Experiments in raised beds

Thanks for the helpful comments and ideas and links. Please keep them coming!
As the design for this garden won't be complete until May at the earliest and I'm going back to the UK for 3 months in June, the first plan of action is to 'grow' soil in the kitchen and training gardens.
For our zone 2 and 3 areas we've decided to plant green manures and we're going to have our own section of alley cropping: sannhemp(a fast-growing nitrogen fixer that provides excellent chop and drop material) and possibly sorghum or other drought-resistant cereal crop.

In the training garden, we'll intersperse small leguminous trees with some ground cover nitrogen fixer like clover(any suggestions of which one?-apparently Alysicarpus vaginalis is grown for pasture and green manure in many areas of central and southern Africa some of them much drier than here). I'm trying to rein in my excitement about developing a small forest garden here but if that is part of the design, I think these choices will be good preparation for that-any comments?
In the Kitchen Garden(zone 1) we are experimenting with a variety of different raised beds so that when implementing the design we can choose the ones that were most efficient and easy to use.

We started with a regular bed built up of topsoil, compost mixed with a little well-rotted horse manure, cardboard and straw and pawpaw leaf mulch (in the foreground)

The second bed we made is based on keyhole beds in Lesotho but adapted to better suit our environment (we've added a water-harvesting trench around the sides and back which is filled with organic material like bark, wood and straw and some soil- the bed is in a corner on the downward slope of the garden so water drains in that direction) and built it with logs we had to hand rather than rocks, which are in shorter supply here. We filled the bed itself with tin cans, branches and bark, subsoil, topsoil, compost and a little manure, a thick layer of newspaper (to keep in moisture and to smother weeds) and a layer of mulch.

We also want to build a bed by re-cycling tyres, a resource we use a lot here and have a supply of. I would also like to experiment in this bed to determine which plants are suited to being grown in the tyres as I've noticed differing results in the plants already being grown in the garden. My suspicion is that, because they create heat, the soil in the tyres dries more quickly and so they are more suited to drought-resistant, heat loving plants.

We'll also try a bed made and maintained in the way most people here do on their homesteads. Like the sweet potato spiral in this photo.
We'll record the following information for a period of 6 months and try to determine which method or combination of methods will suit our site:

• man hours and ease of building and maintenance- intial and ongoing
• monetary cost and potential to re-use current resources
• yield
• prevalence of pests and diseases

I hope this will guide my choices and help other members of the team to feel included in the decisions we make as well as to clarify the reasoning behind our design.

Any comments or suggestions will be very gratefully received. Internet access here is a bit dodgy so rapid replies are often not possible!! Sometimes it goes off for days. More time to spend in the garden and the hammock!