This is an interesting conversation, good points on both sides. John’s idea can work, I suspect yield will be lower but you can try it. Mustard is ideal for September sowing because of how it dies in frost, though it needs -5C at least. For spring growing I am not sure.
I think its better not to dig them in because when doing that, there is a period of 2-4 weeks when the green matter, stems and roots are breaking down in the soil, and taking nutrients to do so.
