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Table 2.2 Mean density (ind. m -2 ) and relative numbers (%) of earthworm species in sample plots during observation period (1992 – 1998) Dobele 1 Species 1992 1993 1994 1995 1996 1997 1998 % Total Aporrectodea caliginosa 68 136 323 277 49 182 80 96 Aporrectodea rosea 5 2 0 0 0 0 0
Figure 2.1. All season mean density of earthworms per sample in sample plots. Columns having equal letters are not statistically different (ANOVA, F-test; α = 0,05) Field relief also has impact on earthworm populations. At the higher terrain position, where soil surface erosion is more apparent, earthworm density may be significantly less than in the lower part (Атлавините, 1975). Considerable factor, which may have great impact in the dry summer months, is level of groundwater, which in the lower parts of relief often is found closer to the soil surface. Comparing earthworm density in the sampling plots of different relief location, it is evident that the density is higher in the plots of lower relief location (Table 2.2). Especially it is evident in Priekuli sampling plots. Differences in Dobele are less abvious. Earthworm density dynamics in the sampling plots was greatly related with meteorological conditions, especially with rainfall during the earthworm activity period. After prolonged periods of dry and hot weather in summer (1992 and 1996), the population of earthworms as a rule significantly reduced, whereas the increase of the population was related with favorable humidity conditions in spring and summer (1992, 1995 and 1997-1998). In Baldone sandy soils, which were not cultivated for a longer period of time, the meteorological factors did not have such an impact. Permanent vegetation (gramineae) on the surface of the soil forms such a protecting layer, which reduces the impact of unfavorable meteorological conditions, thus facilitating more even earthworm allocation in the soil. Soil cultivation has a great impact on earthworm communities. In intensively 17
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 and 10: 1. EARTHWORMS IN AGRICULTURAL LANDS
Page 11 and 12: Summing up data of numerous researc
Page 13 and 14: 1.3. Earthworm impact on gricultura
Page 15: period. The samples were hand sorte
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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