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Agronomic and Economic Considerations on Michigan Farms

MSU Phosphorus and Potassium

Fertilizer Recommendations for Field Crops

The key ingredients: • Soil Test Information • Yield Goal • Buildup, Maintenance and drawdown

Soil sampling

‘Sample should represent the field’

• Sampling pattern for three separate uniform fields

• Each sample should be composed of at least 20 cores

Loam Formerly 2 fields

now all 1 field

Sand

Muck

Never limed

Limed 5 years ago

3 zones 2 zones 2 zones

15 T/a manure

last year

No manure Flat

Poorly drained

2 zones 3 zones

Zone delineation (non-uniform)

MSU Phosphorus and Potassium

Fertilizer Recommendations for Field Crops

The key ingredients: • Soil Test Information • Yield Goal • Buildup, Maintenance and drawdown

Building up low soil testing soils to a critical level Adding P and K to maintain that level year after year Flexibility to change the rate

Buildup and Maintenance Approach


0 15 30 45 ppm Critical level - Soil test level to achieve economic optimum (95-97% of the maximum yield)

Critical Soil Test P Value The soil test level where you achieve economic optimum yield (95-97% of the maximum yield)

Critical Soil Test P Level

Crop

Critical P level (ppm)

Corn 15

Soybean 15

Wheat 25

Alfalfa 25

The soil test level where you achieve economic optimum yield (95-97% of the maximum yield)



0 15 30 45 ppm Critical level - Soil test level to achieve economic optimum (95-97% of the maximum yield)


MSU recommended P fertilizer practices

Soil Test Level Recommended Fertilizer Rate

Buildup range (< Critical level) Apply rates to buildup to critical level plus crop removal rate

Maintenance range (>critical level) Only apply crop removal rate

Drawdown range (> maintenance limit) only starter P or No Phosphorus

Crop Yield lb P2O5/A removed

lb K2O/A removed

Corn 180 Bu 67 48

Soybean 45 Bu 36 63

Wheat 75 Bu 47 28

Alfalfa 4 Tons 52 200

Phosphorus and Potassium Removal Rates (based on the yield goal in soil test)

MSU Soil Test Lab Report

The bar chart closely corresponds to the buildup (below

optimum), maintenance (optimum) and drawdown ranges

(above optimum).

Soil Test Lab Report

The bar chart closely

corresponds to the

Below optimum

(Buildup )

Optimum

(Maintenance)

Above Optimum

(Drawdown)

Analysis

Recommendation

*


Critical Soil Test K Level

Crop

Critical K level (ppm) CEC = 10 me/100g

Corn 100

Soybean 100

Wheat 100

Alfalfa 100

Potassium is positively charged and attracted to clay or

organic matter (Limited losses to environment)

• P in soil – Many years to build-up and drawdown

• Applying manure to meet all the N needs of corn

leads to over application of P

• Maintain soil pH range at 6.0-6.8 (Use lime if

necessary – good return to investment)

• P and K can be applied in the fall or spring

(Fall K fertilizer applications on sandy soils with low

organic matter are discouraged)

P and K Management Considerations

More information on this approach – Special situations

will be discussed at the advanced session

Macronutrients – Nitrogen (N), Phosphorus(P), and Potassium(K)

Required in large amounts and likely to be deficient

Secondary Nutrients – Calcium (Ca), Magnesium(Mg) and Sulfur(S)

Required in large amounts but less likely to be deficient

Micronutrients – Manganese (Mn), Zinc (Zn), Boron (B), Copper (Cu), Iron (Fe), and Molybdenum (Mo) Required in trace amounts

18 Essential Plant Nutrients

Carbon (C), Oxygen (O), and Hydrogen(H) are derived from atmospheric carbon dioxide and soil water

• A sketch map indicating each soil unit/management zone

• Physical make-up of the soil

• Accurately determine available nutrients.

• Evaluate the probability of deficiencies, excesses or imbalances.

• Serve as a basis for making fertilizer recommendations.

• Determine the soil pH.

What does a soil tests show

Sampling a Field

2. Grid

• A sketch map indicating each soil unit/management zone to be sampled will be helpful.

• Here are some examples:

Whole Field • Sampling pattern for three separate uniform fields

• Each sample should be composed of at least 20 cores

Grid – Systematic sampling

• Used where nutrients will be applied variably

• Can be useful if purchase/rent new ground and past history not well known

• Plus – good assessment of nutrient variability

• Minus – expensive

Grid

• Sample locations have GPS coordinates

• Sample consists of at least 10 cores composited within a 10’ radius of grid point


• apply only the maintenance rate (crop removal) and

not buildup

• In the drawdown range, skip any P and K application

Short term strategy or on rented land


Short term strategy or on rented land

• Apply P and K first to fields most in need (below critical level) and then allocate the remaining fertilizer to fields with adequate levels

• Only band application 25 - 40 lb/A P and K

• On fields that have the same soil test levels, applying fertilizer at 70% of the recommended rate on all acreage will provide a higher economic return than applying the full rate on 70% of field acres and none on 30% of the acres.

Field Recommended Rate lb/A

Application rate lb/A

(option 1)

Application rate lb/A

(option 2)

1 100 70 100

2 100 70 100

3 100 70 10

Situation – Low testing soil but need to cut down fertilizer. Recommendation 300 lb. Only have 210 lb. (30% reduction)

Fertilizer Grade A bag of 10-10-10 fertilizer contains 10 % nitrogen, 10 % phosphate and 10 % potash A bag of 46-0-0 fertilizer contains 46 % nitrogen, 0 % phosphate and 0 % potash A bag of 0-0-60 fertilizer contains 0 % nitrogen, 0 % phosphate and 60 % potash

If the soil test recommendation is for 120 lb/A potassium, then use a 200 lb of potash (0-0-60).

N-P-K Fertilizers

Common Fertilizer Grade Nutrient Cost

$/ton fertilizer*

Urea 46-0-0 N 564

Anhydrous Ammonia 82-0-0 N 785

UAN 28% N 385

Triple Super Phosphate

0-46-0 P205 614

Muriate of Potash 0-0-60 K20 630

Diammonium Phosphate (DAP

18-46-0 N and P 634

Monoammonium Phosphate (MAP)

11-48-0 N and P 704

Ammonium Polyphosphate

10-34-0 N and P 849

Bulk 19-19-19 N, P and K 615

Bulk 6-24-24 N, P and K 627

Bulk 16-35-5 + Zn + S N, P, K, Zn, S 726