I don't know about barley, but with alfalfa you better be prepared to deep till. It has a strong root system. Farms, which will be plowed, can use it. But I don't think it makes sense for a home garden myself.
Also, if you're growing any of these as a green manure, why does it matter if the rabbits eat 'em? They'll merely exchange the green manure for real manure, so it's a trade-off.
Sis I have tryed this and had good results. This is a bit long.
"""" ALFALFA and TRIACONTANOL as a plant stimulant (from a lecture by D. L. Hinerman, MD)
For more than 50 years, alfalfa has been used as a plant stimulant. The responsible chemical for this action is triacontanol which is ubiquitous, occurring widely in nature as a waxy coating on many plants and as a major component of beeswax. Triacontanol has been called "the most potent growth hormone ever used on plants."
One of the best sources of triacontanol is the extraction from alfalfa hay (medicago sativa) in one of the following ways:
1. soad 5 tablets (500 to 600 mg of compressed alfalfa purchased from natural food stores) in one gallon of water for 24 hours. Agitate, drench plants with mixture as many as five times during the growing season.
2 Add 2-3 cupfuls of alfalfa meal (purchased from farm food stores, being careful that the meal has not been denatured by high heat) to one yard of soil or growing media.
2. use alfalfa meal or chopped alfalfa has as a light mulch or top dressing to soil around plants and apply water.
3. use potent solvents. The resultant solution is much too concentrated. Only a small trace can be used (0.01 cc); not recommended for average grower.
Beneficial results as as follows:
1. Early breaking of dormancy
2. Doubling of weight of plants in one year
3. Up to three years of growth in one growing season
4. Root system greatly increases
5. Possible stimulation of mycorrhize and reported inhibition of pathogenic organism
6. Doubling of number and size of flower buds, flowers and seeds
7. Much improved quality of growth with increased number, thickness and color of leaves.
I have used alfalfa and its active principle triacontanol on all plants that I have grown with excellent results. The above article was submitted to the Great Lakes Regional Editor for publication in the fall edition - 1993, page 9. This region is part of the AHS. Article submitted by Clarence Owens of Jackson, MI and is now being reprinted with his permission.
We currently are using alfalfa meal (standard 17% animal food) in fifty pound bag on all our prennial plantings and have been doing so for over eight years. We feel that the use of alfalfa meal has played an important part in our plants growing to tremendous size. We also seem to be finding a tremendous number of sports. So you suppose - just maybe - this alfalfa meal may have something to do with that? """