Stefan Schrader

Earthworm casting: Stabilization or destabilization of soil structure?

Abstract The aim of the study was to determine the effect of the gut passage through earthworms on the aggregate stability of soils varying in texture, carbonate and organic matter content. The soil material used originated from the Ap and B horizon of a loam soil (Gleyic Luvisol) and from the Ap and P horizon of a clay soil (Calcaric-Vertic Cambisol). Sieved aggregates of 1–2 mm size were filled into vessels and inoculated separately with two earthworm species: the anecic detritivorous Lumbricus terrestris and the endogeic geophagous Aporrectodea caliginosa . The casts of both species were collected for the determination of chemical (total carbon, organic carbon, CaCO 3 , C-to-N ratio, pH) and physical factors (particle size distribution, water stable aggregation, tensile strength). These data were compared with those of natural and remoulded (physical data only) soil aggregates which were not influenced by earthworms. Remoulded aggregates were artificially formed simulating mechanical processes in the earthworm gut. Differences were detected between the earthworm species in the same soil as well as between casts of the same species but from different soils. The contribution of earthworm activity to the cast stability depends decisively on the original composition of the parent soil. The tensile strength of casts was positively correlated with the clay and carbonate content of the parent soil. For the water stable aggregation the correlation was inverse. Moulding processes in the earthworm gut destabilize the soil structure but at the same time biochemical processes act as an antagonistic stabilizing system. The more sensitive the parent soil is to physical disturbance the more effective is the casting for the water stable aggregation but less effective for the tensile strength.

Morphological, physical and biochemical characteristics of burrow walls formed by earthworms

Abstract The influence of two anecic earthworm species, Lumbricus terrestris and Aporrectodea giardi, on the soil adjacent to their burrows was studied in the laboratory. The morphological, physical and biochemical characteristics of the burrow walls were compared with those of casts and surrounding soil by scanning electron microscopy and measurement of water stable aggregation (WSA), enzymatic activities and elemental content (C and N). For both species, we observed a reduction in porosity in the inner layer and to a lesser extent in the outer layer of burrow walls as compared to the surrounding soil. This is apparently due to the fine texture of subsurface casts constituting the inner walls, and to the compaction occurring during burrow formation and use. In contrast, the WSA of the burrow walls was not increased compared to the surrounding soil. Enzymatic activities and C and N content of burrow walls and casts were enhanced compared to the parent material. The behaviour of earthworms in, e.g. incorporation of litter into burrows, selection of the finest soil particles providing adsorption sites for enzymes, re-using burrows resulting in a frequent input of mucus to the burrow walls, may explain the observed differences. These differences were more or less pronounced depending on the morphoecological characteristics of the earthworms. The results indicate that earthworm burrow walls may influence the movement of water and solutes from channels to soil matrix and vice versa and may also have a great impact on microbial activities.

Importance of food quality on selected enzyme activities in earthworm casts (Dendrobaena octaedra, Lumbricidae)

Dehydrogenase (DHA), acid (SPA) and alkaline (APA) phosphomonesterase activities in the casts of Dendrobaena octaedra were analysed while the animals were oAered one of six diAerent food sources. The food consisted of air dried leaves of dandelion, lupin, rye, alder, beech and larch. The food consumption rate of the earthworms lay between 11.1 mg (dandelion) and 0.3 mg dw g ˇ1 fw d ˇ1 (larch) while the cast production varied between 252 mg (dandelion) and 835 mg dw g ˇ1 fw d ˇ1 (beech). A deterioration of the food quality caused a reduction of the food consumption rate, but simultaneously the mean turnover rate of soil aggregates was enhanced. The enzyme activities were influenced by the food which aAected the specific nutrient state of the casts. DHA, SPA and APA were significantly correlated with the organic C and the total N content of the casts. Interenzymatic correlations illustrated the applicability of the three enzyme activities as useful indicators of the influence of earthworms and their food on soil quality. 7 2000 Elsevier Science Ltd. All rights reserved.

Nutrient content of earthworm casts influenced by different mulch types

Abstract 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.

Soil structure rehabilitation of arable soil degraded by compaction

Abstract Soil degradation, especially compaction, due to wheeling with heavy machinery is a problem on arable land, which may rise in the future due to increasing weight. In a combined laboratory and field experiment, the rehabilitation of soil structure was investigated. We tried to differentiate between the rehabilitating effects of intrinsic soil processes and that of biological activity, especially earthworm burrowing. Therefore, undisturbed soil monoliths were taken in spring 1997 from arable land, which was compacted in spring 1995. All monoliths were taken from an agricultural field under conventional tillage (CT) or conservation tillage (CS). One part of the field was compacted six times by repeated wheeling with 5 Mg wheel load at one date in spring 1995, another part remained uncompacted. After defaunation, part of these soil monoliths had been inoculated with individuals of anecic Lumbricus terrestris , or endogeic Aporrectodea caliginosa , or remained uninoculated and were stored for 6 months. Using X-ray computed tomography for analysis, the structural parameters total void length, total void volume, tortuosity, and continuity of the monoliths were quantified. In the case of earthworms, the development of void length and void volume over the investigated time was calculated. Intrinsic soil processes have a strong influence on soils, which can obviously lead to a “natural compaction”, as shown for the 1997 uncompacted monoliths. The reduction in total void length, total void volume, and tortuosity appears to be intensified by tillage operations and field traffic. Compacted soil monoliths showed a clear reduction in the parameters in 1995 after the compaction event, but showed an increase in 1997. This suggests a considerable soil structure rehabilitation during this time. This rehabilitation might be more the result of intrinsic soil processes and biological activity than of soil tillage, especially plowing. The increase in the parameters values was obviously higher in soil from CS plots. Depending on their ecology, burrowing activity of lumbricid worms can be affected or not by a 2-year-old soil compaction. Burrowing activity of anecic L. terrestris seems not to be affected negatively, whereas endogeic A. caliginosa appears to have a reduced burrowing activity in formerly compacted soil. The effect of tillage systems on earthworm burrowing parameters appears to be minor. The combination of intrinsic soil processes and earthworm burrowing activity has a positive effect on soil structure rehabilitation after a heavy compaction event. But it has to be underlined that the effects of the compaction event are visible in earthworm burrowing activity even 2 years later.

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.

Influence of mulch and soil compaction on earthworm cast properties

Abstract 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 1.5xa0Mgxa0m−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.

Influence of food quality on the physical and chemical properties of detritivorous earthworm casts

Abstract Laboratory experiments were conducted with Lumbricus terrestris , Lumbricus rubellus and Dendrobaena octaedra to study the effects of different food sources on physical and chemical cast properties. Earthworm species were kept separately in special microcosms filled with a loamy soil and offered leaves of dandelion ( Taraxacum officinale ), lupin ( Lupinus polyphyllus ), rye ( Secale cereale ), alder ( Alnus glutinosa ), beech ( Fagus sylvatica ) and larch ( Larix decidua ), diets which differed in palatability, C/N-ratios and secondary plant compounds. Cast production was monitored in relation to earthworm species and food. Enzyme activities (acid and alkaline phosphomonesterase), texture, water stable aggregation and tensile strength of casts were compared with those of the soil. Water stable aggregation was influenced by the food source and the earthworm species. The tensile strength of the casts was also species specific. Although D. octaedra produced the highest and L. terrestris the lowest amount of water stable aggregates, the tensile strength of the casts was lowest for D. octaedra and highest for L. terrestris .

Longterm effects of soil compaction and tillage on Collembola and straw decomposition in arable soil

Summary Soil core samples were taken from May 1996 to October 1996 at four week intervals to assess the longterm effects of compaction due to soil tillage on Collembola in arable land. Two different tillage systems were studied: conservation tillage (CS) with rotary harrowing to 120 mm depth and conventional tillage (CT) with a mould board plough to 300 mm depth. Soil compaction was achieved by wheeling with graded loads: 0t, 2 × 2.5t and 6 × 5.0t (wheeling frequency × wheel load) in early spring 1995. Litter decomposition rate was investigated by the minicontainer-method, using two different mesh-sizes: 20 μm (excluding mesofauna) and 500 μ (including mesofauna). The substrate used was winter wheat straw, corresponding to the crop cultivated on the field. We recorded 25 species of Collembola. The abundance of Collembola during the growing season was at a minimum in June in both tillage systems. Thereafter, numbers of individuals increased, probably due to better nutrition. Mesaphorura krausbaueri s.l. was eudominant in CS. In CT Folsomia fimetaria and M. krausbaueri s.l. reached high abundances at the end of August. Harvesting and tilling supported population growth in CS, while numbers in CT decreased. The collembolan species showed different preferences in regard to the tillage system and the grade of compaction. During the first 4 weeks of exposure the decomposition rate of straw was highest. The decomposition rate in the minicontainers with 20 μm mesh-size was higher due to better moisture conditions for the microorganisms. After harvest and tilling the decomposition rate increased, especially in the CS-plots, because of aeration and incorporation of residues. Population fluctuation in the minicontainers was caused by migration of Collembola in response to changing moisture conditions. The main species in the minicontainers were large and mobile. Compared to the surrounding soil, species diversity was reduced.

Tillage systems and soil compaction—their impact on abundance and vertical distribution of Enchytraeidae

Abstract We quantified the development of Enchytraeidae (potworms) abundances and vertical distribution in mechanically stressed soils for 1 year. To assess the effects of soil compaction due to cultivation practice on arable land, two agricultural locations were chosen, differing in soil type, annual rainfall, and soil tillage: (1) conservation tillage (CS) with rotary harrow and conventional tillage (CT) with plough, (2) conventional tillage with spading machine in two depths (CT (shallow) and CT (deep)). Three plots of each tillage system were mechanically compacted by wheeling with graded loads: 0 t, 2 × 2.5 t, 6 × 5 t (wheeling frequency X wheel load) in early spring 1995. CS had a positive effect on the abundances. The different tillage depth of the systems used influenced the vertical distribution. Soil compaction resulted in significantly lower individual numbers and a disturbed vertical distribution. The abundances did not regenerate in one annual cycle on the mechanically compacted plots but vertical distribution did. Because of the low abundances, the Enchytraeidae on the compacted plots cannot fulfil their important function in microstructure development and their effects on soil properties. Furthermore, there are hints towards an increased sensitivity to soil frost events in compacted CT plots.