The USDA Land Capability Classification-LCC technique

Land evaluation can be defined as the process of evaluating land performance when used for specified purposes (FAO, 1985), it is a method used to explain or predict the utilised potential of land (Van Diepen et al., 1991). Once the land potential is determined; land use planning can proceed rationally, at least with respect to what the land resource is capable of (FAO, 1993). Thus, land evaluation is a tool for strategic land-use planning. It predicts land performance, both in terms of the expected benefits, constraints, as well as the expected environmental degradation when the land is used (Rossiter, 1996).

Rossiter (1996, p. 166) advises that the logic that makes land evaluation possible and useful includes: (1) land varies in its physical, social, economic, and geographic characteristics ("land is not created equal"); (2) this variation affects land uses: there are areas more or less suited to each use type in physical or economic terms; (3) the variation is at least in part systematic, with definite and knowable causes; (4) the variation (physical, political, economic and social) can be mapped by surveys, for example the total area can be divided into smaller regions with less variability than the entire area; (5) the behaviour of the land when subjected to a given use can be predicted with some degree of certainty, depending on data quality on the land resource and sufficient understanding about the relation between land and land use; (6) land suitability for the various actual and proposed land uses can be systematically described and mapped; (7) decision makers such as land users, land-use planners, and agricultural support services can use these predictions.

Land evaluation originated from the need for a comprehensive assessment on land performance when used for different purposes. Many countries had developed their own systems for land evaluation by 1970 (FAO, 2007b). Land assessment techniques

and approaches evolved midway through the 20th _{century in response to devastating}

land degradation throughout Australia, Africa, India and the United States (Burrough, 1978).

Before the generation of the Framework for Land Evaluation formed by the FAO (1976), the land capability technique developed by the U. S. Department of Agriculture

(USDA), (Klingebiel and Montgomery, 1961) pioneered land evaluation endeavours and this is still the principal method used worldwide, either directly or in modified forms (Hanson et al. 2001; FAO, 2007b). The latest version of the National Soil Survey Handbook (NSSH) was updated on the 18/10/2009 by the USDA (USDA, 2010a). In the NSSH, land potential is assessed based on soil properties using soil potential ratings associated with other resource information, as a guide to making land use decisions.

The soil potential ratings help decision makers to determine the relative suitability of soils (relative quality) for a particular use as compared with the suitability of other soils in a given area. They often concentrate on yield or performance level; the relative cost of applying modern technology to minimize the effects of any soil restrictions, and the adverse effects of continuing limitations, on social, economic, or environmental values (USDA, 2010a).

Definition of soil potential rating (USDA, 2010a, wp), includes five classes: (1) very high potential: production/ performance is at least at local standards or above because soil conditions are exceptionally favourable, installation or management costs are low, and soil limitations are insufficient; (2) high potential: production/ performance is at or above the level of locally established standards, the cost of measures to overcome soil limitations are judged locally to be favourable in relation to the expected performance or yields, and soil limitations that continue after corrective measures are installed do not detract appreciably from environmental quality or economic returns; (3) medium potential: production/ performance is somewhat below locally established standards, the costs of measures to overcome soil limitations are high, or soil limitations that continue after corrective measures are installed detract from environmental quality or economic returns; (4) low potential: production/ performance is significantly below local standards, measures that are required to overcome soil limitations are very costly, or soil limitations that continue after corrective measures are installed, detract appreciably from environmental quality or economic returns, and (5) very low potential: production/ performance is much below

measures are installed seriously detract from environmental quality or economic returns.

Soil interpretation can be used to determine the potential of soil which in turn can be used for land potential evaluation. The USDA method reveals that primary land potential was assessed based on physical parameters such as soil depth, soil structure, soil texture, landform, altitude, rainfall, temperature and growing season. The technique utilises the parametric approach to land classification, which gathers specific physical parameters independently and then combines them to form land capability classes (Land Capability Classification-LCC) (Hanson et al., 2001).

The LCC purpose was to offer recommendations for land users on the most appropriate use of their farms. Land mapping units were classified into eight classes driven by the basic ability to support general kinds of land use (e.g. produce common cultivated crops and pasture plants) without degradation or significant off-site effects (USDA, 2010a). Every class is determined by limitations to land use such as erosion hazard, flood risk, slope gradient, stoniness, low fertility, rooting zone restriction and climate. Thus, as limitations increase, land-use options decrease (Hanson et al., 2001). The first four classes relate to arable land, in which the limitations to the use and need for conservation measures and required careful management, increase with class number (Helms, 1992; FAO, 2007b, p. 5; USDA, 2010a, wp). The remaining four classes are unsuitable for cropland, but may have uses for pasture, woodland, grazing, wildlife, recreation and other purposes (FAO, 2007b, p. 5; USDA, 2010a, wp).

In the broad classes, subclasses indicate special limitations such as erosion, excess wetness, problems in the rooting zone, and climatic limitations. Within the subclasses, capability units present some indication of expected yields and management needs. The capability units are soil groups that have common responses to pasture and crop plants under similar systems of farming but requiring different management. Units are locally defined for each survey and are described in detail, which make the system applicable to local situations. The first category listed in the LCC system, is a grouping of one or more individual soil mapping units having similar potentials and continuing limitations or hazards (FAO, 2007b; USDA, 2010a, wp).

Despite identification for local land use and management, the LCC only considers relatively permanent, static land characteristics and does not take into account socio- economic components. The system provides a general appraisal, and does not assess capability separately for each kind of land use. It relies on a ranking of kinds of use in an implied order of desirability, with agriculture preferred over forestry, and both over wildlife conservation (FAO, 2007b). The USDA LCC system will be revisited in the coming sections of this Chapter.

Adoptions of the USDA LCC technique

The LCC developed by the USDA technique was disseminated, modified and applied in many parts of the world.

Rowe et al. (1981) built specific guidelines for land capability assessment in Victoria, Australia. In the guidelines, land capability is grouped into only five classes from very high capability to very low capability corresponding to an increase in limitations. The authors also formed a set of land capability rating tables for engineering uses, septic waste disposal, earth resources, land-based recreation, grazing, cropping, and forestry. The British Land Capability Classification, adapted from the USDA technique, is an assessment of the land capability from known relationships between crop production and management and the soil physical factors, topography and climate. It is essentially a negative approach in which land is graded according to mixed qualitative and quantitative measures of limitations to land capability. Land capability is rated into seven classes. Class 1 land has a wide range of uses with few (if any) limitations, the remaining six classes suffer from increasingly severe limitations and are progressively less flexible in the range of their potential land uses. Land capability subclasses are defined on the basis of one of more permanent or semi-permanent physical factors that limit production. (http://www.geog.leeds.ac.uk).

In recent years, the LCC has gained international recognition as a tool for land resource assessment. Many studies have reported on the use of the LCC. Land capability classification for agriculture in British Columbia, Canada (MAF and ME,

Post-mining land capability assessment at Quintette Operating Corporation (Smyth and Bittman, 1998), Mapping Land Resource Potential and Agricultural Pressure in

Papua New Guinea (Hanson et al. 2001), Land Capability Assessment for Onsite

Domestic Wastewater Management (EPA, 2003), Soil-landform units, land capability analyses and lands hazards (Robinson et al., 2004), Developing a land capability system for the Western Plains of New South Wales (Smith et al., 2004), a revised land and soil capability classification for New South Wales, Australia (Murphy et al., 2004).

Several other studies concentrated on methods, techniques, or procedures for execution of the LCC. Guidelines for Land Capability Assessment for Local Rural Strategies, Western Australia (The State Planning Commission, 1989), Land Capability Handbook-Guidelines for the Classification of Agricultural Land in Tasmania, Australia (Grose, 1999), Land Capability Assessment Guidelines (The ACT Parliamentary Counsel, 1999), Guidelines for Soil Quality Assessment in Conservation Planning (USDA, 2001), Land Capability Classification System for Forest Ecosystems in the Oil Sands in Canada: Field Manual for Land Capability Determination (CEMA, 2006), as well as National Soil Survey Handbook updated on 18/10/2009 by the USDA (2010a).

As a part of the USDA-ARS Soil Resource Management National Program, Andrews et al. (2004) designed the Soil Management Assessment Framework (SMAF). The framework has flexibility to accommodate site-specific differences due to soil, crop, climate and other factors within the scoring curves. It can help select appropriate soil quality indicators, interpret their measurement outcomes, and integrate the interpretations to accurately assess the effects of management practices on overall soil function. However, the authors also recognized that, the framework needed to be referenced with each of the biological, chemical and physical indicators under a variety of management practices and ecosystems to improve selection rules and interpretation algorithms relative to management goals and site-specific factors.

The SMAF is specified by a study on Soil Quality Assessment in the Iowa South Fork

Watershed (Karlen et al., 2007). The study describes soil quality assessment samplings

determine what conservation practices are needed to protect soil and water resources within the South Fork Watershed of the Iowa River, as well as revealing indicators to further improve the SMAF assessment tool.

A majority of the approaches and techniques in the studies above have been modified from the original USDA method; the USDA technique has been improved and developed flexibly to suit a wide range of different specific conditions in the field of land capability assessment. This provides a critical opportunity for the LCC to be become an international standard for land capability determination.