V. Aranda

Biochemical activity and chemical-structural properties of soil organic matter after 17 years of amendments with olive-mill pomace co-compost.

This study evaluates soil fertility, biochemical activity and the soils ability to stabilize organic matter after application of composted olive-mill pomace. This organic amendment was applied in two different olive groves in southern Spain having different soil typologies (carbonated and silicic). Olive grove soils after 17 years of organic management with application of olive-mill pomace co-compost were of higher quality than those with conventional management where no co-compost had been applied. The main chemical parameters studied (total organic carbon, total nitrogen, available phosphorus, exchangeable bases, cation exchange capacity, total extractable carbon (TEC), and humic-to-fulvic acids ratio), significantly increased in soils treated with the organic amendment. In particular, the more resistant pool of organic matter (TEC) enhanced by about six and eight fold in carbonated and silicic soils, respectively. Moreover, the amended silicic soils showed the most significant increases in enzyme activities linked to C and P cycles (β-glucosidase twenty-five fold higher and phosphatase seven fold higher). Organic management in both soils induced higher organic matter mineralization, as shown by the higher pyrrole/phenol index (increasing 40% and 150% in carbonated and silicic soils, respectively), and lower furfural/pyrrole index (decreasing 27% and 71% in carbonated and silicic soils, respectively). As a result of mineralization, organic matter incorporated was also more stable as suggested by the trend of the aliphatic/aromatic index (decreasing 36% and 30% in carbonated and silicic soils, respectively). Therefore, management system and soil type are key factors in increasing long-term C stability or sequestration in soils. Thus application of olive-oil extraction by-products to soils could lead to important mid-to -long-term agro-environmental benefits, and be a valuable alternative use for one of the most widespread polluting wastes in the Mediterranean region.

Evolution of organic matter fractions after application of co-compost of sewage sludge with pruning waste to four Mediterranean agricultural soils. A soil microcosm experiment

The effect of co-compost application from sewage sludge and pruning waste, on quality and quantity of soil organic carbon (SOC) in four Mediterranean agricultural soils (South Spain), was studied in soil microcosm conditions. Control soil samples (no co-compost addition) and soils treated with co-composts to a rate equivalent of 140 Mg ha(-1) were incubated for 90 days at two temperatures: 5 and 35 degrees C. The significances of incubation temperature and the addition of co-compost, on the evolution of the different fractions of SOC, were studied using a 2(3) factorial design. The co-compost amendment increased the amounts of humic fractions: humic acids (HA) (1.9 times), fulvic acids (FA) (3.3 times), humin (1.5 times), as well as the free organic matter (1.4 times) and free lipids (21.8 times). Incubation of the soils enhanced its biological activity mainly in the amended soils and at 35 degrees C, leading to progressive SOC mineralization and humification, concomitant to the preferential accumulation of HA. The incubation results show large differences depending on temperature and soil types. This fact allows us to select suitable organic amendment for the soil when a rapid increase in nutrients through mineralization is preferred, or in cases intending the stabilization and preservation of the SOC through a process of humification. In soils with HA of more than 5 E(4)/E(6) ratio, the incubation temperature increased rates of mineralization and humification, whereas lower temperatures limited the extent of both processes. In these soils the addition of co-compost in spring or summer is the most recommendable. In soils with HA of lower E(4)/E(6) ratio (<5), the higher temperature favoured mineralization but not humification, whereas the low temperature maintained the SOC levels and even increased the HA/FA ratio. In these soils the moment of addition of organic amendment should be decided depending on the effect intended. On the other hand, the lower the SOC content in the original soil, the greater are the changes observed in the SOC after amendment with co-compost. The results suggest that proper recommendations for optimum organic matter evolution after soil amendment is possible after considering a small set of characteristics of soil and the corresponding soil organic matter fractions, in particular HA.

Precipitation of Carbonates and Phosphates by Bacteria in Extract Solutions from a Semi-arid Saline Soil. Influence of Ca2+ and Mg2+Concentrations and Mg2+/Ca2+ Molar Ratio in Biomineralization

We examine the ability of bacteria from a saline soil (Arenic-Gypsic-Hyposalic Solonchak) from the Santa-Pola marine saltern (Alicante, Spain) to precipitate carbonate and phosphate minerals. Solid culture media were prepared from natural soil extracts, from natural soil extracts amended with organic material in different proportions, and by modifying the Ca 2+ and Mg 2+ concentrations and the Mg 2+ /Ca 2 + molar ratio. A high percentage of moderately halophilic bacteria were able to form biominerals (calcite, magnesian calcite and/or struvite) in natural soil extracts with small amounts of added organic material and in ionically modified natural soil extracts. Light microscopy revealed three different types of bio-mineralization: colonies that precipitate carbonates, colonies that precipitate struvite, and colonies that precipitate both types of minerals. The precipitation of carbonates and struvite is not simultaneous, but successive. The concentration of Ca 2+ and the Mg 2+ /Ca 2 + molar ratio were more influential than the absolute amount of Mg 2+ on the precipitation of minerals. The higher the calcium concentrations are, the more carbonate-forming colonies there are and the fewer struvite-forming colonies. The bioliths precipitated were analyzed by Powder X-Ray Diffraction (PXRD) and Scanning Electron Microscope (SEM). In the magnesian calcites precipitated (Ca 1 − n Mg n CO 3 ), “n” (amount of magnesium that replaces calcium by formula) varied from 0.058 to 0.342. Struvite crystals are polyhedral and around 500 μm, while carbonate crystals are smaller (< 100 μm), spherical and usually in aggregates. The precipitation of minerals studied shows an active role of the bacteria, but the geochemical conditions are clearly influential. It may therefore be considered “induced biomineralization.” The results point out the possibility that in some soils the C, N, P, Ca and Mg cycles are coupled due to bacterial biomineralization.

Are Mediterranean mountains Entisols weakly developed? The case of Orthents from Sierra Nevada (Southern Spain)

Two Orthents from Sierra Nevada National Park (Spain), classified as loamy-skeletal mesic Typic Xerorthent and loamyskeletal frigid Lithic Cryorthent were studied. They were situated at 1460 and 2000 m, derived from micaschists and quartzites under Mediterranean mountain climate conditions with mesic and cryic temperature regimes and xeric moisture regime. These Orthents are weakly developed, as shown by their reduced thickness, their lack of diagnostics subsurface horizons, sandy loam textures, skeletal, and lithochromic colors. Quartz is present in significant amounts, particularly in the fine light sand fraction. Analysis of the quartz grains of the fine light sand by scanning electron microscope (SEM) and backscattered electron images (BSE) revealed the presence of significant physical and chemical alteration features such as fractures, corrosion gulfs, fields of etch pits and dissolution of intergranular surfaces. This process is confirmed by electron microprobe analysis (EMPA) since the edges of the quartz grains have a higher proportion of cations other than Si, compared to their centre. Further evidence indicates the authigenic nature of the process. Starting from quartz etching an assessment of soil weathering has been made (W index from Marcelino et al. (1999). The alteration of the quartz, together with the development of a ultramicrofabric with several fabric units (investigated with SEM), and other characteristics (mineralogical, chemical, etc.) are considered indicative of some pedogenic evolution. These facts are especially interesting in the case of weakly developed Mediterranean mountain soils from Sierra Nevada, where processes of chemical weathering have traditionally not been considered very active. D 2003 Elsevier B.V. All rights reserved.

Near-infrared spectroscopy and X-ray fluorescence data fusion for olive leaf analysis and crop nutritional status determination

Leaf analysis is a useful way of diagnosing the nutritional status of the plants and therefore fast methods of analysis are demanded to aid in fertilization management decisions. In this work, a strategy based on the combined use of near-infrared spectroscopy (NIR) and portable energy dispersive X-Ray Fluorescence (EDXRF) is proposed as a suitable cheap and rapid alternative to traditional wet analytical methodologies. The approach has the major benefit of minimal sample preparation since leaves need to be only dried and ground. The ability of both techniques individually and applying two strategies of data fusion for the prediction of the most important plant nutrients, namely N, P, K, Ca, Mg, Mn, Zn, and B was tested. Predictive models were constructed using Partial Least Squares (PLS) to correlate the spectra with the nutrient contents. Models of unequal prediction performance in terms of the ratio of predictive deviation (RPD) were obtained for the different parameters when considering both techniques separately. Low-level data fusion, which consists of a concatenation of the raw data from both techniques, showed little improvement and even decreased the predictive ability for some elements. Better results were obtained with mid-level data fusion, that is, merging data after a feature extraction step performed by means of Principal components analysis (PCA). The results show that a fair quantitative prediction is possible for Ca, K and Mn with RPDs ≥ 2 for external validation, whereas models for N and P allowed a semiquantitative estimation. Mg and B models were less satisfactory and can be used only for distinguish between low and high levels, while Zn content cannot be predicted. Finally, the potential of the fusion of FT-NIR and EDXRF spectroscopic data for the fast screening of olive crop nutritional status has been tested. Deficiencies in important elements like N and K has been successfully detected.

A new soil quality index based on morpho-pedological indicators as a site-specific web service applied to olive groves in the Province of Jaen (South Spain)

Abstract Soil quality has become a fundamental concept in soil science and agriculture, but it can be difficult to apply its theoretical and experimental approaches to poorly surveyed zones where precision techniques are far from being applied. In this paper, we propose a new technique that enables little-used qualitative morpho-pedological data to be managed and integrated into a single Field Soil Quality Index (FSQI). Nonlinear Principal Component Analysis (NLPCA), a technique able to handle categorical data, is applied here to deal with morpho-pedological indicators. When categorical values are transformed, they can be properly analyzed and interpreted. This procedure requires less expert knowledge, so it can help soil quality assessments by non-experts. We applied the FSQI protocol to soils in the most important olive-growing area in the world, Jaen Province (Southern Spain), which has serious problems with soil degradation and erosion. First, a soil database for the study area was compiled, including 18 morphological attributes for 131 surface horizons belonging to eight Land Use Types. Secondly, the NLPCA provides optimal scalings and attribute weights that transform and integrate morphological indicators into a simple weighted additive index (FSQI). Thirdly, the scaling functions and weights found were applied to the same attributes of an evaluation set comparing two soil management types (conventional vs. organic) in olive groves. The FSQI means for the first (conventional) were significantly lower than in the organic groves (0.278 vs. 0.463, P

Humic acid adsorption and its role in colloidal-scale aggregation determined with the zeta potential, surface free energy and the extended-DLVO theory

Summary The effect of colloidal forces involved in the adsorption of commercial humic acids (HA s) and particle cohesion was studied in the soil of an organic olive grove with the extended D erjaguin, L andau, V erwey and O verbeek (extended‐ DLVO) theory. Total interaction energy was determined from the zeta potential (ζ) and surface free energy, measured under different experimental conditions [natural and hydrogen peroxide (H2O2) organic matter‐free mineral surfaces]. The soil was clayey, dominated by illite and vermiculite. It showed electron‐donor behaviour, with negatively charged surfaces and zeta potential < 0 mV. Decreasing mV in the zeta potential, ζ, curves and electron‐donor component, γ –, when adding HA to natural surfaces showed effective HA adsorption, but only when soil organic matter had not been removed previously. Isotherms confirmed adsorption by natural soil (> 2.5 mg C g−1). Because the isotherms showed no relation with temperature, adsorption would be better attributed to weak physical interactions. On natural surfaces with HA, soil particle attraction forces increased slightly (≈50 kT) through decreasing soil wettability. However, this effect on total surface energy was overcome largely by increasing electrostatic repulsive energy caused by the adsorption of negatively charged HA (> 300 kT). The DLVO ‐extended model showed that natural surfaces without H2O2 treatment or added HA seem to be the most favourable state for colloidal aggregate stability. We recommend some caution about the type and quality of organic matter added to increase organic carbon in soil. HighlightsWe applied the extended DLVO model to study humic acid adsorption and its effects on soil structure.Adsorption on soil surfaces with their natural organic matter was mostly by weak physical forces.Adsorption increased the total particle interaction energy through an increase in electrostatic repulsion.Adsorption of some types of organic matter might decrease the colloidal stability of aggregates.