These are rough numbers, but gets the idea across:

In the first 30 days, the amount of P2O5 utilized by these crops are:

Winter Wheat  ~ 25 lbs/ac

Corn               ~5 lbs/ac

Soybeans - less than 1 lb/ac

Ergo, in my part of the world, multi-year replicated research shows wheat response of ~ 7 bu/ac to 75 lbs of MAP or 6 gal of 10-34-0 with the seed, corn often shows response - but not always economical, and soybeans - seldom a response, almost never an economical one. The figures above go a ong way to explaining why.

Luke   aka Ken SWOnt