Assessment of recovery of population, biomass and reproduction of the earthworm Drawida willsi following the application of malathion under field conditions

 The recovery of population, biomass and reproduction of a dominant crop field earthworm (Drawida willsi, Michaelsen) was assessed following the application of two recommended agricultural doses of malathion (2.2 mg kg^–1– single dose and 4.4 mg kg^–1– double dose) in a rice field agroecosystem for a period of 105 days. The average worm population and biomass showed 12% and 21% decline, respectively, in plots treated with single and double doses of malathion, compared with control. The peak of worm population was observed after 60 days in control (plot I) and this peak value was shifted by 15 days (i.e. observed after 75 days) in malathion-treated plots (plots II and III) indicating delay in growth and maturation of the worms following the application of malathion. Inhibition in the total number of cocoons produced, and thus in the rate of reproduction, was also observed in malathion-treated plots. The peak rate of reproduction (1.71 cocoons adult^–1) was observed after 60 days in control plots and after 75 days (1.57 and 1.40 cocoons adult^–1) in single and double dose malathion-treated plots, respectively. One-way analysis of variance showed significant differences in the population size and biomass of D. willsi up to 75 days, in rate of reproduction up to 90 days, and no difference thereafter. This indicates that, under field conditions, D. willsi worms took about 75–90 days after application of malathion to resume normal population, biomass and reproduction, and hence we suggest that a second application of malathion in single and double agricultural doses should be avoided before this time. Received: 7 September 1999     

The influence of feeding patterns on growth and reproduction of the vermicomposting earthworm Eisenia fetida (Oligochaeta)

Summary Observations in outdoor culture beds indicated that food availability and frequency of feeding influenced worm density. In order to study the role of feeding status on the growth and reproduction of Eisenia fetida, pre-clitellate specimens were kept for 180 days under controlled conditions. A control group was regularly provided with freshly produced cattle manure while the experimental groups were fed only sporadically and at some stage even starved by removing some of the substrate. Worm growth, maturation, and cocoon production were monitored. The role of food availability was highlighted by this study. Both worm growth and cocoon production were correlated closely with the feeding pattern that was followed. This study also showed that freshly produced, urine-free, cattle manure proved an excellent food source provided it was added in such a way as to prevent the development of anaerobic conditions. Regular feeding gave high growth and reproduction rates.     

Reproduction of the African earthworm,Eudrilus eugeniae (Oligochaeta) — cocoons

Summary Although various authors have contributed to our knowledge of the biology of Eudrilus eugeniae some basic facts about the life cycle and reproduction are still not fully documented. Quantitative observations were made of the cocoons at 25 °C in different substrates. The incubation period for 166 cocoons was 16.89 days, based on cocoons produced by worms between the ages of 70 and 100 days. These cocoons produced a mean 2.12 hatchlings per cocoon after incubation in cattle manure, moist filter paper and distilled water. A smaller batch of cocoons incubated in cattle manure produced a mean of 2.7 hatchlings per cocoon. The hatching success of the cocoons was 84% in cattle manure, 50% in distilled water, and 48% on moist filter paper. The reproductive capabilities of E. eugeniae and Eisenia fetida were compared.     

Rainfall effects on erosion of earthworm casts and phosphorus transfers by water runoff

 We investigated whether, under a temperate climate and in a maize crop, earthworm casts could contribute to soil erosion and further favour the exportation of phosphorus by runoff waters. Recording of casts was made in compacted (wheel-tracks) and non-compacted inter-rows, for a 2-month period in spring. To assess the rainfall impact on cast evolution, half of the observation sites were protected against rain splash by a nylon mesh placed above the soil surface. The water runoff was collected and analysed for sediment contents and phosphorus concentration. The mean annual production of surface casts was calculated to be 34 kg (dry weight) year^–1 kg^–1 earthworm (fresh weight). Synchronization between cast erosion and rainfall events was shown under natural conditions (unprotected sites). The erosion rate was 4 times greater over rainy periods than dry ones, reaching 80% of cast numbers. It appeared that not the runoff effect but the splash effect, due to the kinetics of the drops, disrupted casts. Newly formed casts disappeared first, with the erosion rate decreasing twofold for casts more than 10 days old. Cast erosion and runoff, as well as worm casting activity, were greater under compacted sites than under non-compacted sites, indicating an influence of earthworms on soil erosion from compacted soils. The total phosphorus content was similar in casts and uningested soil (0.80 mg phosphorus g^–1). Potential phosphorus losses from cast erosion was calculated to reach 25–49 mg phosphorus m^–2 per rainfall event depending on soil compaction. The amounts of particulate phosphorus recovered in water runoff after each rainfall event varied from 1 mg to 11 mg phosphorus. These results are compared and discussed. Received: 20 October 1998     

Uptake and toxicity of copper and zinc for the African earthworm,Eudrilus eugeniae (Oligochaeta)

Growth rate change in earthworms is considered to be a suitable endpoint when determining sublethal effects. In this study we evaluated growth and maturation in the vermicomposting earthworm speciesEudrilus eugeniae as marker of sublethal toxicity of copper and zinc. We also compared routes of uptake. Apart from exposing worms experimentally for 73 days to contaminated food, a series of contact filter paper tests was also performed to determine LD₅₀ for copper and zinc. Both copper and zinc at sublethal concentrations affected growth and maturation in worms exposed to contaminated food. These worms had a copper content of 34.5 g g^–1 after 73 days and a zinc content of 184.9 g g^–1, showing a differential uptake. Copper was more toxic than zinc. Also in the contact test worms did take up more zinc than copper and the LD₅₀ (48 h) for copper was 0.011 mg cm^–2 and for zinc 0.066 mg cm^–2, which translated to body burdens of 6 g g^–1 for copper and 131 g g^–1 for zinc. Indications were that a regulatory mechanism existed for both metals. Both metals were taken up through the body wall at a relatively fast rate. This study indicated that the skin was the major route of metal uptake. This study also showed a poor relation between the two types of tests for purposes of evaluating lethality of zinc and copper.     

Effect of coffee residues on growth and reproduction of Hyperiodrilus africanus (Oligochaeta, Eudrilidae) in Ivory Coast

Hyperiodrilus africanus (Beddard) is a 12-cm to 16-cm-long earthworm, which is widely distributed in West and Central Africa. It lives in the upper 10–20 cm of the soil, and feeds on a mixture of soil and above-ground litter. Cocoons obtained in the laboratory hatched on average 17 days after deposition and produced two juveniles on average. Paired individuals fed soil amended with 2% coffee residues grew significantly (P<0.05) faster than those in the control soil. Daily individual weight increments were respectively 6.1 mg worm^–1 day^–1 and 1.0 mg worm^–1 day^–1 in supplemented and control soil. The generation time was short, and cocoon production reached 9.6 month^–1 (i.e. 115 cocoons adult^–1 year^–1). When H. africanus collected from the field were raised in the laboratory, they grew slowly, laid fewer cocoons and mortality was high. Demographic parameters indicated an improvement when H. africanus were raised in batches rather than individually. Mating enhanced cocoon production although parthenogenesis was possible. Received: 4 April 1997     

Moisture preferences,growth and reproduction of the compost worm Eisenia fetida (Oligochaeta)

Summary Although moisture requirements of Eisenia fetida are considered to be generally known, very few in-depth studies have been performed. The moisture preferences of juveniles as well as adults of this species were determined in moisture towers containing cow manure with a particle size bigger than 500 and smaller than 1000 m and an organic matter content of 54%. The clitellate worms showed a wider preference range than the juveniles but deposited most of their cocoons within the narrow range of 65%–70% moisture — a moisture range preferred by 80% of the juveniles. Growth studies of newly hatched worms at various moisture levels over a period of 90 days showed that growth rate and final biomass were influenced by moisture availability with a very low rate of growth at low as well as at high moisture levels. The change in biomass of clitellate specimens as well as their consecutively produced cocoons were monitored at different moisture levels. A clear relationship between mass of cocoons and biomass of the producing worms was established at presumably favourable moisture conditions. Furthermore, the relation between cocoon mass and the production rate of cocoons was also determined, which showed that cocoon mass increased concomitantly with increase in cocoon production. The study also showed that clitellum development was increased at moisture levels above 64%. The onset of cocoon production was, however, earliest at slightly lower moisture levels, from which it is concluded that the optimal moisture level for growth and development of clitella are not necessarily optimal for the production of cocoons.Dedicated to the late Prof. Dr. M.S. Ghilarov     

Influence of animal wastes on growth and reproduction of the African earthworm species Eudrilus eugeniae (Oligochaeta)

The growth and reproduction of Eudrilus eugeniae were evaluated in four animal species wastes under laboratory conditions. Two hatchlings were introduced in 100 g of each animal waste i.e. cow, sheep, pig, and chicken after 15 days of pre-composting. Biomass gain, mortality, sexual maturity, and cocoons production were monitored periodically for 21 weeks. No mortality was observed in any waste. The maximum weight gain per worm and the highest growth rate per worm per week were obtained in chicken waste. Net biomass gain per worm were 1.01 ± 0.52 g, 1.318 ± 0.07 g, 0.87 ± 0.1 g, and 1.69 ± 0.15 g respectively for cow, sheep, pig, and chicken wastes. The highest number of cocoons produced per worm per day was obtained in chicken waste followed in decreasing order by sheep, cow, and pig waste. The mean number of cocoons produced per worm per day in chicken waste was 40.87% greater than these produced per day in pig waste.Among the four animal species, chicken, sheep, and cow were the most favourable wastes for the growth and reproduction of E. eugeniae, and hence can be recommended as feed materials in large scale vermicomposting facilities.     

Beneficial effects of blue-green algae and Azolla, excluding supplying nitrogen, on wetland rice fields: a review

 The role of blue-green algae (BGA) and Azolla in supplying N to rice fields is well documented. In addition, they also bring about, directly or indirectly, a number of changes in the physical, chemical and biological properties of the soil and soil-water interface in rice fields. For example, BGA liberate extracellular organic compounds and photosynthetic O₂ during their growth, while Azolla prevent a rise in the pH, reduce water temperature, curb NH₃ volatilisation and suppress weeds; and both of them contribute biomass. On decomposing, they influence the redox activity and result in the formation of different organic acids in soil. All such changes brought about by BGA and Azolla in soil may ultimately influence plant-available nutrients and also soil characteristics. An attempt has been made in this review to highlight these effects of BGA and Azolla in rice fields and discuss their possible implications relating to management and productivity of rice-field systems. Received: 4 February 1998     

Effects of earthworm density on growth, development, and reproduction in Lumbricus rubellus (Hoffm.) and possible consequences for the intrinsic rate of population increase

In this paper, the influence of earthworm density is assessed on the life-history parameters: growth, development, reproduction, and survival of Lumbricus rubellus (Hoffm.). Density ranges from two to nine earthworms in 1-l containers, corresponding to field densities of 300-1350 earthworms m⁻². Earthworms were kept under optimal laboratory conditions, with a surplus of food. The results show that at high earthworm density, individual growth is retarded, maturation delayed and cocoon production decreased, even when food is optimal. The integration of these results into a Dynamic Energy Budget model suggests that the food intake of individual earthworms is lower at the higher tested densities. This lower food intake is most probably driven by competition for space at the higher densities. The lower food intake results in a lower intrinsic rate of population increase which is negative at the highest tested density.     

Soil organic carbon stocks, storage profile and microbial biomass under different crop management systems in a tropical agricultural ecosystem

 We investigated the soil organic C and N stocks, storage profiles and microbial biomass as influenced by different crop management systems in a tropical agricultural ecosystem. The different crop management systems significantly affected the C and N stocks and microbial biomass C and N at different soil depths. Amongst the systems evaluated, the rice-wheat system maintained a higher soil organic C content. Inclusion of legumes in the system improved the soil organic matter level and also soil microbial biomass activity, vital for the nutrient turnover and long-term productivity of the soil. Irrespective of the cropping system, approximately 58.4%, 25.7% and 15.9% of the C was distributed in 0–15, 15–30 and 30–60 cm depths, respectively. Received: 10 October 1999     

Terbuthylazine and carbofuran effects on growth and reproduction within three generations of Eisenia andrei (Oligochaeta)

Sublethal effects of terbuthylazine and carbofuran on the growth and reproduction of Eisenia andrei were investigated over a period of three generations. Reproduction was assessed by measuring the coccon production of worms treated chronically with pesticides. Inhibition of cocoon production was found in the parental generation. Hatchlings were raised from cocoons to provide the F₁ generation. During raising a more rapid growth of juveniles treated with terbuthylazine was observed, compared with the growth of untreated worms. The increase in vitality was also found in cocoon production. Groups treated with terbuthylazine produced more cocoons than controls. The F₂ generation was raised from hatchlings of the F₁ generation, and here, also the terbuthylazine treatments increased earthworm growth, but not cocoon production. Exposure to carbofuran decreased cocoon production in all generations. Growth of the F₁ generation was not influenced by low concentrations of carbofuran.     

Effects of yeast on the growth and reproduction of the saprophagous millipedePolydesmus angustus (Diplopoda, Polydesmidae)

The millipedePolydesmus angustus was reared in the laboratory from hatching to maturity, reproduction and death. Two food types were used: dead leaves alone or dead leaves supplemented monthly with dry food yeast (Saccharomyces cerevisiae) at a rate not exceeding 5% of leaf dry weight. Growth, survival, adult live weight and fertility were compared between females reared on the two diets. Although the species was able to complete its life cycle on dead leaves alone, several parameters were strongly affected by the addition of yeast: growth was significantly faster, adult females became significantly larger and there was a 4.3-fold increase in fertility. Only survival was unaltered by the addition of yeast. The comparison between these laboratory results and field data on female fertility and live weight suggests that the natural diet of millipedes includes foods of higher quality than dead leaves. Possible sources of high-quality food in natural conditions are discussed.     

The earthworm population of a winter cereal field and its effects on soil and nitrogen turnover

The earthworm population in a winter cereal field in Ireland was studied over a 3-year-period and its effects on soil and N turnover were assessed. The mean annual population density was 346–471 individuals m^-2 and the mean biomass was 56.9–61.2 g m^-2. Twelve species were recorded, the most abundant being Allolobophora chlorotica followed by Aporrectodea caliginosa, and 242 mg at 5°C to 713 mg at 10°C in the case of juvenile Lumbricus terrestris. Gut contents (dry mass of soil) comprised 6.7–15.5% of the A. caliginosa live mass, and 9.7–14.7% of the Lumbricus terrestris mass. Annual soil egestion by the field population was estimated as 18–22 kg m^-2. Tissue production ranged from 81.7 to 218.5 g m^-2, while N turnover resulting from mortality was calculated as 1.5–3.9 g m^-2 depending on the year and the method of calculation. Earthworms were estimated to contribute an additional 3.4–4.1 g mineral N to the soil through excretion, mucus production, and soil ingestion. Independent estimates of N output via mucus and excretion derived from ¹⁵N laboratory studies with Lumbricus terrestris were 2.9–3.6 g m^-2 year^-1.     

Arbuscular mycorrhizae in a long-term field trial comparing low-input (organic, biological) and high-input (conventional) farming systems in a crop rotation

 Arbuscular mycorrhizal (AM) root colonization was studied in a long-term field trial in which four farming systems currently in use in Switzerland were continuously applied to a randomized set of plots at a single field site from 1978 till 1993. There were two low-input farming systems (organic and bio-dynamic) and two high-input (conventional) farming systems (according to Swiss guidelines of integrated plant production with and without farmyard manure). The systems had an identical 7-year crop rotation and tillage scheme and differed essentially only in the amount and type of fertilizer supplied and in plant protection management. The percentage of root colonization by AM fungi was determined in field samples 2–3 times over the growing season in crops in the rotation, namely in winter wheat (Triticum aestivum L. cv. Sardona), vetch-rye and grass-clover. We found the percentage of root length colonized by AM fungi to be 30–60% higher (P≤0.05) in the plants grown in soils from the low-input farming systems than in those grown in conventionally farmed soils. Approximately 50% of the variation of AM root colonization was explained by chemical properties of the soils (pH, soluble P and K, exchangeable Mg), the effect of soluble soil P being most pronounced. The potential of the field soils from the differently managed plots to cause symbiosis with AM fungi was tested in a glasshouse experiment, using wheat as a host plant. Soils from the low-input farming systems had a greatly enhanced capacity to initiate AM symbiosis. The relative differences in this capacity remained similar when propagules of the AM fungus Glomus mosseae were experimentally added to the soils, although overall root colonization by AM fungi was 2.8 times higher. Received: 27 August 1999     

Behaviour of arbuscular-mycorrhizal fungi on Vigna luteola growth and its effect on the exchangeable (32P) phosphorus of soil

 The effect of the inoculation of Glomus mosseae and Scutellospora fulgida, singly or in mixed inocula, was tested on the growth and mycorrhizal characteristics of Vigna luteola. Soil depletion by mycorrhizal inoculation was determined as exchangeable ³²PO₄. Five treatments were performed: non-inoculated control (C); inoculated with a suspension of microorganisms free of mycorrhizae (M); inoculated with S. fulgida plus microorganisms (Sf+M); inoculated with G. mosseae plus microorganisms (Gm+M) and a treatment inoculated with both S. fulgida and G. mosseae plus microorganisms (Sf+Gm+M). G. mosseae was the most efficient fungus in promoting growth of V. luteola. This fungus produced higher shoot dry weight, P uptake in shoots (P_shoot) and P_shoot/arbuscules ratio than the S. fulgida inoculum, even though percent arbuscular-mycorrhizal (AM) colonization was similar for the two single AM-inoculated treatments. The highest value of isotopically exchangeable P was recorded for treatment M (P<0.05). In comparison with M, Gm+M treatment reduced the different P pools more than Sf+M treatment. C_p values were reduced to half by Gm+M and Sf+M treatments and were minimum for the combined treatment. Pools A (exchangeable phosphate between 1 min and 1 day) and B (exchangeable phosphate between 1 day and 3 months) were reduced by Gm+M treatment in contrast to Sf+M, which left them unchanged. The depression of isotopically exchangeable P for all pools obtained for the Sf+Gm+M treatment suggested that specific characteristics of fungi caused differences in P absorption, which in addition was altered by the possible interactions among them, when multiple inocula were used in a soil low in native P. Received: 29 January 1999     

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.     

Interaction of biochemical quality and particle size of crop residues and its effect on the microbial biomass and nitrogen dynamics following incorporation into soil

 Mineralization of N from organic materials added to soil depends on the quality of the substrate as a carbon, energy and nutrient source for the saprophytic microflora. Quality reflects a combination of biochemical and physical attributes. We investigated how biochemical composition interacts with particle size to affect the soil microflora and N dynamics following incorporation of crop residues into soil. Four fresh shoot and root crop residues were cut into coarse and fine particle sizes, and incorporated into sandy-loam soil which was incubated under controlled environment conditions for 6 months. In the case of the highest biochemical quality material, potato shoot (C/N ratio of 10 : 1), particle size had no effect on microbial respiration or net N mineralization. For lower biochemical quality Brussels sprout shoot (C/N ratio of 15 : 1), reducing particle size caused microbial respiration to peak earlier and increased net mineralization of N during the early stages of decomposition, but reduced net N mineralization at later stages. However, for the lowest biochemical quality residues, rye grass roots (C/N ratio of 38 : 1) and straw (C/N ratio of 91 : 1) reducing particle size caused microbial respiration to peak later and increased net immobilization of N. For Brussels sprout shoot, reducing particle size decreased the C content and the C/N ratio of residue-derived light fraction organic matter (LFOM) 2 months following incorporation. However C and N content of LFOM derived from the other materials was not affected by particle size. For materials of all qualities, particle size had little effect on biomass N. We conclude that the impact of particle size on soil microbial activities, and the protection of senescent microbial tissues from microbial attack, is dependant on the biochemical quality of the substrate. Received: 3 July 1998     

The impact of a low humus level in arable soils on microbial properties, soil organic matter quality and crop yield

 In arable soils in Schleswig-Holstein (Northwest Germany) nearly 30% of the total organic C (TOC) stored in former times in the soil has been mineralized in the last 20 years. Microbial biomass, enzyme activities and the soil organic matter (SOM) composition were investigated in order to elucidate if a low TOC level affects microbial parameters, SOM quality and crop yield. Microbial biomass C (C_mic) and enzyme activities decreased in soils with a low TOC level compared to soils with a typical TOC level. The decrease in the C_mic/TOC ratio suggested low-level, steady-state microbial activity. The SOM quality changed with respect to an enrichment of initial litter compounds in the top soil layers with a low TOC level. Recent management of the soils had not maintained a desirable level of humic compounds. However, we found no significant decrease in crop yield. We suggest that microbial biomass and dehydrogenase and alkaline phosphatase activities are not necessarily indicators of soil fertility in soils with a high fertilization level without forage production and manure application. Received: 12 December 1997