We really like our RR alfalfa.... zero weeds, and don't have to wait 28 days to harvest like if sprayed with Raptor.  

There was a discussion a couple days ago about treated seed.  If treated seed and RR is combined, the net effect can get the viable plants below the needed threshold.  Remember, some seed has 35% coating, and about 10% of the seed is NOT resistant to roundup..... hence they recommend spraying it early, before the plants compete with one another.  

I've seen where guys only plant 12 to 15  pounds, and yes, that should be enough, but at 35% treated seed, you only have 10 or less pounds of actual seed, then after it grows, the rup will kill 10% of the remaining plants, effectively only giving you 9 or less effective pounds of alfalfa..... yes in a perfect situation, that can product a top yield, but if anything isn't just right.......

We currently plant Pioneer , and part of the reason is they only have a 9 or 10% coating...... it has worked well, but plenty of others will as well.