Inorganic and organic phosphorus pools in earthworm casts (Glossoscolecidae) and a Brazilian rainforest Oxisol

We compared differences in soil phosphorus fractions between large earthworm casts (Family Glossoscolecidae) and surrounding soils, i.e., Oxisols in 10 year-old upland agroforestry system (AGR), pasture (PAS), and secondary forest (SEC) in the Central Brazilian Amazon. AGR and PAS both received low-input fertilization and SEC received no fertilization. We found that earthworm casts had higher levels of organic hydroxide P than surrounding soils, whereas fertilization increased inorganic hydroxide P. Inorganic P was increased by fertilization, and organic P was increased by earthworm gut passage and/or selection of ingested materials, which increased available P (sum of resin and bicarbonate fractions) and moderately available P (sum of hydroxide and dilute acid fractions), and P fertilizer application and land-use increased available P. The use of a modified sequential P fractionation produced fewer differences between earthworm casts and soils than were expected. We suggest the use of a condensed extraction procedure with three fractions (Available P, Moderately Available P, and Resistant P) that provide an ecologically based understanding of the P availability in soil. Earthworm casts were estimated to constitute 41.0, 38.2, and 26.0 kg ha⁻¹ of total available P stocks (sum of resin and bicarbonate fractions) in the agroforestry system, pasture, and secondary forest, respectively.     

Degradation dynamics of surface earthworm casts in grasslands of the eastern plains of Colombia

 Earthworms are generally considered to fit the definition of ecosystem engineers. The casts they produce are recognised to have a great importance in the regulation of soil processes. Lifetimes and degradation rates of these structures remain poorly known. In this study, the dynamics of disappearance and the changes in the physical properties of the surface casts of the anecic earthworm Martiodrilus carimaguensis were assessed in a native savanna and an intensive pasture. In both systems, casts were composed of superposed layers deposited by earthworms over a period of at least a few days. The half-life of casts ranged between 2 months and 11 months in the pastures (trampled and protected, respectively), and 5 months in the savanna. Some dry casts remained at the soil surface for more than 1 year after having been excreted. The disappearance of casts was mostly attributed to rain-drop impact and the effect of animal trampling. The bulk density of fresh casts was higher (+17%, P<0.05) or equivalent (–1%, P>0.05) to that of the surrounding soil, in the savanna and the pasture, respectively. Fresh cast aggregates were of larger size than bulk soil aggregates (about +70% in both systems, P<0.05). Bulk density and the size of cast aggregates decreased with cast ageing (from –29% to –24% for bulk density, and from –68% to –80% for size, in the pasture and the savanna, respectively). Macroinvertebrates were observed digging into casts, and were assumed to be partly responsible for the physical degradation of casts with time. Received: 12 November 1999     

What happens to earthworm casts in the soil? A field study of carbon and nitrogen dynamics in Neotropical savannahs

In the Oxisols of the eastern plains of Colombia, the large native anecic earthworm Martiodrilus sp. is an abundant ecosystem engineer producing long-lasting casts and burrows. Casts deposited in the soil by this species have been estimated at several tonnes per hectare per year. The physical and chemical processes occurring in these casts have never been studied. In this study, we compared the dynamics of water content (WC), total C (C_tot), and available N (N_avail) contents, and the distribution in size of aggregates in ageing below-ground casts of this species and in the bulk soil. In a native herbaceous savannah and a sown grass/legume pasture (Brachiaria humidicola, Arachis pintoi, Desmodium ovalifolium and Stylosanthes capitata), fresh surface casts were experimentally injected into artificial burrows of 1 cm Ø and 10 cm depth and sampled at different dates during a total period of 120 days. The injection procedure used resulted in a 34% decrease in WC of the casts from the sown pasture and reduced the mean mass diameter (MMD) of the aggregates of casts from the savannah by 19%. Other properties were not significantly affected by the procedure.For injected casts in both grasslands, MMD and C_tot were stable during cast ageing while WC and N_avail were initially at levels several times higher than the bulk soil and decreased to similar bulk soil values with ageing. The C_tot was twice and one third higher in casts compared with the bulk soil in the pasture and the savannah, respectively. Overall means for cast MMD (8.3 and 7.4 mm) were twice as high as those in the bulk soil (3.8 mm) in the savannah and the pasture, respectively. However, MMD was not significantly different between the casts and the bulk soil in two occasions in the pasture. Available nitrogen (N_avail) in injected casts was initially greater than bulk soil levels, reaching maximum levels just after injection (116 and 93 mg kg⁻¹) and remained significantly greater during 1-2 weeks, in the savannah and the pasture, respectively. In conclusion, the tonnes of casts deposited in the soil profile by Martiodrilus sp. each year are likely to contribute greatly to plant nutrition and to the regulation of the soil structure. For each anecic earthworm species, the ecological impact of its below-ground casts is likely to be as important as its surface casts.     

Assessing the organic phosphorus status of an Oxisol under tropical pastures following native savanna using 31P NMR spectroscopy

³¹P nuclear magnetic resonance (NMR) spectroscopy, P fractionation, and a P sorption experiment were used to follow the changes in P in the A horizons (0–10 cm) of acid savanna soils, Colombia, after little P fertilization and 15 years' continuous growth of a grass (Brachiaria decumbens) and a grass/legume (B. decumbens+Pueraria phaseoloides) pasture. Ready P supply as analyzed by Bray P was low under native savanna (1.3 mg kg^-1 soil) and responded moderately on pasture establishment. Concurrently, the affinity of the soil for inorganic P declined slightly after pasture establishment. ³¹P NMR spectroscopy revealed that P associated with humic acids was dominated by monoester P followed by diester P. Smaller proportions were observed for phosphonates, teichoic acid P, orthophosphate, and pyrophosphate. P associated with fulvic acids had lower proportions of diester P and higher contents of orthophosphate. Under native savanna the reserves of labile organic P species (phosphonates and diester P including teichoic acid P) associated with humic and fulvic acids were 12.4 and 1.1 kg ha^-1, respectively, and increased to 18.1 and 1.8 kg ha^-1 under grass pasture, and to 19.5 and 2.3 kg ha^-1 under grass/legume pasture. These data emphasize the importance of labile organic P species in the P supply for plants in improved tropical pastures, and further indicate that humic acid P in particular responds to land-use changes within a relatively short time-scale. Earthworm casts were highly abundant in the B. decumbens+P. phaseoloides plot and were enriched in labile organic P species. We conclude that earthworm activity improves the P supply in soil under tropical pastures by creating an easily available organic P pool.Dedicated to Professor J.C.G. Ottow on the occasion of his 60th birthday     

Characteristics of earthworm casts affecting herbicide sorption and movement

Various physical and chemical characteristics of earthworm casts collected from a laboratory incubation and a field experiment were examined in relation to their effect on the sorption and the movement of three ¹⁴C-labelled ionic herbicides: atrazine, 2,4-dichlorophenoxyacetic acid, and metsulforon methyl. The earthworm casts contained higher levels of fine fractions and total and soluble C. This is attributed to the grinding action of the earthworm gut and selective feeding on zones with higher organic matter and fine size fractions. The earthworm casts had a higher pH than the source soil, resulting in a higher number of surface negative charges. The earthworm casts sorbed higher amounts of herbicides than the source soil, mainly due to the increases in the amount of organic C and fine size fractions. The incrased sorption of herbicides by the casts resulted in decreased leaching.     

Spatial dissociation between two endogeic earthworms in the Colombian “Llanos”

Although there has been a growing interest in the study of soil fauna spatial distribution during the past decade, the identification of the environmental driving factors behind the population patterning are difficult to highlight. Soil physico-chemical heterogeneity is partly responsible for structuring the population. However, the available statistical analyses show that the proportion of the population spatial variance that can be ascribed to soil habitat variability is modest. We studied the spatial distribution of two medium-sized endogeic earthworm species (Andiodrilus sp. and Glossodrilus sp.) and the spatial segregation between them. The survey was undertaken in a native savanna and a grass-legume pasture in the Colombian “Llanos”. The presence of spatial dependence in the data (i.e. earthworm counts) was tested using two different approaches: the Spatial Analysis using Distance IndicEs (SADIE) analyses and cross-coregionalization. The SADIE index allowed for testing the spatial association or dissociation between earthworm counts. The spatial organization of both species was well structured in the natural savanna while they were randomly distributed in the pasture in almost all sampling dates. When the spatial distribution was different from randomness it was always aggregated irrespective of the land-use system. There was no absolute stable spatial pattern in the natural savanna although a general pattern seemed to emerge. On the contrary, no pattern was observed in the pasture. Both species displayed opposite spatial distributions (P < 0.05) that were of different intensity depending on the sampling date. The presence of opposite patches and gaps suggests the presence of a competitive exclusion phenomenon (at least spatial) that deserves further investigations.     

Surface activity of soil ecosystem engineers and soil structure in contrasted land use systems of Colombia

This study describes the impact of the conversion of native Colombian savannahs into crops and pastures on: (1) the quantity and diversity of the bio-structures produced by soil ecosystem engineers and (2) soil structure. Bio-structure diversity decreased in all agroecosystems (12 types in the savannah, four to six in pastures and three in crops). Bio-structures were mostly earthworm casts in native savannah and pastures, and ant mounds in crops. Compared with the savannah (750 cm³ m^–2), their volume increased in the old pasture (+48%) and decreased in recent pasture and crops (–65% to –97%). Soil structure was similar to savannah soil in the older pasture, but was sharply affected in annual crops. In contrast to crops, pastures appear to sustain soil structure and are also suitable for engineering activity.     

Changes in nutrient pools,microbial biomass and microbial activity in soils after transit through the gut of three endogeic earthworm species of the genus Postandrilus Qui and Bouché, 1998

Purpose

Endogeic earthworms play a significant role in biogeochemical cycles due to the large amount of soil they ingest, and because after transit through their guts, casts usually show differences in nutrient contents and microbial populations with bulk soil. Here, we studied how three endogeic earthworm species, Postandrilus majorcanus, Postandrilus sapkarevi and Postandrilus palmensis, inhabiting soils in Majorca island (Balearic Islands, W Mediterranean), modify nutrient pools and microbial communities of soil.

Materials and methods

To do this, we analysed C, N and P pools, microbial biomass (phospholipid fatty acids, PLFA) and microbial activity (fluorescein diacetate hydrolysis, FDA) in paired samples of bulk soil and fresh casts.

Results and discussion

The mineral and organic N contents were generally enhanced in casts produced by all three earthworm species. However, inorganic P and organic C contents were only higher in P. sapkarevi (32 %, only P) and P. majorcanus casts (100 % for both soil nutrient pools) than in bulk soil. Bacterial and fungal biomass were only higher than in bulk soil in P. majorcanus casts (65 and 100 %, respectively), but without effects on microbial activity, that was lower in P. palmensis casts (26 %). Earthworm gut transit strongly influenced the soil microbial community structure, resulting in differences between casts and soils.

Conclusions

The increased nutrient mineralization (6-, 1.3- and 1.4-fold for N, C and P, respectively) in casts produced by these earthworm species is of particular importance because of the amount of casts released and the seasonal variations in earthworm activity, which may favour plant growth.     

Effect of biosolid amendment on enzyme activities in earthworm (Lumbricus terrestris) casts

We studied the effect of amendment of sewage sludge biosolids on enzyme activity in soil and earthworm (Lumbricus terrestris) casts. Enzyme activities and contents of nutrients and organic matter of surrounding soil were compared with the corresponding properties of earthworm casts. This short time experiment was conducted at 20 ± 0.5 °C in the laboratory, simulating field conditions of biosolid treatments. In general, all of doses of biosolid treatments influenced the enzyme activity and contents of nutrients and organic matter of earthworm casts and surrounding soil. Enzyme activity such as urease (UA), alkaline phosphatase (APA), and arylsulfatase (ASA) and the contents of organic matter and nutrients N and P in earthworm casts and surrounding soil increased with increasing biosolid application. Without biosolid additions, enzyme activities in cast of L. terrestris exceeded those in the soil. In contrast, when biosolid was added, DHA in casts was lower than the soil. Activities of UA and APA were consistently higher in L. terrestris casts than in soil of all biosolid treatments. Biosolid amendments generally increased ASA at low doses, but at higher doses, ASA decreased. In general, organic matter and contents of N and P were higher in surface casts of L. terrestris and soils than in the control soil. Activities of UA, APA, the contents of organic carbon and nutrients N and P in soil and casts showed positive correlations. On the contrary, ASA and DHA were negatively correlated with the contents of organic matter and nutrients.     

Carbon and nitrogen dynamics in ageing earthworm casts in grasslands of the eastern plains of Colombia

 The effects of a large species of anecic earthworm, Martiodrilus carimaguensis Jiménez and Moreno, on soil C and N dynamics were investigated in a native savanna and a man-made pasture of the eastern plains of Colombia. We compared, across time (11 months), the total C, total N, NH⁺ ₄ and NO^– ₃ contents in the earthworm casts, the underlying soil and the adjacent soil. Additional sampling of root biomass and macrofauna was performed. In the two management systems, the total C and N contents were higher in casts (4.33–7.50%) than in the bulk soil (2.81–4.08%), showing that the earthworms selected food substrates with high organic contents. In general, C contents significantly increased during cast ageing (+100%), possibly because of CO₂ fixation processes, dead root accumulation and/or macrofaunal activities in casts. In fresh casts, NH⁺ ₄ levels were very high (294.20–233.98 μg g^–1 dry cast) when compared to the soil (26.96–73.95 μg g^–1 dry soil), due to the intense mineralisation processes that occurred during the transit of soil and organic matter through the earthworm gut. During the first week of cast ageing, NH⁺ ₄ levels sharply decreased, while NH^– ₃ levels showed successive peaks in the casts, the underlying soil and the adjacent soil. These results suggested the rapid production of NO^– ₃ by nitrification processes in the fresh casts, followed by diffusion to the nearby soil, first vertically, then horizontally. After 2 weeks of cast ageing, NH⁺ ₄ and NO^– ₃ levels only showed slight variations, likely because of organic matter protection in stable dry casts. The root biomass was higher (1.6–4.7 times) below the old earthworm casts. The ecological significance of these results is discussed. Received: 22 October 1998     

Comparative study of earthworm communities,microbial biomass,and plant nutrient availability under 1-year <Emphasis Type="Italic">Cajanus cajan</Emphasis> (L.) Millsp and <Emphasis Type="Italic">Lablab purpureus</Emphasis> (L.) Sweet cultivations versus natural regrowths in a guinea savanna zone

In tropical savannas where soils are generally sandy and nutrient poor, organic farming associated with enhanced soil biological activity may result in increased nutrient availability. Therefore, legumes have been introduced in the humid savanna zone of Côte d’Ivoire, owing to their ability to fix atmospheric N and to continually supply soil with great quantity of organic materials in relatively short time. The main objective of this study was to assess the influence of two legume (Cajanus cajan and Lablab purpureus) cultivations on earthworm communities and P and N availability. Trials were carried out under farmers' field conditions; C. cajan was planted on savanna soils (trial 1) while L. purpureus was established on new Chromolaena odorata-dominated fallow soils (trial 2). Native vegetations were considered as controls. Changes in soil properties (earthworm abundance and diversity, microbial biomass carbon (MBC), and plant available P and N) were assessed using the biosequential sampling. After 1 year, both the legume stands showed a significantly higher density of earthworms, compared with the respective controls. This trend was linked to an increase in the abundance of the detritivores Dichogaster baeri Sciacchitano 1952 and Dichogaster saliens Beddard 1893, and the polyhumic Stuhlmannia zielae Omodeo 1963. Equally, legume had beneficial impacts on the average number of earthworm species, the Shannon–Weaver index of diversity and MBC in savanna (trial 1). Available P and ammonium significantly increased under both legume cultivations and were significantly and concurrently linked to litter quality and earthworm activities as shown by multiple regressions. As a result, legumes could improve nutrient availability in the sandy soils of central Côte d’Ivoire by positively affecting soil biological activity and this could bring farmers to cultivate crops on savanna lands.     

Short- and long-term effects of the endogeic earthworm Millsonia anomala (Omodeo) (Megascolecidæ, Oligochæta) of tropical savannas,on soil organic matter

Summary This study aimed to establish the effects of Millsonia anomala, a tropical geophagous earthworm common in the humid savannas of Lamto (Ivory Coast), on soil organic matter dynamics over different time scales under laboratory conditions. The texture of casts produced by the worms fed on a shrub savanna soil was not significantly different from that of the soil, which showed that M. anomala ingested soil particles without selection. Physical fractionation of soil organic matter showed that the coarse organic fraction (250–2000 m) was depleted by 25–30% in fresh casts compared to the control noningested soil; this was mainly due to a fragmentation of coarse organic debris. Incubation of casts and a 2-mm sieved control soil under laboratory conditions for more than 1 year showed that the C mineralisation rate was almost four times lower in the casts (3% year^-1) than in the control soil (11% year^-1). We therefore concluded that on a long time scale M. anomala populations may significantly reduce the decomposition rate of soil organic matter in Lamto savannas.     

Phospholipid fatty acid profiles and xylanase activity in particle size fractions of forest soil and casts of Lumbricus terrestris L. (Oligochaeta,Lumbricidae)

Earthworms are key agents in organic matter decomposition, as they remove surface plant litter material and mix it with mineral soil. Plant litter material is comminuted in the gizzard of anecic earthworms and this is enhanced if sand particles are available. We hypothesize that this comminution of soil and litter will result in changes in the distribution of soil organic matter and soil microorganisms in the different particle-size fractions. We investigated soil organic matter content, xylanase- and microbial activity and community structure in bulk soil and particle size fractions of Lumbricus terrestris L. casts and in soil with and without the addition of beech litter.Earthworm gut passage did not affect the particle-size distribution but the content of soil organic matter was decreased in the fine sand fraction in treatments without litter (−6.80%) and increased in treatments with litter (+33.23%). The soil organic matter content of the clay fraction tended to be higher in earthworm casts. Xylanase activity was at a maximum in the fine sand fraction, lower in the coarse sand fraction and at a similar minimum in the silt- and clay-sized fraction. In the coarse sand fraction of the cast and litter treatments xylanase activity was increased by 39.1% and 124.8%, respectively. In the silt-sized fraction of casts the addition of litter increased xylanase activity (+58.6%) whereas, in casts without litter it was decreased (−36.25%). In the particle size fractions of casts, the content of bacterial PLFAs was decreased in the fine sand fraction and tended to be decreased in the clay fraction compared to the respective fractions in soil. In the silt fraction the fungal-to-bacterial PLFA ratio was higher in casts than in soil.We conclude that earthworms stabilize soil organic matter in cast aggregates predominantly by increasing the soil organic matter content in the clay fraction where it becomes protected against microbial attack. Organic matter in the coarse and fine sand fractions is decomposed primarily by fungi; xylanase is very active in these sand fractions and incorporation of litter into these fractions by the earthworms increased fungal biomass. Comminution of litter during passage through the earthworm gut increased the biomass and activity of fungi also in the silt fraction. The use of PLFA profiles in combination with other quantitative microbial methods improves the understanding of stabilizing and mobilizing processes in earthworm casts.     

Disc harrowing intensity and its impact on soil properties and plant growth of agropastoral systems in the Llanos of Colombia

Oxisols such as those of the Colombian Eastern Plains (Llanos) are susceptible to physical, chemical and biological degradation once brought into cultivation, especially under intensive use of machinery. The main objective of this study was to determine the impact of intensive disc harrowing (2, 4 or 8 disc harrow passes per year over 3 years) on soil physical and chemical properties, soil phosphorus dynamics, plant growth and nutrient acquisition of contrasting agropastoral systems on an Oxisol. The three main systems tested after 2 years of upland rice cultivation were grass-alone pasture (Brachiaria dictyoneura), green manure (Crotalaria juncea), and maize (Zea mays). Native savanna treatment was used as a control. Intensive disc harrowing improved macroporosity values of 0–5 cm soil layer up to 59% for grass-alone pasture system compared to native savanna. Disc harrowing significantly reduced bulk densities for pasture and green manure systems compared to the native savanna in the 0–5 cm soil layer. Intensive disc harrowing significantly improved volumetric moisture content of green manure and maize systems at 5–10 cm soil depth. The distribution of biologically, moderately and sparingly available P, organic P and total P varied under green manure, maize and grass-alone pasture systems. Two passes of disc harrow per year were sufficient for grass-alone pasture, while maize showed greater aboveground production and nutrient acquisition at 8 passes of disc harrow per year. The maize and green manure cropping systems were better than the grass-alone pasture system at separating the effect of increased number of disc harrow passes on soil physical and chemical characteristics.     

蚯蚓粪施用量对黄土区典型土壤团聚体及其有机碳分布的影响

为探究蚯蚓粪施用量对黄土区典型土壤团聚体及其结合碳的影响,该研究采用土柱培养试验,研究了黄绵土(CS)、黑垆土(DS)和风沙土(AS)团聚体和有机碳的数量及稳定性对不同蚯蚓粪施用量(0、1%、3%和5%)的响应。结果表明,施用蚯蚓粪后粒径不大于0.25 mm团聚体含量在CS和DS中降低了9.2%～24.7%和7.0%～21.3%;AS中在3%和5%用量条件下减少了25.9%～34.0%。3%用量蚯蚓粪对CS、DS和AS水稳性团聚体数量、平均重量直径、几何平均直径和粒径大于0.25 mm团聚体含量提高有显著作用,但用量增加至5%后效果未进一步改善。施用1%～5%用量蚯蚓粪可使土壤有机碳增加17.9%～66.9%,同时也提高了各级团聚体结合碳含量。施用蚯蚓粪后,不大于0.25mm团聚体对总有机碳贡献率在CS和DS中降低了21.4%～41.1%和15.7%～20.4%,3%和5%用量处理间没有差异。各级团聚体中易氧化碳含量随蚯蚓粪施用量的增加而增大。综合考虑土壤团聚体和有机碳对蚯蚓粪施用量的响应可知,3%用量蚯蚓粪即可有效提升土壤团聚体和有机碳稳定性。研究可为合理利用蚯蚓粪对黄土区土壤结构进行改良提供依据。     

The efficiency of soil hand-sorting in assessing the abundance and biomass of earthworm communities. Its usefulness in population dynamics and cohort analysis studies

Pit digging and manually revising soil blocks is a frequently used method used for field studies of earthworm communities. The aim of this study was to compare the efficiency of hand-sorting (HS) to extract small earthworms, ca. 0.2 g, and the usefulness in studies of population dynamics and cohort analysis. Many earthworms are not recovered when revising manually the soil. Factors include soil characteristics, i.e. moisture, texture, etc. and also a human factor, which is more relevant if the study is conducted in the long-term. We used data collected in a field study of earthworm communities during 2 years in the savannas of Colombia. Small soil blocks (20 × 20 × 20 cm) were dug out in order to collect the smallest earthworms by washing-sieving (WS) and compare the results with the standard HS of large monoliths (100 × 100 × 50 cm). In fact, this methodology has rarely been addressed in earthworm population field studies. Our results showed that HS efficiency varied owing to the species and ranged from 31.4% up to 100% in the savanna and from 44% to 80% in the pasture, for two small species, i.e Aymara n. sp. (epigeic) and Ocnerodrilidae sp. (endogeic). In the case of the Glossodrilus n. sp. (endogeic) these values were similar, i.e. 51.7% and 58.1%, in the savanna and pasture, respectively. We also used frequency tables to calculate the average efficiency of HS 1 m² soil cores for each weight class in each species in order to obtain a population density correction factor. This allowed us to make corrections in earthworm density in the histograms for population dynamics analysis. We conclude that this method should be the modus operandi in long-term earthworm demography studies.     

Microbial activity and nutrient dynamics in earthworm casts (Lumbricidae)

Summary Microbial respiration, microbial biomass and nutrient requirements of the microflora (C, N, P) were studied in the food substrate (soil taken from the upper 3 cm of the mineral soil of a beech wood on limestone), the burrow walls and the casts of the earthworm Aporrectodea caliginosa (Savigny). The passage of the soil through the gut caused an increase in soil microbial respiration of about 90% over a 4-week period. Microbial biomass was increased only in freshly deposited casts and decreased in aging faeces to a level about 10% lower than in soil. Microbial respiration of the burrow walls was only increased over a shorter period (about 2 weeks). The microflora of the soil and the burrow walls was limited by P, whereas in earthworm casts, microbial growth was limited by the amount of available C. In aging faeces the P requirement of the microflora increased and approached that of the soil. Immobilization of phosphate in earthworm casts is probably caused by mainly abiotic processes. C mineralization by soil microflora fertilized with glucose and P was limited by N, except in freshly deposited casts. Ammonium, not nitrate, was responsible for this process. N dynamics in earthworm casts are discussed.     

The interactions between soil type and earthworm species determine the properties of earthworm casts

Earthworms are recognized to increase soil porosity, reorganize soil structure, and stimulate soil microflora and nutrient mineralization. The properties of earthworm casts should depend both on earthworm species or ecological group and on soil properties. Interactions between earthworm species and soil types have been suggested, but only poorly demonstrated. In order to better understand those interactions, two hypotheses led our study: (1) Soil type has a greater influence on cast properties than earthworm; (2) Earthworms from different species influence cast properties differently; (3) The intensity and direction of the impact of each earthworm species on cast properties vary with soil properties. Fifteen physical and chemical variables (N–NH₄⁺, N–NO₃⁻, total organic C and N, C/N ratio, CaCO₃, pH, P, K⁺, Mg²⁺, Mn²⁺, Na⁺, CEC, moisture, wettability) were measured in casts of three earthworm species (Lumbricus terrestris, Allolobophora chlorotica and Aporrectodea rosea) produced in three temperate soils. Univariate and multivariate analyses showed that earthworm species and soil types significantly impacted cast properties. pH, N_t, K and Mg contents were interactively altered by both factors. Multivariate analysis showed that a difference of soil type had a major impact on casts properties (62%) compared to the impact of a difference of earthworm species (10%). Cast properties were most impacted by L. terrestris, then by A. chlorotica and last by A. rosea. The response ratio (ratio of the properties of the casts to the properties of the bulk soil) was used to quantify the effect of earthworm species compared to the control soil. It showed a higher response of variables in casts in nutrient-rich soils, especially in casts of L. terrestris. The interactions between earthworm species and soil types on cast properties were discussed with regards to earthworm ecology, properties of the soil, and earthworm modifications of cast microflora.     

Nutrient content of earthworm casts influenced by different mulch types

The aim of this study was to investigate the effects of different mulch types on the quality and quantity of casts of different lumbricid earthworm species. Nutrient contents (organic carbon C_org, total nitrogen N_t and inorganic phosphate Pi), and acid phosphatase activity (SPA) of earthworm casts and soil aggregates were measured and then compared. This short time experiment was conducted in the laboratory, simulating field conditions of mulch management in temperate agroecosystems. In microcosms, the two common field species Lumbricus terrestris and Octolasion cyaneum were inoculated. Barley, lupin, maize, or sugarbeet were used as mulch according to amounts usually applied in the field. Nutrient contents and phosphatase activity in worm casts were generally enhanced compared to the soil. Nutrient values were higher in the casts of the detritivorous L. terrestris than those of the geophageous O. cyaneum. Conversely, the phosphatase activity was increased in the casts of O. cyaneum compared to L. terrestris in case of the barley and sugar-beet treatments. Cast production was related to the earthworms' change of biomass (ΔB) as well as, in the case of L. terrestris, to nitrogen content of the mulch. Due to their chemical compounds, the mulch types influence both the food selection of the worms and the acceptance by microorganisms.