Semiarid Mediterranean Soil Research Articles

Effects of long-term organic and mineral fertilizers on bulk density and penetration resistance in semi-arid Mediterranean soil conditions

Soil aggregation is of great importance in agriculture due to its positive effect on soil physical properties, plant growth and the environment. A long-term (1996–2008) field experiment was performed to investigate the role of mycorrhizal inoculation and organic fertilizers on some of soil properties of Mediterranean soils (Typic Xerofluvent, Menzilat clay–loam soil). We applied a rotation with winter wheat ( Triticum aestivum L .) and maize ( Zea mays L.) as a second crop during the periods of 1996 and 2008. The study consisted of five experimental treatments; control, mineral fertilizer (300–60–150 kg N–P–K ha −1), manure at 25 t ha −1, compost at 25 t ha −1 and mycorrhiza-inoculated compost at 10 t ha −1 with three replicates. The highest organic matter content both at 0–15 cm and 15–30 cm soil depths were obtained with manure application, whereas mineral fertilizer application had no effect on organic matter accumulation. Manure, compost and mycorrhizal inoculation + compost application had 69%, 32% and 24% higher organic matter contents at 0–30 cm depth as compared to the control application. Organic applications had varying and important effects on aggregation indexes of soils. The greatest mean weight diameters (MWD) at 15–30 cm depth were obtained with manure, mycorrhiza-inoculated compost and compost applications, respectively. The decline in organic matter content of soils in control plots lead disintegration of aggregates demonstrated on significantly lower MWD values. The compost application resulted in occurring the lowest bulk densities at 0–15 and 15–30 cm soil depths, whereas the highest bulk density values were obtained with mineral fertilizer application. Measurements obtained in 2008 indicated that manure and compost applications did not cause any further increase in MWD at manure and compost receiving plots indicated reaching a steady state. However, compost with mycorrhizae application continued to significant increase (P < 0.05) in MWD values of soils. Organic applications significantly lowered the soil bulk density and penetration resistance. The lowest penetration resistance (PR) at 0–50 cm soil depth was obtained with mycorrhizal inoculated compost, and the highest PR was with control and mineral fertilizer applications. The results clearly revealed that mycorrhiza application along with organic fertilizers resulted in decreased bulk density and penetration resistance associated with an increase in organic matter and greater aggregate stability, indicated an improvement in soil structure.

Soil quality indicator response to tillage and residue management on semi-arid Mediterranean cropland

No-tillage (NT) practices for rainfed cereal production in semi-arid Mediterranean soils can conserve water and increase crop productivity, but producers are reluctant to adopt NT because of potential increases in penetration resistance and bulk density. We hypothesized that understanding soil quality could encourage NT adoption, but methods for selecting and assessing soil quality indicators needed to be developed for this region. Our objectives were to (1) identify the most sensitive indicators for evaluating long-term tillage and residue management within this region using factor analysis, and (2) compare soil quality assessment using those indicators with traditional evaluations using changes in water retention, earthworm activity and organic matter stratification ratio. Several soil physical, chemical, and biological indicators were measured within conventional tillage, minimum tillage, and NT (with and without stubble burning) treatments that represent a wide agro-climatic area in NE Spain. Sampling depth and management treatments significantly affected several indicators when evaluated individually and collectively. Principal component analysis identified three factors that accounted for 75 and 85% of the variation in soil measurements for 0–5- and 5–15-cm depth increments. Only two factors per depth showed significant differences among the four treatments. For both depth increments, one factor grouped soil physical attributes, and the other organic matter and biological properties. The indicators with the greatest loadings were identified as the most sensitive in each factor. These were penetration resistance, particulate organic matter (POM) and total organic matter within the 0–5 cm layer, and aggregate stability and POM within the 5–15-cm increment. Factor scores were positively correlated to soil water retention, earthworm activity and organic matter stratification, which were all greater in NT, regardless of stubble management. We conclude that (1) multivariate analyses are useful for selecting appropriate soil quality indicators, and (2) that adopting NT on Mediterranean semi-arid cropland can have several positive effects on soil quality within this region.

Biochemical properties and barley yield in a semiarid Mediterranean soil amended with two kinds of sewage sludge

Recycling sewage sludges as soil organic amendment and as a source of macro- and micronutrients represents a promising agricultural practice, especially in Mediterranean areas, where soils commonly exhibit low organic matter contents. However, this organic waste must be treated to avoid potential hazardous effects over the soil or the plants. For this aim, there are different treatments, some of them of contrasted feasibility, such as composting. However, the implementation of recent technologies, like thermal-drying, allows obtaining in less time a final product with exceptional handling conditions. This modern treatment has been introduced in an increasing number of wastewater treatment plants during the last years. Nevertheless, the effects of thermally dried sewage sludge on soil biota and crop yields have not been widely studied to date. In this work, composted and thermally dried sewage sludges were applied to a cropped soil over a three-year period, with different frequencies (single or yearly applications) and at two rates (20 and 80 t ha −1), to investigate and compare their cumulative and residual effects on the yield of barley and on chemical, biological and biochemical soil properties. In the cumulative experiment high doses of both sewage sludges caused an increase of the total organic C contents but also a significant decrease in crop yield, as well as in enzyme activities and microbial biomass C contents. In contrast, cumulative applications of both types of sewage sludge at low doses showed, in general, better barley yield parameters as well as significantly higher microbial biomass C contents, particularly for the composted one. The best results for barley yield were obtained in soils amended once with sewage sludge, particularly for those amended with the composted sewage sludge. These results may be attributed to a possible deleterious effect over soil properties derived from the use of excessive doses. Besides, the results stood out the benefits derived from the application to soil of the composted sewage sludge, which presented a much more mature and stable organic matter than the thermally dried sewage sludge.

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.

Pinus halepensis Mill. plantations did not restore organic carbon, microbial biomass and activity levels in a semi-arid Mediterranean soil

Maquis is a dense evergreen shrub layer which, in semi-arid Mediterranean lands, is commonly linked to the presence of well-conserved soils with large contents of mineralizable substrates. It was our aim to test whether: (i) maquis promotes soil microbial biomass and activity, and (ii) mature pine plantations without a shrubby understory support microbial biomass and activity levels comparable to those of stands with maquis. Surface soil samples were taken in four sites that sustain pine plantations (PP), maquis with pines (MP), maquis (MQ) and grasslands (GS). Microbial biomass was inferred from the C content in the soil microbiota. The ATP content in fresh samples and the CO 2–C production from incubated samples were used to assess microbial activity, as was the activity of β-glucosidase and alkaline phosphatase. Topsoils under maquis (MP and MQ) were the most fertile, both chemically (high organic carbon contents) and physically (low bulk density, high aggregate stability) and showed by far the largest levels of microbial biomass and activity. These levels in soils under PP, which sustained a successful plantation in terms of tree canopy density but lacked the shrubby understory, were significantly smaller than those of the adjacent shrubland with pines (MP). Redundancy analysis extracted a main axis explaining 67% of the variation of the microbiological soil properties, which was interpreted as an environmental gradient of soil fertility. Along this axis, the samples were separated according to the presence or absence of a maquis dominated by late-successional species; other factors such as soil type, slope position and aspect were less influential. The effects of afforestation practices on the detritus-based system should be considered in the design of future forest restoration strategies in desertification-threatened lands.

Agronomic application of olive mill wastewaters with phosphate rock in a semi-arid Mediterranean soil modifies the soil properties and decreases the extractable soil phosphorus

Olive mill wastewater (OMW), a by-product of the olive-mill industry, is produced in large amounts in Mediterranean countries. The presence of indigenous phosphate deposits in some countries like Tunisia provides an incentive for direct application or local chemical treatment at low cost to improve the solubility of low reactive phosphate rocks (PRs). The use of naturally occurring low-molecular weight organic acids (LMWOAs) that are present in OMW represents a new perspective in PR research and a possible solution for the recycling of the OMW. The present work was aimed at evaluating, under natural situations (field of olive trees), the effects of agronomic application of OMW (amounts applied: 30, 60 m 3 ha −1) with PR (amounts applied: 150 kg ha −1) on olive trees soil properties. We measured organic C, nitrogen (N), extractable phosphorus (P), exchangeable calcium (Ca), and exchangeable potassium (K), as well as other properties (pH and electrical conductivity). Our data provide evidence that agronomic application of OMW with PR has important effects on soil properties. Increases in organic C, total N, extractable P and exchangeable potassium (K) were found after the first agronomic application of OMW and PR. These increases were only temporary, following the second agronomic application of OMW and PR, significant reductions were detected in the extractable soil P (19.67 mg kg −1 in the control soil vs. 8.99 mg kg −1 in the amended soil). Changes in the extractable soil P could alter plant productivity and plant community structure because shifts in nutriment availability can affect the balance between limiting and non-limiting nutrients.

Surface and subsurface organic carbon, microbial biomass and activity in a forest soil sequence

The distribution of organic carbon, microbial biomass and activity, from the surface down to 70 cm, was investigated through three semiarid Mediterranean soils: (1) a Typic Calcixeroll covered with a native pinewood (NP), (2) a Typic Calcixerept under a mature pine plantation (PP) on abandoned agricultural terraces and (3) a Typic Haploxerept under a grassland (GS). NP and GS had the highest and lowest soil organic carbon (SOC) pools, respectively. Both of them had decreasing SOC contents with depth. PP, which held intermediate SOC levels, showed an increase in total organic C and humic substances C with depth due to their mineralization in the anciently ploughed topsoil layer. The soils were similarly ranked as regards their microbial biomass and activity: NP>PP>GS. In general, the microbial communities were less dense and active towards the deeper horizons. More specifically, PP and GS had a very populated and active top 20-cm layer, which was attributed to the dense root system of their grass cover. NP maintained high microbial biomass and activity levels from 0 to 70 cm, progressively diminishing along with shrub root density (e.g. microbial biomass C dropped from 2342 to 394 mg kg −1 soil). The latter soil presented the sharpest drop of its microbial properties with depth, what was considered an indicator of its quality. Generally decreasing patterns of microbial biomass and activity were not always coincident with previously published gradients of microbial metabolic abilities and genetic structure. This reinforces the need of combining biomass, activity and biodiversity measurements if the ecosystem's functioning is to be fully understood and a real monitoring of degradation processes and restoration strategies is to be achieved.

Microbial Community Structure at Different Depths in Disturbed and Undisturbed Semiarid Mediterranean Forest Soils

Metabolic abilities and micrfiobial community structure were investigated through three semiarid Mediterranean soils of SE Spain. The soils were (1) a Typic Calcixerept under an adult pine plantation (PP), growing on abandoned agricultural terraces; (2) a Typic Calcixeroll under a native pinewood (NP); and (3) a Typic Haploxerept covered with a grass steppe (GS). PP and NP were similar as regards their genesis, but the former used to be tilled. NP and GS were undisturbed and supported natural and seminatural vegetation, respectively. Seven samples in 10-cm depth increments were taken in triplicate along each soil profile. Community-level physiological profiles based on sole-C-source use were determined to characterize the metabolic abilities. A 16S rDNA polymerase chain reaction-denaturing gradient gel electrophoresis analysis was performed to investigate the microbial genetic structure. Plant cover and land-use history were major determinants of microbial community structure. Microbial communities residing in soils under a native pinewood, the most diverse and stable plant cover, were the most complex both metabolically and genetically. The microbial community structure distinctly changed with depth, related to the quantity and quality of total organic carbon. Both undisturbed soils showed falling gradients of metabolic and genetic complexity, which were invariably of a greater magnitude in the mature woodland than in the grass steppe. In the planted pinewood, however, the substrate-use diversity increased with depth, apparently a response to the depleted metabolic abilities within its upper layer (0-30 cm). Tilling and plant cover removal might be responsible for such a perturbation. In the same profile, molecular fingerprint patterns of the topsoil layer (0-10 cm) indicated a disturbed genetic structure that might underlie the loss of metabolic abilities. However, the genetic structure of the deeper layers of the planted and native pinewoods was not dissimilar, revealing that equivalent genetic resources perform different environmental functions under changing soil scenarios.

Short-term effects of olive mill waste water (OMW) on chemical and biochemical properties of a semiarid Mediterranean soil

Olive mill waste water (OMW), a by-product of the olive mill industry, is produced in large amounts in Mediterranean countries. Olive mill waste water contains a high organic load, substantial amounts of plant nutrients but also several compounds with recognized toxicity towards living organisms. Moreover, OMW may represent a low cost source of water. Thus, the use of OMW for soil fertigation is a valuable option for its disposal, provided that its impact on soil chemical and biochemical properties is established. Investigations were performed on the short-term influence of OMW on several chemical and biochemical properties of a soil from a continental semi-arid Mediterranean region (Morocco). The soil was amended with 0, 18 and 36 ml 100 g −1 soil of OMW (corresponding to a field rate of 0, 40 and 80 m 3 ha −1, respectively) and changes in various functionally related properties such as microbial biomass, basal respiration, extractable C and N, and soil hydrolases and oxido-reductases activities were measured over time. The variations of the main physical and chemical properties as well as the residual phytotoxicity of OMW amended and non-amended soils as assessed by tomato seed germination tests were also monitored. Temporary and permanent changes in several chemical and biochemical soil properties occurred following OMW application, thus being these properties varied in sensitivity to the applied disturbance. A sudden increase of total organic C, extractable N and C, available P and extractable Mn and Fe contents were measured. Simultaneously, a rapid increase of soil respiration, dehydrogenase and urease activities and microbial biomass (at 14 day incubation) of OMW amended soils occurred. In contrast, the activities of phosphatase, β-glucosidase, nitrate reductase and diphenol oxidase decreased markedly. The soil became highly phytotoxic after OMW addition (large decline of soil germination capability), mainly at 80 m 3 ha −1 OMW. After 42 days' incubation, however, a complete recovery of the soil germination capability and a residual phytotoxicity of about 30% were observed with 40 and 80 m 3 ha −1 OMW, respectively. These findings indicate that the impact of OMW on soil properties was the result of opposite effects, depending on the relative amounts of beneficial and toxic organic and inorganic compounds present. The toxic compounds contained in OMW most likely counteracted the beneficial effect of organic substrates provided, which promoted the growth and activity of indigenous microorganisms.

Effects of compost, mycorrhiza, manure and fertilizer on some physical properties of a Chromoxerert soil

Addition of organic materials of various origins to soil has been one of the most common rehabilitation practices to improve soil physical properties. Mycorrhiza has been known to play a significant role in forming stable soil aggregates. In this study, a 5-year field experiment was conducted to explore the role of mycorrhizal inoculation and organic fertilizers on the alteration of physical properties of a semi-arid Mediterranean soil (Entic Chromoxerert, Arik clay-loam soil). From 1995 to 1999, wheat ( Triticum aestivum L.), pepper ( Capsicum annuum L.), maize ( Zea mays L.) and wheat were sequentially planted with one of five fertilizers: (1) control, (2) inorganic (160–26–83 kg N–P–K ha −1), (3) compost at 25 t ha −1, (4) farm manure at 25 t ha −1 and (5) mycorrhiza-inoculated compost at 10 t ha −1. Soil physical properties were significantly affected by organic fertilizers. For soil depths of 0–15 and 15–30 cm, mean weight diameter (MWD) was highest under the manure treatment while total porosity and saturated hydraulic conductivity were highest under the compost treatment. For a soil depth of 0–15 cm, the compost and manure-treated plots significantly decreased soil bulk density and increased soil organic matter concentration compared with other treatments. Compost and manure treatments increased available water content (AWC) of soils by 86 and 56%, respectively. The effect of inorganic fertilizer treatment on most soil physical properties was insignificant ( P>0.05) compared with the control. Mycorrhizal inoculation+compost was more effective in improving soil physical properties than the inorganic treatment. Organic fertilizer sources were shown to have major positive effects on soil physical properties.

Effects of sewage sludge amendment on humic acids and microbiological properties of a semiarid Mediterranean soil

The residual effects of adding 40 t ha−1 sewage sludge (SL) to a degraded soil cropped with barley were investigated after 9 and 36 months in a field experiment under semiarid conditions. The principal soil properties were apparently still affected by SL amendment 9 months after application but the effects disappeared after 36 months. With respect to control soil humic acids (HAs), the SL-HA was characterized by higher contents of S- and N-containing groups, smaller contents of acidic groups, a prevalent aliphaticity, extended molecular heterogeneity, and smaller degrees of aromatic polycondensation and humification. Amendment with SL caused an increase in N, H, S and aliphaticity contents and a decrease in C/N ratios and O and acidic functional group contents in soil HAs isolated 9 months after SL application. These effects tended to decrease after 36 months, most probably because the slightly humified SL-HA was mineralised over time through extended microbial oxidation, while only the most recalcitrant components such as S-containing and aromatic structures were partially accumulated by incorporation into soil HA. Microbial biomass, basal respiration, metabolic quotient and enzymatic activities increased in soil 9 months after SL application, possibly because of increased soil microbial metabolism and enhanced mineralisation processes. After 36 months these properties returned to values similar to those of the unamended soil, presumably due to the loss of energy sources.

Improvements in soil quality and performance of mycorrhizal &lt;I&gt;Cistus albidus&lt;/I&gt; L. seedlings resulting from addition of microbially treated sugar beet residue to a degraded semiarid Mediterranean soil

Improvements in soil quality and performance of mycorrhizal &lt;I&gt;Cistus albidus&lt;/I&gt; L. seedlings resulting from addition of microbially treated sugar beet residue to a degraded semiarid Mediterranean soil

Improvements in soil quality and performance of mycorrhizal Cistus albidus L. seedlings resulting from addition of microbially treated sugar beet residue to a degraded semiarid Mediterranean soil

Abstract. A field experiment was undertaken to assess the effectiveness of a combined treatment, involving addition of Aspergillus niger‐treated sugar beet (SB) residue in the presence of rock phosphate and mycorrhizal inoculation of seedlings with Pisolithus tinctorius. The aim was to improve the physical, chemical, biochemical and biological properties of a degraded semiarid Mediterranean soil. Short‐term effects of such improvements on the establishment of Cistus albidus L. seedlings were evaluated. Eight months after planting, macronutrients (NPK), total carbohydrates, water‐soluble C, water‐soluble carbohydrates, microbial biomass C and enzyme activities (dehydrogenase, urease, protease, acid phosphatase and β‐glucosidase) measured in the rhizosphere soil of C. albidus were increased greatly by addition of fermented SB residue. Soil structural stability improved only with the fermented SB addition (about 79% higher in the amended soils than in the non‐amended soils). The mycorrhizal inoculation was the most effective treatment in improving the growth of C. albidus plants, but only slightly improved soil quality. Growth of inoculated plants was about 33% greater than plants grown in the amended soil and about 131% greater than control plants. The combined benefit of mycorrhizal inoculation of seedlings and addition of fermented SB residue to soil on plant growth was similar to that of the treatments applied individually.

Implications from concentrations and isotopic data for Pb partitioning processes in soils

Lead concentrations and stable isotopic measurements were examined in the different chemical fractions of Czech forest soils to investigate the mechanisms of Pb partitioning. A method of selective sequential dissolution (SSD) was employed that distinguished between five different fractions: exchangeable, surface bound, organic matter, Fe-oxides, and silicates (non-labile). From an analysis of the concentrations and isotopic compositions associated with the different fractions, it is apparent that Pb in the deep Czech mineral soils is of predominantly natural origin and is primarily associated with silicates (69–81%) and Fe-oxides (11–19%). Natural Pb associated with surface bound and organic matter fractions in mineral soils accounts for only 7 to 15%. Anthropogenic Pb in the Czech soils is concentrated primarily in the organic horizons and is strongly associated with the surface-bound and organic matter fractions in which the proportion of total Pb is 33 to 50% and 23 to 47%, respectively. At high and low levels of contamination, Pb isotopic signatures within the labile fractions of the same soil samples are generally homogenous, although a degree of heterogeneity among these fractions is noted in samples of intermediate degrees of contamination. Such heterogeneity probably reflects different levels of natural and anthropogenic Pb mixing. Determination of the mass-normalized affinity of Pb to the primary components using solid-solution distribution coefficients suggests that in Czech forest soils, the order of affinity may be summarized as Fe-oxides > organic matter > silicates. A similar treatment of the data reported for semiarid Mediterranean soils indicates the prevailing order to be Fe-oxides > carbonates > organic matter > silicates. The general similarity of the behaviour of Pb with respect to the different soil components in both temperate and semiarid soils suggests that these orders of affinity may have wider significance for a variety of other soil types.

The use of urban organic wastes in the control of erosion in a semiarid Mediterranean soil

The use of urban organic wastes in the control of erosion in a semiarid Mediterranean soil

The use of urban organic wastes in the control of erosion in a semiarid Mediterranean soil

Abstract. A two year field experiment was carried out in a semiarid Mediterranean area in order to evaluate, the effect on soil erosion of adding different urban organic wastes: a stabilized municipal waste (compost), an unstabilized municipal waste, and an aerobic sewage sludge. All the treatments significantly reduced soil erosion, compared to the control soil. The soil amended with compost was the most effective treatment, reducing soil loss by 94% and runoff by 54%.

Water‐retention capacity in fine earth and gravel fractions of semiarid Mediterranean Montane soils

Water retention capacity was studied in fine earth and gravel from loamy‐textured soils with medium‐low carbon content in a semiarid Mediterranean montane location. Sierra Gador, southeastern Spain. In fine earth, typical water retention curves were established at six soil water potentials (‐10, ‐33, ‐100, ‐500, ‐1000, and ‐1500 kPa), and the water retention was compared against different physical, chemical, and miner‐alogical properties. Percent total sand and organic carbon content were the variables that gave the best fit in the pedotransfer functions for the calculation of water retention at ‐33 and ‐1500 kPa. Results for water retention in gravel at ‐33 and ‐1500 kPa show that gravel can make a significant contribution to the available water in the soil. Bulk density of gravel was the property most closely related to water content at both soil water potentials, and was the variable that gave the best fit in the pedotransfer functions. Other properties that were useful with this function were citrate‐ditionite extractable Fe content, quartz, feldspathic, and phillosilicates content. In semiarid environments, the greatest differences in water retention are found between soils derived from different parent materials, regardless of their taxonomic relation.

Effect of Bituminous materials on soil aggregation

Soil physical degradation is a progressive problem in most semiarid Mediterranean soils. The use of organic amendments is one of the most widely used remedial practices. Asphaltic emulsions are used to take advantage of their binding properties and hydrophobic nature. Two soils, similar with regard to their degree of physical degradation, were studied. Soil F was considered as a standard in terms of its physical characteristics, and soil D displayed an incipient state of degradation. Both soils were treated with an asphaltic emulsion, as well as with a distillation residue and a series of organic materials prepared in the laboratory, consisting of composting asphaltic products with a mixture of cereal straw and cattle manure. Both the asphaltic emulsion and the bituminous residue, as well as the composted mixtures resulting from these products with straw and cattle manure, had a favorable effect on the aggregate content of the soils, especially for soil D. In the degraded soil this was due to the adherent...