Yeah that's where I pulled it from. I'm just more curious the origin of why the rules like that are in place. I'm just south of 210 and I can't imagine my soil is that much different from the soil a couple miles north.
I am guessing it has more to do with cash cropping than actual ability of seeds to germinate.
Planting interval: Different soils, different amount of organic matter, time northern soils remain frozen, or soil temperatures prevent break down of herbicide????