because rainfall won't provide enough moisture for more growth. Irrigated or subirrigated alfalfa should have 40 to 55 shoots coming from four to six plants. With the extra moisture, more plants can be productive.
Will adding alfalfa guarantee an improved stand? Thin stands can be thickened — sometimes. However, problems can and do occur. For example, diseases are common in older fields; these diseases can quickly infect your new seedlings and cause the new stand to decline more rapidly. Also, existing alfalfa plants and weeds will compete with your new seedlings and might prevent them from establishing. This competition must be controlled.
Finally, alfalfa itself produces chemicals that inhibit seedling growth of new alfalfa plants. This is called autotoxicity. We can't predict when this will happen or its severity, but we do know it is less of a problem on irrigated sites, especially on light-textured soils.
Tips for Successful Thickening
If you do try to thicken your alfalfa:
- Minimize weed competition; Roundup and Gramoxone can help.
- Get your seed in the soil early, using a drill that will place seed about one-half inch deep.
Given the potential problems noted here to creating a thicker stand, you also may want to consider whether this might be a good time to consider rotating to a different crop.