Fields of flowers

We came across several rather lovely fields of flowers today which I believe are a mix of phacelia, flax, buckwheat and the occasional sunflower. I've never seen fields like this before but after much googling I think these are fast growing annuals that are grown as a cover crop. Their primary purpose is to shield and enrich the soil which would otherwise be left bare. Apparently these crops can boost the yield of subsequent cash crops. Looks pretty too and the bees love it!