Fire usually induces water repellency (WR) in soils. Reduction in infiltration rates, increase of runoff and erosion are some of the consequences of WR in fire-affected soils. Most forest soils can develop WR by burning; however some previous observations in burned terra rossa soils have shown little changes in WR. Laboratory controlled experiments have been done with samples of terra rossa from 14 different sites. The objectives are to confirm whether the observed is a common behaviour of terra rossa and to explore the factors controlling the wettability of this soil type after burning. Samples from the upper 2.5 cm of terra rossa were collected from 12 forest sites of the Alicante province (Spain), and from 2 sites in the "Mt. Carmel", Haifa (Israel) with similar environmental conditions. Laboratory burning of samples at 250 °C, 300 °C and 350 °C was performed with and without the addition of litter of Pinus halepensis. The results confirm that all soils have a very low susceptibility to become water repellent by burning. Without the addition of litter, WR was not detected in any soil sample at any temperature of burning. With the addition of litter, WR was present only in six of the soils after some of the heating treatments. Although all soils had enough soil organic matter (SOM) to develop WR by heating, the ratio between SOM and clay content was considerably lower compared to other types of forest soils of the region in which WR has been found after forest fires. This could explain in part the lower susceptibility of terra rossa to become water repellent by burning since, as some authors have indicated, fine-textured soils are less prone to develop soil WR due to their high specific surface area. From mineralogical analysis of the clay fraction we found that the dominant clay types in the studied terra rossa were kaolinite and illite, with the exception of one soil where Ca-montmorillonite content is higher than kaolinite and illite. Ca-montmorillonite was present in only three of the soils. Comparing the soil properties between the group of terra rossa that in no case become water repellent (wettables) with the group that in some cases developed WR (potentially water repellents), some differences were found: the kaolinite content is higher in the wettables group (P < 0.05), and the soils containing Ca-montmorillonite are in the group of potentially water repellents. A clear separation between the 2 groups was found when we compared SOM vs kaolinite contents, the kaolinite content being the main factor contributing to this separation. These results are in agreement with those obtained in experiments with clay additions to water repellent soils in order to reduce the WR, and also with some studies which found that kaolinite is one of the most effective clay minerals for this purpose.
Bibliographical noteFunding Information:
This research was supported by the CICYT co-financed FEDER project CGL2006-011107-C02-01/BOS, the Spanish Government Project for International Cooperation PCI2006-A7-0576 and the complementary action CGL2007-28764-E, and the SOLIPHA project VVCE-0033-07, the VEGA project 1/3058/06. V. Arcenegui acknowledges the grant received from the “Caja de Ahorros del Mediterráneo”. Authors also thank to the staff of Montgó Natural Park, M.L. Calero for laboratory support, Frances Young for improving the English, and to the editor and two anonymous reviewers for valuable comments to improve the manuscript.
- Chromic luvisol
- Soil hydrophobicity
- Water repellency
ASJC Scopus subject areas
- Soil Science