On the basis of soil parameters provided by the Harmonized World Soil Database (HWSD) seven key soil qualities important for crop production have been derived, namely: nutrient availability, nutrient retention capacity, rooting conditions, oxygen availability to roots, excess salts, toxicities, and workability. Soil qualities are related to the agricultural use of the soil and more specifically to specific crop requirements and tolerances. For the illustration of soil qualities, maize was selected as reference crop because of its global importance and wide geographical distribution.
Toxicities (SQ.6)
Low pH leads to acidity related toxicities, e.g., aluminum, iron, manganese toxicities, and to various deficiencies, e.g., of phosphorus and molybdenum. Calcareous soils exhibit generally micronutrient deficiencies, for instance of iron, manganese, and zinc and in some cases toxicity of molybdenum. Gypsum strongly limits available soil moisture. Tolerance of crops to calcium carbonate and gypsum varies widely (FAO, 1990; Sys, 1993).
Low pH and high calcium carbonate and gypsum are mutually exclusive. Acidity related toxicities such as aluminum toxicities and micro-nutrient deficiencies are accounted for respectively in SQ1, nutrient availability, and in SQ2, nutrient retention capacity. This soil quality SQ6 is therefore only including calcium carbonate and gypsum related toxicities. The most limiting of the combination of excess calcium carbonate and gypsum in the soil, and occurrence of petrocalcic and petrogypsic soil phases is selected for the quantification of SQ6.
Note that the classes used in the Soil Quality evaluation are:
1: No or slight limitations
2: Moderate limitations
3: Sever limitations
4: Very severe limitations
5: Mainly non-soil
6: Permafrost area
7: Water bodies
Remember that classes are qualitative not quantitative. Only classes 1 to 4 are corresponding to an assessment of soil limitations for plant growth. Class 1 is generally rated between 80 and 100% of the growth potential, class 2 between 60 and 80%, class 3 between 40 and 60%, and class 4 less than 40%.
Data publication: 2012-03-01
Citation:
Full acknowledgement and referencing of all sources must be included in any documentation using any of the material contained in the Harmonized World Soil Database, as follows:
FAO/IIASA/ISRIC/ISSCAS/JRC, 2012. Harmonized World Soil Database (version 1.2). FAO, Rome, Italy and IIASA, Laxenburg, Austria.
Contact points:
Metadata Contact: CBL Global Soil Partnership
Resource Contact: Ronald Vargas
Resource constraints:
All rights reserved. No part of this Harmonized World Soil Database may be reproduced, stored in a retrieval system or transmitted by any means for resale or other commercial purposes without written permission of the copyright holders. Reproduction and dissemination of material in this information product for educational or other noncommercial purposes are authorized without any prior written permission from the copyright holders provided the source is fully acknowledged.
Online resources:
Download - Soil Toxicities (TIF, 71,2MB)
Download - Report: Harmonized World Soil Database v.1.2 February 2012
