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 vesicular�arbuscular 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: 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.

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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 �El Teularet experimental station� 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.

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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 (2003�2005 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: 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.

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 � SOCa). Consequently, the residuals (SOCc � 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 � 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 � 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: 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 (0�20% in 2% interval) were evaluated in a soil heated at seven different temperatures (100 °C�700 °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: 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, 2�1, 1�0.5, 0.5�0.25 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: Information about the mineralisation rates and effects on soil microorganisms must be obtained prior to the rational use of organic wastes in agriculture or forestry. The objective of this work was to study the mineralisation of two manures derived from the solid phase of pig slurries and the effects on the soil microbial biomass of an agricultural soil. Samples of this soil were mixed at two different rates with two manures derived from the solid phase of pig slurry (composted, CSP, and non-composted, NSP), and then were incubated during 163 days. Carbon mineralised from manures was fitted to first-order kinetic model, and small differences were found between manures despite the composting of one of them. Approximately 45% of the C added was mineralised in the experimental period. The soil microbial biomass C (Cmic) was increased by the amendments according to the application rate. The sudden increases of the qCO2 in the treated samples were ephemeral. The most appreciable differences between these manures were those related with net N mineralisation, being greater in the NSP-treated samples. The application of the solid phase of pig slurries, composted or not, could be a feasible practice to enhance in a short-term the microbial biomass of agricultural soils. In order to avoid an excessive release of inorganic N, the use of composted materials is preferred

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: 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: 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: 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 � 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: 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 (200�500°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 (901�3600 s), were found in the range of 300�350°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: 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: 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.

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