Evaluating Alfalfa Stands in the Spring

February 24, 2011 in Uncategorized

As an alfalfa field matures, plant stands tend to thin out.  Below is an article, written by Richard Taylor, which describes when and how to evaluate alfalfa stands. Spring no-till seeding of a grass, such as orchard grass, is an option for alfalfa fields that have thinned out.  Rotating to another crop such as corn is also an option since it can utilize nitrogen left from the alfalfa.

When and how should you evaluate an alfalfa stand?

Below are descriptions of two methods that can be used to determine the viability of an alfalfa stand. An alfalfa producer should use not only one of these methods but their feel for the vigor of the particular stand they wish to evaluate as well as the production history of that field.

The first method consists of counting the number of plants per square foot. Current research information suggests that when stand counts fall below 3 to 5 plants per square foot, it’s time to either rotate out of pure alfalfa or interseed a grass crop such as festulolium, tetraploid ryegrass, or annual ryegrass or interseed another legume not hurt by the autotoxicity seen in year old or older alfalfa stands. Red clover is the legume of choice and should be planted at 6 to 8 lbs pure live seed per acre either by broadcasting it on in very early spring or seeding it with a no-till drill (plant either in very early spring or in early to mid-Sept after the last harvest of the season).

The second evaluation method derives from research out of Wisconsin by Dr. Dennis Cosgrove that indicates that stem number rather than plant number is a more accurate determination of when to plow down or interseed an alfalfa stand. Cosgrove suggests using a value of 55 or more stems per square foot to indicate that the stand will produce maximum yield. A reduction in stem number per square foot to 40 stems or less will result in a 25 percent yield reduction. At this critical level, alfalfa fields begin to lose profitability and should be rotated to another crop for one or two years.

Although you can get some idea on the potential of your alfalfa stand by counting either the number of plants or the number of tillers per square foot, you will need also to consider checking on the health of those plants to have an accurate basis for a decision on keeping or destroying an alfalfa stand. To do this in the spring when new growth is about 4 to 6 inches tall, check a random one square foot site for each 5 to 10 acres of alfalfa or at least 4 to 5 sites on small fields. Dig up several plants at each site and slice open the crown and root (longitudinally) with a sharp knife to determine the health of the crown and tap root. Healthy roots and crowns will be firm and white to slightly yellow in color. Diseased roots will have dark brown areas extending down the center, especially if crown rot is a problem. Reduce your counts of plants per square foot or tillers per square foot so only the healthy plants present are counted. Plants with roots that are mushy or soft are likely to die; and although those with a few brown spots may survive, the overall vigor of the stand will be compromised by the presence of disease.

If you must decide on whether to reseed before growth begins in the spring (and you do not plan to take a first harvest of alfalfa before planting another crop) or after a very hard winter with significant heaving or winter injury, base your decision to reseed on the number of plants per square foot (Table 1). If a decision to reseed can be made during the growing season or after about 4 to 6 inches of growth has occurred in the spring, either evaluation method can be used (Table 1). In Table 1 below, I’ve modified various estimates for good, marginal, and poor stands to give the grower possible guidelines to consider in making a decision on keeping the stand or interseeding a grass or other legume.

Table 1.  Suggested plants per square foot or tillers per square foot () criteria for evaluating alfalfa stands on Delmarva.
Age of stand
Good stand
Marginal stand
Consider replacement* or renovation**
with interseeded grass or red clover
Plants per square foot with spring tillers per square foot in parentheses
New
25-40 plts (> 75)
15-25 plts (< 55)
< 15 plts (< 50)
1 year old
> 12 plts (> 60)
8-12 plts (< 55)
< 8 plts (< 45)
2 years old
> 8 plts (> 55)
5-7 plts (< 50)
< 5 plts (< 40)
3 years old
> 6 plts (> 50)
4-6 plts (< 45)
< 4 plts (< 40)
4 years old or older
> 4 plts (> 50)
3-4 plts (< 40)
< 3 plts (< 40)

*, If the stand is to be plowed for replacement, growers often find it economically favorable to take a first cutting and then plow and plant a rotational crop that can use the nitrogen mineralized from the decomposing alfalfa plants. Rotate out of alfalfa at least until the next fall (14 to 18 months) but preferably for 2 to 4 years. This will allow time for a reduction in the potential for alfalfa diseases and provide the grower the opportunity to correct soil nutrient and pH (acidity) problems as well as make use of the residual N mineralization potential that exists in a field following an alfalfa crop.
**, If you consider renovation or extending the stand life, try no-tilling a grass crop such as orchardgrass, tetraplpoid annual or perennial ryegrass, or one of the new varieties of festulolium (a cross between meadow fescue and one of the ryegrasses). The grass will increase your tonnage especially if you fertilize for the grass with nitrogen fertilizer. This also has the effect of driving out alfalfa at the same time as production levels are maintained for an additional year or two. Another option for extending an alfalfa stand’s life for 1 to 2 years is to seed in 6 to 8 lbs of red clover per acre. This option will maintain the higher protein production from the field.

Information from “Evaluating Alfalfa Stands in the Spring” written by Richard W. Taylor, Extension Agronomist, University of Delaware, rtaylor@udel.edu.   

Overseeding Cover Crops

September 21, 2009 in Uncategorized

Overseeding cover crops can be successful but should be done into standing crops for best effect. The following is more information.

An option for getting an earlier establishment on fall seeded cover crops is to over-seed. This practice requires using a helicopter, airplane, or ground rig with high clearance to apply seed over the top of soybeans or corn before harvest. By doing so, the cover crop seed has more time to become established versus waiting until after grain harvest. The risk with this method is that seed to soil contact is more difficult and seed may not germinate until after a significant rainfall.

The most adaptable cover crop to use with overseeding is cereal rye. It has a denser seed with more weight: therefore, higher percentage of the seed will fall through crop canopy to make soil contact compared to lighter seed such as annual ryegrass. Wheat or barley can also be used but do not produce as much growth as rye. Spreading patterns with cereal rye when using aerial application will also be more accurate. Overseeding into soybeans or corn should be completed before leaves drop. When leaves yellow and begin to droop down is a good time to overseed. Seed will more easily reach the soil and be covered with the dead leaves which will help retain moisture and aid in germination. Cereal rye will continue to grow throughout the fall even as temperatures drop into the 40’s. This growth will add organic matter to the soil, help correct soil compaction, and could be grazed or harvested for forage in early winter or next spring.

Information from “Overseeding Cover Crops” by Alan Sundermeier in the September 21 edition of the Crop Observation and Recommendation Network newsletter from the Ohio State University http://corn.osu.edu/index.php?setissueID=312#D

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