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most important species in the soil formation processes. Often found in agricultural communities is also Lumbricus rubellus. Very important are also Aporrectodea rosea and Lumbricus terrestris. Whereas in more acidic soils (pH 4.4- 5.3), e.g. peat, under the moss on dolomite and sand, is found Dendrobaena octaedra. The richest agriculture lands in earthworms are the loamy sod carbonate soils. In fields earthworms normally live in the top 10 cm of the soil. In autumns they burrow deeper in the soil. The earthworm population increases in perennial pasturelands, whereas tillage has an adverse impact. The sandy soils shall be regularly cultivated and fertilized, otherwise the population of earthworms reduces, or they may disappear completely (Эглитис, 1954). Earthworm dependence on soil properties have been widely researched in Lithuania. According to data of O. Atlavinite (Атлавините, 1975), earthworms mostly habit in loam, less in sandy loam, least in sandy soils and peatlands. The dominant are such species as Aporrectodea caliginosa, Aporrectodea rosea and Allolobophora chlorotica. The dominant species in the acidic podsol soils usually is Dendrobaena octaedra. Often found are also Dendrodrillus rubidus tenuis and Lumbricus rubellus. However, majority of earthworms prefer less acid, neutral soils, reaching their maximum density at pH 6- 8. Distribution of the species is largerly determined by the mechanical composition of the soil, content of the organic matter and different agrotechnical activities (Атлавините, 1975; 1990). In the most common agricultural soil types of Estonia are found 6 earthworm species. The dominant is endogeic Aporrectodea caliginosa. Probably this species in Estonia has occured only with development of agriculture. The second most usualy found species is Lumbricus rubellus (Timm, 1970). Earthworm species Aporrectodea caliginosa, Aporrectodea rosea and Lumbricus rubellus are characteristic to intensively cultivated agricultural lands. Allolobophora chlorotica, Lumbricus castaneus and anecic species are more sensitive to land cultivation. Their presence in earthworm communities indicates on favorable agricultural conditions. The brown soils are mentioned as the most appropriate for earthworms (Ivask et al., 2006; Ivask et al., 2007). 10
Summing up data of numerous researches on the dominant earthworm species in agricultural lands in Scandinavia, Central Europe and Eastern Europe, it has to be concluded that the most common species is Aporrectodea caliginosa. Whereas in acidic soils increases proportion of Dendrobaena octaedra and Lumbricus rubellus. 1.1. Earthworm impact on soil properties and microorganisms Even in insignificant density earthworms may have great impact on soil aeration and water infiltration. Earthworm presence may reduce soil compaction which has occured due to agrotechnical activities. Earthworms have great impact on soil horizon mixing, and dragging of the the upper layer, which is rich in organic matter, into the deepest horizons (Lee, 1985; Curry, 1988). Earthworms may have a significant impact on the chemical properties of the soil. They drag down into the soil plenty of partly dispersed plant remains. In the digestive tracts the remains are being macerated, mixed up with mineral particles of the soil, enriched with Ca 2+ ions from calcium glands and returned to the soil as casts (Stewart et al., 1980). Casts presence in the soil significantly improves its fertility. The casts have a positive impact on aeration, water infiltration, quantity of water. Increases soil active surface area, development of pore and channel system, which allows the roots of plants to penetrate into the soil. In casts is being observed bacteria and soil microscopic fungus activity increase. As well as the activity of microorganisms is being stimulated in earthworm digestive tracts (Lee, 1985; Schrader, Seibel, 2001). Increased activity of microbiological and digestive enzymes is being observed in the central intestine of earthworms (Curry, Schmidt, 2007). Researches indicate not only on symbiotic relations of earthworms and microogranisms, but also on active use of microorgranisms as nutrition- especially the species Aporrectodea caliginosa, which feeds on well decomposed detritus with high concentration of microorganisms (Kristufek et al., 1994; Kristufek et al., 1995). Other products of earthworm metabolism also descend into the soil (Lee, 1985). Earthworms induce total oxygen mineralization in agricultural ecosystems. The earthworm feeding activity increases content of oxygen available to plants in the soil, 11
Page 1 and 2: UNIVERSITY OF LATVIA FACULTY OF GEO
Page 3 and 4: CONTENTS CONTENTS .................
Page 5 and 6: environmental factors, as well as o
Page 7 and 8: Aprobation of te Results Te results
Page 9: 1. EARTHWORMS IN AGRICULTURAL LANDS
Page 13 and 14: 1.3. Earthworm impact on gricultura
Page 15 and 16: period. The samples were hand sorte
Page 17 and 18: Figure 2.1. All season mean density
Page 19 and 20: 3. CHANGES OF EARTHWORM COMMUNITIES
Page 21 and 22: ubidus tenuis, whose propotion is i
Page 23 and 24: soil liming has facilitated great b
Page 25 and 26: 3.4.2. The total earthworm populati
Page 27 and 28: population of earthworms in all of
Page 29 and 30: of Aporrectodea caliginosa, emerge
Page 31 and 32: Table 3.5 The chemical properties o
Page 33 and 34: For the reciprocal comparision of t
Page 35 and 36: observed by the author of the docto
Page 37 and 38: Figure 3.3. Possible process of pin
Page 39 and 40: CONCLUSIONS 1. Reasearches conducte
Page 41 and 42: LITERATURE Abrahamsen, G. 1972. Eco
Page 43 and 44: Latvian Academy of Sciences, B, 7 (
Page 45: беспозвоночныхмор

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