If you look at this page (and I've found several similar):
http://www.gordonengland.co.uk...
scroll down to "electric flux density" and you'll see coulomb per square metre written as C m-2. Above that they use -3 for per cubic metre. So I would say the Japanese study means per square metre, the minus sign indicating per.
The recommendation I have for home lawns here (Ontario) is 2-3 lbs of N per 1000 square feet per year (split into three applications), so not that much different from your figure considering the difference in our growing seasons. It would be much higher for something like sports turf.
Edit: I wonder if for the Sunset analysis the amounts are for dry weight.
