Crop Fertilizer Recommendation Calculator

Instructions for Using the Calculator

Once you've selected the state and county you can begin entering field and soil test data. If you checked the Load example for selected state box when you selected the state, the calculator skips the county selection and loads an example for the selected state. You can try out the calculator by changing the example data. When you're ready to enter your own data, click the Restart button, then select your state and county.

At a minimum fill in the columns that are flagged with an asterisk (*). These columns are required to calculate your state's fertilizer recommendations. Note that a required checkbox column should just be left unchecked if that item is not present or does not apply.

Columns flagged with a cross () are optional but may be required for some crops or in some situations. If you have the data for optional columns, it's a good idea to enter the data even though it may not be required.

Unflagged columns are not used by your state's recommendations. You can fill in the unflagged columns if you want for completeness, but the values you enter in these columns will not affect the recommendations.

Once you've filled in a table, click the Next button to proceed to the next table. At any time you can click the Back button to return to the previous table (note this is not the same as clicking your browser's "Back" button) or the Restart button to start over with the calculator. If available, you can click the Calculate button to calculate and display the results without proceeding to the next table. If you need more rows in the Field/Crop table, click the Add Rows button after entering the number of additional rows you want to add (the default is 3).

When you're all done entering data and have the results you want, you may want to print a report (see the printing tips below). You can also click the Download Plan button to save your data as an MMP plan file on your local computer. This plan file can be opened by the current version of MMP.


Operation Name

Enter the name of the farm operation.


Field/Crop Information

Field ID Enter a field ID for each field.

Subfield Optionally, you can enter a subfield ID for each field if a field has been subdivided into subfields.

Predominant Soil Type Select the field's predominant soil type. The pick list contains all soils for the county you selected earlier.

Each soil description in the list is made up of four pieces of information, as in this example:

Beaucoup SIL (Bb 0-2%)

In this example, Beaucoup is the soil's component name, SIL is the soil's surface texture, Bb is the soil's map unit symbol, and 0-2% is the soil's slope range.

Tip: Click the Soil Info button to generate a report with information on all soils in the county.

Planned Crop Select the field's planned crop. The pick list contains all crops for which fertilizer recommendations are available for the state you selected earlier. The crop's yield units are indicated in parentheses following the crop name.

Tip: Click the Crop Info button to generate a report with information on all crops.

Planned Crop's Yield Enter the planned crop's yield goal in the units indicated after the crop name.

Planned Crop's % Legume With a planned forage crop, enter the percent of the stand that will be legume.

Previous Crop Select the field's previous crop. The crop's yield units are indicated in parentheses following the crop name

Note: If a cover crop will be planted between the previous year's crop and the planned crop, select the cover crop as the previous crop.

Previous Crop's Yield Enter the previous crop's yield in the units indicated after the crop name.

Previous Crop's % Legume With a previous forage crop, enter the percent of the stand that was legume.

Irrigated w/ Water Check this box if the field is irrigated with water.


Soil Test Data

% OM Enter the field's organic matter content.

P Enter the field's phosphorus level.

P Test Select the test that was used to determine the field's soil phosphorus level. If a state doesn't have different P2O5 recommendations depending on the soil test that was used, you can select N/A.

K Enter the field's potassium level.

Mg Enter the field's magnesium level.

Ca Enter the field's calcium level.

Na Enter the field's sodium level.

Al Enter the field's aluminum level.

Check if in lbs/ac Check this box if the P, K, Mg, Ca, Na and Al levels are in lbs/acre; leave this box unchecked if the test levels are in ppm or are unitless.

Soil pH Enter the field's soil or water pH.

Buffer pH Enter the field's buffer pH.

Est. CEC This column shows the field's estimated cation exchange capacity (in milli-equivalents per 100 grams).

CEC Enter the field's cation exchange capacity if different from the estimate. If you leave this column blank, MMP uses the estimated CEC in any calculations that require CEC.

NO3-N (ppm) Enter the field's nitrate level.

Soil Test Data Tips

  1. A field's P, K, Mg, Ca, Na and Al test levels can be entered in lbs/acre or ppm. Check the Check if in lbs/ac box to indicate lbs/acre or leave the box unchecked to indicate ppm. Note that all five values must be in the same units. If you need to convert a soil test value from ppm to lbs/acre, multiply the value by 2. To convert a soil test value from lbs/acre to ppm, divide the value by 2.

  2. The P and K values must be in terms of elemental P and K. If your test values are expressed in terms of P2O5 and K2O, you'll need to convert them. With a P2O5 test value, multiply the value by 0.44 to convert it to elemental P. With a K2O test value, multiply the value by 0.83 to convert it to elemental K.

  3. When you reach the final table of the calculator, if one or more fertilizer recommendation is blank, make sure you've entered enough soil test data.

Fertilizer Recommendations

The crop fertilizer recommendations for your input data are listed in the N, P2O5 and K2O columns. If the indicated Source is linked to a Web site, you can click on the link to view the source that MMP used for the recommendations.

Note: Recommendations include any legume N credit from the previous year's crop, but no other credits. You may need to reduce the fertilizer recommendations to account for previous manure applications, previous multi-year P and K fertilizer applications, or planned applications of irrigation water nitrates or other nutrients (such as starter fertilizers) that are always applied.


Tips on Printing Calculator Results

When you reach the final table of the calculator, you may want to print the input data and results. Here are some tips for producing high-quality printed output.
  1. Make sure you're in the final table of the calculator (Next button is no longer displayed).

  2. Print the page in landscape. With Internet Explorer, select File | Page Setup, then click Landscape under Orientation. With Mozilla, select File | Page Setup, then click Landscape under Format on the Format & Options tab.

  3. Print the page with background colors turned on so you'll see the column dividers in the tables. With Internet Explorer, select Tools | Internet Options, then click the Advanced tab and check the box labeled "Print background colors and images". With Mozilla, check the Print Background box on the Format & Options tab under File | Page Setup.

  4. Adjust the page margins if you want more or less white space around the edges of the printed page. With Internet Explorer, select File | Page Setup to see and change the margin settings. With Mozilla, select File | Page Setup, then click the Margins & Header/Footer tab to see and change the margin settings.