Strange crop

I have been doing a lot of driving for the hospice the last couple of weeks and will be doing so next week as well.
Near to where one of the patients lives are at least four large fields with this crop growing. They tell me its a green manure used to improve the soil. I have looked it up on tinternet and found its called  Phacelia Tanacetifolia, commonly Blue or Purple Tansy.  It is very attractive to bees and other insects and interestingly its seeds (and I quote) "negatively photoblastic", and will only germinate in darkness. 
Interesting what you can learn by blipping