Deriving land-quality indicators from the landscape units used in soils surveys

Jeroen M. Schoorl, A. Veldkamp, Johan Bouma

Research output: Chapter in Book/Report/Conference proceedingChapterAcademicpeer-review

Abstract

One of the largest problems faced by development schemes is incomplete knowledge about the potential that different soils have for agricultural production. Much of this problem can be attributed to soil taxonomy because soil taxonomy schemes, as they presently exist, are inadequate for assisting development. They give too much emphasis to soil genesis (origin) and too little to soil properties relevant for production. In order to address this shortcoming, the concept of soil quality has been introduced. Soil quality was defined by Karlen et al. (1997) as: "the fitness of a specific kind of soil to function within its capacity and within natural and managed ecosystem boundaries, to sustain plant and animal productivity, maintain water and air quality and support human health and habitation." Many studies have been made about soil quality (e.g., Doran and Jones 1996), but there is not yet a well-defined universal methodology to derive soil quality indicators. Doran and Jones present four physical, four chemical, and three biological indicators, which, according to the authors, together represent a minimal data set that can characterize soil quality, but they gave no examples. Gomez et al. (1996) define six soil-quality indicators and give minimum or threshold values for determining sustainability of agricultural systems at the farm level. They imply that a greater degree of sustainability corresponds with higher soil qualities. Doran and Jones list other examples of soil quality studies, including a series of soil characteristics that can be used as indicators of soil quality, but no study yet really addresses the broad spirit or scope of the definition advanced in Karlen et al. (1997). Soils, as described in soil surveys, are 3-D entities with a distinct spatial distribution. Soils are also dynamic, and can change significantly within decades in response to differences in vegetation (Van Breemen 1998), landscape processes (Schoorl and Veldkamp 2001), or management (Droogers and Bouma 1997). When dealing with such multidimensional systems, the issue of scale becomes relevant. A scale can be defined as a range of frequencies for spatial and temporal observations. Resolution below a given scale implies faster and smaller frequencies, which we call noise, and resolution above a given scale implies slower and larger frequencies, which we call "events." Together they define the range of observation frequencies. Actors and processes that operate at the same scale interact strongly with each other, but the organization and context of these interactions are determined by the cross-scale organization of the system (Peterson et al. 1998). In general, processes of interest to humans operate at characteristic intermediate temporal and spatial scales (Holling 1992). Biophysical processes that control plant physiology and morphology often dominate with small, rapid scales. At larger and often slower scales (fields and catchments), crop-weed competition for nutrients, light, and water dominate. At the largest, landscape, scale, climate, and geomorphologic processes determine the structure and dynamics of agroecosystems (O'Neill et al. 1991). All these processes produce scale-specific patterns, which are under natural conditions self-organizing in nature. Examples are the observed relations between climate and soil zones for continents and soil-landscape elements (catenas) within these zones. This implies that one might need different parameters/factors for the different spatial and temporal scales when characterizing soil quality. It is thus necessary to determine systematically at which scale level which property and related process is relevant. Soils are often studied at two important spatial scales: The agroecological zone, often associated with soil groups, and the more detailed soil series, which often coincide in extent with farms and their fields. The overall objective of this study is to generate a more useful scheme for using spatial data on soils to help to design development projects. Specifically, we: Review the traditional concept of soil quality, including a consideration of the effects of spatial scales and the many nonsoil factors that interact with soil quality to determine crop yields. Recommend the replacement of the term soil quality with land quality (LQ), which also takes into account local climate. Define a new operational expression of land quality based on crop yield that takes into account the effects of climate, land utilization type, and management and the definition of a general reference level. Illustrate the land quality concept with several case studies. Suggest further studies to broaden the concept of land quality.

Original languageEnglish
Title of host publicationMaking World Development Work
Subtitle of host publicationScientific Alternatives to Neoclassical Economic Theory
PublisherUniversity of New Mexico Press
Pages251-262
Number of pages12
ISBN (Print)0826337333, 9780826337337
Publication statusPublished - 1 Dec 2007
Externally publishedYes

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