• Nov 24, 2021
  • Article

Planning out your next rotations; how can alfalfa fit?

Nitrogen fertilizer costs are going up in 2022. One opportunity to minimize the impact of this increased cost is to manage the alfalfa rotation to maximize legume credits for the next crop.

Remember that alfalfa with less than 55 stems per square foot will suffer yield reductions. In fact, at 40 stems per square foot a field will have about a 25% yield reduction. Rather than keep the reduced-yielding fields, turning them over to plant new stands will be more economical.

Many growers are overwhelmed by the costs associated with seeding a new alfalfa stand. But what many don’t realize it that the cost of maintaining a poor stand can exceed the value of seeding a new field of alfalfa.

The first value from turned down alfalfa is the nitrogen available for the next crop in the form of legume credits. Table 1 shows, that 150 to 190 lb/a nitrogen depending on the amount of top growth, will be available for the succeeding crop on medium to fine soils if the stand still has 4 or more plants/ft2.
 
Table 1 legume credits for turned down alfalfa
Stand Density Medium/Fine Soils Sandy Soils
-----Regrowth after last cutting------
>8 inches <8 inches >8 inches <8 inches
  -------------lb nitrogen/acre------------
Good, > 4 plt/ft2 190 150 140 100
Fair, 1.5 to 4 plt/ft2 160 120 110   60
Poor, < 1.5 plt/ft2 130   90   80   40
 
Nitrogen benefit is shown in table 2 where adding nitrogen fertilizer to the seeded corn did not increase either silage or grain yield in 5 Minnesota trials.
Table 2. Need of corn for nitrogen fertilizer when
planted following alfalfa
Corn N Rate Corn Silage Yield Corn Grain Yield
Lb N/ac T DM/ac Bu/ac, 15.5%
0 9.77 228
20 9.75 226
40 9.81 228
80 9.78 229
160 9.88 229
LSD (0.10) NS NS
Data are averages over 5 Minnesota locations
 
The second value of turned down nitrogen is the rotational benefit. We know from several studies that corn can yield about 20% more when following alfalfa than when following corn or soybeans. Similar yield responses have been seen for wheat and other crops following alfalfa. Wheat additionally averaged about 1% more protein following alfalfa according to studies done in Winnipeg, Canada.

These two benefits can more than pay for the cost of establishing a new seeding of alfalfa!

When deciding to rotate consider the following:
It is often best to be thinking two years ahead for rotational systems:
  1. Do you know what herbicides have been applied to the field in the last 2 years? Herbicide residual times have increased with many new herbicides. A number of corn herbicides have no plant alfalfa recommendations of two growing seasons following application. Some wheat herbicides have a 10-month residual time, which prohibits fall planting if the herbicide was applied to wheat in the spring. Carryover herbicides are a major reason for stand failure.
  2. Soil test and consider the pH and fertility of the field. If soil pH needs to be raised, lime should generally be applied to the crop preceding alfalfa to allow time for the lime to raise the soil pH.
  3. Evaluate weed density to determine if significant weed problems exist in the field that are best controlled with herbicides in a crop other than alfalfa (e.g., corn or soybeans).
For fields to be planted with alfalfa in 2022 (assuming there is no residual herbicide and it has adequate soil pH) consider what tillage is needed. While many fields will be seeded by reduced or no-till, the field may need to be leveled with a disk after corn to smooth for haymaking.

Consider residue on the field surface. If using a Brillion seeder surface residue should cover less than 20% of the field surface. More surface residue can be tolerated if drilling the seed.

Winter is a good time to check and refurbish equipment. Particularly check meter flow rates from the seed box. Worn meters may put twice as much seed in some rows as adjacent meters. Also, check springs, depth of disk openers seeding and pressure on packing wheels of drills and repair if needed.
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