Posted: December 1, 2023
When planning for manure application to legumes "with manure", interpreting the nitrogen balance after manure, supplemental fertilizer N additions, and the final nutrient balance can be confusing. These issues have been clarified in the NMP 9.x and NBS 7.x releases by adding a report of the legume N removal balance after manure applications in the Crop & Manure Management printouts.
When planning for manure application to legumes "with manure", interpreting the nitrogen balance after manure, supplemental fertilizer N additions, and the final nutrient balance can be confusing. In the Appendix 4 printout, these numbers do not always add up in a readily apparent manner due to the unique nature of legume N requirements given their ability to both take up N from the soil and fix N from the atmosphere. This confusion was compounded in previous versions of the Nutrient Management Plan (NMP) and Nutrient Balance Sheet (NBS) planning tools (NMP versions 8.x and before, NBS versions 6.x and before) because the printout did not report the legume N removal balance after manure applications. These issues have been clarified in the NMP 9.x and NBS 7.x releases by adding a report of the legume N removal balance after manure applications in the Crop & Manure Management printouts.
These issues have recently brought forth two questions about how this is represented in the planning tools.
Question 1
Should supplemental nitrogen fertilizer applied to a legume after a manure application be considered a red flag? The legume can use fertilizer N but should a planner be required to remove it from the plan?
Answer: No Why: The supplemental nitrogen fertilizer is not needed but would be used by the legume. Therefore, it is not an overapplication of nitrogen fertilizer when it is applied up to the removal value. If it is applied in excess of the crop removal value then it would be an over-application of nitrogen.
Question 2
Where did the planner come up with the supplemental nitrogen fertilizer value?
The crop and manure management input sheets have always shown the nitrogen balance after manure that is applied to legumes "with manure". The supplemental nitrogen after manure is greyed out to indicate no fertilizer is needed for the legume to achieve the crop yield goal.
The crop and manure management printout in previous versions of the planning tools didn't show the amount of nitrogen removal still available by the legume after manure is applied. This information is shown in the inputs sheets but was not shown in the printout submitted for plan approval.
An example of this is shown below.
Previous planning tool versions represented supplemental nitrogen fertilizer added to legumes (Appendix 4 Printout)
Here are 3 different application/planning scenarios of the same field
Summary
This update is included in the NMP Version 9.x and NBS Version 7.x planning tools released in October 2023. Hopefully, it will clarify the nitrogen removal values after manure is applied to legumes "with manure".
If a planner chooses to add nitrogen to a legume, it will show how much nitrogen fertilizer can be applied. If nitrogen is applied in excess of removal, then the final balance is shown as excess (negative number).
If you have any questions, please contact:
Don Orner
Education Specialist, Penn State Extension - Nutrient Management
Cell: 610-804-0010
Email: dgo2@psu.edu
