Soil

A B

Figure 8.33 A: Golden Street, Shanghai, China, by SWA landscape architects; B: Paseo de Santa Lucia River Walk, Monterrey, Mexico, by Enrique Albarroa, landscape architect.

Wind can cause a still sheet of water to shimmer as it produces ripples which in turn act as prisms bending and contorting the sunlight that is reflected by the water.

Soil is a living entity. It is living in the sense that it is full of life: billions of microorganisms. These organisms are beneficial to the lives of plants and other living creatures that are dependent on soil. The presence of these microorganisms is central to the process of soil nutrient creation and air and water transfer to other organisms including plants. Soils are the resulting product of geologic, climatic, hydrologic, and biological processes. Soils are created in the process of mountain building and their erosion from wind and temperature fluctuations, water movement, such as streams and surface runoff, and the grinding action of advancing and retreating glaciers. Soil creation is the result of erosive action, deposition, and chemical and biological processes. Plants are contributors to soil creation in several ways. The decomposition process of leaves, branches, and whole trees contributes to the build-up of soil. Various fauna such as worms, bacteria, various microbes, and other life-forms further the breakdown of large soil particles into finer and often nutritionally enhanced chemical nutrients, including nitrogen and other elements important to plant life.

And there are many different types of soils: both found naturally and formulated by landscape architects for specific purposes. The soil needs of plants installed in a designed landscape vary greatly, depending on a range of considerations, including climate, rainfall, location of the planting beds, and the uses that could affect plant performance such as playfields for active sports.

Whenever feasible, landscape architects will include the stockpiling of the valuable surface soils occurring on a project site at the outset of earth-moving operations. Provisions for setting aside these

soils are made in a site grading plan and the earthworks section of the technical specifications. The stockpiled soil is used later during construction for various landscape purposes, such as the preparation of planting beds and lawn areas. In situations where soils suitable for later landscape use are not available, the landscape architect will prepare a technical specification, setting forth the composition of materials (sand, silt, clay, and organic materials) to create appropriate manufactured soils for specific uses. Soil amendments such as lime, fertilizer, organics, and sand are often specified and included in the soil technical specifications. Often times a landscape contractor will purchase or secure soil from another site. The landscape architect will have the final say whether to accept or reject the contractor-furnished soils. The basis of the evaluation will include soil composition, testing, and even approval of the source location. Soils brought from bogs would probably be rejected for a variety of technical reasons, for instance, the material had not been excavated, dried, and properly stored a year in advance of use on a project. Soils that contain sticks, branches and stones of a certain size (that are too large) would be rejected as well as soils containing pieces of concrete, metal, and other potentially harmful materials. The science of soil has a long history involving much research. To the uninitiated, soil is soil. However, it is the responsibility of the landscape architect to ensure the appropriate soil is provided for each landscape application. The same is true for general fill material in site preparation. For instance, gravels used in structural fill for pavements, roads, and structural backfill for walls must meet the standards set in the technical specifications for constructed backfill. Technical specifications for each fill type are included and are a part of the contract document package prepared by the landscape architect and, in some cases, the civil engineer.

Soil Stewardship

Soils can suffer degradation of their plant and microorganism support properties through intense and continuous cultivation or animal overgrazing. Soils can be further degraded with inappropriate water management, contaminated by the impact of poorly managed mineral extraction and the resulting runoff of toxic chemicals. Previously misused and degraded soils can be improved and built up towards their previous healthy condition through the application of systematically employed management techniques. An example of a once-depleted soil is shown in Figure 8.34. This is an example of agriculture land under managed cultivation. The land was once healthy oak-grassland community and was biologically diverse until the 1930s. The Portuguese government decreed that the thin, rocky soils of the Alentejo Province were to be cleared of their oak and grassland cover, then prepared for growing wheat. Predictably and unfortunately, this government policy did not achieve the desired results of production. After a few years of unsuccessful harvests, the program was dropped, leaving vast areas of depleted and mostly denuded land. The other impact from the disastrous government policy was extensive erosion intensified by the lack of soil-holding