Visa Nuutinen

Spatial variation of an earthworm community related to soil properties and yield in a grass–clover field

Abstract Spatial variation in abundance of earthworms, soil properties and herbage yield were surveyed on a 1.4 ha grass–clover field. Sampling and measurements were made in a regular grid (25 m×25 m) of 32 sampling sites during the first and second years after the establishment of the ley. Five earthworm species were present in the field. The total abundance and biomass of earthworms varied from zero to 218 individuals and 18 g dry-weight per m2. The soil properties and herbage mass also varied widely. The majority of variables showed discernible spatial dependence in the first separation distance between the sampling sites. It was usually difficult to model the spatial continuity satisfactorily, because much of the small scale variation was evidently not captured by the sample spacing. Soil clay percentage displayed a particularly clear and continuous spatial gradient. The distributions of Lumbricus terrestris and Dendrodrilus rubidus were distinctly aggregated. For L. terrestris there was some evidence for association with silty soil, while D. rubidus was found only in the area with the lowest clay content. An alternative explanation for the uneven distribution of the two species is the recently started dispersal into the ley. Non-parametric correlation suggested a positive relationships between earthworm activity and both infiltration of water and clover production. When geographical distance between sampling sites was controlled for in the analyses, these correlations were not statistically discernible, but a positive relationship between total numbers of earthworms and soluble soil phosphorus content emerged.

Distribution and abundance of burrows formed by Lumbricus terrestris L. and Aporrectodea caliginosa Sav. in the soil profile

Abstract The distribution of burrows made by Lumbricus terrestris L. and Aporrectodea caliginosa Sav. was studied on an unploughed field. The positions of earthworm burrows were mapped in 9 horizontal planes to a depth of 80 cm in a pit of 70 by 40 cm. Burrow diameter and presence of plant roots growing in burrows were also recorded. Burrows on six of the nine planes were considered as two-dimensional point patterns and analyzed as spatial point processes. A three-dimensional image was constructed for burrows formed by L. terrestris. The total number of burrows ranged between 180 and 1260 m−2 at depths of 80 and 30 cm, respectively. The majority of burrows were evidently formed by A. caliginosa. The smallest size class (2–3 mm) of burrows was dominant at depths between 8 and 40 cm. Deeper in the soil profile, the proportion of larger burrows increased markedly. Burrows formed by L. terrestris appeared to be non-branching, and extended vertically beyond 80 cm. In all soil layers studied, burrow distribution was found to be completely random. The proportion of burrows containing plant roots was between 18 and 60%, at depths of 80 and 15 cm, respectively.

Interaction of Lumbricus terrestris L. burrows with field subdrains

The morphology of Lumbricus terrestris L. burrows was investigated in relation to subsurface tile drain position. The aim was to clarify the causes and consequences of higher densities of L. terrestris previously measuredabove the tiles at the study site. At two pairs of study pits, the plough layer was removed from a 1 m x 2 m area above the tile and at 8 m distance from it. Burrows of L. terrestris were identified at the plough pan, resident worms removed and burrows cast with dyed fibreglass resin. The resin casts were exposed in the profile, depth and length of casts measured and their connections with tiles recorded. In both above-tile pits, two cases were recorded where the cast burrow ended at the tile surface. These contacts indicate the potential importance of burrows in the conduction of water and solutes from the soil surface layers into the tiles. The mean depth of burrows was 1.0 m (se = 0.024, n = 27) above the tiles and 0.83 m (se = 0.036, n = 12) between the tiles. During adverse soil conditions such as droughts, individuals living near the tiles may gain from the shelter provided by their deeper burrows and this could partly explain the higher population densities above the tiles.

Local land use effects and regional environmental limits on earthworm communities in Finnish arable landscapes

In many arable soils, earthworms form the key component of the soil animal community and greatly contribute to soil quality. Our goal was to identify variables that can explain the variation of earthworm communities across Finnish arable fields by focusing on both regional aspects, such as climate and inherent soil properties, and local aspects, such as field management practices and field margins. We sampled the earthworms during the autumn of 2004 and 2005 at 53 sites of cultivated fields and margins, distributed to 11 localities ranging from the southern parts of Finland to the Arctic Circle. Simultaneously, information was collected on topsoil properties, cultivation history, and climatic factors. We found that soil type was by far the best regional variable to explain the variation in total earthworm density, the density being highest in medium coarse soils, i.e., silts and very fine sands. However, soil type had a significant interaction with soil C:N ratio. After accounting for the effect of soil t...

A Field Manipulation of Trophic Interactions in Rock-Pool Plankton

Three rock-pools (ca. 10 Daphnia 1-1, ca. 100 Daphnia 1and > 100 Daphnia 1-1) were each bisected with a plastic curtain. One side of each pool was left intact, while planktivorous fish were introduced into the other side. The succession of the zooplankton and phytoplankton communities in the rock-pools was followed, using quantitative sampling, for one summer. In the experiment the fish eliminated large (> 0.5 mm) herbivorous cladocers from the zooplankton within 20-40 d of introduction. An increase in the numbers of small zooplankton (rotifers, cladocers) then occurred. In the control sides large Daphnia thrived well, though with fluctuating densities, throughout the summer. The response of phytoplankton to the elimination of large herbivores varied between the rock-pools. In terms of species diversity and evenness no obvious differences were observed between control and experiment in the rock-pool with low Daphnia density. In the medium-density rock-pool both species diversity and evenness were lower in the experimental part, while in the high-density rock-pool the opposite was observed. In these two pools elimination of Daphnia resulted in an increase in total numbers of cells 11 of 2-3 orders of magnitude. The difference between control and experimental parts was due to the increase in small cells (< 64 Bm diameter). The elimination of large herbivores resulted in lowered densities (low-density) or elimination (medium and high-density) of filamentous algae from the phytoplankton.

Resource distribution and surface activity of adult Lumbricus terrestris L. in an experimental system

Lumbricus terrestris L. is noted for activities on the soil surface and descriptions of feeding, movement and mating have previously been recorded. The aim of this study was to investigate the effects of resource availability on these behaviours using an experimental system. The laboratory set-up consisted of an arena with a continuous area of 1 m2 with soil-filled tubes to a depth of 1 m. Eighteen mature, field-collected L. terrestris were used and fed with dried barley straw on the soil surface, either evenly or in one patch. Both patterns were applied twice over an experimental period of 56 days. An infrared video system was used to provide permanent records of a 12 :12 hrs dark : light cycle. Earthworm behaviour was classified into three major groups; foraging/exploration, over-surface movements and mating, with time spent in each activity recorded for all individuals. Seventeen earthworms survived to the end of the experimental period. Surface activity peaked one hour after darkness and diminished steadily until lights up. Foraging activity increased by a factor of 1.6 in a resource-rich area whereas away from the patch it reduced by a factor of 0.8 compared with even straw distribution. Over-surface movement increased by a factor of nine after provision of a patchy straw distribution, with two thirds of movements initiated by individuals in a resource poor area. The majority of matings occurred early in the dark period. During even resource distribution, matings occurred equally in different parts of the arena whereas under patchy distribution, more matings were recorded in the resource-rich area. Presented results suggest that resource availability is an important factor affecting different aspects of surface behaviour in L terrestris.

Tillage and crop residue management methods had minor effects on the stock and stabilization of topsoil carbon in a 30-year field experiment

We studied the effects of tillage and straw management on soil aggregation and soil carbon sequestration in a 30-year split-plot experiment on clay soil in southern Finland. The experimental plots were under conventional or reduced tillage with straw retained, removed or burnt. Wet sieving was done to study organic carbon and soil composition divided in four fractions: 1) large macroaggregates, 2) small macroaggregates, 3) microaggregates and 4) silt and clay. To further estimate the stability of carbon in the soil, coarse particulate organic matter, microaggregates and silt and clay were isolated from the macroaggregates. Total carbon stock in the topsoil (equivalent to 200 kg m(-2)) was slightly lower under reduced tillage (5.0 kg m(-2)) than under conventional tillage (5.2 kg m(-2)). Reduced tillage changed the soil composition by increasing the percentage of macroaggregates and decreasing the percentage of microaggregates. There was no evidence of differences in the composition of the macroaggregates or carbon content in the macroaggregate-occluded fractions. However, due to the higher total amount of macroaggregates in the soil, more carbon was bound to the macroaggregate-occluded microaggregates in reduced tillage. Compared with plowed soil, the density of deep burrowing earthworms (Lumbricus terrestris) was considerably higher under reduced tillage and positively associated with the percentage of large macroaggregates. The total amount of microbial biomass carbon did not differ between the treatments. Straw management did not have discernible effects either on soil aggregation or soil carbon stock. We conclude that although reduced tillage can improve clay soil structure, generally the chances to increase topsoil carbon sequestration by reduced tillage or straw management practices appear limited in cereal monoculture systems of the boreal region. This may be related to the already high C content of soils, the precipitation level favoring decomposition and aggregate turnover in the winter with topsoil frost.

Population and behavioural level responses of arable soil earthworms to boardmill sludge application

The response of earthworms to soil application of boardmill waste sludge was quantified in field and laboratory experiments. The influence of one application of 6×104 tonnes ha−1 of unamended sludge was tested against no application on silty-clay arable soil. After 2 years, results in stubble-cultivated soil showed a 1.7 times lower density of earthworms where sludge was added, whereas there was no difference in average earthworm fresh weight. In direct-drilled soil, there was an indication of lower average numbers of Lumbricus terrestris middens when sludge was applied. Negative impacts in the field may have been due to indirect negative effects of the sludge application. In the laboratory, habitat choice tests were undertaken with two common species from the field site using sludge-based mulch and fertiliser products. Aporrectodea caliginosa showed no discernible preference between soil and soil mixed with unamended sludge (mulch), but favoured soil over soil mixed with sludge and chicken manure (fertiliser). Tests with L. terrestris showed a similar pattern. The preference of L. terrestris for the two products was compared with that for chopped barley straw by direct observation of foraging behaviour. Differences in foraging time of L. terrestris for different feeds were not significant, but mass of straw collected was significantly greater compared with either type of sludge treatment.

Daphnia exhibit diurnal vertical migration in shallow rock-pools

We report diurnal changes in vertical distribution ofDaphnia longispina andD. magna in shallow (25–60 cm) rock-pools on Baltic islands, southern Finland. During the daytime shallow rock-poolDaphnia reside in water layers close to the sediment while at midnight they either are evenly distributed throughout the water column, or have a modal peak of distribution in the surface water. Contrary to this pattern, no changes were observed in vertical distribution ofD. longispina at noon and at midnight in a 150 cm deep pond. We suggest that the pattern ofDaphina vertical migration in shallow rock-pools is not satisfactorily explained by predation.