you can also use this too. I think there's a grass version also...I found this useful
N-Calculate - wheat nitrogen response calculator | Yara UK
This calculator uses nitrogen response data to calculate the optimum rate of nitrogen at different wheat and nitrogen prices and also calculates the mar...www.yara.co.uk
Nitrogen fertiliser adjustment calculator for cereals and oilseeds | AHDB
Accounting for fertiliser and grain/oilseed prices, it calculates the adjustment in the amount of nitrogen to apply to cereals and/or oilseeds crops.
ahdb.org.uk