Inhibitors - benefits and limits

Urease inhibitors offer a marked improvement with regard to simple urea or UAN in terms of volatilization. Compared to nitrate fertilizers, however, nitrogen efficiency is still lower. What are the actual differences?

What is the economic value?

Studies in Germany and France have confirmed reduced volatilization losses of urea when combined with NBPT. The main benefit of urea inhibitors lies in nitrogen savings. The savings from urease inhibitors depend on expected urea losses without inhibitors (15 - 25% losses) and on expected mitigation of these losses by inhibitors (60 - 80% reduction of losses). The amount of saved nitrogen can then be calculated for an expected loss from urea and an expected loss reduction from the inhibitor. (see figure 7).

In order to benefit economically from urease inhibitors, the nitrogen savings (in %) need to be higher than the price premium requested for urea with inhibitor compared to straight urea.

Example: With an expected volatilization loss of 20% without inhibitor and a potential reduction of volatilization losses by urease inhibitors of 70%, roughly 14 % of urea can be saved. Therefore, an economic benefit for the farmer can be expected only if the price premium for the inhibitor over straight urea is below 14 %. For UAN the potential savings are typically smaller since losses are smaller.

How about nitrogen efficiency?

Urease inhibitors, however do not solve all issues observed with urea and UAN: 

• The lower spreading accuracy of urea may cause additional yield and quality losses. Wind speed and rainfall forecast has to be considered prior to spreading to avoid uneven nitrogen application. Therefore urea is less appropriate for precision farming. 
• At vegetation start, urea application does not provide instantly the nitrate concentration required to boost root growth and tillering or branching. 
• With urea plus urease inhibitor, late nitrogen applications for high protein are still less reliable when soils are dry and readily available nitrate is lacking. 
• For UAN, the effects of urease inhibitors are significantly smaller than for urea due to lower urea content and subsequent lower volatilization losses to be compensated. 
• Last but not least, the quality of imported urea can vary and further deteriorate the spreading accuracy.

Ecological aspects

Urease inhibitors reduce ammonia volatilization and therefore improve the environmental compatibility of urea and UAN. However, nitrate fertilizers remains the golden standard. This holds especially true if all environmental effects are aggregated to the so-called EcoX index which assesses the environmental impact of eutrophication, acidification, global warming and land use change.