Identification of iron in Earth analogues of Martian phyllosilicates using visible reflectance spectroscopy: Spectral derivatives and color parameters

A range of phyllosilicate compositions have been detected spectroscopically on Mars, but the largest fraction by far corresponds to clay minerals rich in Fe and Mg. Given that most of our understanding of Martian clays comes from remote sensing data, it is critically important to explore the details of how compositional variation affects spectral features of phyllosilicates. The greatest efforts have focused so far on near-infrared (NIR) spectroscopy. Recently, ambiguities have been detected in the NIR spectra of 2:1 phyllosilicates with intermediate FeeMg content that preclude mineral and chemical discrimination. Such ambiguities highlight the relevance of exploring the visible spectral range as a complementary tool to characterize Martian phyllosilicates precisely. This article reports the investigation of laboratory reflectance spectra (330–800 nm) from 34 Earth analogues of Martian phyllosilicates with a wide range of MgeFe composition, including nontronite, celadonite and saponite end-members, as well as interstratified glauconite-nontronite, talc-nontronite, and talc-saponite. The spectra indicated the presence of Fe(III) by absorption modulations and a decrease in total reflectance, especially in samples with tetrahedral Fe(III). Absorption bands at 370 and 420 nm were diagnostic of octahedrically and tetrahedrally coordinated Fe(III), respectively. Band amplitudes in the second derivative of the Kubelka-Munk function correlated positively with Fe(III) content (R2 > 0.8). Standard color analyses of the visible reflectance spectra under the CIE illuminant D65 indicated that the CIELAB color parameter a*10 was positively correlated with tetrahedral Fe(III), b*10 was positively correlated with octahedral Fe(III), and L*10 was negatively correlated with Fe(III) in both structural sites. Because Fe(II) was in relatively low amount, it did not provide clear spectral evidence. Multiple regression models using the amplitude of the diagnostic absorption bands predicted well absolute Fe content in the phyllosilicates (R2=0.89) and the ratio Fe/(Fe+Mg+Al) (R2=0.84). CIELAB color parameters improved the prediction of total Fe (R2=0.92) and the ratio Fe/(Fe+Mg+Al) (R2=0.93). Application of these analyses to Martian data has challenges set by Fe oxide dust coating and spatial and spectral resolution. However, these results mark an avenue to develop testable tools using visible-wavelength spectral data from both satellite and lander probes to help establishing Fe content and mineral identification of Martian phyllosilicates

Biocrust cover and successional stages influence soil bacterial composition and diversity in semiarid ecosystems

Biocrusts are an important drylands landscape component, which enriches the upper millimeters of the soil with organic matter and initiates biogeochemical cycles. However, little is known about the influence of biocrusts on soil bacterial community structure and diversity. Different biocrust types representing a successional gradient were studied. This gradient, from the earliest to the latest successional stages, consisted of an incipient cyanobacterial biocrust < mature cyanobacterial biocrusts < biocrust dominated by the Squamarina lentigera and Diploschistes diacapsis lichens < Biocrust characterized by the Lepraria isidiata lichen. Moreover, in each biocrust type, four different percentages of biocrust cover were also selected. Soil diversity gradually increased with biocrust successional stage and percentage of biocrust cover. The biocrust cover had an important role in the total abundance of bacteria, generally increasing in soils colonized by the highest percentages of cover. Biocrust successional stage was the most important factor, significantly influencing 108 soil bacteria genera, whereas biocrust cover showed significant differences in only 10 genera. Principal Component Analysis showed contrasting microbial composition across the biocrust successional gradient. Some bacterial taxa were dominant in the soil colonized by different biocrust types. Thus, Leptolyngbya, Rubrobacter, Solirubrobacter, Geodermatophilus, etc., were more abundant in incipient cyanobacteria; Nostocales, Chroococcidiopsaceae, Coleofasciculaceae etc., under mature cyanobacterial biocrusts; Truepera, Sphingobacteriaceae, Actinophytocola, Kribella, etc., below the S. lentigera and D. diacapsis community, and Bryobacter, Ohtaekwangia, Opitutus, Pedosphaeraceae, etc., in soils colonized by L. isidiata. Several soil bacteria taxa showed significant correlations (p < 0.05) with chemical soil properties (pH, total nitrogen, total organic carbon, available phosphorous and electrical conductivity). We discuss the role of biocrusts influencing these chemical soil parameters, including the presence of certain metabolites secreted by biocrusts, and also their effects on soil moisture and several physical soil features, as well as their association with different microclimates, all of which could favor a more selective environment for certain bacteria

Pedogenic information from fine-sand. A study in Mediterranean soils

The fine sand fraction (50–250μm) of Mediterranean soils from southern Spainprovides valuable information on soil genesis and the origin of their parentmaterials. This study considers the whole fine sand and heavy fine sand(ρ> 2.82 g cm−3) of Luvisols, Calcisols and Fluvisols, which form achronosequence (ages from 600 to 0.3 ka) of the River Guadalquivir terrace sys-tem. Advanced techniques (X-ray diffraction, inductively coupled plasma massspectrometry, inductively coupled plasma atomic emission spectroscopy, vari-able pressure scanning electron microscope with an energy dispersive X-rayspectroscopy system and Raman analysis) were employed. Inheritance is theprincipal pedogenic process. The whole fine sand consisted of carbonates (cal-cite and dolomite), tectosilicates (quartz, K-feldspar and plagioclases),phyllosilicates (illite/moscovite, biotite, Na-mica, chlorite, kaolinite, inter-stratified vermiculite-chlorite, vermiculite-illite and smectite-illite) and ironoxides (goethite and haematite). The minor minerals (rutile, anatase, ilmenite,zircon, staurolite, monazite, barite, apatite, andalusite, garnet and titanite) areconcentrated, also through inheritance, in the heavy fine sand. However, thereis also substantiated evidence for neoformation of rutile in these soils, neverreported previously. In addition, we report that (a) the geochemical indices cal-culated in fine sand (SiO2/CaO, Chemical Index of Weathering (CIW),Weathering Index of Parker (WIP), Weathering Index (WI), Base DepletionIndex (BDI), Weathering Ratio (WR) and Sr/Zr) are closely related to soil age,allowing chronofunctions to be established, and (b) geochemical indices pro-vide information on the origin of soils and permit the establishment of a“criti-cal point”corresponding to“time zero;”that is, the start of pedogenicalteration of the parent materia

Estimating the mass wetness of Spanish arid soils from lightness measurements

The colour of a soil changes with its water content. This paper investigates the ability of spectrophotometric colour measurement to predict soil mass wetness (w). We looked at the CIELAB parameters (L⁎, C⁎ab, hab) and spectral profile of 76 A soil-horizons from south-eastern Spain to (i) group them by colour, (ii) calibrate within each group the relationships between water content and colour in disturbed and undisturbed samples, and (iii) test the validity of predictive models. Four groups of differently coloured soils were selected from the reflectance curves. Models constructed only with L⁎ (lightness) from the dryness state to the water content at − 33/− 10 kPa explained the greatest variation in w (R2 = 0.77–0.97), regardless of the soil colour or sample type. The decrease in soil lightness with increasing water content was noted mainly at − 1500 kPa, − 400/− 100 kPa, and − 33/− 10 kPa potentials. At intermediate potentials, however, L⁎ did not strongly correlate with w, especially in undisturbed samples, which showed a greater colour variability. Although the predictive models did not give estimates of w with high enough precision (mean relative errors 25.3–56.6%), the measured values below − 1500 kPa, between − 1500 and − 100 kPa, and above − 100 kPa were predicted within the same interval of water potential. The results indicate that predictions of the dryness condition, presence of plant-available water and wetness near to field capacity, but not the specific water content, can be made with reasonable confidence in any soil by using the models calibrated in other soil of similar colour

Construcción de un sistema de información y de ayuda a la decisión mediante lógica difusa para el cultivo del olivar en Andalucía

In Southern Spain, olive (Olea europaea L.) growing is an important part of the economy, especially in the provinces of Jaén, Córdoba and Granada. This work proposes the first stages of an Information and Decision-Support System (IDSS) for providing different types of users (farmers, agricultural engineers, public services, etc.) with information on olive growing and the environment, and also assisting in decision-making. The main purposes of the project reported in this paper are to process uncertain or imprecise data, such as those concerning the environment or crops, and combine user data with other scientific-experimental data. The possibility of storing agricultural and ecological information in fuzzy relational databases, vital to the development of an IDSS is described. The information will be processed using knowledge extraction tools (fuzzy data-mining) that will allow rules on expert knowledge for assessing suitability of land to be developed and making thematic maps with the aid of Geographic Information Systems. Flexible querying will allow the users to collect information interactively from databases, while user information is constantly added. Flexible querying of databases, land suitability and thematic maps may be used to help in decisionmaking.El cultivo del olivo (Olea europaea L.) tiene una enorme importancia económica en la zona sur de España y concretamente en las provincias de Jaén, Córdoba y Granada. En este trabajo se propone la construcción de un sistema de información y ayuda a la toma de decisión (IDSS) que permita en el futuro a distintos tipos de usuarios (agricultores, agrónomos, administraciones públicas, etc.) obtener y manejar información sobre el cultivo de olivar y el soporte ambiental del mismo, así como ayudar en la toma de decisiones. Los principales objetivos desarrollados en este trabajo son el tratamiento de datos inciertos e imprecisos, como es el caso de la información ambiental y sobre cultivos, y la fusión de datos sobre cultivo y otros de carácter científico-experimental. Se describe la posibilidad de almacenar la información de carácter agronómico y ecológico en bases de datos relacionales, que es vital para el desarrollo de un IDSS. La información será procesada a través de herramientas de extracción de conocimiento (minería de datos difusa) y permitirá sobre la base del conocimiento experto el desarrollo de reglas para la clasificación de aptitud del terreno y para la obtención de mapas temáticos con la ayuda de Sistemas de Información Geográfica. La consulta flexible permitirá a los distintos usuarios la consulta interactiva de toda la información almacenada en las bases de datos, así como una implementación constante de las mismas. La consulta flexible de bases de datos, la idoneidad de los terrenos y los mapas temáticos pueden ser de gran utilidad en la toma de decisiones.This work is part of the research projects 1FD97-0244-CO3-2 (financed with FEDER funds) and CGL2004-02282BTE (Spanish Ministry of Education and Science)

Short-term effects of spent coffee grounds on the physical properties of two Mediterranean agricultural soils

We investigated the short-term effects of spent coffee grounds on the physical properties of two Mediterranean agricultural soils (Calcisol and Luvisol). The in vitro assay was performed with two spent coffee grounds doses (60 and 240 Mg ha-1), two incubation times (30 and 60 days) and two modalities: with and without lettuce seedlings (Lactuca sativa var. longifolia). Spent coffee grounds addition increased water retention at -33 and -1500 kPa, and decreased bulk density and plant-available water content. With spent coffee grounds, the percentage of macroaggregates increased, the percentage of meso- and microaggregates decreased and the structural stability of all types of aggregates increased. The stereomicroscopy images showed that: the structural aggregates were rounded, the porosity increased by 316%, the structure was ordered into smaller aggregates, the incorporation of spent coffee grounds particles could occur in intraped cracks and spent coffee grounds particles could act as a binding agent. Scanning electron microscopy also showed that spent coffee grounds particles interacted with mineral particles and integrated into soil structure; moreover, fungal hyphae also developed on many spent coffee grounds particles. If spent coffee grounds effects are compared with those described in the literature for other organic amendments, the same trend was observed in most of the soil physical properties although with a different intensity, principally with regard to structural stability.This work was supported by project AGL2014-53895-R from the Spanish Ministry of Economy and Competitiveness, by the European Regional Development Fund (FEDER) and by project CGL2016-80308-P from the Spanish Ministry of Science and Innovation (2015-2018)

Caracterización de la capacidad agrológica de los suelos del sector noroeste de Sierra Nevada (Granada)

Se emplea el esquema del Ministerio de Agricultura Español denominado: "Caracterización de la Capacidad Agrológica de los Suelos de España a escala 1 :50.000", para interpretar desde un punto de vista agronómico la cartografía de suelos del Sector Noroeste de Sierra Nevada. Las subclases de capacidad agrológica presentes en el área son: IVs, VIw, VIs, Vlc, Vle, VIIe, VIIle. Las clases dominantes son la VII y la VIII, ya que las pendientes de casi toda el área superan el 30 OJo. Le sigue en abundancia la subclase Vle, localizada en las pendientes de la clase D (valor medio de 22 a 23%). El resto de las clases y subclases son minoritarias y aparecen de forma puntual. Las limitaciones de mayor importancia en el establecimiento de las clases de capacidad son en primer lugar, la pendiente y la temperatura y en segundo lugar la pedregosidad superficial, la rocosidad superficial y el exceso de humedad en el suelo. Estos resultados indican que los cultivos agrícolas (sólo posibles en los suelos de la clase IVs) se restringen a pequeñas zonas diseminadas por todo el área y que la mayor parte tiene vocación forestal, pastoral y de reserva natural.The soil map of the Northwest area of the Sierra Nevada it has been interpreted for agronomic purposes by the Spain Agricultural Ministry Scheme, called "Agrological Capacity characterization of the Soil of the Spain, Scale 1.50.000" . In this area the agrological capacity subclasses are: IVs, VIIw, VIs, VIc, Vle and VlIIe. The dominant classes are VII and VIII because the medium slopes are greater than 30 OJo. The subclasse Vle is frequent also (22-23 % of slope). Another subclasses and classes are in minor quantities. The slope and the mean anual temperature are the most important restraints. The surface stoniness, the surface rockiness and the soil moisture regime are important also. AH the results point out the suitability of this area for forestry, grassland and wildlife conservation

Los inceptisoles y entisoles del sector occidental de la Sierra de Gador (Almería)

En el presente estudio se analizan los caracteres morfológicos, las propiedades fisico-quírnicas y la clasificación a nivel de subgrupo de los suelos presentes en el Sector Occidental de la Sierra de Gádor, que pertenecen a los órdenes Entisol e Inceptisol de la taxonomía americana de suelos. Son suelos desarrollados sobre materiales calizo-dolomíticos "in situ" o coluvionados. La altitud oscila entre 400 y 2. 124 m. La pendiente es muy variable, desde llano o casi llano a fuertemente escarpado. Soportan un matorral degradativo y pinares de repoblación. El régimen de humedad es Xérico y el de temperatura Térmico hasta los 1.000 m. y Mésico por encima de esta cota. Los cinco perfiles muestreados se han clasificado como Xerorthent típicos y dos como Xerochrept calcixeróllicos. Los cinco perfiles muestreados se han clasificado, tres como Xerorthent típidiados, como respuesta a diferencias en evolución edáfica, exceptuando aquellos que dependen estrechamente del elevado contenido en bases alcalino térreas del material de origen. El carácter común más relevante es la carencia de epipedón móllico, provocada por la degradación del horizonte orgánicomineral al destruir la vegetación climácica.Morphological and physicochemical properties of five Entisols and Inceptisols from west area of Sierra de Gádor are studied. "Soil Taxonomy" is the employed classification. Most soils are developed 'in situ' or upon colluvium derived from limes tony and dolomitic marbles. 400 to 2.124 m. is the range of altitude. The slopes are variables. The vegetation is a degradated brushwood and reforestated pine woods. The moisture regime is Xeric; the temperature regime changes from Termi to Mesic at 1.000 m. The soils are tipic Xerorthents (three profils) and calcixerollic Xerochrepts (two profils). The analytical and morphological characteristics are variables owing to differencies in pedological evolution within the studied soils. But there are two characteristics in common: the high quantities of the alcalinoterreal bases controled by the parent material, and the absence of mollic epipedón owing to the degradation of climatic vegetation and parallel degradation or /and destruction of mineral organic soil horizons

Soil quality and organic carbon ratios in mountain agroecosystems of South-east Spain

Soil physical and chemical characteristics as well as climatic and geomorphological factors have been determined in 68 sites of a mountain calcimorphic ecosystem (Sierra María-Los Vélez Natural Park, Almería) in Southeastern Spain. Land use and vegetation were natural pine forest, evergreen oak forest, reforested pine forest of different ages, bush, juniper forest, and olive, almond and cereal crops under conventional tillage. By using multivariate data treatments, 17 soil variables were processed. A large part of the total variability was controlled by local topographical features through their effect on moisture retention and vegetation. Most characteristics were significantly correlated with total organic C (mean = 28.5 ± 4.6 g kg− 1), which demonstrates the central role of the organic matter in the functioning of the whole ecosystem. New soil quality descriptors consisting of ratios to soil organic carbon were obtained, informing about the specific activity (per C unit) or performance of the organic matter, independently of its total content. When soil data are directly processed by using principal component analysis, we found a set of high quality soils under natural and old reforested forests, where environmental services provided by soil depend on the high levels of quality descriptors related to organic carbon, e.g. cation exchange capacity (CEC), total porosity, or aggregate stability. When variables such as CEC, porosity and aggregate stability are calculated as ratios to the total organic carbon, a new classification pattern is obtained, allowing to detect soils with organic matter of high maturity which in general do not coincide with soils with high organic matter content. The results suggest the assessment of soil quality based on ratios informing on the organic matter performance should be emphasized as an alternative to direct descriptors based on the total organic carbon content

Biocrust cover and successional stages influence soil bacterial composition and diversity in semiarid ecosystems

Biocrusts are an important drylands landscape component, which enriches the upper millimeters of the soil with organic matter and initiates biogeochemical cycles. However, little is known about the influence of biocrusts on soil bacterial community structure and diversity. Different biocrust types representing a successional gradient were studied. This gradient, from the earliest to the latest successional stages, consisted of an incipient cyanobacterial biocrust < mature cyanobacterial biocrusts < biocrust dominated by the Squamarina lentigera and Diploschistes diacapsis lichens < Biocrust characterized by the Lepraria isidiata lichen. Moreover, in each biocrust type, four different percentages of biocrust cover were also selected. Soil diversity gradually increased with biocrust successional stage and percentage of biocrust cover. The biocrust cover had an important role in the total abundance of bacteria, generally increasing in soils colonized by the highest percentages of cover. Biocrust successional stage was the most important factor, significantly influencing 108 soil bacteria genera, whereas biocrust cover showed significant differences in only 10 genera. Principal Component Analysis showed contrasting microbial composition across the biocrust successional gradient. Some bacterial taxa were dominant in the soil colonized by different biocrust types. Thus, Leptolyngbya, Rubrobacter, Solirubrobacter, Geodermatophilus, etc., were more abundant in incipient cyanobacteria; Nostocales, Chroococcidiopsaceae, Coleofasciculaceae etc., under mature cyanobacterial biocrusts; Truepera, Sphingobacteriaceae, Actinophytocola, Kribella, etc., below the S. lentigera and D. diacapsis community, and Bryobacter, Ohtaekwangia, Opitutus, Pedosphaeraceae, etc., in soils colonized by L. isidiata. Several soil bacteria taxa showed significant correlations (p < 0.05) with chemical soil properties (pH, total nitrogen, total organic carbon, available phosphorous and electrical conductivity). We discuss the role of biocrusts influencing these chemical soil parameters, including the presence of certain metabolites secreted by biocrusts, and also their effects on soil moisture and several physical soil features, as well as their association with different microclimates, all of which could favor a more selective environment for certain bacteria