What is urease inhibitor---NBPT 
     
Though plants can take up and assimilate urea directly shortly after application, the major part dissolves in soil water and is subsequently hydrolyzed. When amide-N, as in urea, UAN or in some NPK fertilizers, is applied to the soil, it is transformed relatively rapidly
(within a few days) through the activity of the ubiquitious soil bacterial enzyme urease to ammonia, CO2 and H2O

This transformation has two major drawbacks:(1)It leads to – sometimes very high – volatilization losses of ammonia if urea is surface 
applied. Such ammonia losses will occur particularly on soils poor in sorption capacity, without plant cover and with a high PH.  Long 
droughts at high temperatures also favor ammonia losses.(2) It can cause severe germination and seedling damage due to ammonia 
and nitrite(NO2–) when the amount placed near the seed is too large.

Urease inhibitor---NBPT is a substance that inhibits hydrolytic action on urea by the enzyme urease.  YMS urease inhibitors---NBPT 
prevent or suppress over a certain period of time the transformation of amide-N in urea to ammonium hydroxide and ammonium through
the hydrolytic action of the enzyme urease. By slowing down the rate at which urea is hydrolyzed in the soil, volatilization losses of ammonia 
to the air (as well as further leaching losses of nitrate) is either reduced or avoided. Thus, the efficiency of urea and of N fertilizers containing 
urea (e.g. urea ammonium nitrate solution), is increased and any adverse environmental impact from their use is decreased 
Daily loss of ammonia-N 










                                           

The amount of NBPT applied is in the range 400 to 1,100 ppm ; the actual amount is adjusted to the cultural practices for the crop being 
grown and the local conditions. Urea treated with NBPT at the recommended rate inhibits the activity of the enzyme urease, regardless of the amount of urea applied.

Solid urea can be treated during a batch or continuous mixing operation. The rubbing of urea granules during the mixing operation is 
sufficient to evenly distribute NBPT across all granules/prills. This ‘self-distribution’ of NBPT in the mixing process avoids the need to treat 
each granule/prill individually.. There is no difference in the performance of NBPT when dispersed inside or applied on the surface of urea granules.
For liquid urea formulations like UAN, NBPT is simply added to the UAN solution just before application.

 Urease inhibitor---NBPT-stabilized urea can be applied as a straight N fertilizer in solid or liquid form. Incorporation is unnecessary even on alkaline soils; and it can also be used for second and third dressings in cereal crops on light sandy soils and on grassland later in the growing season. In a soil incubation study, using a wide range of soil types, the effectiveness of NBPT in lowering ammonia volatilization was greatest in soils with a high pH and low buffering capacity (NBPT decomposes faster in acid soils). Because there are larger ammonia losses from non-amended urea on alkaline soils, NBPT clearly has considerable potential to improve the efficiency of urea for temperate grassland. Furthermore, there is no evidence of any long-term adverse effect on grass production with repeated applications of NBPT-amended urea over a three-year period, and no indication that its efficacy to reduce ammonia losses from urea-treated swards declined when used repeatedly on the same soil.

Studies  of  Urease Inhibitors ---NBPT

 Urease inhibitors---NBPT significantly reduce volatilization losses of ammonia resulting in an increase in plant-available soil N. This 
may result in the formation of more basic amino acids, preferably arginin, a precursor of polyamines, the so-called ‘secondary messengers’
it is assumed that phytohormones as well as polyamines play a special role in ammonium-induced growth stimulation. ammonium nutrition 
activates the arginine-mediated pathway with a greater increase of polyamines.

Applying a  urease inhibitor--NBPT with urea/urea-containing fertilizer will   
prevent or delay for 7 to 14 days the transformation of amide-N to ammonium-N. It      
is particularly beneficial on soils where ammonia losses from applied urea are large,    
on soils whereincorporation of urea into the soil is difficult or impossible, where urea    
is not washed into the soil due to drought and where cultivation of the soil is minimal      
or nil (no-till), and where, in consequence, organic matter has accumulated.
YMS urease inhibitor--NBPT provides the greatest agronomic benefit when urea-  
based fertilizers are surface-applied because ammonia losses are significantly   
reduced and there are opportunities to reduce time- or resource-consuming operations. 
For example, tillage or irrigation operations necessary to incorporate straight urea 
can be avoided, which could save time and fuel. NBPT can be applied pre-emergence,  
pre-plant, side-dress, top-dress or other post-planting applications.

                            Reduction of N-volatilization . 

Ammonia loss due to volatilization following surface application of urea and percentage
reduction in loss due to the addition of NBPT. Summary of eight field experiments on soils
covered with plant residues 

Urease inhibitors---NBPT can control ammonia losses from urine and  
excreta patches and dairy shed effluents, which is most important in countries with        
large areas of grazed pastures.
In cattle or dairy farms, where cattle excreta is a main source of ammonia  
emissions. Feedlot cattle normally retain less than 20% of their dietary N intake.   
Normally, 60 to 80% of the excreted N is lost either through nitrate leaching or 
ammonia volatilization. Ammonia volatilization from cattle and pig excreta  
contributes to odor, adverse environmental impact and loss of valuable nutrients .  
 Urease inhibitors ---NBPT have been shown to delay the hydrolysis of urea in   
slurry, urine or cattle excreta, to reduce ammonia emissions from livestock  
facilities and  to improve the N: P ratio in the organic manure for plant growth.

 Urease inhibitors---NBPT significantly improves N-use efficiency from amide-N.

The optimum concentrations of NBPT for maximum efficacy for the majority of   
growing conditions on different soils and crops  is between 0.04% and 0.1% NBPT. On 
average,  N was applied at 190 kg/ha to winter wheat, split over two or three 
applications, the better availability of N in urea + NBPT increased grain yield by 2% 
and the protein content. Overall, N use efficiency of urea + NBPT was 7% higher     
compared to urea without inhibitor

The following table  shows that grain yields obtained with urea were significantly lower 
than those given by urea treated with NBPT or AN. The average yield for all sites was 
7.3 t/ha, the addition of NBPT to urea increased grain yield by 0.35 t/ha as compared to 
the urea alone treatment; the corresponding yield increase obtained with ammonium 
nitrate was 0.47 t/ha. This study shows that NBPT may be an option to reduce ammonia 
losses and increase grain yield when urea is used for maize production.

Maize grain yield at seven sites responsive to nitrogen in Brazil. Fertilizers were side dressed surface-applied to no-till maize

Effect of surface-applied urea fertilizer, with and without the addition of NBPT, on maize yield (t/ha)