What the research measured
A meta-analysis of published trials found cumulative ammonia loss of 31.0% of applied N for urea and 14.8% for NBPT-treated urea, a 52% reduction, and an average crop yield increase of 5.3% that was limited in coarse-textured soils. In US corn, a 17-state summary of 78 experiments reported average gains of 4.3 bu/ac with surface-applied urea and 1.6 bu/ac with UAN, rising to 6.6 bu/ac at the 59 sites with significant ammonia loss, while yield fell 10 bu/ac or more at 7% of sites. A 14-year southern Illinois comparison showed a 3 bu/ac advantage with conventional tillage and 11 bu/ac over four no-till years.
An international meta-analysis, a 17-state five-year summary of 78 US corn experiments as reported by Wisconsin Extension, NDSU’s regional summary of Illinois and other trials, 1989 Indiana trials at four Purdue locations, and the manufacturer’s claims page.4 independent sources · 1 manufacturer-authored, labelled.What it is. N-(n-butyl) thiophosphoric triamide, a liquid or dry additive coated onto urea (2.0 quarts per ton in the AGROTAIN Advanced formulation, 1.0 quart per ton of UAN) that temporarily blocks the soil enzyme urease, so surface-applied urea stays as urea instead of converting to ammonia gas before rain or tillage moves it into the soil. NDSU describes the delay as about 10 days; the 2006 Wisconsin cost analysis assumed 14 days.
Study conditions and limitations
- The product only matters when urea sits on the surface: Wisconsin notes urea breaks down within 2 to 3 days and up to 20% of applied N can volatilize if it is not incorporated mechanically or by 0.5 to 0.75 inches of rain; the manufacturer defines adequate incorporation as more than 0.5 inch of rain or irrigation or mechanical incorporation deeper than 2 inches.
- Yield responses are not every year: the Wisconsin summary expects benefits 30 to 40% of the time and negative yield effects 5 to 10% of the time, and at Arlington, Wisconsin there was no benefit because 30 to 40 lb N/ac already maximized yield.
- N rate interacts: at Hancock, Wisconsin (1988) NBPT added 8 bu/ac at 70 lb N/ac (135 vs 127) and nothing at 140 lb N/ac (132 vs 134), because the higher rate covered the loss.
- In the meta-analysis the yield benefit was limited in coarse-textured soils and at NBPT rates above 1,060 mg/kg, and the volatilization benefit shrank under high N rates.
- UAN responds less than urea because only 50% of the N in UAN is urea: 1.6 bu/ac against 4.3 bu/ac across the 78 experiments.
- Protection is temporary (about 10 days per NDSU). The manufacturer’s +20 bu/ac average corn figure and its 40% maximum-loss figure are company marketing numbers without a trial list on the page.
Read the sources · 5
- Urease Inhibitor NBPT on Ammonia Volatilization and Crop Productivity: A Meta-Analysis ↗
Regression across published studies put cumulative ammonia loss at 31.0% of applied N for urea and 14.8% for NBPT-treated urea, a 52% reduction; it took 4.8 and 8.3 days for half the total loss to occur for urea and treated urea. Average crop yield rose 5.3%, but gains were limited in coarse-textured soils and at NBPT rates above 1,060 mg/kg.
- Does It Pay to Use Nitrification and Urease Inhibitors? ↗
Summarizes 78 experiments in 17 states over 5 years: NBPT raised corn yield 4.3 bu/ac with surface urea and 1.6 with UAN across all sites, 6.6 and 2.7 at the 59 sites with significant ammonia loss, with yield reductions of 10 bu/ac or more at 7% of sites. At Hancock, WI (1988), 70 lb N as urea plus inhibitor yielded 135 vs 127 bu/ac; at 140 lb N there was no difference.
- Nitrogen Extenders and Additives for Field Crops ↗
NBPT delays ammonia volatilization from surface or near-surface urea for about 10 days. A 14-year southern Illinois study showed a 3 bu/ac corn advantage for urea plus Agrotain over broadcast urea in conventional tillage, and in no-till the advantage was 11 bu/ac over four years.
- No-till Corn, Broadcast Urea, and Urease Inhibitors ↗
Mean yields from 1989 trials at four Indiana locations: urea broadcast on the surface 130 bu/ac, urea plus NBPT 143; UAN broadcast 135, UAN plus NBPT 140; coulter-injected UAN 147; a 20 lb N starter-only control 99.
- AGROTAIN Nitrogen Stabilizer ↗
The company claims more than 1,000 trials over 25 years, up to 40 percent N loss to ammonia volatilization when urea or UAN is not incorporated by more than 0.5 inch of rain or more than 2 inches of mixing, and an average corn yield benefit of +20 bu/ac. Marketing figures without a trial list on the page.
Before you buy, ask
- What did my soil test show, and did the cited studies respond at similar levels?
- What rate, source, and timing were tested, and what did the untreated check receive?
- How does the price per pound of nutrient compare with the sources I already use?
Record
- Sources checked
- October 12, 2026. Every figure shown is printed on the linked page; unit conversions are noted on the chart.
- Company response
- None yet. Makers and suppliers of this product can send corrections, additional trials, or a statement; it is published here, labelled, and never edits the research summary. Send a correction →