Don
The other discussion concerns how much green manure you can generate ‘filling in’ slots around the garden where you are simply not able to grow a crop at that time. Ditto over-wintering.
I don’t have an answer yet, but the field beans I put in in October last year just as an over-wintering crop will provide significant waste for the compost pile – I could have grown many more on another two beds and, in fact, may do in seasons ahead.
That method would be focussing more on generating compost than improving soil structure and fertility directly, as the green manures would be short-term, rapidly growing crops only in the ground for under six months.
I’m like you at the moment, importing horse manure, filching cardboard from the local garden centre skips, recycling newspapers and using grass clippings, not to mention my 10 comfrey plants, in addition to all the spent foliage of harvested crops, to create the 1.5 cubic metres of compost I need to cover the garden sufficiently – that’s 5cm annual coverage.
This season I will also experiment small-scale with a few cover crops (like clover under climbing beans) to see if there is any benefit to the soil from creating complete coverage during the summer……
One of the more interesting approaches I have read about is found at:
http://thefoodiebugle.com/article/kitchen-garden/rotation-rotation-rotation – Tasmin Borlase uses 2.5 years of cover crops in a 12 year rotation to restore fertility to the soil, clearing out the green manure using a pig tractor. She does this professionally I believe……..