Fertilizer Guidelines for Alfalfa
Alfalfa Phosphorus Guidelines
The Olsen test for soil P. We use and recommend the Olsen test, a bicarbonate extraction.
- The threshold we use is 18 ppm, which converts to about 40 lbs/acre in the 0 - 6" depth
- If the soil test is 8 ppm or less, apply 6 - 10 pounds of phosphorus (P2O5) per acre for each ton of alfalfa hay
- If the soil test is > 8 and < 18 ppm, apply 4 - 8 pounds of phosphorus (P2O5) per acre for each ton of alfalfa
- If the soil test is > 18 ppm, apply 2 - 4 pounds of phosphorus (P2O5) per acre for each ton of alfalfa - especially if the soil test pH is > 8.2, the calcium level is > 400 ppm, and the soil texture is silt loam or silty clay loam
- If the soil test is > 24 ppm, apply 1 - 2 pounds of phosphorus (P2O5) per acre f or each ton of alfalfa if the soil test pH is > 8.2, the calcium level is > 400 ppm, and the soil texture is silt loam or silty clay loam
Estimating Alfalfa Yield
0.20 to 0.25 tons of alfalfa production for each inch of water use. Estimate the water use based on location, experience, and weather. Assume approximately 1/4" of water use per day under hot/dry conditions. This means 3.5 - 4.0 inches every two weeks in mid-summer. This means that the crop is producing 0.8 to 1.0 tons of dry matter every two weeks in mid-summer.
Applying Nitrogen to Alfalfa
- If stand is more than 50% grass
- If roots do not have nodules - take a look
- If small test plot shows a positive response to N, apply 10 - 15 pounds of Nitrogen per acre for each ton of alfalfa
Apply 20 - 25 pounds of Nitrogen per acre for each ton of grass.
If the pasture is at least 50% alfalfa, do not apply nitrogen; if the pasture is more than 50% grass, apply nitrogen. The total nitrogen application can be split into 3 applications, starting in early spring (or late winter) and completed not later than June 20th. To determine the actual amount of "material" needed, divide the nutrient requirement by the % nutrient in the fertilizer and multiply by 100. For instance, if the % N is 40% and you want to apply 100 lbs. of N/acre, you need to apply (100 lbs./acre divided by 40) x 100% = 250 lbs. of "material".
Potassium/Potash for Alfalfa:
|Soil Test K||Apply K2O pounds/acre|
If < 1.0 ppm, apply 1-2 lbs/acre
|Copper||0.2 ppm||If < 0.2 ppm, apply 2 lbs/acre Iron 5.0 ppm|
|Iron||5.0 ppm||If < 5.0 ppm, apply 0.25 - 0.5 lbs/acre Manganese 1.0 ppm|
|Manganese||1.0 ppm||If < 1.0 ppm, apply 10 - 20 lbs/acre Zinc 0.5 ppm|
|Zinc||0.5 ppm||If < 0.5 ppm, apply 5 - 10 lbs/acre|
Recommended Rates for Correcting Micronutrient Deficiencies
|Nutrient||Materials||Foliar Spray||Soil Applications|
Zinc Sulfate (ZnSO4)
1/4 to 1/2% solutions or 1 to 2 lbs. of zinc sulfate in 50 gallons water, plus 1 cup household detergent
10 lbs. zinc per acre.
Plow down or band
3 to 5 lbs. zinc per acre. Apply as above.
10 lbs. in 50 gallons at 15-30
gallons per acre (2-1/2%)
(use 1/2% if hand sprayed)
4 lbs. in 50 gallons at 15-30
gallons per acre (use 1/4% if
0.2% solution of manganese
4.5 to 6.5 lbs. manganese sulfate per acre
0.1% solution of copper
|4 to 6 lbs. copper sulfate per acre|
2 oz. Borax in 50 gallons of water to make 1/4%
solution. Add 1 cup
household detergent per 50 gallons.
20 to 25 lbs. of Borax per acre or 2.5 to 3lbs. of B
oron per acre; reduce rate by
2 for sandy soils.
Critical Test Levels Table
If you elect to apply micronutrients, the most efficient source is a chelating agent, EDTA, which is 7-13% copper, 5-14% iron, 5-12% manganese, and 6-14% zinc. HEEDTA is the next best source.
|Element or Soil Characteristic||Normal Soil Test Range||Critical Soil Test Level*|
|Nitrate - N||
|Phosphorus (Olsen)||0-40 ppm||18.0 ppm|
|Potassium||0-500 ppm||250.0 ppm|
|Calcium||0-1000 ppm||400.0 ppm|
|Magnesium||0-100 ppm||40.0 ppm|
|Sulfate-S||0-50 ppm||10.0 ppm|
|Zinc||0-15 ppm||0.5 ppm|
|Manganese||0-10 ppm||1.0 ppm|
|Copper||0-1 ppm||0.2 ppm|
|Iron||0-10 ppm||2.5 ppm|
|Boron||0-10 ppm||1.0 ppm|
|Molybdenum||0-2 ppm||0.1 ppm|
|Electrical Conductivity||0-4 mmhos/cm|
|Cation Exchange Capacity||0-20 meq/100 g|
*The level of a nutrient below which crop yield, quality or performance is unsatisfactory.
Normal Concentrations of Essential Elements in Forage plants and Visual Deficiency Symptoms (source: UNOCAL Solution Sheet, vol. 2(12), 1986)
|Element||Concentration in Dry Tissue||Deficiency Symptoms|
Older leaves yellow-green, reduced shoot growth
|Potassium||1.0 - 4.0% .||Interveinal yellowing, especially on older leaves, leaf tips and margins scorched|
|Phosphorus||02. - 0.6%||Older leaves dark green first, then appear purple or reddish|
|Calcium||0.2 - 1.0%||Deficiency rare, new leaves reddish - brown and stunted|
|Magnesium||0.2 - 0.5%||Interveinal chlorosis, striped appearance, cherry red margins|
|Sulfur||0.2 - 0.6%||Yellowing of older leaves|
|Iron||50-500 ppm||Interveinal yellowing of new leaves|
|Manganese||Very small amounts||Rare, similar to iron deficiency|
|Copper||Very small amounts||Never a problem|
|Zinc||Very small amounts||Rare, growth stunted, thin and shriveled leaves, appears desiccated|
|Boron||Very small amounts||Rare, chlorotic, stunted growth|
|Molybdenum||Very small amounts||Rare, older leaves, pale green|
|Chlorine||Very small amounts||Never a problem|