Suchergebnisse

5 tablas, 1 figura. ; Deciduous oak coppices (Quercus pyrenaica Willd.) of the "Sierra de Gata" mountains (central western Spain) are located on acid rocks and subjected to annual rainfall higher than 700 mm year−1. Accordingly, the soils are acidic (soil pH is often below 5.0) and feature the presence of Mn2+ and Al3+ in the exchangeable complex. The aim of the present study was to assess the response of these soils to the addition of a lime residue from a sugar beet mill to reach pH values close to 7.0 and 6.0 with in situ and in vitro experiments, respectively. Initially, the quality of the lime by-product was evaluated, which showed content close to 75 % CaCO3. Based on that analysis, calculations were accomplished to determine the dose of lime by-product necessary for achieving the targeted soil pH. We first performed an in vitro liming experiment, incubating 0.50 kg soil (0–20 cm layer) with 23.92 g CaCO3 kg−1 soil (20 °C and soil moisture equivalent to that of field capacity). Subsequently, another experiment was done adding an equivalent quantity of sub-product in lieu of the pure CaCO3; the factors monitored were: soil pH, exchange acidity, CEC, and exchangeable bases, every 24 h. The in situ experiment was performed in a forest plot located in Western Spain (Navasfrías), liming with 16.0 Mg DM by-product ha−1 (September 1999). Soil samples (two depths: 0–10 and 10–20 cm) were taken from both the control and the experimental forest plots for monitoring the liming effect. Sampling dates were September and December 1999; June 2000, January, June and September 2001; October 2002 and 2003, and March 2005). The dissolution of the lime by-product at the laboratory was almost immediate, but the effects in the field occurred approximately 2 years after initial liming, since lime dissolution depends on both the amount and distribution of rainfall and, also, on the application procedure. ; This work was possible thanks to the support received from the European Union (PROTOS/TERI Project) of the Spanish Ministry of Education and Junta de Castilla y León (Spain). ; Peer reviewed

9 P. ; Soils located at the Mexican Trans-volcanic Belt (MTB) have a worrying degree of degradation due to inappropriate management practices. Early indicators of soil changes are very useful to alert about negative impacts of wrong managements on these volcanic soils. The aim of this work was to evaluate the short-term effects (4 years) of different agricultural practices on soil organic matter (SOM) quality and to validate the potential of the selected biochemical properties as optimal early indicators of soil quality in Mexican cultivated Acrisols. During 2002–2005 four agronomic management systems: conventional (Tc); improved conventional (Ti); organic (To) and fallow (Tf) were assayed in plots located at the MTB. An uncultivated soil under grass cover (Sg) was used as reference. Soil samples were collected at 0–10 cm depth and were analysed chemically (soil organic C, total N, water-soluble C and humic C), and biochemically (total and extra-cellular enzyme activity). After 4 years, soil organic C, total N, water-soluble C and dehydrogenase activity had higher values in To, followed by Ti treatment. A similar response pattern was observed in the extra-cellular enzyme activity. The highest total enzyme activity was found in Sg, followed by Ti and To treatments, and the lowest values appeared in Tc and Tf. To and Ti increased SOM contents of the degraded Acrisols studied, while Tc and Tf managements decreased the quality of these soils. The results showed that the assayed soil enzymes can be used as indicators of quality changes of these Mexican volcanic soils. ; The authors thank the European Union for supporting the REVOLSO Project (INCO-DEV Program) and the Spanish Ministry of Education & Science. Thanks are also due to C. I. Hidalgo (Colegio de Postgraduados de Montecillo, Mexico) for the mineralogical identification of soil clays analysis and J. Padilla (Colegio de Postgraduados de Montecillo, Mexico), C. Macci, S. Doni and laboratory technicians from the Istituto per lo Studio degli Ecosistemi (CNR, Italy) for theirs lab assistance. ; Peer reviewed

9 p. ; The aim of this study was to determine the effect of land-use and forest cover depletion on the distribution of soil organic carbon (SOC) within particle-size fractions in a volcanic soil. Emphasis was given to the thermal properties of soils. Six representative sites in Mexico were selected in an area dominated by Andosols: a grassland site, four forested sites with different levels of degradation and an agricultural site. Soils were fractionated using ultrasonic energy until complete dispersion was achieved. The particle-size fractions were coarse sand, fine sand, silt, clay and particulate organic matter from the coarse sand sized fraction (POM-CS) and fine sand (POM-FS). Soil organic carbon decreased by 70% after forest conversion to cropland and long-term cultivation; forest cover loss resulted in a decrease in SOC of up to 60%. The grassland soil contained 45% more SOC than the cropland one. Soil organic carbon was mainly associated with the silt-size fraction; the most sensitive fractions to land-use change and forest cover depletion were POM followed by SOC associated with the silt and clay-sized fractions. Particulate organic matter can be used as an early indicator of SOC loss. The C lost from the clay and silt-sized fractions was thermally labile; therefore, the SOC stored in the more degraded forest soils was more recalcitrant (thermally resistant). Only the transformation of forest to agricultural land produced a similar loss of thermally stable C associated with the silt-sized fraction. ; The authors gratefully acknowledge the help of two anonymous reviewers, R. Vela´ zquez-Dura´ n for his assistance in fieldwork, H. Ferreira and A. Valencia for their technical assistance. In addition, we thank the European Union for the support of the REVOLSO Project (INCO Program, ICA4- CT-2001-10052), the Spanish Ministry of Education and Science and UNAM (SDEI-PTID-02) that partially financed the Project. ; Peer reviewed

We compare the silicophytolith record of current soils and Holocene palaeosols from two sedimentary sequences in a region between the Chaco-Pampean Plain and the Puna (Tolombón section in Santa María Valley, and Tafí del Valle section in Tafí Valley), NW Argentina. These two geographic areas are separated by the Aconquija-Cumbres Calchaquíes ranges, a climatic barrier to the wet Atlantic winds. These sequences contain volcanic ash deposits recording two large eruptions occurred during Holocene in the Southern Puna in the Central Volcanic Zone of the Andes, from the Cueros de Purulla volcano (ca. 7820 BP) and the Cerro Blanco Volcanic Complex (ca. 4200 cal BP). These ash-fall deposits buried soils and preserved their silicophytolith record, allowing the use of this palaeoenvironmental proxy to clarify the vegetation prior these two volcanic events. The silicophytolith assemblages yield evidence for a mega/mesothermal xerophytic grassland when Tolombón palaeosol was formed, similar to the present-day environment in the Santa María Valley, with presence of C4 grasses (Chloridoideae and Panicoidae). Instead, the climate was cooler and wetter ca. 4200 cal BP than currently in the Tafí Valley, increasing over time aridity and abundance of C4 grasses (Chloridoidae, Panicoideae), and decreasing the quantity of C3 grasses (Pooideae). Prehistorical and historical land use also contributed to this change. The impact of these large volcanic ash-falls on vegetation did not translate in an abrupt change on phytodiversity. Results point out a stable arid environment during Holocene in the Santa María Valley whereas the Tafí Valley was more sensitive to environmental changes due to its location in the eastern slopes of Aconquija-Cumbres Calchaquíes ranges, more exposed to the wet Atlantic winds. ; MINECO, Spain, CGL2011-23307, Project QUECA Agencia-Ministerio de Ciencia y Técnica, Argentina, PICT-1583-2013 Universidad Nacional de Mar del Plata, EXA 643/13 Canary Islands Government, ULPGC, Research Consolidated Group GEOVOL Generalitat de Catalunya, 2017 SGR 1494, Research Consolidated Group GEOPAM ; Peer reviewed