In the 1940s and 50s, Australian P. A. Yeomans developed a system of water and carbon capture for his farm west of Sydney to combat the unpredictable rainfall regime common to that part of New South Wales. He called this system '"Keyline Design," and went on to write several books on the subject.
From the Permaculture Research Institute of Australia:
"Influenced by the likes of prominent organic agriculture figures in Andre Voison, Friend Sykes, Newman Turner & Louis Bromfield (among many others!) Yeomans has been attributed with being the 1st person to accelerate soil formation through the stacking of methods, overturning the myth that it took 1,000 years to create an inch of topsoil. Yeomans proclaimed that "…the landman’s job is not so much to conserve soil as it is to develop soil, to improve his soil and to make it more fertile than it ever was…". "
Mr. Yeomans thought like a watershed, and developed a suceessful business portfolio based on his ideas that has never been matched in diversity, not in the field of permaculture, nor in the field of agriculture itself! For broadacre applications, Yeomans is a go-to source of life-changing information, as is his student and torch-bearer Darren Doherty. But for the purposes of this article, we will scale his ideas back to the home organic gardening level.
One of the primary concepts espoused by Yeomans, and one of his primary diversions from the Army Corps of Engineers dogma of the time, was the idea that yes, Nature wants to collect and channel water downslope into larger and larger bodies of water, moving that water off of the landscape quickly, but that we, as land managers, would be better served by holding it up high on the slope and moving it away from the drainage line, along what Mr. Yeomans termed the "keyline," and its parallels. In order to do this, our water-harvesting contours must be slightly angled downslope away from the drainage line and back across the dry slope, rewatering the entire production area. How many times have we seen dry pastures with lush green drainage lines? This is the pattern we want to alter. Spread out and retained on the slope, this thin green drain line becomes incredibly productive acreage. And we can do the same thing in the garden.
The central bed in this photo of my garden is what has become of the two beds I built for summer veggies back in May. I had a nice crop of tomatoes, peppers, basil, and sweet potatoes, the latter sweet potatoes working their normal magic on the soil's structure and tilth. In 5 months, a flat of sweet potato slips turned a mound of hard, rocky, clay soil into beautiful, friable topsoil, and yielded about a bushel of storage food.
But I wanted to really get control of the waterflow on this "winter" side of the garden - the north half of the clearing that gets more sun during the low sun-angle months - so I decided to turn those first two beds into a high hugelkultur for raspberries.
A "hugelkultur" is a raised mound filled with half-rotten logs, weeds, debris, and in this case, charcoal from the wood stove (or "biochar" as it has been branded, presumably to improve its appeal). So between the two freshly-harvested summer veggie rows I piled rotting logs from the forest, the leftover summer crop detritus, and a bunch of charcoal I had saved from the stove. For anyone who doesn't know about the benefits of charcoal in the garden, a lot of research has been done on the subject in the last decade, spurred by the recognition of patches of fertile soil in the Amazon basin captured on satellite images. These dark patches, or "terra preta," as they were dubbed, were the remnants of old tribal settlements along the Amazon river that had maintained their fertility for centuries! Apparently any bit of charcoal is loaded with pits and cracks that catch and retain moisture, and serve as cation exchange sites for plant roots and their associated mycorrhizal fungi. The increased cation exchange capacity is largely responsible for the increased fertility, and the persistence of that charcoal in the soil had kept those areas of terra preta significantly more fertile than the surrounding landscape for 500 years or more! And in a rain forest ecosystem! Sold!!
So I now include charcoal in as many planting areas as I can manage, stacking yet another function on the task of wood-burning for heat, cooking, and wash water. The cost, both in dollar terms and in energy spent on the task, of burning wood for heat is thereby diminished by another factor in the process. When fertility in the garden increases as a by-product, the regular chore of cutting and chopping firewood becomes much easier to bear. Ashes also get composted in the humanure pile to "sweeten" the pine shaving-dominated carbon bank that tends to turn out compost too acidic for the garden. Another stacked function. The more our productivity is linked and looped toward a closed system the less like "work" it seems.
Pull soil up from the downslope bed over the debris, and then down from the upslope bed, plant it (in this case with gangly raspberries from a too-shaded area of the food forest), spread compost around the plants, and add a thick layer of mulch. Raspberries typically grow roots only to about 18 inches deep, which is about how high this mound is, and like to have a reliably moist footing. The spongy rotting logs and biochar of the hugelkultur should keep them watered, nourished, and happy for many years. AND, such a tall sponge up high in the garden should go a long way toward capturing every drop of water and scrap of fertility available. I intend to do something similar on the "summer" side of the garden next year, after I've had a chance to see how this structure performs, and how the raspberries take to it.
As David Homgren says, always be leery of great master plans. Develop a site incrementally, organically, as you figure out what works and what doesn't. It does absolutely no good to build and plant this great big beautiful garden only to find out that this crop doesn't like its neighbor, or that this other variety doesn't like your soil. Or, as some well-meaning permies found in New Guinea, that their water-harvesting contour swales in that high rainfall climate super-saturated the mountainside and caused devastating landslides. They thought they were teaching the natives some clever tricks compared to their "primitive" water-shedding methods, only to end up looking like idiots. Don't end up looking like an idiot. Work patiently, and at a human scale, even if people make fun of you for "not getting enough accomplished." The permaculture literature is adamant about this approach, and advocates a "grow by chunking" strategy that duplicates what works, with variations for micro-site variability, and discards what doesn't. Take your time, so that you don't have to spend twice as much of it later.
Here is a good example of what I mean. To the left of my developing low-tunnel you can see the regular undulating pattern of raised beds, overgrown by grass and pioneer species. My neighbor Kathy, bless her efforts, had this great master plan in her mind to build all these raised beds and grow tons of food. She must have spent weeks and weeks piling all that soil up with her shovel, planting huge gardens in the beds, and an obscene amount of water to keep them moist enough to grow anything! Raised beds oriented up and down a slope are good for one thing: shedding water quickly downhill. And they are very good at it, as well as washing precious topsoil down with the rain. My task for our garden then is to reorient the layout into a keyline configuration, harvesting rain and nutrients across the slope, moving them gently outward, away from the drainage line.
Increased moisture better nourishes the soil's microbes, invertebrates, and fungi, and saturates the rotting logs and charcoal, and, coupled with ample carbon biomass on the surface initiates a topsoil-creating positive feedback loop in the garden. With a level of maintenance that decreases year after year, the stacked keyline swales of our developing garden will retain moisture very effectively high on the slope, building soil structure and tilth, multiplying the beneficial microbial and fungal soil community, which in turn builds more stable humic substances necessary for optimum plant health. Healthy, organically-grown plants are able to feed their mycorrhizal partners more increasingly nutritious root exudates - sugars in the first years, then proteins, then more and more high-energy fats as the soil improves. Healthy mycchorizal symbionts, in turn, are then capable of expanding their reach (hundreds of yards away from the garden!), shuttling more water and mineral nutrients back to their favorite florae in those deep raised beds, and converting underlying bedrock into soil humus. Which of course, as I wrote last time, increases the soil's ability to hold water and facilitate cation exchange, creating bigger, healthier plants, capable of fighting their own battles without human intervention, adding more mulch to the soil in the process, more nitrogen and more carbon, more water holding capacity, etc. A mere one percent increase in soil organic carbon increases the soil's ability to retain water by 100,000 gallons per acre! (Yes, it was worth saying again!) And healthy organic soil under permanent mulch coverage managed with a no-till regime contributes about 80,000 lbs of microbial corpses per acre per annum, and another 10,000 lbs of worm castings just as gravy! Doesn't take too long to increase the soil organic carbon content by 1% at that rate.
P. A. Yeomans was right. Under knowledgeable stewardship, it doesn't take 1000 years to build an inch of topsoil. I've done it in, oh, one growing season. By thinking like a watershed, capturing those all-important drops of rain, leaves, dust, etc, we can all do it. It isn't magic, but it sure does feel like it when you help it happen.