Pcdobiologia 35. 185-190 ( 1991) Gustav Fischer Yerlag Jena Zoolog1sches I nstitut, Technischc Universitiil Braunschwcig 1, lnstllut fiir Bodenbiologie. Forschungsanstalt fiir Landwirtschaft, Braunschwcig. Federal Republic of Gcrmany2 A method for studying the morphology of earthworm burrows and their function in respect to water movement STl:FAN SCHRADER 1 and MONIKA JosCHK0 2 With J figures ( A1.:ccptcd 90-10-30) 1. Introduction or The development nr the method we want to present was initiated by the question how earthworm burrows affect water movement. EHLERS ( 1975) among others swdied lhc effect or earthworm burrows in the lield. Since his basic work interest in this scope has 111creased. Recently a technique was developed lo measure percolation in individual burrows 111 the field (EDWARDS et al. . 1989). However. lillle is known yet about the effects of burrow morphology on the percolating water front. By the method of direct visual observation ~ome questions concerning the interrelationship between soil fabric and water movement may be studied more comprehensively. In order LO study the whole burrow system previous authors like EVANS ( 1947). BHATI"t (1962) and MARTIN ( 1982) used planar glass cuvetles. The advantage or this technique •:onsists in the reduction of the soil volume to approximately 2 dimensions. Thus it is possible to corn bi nc 2 kinds of studies: ( 1) A morphological study of changes in the soi 1 fabric due to the burrowing activities of the earthworms. (2) A functional study of water movement in relation to burrow morphology. With the application of nuorescenl stains it 1-, possible to mark the water front and to follow its movement. A simple and effective p..:n:olation ..:4uipmcnt in combination with the. planar cuvelle technique is described. 2. Material and methods 2.1. Planar cuvette technique 2.2. Percolation equipment The planar cuvelles 1.:01N~ted of 2 glas~ sheets ( 14 cm x 14 cm) which were held apart to 0.5 cm hy ::! plaster sticks on hoth sides lach cuvette was filled with soil aggregates (fraction I lo 2 mm) following Al.TI MUI.I.ER and VoR1111n1 ( 1987). As soil ma1erial we used the Ap horizon of a Parabraunerde from lo.:ss fluvisol). It was moistened before filled into the cuvellcs. The maximum possible water content \\JS found to be 17"'• up to which aggregates did not smear. The bulk density was I.) g•cm3. Two ad uh 111dl\ 1duals (with clitcllum) of Allolohoplwrn rnl(~11111.1a (SA VIGNY. 1826) were placed 1)n the soil surface. After CO\enng the cuvellc \\'tlh laboratory film (Paralilm) the lower part rcma111cd open ~landing 1n a tub filled with soil. Thus the earthworms could leave the planar cuvcttes after burrowing through ll The burro" system and the changes in soil fabric were documented by drawing :rnd photographing from both sid.:s ofthecuvette. Usually after 4 days the worms had left the cuvcttc. Pcdobiolog1a 35 ( 1991) 3 185 linked valves hose pipette filled with stain solution . . . ' pipette support I' ' I t ' syringe ·~ glass beads . ··.'1. :;:: . plaster stick planar cuvette burrow system worm cast ··~·: ~:,:.:. : :~ ·;.. : : sol/ matrix vessel Figure I Percolation equ1pmenl. schcmaucally Figure I sho"' schcmaucally the pi:reolation equ1pmcnl. With the help of 2 syringes connected wuh a hattcry of 8 p1pc.:tlc> a stain solution was applied to the soil surface. The soil surface was covered \\ llh a layer of glass beads (4 mm in diameter) in order Lo protect the surface from slake. Furthi:rmore the.: gla'' beads allow a more uniform distribution of the stain solution. The .14uc.:ou, ,t.iin solution contained the nuoresccnt dye rhodamine B (C.I. 45170). At a ..:onccntration or I g I 'do"nward fingering became obvious. During the coursi: of I hour 2 ml of the >tain solution were applied 6 times to the soil surface (each pipette contributed 250 µI per application). This amount 1s i:qu1valcnt to natural rainfall of about 3.3 to 20 mm h- 1• According to BrvF.'.'.' and GrR~IA "" ( 1982) intcns1ues of I to I 0 mm h- 1 may mitiatc macroporc now. After each applicauon the stained percolation front was photographed under UV light with a "a\dCngth or 160 nm (Hl·RAHJS. Fluotest-Forte) 3. Results 3.1. Burrow morphology The burrowing ac11vuy of the earthworms caused various morphological changes of the soil fabric. They can be divided tnto 5 types as shown in Figure 2 (in order to facilitate a comparison between the 2 side~ of the planar cuvette the back side (fig. 2. b) is drawn mi rror-111 verted ). The burrow system (fig. 2) consists of 3 vertical, somewhat tortuous channels of about S mm diameter. In between them the soil fabric remained unchanged. Earthworm cast were put near the surface and along the burrow system sometimes plugging the channels. Furthermore casts may cover the inside of a channel as it can be seen on the left one (rig. 2.a). In this case the channel remains continuous. The middle one is also continuous and well stabilized mainly by a wall of slightly compacted aggregates. More strongly compacted aggregates generally lost their original shape. Only by comparing both sides of the cuvette it is possible to rind out which part of a channel is continuous and which part is plugged by casts. It is estimated that more than 70% of the burrow system are continuous. 3.2. Percolation experiment The following experiment showed the passage of the stain solution after each application. The lst and 2nd application demonstrate that in the unsaturated soil the area directly adjacent to the earthworm channel provides the preferential pathway for the percolating water. Obviously both plugging casts and more strongly compacted walls may function as a 2cm b Figun; 1. Burrow system of Allo/oboplum1 rnligi110.w (SAVIGNY. 18:!6). a. Front side. b Back side. m1rror-111vertcd. D Unchangcd soil fabric. Earthworm cast. Slightly compactcd aggregate~. More ;lrongh compacted aggregates Conttnuou> channel (mucus trace on the glass sheet). Pedobiologia 35 ( 1991) 3 187 barriers. so that the continuous part in the middle or the left channel became nonconducting (fig. 3). In the lower part of the right hand burrow the water of the 3rd and 4th application was dammed up by more strongly compacted soil. During the 5th and 6th application the stained front became wider and branched out horizontally because field capacity was reached. Comparing the stained water front with the burrow morphology it becomes evident as to why a channel is conducting or nonconducting. a 2cm b Figure 3. Stained fronts of the percolating water in dependence on the burrow system (rhodam111e B. I g I). a. Front side. b Back side. m1rror-rnvencd. D Arter the 1s t and 2nd application: I: 4 ml. .. After the :lrd and 4th application: I: 8 ml. After the 5th and 6th application: I: 12 ml. 4. Discussion Morphological changes to soil fabric may be studied easily and directly in planar glass cuvcues filled with soil aggregates or defined size fractions. AL TEMULLER and VORBACH ( 1987) introduced this technique when they investigated the effect of root growth on the soil fabric. They adjusted the arrangement of the cuvettes to root growth to get a favourable output. In our study the burrowing of the earthworms caused 5 different morphological features. The slightly compacted soil along the earthworm channels was the preferential pathway of the percolating water. This result is in agreement with the observations of SrEERSCHNEIDER e1 al. ( 1988). Using a suspended stain (pigmosole-green) they detected preferential now in the compacted parts of an unsaturated sandy soil. According to GRAFF ( 1983) burrowing occurs by the ingestion of soil but mainly by pressing of soil material aside The interrelationship between the morphological and physical 188 Pedob1olog1a 35 ( 1991) 1 conditions of the soil has often been neglected. In this study possible effects of the burrow morphology in respect to water movement became visible. During recent years scveral stains have been used for studying water movement in soil: e.g. methylene blue (Bou~tA & Dq:.KER. 1978: SMETTEM. 1987). ultramarine blue (EHLERS. J 975). pyranine {0MOTI & WtLD. 1979). SMETTEM and TRUDGILL ( 1983) studied the properties of 2 nuorescent stains: sulpho-rhodamine Band lissamine yellow FF. They are resistant to photochemical decay and exhibit a stable nuorescence over a wide pH range (pH 3.5 to 10). The choice of a stain must be determined by its adsorption and solubility or characteristics. Lack a staining in the soil docs not necessarily imply a lack of water 1110\emenl (BOUMA & DEKKER, 1978). ALTEMtiLLER ( 1989) made up the properties of several nuorescent stains and their possible application. He recommends rhodamine B for staining. of soil samples because of its low adsorption by clay and high solubility in water. Fluorescent stains have the advantage of not being much affected by the natural soil colour and mark the stained areas more than diachromes. The use of nuorescenl staining together with the cuvctte technique provide a direct insight in the nature of water now in dependence on earthworm burrows. 5. Acknowledgements \Ve would like to thank Prof. Dr. 0. LARIN!(. Zoological Institute. Techntcal University Braun 'chwc1g. for his support and Prof. Dr. H .-J. AL TE~tOLLl:R. I nstitutc of Plant Nutrition and Soil Sc1cnc..:. FA L Braunschwc1g. for hi.:Jprul comments on the manuscript. Also. we arc grateful for rcceiv111g rc,c;irch funds from the German Research Foundauon (Deutsche Forschungsgcmcin5chaft. DFG. L1 226 7-1) which made 1h1~ ~tudy possible. For reviewing the manuscript we thank Mr. R 1-ftel(S. 6. References At Tt:MOLLER. H .-J.. 1989. Zur nuoreszenzmikroskopischen Darstellung. biologischcr ObJektc 111 Boden-Di.innschliffen. Mitteilgn. Disch. Bodenkdl. Gesellsch. 59. I. 517-522. At.TEM01.1.1:.R. H.-J.. & A. VoRBACH. 1987. Fluoreszenzmikroskopische Wurzeluntersuchungcn im gewachsenen Bodenkontakt VDLU FA-Schriflenreihe 23. KongreClband. 183-193. 13r\'r-..;. K. & P. GF.R~tAN"I. 1982. Macropores and water now in soils. Water Resources Res. 18. 5. JJ 11-1325. B1tA TTt. H. K .. 1962. Experimental study of burrow111g acuvitics of earthworms. Agriculture Pakistan 13. ~. 1-16 Bon11\. J. . & L. W. DEKKl·R. 1978. A case study on 1111iltration 11110 dr) cla) soil. I. Morphological observations. Geoderma 20. 27-40. f-.l>W·\RDS. W M .. M J. Stlll'IT"t o. L.B. OWENS & L. D. NORTON. 1989. Water ;111d nitrate movement 111 carlh\\orm hurrows within Jongterm no-till cornfields. J. Soil & Water Cons. -'4. 240-243 l.11u RS. W .. 1975 Obscnallons on eartll\\orm channels and mliltrauon on tilled and untilkd locs, ,oil Soil Sc1 119. 3. 2-12-249 h '"s. t\. C .. 1947 A method or -;tudy1ng the burrow111g activ111c~ or cartl1\\orms. Ann. Mag. nat. J Ji,1. 11. 14. 643-650 (;1< .\J ~-0 .. I9 XJ. Un>cre Rcgcnwurmcr - Lcxikon i'lir Frcundc dcr Bodcnbiologie. I lannovcr. 112 pp. \I \l<T1'. '-. .\. 1982. The 1ntcract1on between organic matter in soil and the burrowing auivity of 1hrec spcc.:1c, qf carth,qmn> (Oilgochacia. Lumbnc1dac). Pedobiologia 24. 185- 190 o~mTt. U . & /' WtLD. 1979. Use of nuorescent dyes to mark the pathways of solute movement through soil' under leaching conditions I Laboratory experiments. Soil Sci. 128. I. 28- J3. S\IFTTDI. K R J. 1987. Characterization of water entry into a soil with a contrasting tcx1ural class. ,p;11i;1J \anab1lity of 1n!iltra1ion parameters and 111nucncc of rnacroporosity. Soil Sci. 144 . .~ . 167- 17-l -. & S. T. TRUD0tt.L. 1983. An e\'aluat1on of some nuorescent and non-nuoresccnt d)cs in the 1dcn111icat1on of water transmission routes in soils. J. Soil. Sci. 34. 45-56. Sl'Ft RSCll~EIDLR. R .. H. RIN<il & K. II. HARTGE. 1988. Feststoffverlagerung in cim:r homogcm:n Sand pack ung <1m Bcispicl e111cs suspcndicrten farbstoITes. Mitteilgn. Dtsch. Bodenkundl. Gescllsch. 57. 237-242 Pcdobiologia 35 ( 199 I) J 189 ynopsis: Original SCll'lllt}h paper SCHRADER. ST.. & M. Josc11i.:o. 1991. A method for studying the morphology of earthworm burrows and their function in respect to water movement. Pedobiologia 35, 185-190. A method is presented which allows the simultaneous investigation of soil fabric and water movement. Planar glass cuvettes were filled with soil aggregates to study morphological changes of the soil fabric due to the burrowing activity of Allolobophora caliginosa. A simple percolation equipment is introduced for applying a de!ined amount of water lo the soil surface. The migrating water fronts were ,wined b) rhodam111c B. Under UV light this nuorcscent stain showed the preferential pathwa)' of the percolating water in d.:pendcm:c on burrow morphology. This method is or value in observing directly changes 111 soil fabric and water now. Key words: Earthworm burrows. soil fabric. water movement, planar cuvelle. percolation equipment. nuoreseent staining Address of the corresponding author: STEFAN SCHRADER. Zoologisches lnstitut. Technische U111vcrsitat. Pockelsstr I Oa. W-3300 Braunschweig. Federal Republic of German). 190 Pedobiologia 35 ( 1991) 3