Organic matter and polyacrylamide amendment of Norfolk loamy sand

Loamy sand soils of the southeastern USA Coastal Plains often have poor physical properties because they contain cemented subsurface hard layers that restrict root development and yield. Their physical properties can be improved by adding amendments. Polyacrylamide (PAM) amendments and/or organic matter (OM) in the form of ground wheat (Triticum aestivum L.) stubble or pecan (Carya illinoensis) branches were mixed into a blend of 90% E horizon and 10% Ap horizon (to assure microbial presence) obtained from a Norfolk soil (Acrisol or fine-loamy, siliceous, thermic Typic Kandiudult). We hypothesized that incorporation of these amendments would improve soil physical properties by reducing strength and improving aggregation. Amended treatments contained 450 g of soil, OM, and 30 or 120 mg kg⁻¹ of PAM (12 mg mol⁻¹, anionic, and 35% charge density); treatments were incubated for 96 days at 10% (w/w) water content. Twice during the incubation period, treatments were leached with 1.3 pore volumes of deionized water. After leaching and equilibrating to stable water contents, treatments were analyzed for bulk densities and probed with a 5-mm diameter flat-tipped bench-top penetrometer to measure penetration resistances. Though penetration resistances increased for the highest level of PAM amendment, they showed no significance when both PAM and OM were added to the soil. When compared to controls, treatments with PAM at 120 mg kg⁻¹ had decreased bulk densities. Treatments with both rates of PAM had decreased requirements for water needed to maintain treatments at 10% water contents. Aggregation increased with increasing amounts of PAM but showed no consistent trend when both PAM and OM were added to the soil. Because PAM increased aggregation and water holding capacities in these coastal soils, it could reduce the need for deep tillage. However, more work needs to be done to determine an effective mix of PAM and OM.     

Effects of azoxystrobin,chlorothalonil, and ethoprophos on the reproduction of three terrestrial invertebrates using a natural Mediterranean soil

The potential terrestrial toxicity of three pesticides, azoxystrobin, chlorothalonil, and ethoprophos was evaluated using reproduction ecotoxicological tests with different non-target species: the collembolan Folsomia candida, the earthworm Eisenia andrei, and the enchytraeid Enchytraeus crypticus. All reproduction tests were performed with natural soil from a Mediterranean agricultural area (with no pesticide residues) in order to improve the relevance of laboratory data to field conditions. Controls were performed with natural and standard artificial soil (OECD 10% OM). The fungicide azoxystrobin showed the highest toxicity to earthworms (EC₅₀ = 42.0 mg a.i. kg⁻¹ dw soil). Collembolans were the most sensitive taxa in terms of sublethal effects of chlorothalonil with an EC₅₀ of 31.1 mg a.i. kg⁻¹ dw soil followed by the earthworms with an EC₅₀ of 40.9 mg a.i. kg⁻¹ dw soil. The insecticide ethoprophos was the most toxic to collembolans affecting their reproduction with an EC₅₀ of 0.027 mg a.i. kg⁻¹ dw soil. Enchytraeids were generally the least sensitive of the three species tested for long-term effects. Earthworms were not always the most sensitive species, emphasizing the need to increase the number of mandatory assays with key non-target organisms in the environmental risk assessment of pesticides.     

Improved soil structure and citrus growth after inoculation with three arbuscular mycorrhizal fungi under drought stress

In a controlled potted experiment, citrus (Poncirus trifoliata) seedlings were inoculated with three species of arbuscular mycorrhizal (AM) fungi, Glomus mosseae, G. versiforme or G. diaphanum. Two soil-water levels (ample water, −0.10 MPa; drought stress, −0.44 MPa) were applied to the pots 4 months after transplantation. Eighty days after water treatments, the soils and the citrus seedlings were well colonized by the three AM fungi. Mycorrhizal fungus inoculation improved plant biomass regardless of soil-water status but decreased the concentrations of hot water-extractable and hydrolyzable carbohydrates of soils. Mycorrhizal soils exhibited higher Bradford-reactive soil protein concentrations than non-mycorrhizal soils. Mycorrhizas enhanced >2 mm, 1–2 mm and >0.25 mm water-stable aggregate fractions but reduced 0.25–0.5 mm water-stable aggregates. Peroxidase activity was higher in AM than in non-AM soils whether drought stressed or not, whereas catalase activity was lower in AM than non-AM soils. Drought stress and AM fungus inoculation did not affect polyphenol oxidase activity of soils. A positive correlation between the Bradford-reactive soil protein concentrations, soil hyphal length densities, and water-stable aggregates (only >2 mm, 1–2 mm and >0.25 mm) suggests beneficial effects of the AM symbiosis on soil structure. It concluded that AM fungus colonization enhanced plant growth under drought stress indirectly through affecting the soil moisture retention via glomalin's effect on soil water-stable aggregates, although direct mineral nutritional effects could not be excluded.     

Cultivation effects on temporal changes of organic carbon and aggregate stability in desert soils of Hexi Corridor region in China

Sustainable agricultural use of cultivated desert soils has become a concern in Hexi Corridor in Gansu Province of China, because loss of topsoil in dust storms has been recently intensified. We chose four desert sites to investigate the effects of cultivation (cropping) on (i) soil organic C and its size fractions and (ii) soil aggregate stability (as a measure of soil erodibility). These parameters are of vital importance for evaluating the sustainability of agricultural practices.Total organic C as well as organic C fractions in soil (coarse organic C, 0.1–2 mm; young organic C, 0.05–0.1 mm; stable organic C, <0.05 mm) generally increased with the duration of the cultivation period from 0 (virgin soil, non-cultivated) to more than 30 years (p < 0.05). Compared to total organic C in virgin soils (2.3–3.5 g kg⁻¹ soil), significantly greater values were found after 10 to >20 years of cultivation (6.2–7.1 g kg⁻¹ soil). The increase in organic C in desert soils following prolonged cultivation was mainly the consequence of an increase in the coarse organic C. The increase in total organic C in soil was also dependent on clay content [total organic C = 0.96 + 0.249 clay content (%) + 0.05 cultivation year, R² = 0.48, n = 27, p < 0.001]. This indicates that clay protected soil organic C from mineralization, and also contributed to the increase in soil organic C as time of cultivation increased.There was a significant positive correlation between aggregate stability and total organic C across all field sites. The water stability of aggregates was low (with water-stable aggregate percentage ∼4% of dry-sieved aggregates of size 1–5 mm). There was no consistent pattern of increase in the soil aggregate stability with time of cultivation at different locations, suggesting that desert soils might remain prone to wind erosion even after 50 years of cultivation. Alternative management options, such as retaining harvested crop residues on soil surface and excluding or minimizing tillage, may permit sustainable agricultural use of desert soils.     

The relationships between erodibility and erosion in a soil treated with two organic amendments

The influence of two organic wastes, cotton gin crushed compost (CC) and beet vinasse (BV) applied for 5 years on a Typic Xerofluvent under dryland conditions near to Sevilla city (Guadalquivir River Valley, Andalusia, Spain) on soil erodibility (K factor of the USLE and RUSLE) and soil loss was studied. CC and BV were applied at rates of 1780, 5340, and 10,680 kg ha⁻¹ (expressed as organic matter content). When CC was applied to the soil, erodibility factor (K) is correlated with soil loss, highlighting a decrease in K and soil loss when increased the dose of CC applied to the soil. In this respect, K decreased 17% in CC-amended soils respect to control soil at the end of the experiment, and soil loss decreased 36% in CC-amended soils respect to control soil at the end of the experiment and for 45 min and 60 mm h⁻¹. However, when BV was applied, soil physical and biological properties decreased. K decreased 6.4% in BV-amended soils respect to control soil at the end of the experiment, and soil loss increased 59.7% in BV-amended soils respect to control soil at the end of the experimental period and for 45 min and 60 mm h⁻¹. We think that this is because the higher level of Na⁺ (and possibly of fulvic acids) in BV increased the exchangeable sodium percentage (ESP) and reduced structural stability of BV-amended soil, leading to higher soil loss. This explains the relatively higher soil loss in BV-amended soils. These results contradict many previous reports in which soil organic matter prevented soil loss. For this reason, the equation of soil erodibility (K factor of USLE and RUSLE) must have in consideration other aspects such as the chemical composition of the soil organic matter as well as the soil structural stability.     

Rapid estimation of microbial biomass in grassland soils by ultra-violet absorbance

A reliable and simple technique for estimating soil microbial biomass (SMB) is essential if the role of microbes in many soil processes is to be quantified. Conventional techniques are notoriously time-consuming and unreproducible. A technique was investigated that uses the UV absorbance at 280 nm of 0.5 M K₂SO₄ extracts of fumigated and unfumigated soils to estimate the concentrations of carbon, nitrogen and phosphorus in the SMB. The procedure is based on the fact that compounds released after chloroform fumigation from lysed microbial cells absorb in the near UV region. Using 29 UK permanent grassland soils, with a wide range of organic matter (2.9–8.0%) and clay contents (22–68%), it was demonstrated that the increase in UV absorbance at 280 nm after soil fumigation was strongly correlated with the SMB C (r=0.92), SMB N (r=0.90) and SMB P (r=0.89), as determined by conventional methods. The soils contained a wide range of SMB C (412–3412 μg g⁻¹ dry soil), N (57–346 μg g⁻¹ dry soil) and P (31–239 μg g⁻¹ dry soil) concentrations. It was thus confirmed that the UV absorbance technique described was a rapid, simple, precise and relatively inexpensive method of estimating soil microbial biomass.     

Factors influencing earthworm communities in post-industrial areas of Krakow Soda Works

Application of earthworm in soil re-cultivation and re-creation in post-industrial ecosystems make a big challenge for temporal applied zoology. The sediments of the Krakow Soda Works “Solvay” have undergone land reclamation in different ways: older sediments traps were left without any re-cultivation practices; meanwhile the newest ones were reclaimed using standard method (new soil cover planted with combination of grass and leguminous plants). The effect of different treatments on community and population structure of earthworm was estimated during consecutive years 1999–2000. Six localities differing in time of establishment, reclamation processes, vegetation type and soil properties were chosen. Nine species were recorded, among which Aporrectodea caliginosa occurred in all localities, being also the most abundant. Two other species, Lumbricus rubellus and Dendrobaena octaedra, which are epigeic species, become most important in forest assemblages and were characteristic for communities of older succession processes. Abundance of adult forms as well as total biomass were significantly affected by soil depth (r = 0.75, P < 0.05, r = 0.917, P < 0.001, respectively). Species richness however was connected with higher amount of macroelements and average plant height. Shannon diversity index and its evenness negatively correlated only with forestation (r = –0.67, P < 0.05, r = –0.68, P < 0.05, respectively). Niche overlap (α Pianka) for all analysed species extracted two groups differing in environmental requirements. First contained epigeic earthworms, closely related to plant succession (PCA results), the other one grouped endogeic and anecique species correlated significantly with soil depth and plant density. Community structure of earthworms do not reflects succession changes in post-industrial habitats, but is strongly affected by microhabitat factors in local scale (mainly soil depth and plant density).     

The temperature dependence of dicyandiamide (DCD) degradation in soils: A data synthesis

Dicyandiamide (DCD, C₂H₄N₄) is a nitrification inhibitor that has been studied for more than 80 years. However, there are few papers that have examined the use of DCD on dairy farms where cattle graze pasture and where urine is the primary form of nitrogen (N) deposited onto soils. After DCD was applied (10 kg DCD ha^?1) with bovine urine (700–1200 kg N ha^?1) to five soils throughout New Zealand, the reduction in direct nitrous oxide (N₂O) emissions was significant and remarkably consistent (71 ± 8%, average ± standard error). The application of DCD to these soils occurred in autumn and winter; daily average soil temperature (T) was reported but these data were not further analysed. Perusal of the literature suggested no consensus on the temperature dependence of DCD degradation in soils. Based on published data from controlled-environment studies of soils sampled in four countries, we quantified the relation between T and the time for DCD concentration in soils to decline to half its application value (t_½) as t_½ (T) = 168e^?0.084T with parameter standard errors of ±16 d and ±0.011 d^?1, respectively (n = 16). For example, at 5 °C a 1 °C increase in T reduced t_½ from 110 to 101 d whereas at 25 °C the reduction was 20–19 d. Analysing T data from the New Zealand trials using our t_½ (T) function, over 43–89 d when direct N₂O emissions from treated plots became indistinguishable from the controls, the estimated percentage of applied DCD remaining in the soil averaged 43 ± 10%. These calculations suggested the apparently remaining DCD was ineffective with respect to direct N₂O emissions. In the absence of measurements, explanations for this interpretation included vertical displacement of the DCD and sorption onto organic matter in soils. The consistent DCD efficacy from these trials corresponded with T generally <10 °C, so it is suggested as an application criteria for the reduction of direct N₂O emissions from pastoral soils subjected to urine excretion by grazing cattle.     

Comparative survival of conidia of eight species of Bipolaris,Curvularia, and Exserohilum in soil and influences of swine waste amendments on survival

Survival of conidia of eight species of Bipolaris, Curvularia, and Exserohilum in soil was compared to identify the species most suitable for use in experiments to assay fungitoxicity of soils amended with animal wastes and agricultural byproducts. Conidia produced on cellulose-containing substrates were added to soil between porous nylon mesh membranes, incubated for 0–12 weeks, retrieved, and plated on cornmeal agar to induce germination as an indicator of viability. In three experiments, significant variation in spore germination was attributed to fungal species, incubation time in soil, and species × time interactions. Few or no differences in viability of conidia of the eight species were evident prior to incubation in soil, but numerous significant differences (P = 0.05) were observed between species after incubation for 2–12 weeks in soil. Survival of conidia usually was greatest for C. lunata, B. sorokiniana, and B. stenospila; least for B. cynodontis, B. hawaiiensis, and E. rostratum; and intermediate or inconsistent for B. spicifera and C. geniculata. C. lunata, B. sorokiniana, and B. stenospila appear most capable of survival in soil as conidia and most suitable for use as test organisms to evaluate fungitoxicity of amended soils. When conidia of these species were incubated for 4–8 weeks in three soils with and without previous commercial swine waste applications, survival was often significantly (P = 0.05) reduced across soils or in individual soils that had received swine waste. The most frequent and strong reductions in survival of conidia in waste-amended soils were observed with B. stenospila. Results indicate that the eight species of fungi studied differ significantly in ability of conidia to survive in soil, that three species exhibit the greatest potential for survival, that these species may be used to bioassay soils for fungitoxicity, and that conidia of these species exhibit slight to strong reductions in survival in soils that previously received commercial applications of liquid swine waste.     

Accumulation of As,Pb, Zn,Cd and Cu and arbuscular mycorrhizal status in populations of Cynodon dactylon grown on metal-contaminated soils

Metal(loid) accumulation and arbuscular mycorrhizal (AM) status of the dominant plant species, Cynodon dactylon, growing at four multi-metal(loid)s-contaminated sites and an uncontaminated site of China were investigated. Up to 94.7 As mg kg^?1, 417 Pb mg kg^?1, 498 Zn mg kg^?1, 5.8 Cd mg kg^?1 and 27.7 Cu mg kg^?1 in shoots of C. dactylon were recorded. The plant was colonized consistently by AM fungi (33.0–65.5%) at both uncontaminated site and metal-contaminated sites. Based on morphological characteristics, fourteen species of AM fungi were identified in the rhizosphere of C. dactylon, with one belonging to the genus of Acaulospora and the other thirteen belonging to the genus of Glomus. Glomus etunicatum was the most common species associated with C. dactylon growing at metal-contaminated sites. Spore abundance in the rhizosphere of C. dactylon growing at the metal-contaminated soils (22–82 spores per 25 g soil) was significantly lower than that of the uncontaminated soils (371 spores per 25 g soil). However, AM fungal species diversity in the metal-contaminated soils was significantly higher than that in the uncontaminated soils. This is the first report of AM status in the rhizosphere of C. dactylon, the dominant plant survival in metal-contaminated soils. The investigation also suggests that phytorestoration of metal-contaminated sites might be facilitated using the appropriate plant with the aid of tolerant AM fungi.     

Application of biostimulants in benzo(a)pyrene polluted soils: Short-time effects on soil biochemical properties

The bioremediation effects of three biostimulants (BS): WCDS, wheat condensed distillers soluble; PAHE, hydrolyzed poultry feathers; and RB, rice bran extract in a soil polluted with two rates of benzo(a)pyrene (BaP) (50 or 100 mg kg⁻¹ soil, respectively) over 90 days were studied. Their effects on the soil biochemical properties (ATP and urease and phosphatase activities) and ergosterol were determined. Also, extractable BaP in soils was determined during the incubation period. An non-polluted and non-organic-amended soil was used as control. The results indicated that at the end of the incubation period and compared with the control soil, the ATP, ergosterol, urease and phosphatase activities decreased 29.4%, 24.8%, 44.7% and 42.9%, respectively in the non-organic amended soil polluted with polluted 100 mg BaP kg⁻¹ soil. The application of biostimulants to unpolluted soil increased the biochemical parameters. However, this stimulation was higher in the soil amended with PAHE, followed by RB and WCDS. The application of BaP in organic-amended soils decreased the biochemical properties. However, this decrease was lower than for the non-amended BaP polluted soil. Possibly the low molecular weight protein content easily assimilated by soil microorganisms is responsible for less inhibition of these soil biochemical parameters.     

Impact of reduced tillage on carbon and nitrogen storage of two Haplic Luvisols after 40 years

It is broadly accepted that reduced tillage increases soil organic carbon (C_org) and total nitrogen (N) concentrations in arable soils. However, the underlying processes of sequestration are not completely understood. Thus, our objectives were to investigate the impact of a minimum tillage (MT) system (to 5–8 cm depth) on aggregates, on particulate organic matter (POM), and on storage of C_org and N in two loamy Haplic Luvisols in contrast to conventional tillage (CT) (to 25 cm). Surface soils (0–5 cm) and subsoils (10–20 cm) of two experimental fields near Göttingen, Germany, were investigated. Each site (Garte-Süd and Hohes Feld) received both tillage treatments for 37 and 40 years, respectively. In the bulk soil of both sites C_org, N, microbial carbon (C_mic), and microbial N (N_mic) concentrations were elevated under MT in both depths. Likewise, water-stable macroaggregates (>0.25 mm) were on average 2.6 times more abundant under MT than under CT but differences in the subsoils were generally not significant. For surface soils under MT, all aggregate size classes <1 mm showed approx. 35% and 50% increased C_org concentrations at Garte-Süd and Hohes Feld, respectively. For greater macroaggregates (1–2, 2–10 mm), however, differences were inconsistent. Elevations of N concentrations were regular over all size classes reaching 61% and 52%, respectively. Density fractionation of the surface soils revealed that tillage system affected neither the yields of free POM nor occluded POM nor their C_org and N concentrations. Moreover, more C_org and N (15–238%) was associated within the mineral fractions investigated under MT in contrast to CT. Overall, similar to no-tillage, a long-term MT treatment of soil enhanced the stability of macroaggregates and thus was able to physically protect and to store more organic matter (OM) in the surface soil. The increased storage of C_org and N did not occur as POM, as reported for no-tillage, but as mineral-associated OM.     

Use of biostimulants on soil restoration: Effects on soil biochemical properties and microbial community

Four biostimulants (BS): WCDSs, wheat condensed distiller solubles; PA-HE, hydrolyzed poultry feathers; CGHE, carob germ enzymatic extract; and RB, rice bran extract were applied annually at 4.7 t organic matter (OM) ha⁻¹ for a 3-year period to a Xerollic Calciorthid soil to evaluate their efficiency in soil restoration. Their effects on the plant cover, soil enzymatic activities and the structure of the soil microbial community by analysing phospholipid fatty acids (PLFAs) were determined. Application of BS that contain higher amounts of protein and higher percentage of peptides under 3 kDa had a greater effect on the soil biological properties, possibly due to the low molecular weight protein content can be easily assimilated by soil microorganisms. Following 3 years of successive soil amendment, the dehydrogenase activity was 4.6, 9.6, and 17.6% higher in PA-HE-amended soils than in the RB, CGHE and WCDS-amended soils, respectively. The urease activity was 5.3, 14.5, and 28.8% higher in PA-HE-amended soils than in the RB, CGHE and WCDS-amended soils, respectively. The phosphatase activity was 8, 15.3, and 20.2% higher in PA-HE-amended soils than in the RB, CGHE and WCDS-amended soils, respectively. The arylsulfatase activity was 16, 21.1, and 27.2% higher in PA-HE-amended soils than in the RB, CGHE and WCDS-amended soils, respectively. Total soil phospholipid fatty acid (PLFA) concentration was significantly (p < 0.05) higher in BS-amended soil than control soil. Principal component analysis discriminated between the BS-amended soils, mainly based on content of lower molecular weight peptides. Thus, PA-HE and RB were grouped and differentiated from CGHE and WCDS, respectively. After 3 years of treatment, vegetal cover was 11.4, 17.7, 24.1, and 85.8% higher in PA-HE-amended soils than in the RB, CGHE, WCDS treatments and control soil. These results suggested that under semiarid climatic conditions the application of BS with higher amounts of protein (>50%) and a higher percentage of peptides under 0.3 kDa (>60%) notably increased the soil enzymatic activities, induced changes in microbial community because the protein with lower molecular weight can be more easily absorbed by soil microorganisms, and also favoured the establishment of vegetation, which will protect the soil against erosion and will contribute to its restoration.     

Aggregate water-stability,particle-size and soil solution properties in conducive and suppressive soils to Fusarium wilt of banana from Canary Islands (Spain)

The influence of several soil properties on soil conduciveness or suppressiveness to disease caused by the soil fungus Fusarium oxysporum f. sp. cubense was studied in seven field plots of banana plantations, situated in Tenerife and Gran Canaria islands (Canary Islands, Spain). In each plot, soil samples were taken in conducive and suppressive areas to Fusarium wilt. Water-stable aggregates (WSA: 200–2000 μm diameter), soil particle size, and selected soil solution characteristics [pH, electric conductivity (EC) and soluble Na] were determined in the samples. Aggregate water-stability was higher in soils of conducive areas than in suppressive areas. The percentage of WSA in the conducive areas ranged from 460 to 330 g kg⁻¹, while in the suppressive areas the maximum value was 285 g kg⁻¹ and the minimum was 150 g kg⁻¹. The soils had high clay content and the EC and soluble Na tended to be higher in suppressive areas than in conducive areas. Soil solution pH was lower in conducive areas (except sites 1 and 9). Our data provide evidence that in different soil areas of the same plot, the structural stability of aggregates, presumably controlled in part by the clay fraction, soluble Na concentration and EC, is of great importance for the conduciveness or suppressiveness to banana wilt caused by Fusarium oxysporum f. sp. cubense of the soils studied. Finally, we hypothesize that a greater stability of the aggregates forming anaerobiosis could partly explain most of the available Fe found in soil areas where the disease was severe, at least in these types of soils.     

Changes of microbial properties in (near-) rhizosphere soils after phytoextraction by Sedum alfredii H: A rhizobox approach with an artificial Cd-contaminated soil

The ultimate goal of soil remediation is to restore soil health. Soil microbial parameters are considered to be effective indicators of soil health. The aim of this study was to determine the effects of phytoextraction on microbial properties through the measurement of soil microbial biomass carbon, soil basal respiration and enzyme activities. For this purpose, a pre-stratified rhizobox experiment was conducted with the Cd hyperaccumulator Sedum alfredii H. for phytoextraction Cd from an artificial contaminated soil (15.81 mg kg⁻¹) under greenhouse conditions. The plant and soil samples were collected after growing the plant for three and six months with three replications. The results indicated that the ecotype of S. alfredii H. originating from an ancient silver mining site was a Cd-hyperaccumulator as it showed high tolerance to Cd stress, the shoot Cd concentration were as high as 922.6 mg kg⁻¹ and 581.9 mg kg⁻¹ at the two samplings, and it also showed high BF (58.4 and 36.8 after 3 and 6 months growth), and TF (5.8 and 5.1 after 3 and 6 months growth). The amounts of Cd accumulated in the shoots of S. alfredii reached to an average of 1206 μg plant⁻¹ after 6 months growth. Basal respiration, invertase and acid phosphatase activities of the rhizosphere soil separated by the shaking method were significantly higher (P < 0.01) than that of the near-rhizosphere soil and the unplanted soil after 3 months growth, so were microbial biomass carbon, urease, invertase and acid phosphatase activities of the rhizosphere soil after 6 months growth. Acid phosphatase activity of the 0–2 mm sub-layer rhizosphere soil collected by the pre-stratified method after 3 months growth was significantly higher (P < 0.05) than that of other sub-layer rhizosphere soils and bulk soil, and so were microbial biomass carbon, basal respiration, urease, invertase and acid phosphatase activities of the 0–2 mm sub-layer rhizosphere soil after 6 months growth. It was concluded that phytoextraction by S. alfredii could improve soil microbial properties, especially in rhizosphere, and this plant poses a great potential for the remediation of Cd contaminated soil.     

Long-term effect on soil biochemical status of a Vertisol under conservation tillage system in semi-arid Mediterranean conditions

Long-term field experiments are expected to provide important information regarding soil properties affected by conservation management practices. Several studies have shown that soil enzyme activities are sensitive in discriminating among soil management effects. In this study we evaluated the long-term effect of direct drilling (DD) under a crop rotation system (cereals–sunflower–legumes), on the stratification of soil organic matter content and on biochemical properties in a dryland in southwest Spain. The results were compared to those obtained under conventional tillage (CT). Soil biochemical status was evaluated by measuring the enzymatic activities (dehydrogenase, β-glucosidase, alkaline phosphatase and arylsulphatase) during the flowering period of a pea crop. Soil samples were collected in May 2007 at three depths (0–5, 5–10 and 10–20 cm).Total organic carbon (TOC) contents and values of soil enzyme activities were higher in soils subjected to DD than to CT, specifically at 0–5 cm depth. Although a slight decrease of TOC and enzymatic activities with increasing soil depth was observed, no significant differences were found among different depths of the same treatment. This could be related to the high clay content of the soil, a Vertisol. Enzyme activities values showed high correlation coefficients (from r = 0.799 to r = 0.870, p < 0.01) with TOC. Values of activity of the different enzymes were also correlated (p < 0.01).Values of stratification ratios did not show significant differences between tillage practices. The high clay content of the soil is responsible for this lack of differences because of the protection by clay mineral of TOC and soil enzymes activities.Long-term soil conservation management by direct drilling in a dryland farming system improved the quality of a clay soil, especially at the surface, by enhancing its organic matter content and its biological status.     

Differences in soil enzyme activities,microbial community structure and short-term nitrogen mineralisation resulting from farm management history and organic matter amendments

Changes in soil microbial biomass, enzyme activities, microbial community structure and nitrogen (N) dynamics resulting from organic matter amendments were determined in soils with different management histories to gain better understanding of the effects of long- and short-term management practices on soil microbial properties and key soil processes. Two soils that had been under either long-term organic or conventional management and that varied in microbial biomass and enzyme activity levels but had similar fertility levels were amended with organic material (dried lupin residue, Lupinus angustifolius L.) at amounts equivalent to 0, 4 and 8 t dry matter lupin ha^?1. Microbial biomass C and N, arginine deaminase activity, fluorescein diacetate hydrolysis, dehydrogenase enzyme activity and gross N mineralisation were measured in intervals over an 81-day period. The community structure of eubacteria and actinomycetes was examined using PCR–DGGE of 16S rDNA fragments. Results suggested that no direct relationships existed between microbial community structure, enzyme activities and N mineralisation. Microbial biomass and activity changed as a result of lupin amendment whereas the microbial community structure was more strongly influenced by farm management history. The addition of 4 t ha^?1 of lupin was sufficient to stimulate the microbial community in both soils, resulting in microbial biomass growth and increased enzyme activities and N mineralisation regardless of past management. Amendment with 8 t lupin ha^?1 did not result in an increase proportional to the extra amount added; levels of soil microbial properties were only 1.1–1.7 times higher than in the 4 t ha^?1 treatment. Microbial community structure differed significantly between the two soils, while no changes were detected in response to lupin amendment at either level during the short-term incubation. Correlation analyses for each treatment separately, however, revealed differences that were inconsistent with results obtained for soil biological properties suggesting that differences might exist in the structure or physiological properties of a microbial component that was not assessed in this study.     

Quantifying potato pathogen DNA in soil

An improved method for the direct extraction of DNA from soil involving processing of a relatively large sample (60 g) was developed. The accurate and reliable detection and quantification of the soil-borne potato pathogens Colletotrichum coccodes (black dot), Rhizoctonia solani (black scurf) and Spongospora subterranea (powdery scab) following inoculation of soils was demonstrated. With this method, low levels of target DNA (30–40 pg DNA/g soil) could be detected in field soils. DNA recovery was proportionate across a wide range of inoculum (R² > 0.86) and there was no effect of soil type on the recovery of C. coccodes. The method was used to assess levels of naturally occurring pathogen DNA in 122 soil samples obtained from commercial potato fields.     

Vertical distribution of microbial communities under the canopy of two legume bushes in the Tehuacán Desert,Mexico

Prosopis laevigata and Parkinsonia praecox are the most abundant perennial shrubs in the Tehuacán Desert, forming ’islands of fertility’ that dominate the alluvial terraces. Both species exhibit very similar phenology, with the timing of litter foliage being the only difference between them. P. praecox litter occurs shortly after the rains, while P. laevigata maintains its leaves until the next wet season. As degradable organic matter (OM) is one of the leading factors determining soil biota composition and activity, because of the OM provided by littering, we expected that the vertical distribution of the microbial community in the vicinity of the root zone of P. praecox would be higher in comparison to P. laevigata. One soil sampling was performed; during the rainy season in August, soil samples were collected from a 0–50-cm depth at 10-cm intervals, in the vicinity of the root canopy of four individual plants of each species and the interspaces between them. Soil moisture, organic matter, and counts of bacteria and fungi under shrubs were found to decrease from the upper to deeper layers. Respiratory activity was higher in the deeper layers (p < 0.01) in all three sampling sites. Total bacterial, fungal, and heterotrophic diazotrophs were found to be significantly (p < 0.001) more numerous under shrubs than in the interspace soil. No nitrogen-fixing bacteria were isolated from interplant soils in comparison to the soil samples collected beneath the shrubs. Heterotrophic diazotrophs significantly (p < 0.01) reduced more acetylene under P. praecox (29.0 nmol/g soil) than under P. laevigata (20.1 nmol/g soil). Although the microbial numbers were unaffected by differences in plant phenology, greater nitrogenase activity under P. praecox may influence nitrogen distribution in this arid environment. Due to the fact that only one sampling was undertaken, this study elucidates the differences in the microbial community between the two shrubs, but the dynamics in the above community could not be shown.     

Tag-encoded pyrosequencing analysis of bacterial diversity in a single soil type as affected by management and land use

Impacts of management and land use on soil bacterial diversity have not been well documented. Here we present the application of the bacterial tag encoded FLX amplicon pyrosequencing (bTEFAP) diversity method, which will promote studies in soil microbiomes. Using this modified FLX pyrosequencing approach we evaluated bacterial diversity of a soil (Pullman soil; fine, mixed, thermic Torrertic Paleustolls) with 38% clay and 34% sand (0–5 cm) under four systems. Two non-disturbed grass systems were evaluated including a pasture monoculture (Bothriochloa bladhii (Retz) S.T. Blake) [P] and a diverse mixture of grasses in the Conservation Reserve Program (CRP). Two agricultural systems were evaluated including a cotton (Gossypium hirsutum L.) -winter wheat (Triticum aestivum L.)-corn (Zea mays L.) rotation [Ct–W–Cr] and the typical practice of the region, which is continuous monoculture cotton (Ct–Ct). Differences due to land use and management were observed in soil microbial biomass C (CRP > P = Ct–W–Cr > Ct–Ct). Using three estimators of diversity, the maximum number of unique sequences operational taxonomic units (OTU; roughly corresponding to the species level) never exceeded 4500 in these soils at the 3% dissimilarity level. The following trend was found using the most common estimators of bacterial diversity: Ct–W–Cr > P = CRP > Ct–Ct. Predominant phyla in this soil were Actinobacteria, Bacteriodetes and Fermicutes. Bacteriodetes were more predominant in soil under agricultural systems (Ct–W–Cr and Ct–Ct) compared to the same soil under non-disturbed grass systems (P and CRP). The opposite trend was found for the Actinobacteria, which were more predominant under non-disturbed grass systems (P and CRP). Higher G? bacteria and lower G+ bacteria were found under Ct–W–Cr rotation and highest abundance of actinomycetes under CRP. The bTEFAP technique proved to be a powerful method to characterize the bacterial diversity of the soil studied under different management and land use in terms not only on the presence or absence, but also in terms of distribution.