Mediterranean Agricultural Soils Research Articles

Environmental behavior of the enantiomers of the chiral fungicide metalaxyl in Mediterranean agricultural soils

Improving the existing knowledge on the enantioselectivity of processes affecting chiral pesticide enantiomers in the environment is necessary to maximize the efficacy and minimize the environmental impact caused by the use of pesticides with chiral properties. In this work, the enantioselectivity of the sorption, degradation, and leaching processes of the chiral fungicide metalaxyl in three slightly alkaline, agricultural soils from southern Spain was studied. Batch sorption experiments indicated that the sorption of racemic-metalaxyl on soils, their clay (<2μm) fractions, and a number of model sorbents simulating naturally-occurring soil colloidal particles was non-enantioselective; the S-enantiomer was sorbed to the same extent as the R-enantiomer on all soil materials. Soil incubation experiments revealed that the R-enantiomer of metalaxyl was degraded faster than the S-enantiomer in all three soils, but the extent and enantioselectivity of metalaxyl degradation was soil-dependent, occurring more slowly and with less enantioselectivity in the fine-textured soil (soil 1) than in the coarse-textured soils (soils 2 and 3). For soils 2 and 3, S- and R-metalaxyl dissipation data were very well described by single first-order kinetics, whereas for soil 1 dissipation data were better fitted by two coupled first-order equations. It is suggested that sorption and entrapment of metalaxyl enantiomers in the abundant small-size pores of soil 1 (i.e., pore radius<100nm) could have resulted in a fraction of the fungicide of reduced bioavailability, and consequently, protected from enantioselective degradation. Metalaxyl leaching through soil columns was also enantioselective; the concentration of S-metalaxyl in all leachates collected was greater than that of R-metalaxyl. Despite being non-enantioselective, sorption influenced the enantioselectivity of metalaxyl leaching, as it determined the residence time of the fungicide within the soil column, and consequently, the extent and enantioselectivity of its degradation during leaching.

Environmental Fate of Terbuthylazine in Soils Amended with Fresh and Aged Final Residue of the Olive-Oil Extraction Process

The impact of de-oiled and dried two-phase olive mill waste (DW) amendment on the sorption,degradation, leaching, and persistence of the herbicide terbuthylazine in a Mediterranean agricultural soil were studied under laboratory and long-term field conditions. The results are compared with those of a previous study, where the intermediary by-product of the olive-oil processing technology (OW) was applied to the same soil. The adsorption of terbuthylazine by the soil significantly increased with the increase of the amount of DW in the laboratory and field-amended soils. The amount of terbuthylazine leached was significantly decreased or even not detected in the field-amended soil columns, but leaching losses of the herbicide increased by up to 52.7% in the laboratory amended-soils. The DW soil application significantly increased the half-life of terbuthylazine from 6.7 days for the original soil to 21 and 104 days in the field and laboratory amended soils, respectively. In the field study, DW addition decreased the vertical movement of terbuthylazine through the amended soils and increased the persistence of the herbicide in the upper 5 cm of the soils. This study suggests that DW amendment can play a positive role in preventing contamination of groundwater by terbuthylazine, especially after the transformation of the organic matter by aging processes. The results were quantitatively different from those previously obtained with the intermediary by-product OW, showing the importance of the specific characteristics of the amendment in determining its effect on pesticide environmental fate and behaviour.

Effects of sewage sludge biochar on plant metal availability after application to a Mediterranean soil

Pyrolytic conversion of sewage sludge into biochar could be a sustainable management option for Mediterranean agricultural soils. The aim of this work is to evaluate the effects of biochar from sewage sludge pyrolysis on soil properties; heavy metals solubility and bioavailability in a Mediterranean agricultural soil and compared with those of raw sewage sludge. Biochar (B) was prepared by pyrolysis of selected sewage sludge (SL) at 500°C. The pyrolysis process decreased the plant-available of Cu, Ni, Zn and Pb, the mobile forms of Cu, Ni, Zn, Cd and Pb and also the risk of leaching of Cu, Ni, Zn and Cd. A selected Mediterranean soil was amended with SL and B at two different rates in mass: 4% and 8%. The incubation experiment (200d) was conducted in order to study carbon mineralization and trace metal solubility and bioavailability of these treatments. Both types of amendments increased soil respiration with respect to the control soil. The increase was lower in the case of B than when SL was directly added. Metals mobility was studied in soil after the incubation and it can be established that the risk of leaching of Cu, Ni and Zn were lower in the soil treated with biochar that in sewage sludge treatment. Biochar amended samples also reduced plant availability of Ni, Zn, Cd and Pb when compared to sewage sludge amended samples.

Severe drought-induced community tolerance to heat wave. An experimental study on soil microbial processes

Purpose The purposes of this study were to identify the influence of a severe drought period on the impact of a subsequent heat–drought disturbance on the microbial community of a Mediterranean agricultural soil and particularly to highlight the long-term effects on the microbial catabolic profiles.

Can a Single and Unique Cu Soil Quality Standard be Valid for Different Mediterranean Agricultural Soils under an Accumulator Crop?

The validity of the soil quality standard for copper (Cu) established by the Spanish legislation (Spanish Royal Decree 9/2005) is evaluated in representative agricultural Mediterranean soils under an accumulator crop (Lactuca sativa L. var. Romaine cv. Long Green), considering both the effect of the metal on crop growth (biomass production) and its accumulation in the edible part of the plant. For saline soils, such a soil quality standard seems not to be valid taking into account both of the aspects evaluated. For non-saline soils, the soil quality standard also seems not to be valid since, considering the metal accumulation in the edible part of the plant, the soil quality standard should be above such standard; but considering the productivity function of soil (biomass production), the standard should be much below, meaning that this function is being greatly affected by the presence of high concentrations of Cu. The soil quality standard for each soil considered should correspond to a value between its respective EC50 and EC10 values (effective concentrations of added Cu causing 50% and 10% inhibition on the biomass production), depending on the politicians and/or farmers' compromise with yield production and, therefore, with soil productivity. These threshold values were greater for the soil having more organic matter and clay content, showing that Cu toxicity also depends on these properties. Further research in other agricultural areas of the region would improve the basis for proposing adequate soil quality standards as highlighted by the European Thematic Strategy for Soil Protection.

Bioavailability of N released from N-rich pyrogenic organic matter: An incubation study

In Mediterranean ecosystems, natural wildfires and prescribed burning play an important role. In order to obtain a better understanding of the impact of charcoal on the nitrogen (N) cycling in soil, 15N-enriched pyrogenic organic material (PyOM) obtained from “ Lolium perenne” charred for 4 min at 350 °C was mixed with a typical Mediterranean agricultural soil and incubated for 72 days under controlled conditions. The main objectives were to analyze the availability of N from this material and to obtain more insight into the recalcitrance of PyOM in soils. Addition of artificially produced 15N-PyOM increased the biomass production and N retention. After 72 days of incubation time, 10% of the 15N added to the soil ( 15N add) was incorporated into new grass biomass. Solid-state 15N NMR spectroscopy revealed that at least some of this N derived from the degradation of pyrrole-type structures. Increase of the amide-N intensity in the solid-state 15N NMR spectrum of the incubated soils indicated further that some 15N from the PyOM was also incorporated into new microbial biomass. Our results confirmed a relatively low recalcitrance of N-rich PyOM. Since during its degradation, N is only slowly transferred into a plant-available form, it may contribute to the observed improvement of soil fertility by avoiding fast N losses due to leaching and volatilization as a slow N-release fertilizer.

An appraisal of soil organic C content in Mediterranean agricultural soils

AbstractLow soil organic carbon (SOC) levels in dry areas can affect soil functions and may thus indicate soil degradation. This study assesses the significance of SOC content in Mediterranean arable soils based on the analysis of a broad data set of 2613 soils sampled from Mediterranean grasslands and agricultural land. The distribution in values of SOC, pH, clay and carbonates was analysed according to different climatic areas (semi‐arid, Mediterranean temperate, Mediterranean continental and Atlantic) and with respect to six different land uses (grassland, cereal crops, olives and nuts, vineyards, fruit trees and vegetable gardens). The general trend was for low SOC in arable land and decreased with aridity. In wet areas (Atlantic and Mediterranean continental), acidic soils had a higher SOC content than did calcareous soils, whereas in the Mediterranean temperate area SOC had little relationship to soil pH. In low SOC arable soils, the SOC content was related to clay content. In calcareous arable soils of the Mediterranean temperate zone, SOC content was more closely related to carbonates than to clay. In contrast to the Atlantic area, Mediterranean grassland soils had much lower amounts of SOC than forest soils. Mediterranean calcareous and temperate acidic soils under grassland had SOC‐to‐clay ratios similar to or only slightly greater than that under a crop regime. In contrast, Mediterranean continental acidic soils under grassland had a much higher SOC‐to‐clay ratio than arable soils. This suggests a low resilience of the Mediterranean temperate and calcareous arable soils in terms of SOC recovery after the secession of ploughing, which may be a result of intensive use of these soils over many centuries. Consequently, we hypothesize that the Mediterranean calcareous soils have undergone significant changes that are not readily reversed after ploughing ceases. Such changes may be related to alterations in soil aggregation and porosity which, in turn, are associated with soil carbonate dynamics. Decarbonation processes (the depletion of active carbonates) may therefore be relevant to the reclamation of highly calcareous arable soils through fostering soil re‐aggregation. The article concludes by discussing the suitability of zero tillage, manuring or the introduction of woody species to increase SOC in calcareous arable soils that are highly depleted of organic matter.

Evaluation of the combined effects of dimethoate and spirodiclofen on plants and earthworms in a designed microcosm experiment

Most studies in soil ecotoxicology are designed to assess the effects of individual chemicals on individual test species, using a reference soil (e.g. LUFA 2.2, OECD soil). There is therefore an urgent need for a more comprehensive and integrated approach in order to assess the impact of chemical pollutants on soil ecosystems. In this study, a more realistic scenario in ecotoxicity evaluation was achieved through the use of microcosm-based experiments, using a small-scale terrestrial ecosystem (“STEM”) containing Mediterranean agricultural soil. Earthworms ( Eisenia andrei) and turnip seeds ( Brassica rapa) were introduced into the microcosms, in order to examine the effects of the acaricide spirodiclofen and the insecticide dimethoate, both in single and binary combination exposures. Results showed that for plants and earthworms the recommended application dose of both pesticides did not cause impairment of growth, although increasing concentrations resulted in a biomass decrease for both species. Earthworms were found to alter their depth distribution as a response to the combined application of the two pesticides, with this parameter being more sensitive than body mass. The various binary mixtures tested resulted in antagonistic effects on B. rapa shoot length and fresh weight. Regarding the depth distribution of earthworms, antagonism was observed at field dose, as well as at five times the field dose for both pesticides, while synergism occurred at ten times the field dose.

Field inoculation effectiveness of native and exotic arbuscular mycorrhizal fungi in a Mediterranean agricultural soil

In sustainable agriculture, arbuscular mycorrhizal (AM) fungal inoculation in agronomical management might be very important, especially when the efficiency of native inocula is poor. Here, we assessed the effect of native and exotic selected AM fungal inocula on plant growth and nutrient uptake in a low input Trifolium alexandrinum–Zea mays crop rotation. We evaluated the effects of four exotic AM fungal isolates on T. alexandrinum physiological traits in greenhouse. Then, the field performances of T. alexandrinum inoculated with the exotic AMF, both single and mixed, were compared to those obtained with a native inoculum, using a multivariate analysis approach. Finally, we tested the residual effect of AM fungal field inoculation on maize as following crop. Multivariate analysis showed that the field AM fungal inoculation increased T. alexandrinum and Z. mays productivity and quality and that the native inoculum was as effective as, or more effective than, exotic AM fungal isolates. Moreover, the beneficial effects of AMF were persistent until the second year after inoculation. The use of native AMF, produced on farm with mycotrophic plants species, may represent a convenient alternative to commercial AM fungal inocula, and may offer economically and ecologically important advantages in sustainable or organic cropping systems.

Sorption of hydrophobic pesticides on a Mediterranean soil affected by wastewater, dissolved organic matter and salts

Irrigation with treated wastewaters as an alternative in countries with severe water shortage may influence the sorption of pesticides and their environmental effects, as wastewater contains higher concentrations of suspended and dissolved organic matter and inorganic compounds than freshwater. We have examined the sorption behaviour of three highly hydrophobic pesticides (the herbicide pendimethalin and the insecticides α-cypermethrin and deltamethrin) on a Mediterranean agricultural soil using the batch equilibration method. We considered wastewater, extracts from urban sewage sludge with different dissolved organic carbon contents, and inorganic salt solutions, using Milli Q water as a control. All pesticides were strongly retained by soil although some sorption occurred on the walls of the laboratory containers, especially when wastewater and inorganic salt solutions were used. The calculation of distribution constants by measuring pesticide concentrations in soil and solution indicated that pendimethalin sorption was not affected whereas α-cypermethrin and deltamethrin retention were significantly enhanced (ca. 5 and 2 times, respectively) when wastewater or salt solutions were employed. We therefore conclude that the increased sorption of the two pesticides caused by wastewater cannot be only the result of its dissolved organic carbon content, but also of the simultaneous presence of inorganic salts in the solution.

Testing the validity of a Cd soil quality standard in representative Mediterranean agricultural soils under an accumulator crop

The validity of a quality standard for cadmium (Cd) in representative agricultural Mediterranean soils under an accumulator crop ( Lactuca sativa L.) is evaluated in this work considering both its effect on the crop growth (biomass production) and the metal accumulation in the edible part of the plant. Four soils with different properties relevant to regulate the behaviour of heavy metals were selected from the Valencian Region, a representative area of the European Mediterranean Region. For all soils, the effective concentration of added Cd causing 50% inhibition (EC 50) on the biomass production was much higher than the minimum legal concentration used to declare soils as contaminated by cadmium, i.e. 100 times the baseline value for Cd, in Spain (Spanish Royal Decree 9/2005). As expected, Cd toxicity in the crop was higher in the soils having less carbonate content. On the other hand, for all soils, from the second dose on, which represents 10-times the baseline value for Cd, the metal content in crops exceeded the maximum level established for leaf crops by the European legislation (Regulation EC no. 466/2001). Soil salinity and coarse textures make the accumulation of Cd in the edible part of the plant easier. Therefore, the legal baseline soil cadmium content established by the Spanish legislation seems not valid neither from the point of view of the effect on the crop growth nor from the point of view of the metal accumulation in the edible part of the plant. In order to realistically declare contaminated soils by heavy metals, soil quality standards should be proposed taking into account the soil properties. Further research in other agricultural areas of the region would improve the basis for proposing adequate soil quality standards for heavy metals as highlighted by the European Thematic Strategy for Soil Protection.

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 °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 °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.

Effect of organic and mineral fertilizers on soil respiration and enzyme activities of two Mediterranean horticultural soils

The effects of municipal food waste compost addition and mineral fertilization on selected soil microbiological activities were investigated during 3 years of reiterated treatments on two Mediterranean agricultural soils with different organic carbon content. Compost at 15, 30 and 45 t ha−1 (dry matter), mineral (NPK) fertilizers and combined fertilizers with 15 t ha−1 of compost plus two reduced doses of mineral N were applied to both soils. At both sites, organic amendment increased soil respiration, fluorescein diacetate hydrolysis, phosphatase and arylsulphatase activities. The differences in soil microbial activities among treatments, found after 3 years of repeated treatments, were attributable to the variations of soil organic C content and to the impact of soil tillage. Our results show that, in Mediterranean intensively cultivated agroecosystems, annual organic amendments improve the microbial activity of soil and produce cumulative effects, suggesting the usefulness of repeated high-rate compost applications.

Mineralization dynamics and biochemical properties during initial decomposition of plant and animal residues in soil

The use of organic residues as soil amendments or fertilisers may represent a valuable recycling strategy. In this study, a series of laboratory assays was performed to study the effects of the application of organic residues on C and N mineralization and biochemical properties in a Mediterranean agricultural soil. Two crop residues (straw and cotton) and two animal by-products (meat bone meal and blood meal) were added at three rates (5, 10 and 20 mg g −1 on dry weight basis) to a moist (40% water holding capacity) sandy soil and incubated at 20 °C for 28 days. Each residue underwent a different mineralization pattern depending on the nature and complexity of its chemical constituents. In all cases, the addition of the waste produced, after a short lag-phase, an exponential increase in the soil respiration rate, reflecting the growth of microbial biomass. The amount of total extra CO 2-C evolved after 28 days, expressed as % in respect to added C, differed significantly ( P < 0.005) among application doses: 5 > 10 > 20 mg g −1 and residue type: meat bone meal > blood meal > cotton cardings > wheat straw. Plant residues led to a rapid immobilisation of N that affected microbial size and activity and further mineralization. Animal by-products produced an immediate and remarkable increase of mineral N in the soil. However, the large amounts of NH 4 + released in the soil at high rates of animal residues led, in some cases, to temporary adverse effects on microbial biomass growth and nitrification. All residues produced a significant increase in soil microbial biomass size and activity, being the intensity of the response related to their chemical properties.

Effects of De‐oiled Two‐Phase Olive Mill Waste on Mediterranean Soils and the Wheat Crop

Semiarid Mediterranean soils under intensive continuous cultivation have a net deficit of C, and addition of organic wastes is becoming a common practice as a disposal strategy and an interesting solution to redress this deficiency. A 2‐yr greenhouse study using wheat (Triticum aestivum L.) was conducted to evaluate the potential use of the final solid waste of the new technology of olive‐oil extraction (de‐oiled two‐phase olive mill waste, DTPOMW) as a soil conditioner and amendment agent. Two representative Mediterranean agricultural soils, a Typic Haploxeralf (TH) and a degraded Lithic Xerorthent (LX) were used. Treatments included five DTPOMW rates ranging from 0 to 40 Mg ha−1 combined with mineral fertilizer. Significant direct and residual increases in organic C, total N, available K, cation exchange capacity, and aggregate stability were observed in both soils; however, available P decreased significantly. In the first year of the experiment, an application of 40 Mg DTPOMW ha−1 had a depressive effect on grain yield and on the N and P content in the wheat grain for the LX soil, while in the TH soil there was a positive effect on yield at the same loading rate. There was an increased residual fertilization and amendment effect of DTPOMW for both soils during the second experimental year, and the grain yields increased by 23 and 202% when 40 Mg DTPOMW ha−1 was applied to the TH and LX soils, respectively. For both soils, the best fits to grain yield vs. DTPOMW rates were with a quadratic regression (R2 = 0.977, P &lt; 0.001 for TH; R2 = 0.983, P &lt; 0.001 for LX). Raw DTPOMW may be a potentially valuable soil amendment agent and source of organic matter, N, and K because it maintains a positive, beneficial effect on wheat grain yield and soil properties for 24 mo following application.

Short-term effects on soil properties and wheat production from secondary paper sludge application on two Mediterranean agricultural soils

This study was conducted under greenhouse conditions to evaluate the potential use of SPS as a fertilizer, amendment and/or liming agent for wheat ( Triticum aestivum L.). Two representative Mediterranean agricultural soils, a Cambic Arenosol (cmAR) and a Cromic Cambisol (crCM) were used. Treatments included four sludge rates ranging from 0 to 40 g kg −1 (equivalent of 0, 38, 88 and 120 Mg ha −1). A significant increment in soil pH, organic carbon, N total, available P and exchangeable K were observed in both soils. Sludge application significantly increased N and decreased Zn, Mn and Cu concentrations in wheat. Wheat grain yields were reduced by 33% and 37% when 120 Mg SPS ha −1 was applied to cmAR and crCM soils, respectively, due apparently to unavailability of Mg. However, straw yields, with much lower Mg requirements, increased significantly with SPS rates. Secondary pulp mill sludge seems to be a potential source of organic matter, N, P, K and a potential soil amendment liming agent for acid soils, when appropriate supplemental fertilizer was provided. For grain crops grown in these soils, addition of Mg is required for proper nutrient balance.

Organic Amendments from Olive Cake as a Strategy To Modify the Degradation of Sulfonylurea Herbicides in Soil

Amending soil with products rich in organic matter, such as raw olive cake or alperujo and its compost and vermicompost, could be a simple bioremediation strategy for soil pollutants such as pesticides. To investigate this hypothesis in relation to sulfonylurea herbicides, these amendments were applied to a Mediterranean agricultural soil at rates 4 times higher than agronomical dosage to stimulate biodegradation of chlorsulfuron, prosulfuron, and bensulfuron, added in a mixture to the soils. Degradation studies were conducted in microbially active and sterile soils to check the importance of biological and chemical degradation of sulfonylurea herbicides in nonamended and amended soil. The addition of alperujo stimulated soil microbial activity, as determined by dehydrogenase activity measurements, but it did not enhance the degradation of the sulfonylurea herbicides. In contrast, compost and vermicompost slightly favored the biological degradation of bensulfuron during the first week of incubation. Chlorsulfuron and prosulfuron were mainly degraded by chemical pathways in all substrates, which is probably due to a competitive or inhibitory phenomenon observed between chlorsulfuron and bensulfuron. The first-order kinetic equation satisfactorily explained the experimental data for chlorsulfuron and prosulfuron; however, a biphasic model, such as that proposed by Hoerl, better predicted the results obtained for bensulfuron.

RESPONSE OF SOIL AND WHEAT CROP TO THE APPLICATION OF TWO-PHASE OLIVE MILL WASTE TO MEDITERRANEAN AGRICULTURAL SOILS

The two-phase centrifugation system for olive-oil extraction produces approximately 4,000,000 Mg per year of semisolid olive mill waste (SOMW) in Spain. Soils under intensive cultivation in the Mediterranean region have a net deficit of C, and SOMW application may represent a solution to this deficiency. A 2-year greenhouse study using wheat (Triticum aestivum L.) was conducted to evaluate the potential use of SOMW as a soil conditioner and soil amendment. Two representative Mediterranean agricultural soils, a Cutanic Luvisol (CL) and a degraded Leptic Cambisol (LC), were used. Treatments included five SOMW rates, ranging from 0 to 40 Mg ha−1, combined with mineral fertilizer. Significant increases in organic carbon, aggregate stability, total N, available K, and cation-exchange capacity were observed in both soils. However, available P decreased significantly. The SOMW application significantly increased N, P, and K uptake by the wheat in the LC soil but decreased P and K uptake in the CL soil. In the second year of the experiment, the SOMW application significantly increased the yield in both soils, and grain yields were increased by 29% and 198% when 40 Mg SOMW ha−1 was applied to the CL and LC soils, respectively. Raw SOMW, thus, seems to be a potential soil amendment agent and a source of organic matter, N, and K, especially in degraded agricultural soils.

Modelling changes in soil organic matter after planting fast-growing Pinus radiata on Mediterranean agricultural soils

Modelling changes in soil organic matter after planting fast-growing Pinus radiata on Mediterranean agricultural soils

Modelling changes in soil organic matter after planting fast‐growing Pinus radiata on Mediterranean agricultural soils

SummaryThe Kyoto Protocol explicitly allows the storage of carbon (C) in ecosystems resulting from afforestation to be offset against a nation's carbon emissions and paves the way for carbon storage in soils to be eligible as carbon offsets in the future. More information is required about how afforestation affects carbon storage, especially in the soil. We report a study in which soil carbon storage in first‐rotation Mediterranean Pinus radiata plantations, established on former cereal fields and vineyards, was measured and modelled. Measurements were made on plantations of several ages, as well as repeat measurements at the same site after 5 years. We tested the ability of two widely used soil organic matter models (RothC and Century) to predict carbon sequestration in Mediterranean forest soils.Increases in the top 5 cm of soil of about 10 g C m−2 year−1 were observed after afforestation of former vineyards, but nitrogen (N) either remained the same or decreased slightly. During afforestation, most organic matter accumulated in the ectorganic layers at a rate of 19 g C m−2 year−1 in former vineyards and 41 g C m−2 year−1 in former cereal fields. The RothC and Century models were sensitive to previous land use and estimated a carbon sequestration potential over 20 years of 950 and 700 g C m−2, respectively. The accurate simulation of the dynamics of soil organic matter by RothC, together with measured above‐ground inputs, allowed us to calculate below‐ground inputs during afforestation. The Century model simulated total C and N, including the ectorganic horizons, well. Simulations showed a depletion of N in the below‐ground fractions during afforestation, with N limitation in the former vineyard but not on former cereal land. The approach demonstrates the potential of models to enhance our understanding of the processes leading to carbon sequestration in soils.