David Badía

Plant Ash and Heat Intensity Effects on Chemicaland Physical Properties of Two Contrasting Soils

Fire passage is accompanied by a heat wave and ash deposition affecting the upper soil layer. Changes in soil properties are directly related to heat intensity, the amounts of ashes deposited, and soil type. We subjected two soils (gypsiferous soil and calcareous soil) to artificial heating and ash incorporation and compared changes in select chemical and physical properties. The two soils studied were selected to provide a wide range of characteristics in soils of the semiarid Ebro Valley (NE Spain). Samples of both soils were heated for 30 minutes in a muffle furnace at temperatures of 25°, 150°, 250° and 500°C. Ashes were added only on soil samples heated at 250°C, in a quantity related to plant biomass growing on each soil (twice the amount in calcareous soil than in gypsiferous soil). Increasing heat intensity increased organic matter combustion as well as nutrient availability. Heating soil to 250°C caused a decrease in pH and an increase in electrolytic conductivity (ECe) and soluble Ca. Heating soil to 500°C caused an increase in pH and a decrease in ECe and soluble Ca. Total N content decreased at temperatures greater than 250°C, with about one-third being volatilized. Changes in chemical properties were similar for both soils although quantitative differences between soils were found. Cation exchange capacity (CEC) was reduced for gypsiferous soil heated to 500°C and to 250°C for calcareous soil. Heating increased sand-sized particles by fusion of clay, greatest in soil heated to 500°C. Soil aggregate stability (SAS) of both soils was reduced by heating to 250°C with greater reductions at 500°C, likely due to a reduction in organic matter and clay size particle content. A negative correlation was observed among SAS and soil erodibility (K-USLE). Bulk density and particle density increased in both soils when heated to 500°C. Water availability increased when soils were heated to 500°C, likely due to texture and structural modifications. Addition of the ashes increased organic matter content, C/N ratio, and pH in both soils and increased nutrient availability. These responses were greater in calcareous than in gypsiferous soil. Physical soil properties were not significantly modified by ash addition.

Effect of Simulated Fire on Organic Matter and Selected Microbiological Properties of Two Contrasting Soils

The effect of heating and ash deposition on microbiological properties was studied in two arid soils in an incubation experiment, simulating the effects of bushfire. Top soil (0-15 cm) was heated to 150°C, 250°C and 500°C for 30 minutes; unheated soil was taken as a control (25°C). Samples of the soil heated to 250°C were mixed with black ash (1%, w/w) for analysis of their effect on microbial population and activity. Soils were incubated for nine months and their basal respiration was assessed three times a month. Normalized and specific respiration, biomass-C, bacteria, and fungi numbers were analyzed one month after heating and in the final month of incubation to assess short-term and long-term effects of fire on soil microbiology. At the start of the incubation period and for intermediate heating treatments (150°C and 250°C), basal and specific soil respiration and biomass-C were enhanced in calcareous soil but depleted in gypsiferous soil. At the highest temperature (500°C), these biological properties, as well as specific respiration and colony forming units, were significantly reduced in both soil types and for each period of sampling. At the end of the incubation period, all biological properties maintained the differences between treatments but with lower values than at the beginning of the incubation. Black ash addition increased basal respiration in both soils but did not affect other biological properties. These results demonstrate the existence of both labile and permanent effects of soil burning and a differential response on C dynamics as a function of soil properties.

Fire and Rainfall Energy Effects on Soil Erosion and Runoff Generation in Semi-Arid Forested Lands

A study on the effects of fire and torrential rainfall on the soil erosion and hydrology of Pinus halepensis L. forest of the semi-arid Central Ebro Valley (NE-Spain) were carried out. A portable sprinkler-based rainfall simulator was used with two levels of rainfall energy (12,6 J m−2 mm−1 and 24,7 J m−2 mm−1) and similar intensity (85 ± 8 mm h−1). Rainfall simulations were conduced immediately after artificial burn of litter cover on nine different micro-plots and compared with paired unburned areas (2-soil status × 2 rainfall energies × 9 plots or replicates). In each rainfall simulation, the soil loss, soil infiltration (calculated by Horton model), wetting front, runoff coefficient, and runoff quality (EC and pH) were measured. Fire increased significantly the sediment loss: 18.5 times with fine rainfall and 33.6 with coarse rainfall. Sediment losses were as solutes dissolved in overland flow, mainly in unburned plots, and as particles in suspension, mainly in burned plots. Fire increased runoff quantity (about 1.6 times) and decreased quality (by increasing significantly both EC and pH). These results indicate that when litter cover was burned, first rainfalls duplicate runoff and increase 20–30 times soil erosion in relation to unburned plots, especially with high rainfall energy. Soil infiltration decreased significantly in burned plots, with the highest rainfall energy. Because there is a high post-fire degradation risk, a restoration strategy for a short-term response should be designed on steep slopes with erodible soils, especially in arid Mediterranean areas where torrential rainfall and wildfire are highly probable and their occurrence will increase with climate change.

Straw management effects on CO2 efflux and C storage in different Mediterranean agricultural soils.

The crop residues buried in semiarid soils as a carbon sink are evaluated. Both C-CO2 evolved and C sequestered from agricultural soils amended with barley straw were measured seasonally over 2 farming seasons in a semiarid environment (NE Spain). Six experimental soils with low organic matter content and contrasted properties were selected. The CO2 efflux, as a result of soil microbial activity, showed a significant seasonal variation according to changes in both soil moisture and temperature being the spring and early summer when respiration rates get higher. On annual average, more organic, calcareous soils, evolved higher carbon dioxide efflux (up to 53 mg CO2/kg and day) than soils with high levels of gypsum or more soluble salts (up to 25 mg CO2/kg and day), which have a lower percentage of organic carbon. Straw residue incorporation increases these CO2 emissions significantly for each soil type. Although CO2 emissions are significantly and negatively correlated with the C storage, straw addition increases soil organic C content, at the end of the period of study. In calcareous soils were stored up to 550 kgC/ha and year, gypseous soils up to 1135 kgC/ha and year and saline soils up to 1450 kgC/ha and year. According to the amount of stored C in the different soil types, the isohumic coefficient of barley straw ranges from 0.087 to 0.259 (kg of humus formed from 1 kg of dry straw).

AT WHAT DEPTH ARE THE PROPERTIES OF A GYPSEOUS FOREST TOPSOIL AFFECTED BY BURNING

10 paginas, 3 figuras, 4 tablas, 71 referencias.-- Special Issue: Advances Towards an Integrated Assessment of Fire Effects on Soils, Vegetation and Geomorphological Processes

Occurrence and intensity of wild boar disturbances, effects on the physical and chemical soil properties of alpine grasslands

Background and aimsPhysical and chemical soil properties determine local plant conditions and resources, affecting plants’ ability to respond to disturbances. In alpine grasslands, wild boar disturbances occur at different intensities, what may affect differently their soil properties. Alpine soils from five contrasted plant communities were explored within and outside disturbances, accounting for an overall and community scale effect. Additionally, we analysed the effect of disturbance intensity on soil NO3--N and NH4+-N.MethodsSoils were analyzed for physical (bulk density, moisture content and electrical conductivity), and chemical properties (pH, total N and C, oxidizable C, C:N ratio, available K, P, Ca2+, Na+ and Mg2+). Resin bags were used to compare the effect of the disturbance occurrence and intensity on soil NO3--N and NH4+-N.ResultsBulk density, total N and NO3--N concentration were significantly higher in disturbed areas, while soil moisture, C:N, NH4+-N, Na+, Mg2+ and Ca2+ concentrations were significantly lower. However, low disturbance intensity reduced NO3--N and increased NH4+-N concentrations.ConclusionsWild boar occurrence and intensity strongly alter physical and chemical conditions of alpine soils, increasing soil compaction, and altering the availability of N forms. These changes may affect most plant species, thus affecting the structure and dynamics of alpine plant communities.

Ten-year growth of woody species planted in reclaimed mined banks with different slopes

In landscape reconstruction in an opencast coal mine, a gradient of slopes can be obtained. The slope gradient can affect different processes, such as plant growth, especially in semi-arid conditions. On the other hand, to favor the heterogeneity of habitats and ensure long-term restoration, late successional woody species have been planted but with heterogeneous results. In this study, the effect of a slope gradient (from 11.4 to 15.5 degrees) on the growth and survival of five Mediterranean woody species 10 years after the reconstruction of mining banks was evaluated. Slope gradient reduced height growth significantly from 10 cm degree−1 (lentish) to 25 cm degree−1 (pine) in 10-year-old woody species. This gradient also reduced basal diameter growth from 0.22 mm degree −1 (juniper) to 0.58 mm degree−1 (pine). Survival and slope were not significantly correlated. Growth and survival of the 10-year-old woody species were equal to or higher than those of the same species in other afforestations in semi-arid conditions. This outcome demonstrates the adequacy of species and applied techniques of restoration that allow a long-term reliability of reclaimed mine slopes.

Influence of livestock soil eutrophication on floral composition in the Pyrenees mountains

AbstractLivestock behaviour in the Pyrenees includes free grazing and a long resting period that provokes the accumulation of dung and urine in some places, so-called camping areas. The aims of this study were (i) to analyze any change in floral composition, and in nutritional and chemical contents of plants in a livestock camping area; and (ii) to relate the floral composition with soil chemical properties. In a linear transect, five sampling zones were established, from the centre of the camping area to the surrounding Nardus stricta-dominant pasture. The above ground plant biomass and the topsoil were sampled in each zone with 6 replicates per zone. Plant species were classified and weighed to calculate above ground biomass, nutritional and chemical contents, and Shannon diversity and evenness indices. Additionally, soils were sampled in two periods, at the beginning and at the end of grazing period. Soil available nutrients (nitrate, ammonium, phosphorus, potassium, calcium and magnesium), total nitrogen, organic carbon and pH were measured.Plant chemical contents (protein, lignin and others) were significantly related to the proportions of grasses, legumes and other plants; so, the protein content is positively correlated with legumes plant biomass while lignin content is negatively correlated with grasses. Both plant and soil nutrients increased linearly towards the centre of the camping area. However, the relationship among plant species richness, diversity and evenness relative to its position along the studied transect was bell-shaped. From the outskirts to the centre of the camping area, plants with low nutrient demand were progressively replaced by those with medium and high nutrients demand and by pioneers. Nardus stricta-dominant pasture has low plant diversity and plant nutrient content as well as a poor soil nutrient availability. The presence of the camping area introduced patches with more soil nutrients and new species in the large spatial scale. However at a small spatial scale, the strong soil nutrient concentration into the centre of the camping area reduced floral composition again. To ensure positive effects of camping areas on plant diversity, and to manage more effectively the nutrients returned to the soil, a reduction in the stocking rate should be pursued.

At What Depth Are The Properties of a Gypseous Forest Topsoil Affected By Burning?: SOIL DEPTH AFFECTED BY BURNING

10 paginas, 3 figuras, 4 tablas, 71 referencias.-- Special Issue: Advances Towards an Integrated Assessment of Fire Effects on Soils, Vegetation and Geomorphological Processes

Burn effects on soil properties associated to heat transfer under contrasting moisture content

The aim of this work is to investigate the topsoil thickness affected by burning under contrasting soil moisture content (field capacity versus air-dried conditions). A mollic horizon of an Aleppo pine forest was sampled and burned in the laboratory, recording the temperature continuously at the topsoil surface and at soil depths of 1, 2, and 3cm. Changes in soil properties were measured at 0-1, 1-2, 2-3, and 3-4cm. Both the maximum temperature and the charring intensities were significantly lower in wet soils than in air-dried soils up to 3cm in depth. Moreover, soil heating was slower and cooling faster in wet soils as compared to dry soils. Therefore, the heat capacity increase of the soil moistened at field capacity plays a more important role than the thermal conductivity increase on heat transfer on burned soils. Burning did not significantly modify the pH, the carbonate content and the chroma, for either wet or dry soil. Fire caused an immediate and significant decrease in water repellency in the air-dried soil, even at 3cm depth, whereas the wet soil remained hydrophilic throughout its thickness, without being affected by burning. Burning depleted 50% of the soil organic C (OC) content in the air-dried soil and 25% in the wet soil at the upper centimeter, which was blackened. Burning significantly decreased the total N (TN) content only in the dry soil (to one-third of the original value) through the first centimeter of soil depth. Soluble ions, measured by electrical conductivity (EC), increased after burning, although only significantly in the first centimeter of air-dried soils. Below 2cm, burning had no significant effects on the brightness, OC, TN, or EC, for either wet or dry soil.