Using Diesel Exhaust Fluid (DEF) as a source of nitrogen for lawns and gardens has become a popular "hack" for DIY enthusiasts. Since DEF is comprised of approximately 32.5% high-purity urea and 67.5% deionized water, it serves as a potent liquid nitrogen fertilizer. However, getting the dilution right is critical to avoid nitrogen burn.
Calculation Results:
Note: 32.5% Urea solution contains approximately 1.5 lbs of Nitrogen per gallon of concentrate.
Understanding DEF as a Fertilizer
Diesel Exhaust Fluid is essentially a standardized urea solution. In the world of agriculture, urea is a common nitrogen source (46-0-0). Because DEF is already in liquid form, it is highly bioavailable for plants, particularly when used as a foliar spray or a soil drench for nitrogen-hungry grasses like Bermuda or Kentucky Bluegrass.
The Chemistry of DEF
The standard composition of DEF is strictly regulated to ensure it doesn't damage vehicle SCR systems. For gardeners, this means you are getting a very clean product:
- Urea Content: 32.5%
- Water Content: 67.5% (Deionized)
- Nitrogen Equivalent: Approximately 15.5% Nitrogen by weight.
How to Use the DEF Fertilizer Calculator
To use the calculator above, simply enter the amount of water your sprayer holds. Then, select your desired intensity. If you are new to using DEF on your lawn, it is highly recommended to start with the "Light Feeding" rate to see how your grass responds.
Recommended Dilution Rates
- Foliar Application: 2 to 4 ounces of DEF per gallon of water. This is safer for the leaf blades and provides a quick "green-up."
- Soil Drench: 4 to 6 ounces per gallon. This allows the nitrogen to reach the root zone for sustained growth.
- The "Golden Rule": Never apply high-nitrogen solutions in the heat of the day. Apply in the early morning or late evening to prevent evaporation and leaf burn.
Safety and Best Practices
While using DEF is cost-effective, it is not a complete fertilizer. It provides Nitrogen, but lacks Phosphorus, Potassium, and micronutrients. Here are a few tips for success:
1. Check for Additives
Ensure the DEF you purchase is "Pure DEF" without any specialized "anti-crystallization" additives which might not be tested for plant safety.
2. Soil Testing
Before embarking on a heavy nitrogen regimen, test your soil. Adding too much nitrogen can lead to excessive top growth at the expense of root health, and can also alter soil pH over time.
3. Watering In
If you are applying DEF at higher concentrations (above 4 oz per gallon), it is wise to "water it in" with a light irrigation cycle after application to ensure the urea moves into the soil profile.
Conclusion
Calculating how much DEF per gallon of water for fertilizer doesn't have to be a guessing game. By using a precise ratio, you can achieve professional-grade lawn results at a fraction of the cost of branded liquid fertilizers. Always remember: with nitrogen, less is often more.