CROP UPDATE: Weather extremes hurt plant growth, development

Posted: Feb. 21, 2013 10:14 am Updated: Mar. 21, 2013 11:15 am


The past five years' weather patterns have really reduced pasture vigor and stand density. We've gone from extremely wet to extremely dry. Neither is good for plant growth and development.

Excessively wet soils have little oxygen to support plant roots and are extremely susceptible to compaction by hoof traffic. Dry soils are just as damaging to plants. Under drought conditions, the plant can't support root or vegetative growth if the plant isn't able to secure enough moisture to grow. As a result of both weather extremes, roots die, and when roots die, a corresponding amount of vegetative growth does as well.

Frost seeding of grasses and legumes can be utilized as a method to improve plant stand. Frost seeding works best in pastures that are grazed short and that have bare ground showing. Having bare ground exposed when frost seeding ensures that the seed can come in contact with the soil so that freezing and thawing will "incorporate" the seed. Closely-grazed plants are weakened, which allows the newly-seeded forage to establish a little easier.

Not all seed can be successfully frost seeded. The seed has to be small enough that freezing and thawing of the soil (expansion and contraction) will actually incorporate the seed. Small seeds, such as legumes, orchard grass and rye grass are better suited than a large-seeded grass such as brome grass.

Frost seeding of legumes into grass pastures is highly recommended for a number of reasons. Not only do the legumes provide a great source of nitrogen, but they also help to carry the pasture during the typically hot and dry summer months when many cool season grasses (fescue, orchard grass and brome grass) are dormant.

Red clover is the most popular legume that is frost seeded. It is a short-lived perennial, lasting 2-3 years in most instances. For this reason you'll need to frost seed somewhat regularly to keep this legume in the stand. Most folks will frost seed 3-4 pounds of red clover per acre each year or 6-8 pounds every other year. Make sure it's inoculated, and don't apply it with any nitrogen fertilizer. You can probably skip the inoculation if the pasture has (or had within the past few years) a good stand of red clover, as the bacteria necessary to allow the plant to fix atmospheric nitrogen are in adequate supply.

You probably shouldn't add nitrogen fertilizer to a grass pasture if you're attempting to introduce legumes, as you're just defeating the purpose. Nitrogen will stimulate the existing grass plants, which can inhibit the developing legume seedling. This small seedling is going to have a tough time growing into an already established stand, so give it all the help you can.

Seed when freezing and thawing (expanding and contracting) of soil will help to incorporate the seed. Best results come from seeding to pastures that have some bare soil exposed, so pastures that have been overgrazed work well. Overgrazing also helps reduce the vigor of the perennial grass to help the young clover plant establish itself. It has to compete with a grass that may have a root system several feet deep and will begin spring growth as temperatures warm.

Research has shown that the addition of a legume (at a 30 percent stand) to the grass pasture will provide all the necessary nitrogen the grass plants will need. That clover will replace 100 pounds of purchased nitrogen.

For those of you wanting to clean up any alfalfa fields of unwanted weeds, now might be a good time to consider the use of a dormant herbicide application.