Maataloustieteellinen A ikakauskirja Vol. 62: 357—367, 1990 Conventional and organic cropping systems at Suitia VII: Earthworms VISA NUUTINEN and JARI HAUKKA* Agricultural Research Centre, Institute of Plant Protection, SF-31600 Jokioinen, Finland Abstract. The earthworm communities were studied in an experiment with eight cropping systems (four conventional and four organic), carried out on silty clay soil. Earthworms were sampled during the three last years of the seven year experiment. Samples were taken with formalin in the autumns of 1986 and 1987 (one replicate of the experiment) and in that of 1988 with formalin and by taking soil-cores (all three replicates). Aporreclodea caliginosa (Sav.) was dominant in all cropping systems. The rest of the iden- tified individuals were Lumbricus rubellus (Hoff.) and L. lerrestris (L.). A few L. castaneus (Sav.) were also found. There were no clear differences in the species composition between the conventional and organic cropping systems. Application of slurry caused a drop in the proportion of Lumbricus. Low total numbers were observed in 1987, possibly due to high winter mortality. In 1988, the average number (and SE) of earthworms was 23 (11.2) 92 (49.8) ind. m~ 2 and their total dry weight 1.0 (0.54) 3.2 (1.53) g m-2 . The average number of cocoons in 1988 ranged from 5 (2.5) to 52.5 (26.3) coc. m-2 . The highest abundances of earth- worms and cocoons were observed in the organically cultivated vetch ley. The differences be- tween the treatments in worm abundance were not statistically discernible. The mean size (mg dwt) of juvenile and adult A. caliginosa was similar in different cropping systems. The abundance patterns of earthworms differed in the replicates. This was related to the confoundingeffects of local water-logging and soil compaction in the field. Consistent differ- ences in the soil conditions of the cropping systems resulting from the activity of earthworms are unlikely. Index words: earthworms, cropping systems, Lumbricidae, Aporreclodea, Lumbricus, water-logging Introduction The alternatives to modern chemicalized methods of crop cultivation rely on active soil flora and fauna. Plant nutrients are not given • Present address: National Public Health Institute, Kal- liolinnantie 4, SF-00140 Helsinki, Finland 5 directly as inorganic fertilisers but in organic amendements, which are mineralized by the soil’s decomposer web. Little or no use of biocides and crop rotations with leys consti- tute an attempt to guarantee the biological ac- tivity of the soil. These practices, it is hoped, bring about fertile soil in a sustainable way. 357 JOURNAL OF AGRICULTURAL SCIENCE IN FINLAND https://www.c-info.fi/en/info/?token=6O4fardin6jn0IfT.I8jTNTwVHI2pgCJ4Tv2qhQ.2pFrgOaxkArrTnf2HHUB2W5hIii4QamYBwWaSBjQHYp0axasioqHeoF4jlRQAuZDY82pe8udGkvKsF_1WZRDSNz81n5_tv1fgS1-jejMcMPDXKTSea2HPwZQ5K7HMLJjSQtNYZjA1zpus6PVYMzSnAphsI-8BMDbM8x1bLdNWBw4W9hlT4kMBwR3kA Abundance of earthworms is one of the par- ticularly desirable soil characteristics (e.g. Arden-Clarke and Hodges 1988), as apart from contributing to the breakdown of or- ganic matter, earthworms ameliorate a num- ber of soil features (reviewed in Lee 1985). The differences between conventional and organic farming are potential effectors of earthworm abundance. The quality and quan- tity of nitrogenous fertilisers are known to af- fect both the abundance of earthworms and the species composition of the earthworm community (Edwards and Lofty 1982, Lofs- Holmin 1983 a, Lee 1985). Crop rotation also affects earthworm populations. For ex- ample, the number of earthworms often in- creases in leys which are not ploughed yearly (Edwards 1983), the leguminous leys being particularly suitable for earthworms (Bates 1933, Boström 1988). The biocides used in plant protection, one prominent feature of conventional high input farming, influence earthworms. The most harmful substances are found among fungicides, whileherbicides and insecticides, in normal doses, seem to be of little or no harm (Andren and Steen 1978, Lee 1985). Below we summarise the observations on the earthworm communities in an experiment where the effects of conventional and organic cropping systems on soil fertility were inves- tigated. The study is merely descriptive. The first sampling was done in the fifth year and the last in the final year of the experiment. All threereplicates were sampled only at the final occasion. As there are no data on the whole six-year rotations of the experiment, the rea- sons behind the patterns of abundance and community composition cannot be discussed withcertainty, nor can the consistency of pat- terns be established. Materials and methods Experiment The experimental field is situated at the Suitia Farm, in Siuntio, Southern Finland (60° 11 'N, 24°10'E). The soil of the field is silty clay (clay-% 51 —62). Details on the characteristics and cultivation history of the experimental field and weather conditions in the area are given in Hannukkala et al. (1990). The experiment, started in 1982, con- sists of eight cropping systems, four organic and four conventional, each having a six-year crop sequence. The number of replicates is three. The cropping systems are nested in the organic and conventional groups of systems. Hannukkala et al. (1990) describe in detail the systems and the experimental design. Earthworms were always sampled on the ‘b’ side in each plot. The cropping systems and their symbols are as follows (applied fertilisers in brackets): Conventional cropping Al = barley monoculture (N-P-K) A 2 = cereal production (N-P-K) A 3 = diverse plant (N-P-K) production B = cattle farm (slurry + N-P-K) Organic cropping Cl = plant production (plant material, composted) C 2 = » » (plant material, not composted) D 1 = cattle farm (slurry, composted) D 2 = » » (slurry, not composted) Similar farm machinery was used in all sys- tems. In organic cropping, no biocides were used, while in conventional cropping various herbicides, fungicides and, to a lesser degree insecticides were applied (Hannukkala et al. 1990). Sampling General Two samples were taken from the both ends of each plot ca. four metres in from the plot margin, avoiding sites where water was stand- 358 ing at the wheel tracks. Thus the sample size per plot was four, and the total number of samples Bx 4 =32 in 1986 and 1987, when only replicate I was sampled, and 3xßx4 =96 in 1988, when all three replicates were sampled. The sample size was not determined by any statistical scrutiny. Four samples per plot were considered sufficient because of practical and economic limitations facing the sampling effort. Sampling was done in August right after the harvest and before cultivations (1986: 27th August; 1987: 27th August; 1988: 15th—18th August). In the plots growing potato, leys or leguminous green manures, the plants were growing during the sampling. Sampling method A wooden frame enclosing a square of 1 m 2 was placed on the ground at the site of sam- pling. Often the frame could not be fitted tightly against the soil surface due to rough- ness and hardness of the soil. Straw and/or growing plants were cut, and plant residues removed from the soil surface. The square was divided into equal halves by stretching an iron wire between opposite sides of the frame. The sampling unit covered an area of 0.5 m 2, from which earthworms were sampled with the for- malin (1986 and 1987) or the combined for- malin/soil core method (1988) (Boucttfi and Gardner 1984). The formalin solution was applied four times. Each time approximately 10 litres was poured from a sprinkling can on the 0.5 m 2 area. 0.25 % solution was used for the first two applications and 0.50 °7o solution for the last two. For 10 minutes after each applica- tion, the emerging earthworms were picked up and placed into small plastic bottles filled with 4 °7o formalin. One person simultaneously sampled both sides of the frame in two adja- cent plots. In 1988, two soil cores (diameter 14.5 cm, depth ca. 20 cm) were taken from the middle of the 0.5 m 2 area after the formalin applica- tion. The soil samples were stored on the field for up to two days before they were taken to the laboratoryand submerged in 4 °7o forma- lin for preservation. About 1 dl of (NaPG 3)6 per 10 litres of solution was added to acceler- ate the dispersion of clay. The samples were kept covered outdoors, and they were mixed gently at intervals of a few days. After four weeks the earthworms and cocoons were wet sieved from the soil samples and preserved in 4 °7o formalin. The soil typically formed small tight clods in the sieving apparatus, and it was found impractical to try to make all of them disperse. It was checked that the clods were not formed particularly around worms or co- coons. Treatment of the material The material was kept in formalinat 10°C for at least four weeks before the identifica- tion and weight determinations. Adults and juveniles were identified according to Sims and Gerard (1985), juveniles only to genus. The only representative of adult Aporrectodea in the field was A. caliginosa; the juvenile Aporrectodea were regarded to be of the same species. The morphs of A. caliginosa (BoucHfi et al. 1988) were not treated separately, nor was the species of the cocoons determined. Only the total numbers and dry weights of worms are reported for 1986 and 1987. After the identification of a worm its for- malin weight was determined. The worms were then dried at 105°C for ca. 24 hours, and their dry weights measured. The weight esti- mates include the gut contents. Thirty earth- worms of the 1986 material were accidentally lost before their dry weights were measured. For them, an estimated dry weight was calcu- lated on the basis of the species-wise regres- sions of dry weight on formalin weight in the rest of the material for 1986. Data of 1987 were used for Lumbricus rubellus. The frequencies per square meter were cal- culated separately for worms and cocoons; for worms the total dry weights were also calcu- lated. Mean abundances for each plot were obtained from the four sample estimates. In 359 each plot, the average size (mg dwt) was de- frequency tables were formed of the pooled termined for adult and juvenile A. caligino- sa, based on the pooled material of 1988. Anova was performed for the plot means of the 1988 material. The original values were log(x+ 1) (dry weights) or square root (num- bers of individuals) transformed to homogen- ize the variances. To evaluate the occurrence of Aporrectodea and Lumbricus in chemical- ly (AI —B) vs. organically (Cl —D2) fertilised cropping systems and in the plots fertilised with slurry (B, Dl, D2) vs. other plots, 2x2 material of 1988. Logistic analysis (McCul- lagh & Nelder 1983) was then performed with the species group as the dependent dicho- tomic variable. The risk level was set at 5 % in all analyses. Results Yearly changes of abundance in replicate I The soil moisture conditions were different Fig. I. Average number (ind. m~ 2 ( +SE)) and total dry weight (g m~ 2 ( + SE)) of earthworms in replicate I (sti- pled: 1986; hatched: 1987; open: 1988). The estimates are the means of four formalin samples. The symbols of the cropping systems are explained in the text. 360 in the three autumns (Hannukkala et al. 1990) and the efficiency of the formalin ex- traction probably was dissimilar in the dif- ferent years. Thus the formalin estimates ob- tained in replicate I are compared only qualitatively. This renders the analysis meagre, but statistical testing is unwarranted. The total catch of individuals in the different years was 315 (1986), 123 (1987) and 232 (1988). Exceptionally high numbers were ob- served in 1986 at A 3 and D 2 (Fig. 1). Com- pared with 1986, the abundance was much smaller in 1987 in A3, Cl and C2. Cl was completely devoid of earthworms, and the three cropping systems had the lowest aver- age of numbers and total dry weights in 1987. In 1988, the abundance of earthworms in A 3 was still very low. This was no longer the case in Cl and C2. Species In 1988, the individuals of Aporrectodea caliginosa (Sav.) comprised 86 % of the ma- terial (total of 1234 ind.). The rest of the iden- tified individuals were Lumbricus terrestris (L.), L. rubellus (Hoff.) and juvenile Lumbri- cus. In addition, a few individuals of L. castaneus (Sav.) were found. 66 % of all Lumbricus were juveniles identified only to genus. In all cropping systems, the majority of the individuals was usually juvenile A. caligino- sa, while adults of the species always formed the largest proportion of the total dry weight (Fig. 2). The proportion of the combined Lumbricus of the total number of individu- als was lowest in B (1.4 %) and highest in Cl (12.4 %). The corresponding figure for the to- tal dry weight was highest in D 2 (14.7 %). Logistic analyses did not reveal statistically discernible difference in the occurrence of Aporrectodea and Lumbricus in organically vs. chemically fertilised cropping systems (p =0.08). In the cropping systems where slur- ry was applied, the proportion of Lumbricus was smaller than in the others (p< 0.001). Abundances in 1988 In the autumn of 1988, when the whole ex- periment was sampled, the estimates of the to- tal earthworm dry weights (g m-2 (SE)) ranged from 1.0(0.54) (A3) to 3.2 (1.53) (D2) (Fig. 3). For the average number of individu- als (ind. m-2 (SE)) the lowest measurement was 23 (11.2) (Al) and the highest 92 (49.8) (D2) (fig. 3). The high mean abundances of D 2 was due to the exceptionally high values in replicate 111. There were no statistically dis- cernible differences in the abundances be- tween organic and conventional groups, and the same holds for the cropping systems within the organic and conventional groups (Table 1). The only significant source of variation Fig. 2. Proportions of different groups of earthworms in the cropping systems in 1988. All individuals from the three replicates have been pooled. ‘Biomass’ refers to total dry weight. Dark grey: juvenileA. caliginosa; light grey; adult A. caliginosa; open: Lumbricus sp.; hatched: unidentified individuals. N =number of individuals. The symbols of the cropping systems are explained in the text. 361 was the interaction between replicate and group of systems (Table 1). The average num- ber of cocoons (coc. m~ 2 (SE)) ranged from 5 (2.5) (A3) to 52.5 (26.3) (D2) (Fig. 4). Again the high estimate in D 2 was due to replicate 111. Uniformly high cocoon numbers were ob- tained in Dl . No ANOVA was performed on Table 1. ANOVA table for the number of earthworms (ind. m~ 2) and their total dry weights (g m~2 ). ‘Group’ refers to the organic and conventional groups of systems, ‘treatment’ to the cropping systems within the two groups. cocoon data, owing to the great heterogenei- ty of variances. Size of A. caliginosa The mean dry weights (mg (SE)) of adult A. caliginosa in different cropping systems were between 96 (8.6) and 136 (22.6). For juveniles the minimum average dry weight was 18 (1.5) and the maximum 32 (4.8). Organic and conventional groups did not differ (adults: p = 0.509; juveniles: p = 0.085), nor did the cropping systems within the organic and conventional groups (adults: p = 0.279; juveniles: p = 0.620). Discussion Sampling method The formalin method did not always work satisfactorily in the prevailing conditions. Par- ticularly at the sites where the soil was un- usually compacted, and when the soil was very moist, infiltration of the solution was poor. This made the picking of worms difficult, and at times the solution spread outside the sampling square. Very often no earthworms emerged during the last application of forma- Fig. 3. Average number (ind. m~2 (±SE)) and total dry weight (g m-2 (±SE)) of earthworms in 1988. The esti- mates are based on three replicate means each based on four formalin/soil-core-samples. The symbols of the crop- ping systems are explained in the text. Fig. 4. Number of cocoons (coc. m~2 (±SE)) in 1988. The estimates are based on three replicate means each based on four soil-core-samples. The symbols of the crop- ping systems are explained in the text. Source df p-value ind. m-2 dwt gm 2 Group 1 0.275 0.689 Treatment (Group) 6 0.443 0.442 Replicate 2 0.131 0.165 Replicate x Group 2 0.037 0.036 362 lin, and it seems evident that less solution would have been enough. Yearly changes in abundance There is no guarantee that the efficiency of the formalin method was similar in the dif- ferent weather conditions of the three au- tumns. The low total catch of individuals in 1987 may reflect a real population low or a failure in sampling caused by the unusually wet conditions where the sampling was done, or a combination of the two. One possible ex- planation for the low numbers in 1987 is the very cold winter of 1986—87 (Hannukkala et al. 1990, Fig. 5). The frost that occurred about a week before the sampling in 1987may also have affected the result. Winter mortality of earthworms is known to be high in North- ern Scandinavia (Boström 1988), and a simi- lar reduction in earthworm abundance on arable land was observed elsewhere in South- ern Finland during the same period (personal observations). It is difficult to distinquish the effects of weather conditions from those of the crop se- quence, and the consistency of any possible pattern cannot be established as only part of a crop sequence was sampled once. The low abundances in 1987 at A3, Cl and C 2 may have been due to the phase of the crop se- quence; potato was grown in all of the plots that year. As the estimates in two of the plots were no longer low in the following year, it is possible that the formalin extraction sim- ply worked particularly poorly in the potato plots in 1987. However, repeated cultivations in potato fields are known to be harmful to soil fauna. In addition, low dehydrogenase ac- tivities and low levels of nitrificationwere ob- served in 1987 in the potato plots (Heinonen- Tanski 1990), indicating low overall biologi- cal activity in the soil. More intensive sampling than here is needed to monitor earthworms in agricultural rota- tions. Earthworm populations react rapidly to changes in the environment (Lofs-Holmin 1983 a, Boström 1988), and non-conclusive sampling may lead to erroneous conclusions. Species The earthworm fauna of the experimental field is typical of cultivated soils of Southern Finland (Terhivuo 1988). The dominance of A. caliginosa is not surprising. In its whole area of distribution, it is among the species most able to persist in arable land (Edwards 1983). This is due to its endogeic habits. It feeds on decomposing below ground organic matter, which is available even under heavy cultivation. Due to its facultative diapause (Evans and Guild 1947), the species can tolerate the relatively strong and rapid tem- perature and moisture changes typical of cul- tivated soil. Good ability of regeneration in- creases the ability of the population to recover from the direct damage which cultivation may cause to individuals (Boström 1988). Litter dwelling (epigeic) species were scarce. They were represented to any considerable de- gree only by L. rubellus. This is understand- able, as the cropping systems poorly provide the litter habitat which the species needs. Deep burrowing (anecic) L. terrestris was also very scarce. The populations of epigeic and anecic species have evidently been low already dur- ing the previous cultivation (Hannukkala et al. 1990) of the field. Either the cropping sys- tems are not suitable for them, or the time from the start of the experiment was too short for them to enter the field. The following points support the first alternative in the case of L. terrestris. In October 1989, the small piles of mixed surface casts and collected litter, a typical sign of the presence ofL. terrestris, were abundant on the ditch banks of the experimental field. As L. terrestris is able to disperse rapidly over relatively long distances (Mather and Chris- tensen 1988), it is reasonable to assume that the prevailing conditions on the field keep its populations low. The ploughing destroys its permanent burrows and buries the majority of the surface residue, the normal food of 363 adultL. terrestris. Results obtained elsewhere show that when organic farming is accompa- nied by minimized tillage, the populations of L. terrestris do increase (El Titi and Ipach 1989). Another negative factor is the locally strong compaction of the experimental field. Compaction affects adversely also A. caligi- nosa (Boström 1986), but it seems to cause more difficulty to theburrowing of L. terres- tris (Rushton 1986, personal observations). It has also been shown by Andersen (1980) that slurries, the animal manure of our experiment, can have deleterious effects on anecic earth- worms. He related this to the toxicity of the liquid penetrating into the burrows. It is pos- sible that the low relative proportion of ge- nus Lumbricus, which was observed in the slurry amended systems in thepresent study, is due to the same effect. Abundances in 1988 As discussed elsewhere in more detail (Korva et ai. 1990), the variation in the topography and drainage of the experimental field introduced an uncontrolled factor into the experiment. Parts of the field were pe- riodically water-logged and covered with ice during winters. The areas with worst drain- age problems were in the flat area covering the organic side of replicate II and the majority of the organic side in thereplicate 111 (for the field map see Hannukkala et al. 1990, Fig. 2). During the sampling in 1988, thepoor soil structure in these areas was evident. The highest total dry weight of the field was observed in D 2 (organic vetch mixture) of replicate 111. The plot lay on the sloping re- gion, outside the flat area. The plots with the second (B; conventional ley) and third (Dl; organic vetch mixture) highest abundances of replicate 111 were both right next to D2. In replicate II the abundance was highest in A2 (conventional barley), which lay towards the south end of the replicate, where the soil sur- face starts to slope to the river. Also in repli- cate II the plots with the second (B; conven- tional ley) and third (Al; conventional bar- ley) highest abundances lay next to the plot with the highest abundance. In replicate I the highest abundances were considerably lower than in II and 111, and there was no clear area of high abundance. The drainage problems in the central area of the field possibly caused the very different response of earthworms in the replicates, and thus contributed to the significant interaction between replicate and group of systems (Ta- ble 1). Earthworms are known to flee from flooding, and areas of prolonged water-log- ging have low population densities and little signs of earthworm activity (Boone et al. 1976, Carter et al. 1982). Further, poorly drained clayey soils easily get compacted, and this also stresses the earthworms (Boström 1986). In general, the abundance of earthworms in 1988 was of the same order of magnitude as reported for cultivated soils elsewhere in Scandinavia. Boström (1988) studied earth- worms in an experiment on cultivated loam soil with sampling methods comparable to ours. In her study the number of earthworms under fertilised and unfertilised barley were on average slightly over 30 and in grass ley slightly below 50 ind. m-2 . The abundance was highest, a little over 160 ind. m-2 , in lu- cerne ley. Comparison with our biomass esti- mates is difficult because of methodological differences. A. caliginosa was as dominant as in our material. The effects of different fertilisers on earth- worm abundance have usually been attribut- ed to changes in the amount of available food (Edwards 1983). As fertilisers affect the plant production, they also tend to influence the amounts of crop residues below and above ground, the food of detrivores. Organic fer- tilisers, such as farmyard manure (FYM), slur- ries and green manures, do not only influence plant production but are themselves earth- worm food. The variety of fertilisers and the conditions in which they are used have led to differening conclusions on the effects of fer- tilisation on earthworms, particularly so in the case of inorganic fertilisers (Lee 1985, Bo- ström 1986). Edwards and Lofty (1982) 364 reported a positive correlation between the amounts of inorganic N applied and the abun- dance of earthworms in crop cultivations. The increase was strongest in the endogeic species, which consume organic matter below ground. The greatest total increase was observed when both inorganic N and FYM were applied, this being partly due to the increase in L. terres- tris. Lofs-Holmin (1983 b) studied earth- worms in a clayey field, and did not observe any relationship between the quality or quan- tity of inorganic N-fertilisers and earthworm abundance. A rapid temporary increase in the population density of A. caliginosa after FYM application was observed (Lofs-Holmin 1983a). One factor contributing to the relatively uniform abundances in our cropping systems in 1988 could be that the low crop yields, and thus lower production of food for earth- worms, in the organic plots (Korva and Varis 1990) were partly compensated by the organic manures and higher production of weeds in organic plots (Kauppila 1990). As there were no measurements of the soil or- ganic matter content, this assumption cannot be verified. The similar size of the dominant A. caliginosa in different cropping systems suggests that the living conditions in them were not very different with regard to the en- dogeic earthworm. However, the high num- ber of cocoons together with the high propor- tion of juvenile A. caliginosa in the vetch mix- tures D 1 and D 2 fertilised withslurry indicate to strong production of offspring in these sys- tems. It is known that cocoons are produced more by earthworms feeding on animal dung than by those fed with plant litter (Evans and Guild 1948). In addition, soil conditions un- der leguminous leys are regarded suitable for annelids, as the tap roots of legumes penetrate deep and do not dry the top soil as heavily as grass roots (Bates 1933, Lagerlöf et ai. 1989). A number of fungicides potentially harm- ful to earthworms were used at Suitia in con- ventional cropping. The seed of the cereals was treated with mercury and tiophanate- methyl based fungicides. In 1987, tiabendazol was applied on potato seed tubers, and in 1984 and 1987, potato was sprayed with copper oxychloride. All four substances are harmful to earthworms even at normal dose rates (Lee 1985), although we do not know wheth- er the effects of seed treatments have been studied. The effects of the applications can- not be judged reliably on the basis of our ma- terial. In farm surveys, organic farms were ob- served by Gehlen and Schröder (1985) to have higher earthwormabundances than con- ventional farms, while Kleyer and Babel (1984) did not find clear differences in the soil characteristics of organic and conventional farms caused by the earthworms. Our results cannot be compared with these in any straight- forward manner, as the studied agricultural rotations, cultivation practices and environ- mental conditions differ widely. Trolldenier (1987) reviewed the literature on the soil life in different cropping systems and concluded that neither of the two farming systems (con- ventional vs. organic) is definitely ‘superior’ from the soil biological point of view. Our es- timates of earthworm abundance from 1988, together with the slight qualitative differences in the earthworm communities, seem to be in line with his view. It is unlikely that there would be any consistent differences in the soil conditions of the cropping systems at the Suitia experiment which could be explained by the activity of earthworms. However, bearing in mind the considerable uncontrolled varia- bility in the soil conditions of the field, the result cannot be generalized. Acknowledgements. We thank Rauno Ukkola, Erja Huusela-Veistola and Simo Veistola for their help with the sampling and treatment of the material, Jukka Kor- va and Asko Hannukkala of the Suitia Project for help- ful discussions, Jari Heikkilä, Helvi Heinonen-Tanski and Veikko Huhta for commenting on the manuscript, Sevas- tiana Kuusamo for improving the English and the per- sonnel of the Suitia Farm for logistic support. The study is a part of the project ‘The role of soil macrofauna in field crop cultivation’ funded by the National Research Council for Agriculture and Forestry of the Academy of Finland. 365 References Andersen, C. 1980. The influence of farmyard manure and slurry on the earthworm population (Lumbri- cidae) in arable soil. In: Soil biology as related to land use practices (Ed. D. Dindal), pp. 325—334. Proc. Vllth Int. Soil Zool. Coll., Syracuse, USA. EPA Washington DC: 560/13 —60—038. AndrEn, O. & Steen, E. 1978. Bekämpningsmedlens in- verkan pä markens organismer. 1. 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Kasvinsuojelun tutkimuslaitos, 31600 Jokioinen * Nykyinen osoite: Kansanterveyslaitos, Kalliolinnantie 4, 00140 Helsinki Tutkimme lierojen runsautta ja lajistoa Suitian koe- tilalla Siuntiossa kokeessa, jossa verrattiin neljää tavan- omaista ja neljää luonnonmukaista viljelyjärjestelmää hie- susavikentällä. Näytteitä otettiin seitsenvuotisen kokeen viidentenä (1986) ja kuudentena (1987) syksynä forma- liinimenetelmällä yhdestä kerranteesta ja viimeisenä syk- synä (1988) formaliini-huuhtelunäyte-menetelmälläkai- kista kolmesta kerranteesta. Peltoliero ( Aporrectodea caliginosa) oli selvästi yleisin laji kaikissa viljelyjärjestelmissä. Lajin yksilöt olivat kool- taan samanlaisia eri viljelyjärjestelmissä. Muut koeken- tällä esiintyneet lajit olivat kasteliero (Lutnbricus lerres- Iris), onkiliero (L. rubellus) sekä hyvin harvalukuinen rus- koliero (L. castaneus). Tavanomaisten ja luonnonmukais- ten viljelyjärjestelmien lieroyhteisöissä ei havaittu selviä eroja. Lietelannan levittäminen oli vähentänytLumbricus- suvun lierojen osuutta. Lierojen runsaudessa havaittiin vuosittaista vaihtelua, jonkasyitä on vaikea osoittaa tarkasti. Viljelykierron vai- he, sääolojen muutokset janäytteenottomenetelmän te- hokkuuden vaihtelu ilmeisesti kaikki vaikuttivat runsaus- arvioihin. Vuonna 1987 havaittiin yleisesti alhaisia tiheyk- siä, mikä mahdollisesti johtui edeltäneen talven poikkeuk- sellisesta kylmyydestä. Vuoden 1987 alhaisimmat liero- tiheydet mitattiin perunaa kasvaneissa ruuduissa. Vuonna 1988 lierojen lukumäärä oli (suluissa keskiar- von keskivirhe) 23 (11.2) 92 (49.8) yksilöä m~ 2 ja ko- konaiskuivapaino 1.0 (0.54) 3.2 (1.53) g m-2 . Liero- jen munakoteloiden määrä vaihteli välillä 5 (2.5) 52.5 (26.3) m-2 . Runsaudet olivat suurimmillaan luonnonmu- kaisesti viljellyllä virnanurmella. Viljelyjärjestelmät eivät poikenneet tilastollisesti merkitsevästi toisistaan lierojen runsaudessa. Ainoa merkitsevä vaihtelun lähde oli vuo- rovaikutus hierarkkisen koejärjestelyn ylimmän tason (ta- vanomaiset vs. luonnonmukaiset viljelyjärjestelmät) ja kerranteen välillä (p =0.04). Tuloksen selittänee kentän ojitusongelmien aiheuttama huomattava vaihtelu eri ker- ranteiden olosuhteissa. Pääosa kahden kerranteen luon- nonmukaisesti viljellyistä ruuduista sijaitsi alueella, joka oli veden vaivaama, tiivistynyt ja talvisin jään peitossa. Tämä oli ilmeisesti vähentänyt lieroja vaikeuttaen käsit- telyjen vaikutusten arviointia. On epätodennäköistä että kokeen viljelyjärjestelmien maan laadussa olisi systemaattisia lierojen toiminnan ai- heuttamia eroja. Kentän kuivatusongelmien vuoksi ei ha- vaintojamme lierojen runsaudesta eri viljelyjärjestelmis- sä voi yleistää. 367