Effects of cultivation on soil microbiological properties in a freshwater marsh soil in Northeast China

The Sanjiang Plain has become an intensive area of land use/cover change in China. However, little is known about the effect of cultivation on soil microbiological properties in this freshwater marsh ecosystem. Our objective was to evaluate the effect of cultivation on mineralizable, microbial biomass, and total C in the Sanjiang Plain of Northeast China. Soil microbial biomass C (MBC) was 4346 ± 309 mg kg⁻¹ in undisturbed marsh and 229 mg kg⁻¹ in soil cultivated for 15 years. Undisturbed marsh soil had the highest microbial quotient (3.64%), which declined with increasing cultivation time (R² = 0.97, p < 0.01). Metabolic quotient increased with increasing cultivation time. Soil C mineralization in undisturbed marsh was 3.5 times that in soil cultivated for 1 year, and was 12 times that in soil cultivated for 15 years. Cultivation strongly affected measured soil microbiological properties.     

Effects of vegetation on soil microbial C,N, and P dynamics in a tropical forest and savanna of Central Africa

The forest–savanna transition zone is widely distributed on nutrient-poor oxisols in Central Africa. To reveal and compare the nutrient cycle in relation to soil microbes for forest and savanna vegetation in this area, we evaluated seasonal fluctuations in microbial biomass carbon (MBC), nitrogen (MBN), and phosphorus (MBP) for 13 months as well as soil moisture, temperature, soil pH levels, and nutrients for both vegetation types in eastern Cameroon. Soil pH was significantly lower in forest (4.3) than in savanna (5.6), and soil N availability was greater in forest (87.1 mg N kg⁻¹ soil) than in savanna (32.9 mg N kg⁻¹ soil). We found a significant positive correlation between soil moisture and MBP in forest, indicating the importance of organic P mineralization for MBP, whereas in savanna, we found a significant positive correlation between soil N availability and MBP, indicating N limitation for MBP. These results suggest that for soil microbes, forest is an N-saturated and P-limited ecosystem, whereas savanna is an N-limited ecosystem. Additionally, we observed a significantly lower MBN and larger MB C:N ratio in forest (50.7 mg N kg⁻¹ soil and 8.6, respectively) than in savanna (60.0 mg N kg⁻¹ soil and 6.5, respectively) during the experimental period, despite the rich soil N condition in forest. This may be due to the significantly lower soil pH in forest, which influences the different soil microbial communities (fungi-to-bacteria ratio) in forest versus savanna, and therefore, our results indicate that, in terms of microbial N dynamics, soil pH rather than soil substrate conditions controls the soil microbial communities in this area. Further studies should be focused on soil microbial community, such as PLFA, which was not evaluated in the present study.     

Effects of nonylphenols on soil microbial activity and water retention

The main aim of this study is to analyze the influence of 4-nonylphenol (NP) on soil water retention and biological activity. Two doses of 4-nonylphenol (25 and 50 mg kg⁻¹) were tested in a loam soil with and without peat amendment. In general, one week after the start of the experiment, the soil water content retained at −0.75 MPa of soil suction was 18% higher in the soil amended and its basal respiration (BR) was 15% higher than soil without peat. In contrast, the microbial activity indices (CM: coefficient of mineralization or BR:total organic carbon (TOC) ratio; Cmic:Corg: microbial biomass carbon (MBC):TOC ratio; qCO₂: metabolic quotient or BR:MBC ratio) were higher in the soil without peat, compared to the soil amended with peat. On the other hand, the addition of NP to soil was able to modify soil biological but not physical (water retention, desorption) properties. When soil was amended with peat, MBC was reduced one week after applying NP. In contrast, no effects of NP on MBC were observed in the soil without peat. BR was reduced by 16% one week after applying 50 mg kg⁻¹ of NP to soil with peat, and was increased by 46% one week after applying 25 mg kg⁻¹ of NP to soil without peat. The effects of NP on MBC and BR could be associated more with the adsorption of NP by soil organic matter, while changes in CM or Cmic:Corg ratio were more closely related to changes in soil water retention. The potential toxic effects of NP (high qCO₂ values) were only observed in the absence of peat amendments. Peat addition reduced NP toxic effects on microorganisms.     

Microbial biomass in a semi arid soil of the central highlands of Mexico cultivated with maize or under natural vegetation

Microbial biomass (MB) is the key factor in nutrient dynamics in soil, but no information exists how clearing of vegetation to cultivate maize in the central highlands of Mexico might affect it. Soil MB was measured with the chloroform fumigation incubation (CFI) and fumigation extraction (CFE) techniques and the substrate-induced respiration (SIR) method in soil sampled under or outside the canopy of mesquite (Prosopis laevigata) and huisache (Acacia tortuoso), N₂ fixing shrubs, and from fields cultivated with maize. Microbial biomass C as measured with the CFI technique ranged from 122 mg C kg⁻¹ in agricultural soil to 373 mg C kg⁻¹ in soil sampled under mesquite shrubs. Microbial biomass N as measured with the CFI technique ranged from 11 mg N kg⁻¹ in agricultural soil to 116 mg N kg⁻¹ in soil sampled under mesquite shrub. The ratio of microbial biomass C as measured with CFI related to the ninhydrin-positive compounds (NPC) was 12.23 after 1 day and 8.43 after 10 days while the relationship with extractable C was 3.15 and 2.96, respectively. The metabolic quotient (qCO₂) decreased in the order OUTSIDE > MESQUITE > HUIZACHE > AGRICULTURE, and the microbial biomass:soil organic C ratio decreased in the order MESQUITE > HUIZACHE > OUTSIDE > AGRICULTURE using SIR to determine the microbial biomass. It was found that converting soil under natural vegetation to arable soil was not only detrimental for soil quality, but might be unsustainable as organic matter input is limited.     

Effect of land-use and elevation on microbial biomass and water extractable carbon in soils of Mt. Kilimanjaro ecosystems

Microbial biomass carbon (MBC) and water-extractable organic carbon (WOC) – as sensitive and important parameters for soil fertility and C turnover – are strongly affected by land-use changes all over the world. These effects are particularly distinct upon conversion of natural to agricultural ecosystems due to very fast carbon (C) and nutrient cycles and high vulnerability, especially in the tropics. The objective of this study was to use the unique advantage of Mt. Kilimanjaro – altitudinal gradient leading to different tropical ecosystems but developed all on the same soil parent material – to investigate the effects of land-use change and elevation on MBC and WOC contents during a transition phase from dry to wet season. Down to a soil depth of 50 cm, we compared MBC and WOC contents of 2 natural (Ocotea and Podocarpus forest), 3 seminatural (lower montane forest, grassland, savannah), 1 sustainably used (homegarden) and 2 intensively used (maize field, coffee plantation) ecosystems on an elevation gradient from 950 to 2850 m a.s.l. Independent of land-use, both MBC and WOC strongly increased with elevation on Mt. Kilimanjaro corresponding to ecosystem productivity and biodiversity. Through the agricultural use of ecosystems MBC and WOC contents decreased – especially in surface layers – on average by 765 mg kg⁻¹ for MBC and 916 mg kg⁻¹ for WOC, compared to the respective natural ecosystems. The decrease with depth was highest for forests > grasslands > agroecosystems and also was positively correlated with elevation. We conclude that MBC and WOC contents in soils of Mt. Kilimanjaro ecosystems are highly sensitive to land-use changes, especially in topsoil. The MBC and WOC contents were considerably reduced even in sustainable agricultural systems. Since MBC and WOC are very fast reacting and sensitive C pools, we expect a decrease in other soil C pools accompanied by a strong decrease in fertility and productivity due to changes in land use from natural to agricultural ecosystems.     

Structural and functional diversity of bacterial community in soil treated with the herbicide napropamide estimated by the DGGE,CLPP and r/K-strategy approaches

Napropamide is one of the most commonly used herbicide in agricultural practice and can exhibit toxic effect to soil microorganisms. Therefore, the main objective of this study was to examine the genetic and functional diversity of microbial communities in soil treated with napropamide at field rate (FR, 2.25 mg kg⁻¹ of soil) and 10 times the FR (10 × FR, 22.5 mg kg⁻¹ of soil) by the denaturing gradient gel electrophoresis (DGGE) and the community level physiological profile (CLPP) methods. In addition, the r/K-strategy approach was used to evaluate the effect of this herbicide on the community structure of the culturable soil bacteria. DGGE patterns revealed that napropamide affected the structure of microbial community; however, the richness (S) and genetic diversity (H) values indicated that the FR dosage of napropamide experienced non-significant changes. In turn, the 10 × FR dosage of herbicide caused significant changes in the S and H values of dominant soil bacteria. DGGE profiles suggest an evolution of bacteria capable of degrading napropamide among indigenous microflora. Analysis of the CLPPs indicated that the catabolic activity of microbial community expressed as AWCD (average well-color development) was temporary positively affected after napropamide application and resulted in an increase of the substrate richness (S_R) as well as functional biodiversity (H) values. Analysis of the bacterial growth strategy revealed that napropamide affected the r- or K-type bacterial classes (ecotypes). In treated-soil samples K-strategists dominated the population, as indicated by the decreased ecophysiological (EP) index. Napropamide significantly affected the physiological state of culturable bacteria and caused a reduction in the rate of colony formation as well as a prolonged time of growth rate. Obtained results indicate that application of napropamide may poses a potential risk for soil functioning.     

Effects of atrazine on microbial activity in semiarid soil

The effect of an atrazine formulation on microbial biomass, microbial respiration, ATP content and dehydrogenase and urease activity in a semiarid soil and the influence of time on the response of soil microbial activity to the herbicide treatment were assessed. The atrazine formulation was added to soil as aqueous solutions of different concentrations of active ingredient to obtain a range of concentrations in the soil from 0.2 to 1000 mg kg⁻¹. Microcosms of soil with the different herbicide concentrations and untreated control soil were incubated for 6 h, 16 and 45 days. In general, an increase in the measured microbiological and biochemical parameters with atrazine concentration in soil was observed. The increase in microbial activity with atrazine pollution was noticeable after lengthy incubation.     

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.     

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 CO₂-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 NH₄⁺ 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.     

Influence of carbon amendments on soil denitrifier abundance in soil microcosms

It is known that carbon (C) amendments increase microbial activity in anoxic soil microcosm studies, however the effects on abundance of total and denitrifier bacterial communities is uncertain. Quantitative PCR was used to target the 16S rRNA gene for the total bacterial community, the nosZ functional gene to reflect a broad denitrifier community, and functional genes from narrow denitrifier communities represented by Pseudomonas mandelii and related species (cnorB_P) and Bosea/Bradyrhizobium/Ensifer spp. (cnorB_B). Repacked soil cores were amended with varying amounts of glucose and red clover plant tissue (0–1000 mg C kg^? 1 of soil) and incubated for 96 h. Carbon amendment significantly increased respiration as measured by cumulative CO₂ emissions. Inputs of red clover or glucose at 1000 mg C kg^? 1 of soil caused increased abundance in the total bacteria under the conditions used. There was about an approximate 2-fold increase in the abundance of bacteria bearing the nosZ gene, but only in treatments receiving 500 or 1000 mg C kg^? 1 of soil of glucose or red clover, respectively. Additions of ≥ 500 mg C kg^? 1 soil of red clover and ≥ 250 mg C kg^? 1 of glucose increased cnorB_P-gene bearing denitrifiers. Changes in abundance of the targeted communities were related to C availability in soil, as indicated by soil respiration, regardless of C source. Applications of C amendments at rates that would occur in agricultural soils not only increase microbial activity, but can also induce changes in abundance of total bacterial and denitrifier communities in studies of anoxic soil microcosms.     

Effects of long-term sewage irrigation on agricultural soil microbial structural and functional characterizations in Shandong,China

Soil samples taken from a sewage irrigation area, a partial sewage irrigation area and a ground water irrigation area (control area) were studied with the methods of Biolog and FAME. It was found that the microbial utilization of carbon sources in sewage irrigation areas was much higher than that of control area (P < 0.05). With the increasing of the amount of sewage irrigation, microbial functional diversity slightly increased by the Biolog analysis; however, the amount of epiphyte decreased by the FAME analysis. The results also showed that the Cr, Zn contents were positively correlated with the values of AWCD and the microbial diversity, while Hg content showed negative correlation with the microbial parameters (AWCD of 72 h and Shannon index). Our studies suggested that sewage irrigation resulted in an obvious increase of heavy metals content in soil (P < 0.05), although the maximum heavy metals concentrations were much lower than the current standard of China. Other soil basic characteristics such as cation exchange capacity (CEC), total nitrogen (N_t) and organic matter in sewage irrigation areas obviously increased (P < 0.05). Therefore, it is demonstrated that long-term sewage irrigation had influenced soil microorganisms and soil quality in the studied soils. As a result, it is important to monitor the changes in agricultural soils. Furthermore, our results also confirmed that the methods of Biolog and FAME are effective tools for the assessment of soil microbial structure/function and soil health.     

Soil microbial biomass and organic matter fractions during transition from conventional to organic farming systems

The aim of this study was to investigate the response of soil microbial biomass and organic matter fractions during the transition from conventional to organic farming in a tropical soil. Soil samples were collected from three different plots planted with Malpighia glaba: conventional plot with 10 years (CON); transitional plot with 2 years under organic farming system (TRA); organic plot with 5 years under organic farming system (ORG). A plot under native vegetation (NV) was used as a reference. Soil microbial biomass C (MBC) and N (MBN), soil organic carbon (SOC) and total N (TN), soil organic matter fractioning and microbial indices were evaluated in soil samples collected at 0–5, 5–10, 10–20 and 20–40 cm depth. SOC and fulvic acids fraction contents were higher in the ORG system at 0–5 cm and 5–10 cm depths. Soil MBC was highest in the ORG, in all depths, than in others plots. Soil MBN was similar between ORG, TRA and NV in the surface layer. The lowest values for soil MBC and MBN were observed in CON plot. Soil microbial biomass increased gradually from conventional to organic farming, leading to consistent and distinct differences from the conventional control by the end of the second year.     

The combined effects of earthworms and arbuscular mycorrhizal fungi on microbial biomass and enzyme activities in a calcareous soil spiked with cadmium

Earthworms and arbuscular mycorrhizal fungi (AMF) are known to independently affect soil microbial and biochemical properties, in particular soil microbial biomass (SMB) and enzymes. However, less information is available about their interactive effects, particularly in soils contaminated with heavy metals such as cadmium (Cd). The amount of soil microbial biomass C (MBC), the rate of soil respiration (SRR) and the activities of urease and alkaline phosphatase (ALP) were measured in a calcareous soil artificially spiked with Cd (10 and 20 mg Cd kg⁻¹), inoculated with earthworm (Lumbricus rubellus L.), and AMF (Glomus intraradices and Glomus mosseae species) under maize (Zea mays L.) crop for 60 days. Results showed that the quantity of MBC, SRR and enzyme activities decreased with increasing Cd levels as a result of the elevated exchangeable Cd concentration. Earthworm addition increased soil exchangeable Cd levels, while AMF and their interaction with earthworms had no influence on this fraction of Cd. Earthworm activity resulted in no change in soil MBC, while inoculation with both AMF species significantly enhanced soil MBC contents. However, the presence of earthworms lowered soil MBC when inoculated with G. mosseae fungi, showing an interaction between the two organisms. Soil enzyme activities and SRR values tended to increase considerably with the inoculation of both earthworms and AMF. Nevertheless, earthworm activity did not affect ALP activity when inoculated with G. mosseae fungi, while the presence of earthworm enhanced urease activity only with G. intraradices species. The increases in enzyme activities and SRR were better ascribed to changes in soil organic carbon (OC), MBC and dissolved organic carbon (DOC) contents. In summary, results demonstrated that the influence of earthworms alone on Cd availability is more important than that of AMF in Cd-polluted soils; and that the interaction effects between these organisms on soil microorganism are much more important than on Cd availability. Thus, the presence of both earthworms and AMF could alleviate Cd effects on soil microbial life.     

氮素浓度和水分对水稻土硝化作用和微生物特性的影响

为了明确不同氮素浓度和水分对土壤硝化作用和微生物特性的影响,特别是高氮素浓度下的响应特异性,以红壤水稻土为供试土壤,设置4个硫铵用量水平[0(CK)、120 mg(N).kg-1(A1)、600 mg(N).kg-1(A2)、1 200 mg(N).kg-1(A3)],调节土壤水分为饱和持水量(WHC)的40%、60%和80%,研究了短期内不同氮素浓度和不同水分条件下土壤硝化作用、微生物生物量碳和微生物功能多样性的变化。结果表明:在40%、60%和80%WHC水分条件时,硫铵A2、A3浓度处理土壤硝化率和硝化速率普遍较低,硫铵A1浓度处理硝化率和硝化速率随土壤含水量的升高而升高;同含水量时随硫铵用量的升高而显著降低。在40%、60%和80%WHC水分条件时,微生物生物量碳随硫铵浓度的升高而降低;同浓度硫铵用量水平时,微生物生物量碳的变化基本表现为:60%WHC80%WHC40%WHC。分析发现不同水分和硫铵处理之间存在交互作用。BIOLOG分析显示:不同氮素浓度和不同水分处理,60%WHC下A1处理的平均吸光值(AWCD)和Shannon、Simpson、McIntosh指数最大,其次为60%WHC的硫铵CK处理,而不同水分下硫铵A2、A3处理,其AWCD值和Shannon、Simpson、McIntosh多样性指数都较低,进一步说明过量施肥导致微生物活性降低。不同氮素浓度和水分条件下土壤微生物和生化性状不同,过量施用化肥后将有可能造成土壤微生物性状和生化功能衰减。     

Surface soil responses to silage cropping intensity on a Typic Kanhapludult in the piedmont of North Carolina

Although reduced tillage itself is beneficial to soil quality and farm economics, the amount of crop residues returned to the soil will likely alter the success of a particular conservation tillage system within a farm operation. We investigated the impact of three cropping systems (a gradient in silage cropping intensity) on selected soil physical, chemical, and biological properties in the Piedmont of North Carolina, USA. Cropping systems were: (1) maize (Zea mays L.) silage/barley (Hordeum vulgare L.) silage (high silage intensity), (2) maize silage/winter cover crop (medium silage intensity), and (3) maize silage/barley grain—summer cover crop/winter cover crop (low silage intensity). There was an inverse relationship between silage intensity and the quantity of surface residue C and N contents. With time, soil bulk density at a depth of 0–3 cm became lower and total and particulate C and N fractions, and stability of macroaggregates became higher with lower silage intensity as a result of greater crop residue returned to soil. Soil bulk density at 0–3 cm depth was initially 0.88 Mg m⁻³ and increased to 1.08 Mg m⁻³ at the end of 7 years under high silage intensity. Total organic C at 0–20 cm depth was initially 11.7 g kg⁻¹ and increased to 14.3 g kg⁻¹ at the end of 7 years under low silage intensity. Stability of macroaggregates at 0–3 cm depth at the end of 7 years was 99% under low silage intensity, 96% under medium silage intensity, and 89% under high silage intensity. Soil microbial biomass C at 0–3 cm depth at the end of 7 years was greater with low silage intensity (1910 mg kg⁻¹) than with high silage intensity (1172 mg kg⁻¹). Less intensive silage cropping (i.e., greater quantities of crop residue returned to soil) had a multitude of positive effects on soil properties, even in continuous no-tillage crop production systems. An optimum balance between short-term economic returns and longer-term investments in improved soil quality for more sustainable production can be achieved in no-tillage silage cropping systems.     

Biochar soil amendment increased bacterial but decreased fungal gene abundance with shifts in community structure in a slightly acid rice paddy from Southwest China

Biochar’s role on greenhouse gas emission and plant growth has been well addressed. However, there have been few studies on changes in soil microbial community and activities with biochar soil amendment (BSA) in croplands. In a field experiment, biochar was amended at rates of 0, 20 and 40 t ha⁻¹ (C0, C1 and C2, respectively) in May 2010 before rice transplantation in a rice paddy from Sichuan, China. Topsoil (0–15 cm) was collected from the rice paddy while rice harvest in late October 2011. Soil physico-chemical properties and microbial biomass carbon (MBC) and nitrogen (MBN) as well as selected soil enzyme activities were determined. Based on 16S rRNA and 18S rRNA gene, bacterial and fungal community structure and abundance were characterized using terminal-restriction fragment length polymorphism (T-RFLP) combined with clone library analysis, denaturing gradient gel electrophoresis (DGGE) and quantitative real-time PCR assay (qPCR). Contents of SOC and total N and soil pH were increased but bulk density decreased significantly. While no changes in MBC and MBN, gene copy numbers of bacterial 16S rRNA was shown significantly increased by 28% and 64% and that of fungal 18S rRNA significantly decreased by 35% and 46% under BSA at 20 and 40 t ha⁻¹ respectively over control. Moreover, there was a significant decrease by 70% in abundance of Methylophilaceae and of Hydrogenophilaceae with an increase by 45% in Anaerolineae abundance under BSA at 40 t ha⁻¹ over control. Whereas, using sequencing DGGE bands of fungal 18S rRNA gene, some bands affiliated with Ascomycota and Glomeromycota were shown inhibited by BSA at rate of 40 t ha⁻¹. Significant increases in activities of dehydrogenase, alkaline phosphatases while decreased β-glucosidase were also observed under BSA. The results here indicated a shift toward a bacterial dominated microbial community in the rice paddy with BSA.     

Earthworm colonisation of abandoned arable soil polluted by copper

The distribution, density and biomass of earthworms were investigated at the copper polluted site, Hygum (Denmark). In 1994, shortly after farming of the area was abandoned, only four earthworm species were present and their distribution was restricted to areas where copper concentration did not exceed 200 mg kg^?1 dry soil. Sixteen years later (in 2010), without any agricultural activity, ten species of earthworms were found, in particular, epigeic species were present where soil copper concentrations reached >1000 mg kg^?1 dry soil.     

Effects of tillage and nitrogen management on soil chemical and physical properties after 23 years of continuous sorghum

Long-term tillage and nitrogen (N) management practices can have a profound impact on soil properties and nutrient availability. A great deal of research evaluating tillage and N applications on soil chemical properties has been conducted with continuous corn (Zea Mays L.) throughout the Midwest, but not on continuous grain sorghum (Sorghum bicolor (L.) Moench). The objective of this experiment was to examine the long-term effects of tillage and nitrogen applications on soil physical and chemical properties at different depths after 23 years of continuous sorghum under no-till (NT) and conventional till (CT) (fall chisel-field cultivation prior to planting) systems. Ammonium nitrate (AN), urea, and a slow release form of urea were surface broadcast at rates of 34, 67, and 135 kg N ha⁻¹. Soil samples were taken to a depth of 15 cm and separated into 2.5 cm increments. As a result of lime applied to the soil surface, soil pH in the NT and CT plots decreased with depth, ranging from 6.9 to 5.7 in the NT plots and from 6.5 to 5.9 in the CT plots. Bray-1 extractable P and NH₄OAc extractable K was 20 and 49 mg kg⁻¹ higher, respectively, in the surface 2.5 cm of NT compared to CT. Extractable Ca was not greatly influenced by tillage but extractable Mg was higher for CT compared to NT below 2.5 cm. Organic carbon (OC) under NT was significantly higher in the surface 7.5 cm of soil compared to CT. Averaged across N rates, NT had 2.7 Mg ha⁻¹ more C than CT in the surface 7.5 cm of soil. Bulk density (Δ_b) of the CT was lower at 1.07 g cm⁻³ while Δ_b of NT plots was 1.13 g cm⁻³. This study demonstrated the effect tillage has on the distribution and concentration of certain chemical soil properties.     

Deep-burrowing earthworm additions changed the distribution of soil organic carbon in a chisel-tilled soil

We investigated the influence of earthworms on the three-dimensional distribution of soil organic carbon (SOC) in a chisel-tilled soil. By burrowing, foraging, and casting at the surface and throughout the soil, anecic earthworms such as Lumbricus terrestris L. may play a major role in regulating the spatial distribution of organic matter resources both at the surface and within the soil. In the fall of 1994, we manipulated ambient earthworm communities, which were without deep burrowing species, by adding 100 earthworm individuals m⁻² in spring and fall for 3 years. Overall, the biomass of L. terrestris was increased with earthworm additions and total earthworm biomass declined compared with ambient control treatments. To investigate the spatial variability in soil organic carbon due to this shift in earthworm community structure, we sampled soil on a 28×24 cm grid from the surface to 40 cm in four layers, 10 cm deep. Samples were analyzed for total carbon. We found that additions of anecic earthworms significantly increased average soil organic carbon content from 16.1 to 17.9 g C kg⁻¹ for the 0–10 cm soil, and from 12.4 to 14.7 g kg⁻¹ at 10–20-cm depth, and also changed the spatial distribution of soil organic carbon from uniform to patchy, compared with the ambient treatment.     

Production of carbon dioxide and nitrous oxide in alkaline saline soil of Texcoco at different water contents amended with urea: A laboratory study

Soil of the former lake Texcoco is alkaline saline with pH often >10 and electrolytic conductivity (EC) >70 dS m^?1 with rapidly changing water contents. Little is known how fertilizing this area with urea to vegetate the soil would affect emissions of carbon dioxide (CO₂) and dynamics of N. Texcoco soil with electrolytic conductivity (EC) 2.3 dS m^?1 and pH 8.5 (TEXCOCO A soil), EC 2.0 dS m^?1 and pH 9.0 (TEXCOCO B soil) and 200 dS m^?1 and pH 11.2 (TEXCOCO C soil) was amended with or without urea and incubated at 40% of water holding capacity (WHC), 60% WHC, 80% WHC and 100% WHC, while emissions of nitrous oxide (N₂O) and CO₂ and dynamics of ammonium (NH₄⁺), nitrite (NO₂^?) and nitrate (NO₃^?) were monitored for 7 days. An agricultural soil served as control (ACOLMAN soil). The emission of CO₂ increased in the urea amended soil 1.5 times compared to the unamended soil, it was inhibited in TEXCOCO C soil and was >1.2 larger in soil incubated at 40%, 60% and 80% WHC compared to soil incubated at 100% WHC. The emission of N₂O increased in soil added with urea compared to the unamended soil, was similar in TEXCOCO A and B soils, but was <0.2 mg N kg^?1 soil day^?1 in TEXCOCO C soil and generally larger in soil incubated at 60% and 80% WHC compared to soil incubated at 40% and 100% WHC. The water content of the soil had no significant effect on the mean concentration of NH₄⁺, but addition of urea increased it in all soils. The concentration of NO₂^? was not affected by the water content and the addition of urea except in TEXCOCO A soil where it increased to values ranging between 20 and 40 mg N kg^?1. The concentration of NO₃^? increased in the ACOLMAN, TEXCOCO A and TEXCOCO B soil amended with urea compared to the unamended soil, but not in the TEXCOCO C soil. It decreased with increased water content, but not in TEXCOCO C soil. It was found that the differences in soil characteristics, i.e. soil organic matter content, pH and EC between the soils had a profound effect on soil processes, but even small changes affected the dynamics of C and N in soil amended with urea.