Agricultural & Environmental Services Laboratories

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COVER CROP NITROGEN AVAILABILITY CALCULATOR

Welcome:

Cover crops can provide nitrogen (N) to the following cash crops by scavenging N in the soil or, in the case of legumes, by fixing N from the atmosphere. However, some cover crops can reduce the available N to following cash crops by immobilization. It can be difficult to know how much available N a cover crop will provide or if it will immobilize N. The amount of available N depends on the amount of biomass and the cover crop quality as well as soil temperature and moisture conditions. This calculator was developed to help provide guidance for N management when using cover crops.

What to Expect from the Nitrogen Calculator:

This calculator will predict how much and when nitrogen will be available from aboveground cover crop biomass.

  • If the calculator gives you a positive number, this is a N credit, which can be subtracted from your target N fertilizer rate.
  • If the calculator gives you a negative number, this is a N debit, and you should add additional N fertilizer at planting to account for the N immobilized by the cover crop.

You will need to have measured cover crop biomass in your field and have an analysis of the cover crop nitrogen, carbohydrates, cellulose and lignin to use this calculator.

Instructions:

Click the calculator tab located in the red bar above to start. Answer questions in order to use the calculator. If you have questions, use the contact tab for any help with the calculator. We will get back to you as soon as possible.

If you need instructions, click the Instructions tab above.

Please answer the questions below and click "Next Page" when complete.

Background

Name:
Was the cover crop residue analyzed by the Agricultural and Environmental Services Labs?
  • If so, please enter the Lab Number.
  • IF NOT, leave blank and enter data from another laboratory in the section below.
Lab No.
Please enter the field name
Enter the sample ID
To choose the closest weather station, what county is your farm located in?
(OR Choose from interactive map.)

What is the CASH crop?
What is your target nitrogen fertilizer rate?
(If unknown, see crop recommendation sheet for your cash crop here.)
lbs N/acre
What is the planting date of the cash crop? mm/dd/yyyy
What is the COVER CROP?
When was the cover crop killed or incorporated? mm/dd/yyyy

Please answer the questions below and click "Next Page" when complete.

Background

Is this a high organic matter soil?
(High organic matter soils are usually those that have been managed using conservation tillage with cover crops or organically for at least three years.)
Cover crop residue will be
Dry cover crop biomass lbs/A
Nitrogen in cover crop 0.3-5.0%
Carbohydrates in cover crop 0-100%
Cellulose in cover crop 0-100%
Lignin in cover crop 0-100%
Carbohydrates + Cellulose + Lignin should equal 100%

Is this information correct?

Name:
Field Name:
Sample ID:
Georgia County:
Weather Station:
Cash Crop:
Cash Crop Planting Date:
Target Nitrogen Fertilizer Rate:
Cover Crop:
Cover Crop Termination Date:
High Organic Matter Soil:
Cover crop residue was:
Dry Cover Crop Biomass:
Nitrogen in Cover Crop:
Carbohydrates in Cover Crop:
Cellulose in Cover Crop:
Lignin in Cover Crop:
RESULTS: —
Running Model

Your cover crop was terminated on .

The cover crop is predicted to release lbs of N per acre from the aboveground biomass over three months. This is a N .

The cover crop is predicted to release:

  • lbs of N per acre in the first two weeks after termination.
  • lbs of N per acre in the first four weeks after termination.

Your target nitrogen fertilizer rate was lbs N/ac.

Your recommended N after crediting nitrogen from the cover crop is lbs N/ac.

The available N reported above from the cover crop decompositions is considered a N credit if positive or a debit if negative. The amount of N fertilizer recommended may be reduced by a credit or increased by a debit. Here are examples:

N Credit Example: N Debit Example:
Recommended or Target N = 150 lbs N/ac
Predicted Cover Crop N = 50 lbs N/ac
Recommended N after Credit = 150 - 50 = 100 lbs N/ac 		Recommended or Target N = 150 lbs N/ac
Predicted Cover Crop N = - 20 lbs N/ac
Recommended N after Debit = 150 - (-20) = 150 +20 = 170 lbs N/ac
RESULTS: —

For questions about how to use the calculator, contact your local County Extension Agent.

Additional information can be found in the following Extension publications: