A couple of questions for clarification...

a) Will they let you use their planting equipment if you plant corn?

b) Will they let you use their sprayer if you plant corn?

c) if you can use their equipment to grow corn, then what kind of planter is available?

I would not be keen on spreading soybean seed with a fertilizer cart, although that could possibly be done. 

As far as the sprayer, there is no reason why a current sprayer can't be use to spray soybeans.  The products you would use are different, but there is no reason why you could use their sprayer to spray beans - if they will let you do that.

Frankly, I would start with what you know - corn - realize that corn is your more expensive crop to put in.  Starting with something that you know nothing about has its own risks.