If it is a 145/135 semi-mounted there are a lot of bolted connections. Can you loosen the bolts enough that the broken part can be realigned without forcing it? If not, you may have bent the broken part or bent some additional parts when the re-welded part let go. You could try finding a replacement for the broken part, but if other parts are also bent there is a very good chance that the replacement part will not fit.
As rrlund suggested, look for a replacement plow. Those 145's used to sell in the range between scrap value and $100 plus per bottom.
Plowing ground that is too dry might be counter productive, you just dry it out further. Try it again after some rain has soaked in to soften the soil and the top is dry enough to get some traction. In good soil your 90 hp tractor should pull that 4x16 plow at 5 MPH or more, is that 3rd or 4th gear on your tractor?