Mobility of sulphate in experimentally acidified soils from Galicia (NW Spain)

Retention of S0₄ ^2? was investigated in Galician soils throughout an intense regime of acidification. Experiments consisted of the addition of an H2SO4 solution (pH 2.7) to columns of 6 soils of contrasting properties over 1, 2, or 5 months. Leachates were obtained continuously throughout the experiment for analysis, and analysis made of the solid fractions after 1, 2 or 5 months. The greatest capacities for retention of S0₄ ^2? were found in soil developed from serpentine and micaschist; the lowest in soils from granite, slate and sandy sediments. The surface horizons, especially those rich in organic matter, displayed low retention of 5042-. The amount of S0₄ ^2? adsorbed throughout the experiment depended on the content of crystalline forms of Fe and with the Fe and Al extracted with dithionite-citrate.The low retention of S0₄ ^2? in the organic horizons and the slightly negative relation with the organic matter suggest an inhibitory effect of the organic matter on the S0₄ ^2? retention process. Results of the study show, that under conditions of moderate acidity, SO₄ ^2? retention occurs in the form of adsorption; in strongly acidic conditions, the precipitation of aluminium-sulphate minerals may provide an additional retention mechanism.     

Expression of andic properties in soils from Galicia (NW Spain) under forest and agricultural use

The organic matter (OM) of soils with andic properties has long been considered highly stable because of the presence of Al–humus complexes and sorption of organic ligands onto amorphous compounds. In this study, we characterized soils under different land use regimes located within an amphibolitic massif close to Santiago de Compostela (Spain), where soils with andic properties are present. Slash and burn agriculture was a common practice in the area until the second half of the 20th century. Thereafter, modern agriculture was progressively introduced into the area (AGR soils), and the rest of the land was either reforested or abandoned (FOR soils). We found that the mean organic C content of AGR soils (48.7 g kg^?1) was ～ 50% that of FOR soils (94.2 g kg^?1). Mean soil pH was significantly greater (P < 0.05) in the AGR than in the FOR soils (4.95 compared with 4.63), which is attributed to liming and Ca‐phosphate fertilization of the former. Mean concentrations of the Al forms studied (extractable with CuCl₂, sodium pyrophosphate, ammonium oxalate, or NaOH) were significantly smaller (P < 0.01) in AGR (1.4, 4.9, 9.3, 11.0 g kg^?1, respectively) than in FOR soils (3.9, 10.2, 16.5, 17.9 g kg^?1, respectively). The results show the vulnerability of the OM and Al–humus complexes in these soils to modern agricultural practices, which has led to the attenuation – and in some cases even the disappearance – of andic soil properties in a relatively short time (< 30 years) following changes in land use/management. We propose the inclusion of the formative element ‘andic’ in the criteria for the definition of Umbrisol subunits; this would avoid the abrupt discontinuity observed in the current World Reference Base classification.     

Thermodynamic parameters of enzymes in grassland soils from Galicia, NW Spain

The thermodynamic parameters of the enzymes catalase, dehydrogenase, casein-protease, α-N-benzoyl-l-argininamide (BAA)-protease, urease, Carboxymethyl (CM)-cellulase, invertase, β-glucosidase and arylsulphatase, were investigated in grassland soils from a European temperate-humid zone (Galicia, NW Spain). The effect of temperature on enzyme activity was determined at 5, 18, 27, 37, 57 and 70 °C. The temperature-dependence of the rate of substrate hydrolysis varied depending on the enzyme and soil. In general, the soil containing the least amount of organic matter (OM) showed the lowest enzyme activity for all temperatures and enzymes, whereas soils with similar OM contents showed similar levels of activity for the entire temperature range. Temperature had a noteworthy effect on the activity of oxidoreductases. Product formation in the reaction catalyzed by dehydrogenase increased with increasing temperature until 70 °C, which was attributed to chemical reduction of iodonitrotetrazolium violet (INT) at high temperatures. Catalase activity was not affected above 37 °C, which may be explained either by non-enzymatic decomposition of hydrogen peroxide or by the fact that catalase has reached kinetic perfection, and is therefore not saturated with substrate.The Arrhenius equation was used to determine the activation energy (E_a) and the temperature coefficient (Q₁₀) for all enzymes. The values of E_a and Q₁₀ for each enzyme differed among soils, although in general the differences were small, especially for those enzymes that act on substrates of low molecular weight. In terms of the values of E_a and Q₁₀ and the differences established among soils, the results obtained for those enzymes that act on substrates of high molecular weight differed most from those corresponding to the other enzymes. Thus the lowest E_a and Q₁₀ values corresponded to BAA-protease, and the highest values to CM-cellulase and casein-protease. Except for catalase in one of the soils, the values of E_a and Q₁₀ for the oxidoreductases were similar to those of most of the hydrolases. In general, the effect of temperature appeared to be more dependent on the type of enzyme than on the characteristics of the soil.     

Effect of management and climate on biochemical properties of grassland soils from Galicia (NW Spain)

Biochemical properties are considered to be the best indicators available at present for assessing soil quality. However, there are still many gaps in our knowledge about how these properties are affected by abiotic factors and how these factors interact with soil management. With the aim of understanding how climate and soil management affect soil biochemical properties in grasslands soils from a temperate-humid area (Galicia, NW Spain), a total of 60 soils were analyzed for several microbial and biochemical properties. Grasslands were divided into groups according to the type of management applied (native compared with intensive) and to the climate in the area where they were sampled (Mediterranean subhumid with centroeuropean drift climate compared with Atlantic climate). We found that management had a greater influence on soil biochemical properties than climate. Altitude, which strongly influences climate in the region where the soils were analyzed, was found to be a significant factor that affected most soil biochemical properties. In conclusion, the results show that microbially-mediated processes are greatly affected by both, management and abiotic factors and that, for some properties (like net N mineralization and cellulase and casein-protease activities), abiotic factors can have an important influence on soil biochemical properties.     

Response of some soils of Galicia (NW Spain) to H2SO4 acidification

This paper presents the results of an acidification experiment, consisting of seven consecutive equilibrations of repesentative soils of Galicia with a H₂SO₄ solution (pH 3). Different responses to soil acidification, such as SO₄ retention and cation release, were evaluated. In soils derived from gabbro and amphibolite, SO₄ retention and Al release were the principal acid neutralization mechanisms, whereas in soils derived from granite, schist, shale and sandstone Al release was the main process. The SO₄ retention was significantly correlated with Al and Fe extracted with dihionite-citrate-bicarbonate and crystalline Fe. The released base cations came mainly from exchange sites, though sometimes also from other sources, probably by mineral weathering. The major sources of Al in these soils were metalorganic complexes and weatherable minerals. Solutions with pHs close to 4 are in equilibrium with gibbsite, kaolinite, jurbanite and alunite; at lower pH values, with jurbanite and alunite.     

Pedological and geomorphological cycles in a catena of Galicia (NW Spain)

A catena developed on gabbro in Galicia, N.W. Spain, was studied. The methods utilized, consisting of macro- and microscopic mineralogical and morphological observation, allowed the identification of different features produced by the action of pedological and geomorphological processes. The application of Butler's K cycle concept allows a relative sequence of events to be established in which pedogenetic processes are integrated within the general framework of the evolutionary history of the slope. Five K cycles could be recognized, beginning with a phase of deep weathering and ending with the present phase of incipient soil formation. In between feature a.o. phases of solifluxion, the formation of an argillic horizon and the development of a stoneline.     

Andosols developed from non-volcanic materials in Galicia, NW Spain

A set of well-drained soils in Galicia, formed from gabbros, amphibolites and schists, with udic moisture and mesic temperature regimes, are studied. All but one of the surface horizons show an'exchange complex dominated by amorphous material'(ECDAM); consequently, most soils are classified as Andosols (FAO) or as different subgroups of Dystrandepts (Soil Taxonomy). The soils on gabbros and amphibolites frequently have'andic properties'so, following the ICOMAND proposals, five of the 12 soils studied may be characterized as Andisols. Many of the five soils have properties comparable to those of soils from volcanic areas, especially to those called'non-allophanic Andosols', which have an abundance of active-Al, mainly in the form of Al-humus complexes.     

Comparison of indirect methods for the determination of percent exchangeable aluminium in acid soils of Galicia (NW Spain)

Abstract

Ten easily determined soil parameters related to soil acidity were evaluated for their potential to provide simple, indirect estimates of the exchangeable aluminium percentage (PAL). These parameters were correlated with the PAL in 0.6N BaCl₂ extracts of soils collected from lime trials on 4 different parent materials. Six rates of lime (0, 0.75, 1.5, 3, 6, 12 t/ha) were added 3–4 years prior to collection of the samples. The soil parameters examined were the pH of soil suspensions with SMP, Woodruff and New Woodruff buffer solutions; the pH of 1, 5 and 10mM CaCl₂ and 0.6N BaCl₂ soil extracts, and the aluminium content of 1, 5 and 10mM CaCl₂ soil extracts. The best correlations with the exchangeable aluminium percentage for all soils considered, were those based on the aluminium content of the 5mM CaCl₂ extract (r=0.976, n=24) followed by the pH of the 0.6N BaCl₂ extract (r=0.945, n= 24). Both these methods are suggested as reliable indirect estimates of soil exchangeable alumimium percentage where availability of staff or equipment restrict direct determinations.     

Copper fungicide residues in Australian vineyard soils

Copper (Cu) concentrations were measured in Australian vineyard soils to assess the extent and magnitude of Cu accumulation resulting from the use of Cu-based fungicides and to indicate the likely risks to long-term soil fertility. Soil samples were collected from 98 vineyards across 10 grape-growing regions of Australia and analyzed for total Cu concentrations. Ninety-six percent of vineyards surveyed had elevated Cu concentrations in soil compared to the background Cu concentrations in nearby soil in its native state. Concentrations of total B, Co, Cr, Pb, and Zn were similar to background concentrations and below reported toxicity guideline values. Cu concentrations in Australian vineyard soils were generally much lower (6-150 mg kg (-1)) than those reported in the soils of vineyards in parts of Europe (i.e., 130-1280 mg kg (-1)). Concentrations of total Cu were generally below those concentrations reported to cause lethal effects to soil invertebrates; however, Cu exceeded concentrations known to cause sublethal effects (i.e., inhibit growth, affect reproduction, induce avoidance behavior) to those (or related) invertebrates.     

Aluminium Toxicity Risk for Pinus pinaster in Acid Soils (Galicia,NW Spain)

The influence of bedrock on aluminium toxicity and aluminium speciation in the soil solution was studied in four Pinus pinaster plots. Growth and biomass parameters in the acidic soils were also evaluated in relation to different Al toxicity indices. The plots were developed over slate, biotitic schist, mica schist and granite. Samples of rhizospheric and non‐rhizospheric soil, 1‐year‐old needles and roots were collected in each study plot. Total Al, reactive Al, acid‐soluble Al, non‐labile and labile Al and Al species (Al³⁺, Al‐OH, Al‐F and Al‐SO₄) were determined in soil solution. Reactive Al dominated over the acid‐soluble Al, and the non‐labile Al predominated over the labile Al in all soils, but particularly over mica schist. In the biotitic schist soil, the Al forms and total Al were lower, whereas concentrations were always higher over mica schist. The Al forms considered most toxic were Al³⁺ and Al‐OH, and Al concentrations were highest over slate and mica schist. Al toxicity indices in soil, needle and roots showed a risk of toxicity in mica schist, slate and granite. The stand site indices over slate and mica schist were lower, consistent with the high labile Al and Al³⁺ + Al‐OH in soil solution. Despite the high stand site index over granite, the growth efficiency was low, in accordance with very low ratios of Ca/Al in needles or fine roots. This confirmed the adaptation of maritime pine to granitic substrates. Copyright © 2016 John Wiley & Sons, Ltd.     

Geographic distribution and genetic resources of Dactylis in Galicia (northwest Spain)

Three Dactylis glomerata subspecies can occur in Galicia (Spain): subsp. glomerata, subsp. izcoi and subsp. marina. The second includes diploid and tetraploid populations adapted to acid soils. The third subspecies comprises natural tetraploid populations mainly on sea cliffs, with high digestibility. Dactylis taxonomy is difficult due to the existence of different ploidy levels and to free hybridization at the tetraploid level. This difficulty increases in Galicia, where there is a rich flora with relics and hybrids. The advance of human technology makes necessary the collection of natural Dactylis resources. In this paper, Dactylis distribution in Galicia is described. Tetraploid populations from subsp. izcoi have a wider ecological range than diploids (Galician diploid). These diploids and the subsp. marina are more widespread than formerly recognized. Morphologically, subsp. glomerata and izcoi are more similar than hitherto reported. It is suggested that the subspecies are adapted ecotypes which hybridize. They are useful genetic resources for pasciculture on acid soils and agroforestry.     

Smectite formation produced by weathering in a coarse granite saprolite in Galicia (NW Spain)

Weathering of a calcalkaline granite was studied in the south of Galicia (NW Spain) where the average annual precipitation is 1400 mm and the average annual temperature is 12°C. The original rock contains perthitic K-feldspars, plagioclases with inclusions of muscovite and opaque minerals, quartz and chloritized biotite, with apatite, zircon, sphene and opaques as accessories. In the saprolite the structure of the rock is preserved, the plagioclases show up to grade 4 weathering and the biotites, between 2 and 3. Weathering in quartz and potassium feldspar crystals is manifested only by fracturing. Biotite changes following the parallel linear model and its weathering products are interstratified biotite–vermiculite and iron oxyhydroxides. The plagioclases change to a microgranular material by pseudomorphic transformation. This material, which substitutes the plagioclase, includes small clearly delimited units which retain zones with the optic characteristics of muscovite. X-ray diffraction analyses of microsamples show that they are formed by 1:1 diocthaedral phyllosilicate, smectite and a small quantity of mica. From these facts we concluded that smectite is formed inside the plagioclase crystals, and probably originates from the inclusions of muscovite contained in these crystals, as it is suggested by the microscopic study which shows the increase in volume which occurs when the crystals of muscovite are transformed.     

Throughfall,runoff and soil erosion after prescribed burning in gorse shrubland in Galicia (NW Spain)

The first‐year effect of two different prescribed burning treatments on throughfall, runoff and soil erosion was evaluated in gorse shrubland (Ulex europaeus L.) in Galicia (NW Spain). The treatments compared were: intense burn, light burn and control (no burn). Accumulated annual throughfall represented between the 81 and 87 per cent of total rainfall in intensely burned and lightly burned areas, respectively, whereas in the unburnt areas it was 60 per cent. No significant differences between burning treatments were found for the annual throughfall. However, runoff was significantly greater in intensely burned plots (1·5‐times) than in lightly burned plots. Burning also resulted in a significant increase in runoff (between 2·5 and 1·7‐times, respectively) compared with controls. Total soil losses were small in all treatments, but the intense burn caused significantly greater soil erosion (5·8‐times) compared with the unburned areas. Soil losses after the light burn did not significantly differ from the control although they were higher (2·3‐times). The relationships obtained between erosion and several rainfall parameters were significantly different in burned areas compared to the control. The same response was observed for runoff. Annual erosion losses showed a strong dependence on percentage of bare soil even for small values of this variable. Litter thickness was also a very important variable influencing on erosion rates. This study indicated that by combining ignition techniques and high litter moisture content to maintain the percentage of bare soil below 85 per cent, soil erosion was low. Nevertheless, this result was constrained by the low rainfall that occurred during the study. Copyright © 2005 John Wiley & Sons, Ltd.     

Potassium fixation in suspensions of soils of Galicia (N.W. Spain)

Abstract

Potassium (K) fixation in soils treated with K‐rich fertilizer is important in limiting leaching of this ion, and thus the risk of high salinity in waters. We studied this capacity for aqueous suspensions of a group of soils of Galicia (N.W. Spain) and found that fixation increased with K dosage, increased slightly with contact time, and decreased with increasing temperature (between 3 and 40°C). Potassium fixation was barely influenced by the mineralogy of the clay fraction but was greater in soils with greater fine particle content. Modified Freundlich equation successfully modelled the effects of K addition, temperature, and contact time on fixation. The influence of temperature was greater in illitic soils than in mixed soils. The results indicate that Galician soils have little capacity for K fixation.     

NaOH‐extractable organic matter of andic soils from Galicia (NW Spain) under different land use regimes: a pyrolysis GC/MS study

The objective of this study was to determine to what extent the attenuation or loss of andic soil properties caused by land use change – from forest (FOR, average C content 118.2 ± 23.7 g kg^?1) to agricultural land (AGR, average C content 55.7 ± 16.7 g kg^?1) use – is reflected in soil organic matter (SOM) at the molecular level. For this, NaOH‐extractable SOM of A horizons from 17 soils developed on amphibolitic parent material in NW Spain was studied by pyrolysis gas chromatography spectrometry (Py‐GC/MS). We also included two buried andic A horizons (PAL, 2200 cal yr BP in age) on the same parent material, as a reference for the molecular composition of SOM from soils without recent litter additions. Organic matter of PAL soils had a composition largely different from that of superficial soils (FOR and AGR), with an important relative contribution of microbial polysaccharides and N‐compounds, and an absence of compounds that characterize fresh plant litter (e.g. lignins). In the superficial soils, the relative contribution of lignin‐derived compounds was greater in AGR than in FOR soils. Differences were also observed in the relative contribution of aliphatic compounds, FOR soils being enriched in this type of components compared with AGR soils. The results indicated that land use change from FOR to AGR, which was accompanied by a decrease in total SOM, resulted in an enrichment in primary SOM. The smaller relative abundance of primary SOM derivatives in andic FOR soils indicates that these compounds were quickly degraded in Andisols.     

Speciation and Solubility Control of Aluminium in Soils Developed from Slates of the River Sor Watershed (Galicia,NW Spain)

The Al species in the soid and liquid phases were studied in eight soils developed from slates in a watershed subjected to acid deposition. From soil solution data the mechanisms possibly controlling Al solubility are also discussed. The soils are acidic, organic matter rich and with an exchange complex saturated with Al. In the solid phase, more than 75% of non-crystalline Al was organo-Al complexes, mostly highly stable. In the soil solutions, monomeric inorganic. Al forms were predominant and fluoro-Al complexes were the most abundant species, except in soil solutions of pH<4.8 and Al L/F ratio >3, in which Al³⁺ predominated and sulphato-Al complexes were relatively abundant. The most stable phases were kaolinite, gibbsite and non-crystalline Al hydroxides. In most samples, Al solubility was controlled by Al-hydroxides. Only in a few cases (solutions of pH 4-5, Al³⁺ activity >40 µmol L-¹ and SO₄ content >200 µmol L-¹), Al-sulphates such as jurbanite also could exert some control over Al solubility. In adition to these minerals, a possible role of organo-Al complexes or the influence of adsorption reactions of sulphate is considered, especially for samples with very low Al³⁺ content (<0.5 µmol L-¹).     

Chemical and mineralogical changes in a polygenetic soil of Galicia,NW Spain

The soils of Galicia, NW Spain, developed on gabbro often include one or more buried profiles. In the modern overlying soil, gibbsite is common and the Fe oxyhydroxides include maghemite. In the buried soil interstratified kaolinite–smectite is abundant, gibbsite is present in traces and the Fe oxyhydroxides are mostly formed by goethite. Chemical and mineralogical data show that the modern soil has developed under strongly leaching conditions that contrast with those in which the buried soil formed. We suggest that the interstratified kaolinite–smectite is a relict mineral that helps reconstruction of the pedogenetic history of these soils.     

Micromorphological evidence of black carbon in colluvial soils from NW Spain

Biomass burning produces a residue called black carbon (BC). Black C is generally considered to be highly resistant against biodegradation and has a potential role in the global C cycle, but is difficult to identify and quantify when subjected to prolonged degradation in terrestrial sediments. The colluvial soils from Campo Lameiro (NW Spain), also known as ‘Atlantic rankers’, are rich in organic matter (up to 140 g C kg^?1 soil). A micromorphological study was undertaken to test the hypothesis that a large proportion of the organic matter was derived from BC formed during Holocene wildfires (up to > 6000 years ago). As roughly estimated from image analysis of 12 thin sections, the volumetric BC contribution ranged between 10 and 60% (26% on average) of the organic matter. This is a conservative estimate as additional morphologically unrecognizable BC was present in the microgranular matrix of coalesced excrement. We conclude that (i) currently unknown quantities of BC are stored in Atlantic rankers and (ii) analysis of thin sections is an effective tool to identify BC.     

Laboratory study of phosphate desorption kinetics in soils of Galicia (N.W. Spain)

Abstract

The kinetics of phosphate (P) desorption from surface horizons of 31 soils of Galicia (N.W. Spain) varied with the dose of added P (D = doses studied were equivalent to 200, 500, 1000, and 2000 μg P per g soil) and the soil‐P contact time (T = 7,180, and 360 days). Kinetic data for P desorption in aqueous suspensions of soil were fitted by zero order (Z), first order (F), second order (S), parabolic diffusion (PD), Elovich‐type (ET), and two‐constant equation (TC). TC equations gave the best fits (mean r² = 0.947±0.082). In linearized plots of Z, ET, and PD equations, the slope (K), which gives a measure of the rate of P desorption, increases with D and decreases with increasing T. In corresponding plots of F, S, and TC equations, K describes the constancy of the rate as P desorption progresses, and decreases with increasing D and increases with T. The y‐intercept of the above plots corresponded to a function of Co (the concentration of initially desorbable phosphate) in all cases. For all equations, Co increases dis‐ proportionately with D and exponentially with T. Since the kinetic parameters Co and K vary with sorption conditions, they cannot be considered characteristic of the tendency of a soil to release phosphate. A modified Freundlich equation with independent variables T, D, and t (soil‐water contact time) was also fitted to the kinetic data (mean R² = 0.959+0.031); the exponents (ß1, ß2, and ß3, respectively) of these independent variables indicate how each one influences P desorption in a given soil.     

Limiting factors for reforestation of mine spoils from Galicia (Spain)

Mined areas are a continuing source of heavy metals and acidity that move off site in response to erosion. Revegetation of the mine tailings could limit the spread of these heavy metals and acidity. This study was conducted to evaluate, at four tailings on opencast mines of Galicia (Touro: copper mine; and Meirama: lignite mine, NW Spain), the chemical and physical soil quality indicators and limiting edaphic factors concerning forest production. Selected zones were: (1) The tailings formed by the waste materials from the depleted Touro mine; (2) the decantation site of deposited sludge coming from the copper extraction in the flotation stage; (3) and (4) tailings of 3 and 10 years old of the Meirama lignite mine. The main physical limitations of the mine soils are the low effective depth (<50 cm), high stoniness (>30 per cent) and high porosity (>60 per cent); which make them vulnerable to soil erosion and seriously interferes with the forest production. Soils coming from the decantation site of copper mine do not have physical limitations. The main chemical limitations of mine soils are their acidity (pH from 3·62 to 5·71), and aluminium saturation (>60 per cent in copper mine soils, and >20 per cent in lignite mine soils), low CECe (from 5·34 to 9·47 cmol₍₊₎ kg⁻¹), organic carbon (from 0·47 to 7·52 mg kg⁻¹) and Ca²⁺ and Mg²⁺ contents, and imbalance between exchange bases. Mine soils coming from the decantation site of copper mine soils are strongly limited by the high Cu content (1218 mg kg⁻¹). Lime and organic amendments are the most important factors in providing a suitable medium for plant growth. Copyright © 2004 John Wiley & Sons, Ltd.