I have been working with a Turf/Fert dealer in my area who is promoting a 15-0-7 product for primary lawn feeding (I live in MN). Primary source of N is Ammonium Nitrate, dealer says has low acid/salt index. Seeing that this product seems to be all fast release N, does it seem appropriate for feeding a northern lawn in spring and more importantly, fall? It seems to be there should be some form of slow release N in the product (one bag applies 0.85 lbs of N per 1K). What do you guys think about this - I want to be sure I am getting a quality product, and I really don't want to burn lawns with this stuff.