I finally stopped sanding pine like it was oak, and a guy at the lumber yard in Boise called me out on it
For the first four years I was building cabinets, I treated every board the same. I would grab 80 grit, lean into it, and sand pine until it felt like glass. Then about 8 months ago I was picking up a load of knotty pine at a yard outside Boise and the old guy at the counter asked what I was using on it. I told him 80 then 120 then 220, and he just shook his head. He said pine is soft, so heavy grit digs grooves you can't see until you hit it with stain, and the stain pools in those grooves and turns the whole face blotchy. I switched to 120 and then 180, took maybe 5 minutes longer per door, and my last kitchen job stained dead even for the first time. Cost me about $40 in paper I was wasting on the heavy grit anyway. So what grit are you all actually running on soft woods, and do you go all the way to 220 or stop earlier?
Something a buddy told me years ago finally clicked reading this. He said the old timers around him never went past 150 or 180 on pine because going finer just burnishes the surface and then stain can't soak in even. I ran 120 then 180 on some knotty pine cabinet doors last month and the stain went on way more even than my old 220 habit. The blotching I used to blame on the wood was probably half my own sanding. Only thing I'd add is a quick wipe with a damp rag between grits to raise the grain, that made a difference for me too.