Mediterranean Agricultural Soils Research Articles

Occurrence, dissipation kinetics and environmental risk assessment of antibiotics and their metabolites in agricultural soils

Antibiotics are among the emerging contaminants of greatest concern to the scientific community. However, the occurrence and behaviour of their metabolites in soils have been scarcely studied. To address this research gap, this study investigates the occurrence, sorption, dissipation kinetics, and environmental risk of highly important antibiotics (sulfamethazine, sulfadiazine, sulfamethoxazole, trimethoprim) and their main metabolites in Mediterranean agricultural soils. Batch experiments were conducted under natural conditions for 120 days. Five different dissipation kinetics models were applied to elucidate antibiotics degradation. The sorption isotherms were evaluated by three different models. Most of the antibiotics and metabolites tested showed a good fit with the Linear Isotherm model (R2 >0.96) and biphasic dissipation kinetic models (R2 >0.90). The dissipation and the endpoints values (DT50 and DT90) depended on the soil type properties. A Lixisol soil demonstrated reduced degradation of the investigated compounds. Trimethoprim showed the highest persistence, followed by sulfamethazine, sulfamethoxazole, and sulfadiazine. Parent compounds exhibited lower degradation rates than their metabolites. Remaining antibiotic concentrations were found to be below the predicted no-effect concentration in soil, suggesting that they may not pose a risk to terrestrial biota. This study provides valuable insights into the behaviour of these antibiotics and their metabolites in soil.

An enantioselective study of the behavior of the herbicide ethofumesate in agricultural soils: Impact of the addition of organoclays and biochar

Chiral pesticides that are still commercialized and incorporated into the environment as racemic mixtures of enantiomers require evaluation of the enantioselectivity of their biological activity and environmental fate processes for a better prediction of their field efficacy and environmental risks. In this work, we successfully separated the enantiomers of the chiral herbicide ethofumesate (ETFM), determined their absolute configuration, and characterized their herbicidal activity as well as their adsorption, degradation, enantiomerization, and leaching in Mediterranean agricultural soils. While the herbicidal activity of R-ethofumesate to the sensitive species Portulaca grandiflora was greater than that of S-ethofumesate, the adsorption, degradation, and leaching of the herbicide showed negligible enantioselectivity and enantiomer interconversion did not occur in soils. The adsorption of both enantiomers showed a positive correlation with the soil organic carbon content (r = 0.856, P = 0.015), and their degradation in soils occurred slowly (DT50 > 60 days) and at similar rates independent of their application as individual enantiomers or as a racemic mixture of enantiomers. The addition of three highly adsorptive materials to a scarcely adsorptive soil increased the adsorption of the enantiomers of ETFM and delayed their degradation without affecting the non-enantioselective character of the processes. As a result of their high adsorption capacity, the materials were highly effective in reducing the leaching of both enantiomers of ETFM through soil columns. The results of this work indicate that the application of single-enantiomer ETFM formulations, based on a higher herbicidal activity or a lower toxicity to non-target organisms of the formulated enantiomer, would reduce considerable exposure risks associated with incorporating into the environment the less favorable enantiomer, as this would show long persistence and high leaching potential in soils similar to its optical isomer.

Impact of Different Irrigation Methods on the Main Chemical Characteristics of Typical Mediterranean Fluvisols in Portugal

The sustainable management of Mediterranean agricultural soils, characterized by salinization and low organic matter content, requires a thorough understanding of their temporal and spatial evolution. The focal point of this investigation encompasses an area of 6769 ha within the Portuguese Mediterranean basin, from which as many as 686 topsoil specimens were acquired during the periods 2001/2002 and 2011/2012 for the purpose of scrutinizing soil organic matter (SOM) content, pH measured in water, and electrical conductivity (EC). The methodology employed both classical and geostatistical techniques, and the terrestrial samples were classified in accordance with the irrigation mechanisms in use (namely, drip and sprinkler systems), subsequently juxtaposed with their counterparts in rainfed systems. Predictive maps were generated using the Ordinary Kriging algorithm for spatial interpolation. The findings demonstrate that irrigated Fluvisols displayed lower SOM content compared to rainfed soils, with sprinkler-irrigated soils experiencing a 16.1% decrease and drip-irrigated soils showing a more pronounced 26.6% decrease. Moreover, drip-irrigated soils contained 12.5% less SOM compared to sprinkler-irrigated soils. The pH levels stabilized at around 6.6 in both rainfed and irrigated soils, with no significant differences observed between the irrigation methods. Furthermore, irrigated Fluvisols exhibited higher EC values compared to rainfed soils, with both sprinkler and drip-irrigated soils showing values that were 35.2% higher. These results underscore the impact of irrigation practices on soil properties, including elevated EC values due to increased soil salt accumulation. The study highlights the necessity of considering specific irrigation systems and associated practices to ensure sustainable soil health and productivity. Adopting management approaches that account for these factors is crucial for preserving optimal soil conditions in Mediterranean agricultural systems.

Evolution of Maize Compost in a Mediterranean Agricultural Soil: Implications for Carbon Sequestration

Compost amendments, apart from improving fertility and the general characteristics of agricultural soils, have known implications for global C cycling and sequestration in soils. Their effects are usually assessed via the quantification of soil organic carbon (SOC) pools, usually labile (fast) and recalcitrant (slow) pools, with varying intrinsic decomposition rates and distinct resident times. However, the real C-sequestration potential of organic additions to soil is still under discussion. In this study, a field trial and a lab incubation experiment were designed to study the C-sequestration mechanism in an agricultural Mediterranean soil. Soil with a history of C3 photosystem crop was amended with two maize composts from maize harvesting surpluses (C4 photosystem) with different maturity stages (AC: aged compost; NC: new, less mature compost). The evolution of SOM was monitored for 6 months using complementary analytical techniques, including analysis of stable C isotopes (IRMS), thermogravimetry (TG) and C-stock and priming effect (PE) modelling. Based on the natural C-isotope labelling, the proportion of new C was calculated. More than 50% of the C added to the soil with the compost was incorporated into the SOM in only 6 months. However, the application of maize compost did not always enhance soil C-sequestration capacity. The addition of compost caused a general PE, enhancing SOM decay and reducing the fast (labile) SOM mean residence time (MRT) (11.2 days). This was more pronounced with the addition of a higher dose of AC, causing a PE up to a 718%. On the other hand, a higher MRT (54.4 days) occurred in soils with NC applied, likely due to its deleterious effects, limiting heterotrophic activity. Despite that, the average MRT of the slow (recalcitrant) SOM pool was lower than usually reported. The application of higher doses of both composts generally showed greater MRT values compared to control (1.7 years vs. 3.8 and 2.9 years for NC and AC, respectively), leading to an increase in this more stable C pool and effective soil C sequestration. The results described in this work may help readers to better understand SOM dynamics and may be of use in designing appropriate management strategies for improving OM quantity and quality and to optimize C storage in Mediterranean soils.

Thermodynamic and Kinetic Investigation of the Adsorption and Desorption of Trimethoprim and Its Main Metabolites in Mediterranean Crop Soils

The adsorption-desorption processes of organic pollutants into the soil are one of the main factors influencing their potential environmental risks and distribution in the environment. In the present work, the adsorption-desorption behavior of an antibiotic, trimethoprim (TMP), and two of its main metabolites, 3-desmethyltrimethoprim (DM-TMP) and 4-hydroxytrimethoprim (OH-TMP), were assessed in three Mediterranean agricultural soils with different physicochemical characteristics. Results showed that the adsorption kinetic is performed in two steps: external sorption and intraparticle diffusion. The adsorptions of the studied compounds in soils were similar and fitted to the three models but were better fitted to a linear model. In the case of DM-TMP and OH-TMP, their adsorptions were positively correlated with the soil organic matter. In addition, desorption was higher in less organic matter soil (from 1.3 to 30.9%). Furthermore, the desorptions measured for the TMP metabolites were lower than those measured in the case of TMP (from 2.0 and 4.0% for OH-TMP and DM-TMP, respectively, to 9.0% for TMP).

Sorption–Desorption of Imazamox and 2,4-DB in Acidic Mediterranean Agricultural Soils and Herbicide Impact on Culturable Bacterial Populations and Functional Diversity

In this study, we investigated the sorption–desorption behavior of imazamox (IMZ) and 2,4-DB (DB) in two typical acidic Mediterranean agricultural soils and the impact of these herbicides on culturable soil bacterial populations, enzyme activities and functional diversity when applied at concentrations higher than recommended doses (10×, 50×, 500×). Herbicide sorption was similar in both soils and IMZ was less retained compared to DB (~0.5 vs. 40 µg g−1 soil, respectively). IMZ desorption was remarkable (70–100%) while that of DB was more limited, i.e., ~40%. Three days after spiking (DAS), IMZ and DB significantly increased the number of soil-culturable heterotrophic bacteria, actinomycetes and Pseudomonas spp., soil respiration and the potential catabolic capacity of soil microbial communities. Soil dehydrogenase activity increased by ~56–70% in IMZ-treated soils while being reduced by ~33–41% in DB-treated ones. β-glucosidase activity showed a soil-dependent behavior, while the pattern of C source utilization suggested a change of soil microbial community structure after herbicide (especially DB) spiking. At 30 DAS, the herbicides’ impact on soil microorganisms, enzyme activity and functional diversity was still visible. Moreover, a toxic effect of DB (at 50× and 500×), but not IMZ, was recorded vs. Rhizobium sullae, the bacterial symbiont of Hedysarum coronarium. The obtained results indicated that IMZ and DB are poorly sorbed and highly desorbed by both soils. Moreover, at the tested concentrations, IMZ and DB can have short- and medium-term impacts on the microbial component and the related activity of the investigated soils, likely affecting a range of ecosystem services provided by soil microorganisms.

ScenaLand: a simple methodology for developing land use and management scenarios

Scenarios serve science by testing the sensitivity of a system and/or society to adapt to the future. In this study, we present a new land use scenario methodology called ScenaLand. This methodology aims to develop plausible and contrasting land use and management (LUM) scenarios, useful to explore how LUM (e.g. soil and water conservation techniques) may affect ecosystem services under global change in a wide range of environments. ScenaLand is a method for constructing narrative and spatially explicit land use scenarios that are useful for end-users and impact modellers. This method is innovative because it merges literature and expert knowledge, and its low data requirement makes it easy to be implemented in the context of inter-site comparison, including global change projections. ScenaLand was developed and tested on six different Mediterranean agroecological and socioeconomic contexts during the MASCC research project (Mediterranean agricultural soil conservation under global change). The method first highlights the socioeconomic trends of each study site including emerging trends such as new government laws, LUM techniques through a qualitative survey addressed to local experts. Then, the method includes a ranking of driving factors, a matrix about land use evolution, and soil and water conservation techniques. ScenaLand also includes a framework to develop narratives along with two priority axes (contextualized to environmental protection vs. land productivity in this study). In the context of this research project, four contrasting scenarios are proposed: S1 (business-as-usual), S2 (market-oriented), S3 (environmental protection), and S4 (sustainable). Land use maps are then built with the creation of LUM allocation rules based on agroecological zoning. ScenaLand resulted in a robust and easy method to apply with the creation of 24 contrasted scenarios. These scenarios come not only with narratives but also with spatially explicit maps that are potentially used by impact modellers and other end-users. The last part of our study discusses the way the method can be implemented including a comparison between sites and the possibilities to implement ScenaLand in other contexts.

Soil management and compost amendment are the main drivers of carbon sequestration in rainfed olive trees agroecosystems: An evaluation of chemical and biological markers

Traditional olive groves are considered at high risk of erosion and desertification due to low organic matter inputs and scarce vegetation cover coupled to highly intensity tillage, leading to a further decrease in soil organic carbon contents. In a context of climate change, carbon sequestration through waste management in the framework of a circular economy becomes of primary importance for rainfed Mediterranean agricultural soils. To unveil the mechanisms of carbon sequestration in those agroecosystems, we evaluated the effect of the application of two composts (olive waste “alperujo” and biosolid) at two different doses coupled to the sustainable soil management allowing spontaneous vegetation growing on the soil surface.With this aim, solid state nuclear magnetic resonance was used to trace the evolution of the chemical composition of compost-derived and soil-derived organic matter. Successively, the activity of soil microbial community after the compost addition was monitored by measuring two enzymatic activities (β-glucosidase and dehydrogenase) and soil CO2 respiration. Lastly, the adaptation of microbial communities was quantified using the genes encoding soil enzymes associated with C cycling -glucosidase and laccase-like multicopper oxidases. The results of this study show that biosolid compost has a higher potential for C storage at mid-term (24 to 30 months after first application) than alperujo compost, yielding up to 50% net C sequestration in the topsoil in addition to the compost-derived C applied. We attribute these results to biosolid compost chemical composition, closer to that of the native organic matter, which led to a less abrupt adaptation of soil microbial functioning (lower flushes of water soluble C, lower number of copies of genes encoding enzymatic activities) to the new C source, if compared to alperujo compost. The results encourage the reduction of soil perturbation and the use of organic amendments instead of mineral fertilizers to increase carbon storage and improve sustainability of olive groves in the Mediterranean agroecosystems.

Spent coffee grounds by-products and their influence on soil C–N dynamics

SCG are a bio-waste generated in great amount worldwide which are attractive as soil amendment for their high content of organic matter and nutritive elements. Nevertheless, several studies have shown that soil application of untreated SCG has detrimental agronomic and environmental effects due to their high degradability and content of noxious compounds (phenols, caffeine, and tannins). However, SCG can be valorised, in the frame of circular economy, by extraction of energy and valuable products (carbohydrates, proteins, bio-oil, bio-diesel) and generation of solid by products (biochar, hydrochar, compost) that can be utilized as soil fertilizers and amendments.Therefore, the aim of this work was the characterization of different solid SCG by-products (as second-generation products) and their assessment as effective organic amendments. The novelty of this study is that for the first time 8 different by-products derived from the same SCG were characterized and comparatively evaluated for their impact on the C and N cycles of soil. SCG was collected and treated to generate 8 different SCG by-products (biochars produced at 270 and 400 °C, hydrochars produced at 160 and 200 °C, vermicompost, defatted SCG and biochars produced from defatted SCG at 270 and 400 °C). SCG and derived by-products were characterized for SEM micromorphology, pH and EC values, and C, N, H, O, volatile matter, fixed C, LOI, carbonates, water soluble C and N, NO3− and NH4+ content. SCG and SCG by-products assessment as organic amendments was performed with an incubation experiment. The residues were added (2.5%) to a moist Mediterranean agricultural soil and the amended soil samples were placed in mesocosms and incubated at 20 °C for 30 days. During incubation, CO2 and N2O emissions were measured every 6 h by means of a gas chromatography automated system for GHG sampling and measurement. The percentage of added C remaining (CR) in the soil was calculated by fitting the cumulative respiration of amended soil to a two-pool model. After 2, 7 and 30 days of incubation, the control and amended soils were sampled and analyzed for their content of extractable organic C, N, NO3− and NH4+ and microbial biomass C and N. Results showed that SCG by-products presented a great variability in their properties. SCG and hydrochars presented higher contents in volatile matter and water soluble C and N, and low content of fixed C, while biochars showed an opposite behaviour. SEM images confirmed the different characteristics of the SCG by-products: the biochar presented a porous structure, honeycomb-like form, due to the loss of the more soluble compounds, while the SCG and hydrochars' pores were filled with amorphous carbonaceous materials. Consequently, soil addition of SCG by-products showed a distinct impact on C and N cycle and microbial biomass content. Addition of SCG and hydrochars generated the highest cumulative CO2–C emissions (2103–2300 μg g−1), the lower amount of CR (86.8–88.6%), increased the soil extractable organic C and microbial biomass C and N and caused N immobilization. On the other hand, the addition of biochars generated lower CO2–C emissions (542–1060 μg g−1), higher amounts of CR (96. 3–99.9%) and lower amounts of extractable compounds and microbial biomass C and N, generating also N immobilization, but to a lesser extent. The addition of vermicompost generated 723 μg g−1 of CO2–C and 98% of CR remaining. However, this by-product did not generate N immobilization being able to act as N fertilizer. None of the residues generated N2O emissions. The different properties of the SCG by-products and their impact on C and N cycle indicated that they can be effectively applied to soil to exert different agronomical and environmental functions.

Short-Term Effects of Biosolid Application on Two Mediterranean Agricultural Soils and Durum Wheat Yield

This study evaluated the effects of de-inking paper sludge (DPS) and sewage sludge (SS) application on soil properties, and durum wheat growth and yield. A pot experiment was performed on Calcaric cambisol (clCM) and Cromic Luvisol (coLV) soils. Three DPS rates (0, 30, and 60 Mg ha−1) were studied with and without nitrogen fertilizer (280 kg NH4NO3 ha−1). DPS was also mixed with SS at two rates (5 and 10 Mg ha−1) to highlight the benefits of organic nitrogen compared to mineral nitrogen. DPS improved total organic carbon and nitrogen, mineral nitrogen, and soils cation exchange capacity, the 30% rate provided the greatest improvement in both soils. DPS increased grain and root P, K, Ca, and Mg contents in both soils. It also increased wheat straw N, P, Mg, and Ca for the same soil compared to the control. Mixed DPS treatments with nitrogen fertilizer enhanced grain yield by up to 38% and increased root biomass in the studied soils. Thus, DPS is a potential source of organic matter and a liming agent for acid soils when appropriate supplemental fertilizer is provided.

Sorption and dissipation of the allelochemicals umbelliferone and salicylic acid in a Mediterranean soil environment: Effect of olive-mill waste addition

Allelochemicals are receiving much attention as natural alternatives to synthetic pesticides. Very little is known, however, about the processes to which allelochemicals are subjected once they reach the soil environment, despite the fact that it is widely recognized that such processes can dramatically influence their bioactivity and applicability as eco-friendly pesticides. The objectives of this study were to characterize the sorption and dissipation of two phenolic allelochemicals, umbelliferone (UM) and salicylic acid (SA), after their simultaneous application to a Mediterranean agricultural soil and to assess to what extent sorption and dissipation were affected by amending the soil with an agro-industrial organic waste (olive-mill waste, OMW), as a common agronomic practice in Mediterranean agricultural systems. In experiments conducted under standard laboratory conditions, UM (pKa = 7.5) showed greater sorption than SA (pKa = 2.8) and both allelochemicals displayed very short half-lives in the tested soil (DT50 < 1 day). Furthermore, the addition of OMW increased the sorption of UM and the half-lives of both SA and UM in the soil. A field experiment conducted on unamended and OMW-amended soil plots confirmed the ability of OMW to increase the persistence of SA and UM under a real Mediterranean soil environment and showed that, for all treatments, the allelochemicals displayed higher half-lives in the field than under standard laboratory conditions. This was attributed to reduced biodegradation of UM and SA under progressive soil drying, which was thus identified as a factor that can prolong the persistence of allelochemicals in semi-arid soil environments. We highlight the need to test the environmental fate of allelochemicals under specific agro-climatic scenarios and illustrate how management practices can help increase their soil persistence so that their bioactivity can be better expressed.

Bioavailability, mobility and leaching of phosphorus in a Mediterranean agricultural soil (ne Spain) amended with different doses of biosolids.

The precipitation of sparingly soluble calcium phosphate in calcareous soils decreases the bioavailability of macronutrients, which makes their addition by way of fertilisers necessary. Sludge resulting from treating urban wastewater does not only provide significant amounts of phosphorus, but also helps lower the pH, thus increasing its bioavailability. The loss of part of soil nutrients due to irrigation or rain can contaminate groundwater. In order to assess the movement of phosphorus, a experiment was conducted on percolation columns, to which different doses of wastes were applied. The pH decreased by as much as 0.89 units, as well as the assimilable and soluble P, in intervals of 20cm of depth, obtaining maximum values of 254mg Pkg-1 and 1455μg Pkg-1 respectively, and the P present in the leached water collected, which did not surpass 95μg PL-1. The intent was to learn which was the majoritarian inorganic formed crystalline phase that immobilised the movement of phosphorus through the percolation column. The results obtained by the diffraction of X-rays are not conclusive, although they point to the formation of octacalcium phosphate. The diffractograms of the studied samples have similar diffraction lines to those of apatites.

Soil fertility and bacterial community composition in a semiarid Mediterranean agricultural soil under long‐term tillage management

AbstractThis research attempted to investigate a part of the United Nations sustainable development goal 15, dealing with preventing land degradation and halting the loss of microorganisms’ diversity. Since soil deterioration and biodiversity loss in the Mediterranean area are occurring because of intensive management, we evaluated some biochemical and microbiological parameters and bacterial biodiversity under long‐term conventional tillage (CT) and no‐tillage (NT) practices, in Basilicata, a typical Region of Southern Italy, characterized by a semiarid ecosystem. The highest biological fertility index (BFI) (composed of soil organic matter, microbial biomass C, cumulative microbial respiration during 25 days of incubation, basal respiration, metabolic quotient and mineralization quotient) was determined for the 0–20 cm of NT soil (class V, high biological fertility level). The analysis of the taxonomic composition at the phylum level revealed the higher relative abundance of copiotrophic bacteria such as Proteobacteria, Actinobacteria and Bacteroidetes in the NT soil samples as compared to the CT soil. These copiotrophic phyla, more important decomposers of soil organic matter (SOM) than oligotrophic phyla, are responsible of a higher microbial C use efficiency (CUE) in tilled soil, being microbial community composition, C substrates content and CUE closely linked. The higher Chao1 and Shannon indices, under the NT management, also supported the hypothesis that the bacterial diversity and richness increased in the no‐till soils. In conclusion, we can assume that the long‐term no‐tillage can preserve an agricultural soil in a semiarid ecosystem, enhancing soil biological fertility level and bacterial diversity.

Long-term impacts of conservation tillage on Mediterranean agricultural soils: shifts in microbial communities despite limited effects on chemical properties

Mediterranean ecosystems are especially sensitive to the effects of intensive agriculture. Therefore, sustainable practices based on the protection of organic matter and water in soil are of great interest in these systems. Among these practices, tillage and crop rotation could induce changes in soil properties and consequently on soil microbial communities, which play a fundamental role in soil fertility. In this work we evaluated the changes in some soil chemical and biochemical properties induced by different tillage types -non-tillage (NT), reduced tillage (RT) and traditional tillage (TT)- in a trial that was established 10 years ago in a typical Mediterranean crop rotation. Phospholipid fatty acid analysis (PLFA) was performed to test the effect of tillage on the structure of the soil microbial community. Two soil samplings were performed, one after tillage operation (fallow period) and the other during the late stage of a legume crop to compare the effects of long-term tillage and crop development in these variables. Results indicated that conservation tillages (NT and RT) had positive effects on soil chemical properties (mainly on soil N) in comparison to TT, especially during the fallow period. Crop production, however, was similar between treatments. Some biochemical (enzyme activities) and biological (PLFA profile) parameters were better indicators of the effect of tillage type on soil than chemical variables. PLFA profiles were more different among tillage types during the fallow period, but when PLFAs were assigned into functional groups the tillage effect was more evident after crop development, when conservation tillage (NT and RT) promoted a higher abundance of soil fungi over bacteria. We strongly recommend that PLFA analysis should be performed on fallow period before tillage operations, and to couple PLFA measurement with at least one method of microbial activity in order to fully assess the impact of different tillage systems on soil functioning. The results have allowed, to 1) quantify the effect of tillage on the distribution of bacterial and fungal communities in the soil (PLFA) and on its functionality (enzyme activities) during the development of a legume crop and 2) establish that the combined use of chemical and biological variables is necessary to set up indicators of soil quality in tillage comparison trials.

Hydrophobicity and surface free energy to assess spent coffee grounds as soil amendment. Relationships with soil quality

The aim of this work was to evaluate the effects of spent coffee grounds (SCG), a highly hydrophobic raw material, on the hydrophobicity of two Mediterranean agricultural soils. Physical, chemical, mineralogical and biological soil properties, most of them used to evaluate soil quality, were studied and related to the main hydrophobicity parameters. The in vitro assay was performed with two SCG doses (2.5 and 10%), two soils and two incubation times (30 and 60 days). Hydrophobicity was determined by the water drop penetration time test (WDPT), the contact angle (CA) with H2O, formamide and diiodomethane, and the surface free energy components (SFE) calculated using the Van Oss model. The addition of SCG increased the WDPT, CA and SFE, being the latter which was related to a greater number of soil quality variables. Hydrophobicity was related to lower humus quality index (HQI), and a higher proportion of labile organic matter, as shown by Infrared and UV–vis spectroscopy. An increase in hydrophobicity was related to an improvement of soil physical quality: a high aggregate stability index, saturated hydraulic conductivity, porosity (total and macro), water retention, and a less bulk density. The most critical effect related to the increase in hydrophobicity was the significant decrease in the available water content. The SEM images showed a greater occlusion and stabilization mechanism of the SCG particles incorporated in Vega soil, probably due to its higher content of smectite and carbonates. The appearance of fungal biomineralizations of calcium carbonate is associated with SCG addition and could be considered as an interesting and little studied process of inorganic carbon fixation and secuestration. These results showed that hydrophobicity can afford relevant information that can help to asses soil quality status after an amendment with SCG.

Short-term impact of spent coffee grounds over soil organic matter composition and stability in two contrasted Mediterranean agricultural soils

Spent coffee grounds (SCG) is a biowaste which arouse great interest as soil organic amendment due to the huge amount produced around the world. However, the impact of this residue on soil organic matter (SOM) functionality and stability has been barely studied. Thus, the aim of this work is to study the short-term effects of SCG on the quantity and quality of SOM in two Mediterranean agricultural soils (Vega soil, SV and Red soil, SR) in microcosm conditions. The in vitro assay was performed with two fresh SCG doses (2.5 and 10% w/w), two incubation times (30 and 60 days) and two agricultural soils (SV and SR). SOM fractionation to obtain total extractable carbon, humic acids, fulvic acids, humins and hot water soluble carbon (HWSC) was determined. Spectroscopic UV-Vis and Mid-IR, thermogravimetric and simultaneous differential thermal analysis, as well as scanning electron microscopy (SEM), were also applied in this study. SCG increased all SOM fractions, especially the levels of more labile SOM (HWSC, increased 600–700%) and total extractable carbon (increased to around 200%). SCG also increased humic acids and fulvic acids around 200%, but the functionality of humic acids was affected by a reduction of the functional groups with more recalcitrant and stable character. The tested soils are different from each other (the SV has a more clayish texture and a higher smectite clay content than the SR) which made the behaviour of these soils different. The degree of incorporation of SCG into the soils structure and the interaction between soil and SCG particles (observed by SEM) affected carbon retention under stable forms, increasing carbon stabilization in SV with respect to SR. The short-term effect of SCG on SOM composition and functionality demonstrate that this bioresidue could be used as soil organic amendment, being a valuable alternative use of a polluting waste. Soil type is a key factor since it influences the soil-SCG interaction and consequently SOM stability. To deepen the study of those effects, it would be necessary to analyze the long-term effects, field studies and to test in a greater number of soil types.

The interactive effect of no-tillage and liming on gross N transformation rates during the summer fallow in an acid Mediterranean soil

In the Mediterranean rainfed agriculture, a summer fallow is necessary because of the severe drought and high temperatures. Due to suppressed plant nitrogen (N) uptake during this period, an accumulation of inorganic N in the soil may occur, which could be lost from the system during the first autumn rains. Both mineralization and nitrification rates can be affected by agricultural practices, such as tillage or liming, influencing the amount of available N present in the soil during the fallow period. In this study, we investigated the effects of two common agricultural practices, no-tillage (instead of traditional tillage) and liming, on soil gross N transformations during the summer fallow. Liming increased gross N mineralization (from 1.21 to 1.78 mg N kg−1 day−1) and gross nitrification (from 0.44 to 0.76 mg N kg−1 day−1) while traditional tillage increased N immobilization. Tillage did not affect gross nitrification but the effect of liming on gross N mineralization was enhanced in no-tillage plots. The total bacteria abundance was enhanced by liming and no-tillage and seemed to be responsible for gross N mineralization and immobilization. The gross mineralization, nitrification and microbial immobilization decreased during the summer fallow with an overall reduction by 40%, 56%, 74% and 54% in gross N mineralization, gross nitrification, ammonium immobilization and nitrate immobilization, respectively. The accumulation of ammonium could be interpreted as a consequence of the decoupling between ammonium production and consumption rates. The increase of gross N mineralization and nitrification caused by liming application could result in augmented risks of N losses via nitrate leaching and gaseous losses in autumn, especially under no-tillage. However further studies are required to elucidate the nitrate fate of the in Mediterranean agricultural soils under those management practices.

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

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).

Effects of olive mill wastes with different degrees of maturity on behaviour of S‑metolachlor in three soils

Laboratory and field experiments were conducted on three Mediterranean agricultural soils in so as to investigate the effects of de-oiled two-phase olive mill waste (D) and two-phase olive mill waste (W) and their level of organic matter maturity on the environmental fate of the herbicide S‑metolachlor (SM). Three Mediterranean agricultural soils were amended with fresh (D and W) and composted W (CW) wastes under laboratory conditions. Furthermore, under field conditions, one of the soils was also amended with both wastes (D and W) over 9 years in order to assess the effects of the “aging” transformation (AD and AW treatments, respectively). Significant increases in SM adsorption were observed in all the amended soils, with no reduction in the herbicide's effectiveness. The adsorption process was more reversible with the fresh organic amendments (D or W) than with CW or (even more so) with AD or AW. The fresh amendments also increased the persistence of SM; however the field-aged and composted amendments enhanced its dissipation as a result increased soil microbial activity showed by high levels of soil dehydrogenase activity. The AD- and AW-amended soils, showed the greatest decrease in leaching loss of SM (from 51.9% in original soil to 9.33% in AD and 8.05% in AW), reflecting the strong influence of adsorption-desorption processes on SM leaching. This study has shown that the application of olive mill wastes as organic amendments may be considered a useful strategy to reduce leaching of SM in soils poor in organic matter, especially if those wastes have a high level of organic matter maturity.

Interaction of silver nanoparticles with mediterranean agricultural soils: Lab-controlled adsorption and desorption studies

The production of silver nanoparticles (AgNPs) has increased tremendously during recent years due to their antibacterial and physicochemical properties. As a consequence, these particles are released inevitably into the environment, with soil being the main sink of disposal. Soil interactions have an effect on AgNP mobility, transport and bioavailability. To understand AgNP adsorption processes, lab-controlled kinetic studies were performed. Batch tests performed with five different Mediterranean agricultural soils showed that cation exchange capacity and electrical conductivity are the main parameters controlling the adsorption processes. The adsorption kinetics of different sized (40, 75, 100 and 200 nm) and coated (citrate, polyvinylpyrrolidone and polyethyleneglycol (PEG)) AgNPs indicated that these nanoparticle properties have also an effect on the adsorption processes. To assess the mobility and bioavailability of AgNPs and to determine if their form is maintained during adsorption/desorption processes, loaded soils were submitted to leaching tests three weeks after batch adsorption studies. The DIN 38414-S4 extraction method indicated that AgNPs were strongly retained on soils, and single-particle inductively coupled plasma mass spectrometry confirmed that silver particles maintained their nanoform, except for 100 nm PEG-AgNPs and 40 nm citrate-coated AgNPs. The DTPA (diethylenetriaminepentaacetic acid) leaching test was more effective in extracting silver, but there was no presence of AgNPs in almost all of these leachates.