Keyline design is rooted in the natural topography of the land. It promotes the rapid growth of natural fertility and of topsoil by distributing water more evenly over the landscape and encouraging the development of good soil structure. It does this by adapting to the natural landform and by using subsoil ploughs to create a comb like network of deep subsoil cuts that disturb the soil profile as little as possible. Key-line sub-soiling is only done initially; it is not necessary or desirable to repeat the process annually like traditional plowing practices. It is a mechanism for storing winter rains in the ground for summer use by deeper rooted plants and allows re hydration of the landscape instead of winter rains washing off topsoil into the sea.
The Keyline philosophy and Permaculture in general opposes the practice of conventional plowing (and other agricultural practices) that turn or invert the soil. Doing so disturbs good soil structure and exposes it to erosion by wind and water. It also mixes the thin layer of topsoil into the infertile dirt that lies below and is energy intensive as well.
The modern subsoil plough is a type of narrow tine subsoiler that has evolved from chisel ploughs. It cuts a series of very narrow and yet also very deep — requires sub-soiling to a depth of around 15 inches — parallel fissures into the land that leave most of the top soil undisturbed while opening a pathway deep down into the sub soil structure for both water and air. Doing so promotes a soil environment characterized by accelerated soil biological activity, which leads to increased total organic matter content within the soil.
Thus there are two co-equal aspects to Keyline design. One is the husbandry of water and the spreading out of precipitation using the natural landform as a guide, both to keep water in the land and to prevent erosion of the land. The second key concept is a kind of minimal tillage method that does not turn the soil, but cuts deeply down into the subsoil below to create very narrow cuts down into which water can flow and infiltrate down into the soil. Keyline techniques are particularly well suited to areas of seasonal rainfall followed by dry seasons. The deep thin comb like cuts in the land that are carefully laid out to follow the keyline landform allow the land to soak up much more of the seasonal rain deep into the earth. This is water that would have otherwise been lost to storm runoff, often ending up in the sea. During the dry season this stored water can be reached by deep rooted plants.
It has become one of the central aspects of the practice of Permaculture as a whole and is becoming more and more widely known and adopted as farmers and land owners become aware of its benefits in terms of increased natural soil fertility, water availability and storage, reduced erosion, and reduced need for economically and environmentally expensive chemical and fossil energy inputs in order to produce good crop or grazing yields.
What Is Meant By the Keyline
The Keyline system utilizes the natural undulating form of the land to spread available precipitation and moisten the soil. Our planet earth is a fractal interplay of ridges and valleys that characterized the land everywhere on our weathered planet. The natural form and shape of land… the topographical features of any land anywhere are formed over geologic time scales by the action of the wind and by precipitation and moving water. Instead of allowing rain to rush down from ridges lines and peaks eroding the land as it picks up soil, on its way down to the ravines and valley floors the Keyline system seeks to hold as much of this precipitation on the land as possible and it uses the lands natural shape to guide it.
A Keyline describes the particular contour that runs through all small headwater valleys where an extremely crucial slope incline change occurs. As one moves to elevations that are above this unique contour line the valley’s floor begins to exhibit a steeper rise than the adjacent ridgelines — defining the valleys water catchment edges. While as one moves below this unique contour line the ridges begin to drop off at a steeper rate than the now flatter valley floor.
Try closing your eyes for a second imagining you are soaring up some small headwater valley nestled between twin ridgelines… as you zoom up the valley’s center towards its headwater you will notice that at first the ridges have steep inclines as they fall down to the cut made by the larger valley floor that the headwater valley feeds, but that at some point as you approach the valley’s headwater, which is that “U” shaped terminus at the valley peak, the valley starts to rise rapidly, while the ridge lines rise becomes more flat as they near the higher peak or ridgeline that they forked off from.
As you soar above this key transition line and pause over it your eyes – if they are looking – will be able to pick out a key topographical line above which the valley elevation change is steeper than the two ridges on either edge and below which the valley is flatter and the ridge drop off is instead steeper. This landform is common wherever water has carved landscape.
The Keyline Concept: Capture the Water High and Comb it into the Land
The core idea underlying Keyline design as it pertains to water and precipitation is to capture rainfall at as high an elevation as possible, using the natural land forms as a guide to spread this water out along combed out lines that are laid out according to the landforms Keyline. It seeks to keep this water as high up as possible, for as long as possible. In this manner it promotes the absorption of water into the top soil rather than seeing it lost to runoff.
Often the basic practice of creating this keyline oriented layout of deep combs is augmented with small catchment ponds built at the high catchment areas that are located around the edges of the hilltops. This water management strategy is also quite well known in permaculture circles and is often employed in conjunction with keyline design. The idea is to keep water at as high an elevation as possible and to prevent rapid gully carving runoff – through keyline design and in general by spreading water flows out to stop water from concentrating into rushing, eroding streams racing down to the lowest elevation.
The concept and practice of Keyline land use planning and development was originated by the Australian farmer and engineer Percival A. Yeoman and is described and explained in his books The Keyline Plan, The Challenge of Landscape, Water For Every Farm and The City Forest. Many others in the permaculture movement have adopted these practices and built off of them.
Towards a Sustainable Bounty
Keyline design and more broadly permaculture practices hold a lot of promise to transition the way we grow our food away from a petro-chemical intensive and land destructive mono-crop agro-industrial paradigm towards sustainable low chemical and energy input, but high knowledge food production practices; a way of working with the land, with the water and with nature to produce a sustainable bounty while enriching the sub-soil ecology and growing topsoil.
© 2009, Chris de Morsella. All rights reserved. Do not republish.