Evaluation of World Reference Base for Soil Resources and FAO Soil Map of the World using nationwide grid soil data from Denmark

Abstract

Soil classification is a tool for stratifying and generalizing information on soil resources but most systems are tailored to handle only slightly disturbed soil. We tested the applicability of the legend of the FAO-Unesco Soil Map of the World and the new World Reference Base for Soil Resources by classifying at the highest order 831 profiles from a nationwide 7 km grid survey in Denmark, where soils are developed in Quaternary glacial and marine sediments and intensively farmed. Comparison of the variability of pH and % clay % silt of the master horizons (A, E, B, and C) within and between the major well-drained soil groupings shows that liming, fertilizing and ploughing have produced significantly deeper A-horizons with higher pH, lower % humus and C : N ratios on the two -thirds of the country that is cultivated.`Anthropogenic' mollic and umbric horizons are a common result but the liming causes a random final classification of these surface horizons and, hence, random allocation of the soils in both systems. It separates cultivated soils and their undisturbed equivalents, and results in considerable within-group variation in soil texture. Grouping of cultivated and undisturbed soils, on the other hand, results in wide within-horizon pH ranges for most groups, again compromising the advantage of making useful general statements on the basis of classification.We propose that anthropogenic mollic and umbric horizons should be allowed in any soil group and that anthric properties' should be used to distinguish between profoundly changed cultivated soils and largely undisturbed soils, hereby constructing a two-tier system within each highest-order soil group. We classified the soils according to this proposal.The results show generally narrower ranges for both pH and % clay % silt.We evaluated the within-group homogeneity by multivariate analysis of variance of pH, % clay % silt, % clay, % humus, C : N ratio, exchangeable cations, and CEC. The results (Wilks's Lamda) show a higher degree of group compactness compared to the original FAO and World Reference Base systems.

Appropriate classification of three Swedish soils for agrarian and environmental management

“…In Denmark, 45% of the arable soils have mollic horizons, and almost 25% are classifi ed as Phaeozems according to the WRB (Krogh and Greve 1999). In Sweden, fewer arable soils have been classifi ed, but of those classifi ed, some are classifi ed as Phaeozems/Mollisols (Kirchmann and Eriksson 1993, Kirchmann et al 1996.…”

“…Fourthly, classifi cation according to P status requires an additional chemical analysis. Krogh and Greve (1999) propose the introduction of an anthric horizon meeting all the criteria of mollic or umbric horizons and also showing evidence of disturbance by human activities by one or more properties. The anthric horizon shall not qualify for a Phaeozem if e.g.…”

“…The low fertility is not recognized, but fertilizing and liming could easily change that. The proposal of Krogh and Greve (1999) are focusing on features verifying that the soil would not have a mollic horizon or be a Phaeozem without agricultural infl uence. In this and probably many other Nordic soils, the depth criteria of a mollic horizon would not have been met without the deep mixing of the soil by farming practices.…”

“…In many cases, farming practices, such as ploughing and liming, results in A-horizons/epipedons deep enough and with enough high base saturation to result in classifi cation as mollic or umbric. Thereby, Phaeozems/Mollisols of anthropogenic origin are very common in long-time cultivated soils in large parts of north-western Europe, including Sweden (Kirchmann et al 1999, Krogh andGreve 1999), in spite of the intention to reserve these soil groups for grassland soils (Soil Survey Staff 1974). See Krogh and Greve (1999) for further discussion of man-made mollic and umbric horizons.…”

“…Nordic soil scientists have proposed changes to WRB in order to further improve its credibility (Tiberg et al 1998, Kirchmann et al 1999, Krogh and Greve 1999, Greve et al 2000. Proposed changes regarding classifi cation of cultivated soils and podzolized soils are of special concern for many Swedish soils.…”