GEA - Grupo de Edafología Ambiental - Environmental Soil Science Group Departamento de Agroquímica y Medio Ambiente Universidad Miguel Hernández Edificio Alcudia, Avda de la Universidad s/n. 03202 Elche Alicante Spain
Abstract: El fuego es parte de la naturaleza y la sociedad mediterránea. En España, el número de incendios forestales y la superficie quemada se ha disparado en los últimos 50 años fruto del abandono del medio rural. El impacto del fuego en el suelo es un tema trascendente para entender los espacios forestales y poder gestionarlos con eficacia. Además, para los cientÃficos, las zonas incendiadas suponen un verdadero laboratorio que permiten conocer la adaptación de los ecosistemas y sus estrategias de recuperación ante las alteraciones. En el caso de los suelos, los incendios han permitido conocer los cambios en las propiedades edáficas y los efectos sobre los procesos de generación de escorrentÃa y erosión. Esta imagen del incendio de Aliaga en Teruel (22 de julio de 2009) muestra un territorio diverso y complejo en el que el estudio de la evolución de las propiedades de los suelos, de la vegetación y de las arroyadas permitirán conocer el papel del fuego y que estrategias se deben seguir para su rehabilitación y restauración. Esas investigaciones basadas en el seguimiento de los incendios, o bien la comparación entre parcelas control y quemadas, ha permitido a los investigadores españoles aportar a la comunidad cientÃfica internacional conocimientos de gran valÃa para comprender el sistema edáfico, y su dinámica espacial y temporal. Este libro es un compendio de los trabajos realizados durante 30 años por la comunidad cientÃfica española en torno al efecto de los incendios sobre los suelos
Abstract: Biological soil crusts have a major effect on water flow in soils. Two study sites, located at a pine-forest glade covered with a biological soil crust, formed the basis of our study. The sand soil at the surface (Glade soil) was compared to a control soil (Pure sand) with limited impact of vegetation or organic matter, occurring at 50 xa0;cm depth beneath a glade area. To assess the influence of algae in the biological soil crust on the properties of pure sand, a coccal green alga (Choricystis minor), filamentous green alga (Klebsormidium subtile) and stramenopile alga (Tribonema minus) were isolated from the top layer of glade soil and grown in the lab in Petri dishes on sterile pure sand as monoalgal and bialgal (C. minor and K. subtile) crusts for 3, 5, 7, 9, 11, 13, 15, 17, 19, and 21 xa0;days. At the end of each growth stage, the hydrophysical parameters of crusted sand were estimated after drying at 50 xa0;°C for 15 xa0;h (equivalent to a 3-day hot spell) and compared to the parameters of pure sand. The hydrophysical parameters were substantially different between the two surfaces. The glade soil had an index of water repellency about 18-times that of pure sand and the persistence of water repellency almost 54-times that of pure sand. Both sorptivity and hydraulic conductivity in the glade soil were about 7% those of the pure sand, respectively. The growth of artificial algal crusts, characterized by an increase in organic carbon content from 0.16% to 0.33%, resulted in an increase in water drop penetration time of the dried crusts up to 14-times that of the pure sand and a decrease in the water sorptivity of the dried crusts up to 10% that of the pure sand. Whereas K. subtile crusts (both monoalgal and bialgal with C. minor) had up to a 9% decrease in hydraulic conductivity compared to pure sand, there was no impact of monoalgal C. minor and T. minus crusts on hydraulic conductivity. K. subtile was possibly limited to surface growth, whereas C. minor and T. minus penetrated to depth. Consequently, K. subtile may have clogged the top pores more effectively than the other two strains. The water repellency cessation time increased with an increase in water drop penetration time for all the dried monoalgal and bialgal crusts used in this study. A greater impact of K. subtile on the shifts in hydraulic behaviour could influence water capture and storage, potentially decreasing evaporation during dry periods, but enhancing overland flow diminishing leaching during wet periods.
Abstract: Water repellency (WR) is a common soil property in many fire-affected ecosystems, but it also occurs in long-unburned terrain. It can vary in space at different scales (between point and pedon or slope and catchment) and time (during the same day, between seasons or years, or with a post-fire recovery period). This paper: i) reports on the occurrence and persistence of WR in fire-affected calcareous forest soils under Mediterranean climatic conditions, examining its spatial variability at macro-, meso- and micro-scales, and monthly changes with soil moisture content; and ii) develops exploratory models to estimate the probability of the natural background (not fire-induced) WR to occur through a Mixed-Effect Logistic Regression Model. Four sites with comparable soil and vegetation types were studied, all of them burned in 1979, the third again 1999, and the fourth in April 2008. All sites were sampled immediately after the fire of 2008, a further 17 times until July 2009, and once more in August 2011. At each site, 5 random plots (10 xa0;cm xa0;Ã xa0;10 xa0;cm) were selected for each of the vegetation types: Pinus halepensis, Quercus coccifera, Rosmarinus officinalis and bare soil. In each plot we carried out 10 Water Drop Penetration Time measurements at the surface and at 1 xa0;cm depth. WR was detected in samples from all sites, although WR was most frequent at the soil surface at the sites last burnt in 1979. The recently burned site had similar WR to the long-unburned ones in surface but greater at 1 xa0;cm depth, although for both depths WR was reduced by the following year. WR was still very low in the site burned 10 xa0;years before. Variability of WR between different vegetation types was as high as within the same type at the same site, and similarly high at within sites (1 xa0;ha) and at 10 xa0;cm xa0;Ã xa0;10 xa0;cm plot-scales. The lowest variability was found in bare soil plots because they were mostly wettable. An exploratory model to estimate the probability of WR occurrence was derived for each unburned site. The most powerful explanatory variables for the probability of WR to occur (P xa0;< xa0;0.0001) for both unburned sites were the covariate moisture content together with the category soil surface (associated to the fixed factor soil depth) for one site and P. halepensis (associated to vegetation type) for the other. The model input parameters are straightforward to obtain and the model may be a useful tool in estimating occurrence and fluctuation of soil WR.
Abstract: After a fire, an ash layer is commonly present, which influences soil properties and hillslope hydrology. The wettability of ash, which can vary from highly absorbent to water repellent, is an important characteristic in this context. Recent work has suggested that ash wettability is related to its degree of combustion, which in turn, can be expected to determine ash chemical composition. In this paper we therefore examine the relationship between ash water repellency and ash chemical composition. Ten ash samples with different wettability were each taken from four burned Mediterranean forest sites located at Albaida (A), LlÃber (L), Navalón (N), and Pinoso (P), in the east of Spain. The persistence of water repellency of samples was assessed by the Water Drop Penetration Time (WDPT) test and Fourier Transform-Infrared (FT-IR) analysis was applied to characterise sample chemical composition. Ash water repellency varied from wettable to severely water repellent and differed in terms of maximum WDPT and number of water repellent samples within the four locations. In all FT-IR spectra obtained, the absorbance bands assigned to organic matter and carbonates were dominant. They are subject to change during progressive combustion. The ratios of relevant peak areas were calculated, i.e. between aliphatic bands in the 3000â2800 xa0;cmâ xa0;1 region, other organic matter bands in the 1800â1200 xa0;cmâ xa0;1 region, and of the calcite band at 875 xa0;cmâ xa0;1. These ratios are related to organic matter and calcite contents in ash samples and proved to be closely linked to the measured WDPT values through an exponential relationship. Organic matter content in all water repellent ash samples was more than twice the carbonate content. From the results obtained it is concluded that the water repellency or wettability of wildfire ash is driven by the ratio of remaining organic matter to emerging carbonates, which in turn, is related to fire severity.
Abstract: Soil water repellency (WR) is one of the properties most affected by combustion during a forest fire. Different factors such as temperatures reached, type and amount of fuel, affect the changes observed in this property. Measurements of water repellency can be made directly in the field or in soil samples under laboratory conditions. On the other hand, previous laboratory findings have demonstrated that some soil properties can be key factors controlling the development of WR by burning. One of the objectives of this research was to confirm findings from laboratory-burning under wildfire field conditions. In summer 2008 WR was assessed in five areas recently affected by fires in Mt. Carmel (NW Israel) and Alicante (SE Spain). Study sites are quite similar with regard to vegetation and climate, the main difference between sites being the type of soil and therefore soil characteristics. In each one of the study areas WR was tested beneath Pinus halepensis in both burned and unburned (control) adjacent sites. WR test were conducted under field conditions in triplicate using the water drop penetration time (WDPT) test in the top of the A horizon. A total of 300 field measurements were done. Soil samples from the first 0â2.5 xa0;cm depth were also taken from the same microsites where WR was assessed for laboratory measurements. Estimations of temperatures reached in burned samples were also made using NIR models developed under laboratory conditions. In general terms, without distinguishing between areas, fire increased the frequency of occurrence of WR in affected soils. However, the magnitude of this effect was quite different depending on the studied area. Three of the study sites, showed very low WR values both in burned and unburned areas. The results are in agreement with those from our previous laboratory experiments (Arcenegui et al., 2007; Mataix-Solera et al., 2008), and are not explained as a consequence of different temperatures reached in the soils. Organic matter and clay content together with the mineralogy of the clay fraction seem to be responsible for the different soil behaviour. Although there is a correlation between field and laboratory WR data (R2 xa0;= xa0;0.549; P xa0;< xa0;0.01), the comparison between field and laboratory measurements of WR showed differences, with higher values for the field data. Since the soil water content was very low when field measurements of WR were made â similar to air-dried samples in laboratory â this factor is not suspected to be the responsible. The observed differences could be explained however because the measurements in field were made on the soil surface, while in laboratory the measurements are made in disturbed samples taken from the top to some depth (in our case from 0 to 2.5 xa0;cm). Taking into account that soil WR is a property that can vary with depth probably diminishing in parallel with soil organic matter content, the results seem to be logical. Moreover, the disturbance of samples and the sieving could also be partly responsible for the observed differences.
Abstract: In this paper, we characterize the long-term effect of reforestation on the stabilization of soils affected by strong gully erosion in Prietrž village in South-Western Slovakia. Permanent gullies there were reforested a century ago with the black locust (Robinia pseudoacacia). Reforestation measures induced soil profile development on the gully slopes with distinct humus horizons. Soil-forming processes caused organic matter accumulation, carbonate leaching and a decrease in pH in the surface horizons. One century after reforestation, the key properties of the gully soils closely resemble those of the surrounding agricultural soils. Soil aggregate stability was used as a useful indicator which reflected the impact of reforestation on soil stabilization over the last hundred years. The overall effect of the observed changes is an increase in the aggregate stability of these reforested gully soils. Soil aggregate stability measured by the rainfall simulator method positively correlated with the organic carbon content, and it had negative correlations with carbonate content and soil pH. The values determined for these gully soils do not differ significantly from those in the surrounding non-eroded agricultural soils. The extreme difference in aggregate stability between the topsoils and the parent marl material is responsible for this landscape's susceptibility to severe gully erosion.
Abstract: Hydrological processes after a wildfire may take place under soil conditions altered by heat and by the presence of ash. Soil and ash interact as a two-layer system with poorly understood hydrological properties, especially when ash covers water repellent soil. Here we quantify the effect of an ash layer (0, 5, 15 and 30 xa0;mm depth) covering wettable and water repellent soil on (i) the hydrological response and the mechanism of runoff generation and (ii) the water repellency dynamics, for a rainfall event followed by different drying periods and a second rainfall event. Laboratory rainfall simulation experiments (82.5 xa0;mm xa0;hâ xa0;1 during 40 xa0;min) at small plot-scale (0.09 xa0;m2) were performed and surface and subsurface flow, sediment yield, splash detachment and moisture content evolution determined. Wettable soil without ash cover generated no surface runoff, but as a two-layer system temporary surface runoff was produced when ash became saturated, until water drained through the soil. Wetting and drying changed the hydrological properties of ash, increasing surface runoff for all ash depths. Over water repellent soil, the ash layer delayed and reduced surface runoff proportionally to ash depth (r xa0;= xa0;0.99), reduced soil water repellency and promoted fingered subsurface flow. Ash protected the soil from splash and sheet erosion, particularly for water repellent soil. The results demonstrate that (i) the presence of an ash layer can have contrasting effects on surface runoff, depending on the wettability of the underlying soil, and (ii) a single wetting and drying event can substantially modify ash hydrological properties.
Abstract: This study addressed the impacts of wildfire and, in particular, its severity on the seed bank of the litter/ash layer and the topsoil of a Mediterranean pine plantation (Pinus pinaster Ait.) in north-central Portugal. The study location was selected for presenting a homogeneous pine cover before the fire, on the one hand, and, on the other, heterogeneous patches with distinct degrees of damage to the pine crowns immediately after the fire. The experimental design involved the selection, from the opposite valley side, of three zones with adjacent strips of Low and High Canopy Consumption (L/HCC). Within each of these strips, a transect was laid out along which three plots were established at 10 xa0;m intervals. The same was done in the unburnt area immediately outside the fire perimeter. At each plot, samples were collected within the first two weeks after the fire to: (i) asses viable seed densities for three sampling layers, using the indirect method for a 10-month period; (ii) estimate maximum temperature reached (MTRs) at 0â3 xa0;cm depth, on the basis of Near Infrared Spectroscopy (NIR). Fire severity at the plots was further determined by verifying, in situ, pine canopy consumption (FCC) as well as by measuring the minimum diameter of remaining shrub twigs (TDI). In comparison with the unburnt area, the recently burnt area as a whole revealed a substantial increase in overall densities of viable seeds. Seed bank composition, however, varied markedly within the burnt area but this could be explained reasonably well by differential effects of the wildfire associated with its severity, in terms of the two crown consumption classes as well as the TDI index but not the MTRs. The inclusion of the litter/ash layer and the separation of two soil depths were amply justified by providing clear support for the important role of fire severity, in particular for the two principal taxa (Calluna vulgaris and Erica spp., presumably mainly E. australis).
Abstract: Fires are important but socially and economically unwanted disturbances of the ecosystems. They cannot be considered as a problem, they are global phenomena. Protected areas are created to protect biodiversity, and strict protection is often applied, forgetting that fire had shaped that that we aim to protect. This harsh protection is producing important changes in the protected habitats and is increasing their vulnerability to destructive wildfires. Thus, it is of major interest to incorporate fire management in the protected areas plan, including the (re)use of prescribed fire and traditional burning in order to reintroduce fire regimens, fundamental to the landscape sustainability. This incorporation represents an enormous step in the habitats sustainability. Policies should be more focused on fire prevention than on its suppression.
Abstract: The problem of estimating and predicting spatial distribution of a spatial stochastic process, observed at irregular locations in space, is considered in this paper. Environmental variables usually show spatial dependencies among observations, with lead one to use geostatistical methods to model the spatial distributions of those observations. This is particularly important in the study of soil properties and their spatial variability. In this study geostatistical techniques were used to describe the spatial dependence and to quantify the scale and intensity of spatial variations of soil properties, which provide the essential spatial information for local estimation. In this contribution, we propose a spatial Gaussian linear mixed model that involves (a) a non-parametric term for accounting deterministic trend due to exogenous variables and (b) a parametric component for defining the purely spatial random variation due possibly to latent spatial processes. We focus here on the analysis of the relationship between soil electrical conductivity and Na content to identify spatial variations of soil salinity. This analysis can be useful for agricultural and environmental land management.
Abstract: A field study was conducted in order to study the effects of different wildfire severities on [1] soil organic matter content, [2] soil water repellency, and [3] aggregate stability; [4] the distribution of soil water repellency in aggregate sieve fractions (1-2, 0.5-1, 0.25-0.5 and < 0.25 mm) was also studied. Five similar burned sites and two long-unburned control sites were selected under mixed fir and pine forests in volcanic highlands from Michoacán, Mexico. Soil water repellency was observed in soil samples from all sites, although changes were influenced by fire severity. Sites affected by low severity fires did not show important changes in burned soils in comparison with controls, while high severity fires caused different responses: water repellency was increased or destroyed probably due to temperatures below or above 200-250 °C during burning. The degree of wettability/repellency from the fine earth fraction of burned soils seems to be conditioned by < 0.5 mm aggregates, more than coarser aggregates which always showed a higher degree of wettability. It is suggested that destruction of organic matter during burning occurs principally in coarse aggregates, where combustion can be more intense. Aggregate stability (measured using pre-wetted aggregates between 4 and 4.8 mm) did not change under low severity burning but it was considerably reduced in the case of a high fire severity. Losses of organic matter and destruction of water repellency seem to be the reasons for that reduction in this type of soil in contrast to previous studies, where aggregate stability increased after burning. Changes in both properties (water repellency and aggregate stability) are expected to induce modifications in runoff and soil loss rates at the hillslope scale.
Abstract: The effects of different fire intensities on physiochemical soil properties have been studied in this research. The experiment was conducted in a eucalyptus forested area near the Namadgi National Park (ACT, Australia), and four fire intensities were achieved by adding different amounts of fuel load: 0 xa0;kg xa0;mâ xa0;2 (control), 2 xa0;kg xa0;mâ xa0;2 (low fire intensity), 4 xa0;kg xa0;mâ xa0;2 (moderate fire intensity) and 8 xa0;kg xa0;mâ xa0;2 (high fire intensity). Soil surface peak temperatures reached at each plot were 14, 142, 317 and 525 xa0;°C, respectively. Immediate changes in soil properties under different fuel loads were studied and monitored monthly during a 7-month period. Average pH increased significantly with fuel load immediately after fire and decreased progressively to initial values. Changes in soil pH from burnt plots seem to be caused mainly by an ephemeral ash layer, and the recovery time has been relatively short. The complete oxidation of soil organic matter and the release of substantial amounts of cations after high fire intensity also contributed to increased pH. Only small variations in soil texture have been observed in this study even after high intensity fire, although the clay content decreased slightly during the experiment. This can be due to relatively low pre-burn clay content, but also to spatial variability of texture. In this case, post-fire erosion processes might have contributed to decreased clay content and are probably more important than other processes associated to temperature. Aggregate stability indices showed good correlation coefficients with the organic matter content. The role of organic matter as cementing agent of soil aggregates is extremely important after fire, since aggregate stability indices showed good correlation coefficients with the organic matter content. Low intensity fire enhanced soil water repellency. In this case, fire-enhanced soil water repellency persisted or increased progressively, but decreased below initial levels at the end of the experiment, but soil water repellency was completely destroyed after moderate or high fuel load treatments. The persistence of wettable conditions after destruction of soil water repellency can be considered as an index of fire severity, since it is a direct consequence of strong reduction of organic matter content.
Abstract: Wildfire is the major disturbance in Mediterranean forests. Prescribed fire can be an alternative to reduce the amount of fuel and hence decrease the wildfire risk. However the effects of prescribed fire must be studied, especially on ash properties, because ash is an important nutrient source for ecosystem recovery. The aim of this study is to determine the effects of a low severity prescribed fire on water-soluble elements in ash including pH, electrical conductivity (EC), calcium (Ca), magnesium (Mg), sodium (Na), potassium (K), aluminum (Al), manganese (Mn), iron (Fe), zinc (Zn), silica (SiO2) and total sulphur (TS). A prescribed fire was conducted in a cork oak (Quercus suber) (Q.S) forest located in the northeast part of the Iberian Peninsula. Samples were collected from a flat plot of 40Ã70 m mainly composed of Q.S and Quercus robur (Q.R) trees. In order to understand the effects of the prescribed fire on the soluble elements in ash, we conducted our data analysis on three data groups: all samples, only Q.S samples and only Q.R samples. All three sample groups exhibited a significant increase in pH, EC (p<0.001), water-soluble Ca, Mg, Na, SiO2 and TS and a decrease in water-soluble Mn, Fe and Zn. Differences were identified between oak species for water-soluble K, Al and Fe. In Q.S samples we registered a significant increase in the first two elements p<0.001 and p<0.01, respectively, and a non-significant impact in the third, at p<0.05. In Q.R data we identified a non-significant impact on water-soluble K and Al and a significant decrease in water-soluble Fe (p<0.05). These differences are probably due to vegetation characteristics and burn severity. The fire induced a higher variability in the ash soluble elements, especially in Q.S samples, that at some points burned with higher severity. The increase of pH, EC, Ca, Mg, Na and K will improve soil fertility, mainly in the study area where soils are acidic. The application of this low severity prescribed fire will improve soil nutrient status without causing soil degradation and thus is considered to be a good management strategy.
Abstract: The capacity of different microbial groups to recolonise soil after a fire event will be decisive in determining the microbial community after the fire. Microbial recovery after a wildfire that occurred in Sierra la Grana (Alicante province, southeast Spain) was tracked for 32Â months after the fire. Colony forming units (CFUs) of different microbial groups, microbial biomass, soil respiration, bacterial growth (leucine incorporation) and changes in the microbial community structure (phospholipid fatty acid (PLFA) analysis) were determined directly after the fire and four times during the recovery period. Direct effects were reflected by low values of most microbiological variables measured immediately after the fire. Microbial biomass increased during the first year after the fire but was below the unburned reference site 32Â months after the fire. Bacterial activity and soil respiration showed the highest values immediately after the fire, but decreased to values similar to that of the unburned reference site or even lower (respiration) 32Â months after the fire. Colony forming units of bacterial groups estimated by the plate count method peaked 8Â months after the fire, but then decreased, showing values similar to the unburned reference site at the end of the study, with the exception of spore formers, which were 20 times higher than the reference site 32Â months after the fire. Fungal CFUs were more sensitive to the fire and recovered more slowly than bacteria. Fungi recovering less rapidly than bacteria were also indicated by the PLFA pattern, with PLFAs indicative of fungi being less common after the fire. The recovery of microbial biomass and activity was mirrored by the initially very high levels of dissolved organic carbon being consumed and decreasing within 8Â months after the fire. The wildfire event had thus resulted in a decrease in microbial biomass, with a more bacteria-dominated microbial community.
Abstract: Immediately following a wildfire, a layer of ash and charred material typically covers the ground. This layer will gradually be reduced, being redistributed by rainfall, wind or animals, by partial dissolution and by incorporation into the soil. Ash can increase or decrease the post-fire runoff and erosion response, depending upon the soil and ash properties and the ash thickness. One aspect of ash that has remained unknown and which may affect the variability in the hydrological response of the burned soil is its wettability. This study examines the wettability of ash using the Water Drop Penetration Time (WDPT) test, its relationship with total organic carbon (TOC) content and colour, and its effects when incorporated into the soil. Ash samples (n = 48) were taken from five wildfires in the Mediterranean basin encompassing a range of burn severities. Additional ash material was generated from exposing plant leaves (Rosmarinus officinalis, Pinus halepensis and Quercus coccifera) to specific temperatures in a muffle furnace (200-700 °C). Selected laboratory ash types were also mixed with wettable and water repellent soil material to assess their effect on soil wettability. Over 30% of ash samples from the wildfire sites exhibited water repellency (WR), with WDPT levels ranging from low to extreme. This variability appears to be related to differences in fire severity, combustion completeness of the biomass, vegetation type and subsequent rainfall events. The laboratory-generated ash exhibited a greater frequency and persistence of water repellency at lower furnace temperatures (200-300 °C), with ash from R. officinalis being generally less water repellent than that derived from the other two species. The water repellency levels of ash correlated well with TOC (r = 0.80), whereas neither of these parameters correlated very well with ash colour (r = 0.57 for TOC and r = 0.59 for WR). This suggests that ash colour, which is widely used as a parameter in classifying burn severity in the field, may not necessarily be a very accurate indicator. Adding water repellent ash to wettable soil induced WR, whereas the addition of wettable ash to water repellent soil had the opposite effect. A wetting-drying cycle can reduce the water repellency of a soil-ash mixture. There were substantial differences between wildfire- and laboratory-generated ash in terms of organic carbon content and colour, suggesting that the combustion conditions in a furnace may not adequately represent those in wildfires. In contrast to what is generally assumed, our findings demonstrate that ash from vegetation fires can be water repellent. This is likely to have implications for runoff responses and nutrient fluxes not only when ash is present on the ground surface, but also following its redistribution and incorporation into the soil.
Abstract: Fire can affect soil properties depending on a number of factors including fire severity and soil type. Aggregate stability (AS) refers to soil structure resilience in response to external mechanical forces. Many authors consider soil aggregation to be a parameter reflecting soil health, as it depends on chemical, physical and biological factors. The response of AS to forest fires is complex, since it depends on how fire has affected other related properties such as organic matter content, soil microbiology, water repellency and soil mineralogy. Opinions differ concerning the effect of fire on AS. Some authors have observed a decrease in AS in soils affected by intense wildfire or severe laboratory heating. However, others have reported increases. We provide an up to date review of the research on this topic and an analysis of the causes for the different effects observed. The implications for soil system functioning and for the hydrology of the affected areas are also discussed. Generally, low severity fires do not produce notable changes in AS, although in some cases an increase has been observed and attributed to increased water repellency. In contrast, high severity fires can induce important changes in this property, but with different effects depending on the type of soil affected. The patterns observed can vary from a disaggregation as a consequence of the organic matter destruction, to a strong aggregation if a recrystallization of some minerals such as Fe and Al oxyhydroxides occurs when they are present in sufficient quantities in the soil, after exposure to high temperatures. Because of the complexity of the different possible effects and reasons for the potential changes in the fire-affected soil aggregates, the inclusion of other parameters in the studies is necessary to understand the results. The suggested parameters to include in the examination of AS are: soil organic matter, microbial biomass, water repellency, texture, aggregate size distribution, together with accurate ways of estimating fire severity. More research is needed on what implications there are for soil system functioning with the changes suffered by aggregates after fire. Studies including measurements at very different scales: from AS measurements in the laboratory to erosion rates measured at pedon, slope and catchment scales are also necessary.
Abstract: Previous studies have shown that long-term irrigation with wastewater can lead to the development of soil water repellency. Little is known about the longevity of this effect. Here we address this research gap by examining the effect of long-term (~Â 20Â years) use of low-quality wastewater for disposal purposes, followed by 6Â years of [`]recovery' with no irrigation, on the wettability of calcareous sandy soil (Xerofluvent) under a Populus alba tree stand used as a "green filter" in SE Spain. Water repellency (WR) and soil organic matter content (SOM) were determined for 120 air-dry samples from the plot and 80 control samples from adjacent and otherwise similar non-irrigated areas. To account for plot micro-topography 40 samples each were taken from ridges (R; 0-5Â cm depth), furrows (F; 0-5Â cm), and furrows at depth (FD; 5-10Â cm). The controls included 40 samples each (0-5Â cm depth) from unvegetated and unploughed soil, and from soil under the P. alba plantation. All control samples were non-repellent whereas at the irrigated plot, water repellency was present for 48, 95 and 93% of ridge, furrow and furrow-depth samples respectively. WR and SOM was strongly correlated within the whole sample population (R2Â =Â 0.623**) and within two sample groups (R: R2Â =Â 0.783**; FD: R2Â =Â 0.424**), but weakly within F samples (R2Â =Â 0.072 n.s.). The latter showed the highest frequency and persistence (WDPT) of WR, indicating that not only quantity of SOM is controlling WR. Exploratory kaolinite clay additions (0.5-8%) to samples substantially reduced WR even at the lowest concentration, indicating that this could be a promising amelioration treatment for the WR in the soils investigated here. We conclude that for the conditions studied here (i) long-term use with poor-quality wastewater for disposal had led to the development of soil WR, (ii) a 6-year period of [`]recovery' (i.e. non-irrigation) was insufficient to eliminate the induced WR, and (iii) kaolinite addition could be a promising amelioration treatment for these sandy soils.
Abstract: Water shortage and soil degradation are the two most important environmental problems in the Mediterranean area. For this reason, strategies for soil and water conservation are necessary. Our objective was to evaluate the use of treated wastewater as an irrigation source to help alleviate these problems. Short-term effects on several soil fertility properties were evaluated in an agricultural area located at Biar (Alicante, SE Spain), where grapes (Vitis labrusca) are grown. Three treatments: fresh water (control), and treated wastewaters from secondary and tertiary treatment were evaluated for 2 years. We found a slight increase in soil organic carbon content in plots irrigated with the secondary treatment. These plots also had increased electrical conductivity (EC) and increased available Na content due to the high values of EC in wastewater. Laboratory analyses also show a decrease in aggregate stability for all treatments, presumably due to the wetting and drying (WD) cycles associated with each irrigation dose. These WD cycles may also explain changes in microbial biomass carbon and basal soil respiration. We recommend modifying the dose of irrigation in order to reduce the quantity applied and to increase the frequency of application to avoid the loss of aggregation. We also suggest long-term studies to assess the feasibility of wastewater reuse.
Abstract: Fire causes changes in soil moisture content (MC) and also in other soil properties depending on the maximum temperature reached. However, after fire, MC is partially rapidly restored due to re-equilibrium with air moisture or following rainfall, which in turn affects the near infrared (NIR) spectra of soil. The degree to which MC is restored depends on other soil properties, which are also affected by heating. We studied the effect of soil moisture on the estimation of the maximum temperature reached (MTR) in the soil using NIR spectroscopy. Different pre-treatments of burned samples were applied to modify MC. Different models relating NIR spectra with MTR were developed using partial least squares (PLS) regressions for the different pre-treatments. Models were successfully leave-one-out cross-validated with r2 greater than 0.982 and with the root mean square error of cross-validation (RMSECV) smaller than 28.2 °C. These models were used to predict the MTR for an independent set of soil samples heated at seven temperatures of 100, 200, 300, 400, 500, 600 and 700 °C. The MC of this set of samples was also modified using similar pre-treatments. Accurate estimations of MTR were obtained when the pre-treatment of samples used was similar as that of the set of samples used in the calibration model. Although MC of burned soils can affect MTR estimations, MTR can be estimated using NIR with high accuracy. Each heating temperature produced a gradient of changes leading to different NIR spectra that was not solely due to changes in soil moisture. This fact allows MTR to be estimated from NIR spectra.
Abstract: A field experiment was carried out in a semiarid agricultural Mediterranean area located at the "El Teularet" experimental field in the Enguera Sierra (Valencia, southeast Spain) to assess the influence of different agricultural management systems on indicators of soil biological quality and activity (microbial biomass C, basal respiration, C mineralization coefficients, metabolic quotient (qCO2), respiratory quotient (RQ: moles CO2 evolved/moles O2 consumed), soluble C and dehydrogenase, urease, protease-BAA, phosphatase and [beta]-glucosidase activities), one year after treatment establishment. The management practices assayed were as follows: application of the herbicides paraquat, glyphosate or oxyfluorfen, addition of olive tree pruning residues, ploughing, sowing of oats + addition of crop residues + ploughing, sowing of Medicago sativa, sowing of oats and vetch + addition of crop residues and addition of oat straw. A non-treated plot was used as control soil and a plot under natural vegetation was used as a standard of local, high quality soil. The plots with addition of oat straw had higher values of enzymatic activity, microbial biomass and respiration, reaching similar values to soil under native vegetation. The lowest levels of soil biological quality indicators were observed in the plots with application of some type of herbicide. Low RQ values were observed in these plots as consequence of the scarce-null inputs of organic matter, suggesting an increase in organic matter recalcitrance. The addition of oat straw to soil can be considered an effective technology, due to the rapid improvement of soil quality, for carrying out sustainable agriculture in semiarid Mediterranean agroecosystems.
Abstract: In semiarid ecosystems plant cover plays an important role in the improvement of physical, chemical and biochemical soil properties. With the aim of studying the influence of different plant species on soil properties, and establishing the relationships between them, 160 soil samples from under four different plant species (Pinus halepensis, Quercus coccifera, Juniperus oxycedrus and Rosmarinus officinalis) were taken in a forest area of the province of Alicante (SE Spain). The following soil properties were analyzed in all soil samples: organic carbon content, microbial biomass, soluble organic carbon, aggregate stability, basal respiration, and some eco-physiological ratios. In addition, the near infrared spectra (NIR) of all soil samples were obtained to verify the similarities or differences between soil samples under the four species. Some differences in parameters such as organic carbon content or basal respiration were found mainly between the group of P. halepensis and Q. coccifera with respect to J. oxycedrus and R. officinalis. Despite this, the high organic carbon content found under the four plant species showed an influence on the rest of soil properties. Moreover, using a discriminant analysis with factorial scores from NIR absorbance data did not result in a good classification of samples in terms of the species, reflecting some similarities between them. Our results show that the high contents observed in some parameters under the four species, and the lack of significant differences in most of them, prove the important role of shrubland in semiarid conditions, it being capable of promoting good soil conditions.
Abstract: In Spain, agriculture triggers soil degradation and erosion processes. New strategies have to be developed to reduce soil losses and recover or maintain soil functionality in order to achieve a sustainable agriculture. An experiment was designed to evaluate the effect of different agricultural management on soil properties and soil erosion. Five different treatments (ploughing, herbicide, control, straw mulch and chipped pruned branches) were established in âEl Teularet experimental stationâ located in the Sierra de Enguera (Valencia, Spain). Soil sampling was conducted prior to treatment establishment, and again after 16 months, to determine soil organic matter content (OM), aggregate stability (AS), and microbial biomass carbon content (Cmic). Fifty rainfall simulations tests (55 mm during one hour, 5-year return period) were applied to measure soil and water losses under each treatment. The highest values of OM, AS and Cmic were observed in the straw-covered plot, where soil and water losses were negligible. On the contrary, the plot treated with herbicides had the highest soil losses and a slight reduction in Cmic. Soil erosion control was effective after 16 months on the plots where vegetation was present while on the ploughed and herbicide-treated plots, the practices were not sustainable due to large water and soil losses. Except for the straw mulch plot, soil properties (OM, AS, Cmic) were not enhanced by the new land managements, but soil erosion control was achieved on three of the five plots used (weeds, weeds plus straw and weeds plus chipped pruned branches). Erosion control strategies such as weeds, weeds plus straw mulch and weeds plus chipped branches mulch are highly efficient in reducing soil losses on traditional herbicide-treated and ploughed agricultural land. However, it takes longer to recover other soil properties such as OM, AS, and Cmic.
Abstract: Soil biochemical properties are susceptible to change under sample storage, and as a consequence, these properties have usually been determined in fresh samples, kept cold or frozen for brief periods of time. However, air-dried soil would facilitate routine soil testing procedures in soils from semi-arid Mediterranean areas, which have soil water deficit most of the year. This research aims at assessing the effects of medium-term soil storage (6-9 months) at room temperature on air-dried soil samples from two Mediterranean forest locations for the measurement of various microbiological and biochemical properties (microbial biomass carbon, basal respiration, metabolic quotient, acid phosphatase activity, urease activiy, β-glucosidase activity, and soluble carbon). Storage of air-dried soil samples for 6 months had no significant effects on the studied properties in any location. With regard to samples stored for 9 months, we only found differences at the location with higher mean rainfall in the values of basal respiration, the metabolic quotient and β-glucosidase, and urease activities. Our results show that biochemical properties from Mediterranean semi-arid soils, are medium-term stable in stored air-dried soil samples. Thus, these findings would encourage the selection of biochemical properties on a practical basis, as there is no strict requirement to determine these properties immediately after sampling, as they remain valid for several months.
Abstract: In Eastern Spain, almond trees have been cultivated in terraced orchards for centuries, forming an integral part of the Mediterranean forest scene. In the last decades, orchards have been abandoned due to changes in society. This study investigates effects of changes in land use from forest to agricultural land and the posterior land abandonment on soil microbial community, and the influence of soil physico-chemical properties on the microbial community composition (assessed as abundances of phospholipids fatty acids, PLFA). For this purpose, three land uses (forest, agricultural and abandoned agricultural) at four locations in SE Spain were selected. Multivariate analysis showed a substantial level of differentiation in microbial community structure according to land use. The microbial communities of forest soils were highly associated with soil organic matter content. However, we have not found any physical or chemical soil property capable of explaining the differences between agricultural and abandoned agricultural soils. Thus, it was suggested that the cessation of the perturbation caused by agriculture and shifts in vegetation may have led to changes in the microbial community structure. PLFAs indicative of fungi and ratio of fungal to bacterial PLFAs were higher in abandoned agricultural soils, whereas the relative abundance of bacteria was higher in agricultural soils. Actinomycetes were generally lower in abandoned agricultural soils, while the proportions of vesicularâarbuscular mycorrhyzal fungi were, as a general trend, higher in agricultural and abandoned agricultural soils than in forests. Total microbial biomass and richness increased as agricultural < abandoned agricultural < forest soils.
Abstract: The potential of near infrared (NIR) reflectance spectroscopy to predict various physical, chemical and biochemical properties in Mediterranean soils from SE Spain was evaluated. Soil samples (n = 393) were obtained by sampling 13 locations during three years (2003â2005 period). These samples had a wide range of soil characteristics due to variations in land use, vegetation cover and specific climatic conditions. Biochemical properties also included microbial biomarkers based on phospholipid fatty acids (PLFA). Partial least squares (PLS) regression with cross validation was used to establish relationships between the NIR spectra and the reference data from physical, chemical and biochemical analyses. Based on the values of coefficient of determination (r2) and the ratio of standard deviation of validation set to root mean square error of cross validation (RPD), predicted results were evaluated as excellent (r2 > 0.90 and RPD > 3) for soil organic carbon, Kjeldahl nitrogen, soil moisture, cation exchange capacity, microbial biomass carbon, basal soil respiration, acid phosphatase activity, β-glucosidase activity and PLFA biomarkers for total bacteria, Gram-positive bacteria, actinomycetes, vesicular-arbuscular mycorrhizal fungi and total PLFA biomass. Good predictions (0.81 < r2 < 0.90 and 2.5 < RPD < 3) were obtained for exchangeable calcium and magnesium, water soluble carbon, water holding capacity and urease activity. Resultant models for protozoa and fungi were not accurate enough to satisfactorily estimate these variables, only permitting approximate predictions (0.66 < r2 < 0.80 and 2.0 < RPD < 2.5). Electrical conductivity, pH, exchangeable phosphorus and sodium, metabolic quotient and Gram-negative bacteria were poorly predicted (r2 < 0.66 and RPD < 2). Thus, the results obtained in this study reflect that NIR reflectance spectroscopy could be used as a rapid, inexpensive and non-destructive technique to predict some physical, chemical and biochemical soil properties for Mediterranean soils, including variables related to the composition of the soil microbial community composition.
Abstract: The heat generated during wildfires often leads to increases in soil water repellency. Above a critical heating threshold, however, its destruction occurs. Although the temperature thresholds for repellency destruction are relatively well established, little is known about the specific changes in the soil organic matter that are responsible for repellency destruction. Here we report on the analysis of initially water repellent surface soil samples (Dystric Cambisol, 0â5 cm depth) by transmission Fourier Transform Infrared (FTIR) spectroscopy analysis before and after destruction of its water repellency by heating to 225 °C in order to investigate heating-induced changes in soil organic matter (SOM) composition. Although assignment of absorption bands is made difficult by overlapping of some bands, it was possible to distinguish bands relevant for hydrophobicity of SOM in the soil before heat treatment. The most significant decrease in absorbance following water repellency destruction took place in the frequency area corresponding to stretching vibrations of aliphatic structures within SOM. The results suggest that besides a general decrease of SOM content during heating, the loss of soil water repellence is primarily caused by the selective degradation of aliphatic structures.
Abstract: The aim of this work was to assess the effect of the presence of ash on maximum temperature reached (MTR) estimation using near infrared reflectance (NIR) spectroscopy. The degree of combustion (ash produced by heating to 100, 300, 500 and 700 °C), the type (ash from Pinus halepensis and Rosmarinus officinalis), and different quantities of ash (0â20% in 2% interval) were evaluated in a soil heated at seven different temperatures (100 °Câ700 °C). Results showed that the estimation of MTR on samples with ash, using partial least squares (PLS) models constructed with samples without ash, could be erroneous. Both, ash quantity and degree of combustion affected the estimation of MTR. However, using discriminant analysis, a good classification of samples (> 97% correctly classified) according to the heating temperature classes (unheated, 100, 200, 300, 400, 500, 600 and 700 °C) was obtained despite the presence of ash.
Abstract: Soils from natural ecosystems have specific physical, chemical and biochemical properties determined by the conditions in which these soils have developed. These soils that develop without external disturbance reach a balance amongst their properties. Thus, the creation of a model that represents the established balance of different soil properties from stable ecosystems can be used as a soil quality index, thus any perturbation must lead to modifications in this natural balance. Two regression models with soils from undisturbed forest regions in eastern Spain were previously developed, representing the balance between organic carbon and some physical, chemical and biochemical properties. For undisturbed forest soils, the prediction of soil organic carbon (SOCc) with the calibrated models should be similar to the actual value of this variable (SOCa) (SOCc â SOCa). Consequently, the residuals (SOCc â SOCa) should be around 0. On the contrary, disturbance practices cause a disruption in the balance defined between the different properties and SOC. As a consequence, residuals must be < or >0. Furthermore, the more the degree of degradation increases, the more the values of SOCc must differ from the values of SOCa. According to this, two soil quality indices (SQI) were defined, one for each model, by the calculation of the model residuals (SQI = SOCc â SOCa). The SQIs have been applied to different undisturbed forest soils to evaluate their validity. In addition, they have also been applied to severely altered soils, like agricultural soils, and abandoned agricultural fields, to assess the sensibility of this index to perturbations. After applying the soil quality indices to eleven undisturbed forest soils, it has been verified that a balance exists between organic matter content and different physical, chemical and biochemical properties in forest soils from SE Spain, and the proposed calibrated models are capable of reflecting that balance (SQI â 0). Our results confirm that our models are sensitive to soil perturbation, because agricultural and abandoned agricultural soils have shown an imbalance between organic carbon content and the physical, chemical and biochemical properties (SQI > 0). Moreover, soils from abandoned fields showed lower deviation in the natural equilibrium, indicating a recovery of soil quality.
Abstract: 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 âMt. Carmelâ, 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 Caâmontmorillonite content is higher than kaolinite and illite. Caâmontmorillonite 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 Caâmontmorillonite 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.
Abstract: Alkaline soils are considered much less prone to developing water repellency induced by fire than acidic soils. Here we report on the persistence of water repellency present in calcareous soils immediately after wildfires in 10 burned areas in SE Spain, its distribution in different aggregate size fractions (< 2, 2â1, 1â0.5, 0.5â0.25 and < 0.25 mm) and on results from aggregate stability tests. We also distinguished between soil samples taken beneath pine (Pinus halepensis) and beneath understory vegetation.
Burning appears to have increased the frequency of water repellency occurrence, with 74% of burned samples being classified as water repellent compared to 33% from unburned terrain in the composite fraction (< 2 mm). The persistence of water repellency after fire was highly variable but nevertheless showed statistical differences at p < 0.001 comparing burned vs unburned. Moreover, statistical differences in the persistence of water repellency were found in soil samples taken from beneath pine between burned and unburned, and also beneath understory vegetation. Results showed that soil beneath understory tend to have lower values of water repellency persistence than soil beneath pine.
Burned soils showed higher aggregate stability. A positive tendency was observed between aggregate stability and water repellency. The observed changes in WR and AS could have implications for soil hydrological behaviour.
Abstract: We studied the use of near-infrared (NIR) reflectance spectroscopy as a potential method to estimate a posteriori the maximum temperatures reached (MTR) on burned soils. When soils are heated, the NIR spectra change in accordance with the MTR. Thus, after calibrating, these patterns of NIR could be used as a fingerprint to estimate the MTR in burned soils. Successful validations of the models relating NIR spectra with MTR were obtained in each of the five soils studied (local models), with r2 values ranging from 97.47 to 98.56%. A global model constructed with samples from the five soils studied obtained a similar accuracy, suggesting the presence in soils of some NIR-detectable compounds with similar thermal sensitivity. The influence of the variability caused by the soil type and the duration of heating during model constructions is also evaluated and discussed. The use of NIR presents interesting advantages, such as low cost, low time consumption, minimal pretreatment of samples, no need for chemicals, and accuracy. The results indicate that the MTR could be estimated in burned soils with NIR, offering a new perspective on studies of wildfire effects on soils.
Abstract: Water repellency (WR) is a property affected by fire and of crucial importance in the hydrological behaviour of soils after burning. In dry Mediterranean areas knowledge of the factors that control the development of water repellency by fire is of particular interest. We examined such factors in two calcareous soils, a Regosol and a Luvisol, representative of forest areas of southeast Spain. Heating temperature (200â500°C), vegetation type (Rosmarinus officinalis, Pinus halepensis and Brachypodium retusum), quantity of vegetation litter (control, low and high) and type of soil were selected as factors for assessing the WR induced by fire. The two soils exhibited markedly different WR responses after heating, the Regosol being much more susceptible than the Luvisol. Characteristics such as organic matter and clay content seem to determine the different WR responses to heating. We found that the type and quantity of vegetation litter also control the persistence of induced WR. In general, the order of increasing WR was Brachypodium < Pinus < Rosmarinus, and larger amounts of litter induced more WR. Maximum values of WR, most of them classified as severe (901â3600 s), were found in the range of 300â350°C, whereas beyond this temperature WR was destroyed. These results show that water repellency induced by combustion could be limited by environmental factors such as vegetation type and availability of litter, and that soil type and its characteristics also play a decisive role.
Abstract: Soil biochemical properties are useful indicators of soil quality as they are very sensitive to disturbance. Sample storage or pre-treatments could affect the results in these assays, which are normally determined on fresh samples, kept cold or frozen. The objectives of this study were to (i) evaluate the effect of air-drying or incubation of rewetted air-dried soil samples on microbial biomass carbon (MBC), basal soil respiration (BSR), qCO2 and water soluble carbon (WSC), in soils from different locations, with different degradation status and sampling seasons, and (ii) assess if air-drying or incubation of rewetted air-dried soil samples is an accurate sample storage and pre-treatment procedure for these soil properties in soil quality evaluations under semiarid Mediterranean conditions. Our results showed that air-drying does not have the same effects on MBC, BSR, qCO2 and WSC depending on the geographical situation and sampling date. It seems that the warmest and driest place and season show less variation when using air-dried soil samples, with values representative of those obtained under field-moist conditions. Short incubations (4, 8 and 12 days at 23 °C) provoked a general decrease in all properties, probably due to labile organic compounds depletion. Hence, air-dried soils can be used as part of soil quality analysis to estimate these biochemical properties in summer time in the semiarid region of South-East Spain, because they have not suffered severe affections. Moreover, MBC could also be determined using air-dried soil in the driest zones during all year. In contrast, estimations with incubated soil samples are not, in any case, representative of field-moist soil values.
Abstract: The aim of this work is to obtain an expression using multiple lineal regressions (MLR) to evaluate environmental soil quality. We used four forest soils from Alicante province (SE Spain), comprising three Mollisols and one Entisol, developed under natural vegetation with minimum human disturbance, considered as reference soils of high quality. We carried out MLR integrating different soil physical, chemical and biochemical properties, and we searched those regressions with Kjeldahl nitrogen (N(k)), soil organic carbon (SOC) or microbial biomass carbon (MBC) as predicted parameter. We observed that Mollisols and Entisols presented different relationships among their properties. Thus, we searched different equations for both groups of soils. The selected equation for Mollisols was N=0.448 (P) + 0.017 (water holding capacity) + 0.410(phosphatase) - 0.567 (urease) + 0.001 (MBC) + 0.410 (beta - glucosidase) - 0.980, and for the Entisol SOC = 4.247 (P) + 8.183 (beta-glucosidase) -7.949 (urease) + 17.333. Equations were applied to samples from two forest soils in advanced degree of degradation, one for Mollisols and the other one for the Entisol. We observed a clear deviation in the predicted parameters values related to the real properties. The obtained results show that MLR is a good tool for soil quality evaluation, because it seems to be capable of reflecting the balance among its properties, as well as deviations from it.
Abstract: Sewage sludges are increasingly used in soil amendment programmes, although not without risk since they contain, among other potential hazards, high concentrations of total coliform bacteria. In this paper we have studied the effect of irrigation on the survival of total coliforms in three semiarid degraded soils with different agricultural practices. Fresh sewage sludge was added at 50 g kg(-1) soil, and incubated in both the presence and absence of irrigation. The absence of irrigation led to a sharp decrease in the number of total coliforms in all soils, with the bacteria disappearing in 40 days. Irrigation produced a substantial initial increase in the number of coliforms in the three soils, although after 80 days there was none growing in any of the soils. The results showed that there were significant differences in the survival of coliform bacteria due to the presence or absence of irrigation.
Abstract: Water repellency (WR) is a property that has implications on the hydrologic balance in affected soils. In semi-arid areas where water supply is limited, even slight WR may play an important role in the infiltration and spatial distribution of precipitation into the soil. Acidic and sandy-textured soils have been demonstrated to be more prone to develop WR, but there are studies reporting water repellent properties in other soil types. In the present study we investigated soil WR under four plant species in a semi-arid area with a calcareous, medium-textured forest soil. For this purpose, 160 soil samples were taken at micro-sites under different species (Pinus halepensis, Quercus coccifera, Juniperus oxycedrus and Rosmarinus officinalis). Soil WR was measured with the water drop penetration time (WDPT) test on air-dried samples. Samples with WDPT > 5 s were classified as water repellent. WR was present in 20% of the samples, and its persistence ranged mainly between 10 and 30 s. Under P. halepensis and Q. coccifera, WR occurred more frequently (40 and 30%, respectively) than under J. oxycedrus and R. officinalis (only 5% in both cases). In order to know the causes of the difference in occurrence of WR under the selected species and to establish relationships, soil organic matter (SOM) content and pH were measured for a selection of 66 samples, including all 32 water repellent and 34 wettable samples selected from those taken under the four species (n = 66). A negative relationship between WR and pH was found for all species. Moreover, in the case of P. halepensis soil samples, a positive correlation between WR and SOM content was found. A discriminant analysis allowed for the distinction between water repellent and wettable conditions in calcareous soils, based on the information provided by pH, SOM content and vegetation type. Soil pH turned out to be the most important parameter for discrimination. The hydrological and ecological implications from these results are discussed with special focus on the areas in the region extensively afforested with P. halepensis.
Abstract: For millennia, land use in the Mediterranean region has led to situations in which soil has been severely degraded showing high risks of erosion and impoverishment. Thus, the establishment of soil quality indices is considered to be of crucial importance in determining the state of degradation and recovery of soils. Soils from stable forest ecosystems have specific physical, chemical and biological properties due to the conditions in which they developed. Hence, modelling the balance established among different key soil properties from stable forest ecosystems could be used as a soil quality index, because disturbance practices lead to changes in that natural balance. Here we report the establishment of two soil quality indices under Mediterranean semiarid conditions for forest soils in SE Spain, based on the use of multiple linear regressions integrating different physical, chemical and biochemical properties. As we observed the strong influence that climatic factors have on the values of the different soil properties and their relationships, mean annual precipitation was also incorporated in the regression models as a categorical explanatory variable. Model 1, that explains 92% of the variance in soil organic carbon (SOC), showed that SOC can be calculated by a linear combination of 6 physical, chemical and biochemical properties (acid phosphatase, water holding capacity (WHC), electrical conductivity (EC), available phosphorus (P), cation exchange capacity (CEC) and aggregate stability (AS)). Model 2 explains 89% of the variance in SOC, which can be calculated by means of 7 chemical and biochemical properties (urease, phosphatase and β-glucosidase activities, pH, EC, P and CEC). Our results confirm that a balance exists between the soil organic carbon of high quality soils and some other properties widely recognised in soil quality assessments, due to their sensitivity and the information they provide about the functionality of soils. As disturbance practices should be accompanied by the loss of this balance, SOC calculated by the models (SOCc) is no longer an accurate estimation of the actual SOC determined in laboratory (SOCa). Thus, it is possible to obtain a soil quality index by the calculation of the model residuals: Soil Quality Index = model residual = SOCc â SOCa. For a non-disturbed soil, the soil quality index should be 0 (SOCc = SOCa). In contrast, for disturbed soils, SOCc should be lower or higher than the actual SOC, with values in the soil quality index < 0 or > 0.
Abstract: Soil enzyme activities are useful indicators of soil quality as they are very sensitive to disturbance. Sample storage or pre-treatments could affect the results in these assays, which are normally determined in fresh samples, kept cold or frozen. The objectives of this study were to (i) evaluate the effect of air-drying or air-drying and rewetting on β-glucosidase, acid phosphatase and urease activities in soils from different locations, degradation status and sampling seasons, and (ii) assess if air-drying or air-drying and rewetting is an accurate sample storage and pre-treatment procedure for enzyme activities in soil quality evaluations under semiarid Mediterranean conditions. Our results showed that urease, phosphatase and β-glucosidase activities were hardly affected by air-drying of degraded and non-degraded soils from the two locations studied in all seasons. Short incubations (4, 8 and 12 d at 23 °C) of rewetted air-dried soil at 55% of water-holding capacity showed different patterns depending on the enzyme studied. Urease and β-glucosidase activities were relatively stable during incubation, with several significant (P<0.05) shifts up and down in some soils and samplings. However, acid phosphatase showed an increase in activity with incubation, of between 5% and 50% relative to air-dried samples. These increases followed no pattern and were unrelated to soil characteristics or sampling date. Hence, urease, phosphatase and β-glucosidase activities determined in air-dried soil samples seem to be representative of those obtained under field-moist conditions. In contrast, short incubations of rewetted soil samples can produce fluctuations in these enzyme activities, mainly of acid phosphatase, and estimations in these conditions are not so representative of field-moist soil values.
Abstract: Soil hydrophobicity is known to enhance runoff responses to rainstorms and to increase soil aggregate stability (AS). It has been widely reported for acidic soils particularly under burnt, but also unburnt pine forests following dry periods. Few studies have reported hydrophobicity from alkaline soils, but they have not established whether hydrophobicity also occurs in burnt or unburnt pine forests on alkaline soil. This study examines the wettability and stability of air-dry aggregates and their size fractions (<0.25, 0.25â0.5, 0.5â1 and 1â2 mm) taken from surface layers (0â2.5 and 2.5â5 cm depth) of alkaline, calcareous loamy soils. Four sites in southeastern Spain were sampled with comparable vegetation (>30-year-old Aleppo pine {Pinus halepensis} and associated shrub community), geology (limestone), soil type (Lithic Xerorthents), slope angle and aspect (5â8°SW). Included were three sites (A, B, C) burned, respectively, in 1998, 1999 and 2000, and one unburnt for >30 years (D). Hydrophobicity was detected in samples from all sites. Both spatial frequency and persistence of hydrophobicity (Water Drop Penetration Times (WDPT) ranged from 10 to 600 s), however, was lower than reported from studies of acidic soils under pine. This might be associated with a lower susceptibility of alkaline soils to hydrophobicity development and/or the comparatively low biomass production in the region. Probably because it had been most recently affected by severe fire, spatial frequency of hydrophobicity was higher at site B (53% of samples), compared to A, C and D (6%, 33% and 10% of samples, respectively). In contrast to some previous studies, the finest size fraction of the samples consistently had the highest degree of hydrophobicity. Degree of hydrophobicity was positively correlated with organic matter (OM) content (r=0.714). It is speculated that fine, interstitial hydrophobic organic matter accumulating in the finest sieve fraction contributes to this enhanced hydrophobicity. As shown in previous studies on acidic soils, aggregate stability increased with hydrophobicity (r=0.897 in the fraction 0.25â2 mm) for the samples investigated here. This elevated stability occurs despite an already relatively high level of aggregate stability amongst all samples investigated. Hydrophobicity observed at the study sites was not spatially contiguous and it may therefore enhance overland flow and slope wash over only short distances for most, except the very high intensity rainstorms that occur in the region. The increased stability of hydrophobic soil aggregates against slaking, however, may counter an otherwise enhanced susceptibility to erosion.
Abstract: The reclamation of burned soils in Mediterranean environments is of paramount importance in order to increase the levels of soil protection and minimise erosion and soil loss. The changes produced in the content of total organic carbon (TOC), N (Kjeldahl) and available P, K, Ca and Mg by the addition of different doses of a municipal solid waste compost to a burned soil were evaluated during one year. The effect of organic amendment on the improvement in the vegetation cover after one year was also evaluated. The organic amendment, particularly at a high dose, increased the TOC and N-Kjeldahl content of the soil in a closely related way. The levels of available K in soil were also enhanced by the organic amendment. Although the effects on all three parameters tended to decrease with time, their values in the amended soils were higher than in the control soil, which clearly indicates the improvement in the chemical quality of the soil brought about by the organic amendment. The available P content did not seem to be influenced by organic treatment, while available Mg levels were higher than in the control during the first 4 months following organic amendment. The application of compost to the burned soil improved its fertility and favoured rapid vegetal recovery, thus minimising the risk of soil erosion.
