Diammonium phosphate is a primary source of added nitrogen in many fermentations. DAP is best used in conjunction with yeast products in complex blends, but low-nitrogen musts or adjunct-heavy worts and washes need extra DAP.
Add DAP in stages during the first half of fermentation. DAP stimulates fermentation rate, so if too much is added at once, the yeasts may ferment too fast and too hot.
Adding it in portions gives you the option to slow additions if the ferment is going too fast, which you cannot do if you have added nutrients all at once.
21.2% ammonia nitrogen
100 ppm (10 g/hL) DAP = 21 ppm nitrogen
1 lb/1000G = 25.4 ppm N