The Bremner Contribution to Controlling Nitrogen Transformations in Soils

1. The Bremner Contribution to Controlling Nitrogen Transformations in Soils Larry G. Bundy University of Wisconsin

2. Issues Driving Research • Concern about nitrate-N enrichment of natural waters • Emergence of urea as a major N fertilizer material • Need to enhance agronomic N fertilizer efficiency by controlling losses

4. Control of Nitrogen Transformations • Goals of Bremner research: • Minimize N losses affecting environmental quality • Enhance N fertilizer efficiency • Major area of work in Bremner program • At least 10 former students involved

5. Areas of Research • Inhibition of nitrification • Inhibition of soil urease activity • Mechanisms of and factors affecting inhibitor action • Consequences of inhibitor use on N losses, associated N transformations, and plant response

6. Major Findings – Nitrification Inhibitors • Most effective inhibitors identified: • Nitrapyrin, etridiazole, 2-ethynylpyridine, 3-methylpyrazole-1-carboxamide, dicyandiamide • Includes commercial products • Pesticides evaluated as inhibitors • Most fungicides and some herbicides tested retarded nitrification.

7. Major Findings – Nitrification Inhibitors • Several classes of compounds (including naturally-occurring) evaluated for efficacy as inhibitors • Phenolic, acetylenic, heterocyclic, terpenoids, sulfur-containing • Some acetylenic, heterocyclic, and sulfur-containing compounds are effective • Mechanisms and characteristics of inhibition explored

8. Major Findings – Nitrification Inhibitors • Inhibition by S-compounds due to release of volatile S compounds after addition to soil • Inhibition of urea-N nitrification minimized nitrite accumulation, increased ammonium fixation, and suggested that losses of N oxides during nitrification were minimal • Persistence of inhibitors greatest in higher organic matter soils

9. Major Findings – Urease Inhibitors • Quinones, phosphoroamides, and ammonium thiosulfate evaluated for efficacy as inhibitors • Phosphoroamides found to be the most effective urease inhibitors • N-(n-butyl) thiophosphoric triamide (NBPT) is in use as a commercial product (Agrotain)

10. Major Findings – Urease Inhibitors • Mechanisms and characteristics of inhibition explored • Inhibition of urea hydrolysis by some substituted quinones and phosphoroamides increased on incubation with soil • N-(n-butyl) thiophosphoric triamide (NBPT) decomposes in soil to form N-(n-butyl) phosphoric triamide which is a more potent urease inhibitor

11. Major Findings – Urease Inhibitors • Utility of urease inhibitors for controlling seed germination and plant growth problems from urea fertilizers was evaluated • NBPT reduced germination and growth problems when added to urea (0.01%) • Phytotoxicity from urea can result from urease inhibitor use

12. Major Findings – Urease Inhibitors • Factors affecting efficacy and persistence of urease inhibitors were evaluated • Persistence of phosphoroamides greatest with NBPT • Inhibitory effects of NBPT persisted for more than 28 days. • For quinones and phosphoroamides, efficacy increased with decreasing soil organic matter and increasing sand content

13. Major Findings – Urease Inhibitors • Effects of urease inhibitors on associated N transformations were studied • NBPT and other effective inhibitors reduced ammonia volatilization and nitrite accumulation in urea-treated soils • Generally, urease inhibitors had little effect on denitrification, nitrification, or mineralization of organic N

14. Summary • Bremner research on control of N transformations provided the science base for use of inhibitors to: • Minimize N losses to the environment • Enhance agronomic N use efficiency • Control problems associated with use of urea as a N fertilizer