THURSDAY, JAN 26, 2023: NOTE TO FILE
Module 3-22
Landscape based approaches
4.2. Landscape-based rainwater harvesting
The most important design component of Regenerative Agriculture is for water. Herein the Keyline System defines the process of designing landscapes which can harvest their entire water supply needs from the inherent characteristics of the land formation, similarly, referred to as the Natural Capital. The Keyline System identifies points of inflection or Keypoints in valleys where the slope changes from convex to concave, thus highlighting zones where water discharges down valleys slows down, siltation occurs and clay soils develop, thus making ideal opportunities for catchment dams. The Keypoints in turn determine the Keyline contour swales. The ensuing base map of Keypoints and Keyline contour swales is analysed so that a design is created with interconnecting catchment dams and swales designed to suit specific gradients so that the overflow from one catchment dam can feed lower catchment dams. In this manner, rainwater is channelled onto ridges thereby rehydrating landscapes that would otherwise not benefit from such rainfall infiltration. An illustration of the water design for the Keyline System is shown in Figure 4.3 which shows a typical farm landscape as “undeveloped” and “enhanced” Natural Capital. The dams shown in this figure also have outlets at the base of the earthen dam wall for use as irrigation along swales.
Figure 4.3: An example of Keyline System design for water
PA Yeomans developed the Keyline System on his farm, Yobarnie (see Plate 4.3), in a semi-arid area of Australia that received an average 350mm rainfall per annum. By the time Yeomans had established the series of catchment dams and interconnecting swales, the combined surface area of all the dams was approximately 15% of the total farm area. Yeomans totally transformed his farm so that the annual rainfall was more than sufficient to farm productively. This feature highlights the importance of establishing small catchment dams or detention ponds throughout the farm landscape in order to rehydrate soils and thereby recharge the underlying water table.
Plate 4.3: Yeomans' farm, Yobarnie, Australia
4.3. Drought-, flood- and fire-proofing landscapes
The integration of Water, Access and Forestry in the Keyline System provides an instant solution for effectively drought-, flood- and fire-proofing landscapes. This is possible due to the swale which slows, spreads and sinks rainwater, thereby both drought- and flood-proofing the landscape. The swale also creates a water plume in the soil downslope from the swale. This water plume in turn facilitates a forest belt, which adds to biodiversity, provides a habitat for pollinating insects, acts as a shelter-belt and wind-break. A forest-belt of diverse indigenous trees is unlikely to burn, as opposed to a monoculture plantation, thus providing the fire-proof barrier. This concept is illustrated in Figure 4.4, wherein the swales are sometimes expanded into hugelkultuurs, whilst the benefits from this concept are outlined below:
· promotes rainwater harvesting
· re-charges water tables
· reduces need for irrigation
· mitigates against soil erosion
· provides windbreaks that reduces wind burn, creates beneficial micro-climates and contributes to biomass.
· draws up vital minerals for plant use
· improves biodiversity
· improves soil humus which sequestrates CO2 that mitigates against Climate Change.
Figure 4.4: An illustration of swales and forest belts
4.4. Food Forests
According to the FAO, agroforestry is collective name for land-use systems and technologies where woody perennials (trees, shrubs, palms, bamboos, etc.) are deliberately used on the same land-management units as agricultural crops and/or animals, in some form of spatial arrangement or temporal sequence. This can take the form of a fully-fledged food forest or individual species. An example of a food forest strip with a specific planting pattern that mimics a natural forest is shown in Figure 4.5, which also suffices as a shelter-belt forest strip.
Figure 4.5: An example of a sub-tropical planting plan for a forest strip
4.5. Limited Till with Yeomans Keyline Plow
Besides Yeomans Scale of Permanence or the Keyline System, PA Yeomans also developed a limited till plow which he called Yeomans Keyline Plow as shown in the Plate 4.6 collage. This type of Keyline plow has been successfully used to rehabilitate arid farmland which has lost its soil fertility through too much tillage. Furthermore, this limited till-type technology is a key component for sustainable agriculture for the following reasons:
· It ensures minimum soil compaction
· It aerates soil and facilitates ingress of water
· It provides a micro-climate for a vigorous growth start of crops
· It minimises soil disturbance for micro-organisms
· It promotes the growth of organic carbon (humus) to deeper soils
· It promotes greater retention of soil moisture through organic carbon
· It promotes greater carbon sequestration from the growth of organic carbon
· It promotes soil fertility and biodiversity
· It has relatively lower costs than conventional agriculture
Plate 4.6: Yeomans Keyline Plow with shank pot seeders
The real benefits of the Keyline Plow is its application with the Keyline System of landscape-based rainwater harvesting. Herein, the Keyline contour swale plays a pivotal role in determining the pathways of the Keyline plow. More specifically, in moving parallel to the Keyline contour swale, the shanks of the Keyline plow drill open and aerate avenues for water to seep into the soil and simultaneously drain water across the contours from valleys where soil moisture is abundant, to ridges where soil moisture is lacking as illustrated in Figure 4.6.
Module 3, lesson 23
