By James W. Bauder, Soil & Water Specialist, Dept. of Plant, Soil & Environmental Sciences,Montana State University. From: 1998 Montana Hay Growers Conference Proceedings, Mont. Agr. Exp. Sta. Spec. Rep. 102
 

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

  1. If stand is more than 50% grass
  2. If roots do not have nodules - take a look
  3. 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
<100 ppm
80-100 pounds
100-150 ppm
 50-80 pounds
150-200 ppm
 20-50 pounds
2000-250 ppm
 10-20 pounds

>250 ppm

not necessary

 

Threshold rates for micronutrients - Recommended Rates for Correcting Micronutrient Deficiencies
 Nutrient
Rate
Correction Rate
Boron

1.0 ppm

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

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

Non-Sandy Soils

10 lbs. zinc per acre.

Plow down or band

Sandy Soils

3 to 5 lbs. zinc per acre. Apply as above.
Iron
Iron Sulfate
10 lbs. in 50 gallons at 15-30
gallons per acre (2-1/2%)
(use 1/2% if hand sprayed)
 
 
Iron Chelate
4 lbs. in 50 gallons at 15-30
gallons per acre (use 1/4% if
hand sprayed)
Not recommended
Manganese
Manganese
Sulfate
(MnSO4-H2O)
0.2% solution of manganese
sulfate
4.5 to 6.5 lbs. manganese sulfate per acre
Copper
Copper Sulfate
(CuSO4~5H2O)
0.1% solution of copper
sulfate
4 to 6 lbs. copper sulfate per acre
Boron
Borax
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

0-30 lbs/a
 
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
Chloride
0-50 ppm  
 
pH
0-9
 
Organic Matter
0-4%
 
Electrical Conductivity
0-4 mmhos/cm  
 
Cation Exchange Capacity
0-20 meq/100 g  
 
Sodium
0-10
 

*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
Nitrogen

2.5-6.0%

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