Variable Rate Prescription
Overview
This module include three lessons for creating variable rate fertilizer prescriptions.
Variable Rate Prescription Lesson One
VARIABLE RATE PRESCRIPTIONS
Lesson One: Variable Rate Prescription for Anhydrous Ammonia on a Wheat field.
Overview:
Student will calculate Anhydrous Ammonia fertilizer rates for a Variable Rate Prescription
Objectives:
The student will be able to create a variable rate prescription for a wheat field in North Dakota, using Anhydrous Ammonia as the nitrogen source.
Materials Needed:
Access to the internet
Calculator
Activity:
Step One: Get “base” map ready:
The first step in creating a variable rate fertilizer prescription map is create a base map. This map can be created based on satellite imagery, yield maps, topography, and other geospatial data layers. An agronomist or precision agriculture consultant creates this map for farmers.
The following is an example of a base map that has been created based on several years of yield data that are normalized. In this example, this field will have three management zones that correspond with high, average and low yields in this field.
Step Two: Calculate cost of nutrient:
In this example, we will use Anhydrous Ammonia (NH3) as our Nitrogen source. Anhydrous Ammonia is 82% nitrogen.
Example: If the current price of Anhydrous Ammonia is $328/ton, what is the cost of nitrogen per pound? Answer: $.20 (see several different methods below)
$328/ton of NH3 x 1 ton NH3/2000 lb NH3 x 1 lb NH3/82% nitrogen = $.20/lb N
1 ton of NH3 | 1 pound of NH3 | $.20 | |
Ton of NH3 | 2000 pounds NH3 | 82% N (nitrogen | N |
Your turn:
Current Price of Anhydrous Ammonia = $511/ton
- Convert Anhydrous cost to cost/lb of N =
$511 | 1 ton of NH3 | 1 pound of NH3 | $.31 |
Ton of NH3 | 2000 pounds NH3 | 82% N (nitrogen | N |
Step Three: Determine Nitrogen needs and Fertilizer needs using the NDSU Wheat Nitrogen Calculator
-Open the NDSU Wheat Calculator and utilizing the assumptions below, calculate the amount of N you should provide in each zone. http://www.ndsu.edu/pubweb/soils/wheat/
Current Price of Hard Red Spring Wheat is $4.00
FIELD INFORMATION
-We are assuming this field is in eastern North Dakota
-This field has been in No-Till for more than 5 years
-The previous crop was corn, thus no nitrogen credits
-The organic matter is 4%
-Zone 1 is high productivity ground, Zone 2 is medium productivity ground, Zone 3 is low productivity. See soil test below (soil residual N)
-Soil tests were taken in each of the three zones in the field. The results of the soil test are in the table below:
Zones | Soil Test N | Nitrogen required | NH3 required |
1 – High Productivity
| 25 | 2. 160 | 5. 160/.82=195 |
2 – Medium Productivity
| 25 | 3. 65 | 6. 65/.82=79 |
3 – Low Productivity
| 10 | 4. 15 | 7. 15/.82=18 |
Step 3: Create a prescription map
Utilize precision agriculture software to create the prescription. An example of this can be found on this video. https://www.youtube.com/watch?v=ppCyfkOqm04
8. How many different application amounts of fertilizer are needed in this prescription?
three
9. #5 above goes with which zone: (use bu/ac values from base/zone map above)
168-192 bu/ac on base map (the high production zone)
10. #6 above goes with which zone:
145-168 bu/ac on base map (the medium production zone)
11. #7 above goes with which zone:
78-145 bu/ac on base map (the low production zone)
VARIABLE RATE PRESCRIPTIONS
Lesson One: Variable Rate Prescription for Anhydrous Ammonia on a Wheat field.
Overview:
Student will calculate Anhydrous Ammonia fertilizer rates for a Variable Rate Prescription
Objectives:
The student will be able to create a variable rate prescription for a wheat field in North Dakota, using Anhydrous Ammonia as the nitrogen source.
Materials Needed:
Access to the internet
Calculator
Activity:
Step One: Get “base” map ready:
The first step in creating a variable rate fertilizer prescription map is create a base map. This map can be created based on satellite imagery, yield maps, topography, and other geospatial data layers. An agronomist or precision agriculture consultant creates this map for farmers.
The following is an example of a base map that has been created based on several years of yield data that are normalized. In this example, this field will have three management zones that correspond with high, average and low yields in this field.
Step Two: Calculate cost of nutrient:
In this example, we will use Anhydrous Ammonia (NH3) as our Nitrogen source. Anhydrous Ammonia is 82% nitrogen.
Example: If the current price of Anhydrous Ammonia is $328/ton, what is the cost of nitrogen per pound? Answer: $.20
$328/ton of NH3 x 1 ton NH3/2000 lb NH3 x 1 lb NH3/82% nitrogen = $.20/lb N
1 ton of NH3 | 1 pound of NH3 | $.20 | |
Ton of NH3 | 2000 pounds NH3 | 82% N (nitrogen | N |
Your turn:
Current Price of Anhydrous Ammonia = $511/ton
- Convert Anhydrous cost to cost/lb of N =
Step Three: Determine Nitrogen needs and Fertilizer needs using the NDSU Wheat Nitrogen Calculator
-Open the NDSU Wheat Calculator and utilizing the assumptions below, calculate the amount of N you should provide in each zone. http://www.ndsu.edu/pubweb/soils/wheat/
Current Price of Hard Red Spring Wheat is $4.00
FIELD INFORMATION
-We are assuming this field is in eastern North Dakota
-This field has been in No-Till for more than 5 years
-The previous crop was corn, thus no nitrogen credits
-The organic matter is 4%
-Zone 1 is high productivity ground, Zone 2 is medium productivity ground, Zone 3 is low productivity. See soil test below (soil residual N)
-Soil tests were taken in each of the three zones in the field. The results of the soil test are in the table below:
Zones | Soil Test N | Nitrogen required | NH3 required |
1 – High Productivity
| 25 | 2. | 5. |
2 – Medium Productivity
| 25 | 3. | 6. |
3 – Low Productivity
| 10 | 4. | 7. |
Step 3: Create a prescription map
Utilize precision agriculture software to create the prescription. An example of this can be found on this video. https://www.youtube.com/watch?v=ppCyfkOqm04
8. How many different application amounts of fertilizer are needed in this prescription?
9. #5 above goes with which zone: (use bu/ac values from base/zone map above)
10. #6 above goes with which zone:
11. #7 above goes with which zone:
Variable Rate Prescription Lesson Two
VARIABLE RATE PRESCRIPTIONS – EXERCISE 2
Lesson Two: Variable Rate Prescription for Multiple Scenarios
Overview:
Student will calculate fertilizer rates based on several different scenarios
Objectives:
The student will be able to create a variable rate prescription for a field in North Dakota, using different fertilizers and different crops.
Materials Needed:
Access to the internet
Calculator
Activity:
In this activity, we will utilize several different fertilizers. Use the internet to look up the chemical analysis for each of the following.
Chemical Analysis | Nitrogen | Phosphorus | Potassium |
Urea
| 46 | 0 | 0 |
Anhydrous Ammonia
| 82 | 0 | 0 |
Liquid Ammonium Phosphate
| 10 | 34 | 0 |
Step One: Get “base” map ready:
The first step in creating a variable rate fertilizer prescription map is create a base map. The following map was created by an agronomist using satellite imagery. In this exercise you will explore several different scenarios, using the same management zone map. This base map will be used in all scenarios.
SCENARIO ONE
Step Two: Calculate Cost of Nutrient:
If the current price of Anhydrous Ammonia is $656/ton, what is the cost of nitrogen per pound?
$656 | 1 ton of NH3 | 1 pound of NH3 | $.40 |
Ton of NH3 | 2000 pounds NH3 | 82% N (nitrogen | N |
Utilize the Wheat Nitrogen Calculator to calculate nitrogen rates. http://www.ndsu.edu/pubweb/soils/wheat/
This field is in Eastern North Dakota; the previous crop planted was corn; the field has been in No-Till for 8 years. The green zone (light gray) is high productivity; the yellow zone (lightest color) is medium productivity and the red zone (dark gray) is low productivity. The organic matter is 4.9%.
The farmer wishes to plant wheat and utilize Anhydrous Ammonia. Planning price for wheat is $5/bu. The farmer received a composite soil test for his field of 15 lb N.
Zone | Productivity | Soil Test N | Nitrogen Rec | Fertilizer Rec. |
Green
| High | 15 | 155 | 189 |
Yellow
| Medium | 15 | 75 | 91 |
Red
| Low | 15 | 15 | 18 |
SCENARIO TWO
Step One: Get “base” map ready: The same base map as in scenario one.
Step Two: Calculate Cost of Nutrient:
The farmer reconsiders his options. He thinks that the price of wheat will be closer to $4/bu and he would rather use Urea. Fertilizer prices have gone down also and Urea is currently priced at $276/ton.
If the current price of Urea is $276/ton, what is the cost of nitrogen per pound?
$276 | 1 ton of Urea | 1 pound of Urea | $.30 |
Ton of Urea | 2000 pounds Urea | 46% N (nitrogen | N |
Utilize the Wheat Nitrogen Calculator to calculate nitrogen rates. http://www.ndsu.edu/pubweb/soils/wheat/
Zone | Productivity | Soil Test N | Nitrogen Rec | Fertilizer Rec. |
Green
| High | 15 | 155 | 155/.46=337 |
Yellow
| Medium | 15 | 75 | 75/.46=163 |
Red
| low | 15 | 15 | 15/.46=33 |
SCENARIO THREE
Step One: Get “base” map ready: The same base map as in scenario one and two.
Step Two: Calculate Cost of Nutrient: NH3 will be utilized as in Scenario One.
The price of wheat has tanked, so the farmer would like to try corn next spring. Utilize the NDSU Corn Nitrogen Calculator at https://www.ndsu.edu/pubweb/soils/corn/.
The NDSU Corn Nitrogen calculator is similar to the Wheat Nitrogen Calculator. A big difference is that the calculator doesn’t distinguish between high, medium and low production area. You are able to add or subtract nitrogen per your agronomist recommendation for each management zone of the field.
Hint, you are at the same field as in scenario one. Corn is currently at $4/bu. In his high producing zone, he will add 30 lb of N to the recommendation and in the low producing zone, he will subtract 30 lb of N.
Productivity | Soil Test N | Nitrogen Rec | Fertilizer Rec. | |
Green
| High | 15 | 184+30=214 | 214/.82=261 |
Yellow
| Medium | 15 | 184 | 184/.82=224 |
Red
| Low | 15 | 184-30=154 | 154/.82=188 |
CHALLENGE - SCENARIO FOUR
Rookie mistake, we forgot to subtract the starter fertilizer from the recommendations. The farmer is utilizing liquid ammonium phosphate at 5 gallons/acre for the starter fertilizer. Your research shows that a gallon weighs 11.7 pounds.
For this scenario, we will need to subtract the Nitrogen provided by the starter from the Nitrogen requirements. We will use NH3 for the fertilizer as in scenario one and three.
How much nitrogen is supplied by the starter fertilizer?
5 gallons (NH4)3PO4 | 11.7 pounds (NH4)3PO4 | . 10 lb N | $5.85 lb N or 6 lb N |
Acre | 1 gallon (NH4)3PO4 | 1 pound of (NH4)3PO4 | Acre |
Step One: Get “base” map ready: The same base map as in scenario one and two.
Step Two: Calculate Cost of Nutrient: Urea will be utilized as in Scenario two and three.
Step Three: Determine Nitrogen needs and Fertilizer needs
Zone | Productivity | Soil Test N | N provided by starter | Nitrogen Rec | Fertilizer Rec. |
Green
| High | 15 | 6 | 184+30 – 6=208 | 208/.82=254 |
Yellow
| Medium | 15 | 6 | 184-6=178 | 178/.82=217 |
Red
| Low | 15 | 6 | 184-30-6=148 | 148/.82=180 |
VARIABLE RATE PRESCRIPTIONS – EXERCISE 2
Lesson Two: Variable Rate Prescription for Multiple Scenarios
Overview:
Student will calculate fertilizer rates based on several different scenarios
Objectives:
The student will be able to create a variable rate prescription for a field in North Dakota, using different fertilizers and different crops.
Materials Needed:
Access to the internet
Calculator
Activity:
In this activity, we will utilize several different fertilizers. Use the internet to look up the chemical analysis for each of the following.
Chemical Analysis | Nitrogen | Phosphorus | Potassium |
Urea
|
|
|
|
Anhydrous Ammonia
|
|
|
|
Liquid Ammonium Phosphate
|
|
|
|
Step One: Get “base” map ready:
The first step in creating a variable rate fertilizer prescription map is create a base map. The following map was created by an agronomist using satellite imagery. In this exercise you will explore several different scenarios, using the same management zone map. This base map will be used in all scenarios.
SCENARIO ONE
Step Two: Calculate Cost of Nutrient:
If the current price of Anhydrous Ammonia is $656/ton, what is the cost of nitrogen per pound?
Utilize the Wheat Nitrogen Calculator to calculate nitrogen rates. http://www.ndsu.edu/pubweb/soils/wheat/
This field is in Eastern North Dakota; the previous crop planted was corn; the field has been in No-Till for 8 years. The green zone (light gray) is high productivity; the yellow zone (lightest color) is medium productivity and the red zone (dark gray) is low productivity. The organic matter is 4.9%.
The farmer wishes to plant wheat and utilize Anhydrous Ammonia. Planning price for wheat is $5/bu. The farmer received a composite soil test for his field of 15 lb N.
Zone | Productivity | Soil Test N | Nitrogen Rec | Fertilizer Rec. |
Green
|
|
|
|
|
Yellow
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|
|
|
|
Red
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|
|
|
SCENARIO TWO
Step One: Get “base” map ready: The same base map as in scenario one.
Step Two: Calculate Cost of Nutrient:
The farmer reconsiders his options. He thinks that the price of wheat will be closer to $4/bu and he would rather use Urea. Fertilizer prices have gone down also and Urea is currently priced at $276/ton.
If the current price of Urea is $276/ton, what is the cost of nitrogen per pound?
Utilize the Wheat Nitrogen Calculator to calculate nitrogen rates. http://www.ndsu.edu/pubweb/soils/wheat/
Zone | Productivity | Soil Test N | Nitrogen Rec | Fertilizer Rec. |
Green
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Yellow
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Red
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SCENARIO THREE
Step One: Get “base” map ready: The same base map as in scenario one and two.
Step Two: Calculate Cost of Nutrient: NH3 will be utilized as in Scenario One.
The price of wheat has tanked, so the farmer would like to try corn next spring. Utilize the NDSU Corn Nitrogen Calculator at https://www.ndsu.edu/pubweb/soils/corn/.
The NDSU Corn Nitrogen calculator is similar to the Wheat Nitrogen Calculator. A big difference is that the calculator doesn’t distinguish between high, medium and low production area. You are able to add or subtract nitrogen per your agronomist recommendation for each management zone of the field.
Hint, you are at the same field as in scenario one. Corn is currently at $4/bu. In his high producing zone, he will add 30 lb of N to the recommendation and in the low producing zone, he will subtract 30 lb of N.
Productivity | Soil Test N | Nitrogen Rec | Fertilizer Rec. | |
Green
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|
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|
Yellow
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|
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|
|
Red
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|
CHALLENGE - SCENARIO FOUR
Rookie mistake, we forgot to subtract the starter fertilizer from the recommendations. The farmer is utilizing liquid ammonium phosphate at 5 gallons/acre for the starter fertilizer. Your research shows that a gallon weighs 11.7 pounds.
For this scenario, we will need to subtract the Nitrogen provided by the starter from the Nitrogen requirements. We will use NH3 for the fertilizer as in scenario one and three.
How much nitrogen is supplied by the starter fertilizer?
Step One: Get “base” map ready: The same base map as in scenario one and two.
Step Two: Calculate Cost of Nutrient: Urea will be utilized as in Scenario two and three.
Step Three: Determine Nitrogen needs and Fertilizer needs
Zone | Productivity | Soil Test N | N provided by starter | Nitrogen Rec | Fertilizer Rec. |
Green
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Yellow
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Red
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Variable Rate Prescription Lesson Three
VARIABLE RATE PRESCRIPTIONS
Lesson Three: Variable Rate Prescription with Multiple Fertilizers
Overview:
Student will calculate fertilizer rates of DAP and Urea for a field in eastern North Dakota that will be planted to corn.
Objectives:
The student will be able to create a variable rate prescription for multiple fertilizers and nutrients.
Materials Needed:
Access to the internet
Calculator
Activity:
Step One: Get “base” map ready:
This base map was created by averaging several years of corn yield data. The data was classified using a statistical classification of “natural breaks” for five management zones. Assume this is a field in Eastern North Dakota and it will be planted to corn.
Step Two: Calculate cost of nutrient:
DAP 18-46-0
Urea 46 -0-0
In this example, we will use DAP (Diammonium Phosphate) to meet phosphorus requirements and Urea to meet remaining nitrogen requirements. Phosphorus rates are not determined by utilizing the cost of DAP, thus the cost per lb of nutrient is not needed for phosphorus. However, nitrogen needs are determined based on the cost of fertilizer. In this example then, we only need to calculate the cost of nitrogen from Urea. The cost of urea is $340/ton. What is the cost per lb of nitrogen?
N/lb is:___$340/ton x 1 ton/2000 lb x 1 lb urea/.46 lb Nitrogen = $.37/lb Nitrogen_______________
FIELD INFORMATION
The field is East River, Conventionally tilled, with historic corn yields of 135 lb/acre on the best three zones; 100 bu/acre on the poorer two zones. Medium textured soils. Wheat planted the year prior. 3.3% organic matter. The price of corn is estimated to be $3.70/bushel.
The tables below show the soil test results for each management zone for both phosphorus and nitrogen.
RESOURCE MATERIAL
To determine Phosphorus use following table.
| Soil Test | P Needed | Lb DAP | ||
| Phosphorus |
|
| ||
| Olson |
|
| ||
Zone 1 | 7 | 78 | 78/.46 = 170 | ||
Zone 2 | 8 | 52 | 52/.46 = 113 | ||
Zone 3 | 11 | 52 | 113 | ||
Zone 4 | 9 | 52 | 113 | ||
Zone 5 | 7 | 78 | 170 |
| |
To determine nitrogen, utilize the NDSU corn nitrogen calculator, found at https://www.ndsu.edu/pubweb/soils/corn/ **subtract 30 lb N from zones 4 and 5.
|
|
| Soil Test Nitrate | N Needed
| N provided by DAP | Net N Needed | lb Urea
|
Zone 1
| 85 | 65 | 170 lb DAP x 18%N = 30.6 | 65-30.6=34.4 | 34.4 lb N x 1lb Urea/.46 lb N = 74.8 |
Zone 2
| 90 | 60 | 113 lb DAP x 18% N = 20.3 | 60-20.3=39.7 | 86.3 |
Zone 3
| 100 | 50 | 20.3 | 50-20.3=29.7 | 65 |
Zone 4
| 75 | 75-30=45 | 20.3 | 45-20.3=24.7 | 53.7 |
Zone 5
| 75 | 75-30=45 | 30.6 | 45-30.6=14.4 | 31.3 |
The prescription maps when built in the software will look this this: