CORN Newsletter: 2004-10, April 20, 2004

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C.O.R.N Newsletter 2004-10
April 20, 2004 - April 27, 2004

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Application Rules for Nitrification and Urease Inhibitors
by Robert Mullen


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In order to maximize nitrogen (N) availability during the growing season and minimize N losses prior to plant uptake, nitrification and urease inhibitors products are utilized. The general theory is that application of these additives or land applied materials will inhibit (slow down) N turnover by slowing down a specific process in the soil. Nitrification inhibitors slow oxidation of N to nitrate, causing N to stay in the more immobile form of ammonium. It does not inhibit nitrification indefinitely. The length of inhibition is usually between 4 to 10 weeks depending upon soil temperature and pH. If N fertilizers are applied in the fall (not optimum for summer crops), addition of nitrification inhibitors is encouraged (primarily with anhydrous ammonia – OSU does not recommend other sources of N for fall application). When it comes to spring application of N fertilizers, soil texture, soil drainage, and tillage regimen should be considered. Follow these general rules for applying nitrification inhibitors:

1. loamy soils without improved drainage and clay soils with improved drainage have a good probability of seeing yield increases (>60%)

2. clay soils without improved drainage have a moderate chance of seeing yield increases (35-60%) (N should be applied as close to planting as possible)

3. loamy soils with improved drainage have a better chance of seeing yield increases if N is applied earlier in the spring (early spring – 35-60%, later spring - <35%)

4. no-till systems increase the probability of seeing yield increases.

The most common nitrification inhibitor is N-serve (nitrapyrin). Ammonium thiosulfate (ATS) is a newer nitrification inhibitor that can inhibit nitrification (currently considered less capable than N-serve), but ATS is not compatible with anhydrous ammonia application.

Urease inhibitors block the activity of the urease enzyme which breaks down urea to form ammonium. This allows urea to remain in its un-hydrolyzed form longer increasing its staying power. Hydrolyzed urea can be subject to volatilization losses if incorporation does not follow surface application (either with rain or tillage). This is an attractive material for surface applied urea-based compounds (especially in no-till production). The most common urease inhibitor is Agrotain. Ammonium thiosulfate (ATS) also has exhibited some ability to inhibit the urease enzyme, but much less information is available for ATS.

Readers can subscribe electronically to this newsletter by signing up at http://agcrops.osu.edu/services/email.html. E-mail labarge.1@osu.edu if you have problems subscribing or no longer wish to receive this newsletter.

C.O.R.N. is a summary of crop observations, related information, and appropriate recommendations for Ohio Crop Producers and Industry. C.O.R.N. is produced by the Ohio State University Extension Agronomy Team, State Specialists at The Ohio State University and Ohio Agricultural Research and Development Center. C.O.R.N. Questions are directed to State Specialists, Extension Associates, and Agents associated with Ohio State University Extension and the Ohio Agricultural Research and Development Center at The Ohio State University.

Information presented above and where trade names are used, they are supplied with the understanding that no discrimination is intended and no endorsement by Ohio State University Extension is implied. Although every attempt is made to produce information that is complete, timely, and accurate, the pesticide user bears responsibility of consulting the pesticide label and adhering to those directions.

All educational programs conducted by Ohio State University Extension are available to clientele on a nondiscriminatory basis without regard to race, color, creed, religion, sexual orientation, national origin, gender, age, disability or Vietnam-era veteran status.

Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, Keith L. Smith, Director, Ohio State University Extension.

TDD # 1 (800) 589-8292 (Ohio only) or (614) 292-1868


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