From "Welcome to the Crop Watch News Service" No. 97-7 May 2, 1997 http://cropwatch.unl.edu/1997/sample.htm

EVALUATE ALFALFA STANDS FOR WINTER-INJURY, YIELD POTENTIAL

Early and accurate assessment of alfalfa winter damage can provide the greatest flexibility for replanting or aiding crop recovery.

Optimum yield in dryland alfalfa requires 40 shoots per square foot for maximum yields. To achieve optimum yield in irrigated fields, it's estimated that at least 55 stems per square foot are needed. About one tenth of a ton in yield potential is lost for every shoot below these numbers.

Researchers at the University of Wisconsin have learned that stem count is a much more accurate method of estimating yield potential than plant count. They recommend a two-step process for evaluating stands:

1. Use stem count to estimate current yield potential of the field;

2. Assess root and crown health to determine future yield potential.

In a recent Extension publication Wisconsin researcher Dan Undersander, et al., wrote: "The relationship between stem density and yield potential is constant, regardless of stand age, making this a reliable method for estimating yield potential.

To use this method, select three or four representative areas of the field, marking off a 2-square-foot section in each area.

You many find it useful to build a square measuring 17 inches x 17 inches using 1/2-inch PVC tubing or weld a cable into a ring that is 19 inches in diameter. Count only those stems that are tall enough to be harvested by the mower (over 2 inches tall). Remember to divide your count by 2 to get stems/square foot. Calculate the average stem count for the field and use the graph to estimate yield potential. Visual estimation works best when stands are 6-10 inches tall.

This method will estimate the potential for yield, not actual yield.

Check for these densities in several areas of a field. Since some shoots begin growing later than other shoots, stands with adequate plant density but slightly low shoot density probably will be all right, especially if shoot height and distribution is fairly uniform. But if plant density is low, or shoot growth is not uniform, yields probably will be lowered.

Assessing the health of the stand will help you estimate future yield potential. In fields where winter-injury is suspected, dig and examine tap roots. Plants with only moderate injury have roots that are mostly solid and white, but they may have darker brown areas down 1 to 2 inches in the crown due to crown rot. Check texture: spongy roots suggest injury and a cold and mushy texture indicates diseases. If over 50% of root tissue is damaged, production will be low and survival past this season is unlikely.

MANAGEMENT OPTIONS:

Fields seeded last year:

Kill winter annual weeds with tillage or Gramoxone Extra.

Direct drill (do not broadcast or use cultipacker-type seeders) new alfalfa seed no-till one-half inch into old stand as soon as possible.

Control annual weeds with Poast Plus, 2,4-DB, Buctril or Pursuit.

Manage harvest like a new seeding.

Injured but salvageable established stands:

Topdress 15 to 25 lbs N to help weakened roots and nodules.

Topdress other nutrients according to soil test to avoid deficiencies.

Control annual weeds with Poast Plus, 2,4-DB, Buctril or Pursuit.

Irrigate dry soils but avoid waterlogged soils.

Delay first harvest until 25% to 100% of plants bloom to heal roots.

Leave tall stubble at harvest if new shoots are already growing.

Allow subsequent harvests to begin to bloom.

Avoid late harvests that may interfere with winterizing.

Unsalvageable stands:

Seed oats immediately into injured stand.

Kill remaining alfalfa and seed millet in June.

Seed oats immediately and then millet in July

Kill remaining alfalfa and no-till corn or milo.

Till and plant crop.

Interseed cool-season grasses for alfalfa/grass pasture.

Seed red clover immediately to thicken stands for two to three years.

Seed berseem clover immediately to thicken stands for one year.

More information:

Extension publication CC 360, Reacting to winter-injury to alfalfa, can guide evaluations and management options. It's available from local Cooperative Extension offices.

Bruce Anderson, Extension Forage Specialist (402) 472-6237

From NebGuide G93-652-A "Seeding and Renovating Alfalfa" http://ianrpubs.unl.edu/range/g652.htm

RENOVATING THIN ALFALFA STANDS

Farmers and ranchers often seek ways to thicken existing alfalfa stands to increase production. This practice is often unsuccessful because soil conditions, age of stand, and whether or not the field is irrigated, all influence its effectiveness.

Thickening stands is only useful if production of alfalfa increases. Fertilizer and harvest management must be able to support additional alfalfa plants. Furthermore, sufficient moisture must be available to obtain higher yields. Alfalfa requires 6 to 8 inches of moisture to produce 1 ton of forage. Under dryland conditions, young stands produce high yields because they use the current year's precipitation plus stored soil moisture. After 3 to 4 years, yields decrease because most of the stored soil moisture has been used.

Two to three alfalfa plants per square foot will produce maximum yields in older stands on dryland. Stands thicker than this will not produce more forage because lack of moisture limits production. Therefore, it is usually best to rotate to another crop for several years before reseeding alfalfa.

Under irrigation, 4 to 6 plants per square foot are needed for maximum production. Since soil moisture is not necessarily limiting, establishing more plants may increase production when fewer than six plants per square foot are present.

However, seeding alfalfa into established alfalfa stands is often unsuccessful. Insects and seedling diseases are common. In addition, water-soluble compounds from existing alfalfa plants may inhibit germination and growth of new alfalfa. This condition occurs most frequently when alfalfa is tilled before reseeding or when many live alfalfa plants remain in the stand.

Under certain conditions alfalfa can be interseeded into existing alfalfa to thicken stands. A low-till drill that cuts the sod and places seed in contact with mineral soil is needed. This practice is most practical and successful on irrigated sandy soils. Herbicides are needed to reduce competition from the existing alfalfa and other vegetation. Paraquat, at 1 to 2 pints/acre, will usually provide sufficient suppression of alfalfa and associated grass or weed growth on sandy irrigated sites to allow seedlings to become established. Roundup, at 1 to 2 quarts/acre, is usually needed on heavy or fine-textured soils as well as on some sandy sites to adequately reduce competition. Either herbicide should be applied several days before seeding alfalfa.

Use interseeding only if more plants can be expected to become established and higher, long-term yields will result from more plants. Otherwise, do a total renovation using tillage equipment to prepare a clean seedbed.