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Extension > Agriculture > Nutrient Management > Nutrient/Lime Guidelines > Fertilizer Recommendations for Agronomic Crops in Minnesota > Alfalfa

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Fertilizer Recommendations for Agronomic Crops in Minnesota

alfalfa

Alfalfa

Daniel E. Kaiser, Extension Soil Scientist; John A. Lamb, Extension Soil Scientist; and Roger Eliason, Director, University of Minnesota Soil Testing Laboratory

Revised 2011

An assessment of the need for lime is usually the first consideration for alfalfa production. When soils are acid (pH less than 7.0), optimum alfalfa yields are usually associated with a soil pH in the range of 6.5 to 7.0. There are no management practices that are economic that will decrease soil pH values in excess of 7.4. When soil pH values are calcareous (7.4 and higher), the best strategy is to concentrate on appropriate management of fertilizer.

subsoil map

Figure 1. Reference Map for lime
guidelines.

Two pH values may be printed on a soil test report form. Soil pH is determined by suspending soil in water and taking a reading. If the soil pH is less than 6.0, the sample is placed in a buffer solution and a reading is taken. This buffer pH value determines the rate of lime to apply.

Liming suggestions are listed in Tables 1 and 2. Figure 1 is used to determine location of Area I and Area II. Liming materials that are quarried in Minnesota are analyzed for Effective Neutralizing Power (ENP) and the results are reported as lb. ENP per ton of material.

Suggestions listed on the soil test report forms are given as lb. of ENP per acre. Rate of application (tons per acre) can be calculated from these two pieces of information. Analysis of byproduct liming materials is not required; it is voluntary. Additional information about lime use can be found in FS-5956, Lime Needs in Minnesota, and FS-05957, Liming Materials for Minnesota Soils.

Table 1. Lime guidelines for mineral soils when the soil pH is less than 6.0. The rates suggested should raise the pH to 6.5.

SMP Area 1 Area 2
Buffer Index ENP Ag Lime* ENP Ag Lime*
  lb./acre ton/acre lb./acre ton/acre
6.8 3000 3.0 2000 2.0
6.7 3500 3.5 2000 2.0
6.6 4000 4.0 2000 2.0
6.5 4500 4.5 2000 2.0
6.4 5000 5.0 2500 2.5
6.3 5500 5.5 2500 2.5
6.2 6000 6.0 3000 3.0
6.1 6500 6.5 3000 3.0
6.0 7000 7.0 3500 3.5

*These are approximate guidelines based on the average ENP value of ag lime. An ENP of 1,000 Lb. per ton is an average value for ag lime (crushed limestone) in Minnesota.

Table 2. Lime guidelines for mineral soils when the BUFFER TEST IS NOT USED (Soil pH is 6.0 or higher). The rates suggested should raise the pH to 6.5.

SMP Area 1 Area 2
Buffer Index ENP Ag Lime* ENP Ag Lime*
  lb./acre ton/acre lb./acre ton/acre
6.5 0 0 0 0
6.4 2000 2.0 0 0
6.3 2000 2.0 0 0
6.2 3000 3.0 0 0
6.1 3000 3.0 0 0
6.0 3000 3.0 2000 2.0

* These are approximate guidelines based on the average ENP value of ag lime. An ENP of 1,000 Lb. per ton is an average value for ag lime (crushed limestone) in Minnesota.

Nitrogen

The use of nitrogen (N) is not suggested when alfalfa is seeded in medium or fine-textured soils because a reduction in nodulation might be observed. Small amounts of N fertilizer supplying about 25 lb. N per acre may enhance establishment when alfalfa is seeded in a coarse-textured soil. A small amount of N may be applied when alfalfa is seeded with a nurse or companion crop. This is especially true when soils are sandy. The suggested N rate for this nurse or companion crop situation is 30 lb. per acre.

Phosphate and Potash

Suggestions for the use of phosphate and potash are adjusted for expected yield and the soil test values for phosphorus (P) and potassium (K). The guidelines for phosphate and potash use are listed in Tables 3 and 4. These fertilizers can be top-dressed to established stands or broadcast and incorporated before planting. See FO-03814, Fertilizing Alfalfa in Minnesota for more detailed information about the management of phosphate and potash fertilizers.

Table 3. Phosphate fertilizer guidelines for alfalfa production in Minnesota.

 

Phosphorus (P) Soil Test, ppm*

Expected Yield

Bray:
Olsen:

0-5
0-3
6-10
4-7
11-15
8-11
16-20
12-15
21 +
16 +
ton/acre   P205 to apply (lb./acre)
3 or less   45 35 20 10 0
4   65 45 25 10 0
5   80 55 30 15 0
6   95 65 40 15 0
7   110 80 45 20 0
more than 7   125 90 55 25 0

* Use the following equations to calculate phosphate fertilizer guideline for specific expected yields and specific soil test values for P.

P2O5rec = [18.57 - (0.93) (Bray p), ppm] (Expected Yield)
P2O5rec = [18.57 - (1.16) (Olsen P), ppm] (Expected Yield)

Table 4. Potash fertilizer guidelines for alfalfa production in Minnesota.

 

Potassium (K) Soil Test ppm*

Expected Yield
0-40 41-80 81-120 121-160 161+
tons/acre K20 to apply (lb./acre)
3 or less 145 100 55 10 0
4 190 130 70 10 0
5 240 165 90 15 0
6 290 195 105 15 0
7 335 230 125 20 0
more than 7 380 265 145 20 0

* Use the following equation to calculate potash fertilizer guideline for specific expected yields and specific soil test values for K.

K2Orec = [55.7 - (0.38) (K soil test), ppm] (Expected Yield)

Other Nutrients

Sulfur (S) and boron (B) are two nutrients that might be needed in a fertilizer program for alfalfa. Use of sulfur will probably increase alfalfa production if soils are sandy. However, use of S on fine-textured soils will probably not increase alfalfa yield unless soil organic matter in the top 6-8 inches is 3.0% or less. The soil test for sulfur is not accurate for fine-textured soils and is not recommended. An annual application of 25 lb. S per acre is suggested for sandy soils while 15-25 lb. S per acre is suggested in fine textured soils when soil organic matter is 3.0% or less.

When needed, boron can be top dressed to established stands (Table 5). Because of the low rates of B needed, the B fertilizer should be blended with phosphate and/or potash fertilizers and broadcast for best results. Soils in Minnesota contain adequate amounts of copper (Cu), manganese (Mn), iron (Fe), and zinc (Zn) for optimum alfalfa production and those four micronutrients
should not be needed in a fertilizer program.

Table 5. Boron fertilizer suggestions for alfalfa in Minnesota.

Soil Test for Boron Boron Suggestions
— ppm — Boron to apply (lb./acre)
Less than 1.0 2-4
1.1-5.0 0
more than 5.0 0
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