J. Navarro-Pedreño

Soil organic matter and aggregates affected by wildfire in a Pinus halepensis forest in a Mediterranean environment

et Abstract. Three Mediterranean soils located in the north of the Province of Alicante (Spain) were studied for a year after a forest fire. The percentage of water-stable aggregates (between 0.2 and 4 mm) and organic matter content were measured. Microaggregates (< 0.2 mm) were observed using electron microscopy. The results showed the importance of type of forest fire on soil organic matter and aggregates. Soil structure was more affected by surface fire (which affects mainly brushwood and soil surface) than crown fire (which burns the tops of trees and some brushwood). Accumulation of organic matter from burnt trees and brushwood in areas affected by crown fire and alterations in organic matter content through the soil profile were observed. Surface forest fire affected soil structure more negatively than crown fire as observed using electron microscopy. Soils affected by surface fire may be more easily eroded and recovery of vegetation may be delayed because of effects on soil structure. Organic matter content through the soil profile comparing burnt and adjacent unburnt soil could be used to determine the type of fire. Additional keywords: Forest fire; calcareous soil; Spain; Mediterranean type-areas.

Different Patterns of Aggregate Stability in Burned and Restored Soils

The merits of soil aggregate stability determination by rainfall simulator method were studied. This method is based on the supposition that in standard conditions aggregate breakdown is proportional to the kinetic energy of the rainfall applied. We compared three experiments using four different soils. Two of the experiments were in controlled conditions and the other at field conditions. In one of the laboratory experiments we applied sewage sludge to a degraded soil from a semiarid climate. In the other laboratory experiment a forest soil was heated to 200°C, 400°C and 600°C, and we studied the effect of heat and loss of organic matter in soil aggregation. In the third experiment, carried out in the field, we studied the response of two soils affected by forest fire in different intensities. Aggregate stability percentage and organic matter content of soils were determined to establish trends between these parameters. Aggregate stability in soils subjected to rainfall simulation was used as an indicator for potential degradation or restoration processes of the soils. In some burned soils positive and negative relationships were obtained between aggregate stability percentage and organic matter soil contents due to heat-aggregation processes. It showed that the aggregate stability percentage method based on disruptive energy of a rainfall simulator could not always be used as an index of degradation or restoration of soils or both.

Land-Cover Phenologies and Their Relation to Climatic Variables in an Anthropogenically Impacted Mediterranean Coastal Area

Abstract: Mediterranean coastal areas are experiencing rapid land cover change caused by human-induced land degradation and extreme climatic events. Vegetation index time series provide a useful way to monitor vegetation phenological variations. This study quantitatively describes Enhanced Vegetation Index (EVI) temporal changes for Mediterranean land-covers from the perspective of vegetation phenology and its relation with climate. A time series from 2001 to 2007 of the MODIS Enhanced Vegetation Index 16-day composite (MOD13Q1) was analyzed to extract anomalies (by calculating z-scores) and frequency domain components (by the Fourier Transform). Vegetation phenology analyses were developed for diverse land-covers for an area in south Alicante (Spain) providing a useful way to analyze and understand the phenology associated to those land-covers. Time series of climatic variables were also analyzed through anomaly detection techniques and the Fourier Transform. Correlations between EVI time series and climatic variables were computed. Temperature, rainfall and radiation were significantly correlated with almost all land-cover classes for the harmonic analysis amplitude term. However, vegetation phenology was not correlated with climatic variables for the

The Influence of Soil Properties on the Mobility of Metals Following a Single Application of Polluted Sewage Sludge to Seventy Agricultural Topsoils: A Laboratory Column Study

The main aim of this study was to examine the influence of soil properties on the leaching of Cd, Cr, Cu, Ni, Pb, and Zn following the application of polluted sewage sludge to contrasting topsoils. Seventy agricultural soil samples from different parts of Spain were amended with a single dose of sewage sludge (equivalent to 50 t dry weight ha−1) and a column study was performed under controlled conditions. After two, four, and six months of incubation, 283 ml of distilled water (equivalent to a rainfall event of 25 l m−2) was applied. The leachates were then collected and analyzed for metals. For all of the soils considered, the pH was the most important parameter for the control of mobility metals (except for Cu, determined by the sand and soil organic carbon and only to a lesser extent by the soil pH r2 = 0.604, p < 0.001) and was negatively related to all of the studied metals. For Pb and Zn, soil pH was the single soil property explaining their mobility (r2 = 0.411, p < 0.001 for Pb; r2 = 0.713, p < 0.001 for Zn) while for Cd, Cr and Ni, EC, sand and silt also appeared in the statistical models (r2 = 0.753, p < 0.001 for Cd; r2 = 0.366, p < 0.001 for Cr; r2 = 0.784, p < 0.001 for Ni). In the basic soils, soil texture was the most important soil property controlling the mobility of metals (except for that of Pb, which it only weakly predicted). For the acidic-neutral soils, the soil pH was the most important soil property controlling metal mobility (except for that of Cr, which was mainly determined by the pseudo-total Cr content).

Multi-resolution and temporal characterization of land-use classes in a Mediterranean wetland with land-cover fractions

Four different methods for analysing land-use and land-cover fractions at multiple scales, namely composite operator, t-test, Dutilleul’s modified t-test and ternary diagrams of physical models for process pathways, were applied to sets of multi-resolution images in order to evaluate the usefulness of coarse-resolution satellite data (e.g. the Moderate Resolution Imaging Spectroradiometer; MODIS) in obtaining similar results to those obtainable with moderate-resolution satellite data (e.g. Landsat). A spectral-mixture model based on three endmembers (soil, vegetation and water) was used to determine the land-cover fractions of the main land-use classes of a wetland in southeast Spain. The land-use map was produced by applying the unsupervised k-means classification method to the moderate-resolution image. Spatial and temporal changes in the mixture fractions at multiple resolutions and their corresponding land-cover fraction maps were assessed. Three different t-tests (paired-samples, independent-samples and Dutilleul’s modified t-tests) were used to evaluate the effects of pixel aggregation on land-cover fractions and land-use maps in terms of surface-area estimations. Ternary plots of land-use classes characterized by land-cover fractions were used to visualize environmental processes pathways describing temporal changes in the landscape. The results obtained with moderate- and coarse-resolution data were not significantly different from each other. Land-use and land-cover surface-area estimations were not significantly different between Landsat moderate-resolution (30 m) and Landsat resampled coarse-resolution (300 m) data. Spatial autocorrelation had an important effect when comparing Landsat moderate-resolution (30 m) with MODIS coarse-resolution (250 m) data. In order to minimize these effects Dutilleul’s modified t-test was applied for the comparison of Landsat with MODIS image data. However, this test did not reveal significant differences between both datasets, whereas with the ordinary t-test, significant differences were found, which suggest the existence of a bias by spatial autocorrelation that must be taken into account for up-scaling or down-scaling of remote-sensing data. The results suggest the possibility of using coarse-resolution images (MODIS) to characterize environmental changes with a similar accuracy to those of moderate-resolution images (Landsat), as long as potential spatial autocorrelation effects are taken into account. This finding indicates that a substantial reduction in the costs of conducting wetland management and monitoring tasks can be achieved by using free or low-cost coarse-resolution satellite images.

Spectral indices for the detection of salinity effects in melon plants

Water scarcity and soil salinization affect large semiarid agricultural areas throughout the world. The maintenance of agricultural productivity implies better agricultural practices and a careful selection of resistant crops. A proper monitoring of the physiological status of plants can lead to better knowledge of plant nutritional requirements. Visible and near-infrared (VNIR) radiometry provides a non-destructive and quantitative method to monitor vegetation status by quantifying chemical properties using spectroscopic techniques. In this study, the capability of VNIR spectral measurements to detect salinity effects on melon (Cucumis melo L.) plants was tested. Melon plants were cultivated under multiple soil salinity conditions (electrical conductivity, (EC)1:5: 0.5, 1.0 and 2.5 dS m-1). Spectral data of leaves were transformed into vegetation indices indicative of the physiological status of the plants. The results showed differences for N (p < 0.05), K and Na content (p < 0.01) due to salinity suggesting different degrees of salt stress on the plants. Specific leaf area increased with salinity levels (p < 0.001). The capabilities of VNIR radiometry to assess the influence of soil salinity on melon physiology using a non-destructive method were demonstrated. A normalized difference vegetation index (NDVI750-705), and the ratio between water index (WI) and normalized difference vegetation index (WI/NDVI750-705) showed significant relationships (p < 0.01) with the salinity. Therefore, this method could be used for in-situ early detection of salinity stress effects.

Movement Of Fe, Mn, Cu, And Zn In A Sewage Sludge-treated Soil

Restoration of degraded soils with organic wastes could be a feasible practice to minimise erosion in the Mediterranean area. Today the use of sewage sludge to improve the nutrient contents of a soil is a common practice, In order to study the mobility of some elements through the soil, we have designed an experiment that tries to reproduce the behavior of metals in the soil as a part of the nonsaturated zone, A controlled experiment in a greenhouse using soil columns was used. A calcareous soil from the south-east of Spain was amended with 30000, 90000 and 180000 kg sludge/ha. Iron, manganese, cupper and zinc were analyzed in soil samples at intervals of 15 cm of depth, during four months. Total, available, exchangeable and soluble forms of these micronutrients were analyzed. Positive effects of organic wastes application have been observed. We found that the use of sewage sludge as fertilizer of this calcareous soil increases the bioavailabilit y of iron, copper and zinc. There are not important displacements and movement of the micronutrients along the soil profile.

Mapping Soil Salinization of Agricultural Coastal Areas in Southeast Spain

Soil salt content is a key factor that determines soil chemical quality together with soil reaction, charge properties and nutrient reserves (Lal et al., 1999). An adequate salt supply is essential for an optimum development of photosynthetic mechanism and other biochemical processes in plants (Sitte et al., 1994). Soil salt content constitutes an environmental problem when salt accumulation generates drastic changes in soil physical and chemical properties, adversely affecting soil productivity and plant growth (Richards, 1954; Qadir et al., 2000).

Risk areas in the application of sewage sludge on degraded soils in the province of Alicante (Spain).

Restoration of degraded soils with organic wastes could be a feasible practice to minimise erosion in the Mediterranean area, but this practice shows a risk of soil and groundwater pollution. Currently the use of sewage sludge to improve the nutrient contents of a soil is a common practice. The soil leaching in which a great amount of fertilizers is usually applied, favours the solubilization of inorganic compounds. In order to study the mobility of some of these elements through the soil, we have designed an experiment that tries to reproduce the behaviour of different compounds and heavy metals in the soil as a part of the non-saturated zone. A controlled experiment in a greenhouse using soil columns was used. A calcareous soil from the south-east of Spain was amended with 30000, 90000 and 180000 kg sludge/ha. Nitrate, nitrite, cadmium, and nickel were analyzed in soil samples at intervals of 15 cm of depth, during four months; also leachates were collected at the bottom of the columns and metals and nitrogen forms were thus analyzed. Total, available, exchangeable and soluble forms of these heavy metals were analyzed. We found high concentrations of nitrates and nitrites in leachates, which imply an important environmental risk. No important displacements of polluting metals were found along the soil profile.

Effects of Sewage Sludge Compost on Cynara cardunculus L. Cultivation in a Mediterranean Soil

ABSTRACT The aim of this study was to identify an optimal sewage sludge compost (SSC) application rate to cultivate Cynara cardunculus L. (cynara) in a Mediterranean soil. Five SSC treatments corresponding to 0, 2, 4, 6, and 8 kg compost/m2 (T0, T1, T2, T3, and T4, respectively) were applied to an agricultural plot (South-Eastern Spain). Twelve cynara plants per treatment were grown (January–June). SSC treatments enhanced Cox, Nk, Pburriel, Zn, and Fe. The optimal rates were found between T2 and T3. Cynara leaves’ elemental composition was scarcely affected by SSC. Only Fe increased, differing T2, T3, T4 plants (over 1000 mg Fe/kg) from T0 plants (701 mg Fe/kg). Cynara morphological traits were not affected by SSC treatments. Cynara results did not indicate a clear optimal SSC dose. However, applications between 4 and 6 kg of SSC/m2 are recommended in order to enhance soil organic matter and fertility, factors of special importance in Mediterranean environments.