green manure

a lot of times if you grow stuff on a small scale you can harvest the seeds and so get more that way - its a time v. money type calculation.

If you collect dry seed pods from peas and beans etc., you can sow them as cheap/free ground cover. Cheap seed like lettuce will give rapid cover sprinkled over a small area and maybe even micro greens in the process. All those spare sunflower seeds produce lots of biomass quickly, that and sweetcorn are probably the most prolific in terms of quantity.

As I'm sure you're aware the benefits of green manure are many and varied, but key is the living root that retains the mycorrhizal fungi in the soil which is essential for new plants to establish quickly and flourish. It's a method to recycle via the chop n' drop, the nutrients.
Keeping the organic matter level high.
Holding the soil together to prevent weather erosion and covering to prevent the wash out of nutrients. Lugumes also help fix the atmospheric nitrogen into the soil.
Providing a food source for all the microscopic life forms and worms etc.

Remember even weeds can be green manure, BUT avoid deep rooted things like dock and thistle and ensure you chop and drop before anything gets to flower and reseeds all over your nice clean beds.
Of course good old brown cardboard will achieve some of these things too, as long as the surface is covered.

Sorry if thats teaching granny to suck eggs.

Another possible cheap seed. IF you are driving or cycling about country lanes at the moment there are sometimes spills of grain from the harvest. Gather a little of that and have yourself a quick growing grass like mulch/green manure.

I buy from food section in oriental stores fenugereek 2kg for 2pounds or mustard seeds, sow some marrofats for soup mix all growing perfectly.

Plus one to what Atta said about the marrowfat peas. A box of 'Leos' dried peas will sprout and grow enough if sown now to be 'chopped and dropped' by Sept/Oct.

I also grew lupins in a bed in the front garden and just as well I'm an untidy gardener, there are now loads of seeds on the plants. I'm going to sow some of them in onion beds. I'm sure I'll get some growth on them before the weather turns to cold and I'll chop and drop them into the bed.

Interesting ideas, thanks

I was mainly focussing on protecting soil, but more to think about. Also, given the dry-ness of the year, I've not been able to generate as much compost as I hoped, so I'm hoping that a bit of a dash for growth now the weather is more sensible will give me a bit of additional soil improver.

If you're looking to winter crops, then a lot can be done by trying to keep the fertility already in the soil which tends to get washed out by all the rain we get. Growing Hungarian grazing rye is one example of how this has been attempted.