When I'm putting together fertilizer blends I'm usually working through a few spreadsheets to calculate desired nutrients, product rates, densities, total volumes and cost per acre. I hired a university student taking linear algebra to come up with a solver in excel to do all the calculations I need in a few small steps. I gave him some money towards tuition and he wored with me to develop this spreadsheet.
You can find it here: http://beyondagronomy.com//cmsFiles/documents/document58ea46c177afa.xlsm
Steps to make it work
Enter values in cells coloured yellow.
Enter acres (left), desired nutrients (top right), product density, product analysis, cost per tonne (bottom right)
Press Control R and then hit okay.
Voila! Actual nutrient blend, product rates, volumes and cost marked in green.
If you have any questions I'll do my best to help. SL