Replacing Alfalfa Fields

Have you taken a good look at your alfalfa fields lately? Now is a good time to evaluate those fields and determine if they need to be replaced. Early fall is a great time for evaluation of fields to determine alternative cropping strategies and to allow time for tillage and fertilization. 

Alfalfa has experienced some tough winter conditions in many regions. The plants that survived these harsh winters are now starting to show effects of that stress. In addition to the stress from winter conditions, the stress of harvest, insect pressure or crown rots may have caused plants to weaken and not have enough healthy root to keep producing.

Evaluation of these fields should include digging roots to determine if they are healthy, white and have a firm texture. Roots that are discolored may not survive the upcoming winter, and if they do, may not produce well the next year. If roots are completely discolored or are partially rotted, they may not survive winter.  You can also determine health of the stand by evaluating weed pressure. If weeds are becoming a problem, that may be a sign that the stand is thinning and needs to be replaced. 

Another factor to evaluate is stand density. Fields that have adequate stem density (>55 stems/square foot) can suffer some loss through the winter and still yield well the following growing season. Densities with fewer than 40 stems/square foot will see some yield reduction. That in combination with poor plant health can become a major consideration in termination of the stand (Table 1).

Once it has been determined to replace the thinning stand, producers have a couple of options. The first is to interseed grass for the ability to harvest a grass-alfalfa mix. This is a good option for hay or livestock grazing.  If it is determined to terminate the stand and rotate to another crop, keep in mind you may be able to reduce nitrogen application on that field by 100 lb/acre.

Table 1. Predicted Yield Potential Based on Stand Density1    
 
Stand density (stems/sq ft) Action Predicted yield potential

Greater than 55

Stem density not limiting yield

Same as current year

40 to 55

Some yield reduction expected

If good health, same as current year; if greater than 30% in category 4*, significantly less

Fewer than 39

Consider replacing stand

If good health, same as current year; if greater than 30% in category 4*, significantly less

*Root health = Complete lack of symmetry, few shoots, root rot affects more than 50% of the root’s diameter, vascular tissue is considerably discolored, and plants are unlikely to survive winter.    

Tammy Ott

Agronomist

Sources:

1Undersander, D., Grau, C., Cosgrove, D., Doll, J., and Martin, N. 2011. Alfalfa stand assessment: Is this stand good enough to keep? A3620. Team Forage. University of Wisconsin-Madison. https://fyi.extension.wisc.edu/.    

 

Performance may vary, from location to location and from year to year, as local growing, soil and weather conditions may vary. Growers should evaluate data from multiple locations and years whenever possible and should consider the impacts of these conditions on the grower’s fields. 

 

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