Earthworm Populations Research Articles

Changes in earthworm populations during conversion from conventional to organic farming

The development of earthworms was investigated from 2001 to 2008 on the 176 ha arable fields of Ritzerau Farm (northern Germany) converted 2001–2004 from conventional to organic farming. Earthworms were recorded six times per year on a grid of 85 sampling points, whereas pH was determined in 2001 and 2005 and carbon content in 2001. Weak correlations between earthworm numbers and soil pH or organic matter of soil were found for few species, except for Lumbricus castaneus which was more abundant at pH > 6.5. Lumbricus rubellus benefited most from grain cultivation, Lumbricus terrestris from organic management. Aporrectodea caliginosa and Aporrectodea rosea were mainly related to rainfall and more abundant under 700–900 mm rain per year. Compensation of declined abundance after a period of heavy dryness lasted 0.5–1 year. The enhancement after conversion lasted 2–4 years and numbers increased from 0.2 to a maximum of 4.5 ind /m 2.

우분 분해에 대한 지렁이와 소똥구리의 상호작용

The effect of earthworm and dung beetle on cattle dung pat decomposition was assessed by combining quantification of earthworm density and with or without dung beetle in pats and measurements of the decomposition rate of these pats. Cattle dung decomposition rate was higher in the pots treated with both earthworm and dung beetle than in the pots with either earthworm or beetle alone. After dung beetle and earthworm activity, the growth of oat in earthworm with dung beetle treatment was similar effect with fertilizer treatment. Dung beetle was responsible for dung decomposition until 78% moisture content in the dung, earthworm was responsible for up to 30% moisture of dung, and two group were not shown any activity for decomposition less 30% moisture content of dung. Therefore dung in the different periods could be broken down by each group. The disappearance and conveyance of dung by earthworm and dung beetle was 72% of the initial dung amount. 10.2% of 72% dung was used making brood balls by dung beetle. Earthworm activity was not an impediment on making brood balls by dung beetles. The interaction of earthworm and dung beetle may have a complementary cooperation rather than competition in the same dung pat. Indeed, development of earthworm accelerate to coexist with dung beetles instead without dung beetles. From this result, maximum benefits of the effective earthworm and dung beetle can be achieved, it is needed to preserve population of earthworm and dung beetles in pasture to sustainable agricultural environment.

Influence of texture and amendments on soil properties and earthworm communities

In Canada, the influence of earthworms on soil is considered particularly important in the Southern regions where agriculture has developed. A field experiment was duplicated on a clay loam and a sandy loam soil in the Saint-Lawrence Valley. Both sites were enriched with urban compost or mineral amendment. The effects of amendments on soil properties and the earthworm community were evaluated by uni- and multivariate analyses at two soil depths (0–10 and 10–20 cm) and after two growth seasons. Compost-amended plots had higher pH, wet aggregates stability, total N and C, OM, K and Ca in the 0–10 cm soil layer than plots receiving mineral fertilizer. Two endogeic species, Aporrectodea caliginosa and Allolobophora chlorotica were dominant in both sites. Other species were all epigeic and were rare. Abundance and biomass of earthworms (0–10 cm) were significantly higher in clay loam, with a similar proportion in A. caliginosa (263 ind m −2) and A. chlorotica (228 ind m −2). In sandy loam, A. caliginosa was the most abundant (18 ind m −2), A. chlorotica was scarce (1.3 ind m −2) and epigeic species were absent. The density and biomass of earthworms were significantly higher with compost amendment, up to 12 times in clay loam: A. chlorotica reached a mean density of 420 ind m −2 vs. 36 ind m −2 with mineral amendments, A. caliginosa 344 ind m −2 vs. 183 ind m −2 and epigeic earthworms 19 ind m −2 vs. 12 ind m −2. In co-inertia analysis, the main factors explaining data heterogeneity were soil texture (axis 1) and organic matter content (axis 2). A. chlorotica was associated with OM, while A. caliginosa was associated with silt and clay contents. Additionally, soil wet aggregate stability was the variable that best correlated with endogeic species. The overall earthworm population was low, which is common for tilled agricultural soils, but clearly benefited from the OM input from the urban compost, providing further evidence that fertilization based on organic residues, as implemented in organic agriculture, is highly beneficial for earthworms and soil quality.

Fine-scale spatial and temporal variation in earthworm surface casting activity in agroforestry fields, western Honduras

Abstract Quantification of the spatial and temporal distribution patterns of soil fauna is a relatively new area of research, and has been proposed as the key to understanding the high diversity typical of soil fauna communities. Field research on the relationships among the spatial distribution patterns of trees, litter and earthworm surface casting was carried out in two agroforestry fields in a rugged area of western Honduras. Grid-based sampling at a scale of 2–20 m was employed to determine whether any spatial relationships existed among these variables at this fine scale. Each field was sampled twice at either 2 or 3 week intervals, to determine the short-term stability of spatial relationships. The spatial distribution of litter showed a strong pattern of aggregation, whereas earthworm cast distribution did not exhibit strong spatial autocorrelation. However, the spatial distribution patterns of each of these variables were well explained by the spatial arrangement of trees in both sites. Fitted model cross-semivariograms explained between 70% and 90% of the total variation in cross-semivariance between tree density and litter cover, and between tree density and earthworm cast weight. The results of the study suggest that farmers may be able to manipulate populations of earthworms indirectly by managing the spatial arrangement of trees within their crop fields. Planning the distribution of trees could allow farmers to create ‘patches’ of organic resources within fields, while minimising the negative effects of trees on crop growth due to competition for light, water and nutrients. Over the short time scale of the study, unusually heavy rainfall led to substantial changes in spatial distribution patterns of earthworm cast activity and litter cover, which may otherwise not have occurred. This result emphasises the need to take into account short-term temporal change during ecological studies at fine spatial scales.

<i>Mucuna pruriens</i> and its effect on some physical, chemical and biological properties of a Forest Acrisol

The effect of Mucuna pruriens, a herbaceous legume, on some properties of a forest acrisol was examined in RCBD experiment of four treatments: control, NPK fertilizer, mucuna incorporation and mucuna mulch. At flowering, the fresh biomass was cut at soil level, chopped up and applied to the soil either by incorporation or as mulch. In both cases, mucuna improved the physical, chemical and biological properties of the soil. Available soil moisture content increased from 9.54% to values between 10.20% and 11.40% while bulk density reduced from 1.42 to 1.36 Mg m-3. Total N increased from 0.14% to 0.18%. Organic C and K levels did not change while P was slightly reduced. Earthworm populations in the mucuna plots were three times higher than those plots without mucuna. Mucuna suppressed weed growth. These improvements in the physical and chemical properties are indicators of the potential of M. pruriens in enhancing crop yields.

Solar UVB and warming affect decomposition and earthworms in a fen ecosystem in Tierra del Fuego, Argentina

AbstractCombined effects of co‐occurring global climate changes on ecosystem responses are generally poorly understood. Here, we present results from a 2‐year field experiment in aCarexfen ecosystem on the southernmost tip of South America, where we examined the effects of solar ultraviolet B (UVB, 280–315 nm) and warming on above‐ and belowground plant production, C : N ratios, decomposition rates and earthworm population sizes. Solar UVB radiation was manipulated using transparent plastic filter films to create a near‐ambient (90% of ambient UVB) or a reduced solar UVB treatment (15% of ambient UVB). The warming treatment was imposed passively by wrapping the same filter material around the plots resulting in a mean air and soil temperature increase of about 1.2 °C. Aboveground plant production was not affected by warming, and marginally reduced at near‐ambient UVB only in the second season. Aboveground plant biomass also tended to have a lower C : N ratio under near‐ambient UVB and was differently affected at the two temperatures (marginal UVB × temperature interaction). Leaf decomposition of one dominant sedge species (Carex curta) tended to be faster at near‐ambient UVB than at reduced UVB. Leaf decomposition of a codominant species (Carex decidua) was significantly faster at near‐ambient UVB; root decomposition of this species tended to be lower at increased temperature and interacted with UVB. We found, for the first time in a field experiment that epigeic earthworm density and biomass was 36% decreased by warming but remained unaffected by UVB radiation. Our results show that present‐day solar UVB radiation and modest warming can adversely affect ecosystem functioning and engineers of this fen. However, results on plant biomass production also showed that treatment manipulations of co‐occurring global change factors can be overridden by the local climatic situation in a given study year.

Earthworm populations as affected by crop practices on clay loam soil in a Mediterranean climate

Earthworms influence soil fertility, and their population is known to be influenced by fertilization. The objective of this study is to characterize the abundance of earthworms under three different kinds of rotation-crops (Rotation: cereals–legumes for green manure-cotton), three tillage systems (Conventional Tillage CT, Minimum Tillage MT, & No-Tillage NT) and fertilization (NP: inorganic and FYM: farmyard manure-organic). Significantly higher populations of earthworms were found under the legumes and NT system in contrast to the lowest abundance determined under the cotton and CT system. Earthworm populations benefited more from organic fertilization than from NP. Our study showed that the most important factors for earthworm abundance are the macropores and Corg under Mediterranean conditions. No-till management considerably influenced the improvement of the physical and chemical soil properties and increased the earthworm abundance.

Accumulated Metal Speciation in Earthworm Populations with Multigenerational Exposure to Metalliferous Soils: Cell Fractionation and High-Energy Synchrotron Analyses

Predicting metal bioaccumulation and toxicity in soil organisms is complicated by site-specific biotic and abiotic parameters. In this study we exploited tissue fractionation and digestion techniques, combined with X-ray absorption spectroscopy (XAS), to investigate the whole-body and subcellular distributions, ligand affinities, and coordination chemistry of accumulated Pb and Zn in field populations of the epigeic earthworm Lumbricus rubellus inhabiting three contrasting metalliferous and two unpolluted soils. Our main findings were (i) earthworms were resident in soils with concentrations of Pb and Zn ranging from 1200 to 27,000 mg kg(-1) and 200 to 34,000 mg kg(-1), respectively; (ii) Pb and Zn primarily accumulated in the posterior alimentary canal in nonsoluble subcellular fractions of earthworms; (iii) site-specific differences in the tissue and subcellular partitioning profiles of populations were observed, with earthworms from a calcareous site partitioning proportionally more Pb to their anterior body segments and Zn to the chloragosome-rich subcellular fraction than their acidic-soil inhabiting counterparts; (iv) XAS indicated that the interpopulation differences in metal partitioning between organs were not accompanied by qualitative differences in ligand-binding speciation, because crystalline phosphate-containing pyromorphite was a predominant chemical species in the whole-worm tissues of all mine soil residents. Differences in metal (Pb, Zn) partitioning at both organ and cellular levels displayed by field populations with protracted histories of metal exposures may reflect theirinnate ecophysiological responses to essential edaphic variables, such as Ca2+ status. These observations are highly significant in the challenging exercise of interpreting holistic biomarker data delivered by "omic" technologies.

Biomarkers for the assessment of chlorpyrifos effects on earthworms and on soil functional parameters

The objective of this work was to evaluate the effects of chlorpyrifos on earthworms and on soil functional parameters. An integrated laboratory-field study was performed in a wheat field in Argentina, sprayed with chlorpyrifos at two recommended application rates (240 or 960 g ha-1 style='vertical-align:baseline'> a.i.). Laboratory tests included neutral red retention time, comet assay (single cell gel electrophoresis), and avoidance behavior, each using the earthworm Eisenia andrei exposed in soil collected 1 or 14 days after pesticide application, and the bait-lamina test. Field tests assessed organic matter breakdown using the litterbag and bait-lamina assays. Earthworm populations in the field were assessed using formalin application and hand-sorting. The neutral red retention time and comet assays were sensitive biomarkers to the effects of chlorpyrifos on the earthworm E. andrei; however, the earthworm avoidance test was not sufficiently robust to assess these effects. Feeding activity of soil biota, assessed by the bait lamina test, was significantly inhibited by chlorpyrifos after 97 days, but recovered by the 118th day of the test. Litterbag test showed no significant differences in comparison to controls. Earthworm abundance in the field was too low to adequately test the sensitivity of this assessment endpoint.

Long-term effects of lime on earthworm abundance and biomass in an acidic soil on the south-western slopes of New South Wales, Australia

Earthworm populations were monitored annually over 10 years in an acidic soil on the south-western slopes of New South Wales, Australia. The Typic Fragiochrept soil at the experimental site has a strong texture-contrast profile with a soil pH of 4.0–4.2 in 0.01 M CaCl 2 in the 0–20 cm horizon. We found that the site was dominated by two native species, the megascolecids Spenceriella macleayi and Spenceriella montana, and accompanied by three exotic species, the lumbricid Aporrectodea trapezoides, and the acanthodrilids Microscolex dubius and Microscolex phosphoreus. Total earthworm abundance varied from 61 to 188 m −2. Lime, applied as a treatment, favoured all exotic earthworm species; their abundance was 3 times greater in limed soil than in unlimed soil. This strongly indicated that severe soil acidity was the most likely factor limiting, directly and indirectly, these species at this site. In contrast, the responses of the two native species to lime varied from negative ( S. montana) to non-responsive ( S. macleayi), suggesting that these native species are well adapted to acidic soil conditions, and perhaps to the dry seasonal conditions experienced during 5 of the 10 years the site was sampled.

An updated earthworm list for the British Isles and two new ‘exotic’ species to Britain from Kew Gardens

Exotic earthworms have previously been recorded in the UK. Many of those records are from the Royal Botanical Gardens, Kew. Earthworms were collected from Kew on two separate occasions in 2007 (March and August). In total 6 species were found, of which two are new species records for the British Isles. When updating the British earthworm species list it became apparent that many species are not inhabitants of UK soils but are transitory visitors in greenhouses. Their status in soils is currently unknown. A new system of recording earthworm species in the British Isles is proposed and consists of two parts. Part 1 lists those species found living freely in soils, part 2 lists those species whose status is unknown, many of which are likely to be imported visitors found in greenhouses. The need for systematic sampling of earthworms throughout the UK is highlighted and the possible effects of climatic change on earthworm populations are commented on.

A six year study of earthworm (Lumbricidae) populations in pasture woodland in southern England shows their responses to soil temperature and soil moisture

There are very few studies on the effects of temporal changes in soil properties on ecosystem engineers in UK soils. This study addresses this lack by presenting earthworm diversity data from a six-year seasonality study comprising 72 monthly samples from the litter and soil of pasture woodland in the New Forest, southern England. These data were analysed in the context of soil moisture and soil temperature, key factors affecting earthworm abundance, and factors likely to be strongly affected by future climate change. The data for the whole period were analysed using non-parametric regression and an additive model used to separate within-year and between-year effects. Seasonal patterns are present for all the common species, generally with a maximum in March and a minimum in September. A majority of the five commonest species show a strong decline in abundance during the two extremely dry periods (2002–2003 and 2006). In sharp contrast, the same species showed a relative increase during the very wet summer and autumn of 2007. There was, however, no significant overall trend in either the climate data or the earthworm species data. The epigeic species, Dendrobaena octaedra, showed the largest decline in the driest months which caused a crash to the point where there were no adults sampled during the four dry summer months of 2003. A second congeneric species, Dendrobaena attemsi, also epigeic, appears to have invaded the woodland during the six year period and is increasing rapidly in abundance. This may indicate the start of a shift in the distribution of the two species, as D. octaedra generally has a northern European distribution and is frost-tolerant, while D. attemsi has a southern European distribution and is more drought-tolerant. In contrast, the very wet summer of 2007 seems to have damped the usual periodic seasonal oscillations in earthworm numbers. Endogeic worm species do not show the D. octaedra seasonal pattern as obviously, probably because these species are able to move more freely through the soil and because they are able to aestivate. These changes are likely to be due to a combination of human movement of earthworms (e.g. D. attemsi) and variations in local climate.

Earthworm populations and growth rates related to long-term crop residue and tillage management

Conventional tillage creates soil physical conditions that may restrict earthworm movement and accelerate crop residue decomposition, thus reducing the food supply for earthworms. These negative impacts may be alleviated by retaining crop residues in agroecosystems. The objective of this study was to determine the effects of various tillage and crop residue management practices on earthworm populations in the field and earthworm growth under controlled conditions. Population assessments were conducted at two long-term (15+ years) experimental sites in Québec, Canada with three tillage systems: moldboard plow/disk harrow (CT), chisel plow or disk harrow (RT) and no tillage (NT), as well as two levels of crop residue inputs (high and low). Earthworm growth was assessed in intact soil cores from both sites. In the field, earthworm populations and biomass were greater with long-term NT than CT and RT practices, but not affected by crop residue management. Laboratory growth rates of Aporrectodea turgida (Eisen) in intact soil cores were affected by tillage and residue inputs, and were positively correlated with the soil organic C pool, suggesting that tillage and residue management practices that increase the soil organic C pool provide more organic substrates for earthworm growth. The highest earthworm growth rates were in soils from RT plots with high residue input, which differed from the response of earthworm populations to tillage and residue management treatments in the field. Our results suggest that tillage-induced disturbance probably has a greater impact than food availability on earthworm populations in cool, humid agroecosystems.

Soil compaction by uniaxial loading and the survival of the earthworm Aporrectodea caliginosa

Earthworms are the major component of the soil fauna in temperate agro-ecosystems. Land use and soil management are widely reported to influence earthworm populations. We report simple laboratory experiments in which earthworm survival was tested against uniaxial loads for a range of soil conditions. Across all the experimental conditions 86% of earthworms survived. While greater loads (up to 800 kPa) over longer exposure times (up to 60 s) decreased survival; even under the most severe test conditions 33% of earthworms survived. Our results suggest that decreased earthworm populations in compacted soil are not due to uniaxial loading alone, but may be the result of shearing the soil during loading or from changes to the soil properties.

Decomposition and mineralization of energy crop residues governed by earthworms

Energy crops are increasingly cultivated in agricultural management systems world-wide. A substitution of food crops (e.g. cereals) by energy crops may generally alter the biological activity and litter decomposition in soil due to their varying structural and chemical composition and subsequently modify soil functioning. A soil microcosm experiment was performed to assess the decomposition and microbial mineralization of different energy crop residues in soil compared to a food crop, with or without earthworms. Residues of the energy crops winter rape ( Brassica napus), maize ( Zea mays), miscanthus ( Miscanthus giganteus) and the food crop oat ( Avena sativa) were each provided as food source for a mixed earthworm population, each consisting of one individual of Lumbricus terrestris, Aporrectodea caliginosa, and Octolasion tyrtaeum. After 6 weeks, the rate of litter loss from the soil surface, earthworm biomass, microbial biomass-C and -N, microbial activity, and enzyme activities were determined. The results emphasized, that litter loss and microbial parameters were predominantly promoted by earthworms and were additionally influenced by the varying structural and chemical composition of the different litter. Litter decay by earthworms was highest in N-rich maize litter treatment (C–N ratio 34.8) and lowest in the case of miscanthus litter (C–N ratio 134.4). As a consequence, the microbial biomass and basal respiration in soils with maize litter were higher, relative to other litter types. MBC–MBN ratio in soil increased when earthworms were present, indicating N competition between earthworms and microorganisms. Furthermore, enzyme activities responded in different ways on the varying types of litter and earthworm activity. Enzymes involved in the N-cycle decreased and those involved in the C-cycle tended to increase in the presence of earthworms, when litter with high C–N ratio was provided as a food source. Especially in the miscanthus treatments, less N might remain for enzymatic degradation, indicating that N competition between earthworms and microorganisms may vary between different litter types. Especially, an expansion of miscanthus in agricultural management systems might result in a reduced microbial activity and a higher N deficit for microorganisms in soil.

Suppression of Verticillium Wilt of Eggplant by Earthworms.

The role of earthworms in plant disease has received little attention. To address whether earthworms would affect the severity of Verticillium wilt of eggplant (Solanum melongena) in the field, we grew eggplants in experimental field plots that were naturally infested with Verticillium dahliae in 2005, 2006, and 2007. Three earthworm treatments were compared: (i) no treatment (untreated control), (ii) earthworm populations reduced via chemical eradicants (carbaryl or hot mustard) (reduced treatment), and (iii) earthworm populations increased by addition of adult Canadian nightcrawlers (Lumbricus terrestris, 11 earthworms per m2) (augmented treatment). Compared to the untreated control, the estimates of the area under the disease progress curve (AUDPC) were reduced while estimates of the canopy growth curve (CGC) and the final plant weights were increased in plots augmented with earthworms in all 3 years. In 2 out of 3 years, eggplant yield (weight and number of fruit) was increased in plots augmented with earthworms. When a carbaryl drench was used to reduce earthworm numbers, the treatment resulted in plants with more disease than in the untreated controls in 2005. However, in 2005 and 2006, carbaryl-treated plants had larger CGC values and higher yield than in the untreated controls and were not significantly different from the augmented plots. When a hot mustard extraction procedure was used to reduce earthworm densities in 2007, plant growth, yield, and disease variables did not differ from the untreated control. Although the effects of reducing earthworms were variable and difficult to explain, our findings suggest that augmenting earthworm populations can suppress Verticillium wilt of eggplant, and strategies that increase earthworm numbers may contribute to disease suppression.

High genetic diversity and heterogeneous parasite load in the earthworm Lumbricus terrestris on a German meadow

In parasite–host dynamics, parasites exert frequency-dependent selection on their hosts by favouring rare alleles that may confer resistance against infection. Therefore host populations that suffer strong parasite stress should maintain higher levels of genetic variability. We studied the Lumbricus terrestris– Monocystis sp. host–parasite system at a microgeographical scale. Using three polymorphic microsatellite loci on one large earthworm population sampled at 26 different sites (281 genotypes), we tested the relationship between parasite load and genetic variation in natural samples of the common earthworm L. terrestris. Our analysis yielded the following: (1) parasite load varied significantly across sites in this population; (2) there was no consistent evidence for heterozygote deficiency (observed heterozygosities ranged between 0.74 and 0.87), indicating a low level of inbreeding; (3) there was no significant genetic structuring among sample sites; (4) we could not identify a significant association between parasite load and population genetic diversity; (5) there was considerable population differentiation (15.17%) between our German samples and a Canadian L. terrestris reference population. Our study provides insight into the population genetics of one of the most economically important soil organisms on a microgeographic scale.

Crop Residue Removal Impacts on Soil Productivity and Environmental Quality

Crop residues are a potential source of renewable feedstocks for cellulosic ethanol production because of their high cellulose content and easy availability. Indiscriminate removal as biofuel may, however, have adverse impacts on soil, environment, and crop production. This article reviews available information on the impacts of crop residue removal on soil properties, crop yields, and soil erosion across a wide range of soils and ecosystems. It explicitly synthesizes data on the independent impacts of crop residue removal on soil and environment rather than on the interrelated tillage-crop-residue management impacts. Published literature shows that residue removal adversely impacts near-surface soil physical, chemical, and biological properties. Unmulched soils are prone to particle detachment, surface sealing, crusting, and compaction. Residue removal reduces input of organic binding agents essential to formation and stability of aggregates. It also closes open-ended biochannels by raindrop impacts and reduces water infiltration, saturated/unsaturated hydraulic conductivity, and air permeability, and thereby increases runoff/soil erosion and transport of non-point source pollutants (e.g., sediment and chemicals). Residue removal accelerates evaporation, increases diurnal fluctuations in soil temperature, and reduces input of organic matter needed to improve the soils' ability to retain water. It reduces macro- (e.g., K, P, N, Ca, and Mg) and micronutrient (e.g., Fe, Mn, B, Zn, and S) pools in the soil by removing nutrient-rich residue materials and by inducing losses of soil organic matter (SOM)-enriched sediments in runoff. Residue removal drastically reduces earthworm population and microbial carbon (C) and nitrogen (N) biomass. It adversely affects agronomic production by altering the dynamics of soil water and temperature regimes. The short-term ( < 10 yr) data show nevertheless that residue removal may not always degrade soil physical properties and decrease crop yields in the short term depending on the soil type, topography, and fluctuations in annual weather conditions. Sloping and erosion-prone soils are more rapidly and adversely affected by residue removal than those on flat terrains with heavy texture and poorly drained conditions. Sloping terrains are not only highly susceptible to water and wind erosion but also to tillage erosion. In these soils, therefore, a fraction of the total crop residue produced may be available for biofuel production and other expanded uses. Standard guidelines on when, where, and how much residues to remove need to be, however, established. Modeling rates of residue removal are presently based on the needs of soil cover to control erosion without consideration to maintaining SOM and nutrient pools, enhancing soil physical, chemical, and biological quality, and sustaining crop production. Threshold levels of residue removal must be assessed for principal soil types based on the needs to maintain or enhance soil productivity and improve environmental quality. For those soils in which some residues are removed, best management practices (e.g., cover crops, diverse crop rotations, and manure application) must be adopted to minimize adverse impacts of residue removal. Because indiscriminate harvesting of crop residues for biofuel may deteriorate soil properties, reduce crop yields, and degrade the environment, there exists an urgent research need for developing alternative sustainable renewable energy feedstocks (e.g., warm season grasses and short-rotation woody crops).

Earthworm populations under different tillage systems in organic farming

To understand how earthworms could improve soil porosity in no-tillage organic farming systems, the aim of our study was to compare the effect of different tillage systems on earthworm populations, from conventional (traditional mouldboard ploughing, MP and shallow mouldboard ploughing, SMP) to conservation tillage (reduced tillage, RT, direct drilling or very superficial tillage, NT) in three organic arable systems in France (sites A–C). In a second stage, the effect of earthworm activity on soil porosity under the four tillage systems was assessed at sites A and B. Earthworm abundance, biomass and diversity were measured over a 2–3-year period at the 3 sites. During the same period, soil structure (soil profile description and soil bulk density) and open worm burrows in the soil were assessed at sites A and B. After 3 years of experiments, it was found that at 2 sites earthworm abundance and biomass were higher in NT than with ploughing or reduced tillage. The increase of earthworms in NT is mainly due to anecic species increase. Earthworm abundance and biomass tend to decrease regardless of the tillage techniques employed at sites with a ley, and conversely, tend to increase in NT and RT at sites initially ploughed. In the short term, the increase of anecic species in NT has no effect on soil porosity evolution: NT soils were more compacted than those which were ploughed. A long-term experiment is required to assess the effect of biological activity on the physical components of soil in organic farming.

Impact of five different tillage systems on soil organic carbon content and the density, biomass, and community composition of earthworms after a ten year period

To assess the impact of different types of soil tillage on the density, biomass, and community composition of earthworms, a long-term field study was performed in which soils were tilled in different ways for ten years. This study included five different types of tillage: (i) plough, (ii) grubber, (iii) disc harrow, (iv) mulch sowing, and (v) direct sowing. At the end of the experiment the earthworm density, biomass, and community composition, and the SOC (soil organic carbon) content were determined. The results show that density, biomass, and community composition of earthworm populations varied in relation to the type of soil tillage used. The density of anecic earthworm species decreased when soils were managed by conventional ploughing, relative to reduced tillage practices, whereas conversely the density of endogeic species increased. Additionally, the varying types of soil tillage influenced the abundance and biomass of different earthworm species in different ways. The density of Aporrectodea caliginosa was positively influenced by ploughing, whereas Aporrectodea longa, Lumbricus castaneus, and Satchellius mammalis showed a positive relationship to the grubber and Allolobophora chlorotica to direct sowing. We attribute these changes to modifications in the vertical distribution of SOC and varying potentials for mechanical damage of earthworms by tillage. A decrease in tillage intensity modified the vertical SOC distribution in the topsoil and consequently revealed positive effects on earthworm biodiversity, thus sustaining soil functioning.