Impact of Collembola and Enchytraeidae on soil surface roughness and properties

The aim of the study was to quantify the alteration of soil surface roughness caused by the casting activity of mesofauna. Undisturbed soil monoliths with a surface area of 5000mm² were taken from the upper 4cm of the Ap-horizon in agricultural land. Two tillage systems were studied: conventional tillage (CT) and conservation tillage (CS). The sampling plots were mechanically compacted by wheeling with graded loads. Sampling occurred in spring after compaction and before seeding. The soil monoliths were defaunated before inoculating one half of the monoliths with 150 individuals of Collembola (Folsomia candida) and the other half with 100 individuals of Enchytraeidae (90% Enchytraeus minutus and 10% E. lacteus). Soil surface roughness was measured using a noncontact laser scanner: before inoculation and 6 months later. Photographs show the soil surface covered with casts. Results from laser scanning show that in most cases the surface roughness increased due to mesofaunal activity. However, roughness decreased when cracks were filled with casts. The casting activity and surface roughness changes are highest in uncompacted soil. A high degree of soil compaction significantly reduced the activity at the surface. In most cases the soil surface is more altered in CT than in CS. When the content of carbon and nitrogen were determined, both elements were accumulated in the casts but more by Collembola than Enchytraeidae. The results are discussed in the context of the hemiedaphic (F. candida) and the euedaphic (Enchytraeus spp.) mode of living. Received: 6 December 1996     

Experimental evidence for the role of earthworms in compacted soil regeneration based on field observations and results from a semi-field experiment

In laboratory experiments, earthworms are often observed to burrow through compacted soil layers, leading to the general assumption that these animals play a significant role in regenerating compacted soils in agricultural plots. To demonstrate this role under field conditions, the abundance of earthworm macropores inside compacted zones was estimated on plots under reduced (RT) or conventional tillage (CT). Then, different types of compacted zones typically found in CT (plough pan and compacted clods) and RT plots (compacted volume under wheel tracks) were experimentally simulated in wooden boxes, buried in the field and inoculated with different earthworm species. After 6 weeks of incubation, the number of macropores inside the compacted zones was examined. Field observations showed that approximately 10% and 30% of the compacted zones were colonised by at least one macropore in CT and RT plots, respectively. A significantly greater number of anecics was found in RT plots, but we could not conclude that this ecological type of earthworm plays a more major role in the regeneration process in these plots since there were fewer compacted zones and these covered a smaller area in CT. The semi-field experiment provided evidence that earthworm-mediated regeneration of compacted zones is possible and its nature varies between ecological types of earthworm. Lumbricus terrestris, which makes individual burrows that are vertical and deep, was the main species to cross through the plough pan. The other three earthworm species (Aporrectodea giardi, A. caliginosa and A. rosea) did burrow inside the other types of compacted zones (“wheel tracks” and “compacted clods”). In every case, however, macropore density was far greater in non-compacted zones, illustrating that avoidance of compacted soil by earthworms is important and should be taken into account when extrapolating results from laboratory studies.     

Assessment of earthworm contribution to soil hydrology: a laboratory method to measure water diffusion through burrow walls

The capacity for water diffusion in burrow walls (i.e. the coefficient of sorptivity) either burrowed by Lumbricus terrestris (T-Worm) or artificially created (T-Artificial) was studied through an experimental design in a 2D terrarium. In addition, the soil density of earthworm casts, burrow walls (0–3 mm around the burrow) and the surrounding soil (>3 mm) were measured using the method of petroleum immersion. This study demonstrated that the quantity of water which transits through burrows of L. terrestris in the soil matrix was lower than that transited through soil fractures, due to a reduction of soil porosity in burrow walls (compaction: cast > worms burrow walls > surrounding soil > artificial burrow walls). Earthworm behaviour, in particular burrow reuse with associated cast pressing on walls, could explain the larger burrow wall compaction in earthworm burrows. If water diffusion was lower through the compacted burrows, burrow reuse by the worms makes them more stable (worms would maintain the structure over years) than unused burrows. The present experimental design could be used to test and measure the specific differences between earthworm species in their contributions to water diffusion. Probably, these contributions depend on the presumed related-species behaviours which would determine the degree of burrow wall compaction.     

Role of earthworms in regenerating soil structure after compaction in reduced tillage systems

New non-tillage or reduced tillage agricultural practises are being increasingly adopted but generally result in higher soil compaction. Due to their recognised physical influence mainly through burrow creation, it is often claimed that earthworm activity could alleviate soil compaction in these systems. To put this assumption to the test, an experimental compaction event was carried out on one plot of arable land. The abundance and biomass of earthworms were evaluated in compacted (under wheel tracks) and non-compacted (between wheel tracks) zones, seven times over a two-year period. In addition, the functional consequences of earthworm activity, defined by burrow abundance assessed in 2D and 3D and water infiltration, were measured three times over the same period. The short-term (less than three months) effects of the compaction were clear: soil bulk density increased from 1.46 to 1.57 g cm⁻³, the abundance and biomass of earthworms were greatly reduced (−40% and −70% respectively) and the number and continuity of macroporosity were lower under wheel tracks at least until a depth of 30 cm. After these initial detrimental effects, we observed a rapid recovery of earthworm populations with no statistical difference between compacted and control zones more than three months after the compaction. However, the recovery of soil functional properties linked to earthworm activity, macroporosity and water infiltration, was much slower and took between 12 and 24 months. Despite these modifications, there were no significant changes in soil bulk density with time during the two-year period. This study demonstrates that earthworms are important actors in the regeneration of compacted soil. Although the complete regeneration of compacted soil by earthworms is a slow process, agricultural practises that promote earthworm density and activity should be encouraged in reduced or minimum tillage systems.     

Impact of soil compaction on earthworm burrow systems using X-ray computed tomography: preliminary study

This study is a first approach of the impact of soil compaction due to trafficking by machinery on earthworm burrow systems. To this end, two experiments were established. In the first one, microcosms were incubated in the laboratory for 70 d with Lumbricus terrestris or Aporrectodea giardi. In the second experiment, soil cores were excavated from a sugar beet field mainly colonised by L. terrestris and Aporrectodea caliginosa. The cores were then artificially compacted at 0.12 MPa or 0.25 MPa (which corresponds to the compaction due to trafficking by machinery in the field) or remained non-compacted. The whole cores were submitted to an X-ray computed tomography scan. This method allowed to compare the characteristics of the entire burrow system (total and mean burrowed length, mean length and number of burrows) and of the burrows themselves (number, area and roundness of pores constituting the burrows) in the compacted and non-compacted cores. The results showed that soil compaction contributes to close numerous pores, reduce mean length of burrows and increase the number of fragmented burrows. We concluded that soil compaction affects to a large extent the functionality of burrow systems by fragmenting them and affecting their continuity. This impact increases with the intensity of compaction. The applied soil compaction mainly affected the burrows located in the upper part of the soil. From a general point of view and especially for the upper part of the cores, horizontal burrows seemed to be more affected by compaction than vertical or oblique ones. Globally, the effects of soil compaction were especially observed at the greatest applied pressure (0.25 MPa). At 0.12 MPa, the damage to the burrows was less obvious.     

The effect of tillage type and cropping system on earthworm communities, macroporosity and water infiltration

To test the assumption that changes to earthworm communities subsequently affect macroporosity and then soil water infiltration, we carried out a 3 year study of the earthworm communities in a experimental site having six experimental treatments: 2 tillage management systems and 3 cropping systems. The tillage management was either conventional (CT; annual mouldboard ploughing up to −30 cm depth) or reduced (RT; rotary harrow up to −7 cm depth). The 3 cropping systems were established to obtain a wide range of soil compaction intensities depending on the crop rotations and the rules of decision making. In the spring of 2005, the impact of these different treatments on earthworm induced macroporosity and water infiltration was studied. During the 3 years of observation, tillage management had a significant effect on bulk density (1.27 in CT and 1.49 mg m⁻³ in RT) whereas cropping system had a significant effect on bulk density in RT plots only. Tillage management did not significantly affect earthworm abundance but significantly influenced the ecological type of earthworms found in each plot (anecic were more abundant in RT). On the contrary cropping system did have a significant negative effect on earthworm abundance (104 and 129 ind. m⁻² in the less and most compacted plots, respectively). Significantly higher numbers of Aporrectodea giardi and lower numbers of Aporrectodea caliginosa were found in the most compacted plots. CT affected all classes of porosity leading to a significant decrease in the number of pores and their continuity. Only larger pores, with a diameter superior to 6 mm, however, were adversely affected by soil compaction. Tillage management did not change water infiltration, probably because the increase in macroporosity in RT plots was offset by a significant increase in soil bulk density. However, cropping system had a significant effect on water infiltration (119 vs 79 mm h⁻¹ in the less and most compacted plots, respectively). In RT plots, a significant correlation was observed between larger macropores (diameter > 6 mm) and water infiltration illustrating the potential positive effect of earthworms in these plots.     

Short-term effects of tillage and compaction on nitrous oxide, nitric oxide, nitrogen dioxide, methane and carbon dioxide fluxes from grassland

N₂O, NO, NO₂, CO₂ and CH₄ fluxes were measured simultaneously from tilled and compacted soil in a factorial design to investigate the effect of management on trace gas emissions. Six treatments in combinations of with and without N application, tillage and compaction were investigated for a period of 3 weeks using the closed-chamber technique (for N₂O, CO₂ and CH₄) and the open-chamber technique (for NO and NO₂). Total NO emissions from the tilled plots were 2.4 times greater than from the non-tilled plots, whereas CO₂ emissions were 1.8 times greater from the non-tilled plots. Compaction increased the emissions of N₂O and CH₄ 3.5- and 4.4-fold, respectively, compared with emissions from uncompacted plots. The effects of tillage and compaction on the gaseous emissions are discussed in relation to their production, transport and lifetime within the soil. The results showed that the best option for reducing gaseous emission from fertilised soil, with regards to tillage or compaction, would be the least compacted system, regardless of the tillage status as reflected, at least in the short term, by minimal emissions of N₂O and CH₄ and to some extent those of NO, NO₂ and CO₂.     

Regeneration of compacted soil aggregates by earthworm activity

Soil compaction is a problem of modern agriculture, caused by heavy machinery when used in unsuitable, especially moist, conditions. Some regeneration processes in compacted loess soil were studied in a field experiment near Relliehausen, at the edge of the Solling mountains in Lower Saxony, Germany. Conventional tillage (CT) and conservation tillage (CS) systems were compared. The compaction was induced by the use of different wheel loads. The influence of earthworms was determined by comparing soil aggregates and casts with respect to dry and moist porosity, swelling, and water stable aggregation. For visualisation of the microstructure, a scanning electron microscope was used. The casts were obtained from two earthworm species living for 6 months in the laboratory in monoliths, taken on the plots after the wheeling procedure. The casts showed 10-20% higher values for porosity and about 50% higher swelling values than comparable soil aggregates, while the relative water stability was ca. 10% lower. We conclude that casts are looser and less stable than aggregates from the soil the earthworms ingested. To show the ecological relevance of the changes in the casts, the cast production per hectare per year was calculated. It was especially high in the most loaded soil under CS with endogeic species.     

Assessment of earthworm burrowing efficiency in compacted soil with a combination of morphological and soil physical measurements

Summary Column experiments were carried out to quantify the effect of earthworms on compacted soil. The earthworms (Lumbricus terrestris) were able to burrow into soil which was artificially compacted to a pore volume as low as 40%; they may also penetrate an artificial plough pan deep in the soil. The effect of the burrowing activity of Lumbricus terrestris was quantified by measuring hydraulic conductivities and infiltration rates through the whole soil column (19 cm wide, 40 cm long). Morphological parameters, mainly the vertically projected burrow depth, were correlated with the saturated hydraulic conductivity. The amount of casts deposited by Lumbricus terrestris on the soil surface increased with the degree of soil compaction. The bulk density of casts was always less than that of the original soil.     

Assessment of soil structural differentiation around earthworm burrows by means of X-ray computed tomography and scanning electron microscopy

The burrowing activity of earthworms creates a distinct area around the resulting macropores called the drilosphere, which controls various soil processes. Density and microstructure of the drilosphere were studied and compared with those of the surrounding soil. For this purpose soil cores were separately inoculated with the vertically burrowing earthworm species Lumbricus terrestris. After 70 days some cores were compacted by a hydraulic press (250 kPa) and all cores were analysed by means of X-ray computed tomography. Mean Hounsfield Units were measured for concentric ROI cylinders (ROI = region of interest) of increasing diameters located around vertical macropore sections within selected horizontal slices. Based on these data we estimated stepwise the distribution of bulk density from the inner boundary of the drilosphere to the surrounding soil. In uncompacted soil the bulk density of the drilosphere was increased by 11% over that of the surrounding soil. In cross section, drilosphere and burrow form a concentric area with a total radius up to 2.2 cm. Soil compaction increased the dry bulk density of soil and decreased the diameter of earthworm burrows. Moreover, we found a less dense part of soil between the dense drilosphere and the remaining soil of the compacted core. Scanning electron microscopy revealed that the coarse silt particles of the bulk soil were rearranged to a parallel orientation due to compaction whereas the microstructure of the drilosphere remained unchanged. In any case, the drilosphere revealed a very homogeneous and dense arrangement of silt particles.     

Assessment of the burrow system of Lumbricus terrestris, Aporrectodea giardi, and Aporrectodea caliginosa using X-ray computed tomography

Artificially packed soil columns were inoculated with individuals of different earthworm species (Lumbricus terrestris, Aporrectodea giardi or Aporrectodea caliginosa) and placed under controlled conditions in the laboratory. At the end of the incubation period, which lasted 8 months, three-dimensional reconstructions of the burrow system of each species were obtained using X-ray computed tomography. The particular features of the three burrow systems and the differences between them are discussed in terms of density, orientation and distribution of the burrows and the complexity of the network in relation to variations in soil depth and soil density. Received: 5 February 1997     

Characterization of the burrow system of the earthworms Lumbricus terrestris and Aporrectodea giardi using X-ray computed tomography and image analysis

 The burrow systems of two earthworm species (Lumbricus terrestris and Aporrectodea giardi) were studied in artificially packed soil columns placed in controlled conditions in the laboratory. At the end of the incubation, which lasted 246 days, the burrow systems were characterized on the undisturbed columns using X-ray computed tomography. This method provided a set of digitized images corresponding to horizontal 3-mm-thick sections. The following parameters were measured using image analysis on each section: number of biopores, their volume, and their individual orientation calculated using an elliptical model of the earthworm channel. The profiles of these parameters through the columns showed that the burrow systems of L. terrestris and A. giardi, which are both anecic species, were very different in terms of total volume, number of burrows, burrow orientation and extension with soil depth. These results led us to conclude that the burrow system of L. terrestris can be considered as a permanent structure whereas that of A. giardi is closer to the burrow system of endogeic species. Received: 12 June 1998     

Influence of mulch and soil compaction on earthworm cast properties

The effects of different mulch materials applied to compacted and uncompacted soil on the quantity and the quality of deposited earthworm casts were investigated. Biochemical properties and water stability of soil aggregates were compared with the corresponding properties of worm casts. This short-time experiment was conducted in the laboratory, simulating field conditions of mulch management in temperate agricultural systems. In microcosms Lumbricus terrestris and Octolasion cyaneum were inoculated separately. Barley, lupin, maize, or sugar-beet as straw or leaves were applied as mulch in amounts comparable to those usually found in the field. The soil was compacted artificially to a bulk density of 1.0 or 1.5 Mg m⁻³. In general, plant material and to a lesser extent soil compaction influenced the dynamic processes in the soil affecting microbial activity and water stable aggregation. Higher values of phosphatase activity was measured in compacted soil, while the corresponding enzyme activities in the casts were less affected by compaction. The worm species and the nutritional quality of the food source were factors strongly influencing water stable aggregation. Mulch as well as soil compaction had consequences for the burrowing activity of the worms, which resulted in different rates of cast production depending on the species.     

Quantitative image analysis of earthworm-mediated soil displacement

The way soil is disrupted and deformed by earthworm movement is hard to quantify non-destructively. Two anecic earthworm species, Aporrectodea longa (Ude) and Lumbricus terrestris L., were compared in their effect on the soil around them as they burrow. Image analysis (particle image velocimetry, PIV) was used successfully to quantify the distance and direction of soil particle displacement by earthworm locomotion giving a unique insight into their effect on the soil structure development. The data collected from both species using PIV show a decline in soil displacement at increasing distance from the earthworm’s body. The quantity of soil being displaced was more to the sides of the earthworms (radially) than in front of the prostomium (axially). Also, L. terrestris displaced more soil than A. longa both axially and radially. The findings from this study suggest that PIV image analysis is a viable tool for examining soil displacement by earthworms and the method used has the potential to be applied to other soil organisms.     

Homing ability widens the sphere of influence of the earthworm Lumbricus terrestris L.

We report that the deep-burrowing earthworm Lumbricus terrestris L. possesses short-range homing capability. For 2 months we followed the soil surface activity of 18 field-collected L. terrestris in an experimental laboratory population. We recorded 26 cases where an individual after completely leaving its burrow returned to the burrow by backing along its own outward trail. Maximally, homing occurred from a distance of 0.70 m and after more than 3 h on the soil surface. The evolution of homing ability in L. terrestris is most likely related to the importance of the burrow for survival and reproduction. This adaptation also guarantees individuals an expanded foraging area, which we believe can partly explain the remarkable efficiency of L. terrestris in the burial of surface litter.     

Least limiting water range for different soil management practices in dryland farming in Iran

Integrated evaluation of soil physical properties using the least limiting water range (LLWR) approach may allow a better knowledge of soil water availability. We determined the LLWR for four tillage practices consisted of conventional tillage (CT), reduced tillage (RT), no-tillage (NT) and fallow no-tillage (NT_f). In addition, LLWR was determined for abandoned soils (i.e. control), compacted soils, ploughed compacted soils and abandoned soils with super absorbent polymers (SAPs) application. Soil water retention, penetration resistance (PR), air-filled porosity and bulk density were determined for the 0–5 and 0–25-cm depths. Mean LLWR (0.07–0.08 cm³ cm^?3) was lower in compacted soils than the soils under CT, NT, NT_f, RT, tilled, abandoned and SAP practices but it was not different among tillage practices. The values of LLWR were 0.12 cm³ cm^?3 for NT and CT. LLWR for tilled plots (0.12 cm³ cm^?3) became greater than compacted soils by 1.3 times. Analysis of the lower and upper limits of the LLWR further indicated that PR was the only limiting factor for soil water content, but aeration was not a limiting factor. The LLWR was more dependent on soil water content at permanent wilting point and at PR.     

The apparent electrical conductivity as a surrogate variable for predicting earthworm abundances in tilled soils

Noninvasive geophysical methods have a great potential for improving soil‐biological studies at field or regional scales: they enable the rapid acquisition of soil information which may help to identify potential habitats for soil biota. A precondition for this application is the existence of close relationships between geophysical measurements and the soil organism of interest. This study was conducted to determine whether field measurements of apparent electrical conductivity (ECa) are related to abundances of earthworms in tilled soils. Relationships between ECa and earthworm populations were investigated along transects at 42 plots under reduced and conventional tillage at a 74 ha field on sandy‐loam soil in NE Germany. Relations were analyzed with linear‐regression and spatial analysis. The apparent electrical conductivity (ECa) was quantitatively related to earthworm abundances sampled 5 months after the geophysical measurements. No relationship was found, however, in plots under conventional tillage when analyzed separately. If earthworm abundances were known at every other location along the transects and if the state‐space approach was used for analysis, the analysis of ECa measurements and earthworm abundances indicated that 50% of the earthworm samples could have been substituted by ECa measurements. Further research is needed to fully evaluate the potential of ECa measurements for predicting earthworm habitats in tilled soil.     

Effect of mesofaunal activity on the rehabilitation of sealed soil surfaces

The impact of soil mesofauna on the rehabilitation of soil surfaces sealed by rainfall was investigated in a long-term laboratory experiment. Fifteen undisturbed soil monoliths from the Ap horizon of a Gleyic Podzoluvisol/Haplic Luvisol derived from loess were obtained after conventional tillage and seedbed preparation. The soil of this site is known to be susceptible to surface sealing as a result of rainfall activity. All monoliths were defaunated in a microwave oven and then inoculated with mesofauna, some with 300 individuals of Collembola and others with 200 individuals of Enchytraeidae. Additional monoliths were left uninoculated for comparison. Ten monoliths were then treated with simulated rainfall (intensity: 29 mm h⁻¹; time: 60 min) to form a surface seal. The roughness of all 15 monoliths was measured using a non-contact laser scanner immediately and after 6 and 18 months. Differences in the soil surface roughness were assumed to indicate mesofaunal activities and intrinsic soil processes. Soil surface roughness was significantly different between monoliths with and without rain impact. Monoliths subjected to rainfall showed significant differences in soil surface roughness between those with and without mesofauna as well as between monoliths inoculated with Collembola and Enchytraeidae. The roughness differences detected between unsealed monoliths were not significant. Over the entire experimental time of 18 months the relative changes in sealed uninoculated monoliths were much lower than the alterations as a result of mesofaunal activities. The results show that within a few months the activities of Collembola and Enchytraeidae distinctly contribute to the rehabilitation of sealed soil surfaces and the development of a finely structured soil surface microrelief.     

Effects of conventional and alternative management systems on soil phosphorus content,soil structure,and corn yield

Abstract

Conventional management practices have been associated with increased soil erosion and organic matter loss and the contamination of surface and ground water. Alternative agriculture systems which minimize external chemical inputs and degradation of soil and water resources represent alternatives to conventional management practices. Four different management practices were compared on an alluvial silty loam soil cultivated to grow corn (Zea mays L.). The effects of conventional and reduced tillage and of different chemical inputs on the distribution of phosphorus (P) concentration and on soil porosity were investigated. Results showed that the highest P content was detected in the topsoil (0–10 cm) of the minimum tilled plots even though the amount of P fertilizer added was much lower than the amount added in the conventionally tilled plots. The total porosity was significantly higher in the minimum tilled soil and was related only to the tillage technique. Since the higher porosity was mainly due to the higher proportion of elongated and regular pores, the minimum tilled soil appeared to be more resistant to physical stresses and characterized by a higher biological activity.