I would never expect anything other than A36 grade mild steel in any farm equipment. Alloy metals are reserved for critical things like roll bars on racing cars.
The reason for breaking is typical of MIG welds that are improperly done, lack of penetration and cold lap.
I would definitely grind and repair the other weld while working on the broke one. It is likely of the same quality. I would grind off one side completely, reweld, then grind off the other side completely and reweld it also. Then you can put some of that expensive Kubota orange paint on and reasonably expect it to never break again.