The TT-300 is sold as a nitrogen applicator, not a phos applicator and certainly not for 30 gallons of N either.  It does well as a 10-15 gal/a bridge between planting and side dress or pre plant and an indexed boost.

You could mix some 10-34-0 in with the 28% thru the TT-300 but I would limit the N much lower unless you have a regular Heavy Duty 2x2 (and in with this much N set it 3x3) in the ground, usually single disk fertilizer coulter such as the JD or Kinze HD single disk units.

The thing that hold on to N is when it comes into contact with and latches onto a moist soil particle. There are usually quite a few loose, moist soil particles behind two Curvetines per row. How ever definitely not enough to latch onto 30 gal of 28%!

30 gal of 28% is almost 100 units of N! Depending on soil conditions and weather/rain, 30 gal of 28% N too close to the seed can fry a lot of expensive seed.  jmho and experience.

Jim at Dawn