I have developed a green manure regime in the allotment situation and find it can very quickly become self sustaining. 2o% of my veg area is used for rye and alfalfa on a rotation basis and a semi permanent bed of comfrey occupies about 10%.All my green manure is composted and I am aiming to turn over 2 batches annually. The resultant compost is spread on the surface, usually on my brassica patch. Rye provides bulk, minimises winter leaching and scavenges unused nutrients. I rate alfalfa very highly because in addition to the nutritional qualities in the compost bin; it scavenges to a considerable depth and the deep roots help to open up the soil, much of the root system remains in the ground and seems to benefit subsequent crops. I do not begrudge the lost space, which is not that great when you consider that allotments always have a significant amount of bare ground throughout the year, I aim to minimise this. The biggest drawback is the amount of effort involved, so its not really suitable for everyone but my methods minimise this. Other green manure crops are used to fill in where nec, such as phacelia, buckwheat, clover.
I hope this helps
Pete
