Tires: tires, yanmar tractor, inflation pressure

Question
My Japanese Yanmar tractor was EOM with 5.00x14 lug front tires rated 10ply.  Busted a front tire on a rock then ordered from Hoye.  Hoye advised to replace both front with 4 ply.  After installing new tires I noticed they tried to roll off the rims.  I dumped the dirt from the bucket and backed up about ten feet.  One of them blew out the sidewall on level ground, no load.  
This 4 ply, 10 ply business has me confused.  I ran the tractor for years with the 10 ply tires, never had a problem.  I have asked to replace the tires with 10 ply like I wanted.  Waiting for an answer.
Don  

Answer
Don,

What does the owners manual say about inflation pressure?  Or what does the vehicle manufacturer say about inflation pressure?

What do the 2 different types of tires say about inflation pressure?

And just to be sure we are on the same page:  Are the "4 ply" tires 4 actual plies with a "10 ply rating"?

I need more information to help you.