Could you (and would it be possible) to build a large enough hugelkulture bed with a swale on/in it? Does this concept even make sense? Alternatively, could you build a hugel bed buttressing a stone bund?
This is a long-term soil fertility planting strategy that involves filling a swale with ramial woody debris, similar to the Austrian “hugelkultur” raised bed system. After the swale is dug to capture water, and the ramial woody debris (deciduous woody material not more than 2.5 inches in circumference) is packed down, the woody material is covered with soil or compost. We usually use a mixture of forest and field soil, and mix in some manure, compost, seaweed, and a tad bit of homemade inoculant (from other chestnuts). On steeper hillsides the entire pile is staked in place with a few stakes made from the larger branches of the woody debris.
In The Holistic Orchard, Michael Phillips, explains that the newest growth of deciduous woody plant material contains soluble lignins with a high proportion of nutrients (N, P, K, Ca, Mg, etc…), and a lower Carbon:Nitrogen ratio (30-170:1, as opposed to 400-750:1 as in normal stem or trunk wood). Sapyrophytic microbes that cause white rots break down the hardwood organic matter creating fulvic and humic acids from the lignins (as opposed to polyphenols and allapathic compounds caused by brown rots decomposing softwood cellulose).
This type of woody carbon-based planting technique will create a deep and mycorrhizal-rich soil that will hold water and nutrients. The mycorrhizal associations you’ll be creating from planting this way will help your trees get off to a good start with supportive mineralization processes, healthy anti-biotics, and fungal secretions to stimulate feeder roots.
I have built about 5 beds this year that would qualify as a "hugelswale." I start by digging a ditch about 2 feet deep and 2 feet wide. Then I fill the ditch over grade with rotten wood from around the property. I then backfill with soil and dig a ditch on the uphill side of the "hugelberm." I then cover everything with mulch, the berm and ditch and use the swales ditch as a mulch pit. If i build a series of hugel swales the space between two beds should be ideal for watermelons come summer as this area stays sheltered, moist and nutrient rich from all the chop and drop.