Well because it has a fast-acting Nitrate (NO3-N) component, it works virtually immediately* on application whereas Urea, Ammonium Sulphate, and Ammo, (which is a blend of the first two) need time for its ALL ammonium (NH4-N) based Nitrogen to kick in. The cooler soil temperatures are, the slower that NH4-N will take as the bugs that break it down to the readily available Nitrate (NO3-N0) slow right down too.

% Nitrification of fertiliser NH4-N to NO3-N time in weeks.

Ammonium Sulphate Nitrate is a compound fertiliser containing Ammonium Nitrate and Ammonium Sulphate. Plants can pick up Ammonium Nitrate as is, without further transformation, whereas the NH4-N in Ammonium Sulphate (SOA) will need to undergo nitrification by our bugs into NO3-N before most of the N is plant available. That is not to say NH4-N can’t be taken up by plants, quite the contrary, but as it readily binds to clay colloids and organic matter, it is tightly held in soils as a result. If it is not dissolved in soil solution, it can’t be taken up by plants. That is why a Nitrate component is so necessary especially in cool soils to boost the N supply, therefore, growth and that is why ASN outperforms Urea, SOA, and Ammo every time. 

One will argue that the others are cheaper, but that misses the point. 

Can you grow as much grass with the same amount of N with the alternatives?  

The answer is a definitive NO and if you don’t believe that check out the trial work here.

*provided adequate soil moisture present                                           ®Registered TM of Agri NZ Ltd Tauranga