Ramon Josa

How mudrock and soil physical properties influence badland formation at Vallcebre (Pre-Pyrenees, NE Spain)

Abstract Soils, regoliths and their parent materials were investigated in relation to the development of badlands in the Pre-Pyrenees, in NE Spain, on Late Cretaceous mudrocks under a mountain Mediterranean climate. Whilst all the soils in the area which are developed on mudrocks show a good structure and support a dense plant cover, the bare parent materials slake very rapidly giving rise to badlands characterized by high erosion rates. Several physical, chemical, mineralogical and micromorphological properties of soils, regoliths and related parent materials were analyzed in order to explain their different susceptibility to erosion and to determine which of all these properties are better related to such erosive behaviour. Only micromorphological and porosity properties were able to explain the erosion susceptibility, whilst mineralogical, chemical and physico-chemical (specific surface area) properties were not. Among the aggregate stability tests performed to estimate the relationships of soil components with the susceptibility to erosion, the Emerson test for macroaggregate evaluation, was particularly well suited. Although no good correlation was found between the Emerson test classes and organic matter content, we observed that the degree of slaking in organic-rich horizons, was always lower than in subsurface horizons and regoliths. Consequently, as far as organic rich aggregates are present in the soil surface, the influence of water in producing slaking, swelling and then erosion, will be minimum. However, when regoliths and rocks are uncovered, the influence of water in these particular materials, through freeze-drying and swell-shrinking, will give rise to mudrock desintegration leading to accelerated erosion.

Soil responses to fire in Mediterranean forest landscapes in relation to the previous stage of land abandonment

The current paper presents a study on the interaction between land abandonment and soil responses to fire in old agricultural terraced landscapes. The study area, located near the Guadalest reservoir (E Spain), was partially affected by a forest fire in August 1998. We monitored burned and unburned areas as well as two pre-fire stand ages since agricultural abandonment: 8-15 years (dry grassland with young Pinus halepensis) and >35 years (mature pine forest). We analysed soil surface structure, water repellency and infiltrability, and we monitored plant response, runoff and sediment production for a period of 7 years after the fire. Aggregate stability increased with both time-since-abandonment and fire. Water repellency increased with land abandonment but was not affected by fire. Unburned erosion plots produced almost no runoff, even during heavy rainstorms. Fire scarcely modified runoff and erosion rates in recently abandoned terraces. A dry period following fire restricted plant recovery in burned pine forest. Burned forest plots registered runoff and sediment yields one to four orders of magnitude higher than unburned forest plots. In burned pine forest, the maximum sediment production was registered 3 years after the fire, when rainstorms took place and plant cover was still low. Old agricultural terraces colonised by pines were found to be both vulnerable to degradation as a consequence of fire and highly dependent on post-fire rain for their recovery.

Changes in particle-size distribution influenced by organic matter and mechanical or ultrasonic dispersion techniques

Determination of particle-size distribution employing the most common methods is laborious and time-consuming. The objective of this study was to compare alternative analytical procedures adequate to classify soil texture of cropped soils. Eight Spanish topsoil samples selected according to their organic matter, CaCO3, and clay content, from representative agricultural Xerochrepts were tested. Differences in the methodologies were removal by hydrogen peroxide-treatment or no removal of organic matter and overnight mechanical shaking or ultrasonic physical dispersion. The pipette method was used for determination of particle fractions. Correlation for all the three particle sizes was found among the alternative procedures and the standard methodology (with removal of organic matter and mechanical shaking) and regression equations were developed (R2>0.96). Ultrasonic dispersion was found to be faster than mechanical shaking without significant (p<0.05) changes in reported results. The clay fraction was most affected by the use of modified techniques although the observed decrease did not change the soil textural class of any samples. Organic matter content produced more differences between the results, especially when no pretreatment for destruction of organic matter on samples with organic matter content higher than 2% was conducted. Except for the more organic samples, the advantages associated with no removal of organic matter and ultrasonic dispersion include decreasing the time and work, and allowing accurate measurements of agricultural soil samples.

Influence of tillage on soil macropore size, shape of top layer and crop development in a sub-humid environment**

Topsoil macropores of two plots under no-tillage and conventional tillage were analyzed. A leguminous-cereal rotation was applied for six cycles under dry-land farming system (crop residues were removed). The clay-loam soil shows some vertic characteristics. The main goal is to identify the relationship between the top soil macro and meso-pore distribution for the two tillage systems (at the end of sixth cycle of cultivation) with the annual crop production (rainfall in normal growing period and crop production values are included). Unaltered topsoil samples were taken from 0 to 60 mm (row and interrow positions) and from the immediate depth (60 to 110 mm) in both plots (conventional and no-tillage). The morphometric analyses of 66 polished slices were carried out with the aim to identify differences in soil macro and meso-pore organisation.Soil macropores were classified by size (area) and elongation ratio and by form factor and equivalent pore diameter. No appreciable differences were observed. Soil macro and meso-pore distributions of samples were also compared. The main difference observed between topsoil’s treatments was a different macropore size distribution between topsoil positions. The presence of larger macropores was higher in conventional tillage compared to no-tillage. Samples taken from row and deeper positions of conventional tillage show a somewhat higher amount of macropores in the range between 2 to 2.3 mm equivalent pore diameter. Soil macropores contribute to increase soil aeration and soil drying when topsoil is too wet in critical periods of crop development. Conventional tillage (crop residues removed), provides to the topsoil of a larger lateral and vertical variability of macropore distribution than no-tillage topsoil.

The Effects of Burning and Clearcutting in Forest Floor Layers of Holm Oak Forest

A clearcutting and an experimental fire were carried out in a Ouercus ilex L. forest. The evolution of amounts of forest floor, litter decomposition and respiration was studied. The clearcut plot showed an increase of organic matter because of the input of leaves and branches of slash. The burned plot showed an important loss of OC and N during the first and second years after the fire.

Effects of Air-Drying and Rewetting on Extractable Organic Carbon, Microbial Biomass, Soil Respiration and β-Glucosidase and β-Galactosidase Activities of Minimally Disturbed Soils Under Mediterranean Conditions

The objectives of this study were: (1) to evaluate the effect of air-drying or air-drying and rewetting on microbial biomass carbon (MBC), extracted organic carbon (EOC), basal soil respiration (BSR), the evolution of the respiration process (ERP) and β-glucosidase and β-galactosidase activities in ten native soils with minimal anthropogenic disturbance in Catalonia (NE Spain); and (2) to determine whether air-drying or air-drying and rewetting are accurate sample pre-treatment procedures when the above properties are used to evaluate the quality of the soils. In order to assess the effect of air-drying on the MBC, BSR, ERP and the β-glucosidase and β-galactosidase activities of field-moist soils, the values of these parameters were determined after the field-moist soil samples had been air-dried for one week at room temperature. To evaluate the effect of air-drying plus rewetting on the β-glucosidase and β-galactosidase activities of field-moist soils, air-dried samples were rewetted to 60% of their water holding capacity and kept in the dark at 28°C for 7 days before the assays were performed. In the case of EOC, air-dried values were compared with those of air-dried plus rewetted samples. The results showed that air-drying caused a reduction in the MBC and an increase in the BSR of field-moist soil samples. Rewetting air-dried soils generally increased the activity of the two enzymes. The values of MBC and of β-glucosidase and β-galactosidase activities in air-dried soils had the same ranking as in field-moist soils, whereas air-drying plus rewetting led to a change in the ranking of both enzyme activities compared with field-moist samples. β-glucosidase was probably more protected by humic colloids than β-galactosidase.

Biochemical Characterisation of Minimally Disturbed Soils Under Mediterranean Conditions

Urease, BAA-hydrolase, β-glucosidase and β-galactosidase enzyme activities, total and extractable carbohydrate content, organic C, basal respiration and microbial biomass carbon were determined in soils with minimal anthropogenic disturbance in Catalonia (NE Spain). Superficial layer samples of ten soils were collected in spring 2006 from different zones including a wide range of plant cover, climatic conditions and lithologic characteristics. Data were submitted to variance analysis and Student Newman Keuls test and total and partial correlation coefficients were calculated. Cluster analysis was performed to identify similarity between variables and soil locations.The studied biochemical properties were highly variable between sites. Seven of the 10 variables differed about 10-fold between lowest and highest values while soil respiration showed the lowest variation range (5-fold) and total carbohydrate content and β-galactosidase activity the highest variation range (25-fold and 35-fold respectively). The cluster analysis showed two groups of variables that were useful to biochemically characterize the ten studied soils. One group (organic C, total and extractable carbohydrates, β-glucosidase activity and microbial biomass carbon) represented the organic matter composition and microbial content and microbial activity; and another group (Urease, BAA-protease and β-galactosidase) probably represented the stabilized enzyme activity. Overall, the studied biochemical parameters were found to be suitable for reflecting the main differences (pH, salinity and CaCO3 content) between soil type and location.

Influence of the cultivation system and the relief on the water content of the Ap Horizon of land subject to different use

In this experiment twelve TDR stations are used to monitoring the water content in Ap horizon considering four soil uses: 3 different production systems (no-tillage, minimum tillage and conventional tillage) and one abandoned plot (natural forestry process). This study describes spatial variation of temporal series of data series of soil water content. Moisture content for surface soils was monitored during a growing season, from December 1994 to July 1995.

An advanced process for evaluating a linear dielectric constant–bulk electrical conductivity model using a capacitance sensor in field conditions

Abstract The Hilhorst model was used to convert bulk electrical conductivity (σb) to pore water electrical conductivity (σp) under laboratory conditions by using the linear relationship between the soil dielectric constant (εb) and σb. In the present study, applying the linear relationship εb–σb to data obtained from field capacitance sensors resulted in strong positive autocorrelations between the residuals of that regression. We were able to derive an accurate offset of the relationship εb–σb and to estimate the evolution of σp over time by including a stochastic component to the linear model, rearranging it to a time-varying dynamic linear model (DLM), and using Kalman filtering and smoothing. The offset proved to vary for each depth in the same soil profile. A reason for this might be the changes in soil temperature along the soil profile. Editor D. Koutsoyiannis; Associate editor M.D. Fidelibus

Hardpan in skeletal soils: Statistical approach to determine its depth in a cherry orchard plot

Abstract Skeletal soils are not suitable for agriculture, and often are allocated to marginal uses such as cherry orchards for timber production. These require some agricultural practices (irrigation, soil tillage or weed control) which can contribute to the development of a hardpan. Compacted layers can adversely affect timber production, so subsoiling works are required. This study examined the effect of six years of tillage on hardpan formation in a skeletal soil by means of mechanical impedance measurements with a dynamic penetrometer cone (dynamic cone test), a method that is quick and easy to use, but can suffer from interference by stones. Mechanical impedances along the soil profile were measured in four plots differing in tillage (with or without) and drip irrigation (with or without) treatments. Exploratory data analysis together with statistical inference techniques related to linear general models were applied. The presence of a transitional layer on top of the hardpan is suggested in the non-tilled plot and soil depth that can be explored easily by roots has increased by 20 cm.