Ammoniacal Nitrogen Fertilizer Guide: Lawn Application & Benefits

The Chemistry of Ammoniacal Nitrogen in Turfgrass

Ammoniacal nitrogen (NH4-N) is a positively charged cation that behaves fundamentally differently in soil compared to nitrate or urea. Because soil colloids (clay and organic matter) carry a negative charge, ammoniacal nitrogen binds tightly to the soil matrix via Cation Exchange Capacity (CEC). This electrostatic attraction prevents NH4-N from leaching out of the root zone during heavy rainfall, making it an exceptionally efficient nitrogen source for sandy soils or high-precipitation regions.

However, ammoniacal nitrogen is not immediately available for mass plant uptake in its bound state. It must undergo nitrification—a two-step biological process where soil bacteria (Nitrosomonas and Nitrobacter) convert ammonium into nitrite, and then into nitrate (NO3-N). This conversion rate is heavily dependent on soil temperature and moisture:

• Below 50°F (10°C): Nitrification nearly halts. Ammoniacal N remains in the soil for months, providing a slow-release effect in early spring or late fall.
• 60°F to 85°F (15°C - 29°C): Optimal bacterial activity. Conversion to nitrate occurs within 2 to 4 weeks, providing a steady, prolonged feeding window without the massive flush-and-crash cycle of pure nitrate fertilizers.
• Above 90°F (32°C): Bacterial stress and high evaporation rates can lead to rapid surface volatilization if the fertilizer is not watered in.

Ammoniacal Nitrogen vs. Nitrate vs. Urea

Understanding how ammoniacal nitrogen stacks up against other common fertilizer forms dictates when and where you should use it. The following matrix breaks down the agronomic behavior of the three primary nitrogen forms found in lawn care products.

Data synthesized from University of Minnesota Extension soil nutrient guidelines.

Top Ammoniacal Nitrogen Products for Home Lawns

Most consumer-grade 'weed and feed' products rely heavily on urea. To specifically target ammoniacal nitrogen benefits, you need to look at specialized turf products. Here are the most effective sources available to homeowners in 2026, complete with pricing and NPK profiles.

1. Ammonium Sulfate (21-0-0)

The most accessible and cost-effective pure ammoniacal nitrogen source. It contains 21% ammoniacal nitrogen and 24% sulfur.

• Cost: $25 - $32 per 50 lb bag.
• Best For: Alkaline soils (pH 7.5+) where the acidifying effect of the sulfur and ammonium helps unlock bound micronutrients like iron.
• Application Rate: 4.7 lbs per 1,000 sq ft to deliver 1 lb of Nitrogen.

2. UAN 28-0-0 (Liquid Solution)

A liquid blend containing 50% urea, 25% ammoniacal nitrogen, and 25% nitrate. This provides an immediate green-up (nitrate), a medium-term feed (ammoniacal), and a long-term feed (urea).

• Cost: $45 - $60 per 2.5 gallon jug.
• Best For: Foliar feeding, tank mixing with liquid herbicides, and spoon-feeding programs on golf-course-style home lawns.
• Application Rate: 3 to 4 oz per 1,000 sq ft mixed in 1 gallon of water.

3. Ammonium Nitrate (34-0-0)

Contains exactly 50% ammoniacal nitrogen and 50% nitrate. Due to agricultural regulations and security concerns regarding its use as an oxidizer, pure ammonium nitrate is increasingly difficult for homeowners to source, often restricted to licensed commercial applicators.

• Cost: $40 - $55 per 50 lb bag (where legally available).
• Best For: Rapid green-up in cool soils where urea conversion is too slow, but immediate nitrate is also required.

Step-by-Step Application Protocol for Granular Ammonium Sulfate

To maximize CEC binding and prevent ammonia volatilization, follow this precise application sequence when using 21-0-0 ammonium sulfate on cool-season turf (Fescue, Kentucky Bluegrass, Ryegrass).

1. Calibrate the Spreader: Set a Scotts EdgeGuard broadcast spreader to setting 4.5 (or equivalent medium-coarse setting on Lesco models). This ensures the heavy, crystalline ammonium sulfate prills are thrown evenly without shattering.
2. Measure the Area: Calculate exact square footage. For a 5,000 sq ft lawn, you need exactly 23.5 lbs of 21-0-0 to apply 1 lb of N per 1,000 sq ft.
3. Apply in a Crosshatch Pattern: Apply half the product walking North-South, and the other half walking East-West. Ammonium sulfate can cause severe localized osmotic burn if overlapped heavily.
4. Immediate Water-In: Within 30 minutes of application, run your irrigation system for exactly 12 to 15 minutes (delivering roughly 0.25 inches of water). This dissolves the prills, moves the NH4+ into the thatch/soil interface, and locks it to the CEC before volatilization can occur.
5. Monitor Soil pH: If applying more than twice a season, pull a soil core test. Ammonium sulfate drops soil pH by approximately 0.1 to 0.2 points per 10 lbs of sulfur applied per 1,000 sq ft.

Troubleshooting Common Application Failures

Even experienced turf managers encounter edge cases with ammoniacal nitrogen. Use this diagnostic framework to identify and correct issues.

• Symptom: Lawn smells sharply of ammonia (Windex-like odor) 24 hours after application.
  Diagnosis: Volatilization. The soil pH is likely above 7.4, and insufficient water was applied to move the ammonium into the soil profile.
  Fix: Water heavily immediately (0.5 inches) to force the remaining ammonium into the soil. In the future, switch to a sulfur-coated urea or apply elemental sulfur to lower baseline soil pH.
• Symptom: Tips of grass blades are white and desiccated (tip burn) within 48 hours.
  Diagnosis: Osmotic stress from high salt index or uneven spreader overlap. Ammonium sulfate has a salt index of 69, which is moderately high.
  Fix: Apply 0.5 inches of water to flush excess salts past the root zone. Reduce application rate to 0.5 lbs N per 1,000 sq ft for future passes.
• Symptom: Fertilizer applied, but lawn remains pale yellow after 3 weeks.
  Diagnosis: Cold soil inhibition. Soil temperatures are below 55°F, and nitrifying bacteria are dormant, preventing the conversion of ammonium to plant-available nitrate.
  Fix: Apply a fast-acting liquid nitrate or chelated iron for immediate color, and allow the ammoniacal N to convert naturally as spring soil temperatures rise.

Expert FAQ: Ammoniacal Nitrogen Nuances

Can I mix liquid UAN 28 with selective herbicides like 2,4-D or Trimec?

Yes, but with a critical caveat. Ammoniacal nitrogen lowers the pH of the tank mix. While a slightly acidic pH (5.5 - 6.5) improves the efficacy of many weak-acid herbicides like 2,4-D, dropping the pH below 4.5 can cause the herbicide to precipitate out of the solution, clogging your sprayer nozzles. Always use a compatibility jar test before mixing large batches, and add the UAN to the tank after the herbicide is fully agitated in water.

Is ammoniacal nitrogen safe for newly seeded lawns?

No. Seedling roots are highly sensitive to the osmotic stress and localized acidity generated by the nitrification process. For new seed, rely on a starter fertilizer high in nitrate and phosphorus (e.g., a 10-18-10 NPK where the nitrogen is primarily nitrate-based). Wait until the new turf has been mowed at least three times before introducing ammoniacal nitrogen sources.

How does soil type affect ammoniacal nitrogen retention?

Clay and high-organic-matter soils have a high CEC (often 20-40 meq/100g), meaning they act like a massive sponge, holding ammoniacal nitrogen tightly for weeks. Pure sandy soils, however, have a very low CEC (often 3-5 meq/100g). In sandy soils, ammoniacal nitrogen can still leach if heavy rainfall occurs before nitrification is complete. If you have sandy soil, split your ammoniacal applications into smaller, bi-weekly doses rather than one massive monthly application.

For deeper insights into nitrogen transformations and soil cation exchange dynamics, refer to the Crop Nutrition Resource Center.