The effects of organic residue quality on growth and reproduction of <Emphasis Type="Italic">Aporrectodea trapezoides</Emphasis> under different moisture conditions in a salt-affected agricultural soil

We studied the effects of organic residues with different C/N ratios and soil moisture contents on the growth and reproduction of the earthworm Aporrectodea trapezoides to investigate potential measures to increase its population in a salt-affected agricultural soil. The experiment consisted of eight treatments in a fully factorial design: low or high C/N ratio organic residue, soil moisture at 75 or 95% field capacity (FC), and salinity (as electrical conductivity (EC)) of 3.07 or 4.77 dS m^?1. It was carried out under controlled laboratory conditions for 4 months. In the low C/N ratio organic residue application, there was a significantly greater mean total dry weight and number of clitellate individuals of A. trapezoides, regardless of the soil moisture and salinity content, which may be due to the greater soil microbial biomass and dissolved organic N (DON) derived from the low C/N ratio organic residue. Generally, more cocoons were found in the application of low C/N ratio clover residue at months 2 and 4. At an EC of 3.07 dS m^?1 and moisture content of 75% field capacity (FC), significantly more hatchlings were found when low C/N ratio clover residue was applied compared to the high C/N ratio wheat residue. High soil moisture content (95% FC) resulted in a significantly greater mean total dry weight of A. trapezoides at months 2 and 4 and significantly more clitellate individuals and cocoons at month 4 compared to the low soil moisture content (75% FC), but only when the low C/N ratio residue was applied. In contrast, high soil moisture content (95% FC) resulted in significantly less hatchling numbers at an EC of 3.07 dS m^?1, only when the low C/N ratio residue was applied. These results suggest that the organic residue type and soil moisture content can regulate the growth and reproduction of the earthworm A. trapezoides, which should help to improve the recovery of their populations in salt-affected agricultural soil.     

Effect of Piriformospora indica and Azospirillum strains from saline or non-saline soil on mitigation of the effects of NaCl

Salinity toxicity is a worldwide agricultural and eco-environmental problem. The intent of this study was to determine the salt tolerance of Piriformospora indica and strains of Azospirillum, isolated from non-saline and saline soil, as well as to determine their affect on the tolerance of wheat to soil salinity. In this study, an experiment was conducted to investigate the salt stress tolerance abilities of the endophytic fungi, P. indica, and Azospirillum strains, isolated from non-saline and saline soil, at five NaCl levels (0, 0.1, 0.2, 0.3, 0.4, 0.5 mol L^?1). Additionally, a greenhouse experiment was conducted to test the effects of these selected microorganisms under increasing salinity levels on seedling growth, solute accumulation (proline and sugars), and photosynthetic pigments (Chl a, b, ab) of seedling wheat. Azospirillum strains were isolated in Iran from the root of field-grown maize from non-saline soil with an EC = 0.7 dS m^?1 and from saline soil with an EC = 4.7 dS m^?1. Plants were irrigated with non-saline water–tap water with an electrical conductivity water (ECw) value of 0.2 dS m^?1, as well as low, moderate and severe saline water-irrigation with saline water with an ECw of 4 dS m^?1, 8 dS m^?1 and 12 dS m^?1, respectively. The upper threshold of P. indica salinity tolerance was 0.4 mol L^?1 NaCl in both liquid and solid broth medium. The upper thresholds of the salt adapted and non-adapted Azospirillum strains were 0.2 and 0.4 mol L^?1 NaCl, respectively. The results indicated a positive influence of the organisms on salinity tolerance, more with the saline-adapted Azospirillum strains than the non-adapted strains. P. indica was more effective than the Azospirillum strains. These results could be related to a better water status, higher photosynthetic pigment contents and proline accumulation in wheat seedlings inoculated with P. indica. The benefits of both isolates and P. indica depended on two factors: water salinity and growth stage of the host plant. Inoculation with the two isolates increased salinity tolerance of wheat plants; the saline-adapted Azospirillum strains showed better performance with respect to improved fresh and dry weights at 80 and 100 days after sowing under both non-saline and saline conditions. When compared to plants inoculated with non-saline-adapted Azospirillum strains, those inoculated with adapted Azospirillum strains had much better performance with respect to the presence of photosynthetic pigment (Chl a, b and ab) and proline accumulation. Overall, these results indicate that the symbiotic association between P. indica fungus and wheat plants improved wheat growth, regardless of the salinity. It is concluded that the mechanisms for protecting plants from the detrimental effects of salinity by P. indica fungus and Azospirillum strains may differ in their salinity tolerance and influence the uptake of water, photosynthetic pigment contents and proline accumulation in wheat seedlings.     

Enhancing maize grain yield under salt-affected field conditions using salt-resistant maize hybrids and higher planting density

Background

In arid and semiarid countries, grain yield of maize is increasingly impaired by soil salinity. Beside soil amelioration, the development of salt-resistant cultivars is a possibility to enhance crop yield on salt-affected soils.

Aims

This study aimed at testing yield performance in the field of salt-resistant maize hybrids on a salt-affected soil. In addition, planting density was optimized under the saline conditions.

Methods

Four salt-resistant maize hybrids (Zea mays L. SR-05, SR-12, SR-15, and SR-16) were grown under control (EC = 2.0–2.5 dS m⁻¹) and saline (EC = 10.0–12.0 dS m⁻¹) field conditions and compared to the salt-sensitive maize cv. Pioneer-3906. Planting density (5, 8, or 11 plants m⁻²) was optimized for saline soil conditions for SR-12 and the local hybrid EV-78.

Results

Yield of Pioneer-3906 was significantly reduced under salinity because of inhibited kernel setting, whereas the SR hybrids showed no decrease in grain yield. Based on grain yield, the optimum planting density was 8 plants m⁻² with no further increase with 11 plants m⁻². In contrast to SR-12, for cv. EV-78 no increase of harvest index with 8 relative to 5 plants m⁻² was observed.

Conclusions

Vegetative growth of Pioneer-3906 and the SR hybrids was decreased due to Phase-I effects but neither due to water deficiency nor ion toxicity. The experiment corroborated the salt resistance of the SR hybrids under field conditions. Under saline conditions, optimum planting density of salt-resistant cultivars may be higher than under nonsaline conditions when sufficient water supply by artificial irrigation is guaranteed.     

Salinity and sodicity affect soil respiration and dissolved organic matter dynamics differentially in soils varying in texture

The individual effects of salinity and sodicity on organic matter dynamics are well known but less is known about their interactive effects. We conducted a laboratory incubation experiment to assess soil respiration and dissolved organic matter (DOM) dynamics in response to salinity and sodicity in two soils of different texture. Two non-saline non-sodic soils (a sand and a sandy clay loam) were leached 3–4 times with solutions containing different concentrations of NaCl and CaCl₂ to reach almost identical electrical conductivity (EC_1:5) in both soils (EC_1:5 0.5, 1.3, 2.5 and 4.0 dS m^?1 in the sand and EC_1:5 0.7, 1.4, 2.5 and 4.0 dS m^?1 in the sandy clay loam) combined with two sodium absorption ratios: SAR < 3 and 20. Finely ground wheat straw residue was added (20 g kg^?1) as substrate to stimulate microbial activity. Cumulative respiration was more strongly affected by EC than by SAR. It decreased by 8% at EC 1.3 and by 60% at EC 4.0 in the sand, whereas EC had no effect on respiration in the sandy clay loam. The apparent differential sensitivity to EC in the two soils can be explained by their different water content and therefore, different osmotic potential at the same EC. At almost similar osmotic potential: ?2.92 MPa in sand (at EC 1.3) and ?2.76 MPa in the sandy clay loam (at EC 4.0) the relative decrease in respiration was similar (8–9%). Sodicity had little effect on cumulative respiration in the soils, but DOC, DON and specific ultra-violet absorbance (SUVA) were significantly higher at SAR 20 than at SAR < 3 in combination with low EC in both soils (EC 0.5 in the sand and EC 0.7 and 1.4 in the sandy clay loam). Therefore, high SAR in combination with low EC is likely to increase the risk of DOC and DON leaching in the salt-affected soils, which may lead to further soil degradation.     

Response of microbial activity and biomass to increasing salinity depends on the final salinity,not the original salinity

Salinization is a global land degradation issue which inhibits microbial activity and plant growth. The effect of salinity on microbial activity and biomass has been studied extensively, but little is known about the response of microbes from different soils to increasing salinity although soil salinity may fluctuate in the field, for example, depending on the quality of the irrigation water or seasonally. An incubation experiment with five soils (one non-saline, four saline with electrical conductivity (EC_e) ranging from 1 to 50 dS m⁻¹) was conducted in which the EC was increased to 37 EC_e levels (from 3 to 119 dS m⁻¹) by adding NaCl. After amendment with 2% (w/w) pea straw to provide a nutrient source, the soils were incubated at optimal water content for 15 days, microbial respiration was measured continuously and chloroform-labile C was determined every three days. Both cumulative respiration and microbial biomass (indicated by chloroform-labile C) were negatively correlated with EC. Irrespective of the original soil EC, cumulative respiration at a given adjusted EC was similar. Thus, microorganisms from previously saline soils were not more tolerant to a given adjusted EC than those in originally non-saline soil. Microbial biomass in all soils increased from day 0 to day 3, then decreased. The relative increase was greater in soils which had a lower microbial biomass on day 0 (which were more saline). Therefore the relative increase in microbial biomass appears to be a function of the biomass on day 0 rather than the EC. Hence, the results suggest that microbes from originally saline soils are not more tolerant to increases in salinity than those from originally non-saline soils. The strong increase in microbial biomass upon pea straw addition suggests that there is a subset of microbes in all soils that can respond to increased substrate availability even in highly saline environments.     

Earthworms and rate of breakdown of soybean and maize residues in soil

A field survey was conducted to determine the numbers and biomass of earthworms in soils receiving different tillage and cropping treatments, and to investigate in a greenhouse study the effect of earthworms on the rate of breakdown of soybean (Glycine max) and maize (Zea mays L.) residues. The numbers and biomass of earthworms under continuous soybeans were greater than those present under maize, possibly due to the adverse effects of insecticide and anhydrous ammonia fertilizer used with maize. No-tillage doubled the population of earthworms under soybeans, when compared with ploughing. Numbers (141 m^?2) and biomass (26.5 g m^?2) of earthworms under no-till soybeans were still much lower than the numbers (1298 m^?2) and biomass (224.5 g m^?2) under pasture receiving heavy applications of animal manure. Using 16-1 pots in the greenhouse, the effect of 0, 15 (250m^?2) and 30 (500m^?2) earthworms (Lumbricus rubellus) pot^?1 on the rate of breakdown during 54 days of 50 g of soybean or maize residues in the Raub silt loam (Aquic Argiudoll) was studied. At 36 days, 60% of the soybean residues were recovered from pots to which no earthworms had been added, whereas in the presence of earthworms, only 34% of the soybean residues remained. In the absence of earthworms, 85% of the maize residues were recovered at 36 days, compared with only 52% in the presence of earthworms. At 36 days, 48% of the original maize residues added were still > 2 mm in length in the absence of earthworms, whereas only 26% were > 2 mm in length in the presence of earthworms. Earthworms also increased the aggregate stability of the Raub soil, when determined on moist (19–22% w/w) samples, but had no effect on soil water retention at ?33 and ?1500 kPa. The possible implications of greater earthworm activity on increasing residue incorporation and breakdown and subsequent effects on soil temperatures under no-till maize production are also discussed.     

Miscanthus sinensis and wild flowers as food resources of Lumbricus terrestris L.

Senescent leaves of Miscanthus sinensis contained 36% soluble polysaccharides, 26% cellulose and had a C/N ratio of 45. In 11 wild flower species contents of soluble polysaccharides (21–30%), cellulose (3–16%) and C/N ratio (13–31) were lower. Decomposing leaves of M. sinensis lost weight at a rate of 0.002 day⁻¹, increased the C/N ratio from 45 to about 100, the bacterial biomass from 0.4 to 1 μg C mg⁻¹ dry weight, and decreased the tensile strength from 35 to 10 N. The withdrawal rate of Lumbricus terrestris with senescent leaves of M. sinensis was 30 mg g⁻¹ week⁻¹; the feeding rate was lower. With most senescent wild flowers withdrawal and feeding rates were higher. During decomposition of M. sinensis withdrawal rates increased to about 90, and feeding rates to about 30 mg g⁻¹ week⁻¹. The rates were not related to soluble polysaccharides, cellulose, acid-insoluble residue, C/N ratio and the presence of trichomes on the leaves. The abundance of L. terrestris decreased in a meadow turned into a field of M. sinensis from 55 to 26 earthworms m⁻² and increased in a rotational maize field turned into wild flower strips from 28 to 46 earthworms m⁻². The species richness of earthworms decreased with M. sinensis from 7.2 to 4.7 and increased with wild flowers from 4.7 to 6.7 species per sampling unit.     

Secondary salinity effects on soil microbial biomass

Secondary soil salinilization is a big problem in irrigated agriculture. We have studied the effects of irrigation-induced salinity on microbial biomass of soil under traditional cotton (Gossypium hirsutum L.) monoculture in Sayhunobod district of the Syr-Darya province of northwest Uzbekistan. Composite samples were randomly collected at 0–30 cm depth from weakly saline (2.3 ± 0.3 dS m⁻¹), moderately saline (5.6 ± 0.6 dS m⁻¹), and strongly saline (7.1 ± 0.6 dS m⁻¹) replicated fields, 2-mm sieved, and analyzed for pH, electrical conductivity, total C, organic C (C_Org), and extractable C, total N and P, and exchangeable ions (Ca²⁺, Mg²⁺, K⁺, Na⁺, Cl⁻, and CO₃²⁻), microbial biomass (C_mic). The Na⁺ and Cl⁻ concentrations were 36-80% higher in strongly saline compared to weakly saline soil. The C_Org concentration was decreased by 10% and C_Ext by 40% by increasing soil salinity, whereas decrease in C_mic ranged from 18-42% and the percentage of C_Org present as C_mic from 8% to 26%. We conclude that irrigation-induced secondary salinity significantly affects soil chemical properties and the size of soil microflora.     

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.     

Life cycle and reproductive traits of the earthworm Aporrectodea trapezoides (Dugès, 1828) in laboratory cultures

The parthenogenetic earthworm Aporrectodea trapezoides (Dugès, 1828) is widely distributed all over the world due to European agricultural practices. In order to provide baseline life cycle data, cocoons were obtained from field-collected individuals and their features and viability, incubation period, number of hatchlings and mortality rate were recorded. Singleton and twin earthworms from this first experiment were cultured from hatching during a 490-day period under controlled conditions with biomass, survival, reproductive condition and cocoon production recorded at intervals of 15 days. On average, individuals of isolated-reared A. trapezoides reached maturity at day 153 and body weight at maturity was approximately 1 g. In order to record reproductive traits and differences between field-collected and laboratory-reared individuals, 40 microcosms with an isolated earthworm (20 with field-collected individuals and 20 with laboratory-reared ones) and 40 containing groups of three (20 with each type of individual) were maintained during a complete year under controlled conditions. The amount of soil per individual was the same in both types of microcosm. Both the individuals kept in isolation and those cultured in groups produced cocoons, hence completely proving the obligatory parthenogenetic reproduction in this species without copulation or need of any physical-chemical stimulus. In general, isolated earthworms produced a significantly higher number of cocoons than those in groups of three, and the same was recorded for laboratory-reared earthworms when compared with field-collected ones. This study highlights the importance of knowing the life cycle and reproductive traits of one possible key species in soil management due to its vast distribution and high density in soils, and the species’ highly recommended use in applied studies because of its ease of culture.     

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.     

Effects of vegetation pattern and of biochar and powdery soil amendments on soil loss by wind in a semi-arid region

Dust emission from wind erosion is a widespread phenomenon in arid and semi-arid areas having considerable implications for ecosystems and human well-being. However, few studies have examined the efficiency of biochar amended to soil on wind erosion control. Aimed at studying the effect of biochar on resistance of soils against wind erosion, a wind tunnel experiment was conducted. We tested (a) soils amended with hard waste walnut wood biochar and soft maize cob biochar, and (b) soils amended with powdery waste wood and powdery maize cob, and compared them with (c) non-treated soil, in their susceptibility to wind erosion and also the additional effect of various patterns of vegetation cover. Amending soil with biochar and powdery material did significantly increase their resilience to wind erosion because of increased soil aggregation. In comparison with the non-treated control, the mass flux of un-vegetated soil reduced from 4.42 to 1.86 g m⁻² s⁻¹ for the waste walnut wood biochar, from 4.28 to 1.50 g m⁻² s⁻¹ for maize cob biochar, from 4.11 to 1.44 g m⁻² s⁻¹ for powdery maize cob and from 3.97 to 1.14 g m⁻² s⁻¹ for powdery waste walnut wood. When combining amendments with vegetation, there was still a substantial improvement, though the soil treatments responded differently in terms of soil loss to different vegetation patterns. A single row vegetation pattern had the highest mass flux, while a zigzag vegetation pattern had the lowest. In conclusion, waste wood or maize cobs, whether applied as biochar or as powdery material, are able to fix soil and reduce wind erosion.     

The role of antioxidative metabolism of tomato leaves in long‐term salt‐stress response

The antioxidative protection system as adaptation strategy to high soil salinity in the leaves of two tomato (Lycopersicon esculentum Mill.) hybrids (Buran F1 and Berberana F1) was investigated. Changes in the activity of superoxide‐dismutase (SOD, EC 1.15.1.1), peroxidase (POD, EC 1.11.1.7), ascorbate peroxidase (APX, EC 1.11.1.11), as well as total and oxidized ascorbate concentrations (AA and DHA) in the plant leaves subjected to three salinity levels (EC 3.80 dS m⁻¹, 6.95 dS m⁻¹, and 9.12 dS m⁻¹) relative to non‐saline control were analyzed during the fruiting phase. The obtained results clearly indicate a relation between SOD activity and AA concentration in the antioxidative protection without any peroxidase‐related H₂O₂ detoxification. Increased SOD activity accompanied by high AA concentration was noticed at all salinity levels, but the response of hybrids was specific for the particular salt concentration. The first salinity level (EC 3.80 dS m⁻¹) induced the highest level of AA in the Buran F1 (70%), while in Berberana F1 hybrid leaves the highest AA concentration (64%) was noticed at the third salinity level (9.12 dS m⁻¹). All salinity levels caused a decline in POD and APX activities in both hybrids. The possibility of a predominant role of ascorbate and SOD in the antioxidative protection of mature tomato leaves under long‐term salt stress is discussed.     

Characteristics of earthworms (Eisenia fetida) in PAHs contaminated soil amended with sewage sludge or vermicompost

Earthworms can be used to remove polycyclic aromatic hydrocarbons (PAHs) from soil, but this might affect their survival and they might accumulate the contaminants. Sterilized and unsterilized soil was contaminated with phenanthrene (Phen), anthracene (Anth) and benzo(a)pyrene (BaP), added with or without Eisenia fetida, sewage sludge or vermicompost. Survival, growth, cocoon formation and concentrations of PAHs in the earthworms were monitored for 70 days. Addition of sewage sludge to sterilized or unsterilized soil maintained the number of earthworms and their survival was 94%. The addition of sludge significantly increased the weight of earthworms 1.3 times compared to those kept in the unamended soil or in soil amended with vermicompost. The weight of earthworms was significantly lower in sterilized than in unsterilized soil. Cocoons were only detected when sewage sludge was added to unsterilized soil. A maximum concentration of 62.3 μg Phen kg⁻¹ was found in the earthworms kept in sterilized soil amended with vermicompost after 7 days and 22.3 μg Phen kg⁻¹ when kept in the unamended unsterilized soil after 14 days. Concentrations of Phen in the earthworms decreased thereafter and ≤2 μg kg⁻¹ after 28 days. A maximum Anth concentration of 82.5 μg kg⁻¹ was found in the earthworms kept in sterilized soil amended with vermicompost and 45.8 μg Anth kg⁻¹ when kept in the unamended unsterilized soil after 14 days. A maximum concentration of 316 μg BaP kg⁻¹ was found in the earthworms kept in sterilized soil amended with vermicompost after 56 days and 311 μg BaP kg⁻¹ when kept in the unsterilized soil amended with vermicompost after 28 days. The amount of BaP in the earthworm was generally largest after 28 days, but after 70 days still 60 μg kg⁻¹ was found in E. fetida when kept in the sterilized soil amended with sewage sludge. It was found that E. fetida survived in PAHs contaminated soil and accumulated only small amounts of the contaminants, but sewage sludge was required as food for its survival and cocoon production.     

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.     

Impact on soil fauna of sheep faeces containing a range of parasite control agents

To compare the impact of parasite control agents in sheep faeces, 1 kg quantities of fresh faeces were spread uniformly over 1 m² pasture plots in June 2001 (winter; a time of high earthworm activity). Faecal treatments applied to five replicate plots were C− (none), C+ (from untreated sheep), B (from sheep with an intra-ruminal bolus releasing a benzimidazole anthelmintic—‘albendazole’), ML (from sheep with a bolus releasing a macrocyclic lactone anthelmintic—‘ivermectin’), F (from sheep receiving a daily feed supplement containing chlamydospores of the nematophagous fungus, Duddingtonia flagrans). The disappearance of faeces was assessed visually over the 50 days following faecal application, then soil samples were taken to assess: (a) populations of earthworms and other soil macrofauna, (b) nematodes and other soil microfauna, and (c) the presence of D. flagrans in soil. Faecal disappearance was greatest in F and C+ plots and least in ML and B plots at 12 and 23 days (P < 0.05). Earthworm casting after 23 and 50 days was greater (P < 0.05) in plots with faeces (C+, ML, F, but not B) than in plots without faeces (C−). Greater earthworm activity in plots with faeces was reflected in greater numbers of earthworms, cocoons and greater biomass m⁻² than in C− plots. On the basis of faecal dry weight applied, F plots had most earthworms and ML plots the least. After 50 days total nematodes in 0–5 cm soil showed a treatment effect (P < 0.001), being more abundant in F, C+ and B than in C− and ML plots; enchytraeids, rotifers, tardigrades and copepods showed no treatment effects. A few nematode taxa (Acrobeles, Alaimus, Pungentus, Tylencholaimus) showed significant treatment effects. The greatest effect among nematodes was in nematode channel ratio (NCR) (P < 0.008), with a decrease in F plots; changes in NCR may reflect the impact of earthworm activity on soil processes rather than a direct effect of the fungal treatment on nematodes. D. flagrans did not become established in the soil. During the trial conditions were favourable for earthworms and their activity was high in all treatments receiving faeces, with F and ML plots being the extremes. There was an apparent shift towards fungal-mediated decomposition in F plots. At the end of the 50-day trial, in a period when earthworms were active, there was no evidence of differential effects of any of the anthelmintic treatments on environmental indicators.     

The adverse effects of soil salinization on the growth of Trifolium alexandrinum L. and associated microbial and biochemical properties in a soil from Iran

The aim of this study was to determine the effects of increasing concentrations of salt solutions (including 0.12, 2, 6, and 10 dS m⁻¹) on the growth of berseem clover (Trifolium alexandrinum L.) and related soil microbial activity, biomass and enzyme activities. Results showed that the dry weights of root and shoot decreased with an increase in the concentrations of salt solutions. Soil salinization depressed the microbiological activities including soil respiration and enzyme activities. Substrate-induced respiration was consistently lower in salinized soils, whereas microbial biomass C did not vary among salinity levels. Higher metabolic quotients (qCO₂) and unaffected microbial biomass C at high EC values may indicate that salinity is a stressful factor, inducing either a shift in the microbial community with less catabolic activity or reduced efficiency of substrate utilization. Acid phosphatase and alkaline phosphatase activities decreased with increasing soil salinity. We found significant, positive correlations between the activities of phosphatase enzymes and plant's root mass, suggesting that any decrease in the activities of the two enzymes could be attributed to the reduced root biomass under saline conditions.     

Decomposition of N-labelled maize leaves in soil affected by endogeic geophagous Aporrectodea caliginosa

A microcosm experiment was carried out for 56 days at 12 °C to evaluate the feeding effects of the endogeic geophagous earthworm species Aporrectodea caliginosa on the microbial use of ¹⁵N-labelled maize leaves (Zea mays) added as 5 mm particles equivalent to 1 mg C and 57 μg N g⁻¹ soil. The dry weight of A. caliginosa biomass decreased in the no-maize treatment by 10% during the incubation and increased in the maize leaf treatments by 18%. Roughly 5% and 10% of the added maize leaf-C and leaf-N, respectively, were incorporated into the biomass of A. caliginosa. About 29% and 33% of the added maize leaf-C were mineralised to CO₂ in the no-earthworm and earthworm treatments, respectively. The presence of A. caliginosa significantly increased soil-derived CO₂ production by 90 μg g⁻¹ soil in the no-maize and maize leaf treatments, but increased the maize-derived CO₂ production only by 40 μg g⁻¹ soil. About 10.5% of maize leaf-C and leaf-N was incorporated into the soil microbial biomass in the absence of earthworms, but only 6% of the maize leaf-C and 3% of the maize leaf-N in the presence of earthworms. A. caliginosa preferentially fed on N rich, maize leaf-colonizing microorganisms to meet its N demand. This led to a significantly increased C/N ratio of the unconsumed microbial biomass in soil. The ergosterol-to-microbial biomass C ratio was not significantly decreased by the presence of earthworms. A. caliginosa did not directly contribute to comminution of plant residues, as indicated by the absence of any effects on the contents of the different particulate organic matter fractions, but mainly to grazing of residue-colonizing microorganisms, increasing their turnover considerably.     

Population dynamics of the earthworm Aporrectodea trapezoides (Annelida: Lumbricidae) in a Western Australian pasture soil

Summary The changes in size and age-composition of an earthworm population were studied in a Western Australian pasture developed since 1912. The population size in the surface 10 cm was estimated by handsorting during the cool wet season (19 weeks from May to September). Two species, both exotic, were found, Aporrectodea tranpezoides (Lumbricidae) and Microscolex dubius (Acanthodrilidae). Of the 615 individual speciemens collected, 99.7% were A. trapezoides. The abundance of A. trapezoides increased from 58 m^-2 at the time of the opening rains to 170 m^-2 (88.6 g live weight m^-2) after 10.5 weeks. Near the end of the wet season (in October) the density was 37 m^-2. At the time of the opening rains the population consisted of juvenile and semimature individuals. Clitellate earthworms were found 1 month later and predominated from August (10.5 weeks) to the end of the season. Egg capsules were found from August through October. Egg capsules incubated in the laboratory at 16°C hatched on average after 42 days and produced two juveniles. Juvenile and immature earthworms collected from a quiescent state at the end of summer matured within 1 month when reared in moist soil in the laboratory.     

Effects of conservation tillage drills on soil quality indicators in a wheat–oilseed rape rotation: organic carbon,earthworms and water-stable aggregates

The effects of five conservation tillage drills with crop residue levels covering between 17% and 79% of the soil, and tillage depths ranging from 25 to 200 mm, were examined over 3 years. The tillage systems ranged from a relatively disruptive Farm System to a Low Disruption system, with three intermediate treatments labelled Sumo DTS, Claydon and Mzuri. The study involved field sites on a clay or clay loam soil, where winter wheat and oilseed rape were grown in rotation. In the clay field, the Mzuri and Low Disruption treatments, which produced the highest residue coverage, showed the greatest increase in surface total soil organic carbon (1.1 and 0.48 Mg C ha⁻¹, respectively) between years 1 and 3. The least disruptive tillage system also resulted in the highest density of earthworms (181–228 m⁻²), and the most disruptive system produced the lowest densities (75–98 m⁻²). In the third year, the least disruptive system also showed a higher proportion of water-stable aggregates (29.8%) than the other treatments (22.7%–25.3%). Linear regressions showed positive relationships of both soil organic carbon and earthworm density with surface residue cover, and of the proportion of water-stable aggregates with soil organic carbon.