Farm design

Two of the most serious problems we face are climate change and the loss of fertile land. Climate change brings uncertainty in the availability of water to sustain people and crops. The loss of fertile land mainly through wind and rain erosion, is a natural asset of every farmer whose loss is detrimental to the entire economy of any region.

Water and land – here lies the problem and here lies the solution: developing fertile land, capturing and storing water on rural sites and capable of sequestering huge amounts of atmospheric CO₂.

Hydrological design and the keyline method

Learning how to efficiently design and manage the agricultural landscape in order to make the best use of water resources and restore soil depth and fertility is precisely the aim of the keyline method.

A drop of runoff water takes just a few seconds to travel a long distance, carrying soil with it (Figure 1). Keyline hydrological management helps to maintain the soil in order to avoid erosion problems.

Hydrological design, or keyline design, establishes indispensable criteria to improve the efficient distribution of water on the land, a determining factor in food production of any crop at any scale. Through it, the aim is to achieve a substantial increase in biomass, the elimination of erosion by water, as the soil rapidly absorbs rainwater, deepening the topsoil, recomposing the soil structure and increasing microbiological life.

_{Figure 1. Scheme of how splash erosion affects flat fields}

The origin of the Keyline method dates back to the 1950s when Australian mining engineer, P.A. Yeomans used landscape topography to transport water by gravity over long distances for subsequent use in ore cleaning.

Knowledge of landscape-topography was crucial to understanding the basis of what he called the “landscape permanence scale” or hydrological design for environments subject to climatic uncertainty such as the Mediterranean area.

He established an order of importance of the different factors: climate, landscape form, dams, access roads, trees, structures, fences and soil. These factors allow priority to be given to planning and developing agricultural properties that are resilient to climatic fluctuations.

Normally the criteria by which a property is designed or planned, take little or no account of hydrological factors. However, in light of the current climatic context, it is essential to take these factors into consideration, to collect and store every possible drop of water.

In order to properly understand a landscape, it is first necessary to identify the different elements it is composed of. Generally speaking, any landscape can be categorised into slopes and valleys. What is the difference between a valley and a hillside at the hydrological level? Very simply, hillsides expel water, by gravity, towards valleys.

Hillsides are drier and valleys are wetter. Among the topography of the landscape there is a point of special interest, called the keypoint (Figure 2).

_{Figure 2. Keypoint definition. Source: tcpermaculture}.

This point is located in the valleys, in the area where the velocity of water slows down over the imaginary line that a stream would produce if it had water in it. If the water velocity decreases at this point there is more water accumulation. The keypoint is important because it is a concentration point of water in the landscape.

The objective of the keyline is to move that water. Once the keypoint has been located, then the Keyline can be determined. on the same contour line as the keypoint (Figure 3). Once the Keyline is determined and marked, then parallel lines can be drawn on the topographic map. The parallel lines are drawn both above and below (uphill and downhill) of the Keyline. Using gravity and a channel dug by a plough or other tool, water can be redirected down the slope. Contour plans allow these three-dimensional concepts to be better understood where Pa slight natural slope can be exploited to l divert water from this point by gravity, to the drier area.

_{Figure 3. The Keyline (blue dashed line) is simply a contour line running through the keypoint. Source: TCPermaculture}

The yeomans plough is used to furrow the land where one of its purposes is to transport surplus water from the landscape (Figure 4). The keyline pattern allows channels to be furrowed; without disturbing the soil, without turning the horizon and creating underground lines that water will easily follow.

Another purpose is that it will not disturb roots within the soil, helping to conserve organic carbon in the soil, which in turn will conserve more water at a rate of 70,000 litres per hectare for every 1% organic carbon._[1]

This is what makes the difference. It allows the soil to aerate and decompact creating a fertile soil year after year. It also drastically reduces erosion as it improves infiltration by creating a more structured soil with micro and macro pores.

_{Figure 4. Yeomans plough. Source: Volterra Bio}

Ponds and infiltration channels

As explained above, water is channelled down the slopes and converges at a specific point: the keypoint, which is the starting point of a watercourse. From the keypoint downwards the slope is less steep and the valley wider. This is the place to build the necessary barrier for a pond (Figure 5).

Ponds allow water to be stored in the rainy season and thus create a more humid ecosystem around it, which in turn favours biodiversity, but also keeps the water in an area which can then be used for irrigation when needed. A pond created at the keypoint, provides the highest possible level where it can be used for irrigation.

In addition to providing ecosystem services such as those already mentioned, it expands in the subsoil, loading the groundwater table and increasing its underground availability.

_{Figure 5. Keypoint in a landscape. Source: agwater.wordpress.com}

In general, it is very advantageous not to artificially waterproof ponds. Water will penetrate the soil according to its composition, until it reaches an impermeable stratum. From there, the water level will rise until it fills the pond, but at the same time hydrates the soil vertically and horizontally, providing water and moisture to plants and trees.

The water saturation of the soil, the increase of dew and humidity in the air provides much better conditions for the plants as well as being used for irrigation. What does need to be impermeable is the retaining wall, with a suitable mixture of silt and clay that can be obtained from deeper soil layers.

It should have a spillway including an overflow pipe to prevent erosion in the event of heavy rainfall. It should also include a drainage pipe buried at the base of the slope, with its control valve, which can be connected to an irrigation channel at its outlet. This channel overflows in a laminar manner, hydrating the soil beneath the pond and the slope should be gentle to prevent erosion.

Conclusion

In addition to providing more possibilities to improve water distribution and water use, the keyline design increases the productive capacity of the plots by redistributing water through efficient use of the topography.

The use of keyline design provides more chances of plantation survival due to better hydration of soils. In addition, the construction of ponds in strategic locations can allow for the accumulation of surplus water for use in drier seasons, allowing for water recycling at a relatively low cost.