Do not put DEF on your lawn. This is a bad idea, and here's why:

What DEF actually is

Diesel Exhaust Fluid is 32.5% high-purity urea + 67.5% deionized water. It's designed to be injected into diesel truck exhaust systems (SCR systems) to reduce NOx emissions — it is not a fertilizer product, even though urea is also used in fertilizers.

Why people get tempted

Urea (46-0-0) is a legitimate nitrogen fertilizer, so the logic seems to track: "It's just urea and water, right?" But the math is brutal:

The math on 2.5 gallons over 5,000 sq ft

• 2.5 gal DEF ≈ ~21 lbs of solution
• At 32.5% urea → roughly 6.8 lbs of urea
• Urea is 46% nitrogen → about 3.1 lbs of actual N
• Over 5,000 sq ft, that's ~0.62 lbs N per 1,000 sq ft

That N rate by itself isn't catastrophic (normal app is 0.5–1.0 lb N/1,000 sq ft). But the problems are:

1. Foliar burn. DEF is a concentrated 32.5% solution. Spraying or pouring it directly on grass blades will scorch them like spilling straight liquid fertilizer. Urea fertilizer solutions for turf are typically diluted to 3–10% and watered in immediately.
2. Uneven application. 2.5 gal spread over 5,000 sq ft is only ~0.5 oz per sq ft — nearly impossible to apply evenly without a calibrated sprayer, leading to striping and dead patches.
3. Not agricultural grade. DEF is manufactured to ISO 22241 purity specs for engines, not for plant/soil safety. It's not labeled, tested, or approved for turf use.
4. Volatilization losses. Surface-applied urea without immediate watering can lose 20–40%+ of its N to the atmosphere as ammonia gas.

What to do instead

• Return the DEF to Walmart, or save it for your truck.
• For ~5,000 sq ft, buy an actual lawn fertilizer. A bag of urea (46-0-0) is cheap (~$20–30 for 50 lb at a farm/co-op store) — you'd apply roughly 2 lbs of urea per 1,000 sq ft (= ~10 lbs over your lawn) for a ~1 lb N/1,000 application, spread with a broadcast spreader and watered in.
• Or grab a standard bagged lawn fertilizer (Scotts, Lesco, Anderson's, etc.) sized for 5,000 sq ft — the bag tells you the spreader setting.

What grass type and region are you in? I can recommend a specific fertilizer + timing if you tell me that.