Foliar nitrogen attracts attention because it offers a different delivery pathway: nutrients can be applied to the plant without adding the same fertilizer load to the soil. John Kempf reports crop responses from foliar urea that, in some situations, appeared much larger per unit of nitrogen than responses to soil-applied nitrogen.
The reported response does not establish a conversion ratio between foliar and soil-applied nitrogen.
Foliar uptake depends on crop species, leaf surface, growth stage, formulation, concentration, carrier volume, humidity, temperature, drying time and spray coverage. A rate tolerated by a broadleaf crop may injure corn or another grass. The drone-applied concentrations mentioned during the webinar were explicitly treated as needing further verification.
Listen to this part of the conversation #
Suggested section: 26:30–28:24. The player begins at 26:30; pause when you reach the end of the suggested section.
Listen for the reported comparison between foliar and soil-applied urea, followed by Kempf’s questions about timing, application cost and electrolyte concentration.
Originally published on 3 April 2026 as Podcast Extra: Adjusting Nitrogen Management with John Kempf and MSHC. Full episode: 1:00:54. Audio is streamed from Libsyn.
Start with the question #
A foliar trial should answer a defined question, such as:
- Can a small foliar application complement a reduced soil application?
- Does crop response differ by growth stage?
- Is the response nutritional, biostimulant-like, or simply absent?
- Does the treatment improve yield, quality or nitrogen-use efficiency?
Without a clear question and control, it is easy to credit a spray for normal field variation.
Design a safe comparison #
Use replicated strips and retain the grower-standard program. Change one main factor at a time. Confirm product compatibility, crop label, water quality and leaf-burn risk before application. Apply under suitable conditions and record weather, rate, carrier volume, nozzle or drone setup, coverage and crop stage.
Evaluate short-term leaf response, but do not stop there. Track tissue or sap results where useful, crop growth, injury, yield, quality and the full cost of the pass.
If the trial substitutes foliar for soil nitrogen, compare actual nitrogen quantities and ensure that any reduction does not place the commercial crop at unacceptable risk.
Where the value may lie #
The strongest case for foliar nutrition may not be “feeding the whole crop through the leaf.” It may be using a precisely timed, relatively small application to correct a developing limitation, support a critical growth stage, or reduce one portion of a concentrated soil application.
Questions to take into the field #
- What precise question is the foliar treatment meant to answer?
- Is the formulation, rate and carrier volume safe for this crop and growth stage?
- Can the treatment be replicated while retaining the grower-standard control?
- Will evaluation include injury, tissue or sap response, yield, quality and the full cost of the pass?
- If soil nitrogen is reduced, what stopping rule protects the commercial crop?
What this evidence can—and cannot—show #
Foliar urea uptake is established, but efficiency and safe rate vary widely. The response ratios and concentrated drone applications discussed in this webinar were speaker experience and grower reports requiring verification. Follow local labels and agronomic guidance.
The practical takeaway #
Use the trial to establish whether the foliar treatment improves yield, quality or cost without causing injury or leaving the crop short of nitrogen.
Further reading #
- Original recording and episode notes
- Minnesota Soil Health Coalition
- Advancing Eco Agriculture: Regenerative Nitrogen Management
Source: John Kempf, Regenerative Agriculture Podcast, Podcast Extra: Adjusting Nitrogen Management with John Kempf and MSHC, published 3 April 2026.
Evidence note: Foliar urea uptake is established, but efficiency and safe rate vary widely. The response ratios and concentrated application examples discussed are speaker and grower reports requiring verification, label compliance and crop-specific safety checks. The podcast is produced by Advancing Eco Agriculture, and AEA products mentioned in the wider recording should be understood in that commercial context.