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Extension > Agriculture > Nutrient Management > Nutrient/Lime Guidelines > Fertilizer Recommendations for Agronomic Crops in Minnesota > Grass-Legume Mixtures

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Fertilizer Recommendations for Agronomic Crops in Minnesota

Grass-Legume Mixtures

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

Revised 2011

A wide variety of grass legume mixtures are adapted to Minnesota growing conditions. These mixtures are also a special challenge for fertilizer management which should be focused on maintaining both components (grasses, legumes) of the mixture.

Nitrogen

Use of nitrogen fertilizer is important for maintaining the grass component of the mixture. Excessive nitrogen will stimulate the growth of grasses which will crowd the legumes out of the mixture. Minimum rates will allow the legumes to crowd out the grasses. A rate of 60 lb. of nitrogen per acre is suggested for grass-legume mixtures. This nitrogen should be top-dressed to the established stands in early spring.

Phosphate and Potash

Fertilizers to supply phosphate and potash are necessary to maintain the legume component of the mixture. The suggestions for phosphate and potash use are listed in Tables 1 and 2. The suggested amounts should be top-dressed to established stands in early spring.

Table 1. Phosphate fertilizer guidelines for grass/legume mixtures.

    Phosphorus (P) Soil Test, ppm *

Expected
Yield

Bray: 0-5 6-10 11-15 16-20 21 +
Olsen: 0-3 4-7 8-11 12-15 16 +
ton/acre   — P2O5 to apply (lb./acre) —
2   35 25 15 0 0
3   55 40 25 10 0
4   70 50 30 10 0
5   90 65 40 15 0

* Use one of the following equations if a phosphate guideline for a specific soil test and a specific expected yield is desired.

P2O5 rec = [ 20 — (1.0) (Bray P, ppm)] (Expected Yield)
P2O5 rec rec = [20 — (1.4) (Olsen P, ppm)] (Expected Yield)

Table 2. Potash fertilizer guidelines for grass/legume mixtures.

Expected
Yield
Potassium (K) Soil Test, ppm
0-40 41-80 81-120 121-160 161 +
ton/acre — K2O to apply (lb./acre) —
2 95 65 40 15 0
3 140 100 60 20 0
4 185 135 80 25 0
5 + 230 165 100 35 0

Other Nutrients

Sulfur is an important addition to a fertilizer program if alfalfa and red clover are the legumes included in the mixture. An annual application of 25 lb. sulfur per acre is suggested if the legumes are grown on sandy soils. Use of other nutrients has not increased dry matter production of grasses and legumes used in the various mixtures. Therefore, the use of other nutrients is not suggested at this time.

Liming Considerations

Maintaining a favorable soil pH is one key to maintaining legumes, especially alfalfa in the mixture. The suggested rate of lime should be broadcast and incorporated before the legumes are seeded. Use of lime will not maintain soil pH in the favorable range forever. When pH values drop into the acid range, alfalfa will probably disappear when it is mixed with grasses. Reseeding can be expensive and unless lime is incorporated, there is no way to reseed alfalfa to get a high yielding stand. Therefore, special attention to legumes other than alfalfa is suggested for soils where acid pH values are a problem. Some forage legumes are more tolerant than alfalfa to pH values in the acid range.

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