- Email: [email protected]
Effect of soil compaction on earthworms (lumbricidae) in apple orchard soil
soil Bioi. Biochem. Vol. 24. No. 12, pp. 1.573-1575, 1992 F’riated in Great Britain. All rights reserved
Copyright Q
00384i17/92 $5.00 + 0.00 1992 Pergamon Press Lid
EFFECT OF SOIL COMPACTION ON EARTHWORMS (LUM~RICIDAE) IN APPLE ORCHARD SOIL VkLAV
PItL
Institute of Soil Biology, Czechosiovak Academy of Sciences, Na s;idk&h 7, CS-37005 Ceski Bud&jovice, Czechoslovakia
Summary-The effect of soil compaction on earthworms was investigated comparing earthworm populations in trafficked (T) and untrafficked (U) parts of three apple orchards intensively worked for 10, I5 and 20 yr. The results indicated that high trafiic intensity (up to 200 passages of farm machinery per year) considerably reduced both earthworm density and biomass. The differences between T and U plots were significant (P < 0.01) except in the case of the orchard intensively worked for 15 yr in respect to biomass, and they could be attributed mainly to a reduction of juvenile worms in T plots. The community structure was also affected; epigeic species showed the decrease in proportion in T compared with U plots, while the proportion of hypogeic ones increased.
INTRODUCllON
structuraf damage of the soil due to the use of heavy machinery and extensive vehicular traffic on the fields is an increasing problem connected with modern agriculture. Also in intensively managed orchards, in addition to pesticide impacts, soil compaction represents one of the most severe risks for the soil structure and the inhabiting organisms. Earthworms are known to affect soil structure through their burrowing and casting activities, and it was suggested by several authors (Rushton, 1986a; Joschko et al., 1989) that they may have a significant loosening effect on compacted soil. The investigation of the soil compaction effects on earthworms is, therefore, highly desirable in view of their possible introduction for the amelioration of compacted soils. The aim of the present study was to compare earthworm populations in trafficked and untrafficked parts of apple orchards, which had been intensively worked for various lengths of time. The
MATERM
AND METHODS
The study has been carried out in the fruit growing region of South Bohemia, Czechoslovakia, near Cheltice village (570 m a.s.l., 49”06’N, 14’07’E). The soil type is an entric cambisol, the soil pH 6.6-7.5, the humus form mull. Climatically, the area belongs to the moderately warm region, average temperature and rainfall are 7.3”C and 568 mm, respectively. During 1988-1989, when the earthworms were sampled, the climate was cooler and more humid than usual. Three apple orchards were chosen for the study, which were intensively worked for 10, 15 and 20 yr respectively, and whose soil surface had been kept bare by herbicide spraying. In each orchard, two adjacent rectangular plots, measuring 3 x 25 m each,
were selected, the first (T) intensively trafficked by various machinery-up to 200 times annually and the untrafficked second (U), which acted as a control. Soil bulk density was always higher in trafficked plots (Table I). During the spring and autumn maxima of earthworm activity, populations were sampled to assess the effects of soil compaction upon earthworm density, biomass and species composition. The sampling programme started on 12 April 1988 and was continued on 25 November 1988 and 23 March 1989. A combination of methods was used for earthworm sampling. Five soil cores (625 cm* x 10 cm) were collected uniformly spaced throughout each plot. In order to expel worms from deeper soil layers 0.15% formalin was subsequently applied. Soil samples taken were sorted by hand and then heat-extracted using the modified Meyer’s apparatus (Meyer, 1980). The worms were killed in 1% formalin and stored in 4% solution of the same fixative. The mass of earthworms was established on fixed material, no corrections were made for gut content and for mass loss during preservation. The nomenclature follows Easton (1983). The t-test was used for testing the differences in earthworm density and biomass between trafficked and untrafficked plots of each apple orchard. RESULTS
Average values of earthworm density (ind m-‘) and biomass (g m-*) from 15 samples taken from each plot are presented in Table 2. Densities of earthworms were found to be higher in untrafficked (U) than in trafficked (T) plots of all the three orchards studied, as well as their biomasses but for that in the orchard intensively worked for 15 yr. In
1573
1574
ViiCLAV PItL Table
I. Some
physical properties
(mean -+ SE, n = 5) collected from apple orchards studied in March 1989
of soil sampla
ISA0
IOAO
Bulk density (g cm-‘) Water content (%) Pore space (%)
20 A0
U
T
U
T
u
1.45 * 0.03 18.9 + I.8 45.4 + I.2
1.78 * 0.03 17.6 f 0.1 32.8 f 1.1
1.59~0.01 17.8 c 1.4 40.2 * 0.4
I.81 + 0.03 14.6 & 0.6 31.5 tf: I.3
1.22 ?: 0.05 28.1 i: I.2 54.0 2 I.9
IO AO. 1SAO. 20 AC&-a~ole orchards intensively U: U&affickcd plot; T: &?icked plot.
worked
this last orchard, earthworm biomass was also higher in U than in T, but the difference was not statistically significant (P > 0.05). As concerns adult worms, significant difference between U and T was found in 10yr old orchard only, both in their density and biomass. The density and biomass values of juveniles were always significantly higher in U than in T, except for the biomass in 15 yr old orchard, where although higher in U, it did not differ significantly from T (Table 2). In respect to total earthworm numbers the proportion of juveniles on untrafficked plots was very similar among orchards, ranging between 82 and 85% of the total population (Table 3). On trafficked plots, however, the proportion of juveniles was always smaller, and decreased gradually with the orchard age, from 82 to 55% in 10 and 20 yr old orchards respectively. As regards species composition of earthworm communities, very little effect of soil compaction was found. Although there was low decrease in species number in trafficked plots of 10 and 20 yr old orchards, not even one of the predominating species was eliminated. Predominating species were Lumbricus rubellus (Hoffmeister, 1843), Octolasion lacteum (brley, 1881) and Aporrectodea rosea (Savigny, 1826) in 10 yr old orchard, Dendrobuena octuedra (Savigny, 1826), L. rubellus, 0. lacteum, A. rosea and A. caliginosa (Savigny, 1826) in IS, and A. rosea and L. rubellus in 20 yr old orchards, respectively. HOWever, some differences can be seen in the proportional representation of species between untrafficked and trafficked plots, and therefore in the community structure (Table 3). Generalty, epigeic or epihypogeic species showed more or less marked decrease in proportion in trafficked compared with untrafficked plots, while the proportion of hypogeic species
Table 2. Average density (D) and biomass
for IO,
I5 and
20 yr.
DISCUSSION
The importance of the soil physical structure for the persistence and activity of earthworms has been shown by many authors (e.g. Evans, 1947, Dexter, 1978; Rushton, 1986b). From this point of view, any serious structural damage of the soil may probably lead to the changes in earthworm communities. The problem of soil compaction, actually rising with the development of modem agriculture, is now restricted not only to arable fields with heavy clay soils, but it also concerns other soil types and agroecosystems. In the intensively managed orchards, the susceptibility of soi to compaction is increased by the often used overall herbicide treatment resulting in a herbicide fallow. The results of this study indicate direct detrimental effects of soil compaction on the earthworm fauna in orchards, especially considerable decreases of population density and biomass. Similar results were obtained by Bostrom (1986) in a heavy clay soil of arable fields with different traffic intensities. She showed that both earthworm biomass and density were si~i~cantIy lower in treatments trafficked by tractors (high soil compaction) than in those in which the implement had been hauled by the winch (low soil compaction). Vehicular compaction on human path through pasture was also found to reduce earthworm populations (Piearce, 1984). Aritajat et al. (1977) investigated the influence of soil compaction on earthworms in a I-yr field experiment, in which the soil was compacted by driving with a tractor, once and ten times respectively. On a silt-loam grassland,
(B) of earthworms
sampled
in apple orchards
studied
l5AO
U
T
Adults
I> El
55.5 f 12.2. 22.71 5 4.47.
Juveniles
D B D B
313.6 30.57 369.1 53.34
26.6 + 5.3 10.82 * 2.51 119.5 * 17.9
43.7 f 8.8”’ 21.50 f 5.8’F 199.5 + 1.5.5**
10.39 * 2.29 146.1 + 17.3 21.22 + 3.79
16.43 -f 2.39” 243.2 f l7.237.93 C 7.86”’
f 43.8** _c 3.99’. + 46.6’* + 7.03.’
i: 0.04 24.6 * 1.7 W.7 i I.6
increased. The representatives of anecic earthworms were found solely in untrafficked plots of the orchards.
IOAO
Total earthworms
T
I .47
IJ
10 AO, 15 AO, 20 AO-apple orchards intensiveiy worked for 10, IS and 20 yr. U: Untrafficked plot; T: trafficked plot. D:Indm-‘lt:SE;B:gm-‘+SE. Significance levels: “‘not significant; *P -c 0.05; **P < 0.01.
20.40 T
U
T
48.0 & 9. I 17.28 + 3.94
21.3 5 6.5”’ 8.75 k 3.14”‘
12.8 * 4.3 5.27 * I.68
I IS.2 * IO.5 13.75 k 1.63 163.2 + 15.8 31.03k4.16
107.8 12.82 129.1 21.58
5 t I t
18.0*’ 3.24’* 21.8.’ 3.99”
18.1 1.55 30.9 6.82
k4.6 + 0.48 c 6.1 f 1.79
Effect Table 3. The number,
and ~rowrtion
of soil compaction
(%). of various swcies, samr~led from untratlicked
u NO.
octaedrn Dtdnxiriim rubidw H&d&s mtipae tub. L. castaneus
4 47 1 3
1.2 13.6 0.3 0.9
L. mbe1h.s L. terrertrir 0. laeteum Total immature earthworms Total adult earthworms
205 I 85 294 J2
59.2 2:::
A. cafiginosa A. rosea Dendrobaena
Total earthworms 10AO, I5 AO, 20 A+appk
85.0 IS.0
and trafficked 0
plots of thra
No. -
%
No. ::
t 1.4
92 I I
NO.
%
NO.
%
No.
%
13.6 40.4 0.4 0.4 -
29 I8 49 1 1 -
18.9 II.8 32.0 0.7 0.7 -
5 46 4 I -
4.2 38.0 3.3 0.8 -
4 I4 I -
13.8 48.3 3.4 -
51.2 I.7 0.8 83.5 16.5
IO I6 I3
34.5 ss.2 44.8
100.0
29
100.0
1
18.2 1.5 0.7
82
39.9
47
20.6
2S
16.3
11 112 2s
19.7 81.8 18.2
TO I87 41
G.2 82.0 18.0
TO 107 46
19.6 69.9 30.1
62 2 I IO1 20
IS3
100.0
121
25 2 -
-
100.0 346 100.0 137 100.0 228 orchards intensively worked for IO, I5 and 20 yr.
they recorded significantly reduced worm numbers in
treated compared with untreated plots, however, no differences were found between uncompacted and compacted plots on a clay grassland. Our results showed that juvenile worms were more affected by soil compaction than adult ones. It is well known that, in most species, juveniles are usually found in the upper layers of the soil, while adults usually live deeper down. Hence, juvenile worms are more exposed to the pressure and crushing effect of the tractor wheels. Also, cocoons are often deposited on or near the soil surface, and may be largely damaged by trafficked machinery. In addition, small hatchlings may be strongly affected by unfavourable microclimatic conditions in compacted soils. In all orchards studied, we found more juveniles per adults in untra~cked than in trafficked ptots. Bostrom (1986), who observed the same relationship in corn fields, elucidated that this situation could have arisen if one or more of the following conditions were met: (1) juveniles were more exposed than adults to mechanical damage, (2) the food supply in trafficked plots was lower than in untrafficked plots, and (3) the lower abundance of worms in trafficked plots left more adults unmated. She hereafter affirmed that the food supply was of great importance. In orchards studied, however, where both untrafficked and tratlicked plots were bare (without understory plants), the differences in food supply may not play any significant role, and the other two conditions were probably more important. In addition, the compacted soil may have impaired earthworm locomotion, resulting in fewer mated adults. The changes in earthworm community structure observed in trafficked plots indicated again the more detrimental effect of soil compaction on earthworms living in upper than in deeper soil layers.
T
IJ
T %
auule orchards
20 A0
u
T %
W
ISA0
IOAO
Species
1575
on earthworms
This study clearly showed that the traffic and resulting soil compaction had a direct effect on earthworm community in intensively managed orchards. Further studies are, however, needed to investigate the effects of soil compaction on earthworms in other soils and agroecosystems. REFERENCES Aritajat U., Madge D. S. and Gooderham P. T. (1977) The effects of compaction of agricultural soils on soil fauna. Pedobiologia
17, 262-282.
Bostriim U. (1986) The effect of soil compaction on earthworms (Lumbricidae) in a heavy clay soil. Swedish Jour nal of Agricultural
Research
16, 137-141.
Dexter A. R. (1978) Tunneling in soil by earthworms. Soil Biology & B~ochem~try IO, 447-449. Eastoo E. G. (1983) A guide to the valid names of Lumbri-
cidae (Oligochaetaf. In Earthworm Ecologyfrom Darwin to Vermicuiture (J. E. Satchell, Ed.), pp. 475-485. Chapman & Hail, London. Evans A. C. (1947) A method of studying the burrowing activities of earthworms. Annals and Magazine ofNafurul History
14, 643650.
Joschko M., Diestel H. and Larink 0. (1989) Assessment of earthworm burrowing efficiency in compacted soil with a combination of morphological and soil physical measurements. Biology and Ferti&y of Soils 8, 191-196. Meyer E. (1980f Akti~t~tsdichte, Abundanz und Biomasse der Makrofauna. In tikologische Untersuchungen an Wirbeilosen des Zentralalpinen Xochgebirges (Obergurgl, Tirol) (H. Janetschek, Ed.), pp. I-53. Kommissions,
Innsbruck. Piearce T. G. (1984) Earthworm populations in soils di turbed by trampling. Biological Conservation 29, 241-252.
Rushton S. P. (1985a) Development of earthworm populations on pasture land reclaimed from open-cast coal mining. ~e~b~olog~a 29, 27-32. Rnshton S. P. (1986b) The effects of soil compaction on Lumbricus terrestris and its possible implications for populations on land reclaimed from open-cast coal mining. Pedobiologia 29, U-90.
Copyright Q
00384i17/92 $5.00 + 0.00 1992 Pergamon Press Lid
EFFECT OF SOIL COMPACTION ON EARTHWORMS (LUM~RICIDAE) IN APPLE ORCHARD SOIL VkLAV
PItL
Institute of Soil Biology, Czechosiovak Academy of Sciences, Na s;idk&h 7, CS-37005 Ceski Bud&jovice, Czechoslovakia
Summary-The effect of soil compaction on earthworms was investigated comparing earthworm populations in trafficked (T) and untrafficked (U) parts of three apple orchards intensively worked for 10, I5 and 20 yr. The results indicated that high trafiic intensity (up to 200 passages of farm machinery per year) considerably reduced both earthworm density and biomass. The differences between T and U plots were significant (P < 0.01) except in the case of the orchard intensively worked for 15 yr in respect to biomass, and they could be attributed mainly to a reduction of juvenile worms in T plots. The community structure was also affected; epigeic species showed the decrease in proportion in T compared with U plots, while the proportion of hypogeic ones increased.
INTRODUCllON
structuraf damage of the soil due to the use of heavy machinery and extensive vehicular traffic on the fields is an increasing problem connected with modern agriculture. Also in intensively managed orchards, in addition to pesticide impacts, soil compaction represents one of the most severe risks for the soil structure and the inhabiting organisms. Earthworms are known to affect soil structure through their burrowing and casting activities, and it was suggested by several authors (Rushton, 1986a; Joschko et al., 1989) that they may have a significant loosening effect on compacted soil. The investigation of the soil compaction effects on earthworms is, therefore, highly desirable in view of their possible introduction for the amelioration of compacted soils. The aim of the present study was to compare earthworm populations in trafficked and untrafficked parts of apple orchards, which had been intensively worked for various lengths of time. The
MATERM
AND METHODS
The study has been carried out in the fruit growing region of South Bohemia, Czechoslovakia, near Cheltice village (570 m a.s.l., 49”06’N, 14’07’E). The soil type is an entric cambisol, the soil pH 6.6-7.5, the humus form mull. Climatically, the area belongs to the moderately warm region, average temperature and rainfall are 7.3”C and 568 mm, respectively. During 1988-1989, when the earthworms were sampled, the climate was cooler and more humid than usual. Three apple orchards were chosen for the study, which were intensively worked for 10, 15 and 20 yr respectively, and whose soil surface had been kept bare by herbicide spraying. In each orchard, two adjacent rectangular plots, measuring 3 x 25 m each,
were selected, the first (T) intensively trafficked by various machinery-up to 200 times annually and the untrafficked second (U), which acted as a control. Soil bulk density was always higher in trafficked plots (Table I). During the spring and autumn maxima of earthworm activity, populations were sampled to assess the effects of soil compaction upon earthworm density, biomass and species composition. The sampling programme started on 12 April 1988 and was continued on 25 November 1988 and 23 March 1989. A combination of methods was used for earthworm sampling. Five soil cores (625 cm* x 10 cm) were collected uniformly spaced throughout each plot. In order to expel worms from deeper soil layers 0.15% formalin was subsequently applied. Soil samples taken were sorted by hand and then heat-extracted using the modified Meyer’s apparatus (Meyer, 1980). The worms were killed in 1% formalin and stored in 4% solution of the same fixative. The mass of earthworms was established on fixed material, no corrections were made for gut content and for mass loss during preservation. The nomenclature follows Easton (1983). The t-test was used for testing the differences in earthworm density and biomass between trafficked and untrafficked plots of each apple orchard. RESULTS
Average values of earthworm density (ind m-‘) and biomass (g m-*) from 15 samples taken from each plot are presented in Table 2. Densities of earthworms were found to be higher in untrafficked (U) than in trafficked (T) plots of all the three orchards studied, as well as their biomasses but for that in the orchard intensively worked for 15 yr. In
1573
1574
ViiCLAV PItL Table
I. Some
physical properties
(mean -+ SE, n = 5) collected from apple orchards studied in March 1989
of soil sampla
ISA0
IOAO
Bulk density (g cm-‘) Water content (%) Pore space (%)
20 A0
U
T
U
T
u
1.45 * 0.03 18.9 + I.8 45.4 + I.2
1.78 * 0.03 17.6 f 0.1 32.8 f 1.1
1.59~0.01 17.8 c 1.4 40.2 * 0.4
I.81 + 0.03 14.6 & 0.6 31.5 tf: I.3
1.22 ?: 0.05 28.1 i: I.2 54.0 2 I.9
IO AO. 1SAO. 20 AC&-a~ole orchards intensively U: U&affickcd plot; T: &?icked plot.
worked
this last orchard, earthworm biomass was also higher in U than in T, but the difference was not statistically significant (P > 0.05). As concerns adult worms, significant difference between U and T was found in 10yr old orchard only, both in their density and biomass. The density and biomass values of juveniles were always significantly higher in U than in T, except for the biomass in 15 yr old orchard, where although higher in U, it did not differ significantly from T (Table 2). In respect to total earthworm numbers the proportion of juveniles on untrafficked plots was very similar among orchards, ranging between 82 and 85% of the total population (Table 3). On trafficked plots, however, the proportion of juveniles was always smaller, and decreased gradually with the orchard age, from 82 to 55% in 10 and 20 yr old orchards respectively. As regards species composition of earthworm communities, very little effect of soil compaction was found. Although there was low decrease in species number in trafficked plots of 10 and 20 yr old orchards, not even one of the predominating species was eliminated. Predominating species were Lumbricus rubellus (Hoffmeister, 1843), Octolasion lacteum (brley, 1881) and Aporrectodea rosea (Savigny, 1826) in 10 yr old orchard, Dendrobuena octuedra (Savigny, 1826), L. rubellus, 0. lacteum, A. rosea and A. caliginosa (Savigny, 1826) in IS, and A. rosea and L. rubellus in 20 yr old orchards, respectively. HOWever, some differences can be seen in the proportional representation of species between untrafficked and trafficked plots, and therefore in the community structure (Table 3). Generalty, epigeic or epihypogeic species showed more or less marked decrease in proportion in trafficked compared with untrafficked plots, while the proportion of hypogeic species
Table 2. Average density (D) and biomass
for IO,
I5 and
20 yr.
DISCUSSION
The importance of the soil physical structure for the persistence and activity of earthworms has been shown by many authors (e.g. Evans, 1947, Dexter, 1978; Rushton, 1986b). From this point of view, any serious structural damage of the soil may probably lead to the changes in earthworm communities. The problem of soil compaction, actually rising with the development of modem agriculture, is now restricted not only to arable fields with heavy clay soils, but it also concerns other soil types and agroecosystems. In the intensively managed orchards, the susceptibility of soi to compaction is increased by the often used overall herbicide treatment resulting in a herbicide fallow. The results of this study indicate direct detrimental effects of soil compaction on the earthworm fauna in orchards, especially considerable decreases of population density and biomass. Similar results were obtained by Bostrom (1986) in a heavy clay soil of arable fields with different traffic intensities. She showed that both earthworm biomass and density were si~i~cantIy lower in treatments trafficked by tractors (high soil compaction) than in those in which the implement had been hauled by the winch (low soil compaction). Vehicular compaction on human path through pasture was also found to reduce earthworm populations (Piearce, 1984). Aritajat et al. (1977) investigated the influence of soil compaction on earthworms in a I-yr field experiment, in which the soil was compacted by driving with a tractor, once and ten times respectively. On a silt-loam grassland,
(B) of earthworms
sampled
in apple orchards
studied
l5AO
U
T
Adults
I> El
55.5 f 12.2. 22.71 5 4.47.
Juveniles
D B D B
313.6 30.57 369.1 53.34
26.6 + 5.3 10.82 * 2.51 119.5 * 17.9
43.7 f 8.8”’ 21.50 f 5.8’F 199.5 + 1.5.5**
10.39 * 2.29 146.1 + 17.3 21.22 + 3.79
16.43 -f 2.39” 243.2 f l7.237.93 C 7.86”’
f 43.8** _c 3.99’. + 46.6’* + 7.03.’
i: 0.04 24.6 * 1.7 W.7 i I.6
increased. The representatives of anecic earthworms were found solely in untrafficked plots of the orchards.
IOAO
Total earthworms
T
I .47
IJ
10 AO, 15 AO, 20 AO-apple orchards intensiveiy worked for 10, IS and 20 yr. U: Untrafficked plot; T: trafficked plot. D:Indm-‘lt:SE;B:gm-‘+SE. Significance levels: “‘not significant; *P -c 0.05; **P < 0.01.
20.40 T
U
T
48.0 & 9. I 17.28 + 3.94
21.3 5 6.5”’ 8.75 k 3.14”‘
12.8 * 4.3 5.27 * I.68
I IS.2 * IO.5 13.75 k 1.63 163.2 + 15.8 31.03k4.16
107.8 12.82 129.1 21.58
5 t I t
18.0*’ 3.24’* 21.8.’ 3.99”
18.1 1.55 30.9 6.82
k4.6 + 0.48 c 6.1 f 1.79
Effect Table 3. The number,
and ~rowrtion
of soil compaction
(%). of various swcies, samr~led from untratlicked
u NO.
octaedrn Dtdnxiriim rubidw H&d&s mtipae tub. L. castaneus
4 47 1 3
1.2 13.6 0.3 0.9
L. mbe1h.s L. terrertrir 0. laeteum Total immature earthworms Total adult earthworms
205 I 85 294 J2
59.2 2:::
A. cafiginosa A. rosea Dendrobaena
Total earthworms 10AO, I5 AO, 20 A+appk
85.0 IS.0
and trafficked 0
plots of thra
No. -
%
No. ::
t 1.4
92 I I
NO.
%
NO.
%
No.
%
13.6 40.4 0.4 0.4 -
29 I8 49 1 1 -
18.9 II.8 32.0 0.7 0.7 -
5 46 4 I -
4.2 38.0 3.3 0.8 -
4 I4 I -
13.8 48.3 3.4 -
51.2 I.7 0.8 83.5 16.5
IO I6 I3
34.5 ss.2 44.8
100.0
29
100.0
1
18.2 1.5 0.7
82
39.9
47
20.6
2S
16.3
11 112 2s
19.7 81.8 18.2
TO I87 41
G.2 82.0 18.0
TO 107 46
19.6 69.9 30.1
62 2 I IO1 20
IS3
100.0
121
25 2 -
-
100.0 346 100.0 137 100.0 228 orchards intensively worked for IO, I5 and 20 yr.
they recorded significantly reduced worm numbers in
treated compared with untreated plots, however, no differences were found between uncompacted and compacted plots on a clay grassland. Our results showed that juvenile worms were more affected by soil compaction than adult ones. It is well known that, in most species, juveniles are usually found in the upper layers of the soil, while adults usually live deeper down. Hence, juvenile worms are more exposed to the pressure and crushing effect of the tractor wheels. Also, cocoons are often deposited on or near the soil surface, and may be largely damaged by trafficked machinery. In addition, small hatchlings may be strongly affected by unfavourable microclimatic conditions in compacted soils. In all orchards studied, we found more juveniles per adults in untra~cked than in trafficked ptots. Bostrom (1986), who observed the same relationship in corn fields, elucidated that this situation could have arisen if one or more of the following conditions were met: (1) juveniles were more exposed than adults to mechanical damage, (2) the food supply in trafficked plots was lower than in untrafficked plots, and (3) the lower abundance of worms in trafficked plots left more adults unmated. She hereafter affirmed that the food supply was of great importance. In orchards studied, however, where both untrafficked and tratlicked plots were bare (without understory plants), the differences in food supply may not play any significant role, and the other two conditions were probably more important. In addition, the compacted soil may have impaired earthworm locomotion, resulting in fewer mated adults. The changes in earthworm community structure observed in trafficked plots indicated again the more detrimental effect of soil compaction on earthworms living in upper than in deeper soil layers.
T
IJ
T %
auule orchards
20 A0
u
T %
W
ISA0
IOAO
Species
1575
on earthworms
This study clearly showed that the traffic and resulting soil compaction had a direct effect on earthworm community in intensively managed orchards. Further studies are, however, needed to investigate the effects of soil compaction on earthworms in other soils and agroecosystems. REFERENCES Aritajat U., Madge D. S. and Gooderham P. T. (1977) The effects of compaction of agricultural soils on soil fauna. Pedobiologia
17, 262-282.
Bostriim U. (1986) The effect of soil compaction on earthworms (Lumbricidae) in a heavy clay soil. Swedish Jour nal of Agricultural
Research
16, 137-141.
Dexter A. R. (1978) Tunneling in soil by earthworms. Soil Biology & B~ochem~try IO, 447-449. Eastoo E. G. (1983) A guide to the valid names of Lumbri-
cidae (Oligochaetaf. In Earthworm Ecologyfrom Darwin to Vermicuiture (J. E. Satchell, Ed.), pp. 475-485. Chapman & Hail, London. Evans A. C. (1947) A method of studying the burrowing activities of earthworms. Annals and Magazine ofNafurul History
14, 643650.
Joschko M., Diestel H. and Larink 0. (1989) Assessment of earthworm burrowing efficiency in compacted soil with a combination of morphological and soil physical measurements. Biology and Ferti&y of Soils 8, 191-196. Meyer E. (1980f Akti~t~tsdichte, Abundanz und Biomasse der Makrofauna. In tikologische Untersuchungen an Wirbeilosen des Zentralalpinen Xochgebirges (Obergurgl, Tirol) (H. Janetschek, Ed.), pp. I-53. Kommissions,
Innsbruck. Piearce T. G. (1984) Earthworm populations in soils di turbed by trampling. Biological Conservation 29, 241-252.
Rushton S. P. (1985a) Development of earthworm populations on pasture land reclaimed from open-cast coal mining. ~e~b~olog~a 29, 27-32. Rnshton S. P. (1986b) The effects of soil compaction on Lumbricus terrestris and its possible implications for populations on land reclaimed from open-cast coal mining. Pedobiologia 29, U-90.