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Manage formulas

Jill Carter
  • Updated

Formulas require the Advanced Prescriptions add-on. See Compare Basic and Advanced Prescriptions.

A formula turns your field data into a rate. It takes soil test results, map layer values, crop information, and fixed numbers you set, and calculates a nutrient, seeding, or product rate for each part of the field. Build a formula once, then run it on any field to get a zone map you can turn into a prescription.

This article covers creating, editing, and deleting formulas. To use one, see Run a formula on a field.

Action Where Who
Create a formula Web Enterprise Administrator, Agronomist
Edit a formula Web Enterprise Administrator, Agronomist
Delete a formula Web Enterprise Administrator, Agronomist

For every role and what it can do, see Breakdown of user permissions.

Create a formula

  1. Select Fields, then select the Formulas tab.
  2. Select New formula.
  3. Enter a Name.
  4. Enter a Description. People who run the formula see it, so say what the formula is for and when to use it.
  5. In Output type, choose what the formula calculates:
    • Nutrient rate — then choose the Nutrient output and Rate unit.
    • Seeding rate — then choose the Seed product.
    • Product rate — then choose the Product.
    • Unspecified — for any other value.
  6. Add the variables your expression uses. See Variables you can use.
  7. Write the Expression using your variable names.
  8. Select Save.
The New formula form with name, description, output type, variables, and expression filled in

To start from a working formula, see Example formulas. If you need help writing an expression, email support@farmqa.com.

Variables you can use

Under each variable type, select Add, give the variable a Name, and set its value or source. The name is what you type in the expression.

Variable type What it brings into the expression
Numeric variables A fixed number, like a target yield or a maximum rate. Turn on Prompt for value to enter it each time the formula runs. Turn on Zone-based to set a different value for each zone.
Soil nutrient variables Sample measurements, chosen by soil property, extraction method, and depth. Values are converted to the unit you pick before the formula uses them.
Map layer variables Values from a map layer on the field.
Crop nutrient coefficient variables The nutrient coefficient for the crop assigned to the field in a growing season.
Crop variables A crop in your organization.
Assigned growing season crop variables The crop assigned to the field in a growing season, either the current season or one you choose when you run the formula.

Use interpolated nutrient layers — turn this on to calculate from the interpolated nutrient layers instead of individual sample points. The results keep the same shapes and values as your nutrient layers. It only affects formulas run on sample points. Formulas run on zones aren't affected.

Example formulas

Start from a formula the FarmQA support team already built. Copy it into your account, then change the values to match the recommendations you follow.

Family What it calculates Examples
Phosphorus Phosphorus rate (lb/ac) to build, maintain, or draw down soil test P Alfalfa, corn grain, corn silage, dry beans, soybeans, sugar beets, wheat
Potassium Potassium rate (lb/ac) to build, maintain, or draw down soil test K Alfalfa, corn grain, corn silage, dry beans, soybeans, sugar beets, wheat
Lime Lime rate from soil pH or lime index All crops, MSU lime index, sugar beets
Sugar beet nitrogen Nitrogen rate from soil nitrate Sugar beets, sugar beets after corn
Tri-State Nitrogen, phosphorus, and potassium rates from the Tri-State recommendations (Indiana, Michigan, Ohio) Four formulas

Within the phosphorus and potassium families, every crop uses the same expression. Only the values change, such as yield goal and crop removal rate.

Wheat Phosphate in the formula editor, showing its output type, variables, and expression

 

The Example formulas PDF has every expression as text you can copy, the values for each crop, and a screenshot of each formula.

Use an example

  1. Start a new formula and choose the same Output type as the example. See Create a formula.
  2. Add each variable from the example, using the same name and variable type.
  3. Copy the expression from the PDF and paste it into Expression.
  4. Enter your values, then select Save.

The expression finds variables by name, so a name that doesn't match exactly won't get a value.

Edit a formula

  1. Select Fields, then select the Formulas tab.
  2. Select the formula.
  3. Make your changes, then select Save.

If you leave the formula without saving, FarmQA asks whether to save your changes.

Delete a formula

  1. Select Fields, then select the Formulas tab.
  2. Select the formula, then select Delete.
  3. Confirm that you want to delete it.

You can't delete a formula that a profile uses. Check Related profiles on the formula to see which profiles use it, and remove the formula from those profiles first.

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