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Intensive cultivation can drastically reduce earthworm populations in arable land
European Journal of Soil Biology 38 (2002) 127−130 www.elsevier.com/locate/ejsobi
Intensive cultivation can drastically reduce earthworm populations in arable land James P. Curry *, David Byrne, Olaf Schmidt Department of Environmental Resource Management, Faculty of Agriculture, University College, Dublin 4, Ireland Received 14 August 2000; accepted 22 January 2001
Abstract The impact of intensive cultivation for potato production on the earthworm populations was assessed in two adjacent large field plots. Three successive winter wheat crops had been grown in one plot while winter wheat was grown with minimum cultivation in an understorey of white clover in the other. Both plots were ploughed in spring 1998 and intensively cultivated (grubbing, ridging, bed-tilling, destoning, ridging) prior to planting potatoes. Earthworm populations were reduced from a mean density of 319 individuals m–2 and 55 g m–2 biomass in the conventional wheat plot, and from 1160 individuals and 175 g m–2 biomass in the wheat–clover plot in the 1996/1997 cropping season, to 40–82 individuals and 4–19 g m–2 in June–October 1998 following potato planting. Populations declined to virtually undetectable levels following mechanical potato harvesting in late autumn 1998 and spring cultivation for barley in 1999, remained at very low levels throughout 1999 and had shown no sign of recovering by May 2000. The results show that earthworm populations can be virtually eliminated within a single season by drastic forms of soil cultivation. © 2002 Éditions scientifiques et médicales Elsevier SAS. All rights reserved. Keywords: Earthworms; Lumbricidae; Soil cultivation; Destoning; Potato production
1. Introduction Earthworm populations in cultivated land are generally lower than those found in undisturbed habitats, with population reduction associated with tillage being attributed directly to injury caused by cultivation or indirectly to habitat disruption and reduction in food supply [5–8]. The extent of population reduction depends on the nature and frequency of cultivation. Cuendet [3] estimated that the direct mortality arising from injury caused by ploughing was about 25% in a range of soils in Switzerland. The effects of more intensive forms of cultivation can be considerably greater: for example, Boström [1] reported that rotary cultivation killed 60–70% of the earthworms in grass and lucerne leys in Sweden. Population reductions in the order of 50% have been indicated in a number of studies
* Corresponding author. Tel.: +353-1-706-7093; fax: +353-1706-1102. E-mail address: [email protected] (J.P. Curry).
following ploughing and conventional cultivation for cereal crops [4,9] and potatoes [2]. However, in most cases the effects of cultivation appear to be transitory, and populations generally recover within 6–12 months in the presence of an adequate food supply. Commercial potato production can involve several drastic soil cultivations aimed at producing a fine tilth and removing stones to facilitate mechanical harvesting. The present paper describes the impact of such intensive cultivation on the earthworm populations of two arable field plots with different initial population levels due to different management histories.
2. Materials and methods The study site was located in the Haggard Field on the University Farm at Lyons Estate, Celbridge, County Kildare. The soil is a poorly drained silty loam to silty clay loam of high base status. The pH of the plough layer is 7.8
© 2002 Éditions scientifiques et médicales Elsevier SAS. All rights reserved. PII: S 1 1 6 4 - 5 5 6 3 ( 0 2 ) 0 1 1 3 2 - 9
128
J.P. Curry et al. / Eur. J. Soil Biol. 38 (2002) 127–130
and the C content exceeds 5%. The climate is temperate oceanic, with mean annual temperature 9–10 °C, precipitation 650–750 mm and no marked seasonal pattern of rainfall. Mean monthly temperatures typically range from 4 °C in December–January to 16–18 °C in July–August. The field had been under Italian ryegrass (Lolium multiflorum var. italicum) for 3 years prior to the establishment in 1994 of two adjacent 1 ha plots for conventional winter and wheat drilled directly into a permanent white clover base. Details of crop establishment and management up to autumn 1997 are given in Schmidt and Curry [10]. Following the 1997 harvest, both plots received similar management to the rest of the field. The stubble was grubbed in late autumn, and the field was ploughed to 30 cm and tilled for a potato crop in spring 1998. The soil was grubbed twice, then ridged, bed-tilled, ridged again, destoned and ridged again for potato planting. Compound fertilizer (10:10:20 NPK) was applied at 1 t ha–1; one broad-spectrum herbicidal application was made for weed control, and 13 fungicidal foliar sprays were applied throughout the growing season for the control of late blight. The potato crop was harvested in late autumn using an automatic harvester. The field was deep grubbed, ploughed and tilled the following spring, and barley was sown in
Fig. 1. Impact of cultivation on earthworm populations (means ± S.E.).
March 1999. It was ploughed and harrowed twice in spring 2000 and again sown with barley. Earthworm populations were sampled in April, June and October 1998, in February, May and October 1999, and in February and May 2000 (Fig. 1). Eight to twelve 25 × 25 × 25 cm soil samples were taken from each of the former plots and hand sorted in the laboratory on each sampling date, except in February 1999, when five samples per plot were hand sorted in the field. Earthworms were weighed live (with gut contents) and fixed in 4% formalin, and adults were determined to species level [11].
3. Results A marked increase in earthworm population density and biomass had occurred under the wheat–clover crop while populations had remained relatively stable under conventional wheat [10]. These trends were most pronounced during the third cropping cycle (November 1996–September 1997), when the mean population density ranged from 968 to 1347 individuals m–2 and the biomass from 140 to 200 g m–2 under wheat–clover, compared to 216–435 individuals m–2 and 31–78 g m–2 under conventional wheat.
J.P. Curry et al. / Eur. J. Soil Biol. 38 (2002) 127–130
129
Table 1 Population densities (individuals m–2) of earthworm species in the third year of winter wheat and wheat–clover cropping and in the three following years
Adults Allolobophora chlorotica Aporrectodea caliginosa A. longa A. rosea Lumbricus castaneus L. festivus L. terrestris Murchieona minuscula Satchellius mammalis Juveniles Lumbricus spp. Others Total no. m–2 Numbers of species Total numbers of samples (n)
November 1996–September 1997
April 1998
June–October February–October February–May 1998 1999 2000
Wheat/Clover
Wheat
Fallow
Potatoes
90.7 49.8 21.3 36.4 30.2 3.6 1.8 45.8 25.3
54.2 19.1 6.2 8.0 1.8 0.9 1.8 25.8 3.6
14.0 2.7 0.7 4.7 2.7
1.0 2.4 0.5 0.5
1.4 3.4 8.7
1.0 1.2
3.5
143.1 709.7
3.6 191.5
14.0 156.2
0.8 47.0
1.0 39.0
316 9 36
208 8 24
54 6 32
47 5 48
1158 9 36
The population difference between the former wheat and wheat–clover plots had disappeared by April 1999 following late autumn stubble grubbing and spring ploughing (Fig. 1). In both cases, there was a substantial decline in numbers and biomass compared with September 1997 levels, the decline being more marked (78% for numbers, 67% for biomass) in the wheat–clover plot than in the conventional wheat plot (54% for numbers, 53% for biomass). Earthworms had virtually disappeared from both areas by June 1998 following late spring cultivation for potatoes. Populations recovered slightly in autumn 1998, but no earthworm was found in the 16 samples sorted in May 1999, following late autumn potato harvesting and spring cultivation for barley. Populations remained at barely detectable levels (less than one individual per sample on average) under successive spring barley crops (Fig. 1). Table 1 gives the abundance of the earthworm species recorded. The decline in total earthworm abundance under potato cropping and subsequent spring barley crops was accompanied by a drastic decrease in species richness—from nine under wheat and wheat–clover crops in 1996–1997 to six under potatoes in 1998, five under barley in 1999 and just one under barley in spring 2000. The epigeic and anecic species Satchellius mammalis (Savigny, 1826), Lumbricus spp. and Aporrectodea longa (Ude, 1885) were least tolerant of cultivation, while the endogeics Allolobophora chlorotica (Savigny, 1826), Aporrectodea caliginosa (Savigny, 1826) and A. rosea (Savigny, 1826) were somewhat more tolerant, but only Murchieona minuscula (Rosa, 1906) appears to have survived the effects of continuous cultivation.
Barley
Barley
0.5 0.5 2.5
4.2
4 1 26
4. Discussion While earthworm populations generally decline over time with continuous arable cropping [6,8,9], this tendency tends to be more pronounced under root crops than under cereals. Thus, earthworms were twice as abundant in plots under continuous wheat for 136 years at Rothamsted Experimental Station than in plots growing wheat and root crops [5]. These trends are thought to reflect differences in food supply, with crop residue inputs in the form of dead roots and straw being much greater under cereal crops than under root crops, where most of the organic matter is harvested. However, in view of the previous cropping history of the field, it is unlikely that the decline in earthworm populations under potato cultivation at Lyons can be attributed to food shortage. Some fungicides, notably benomyl and related compounds, are known to be toxic to earthworms [12], but there is no evidence to suggest that the materials applied for blight control in the present case (metalaxyl + mancozeb, fluazinam, fentin hydroxide) could have any appreciable adverse effects. The decline appears to have been caused directly by the very drastic cultivation prior to sowing the potato crop in spring, and again in late autumn during mechanical harvesting. Destoning is likely to have been particularly detrimental as this process involves lifting, agitating and sieving the topsoil in order to remove stones. Automatic harvesting involves essentially similar and equally severe soil disturbance. The lack of population recovery during the two succeeding years under cereal crops is particularly alarming and suggests that the capacity of the
130
J.P. Curry et al. / Eur. J. Soil Biol. 38 (2002) 127–130
population to recover from perturbation may have been fatally compromised.
[6]
C.A. Edwards, J.R. Lofty, The effect of direct drilling and minimal cultivation on earthworm populations, J. Appl. Ecol. 19 (1982) 723–734.
[7]
A.C. Evans, J.W.McL. Guild, Studies on the relationships between earthworms and soil fertility. V. Field populations, Ann. Appl. Biol. 35 (1948) 485–493.
[8]
P.M. Fraser, P.H. Williams, R.J. Haynes, Earthworm species, population size and biomass under different cropping systems across the Canterbury Plains, New Zealand, Appl. Soil Ecol. 3 (1996) 49–57.
[9]
A.D. Rovira, K.R.J. Smettem, K.E. Lee, Effect of rotation and conservation tillage on earthworms in a red-brown earth under wheat, Aust. J. Agric. Res. 38 (1987) 829–834.
References [1]
[2]
[3]
[4]
[5]
U. Boström, Ecology of earthworms in arable land. Population dynamics and activity in four cropping systems, Report 34, Department of Ecology and Environmental Research, Swedish University of Agricultural Sciences, Uppsala, 1988. J.C. Buckerfield, D.M. Wiseman, Earthworm populations recover after potato cropping, Soil Biol. Biochem. 29 (1997) 609–612. G. Cuendet, Predation on earthworms by the black-headed gull (Larus ridibundus L.), in: J.E. Satchell (Ed.), Earthworm Ecology. From Darwin to Vermiculture, Chapman and Hall, London, 1983, pp. 415–424. J.P. Curry, D. Byrne, K.E. Boyle, The earthworm population of a winter cereal field and its effects on soil and nitrogen turnover, Biol. Fertil. Soils 19 (1995) 166–172. C.A. Edwards, Earthworm ecology in cultivated soils, in: J.E. Satchell (Ed.), Earthworm Ecology. From Darwin to Vermiculture, Chapman and Hall, London, 1983, pp. 123–137.
[10] O. Schmidt, J.P. Curry, Population dynamics of earthworms (Lumbricidae) and their role in nitrogen turnover in wheat and wheat–clover cropping systems, Pedobiologia 45 (2001) 174–187. [11]
R.W. Sims, B.M. Gerard, Earthworms, Synopses of the British Fauna (New Series) No. 31, The Linnean Society of London and the Estuarine and Brackish-Water Sciences Association, London, 1985.
[12] A. Stringer, M.A. Wright, The toxicity of benomyl and some related 2-substituted benzimidazoles to the earthworm Lumbricus terrestris, Pestic. Sci. 7 (1976) 459–464.
Intensive cultivation can drastically reduce earthworm populations in arable land James P. Curry *, David Byrne, Olaf Schmidt Department of Environmental Resource Management, Faculty of Agriculture, University College, Dublin 4, Ireland Received 14 August 2000; accepted 22 January 2001
Abstract The impact of intensive cultivation for potato production on the earthworm populations was assessed in two adjacent large field plots. Three successive winter wheat crops had been grown in one plot while winter wheat was grown with minimum cultivation in an understorey of white clover in the other. Both plots were ploughed in spring 1998 and intensively cultivated (grubbing, ridging, bed-tilling, destoning, ridging) prior to planting potatoes. Earthworm populations were reduced from a mean density of 319 individuals m–2 and 55 g m–2 biomass in the conventional wheat plot, and from 1160 individuals and 175 g m–2 biomass in the wheat–clover plot in the 1996/1997 cropping season, to 40–82 individuals and 4–19 g m–2 in June–October 1998 following potato planting. Populations declined to virtually undetectable levels following mechanical potato harvesting in late autumn 1998 and spring cultivation for barley in 1999, remained at very low levels throughout 1999 and had shown no sign of recovering by May 2000. The results show that earthworm populations can be virtually eliminated within a single season by drastic forms of soil cultivation. © 2002 Éditions scientifiques et médicales Elsevier SAS. All rights reserved. Keywords: Earthworms; Lumbricidae; Soil cultivation; Destoning; Potato production
1. Introduction Earthworm populations in cultivated land are generally lower than those found in undisturbed habitats, with population reduction associated with tillage being attributed directly to injury caused by cultivation or indirectly to habitat disruption and reduction in food supply [5–8]. The extent of population reduction depends on the nature and frequency of cultivation. Cuendet [3] estimated that the direct mortality arising from injury caused by ploughing was about 25% in a range of soils in Switzerland. The effects of more intensive forms of cultivation can be considerably greater: for example, Boström [1] reported that rotary cultivation killed 60–70% of the earthworms in grass and lucerne leys in Sweden. Population reductions in the order of 50% have been indicated in a number of studies
* Corresponding author. Tel.: +353-1-706-7093; fax: +353-1706-1102. E-mail address: [email protected] (J.P. Curry).
following ploughing and conventional cultivation for cereal crops [4,9] and potatoes [2]. However, in most cases the effects of cultivation appear to be transitory, and populations generally recover within 6–12 months in the presence of an adequate food supply. Commercial potato production can involve several drastic soil cultivations aimed at producing a fine tilth and removing stones to facilitate mechanical harvesting. The present paper describes the impact of such intensive cultivation on the earthworm populations of two arable field plots with different initial population levels due to different management histories.
2. Materials and methods The study site was located in the Haggard Field on the University Farm at Lyons Estate, Celbridge, County Kildare. The soil is a poorly drained silty loam to silty clay loam of high base status. The pH of the plough layer is 7.8
© 2002 Éditions scientifiques et médicales Elsevier SAS. All rights reserved. PII: S 1 1 6 4 - 5 5 6 3 ( 0 2 ) 0 1 1 3 2 - 9
128
J.P. Curry et al. / Eur. J. Soil Biol. 38 (2002) 127–130
and the C content exceeds 5%. The climate is temperate oceanic, with mean annual temperature 9–10 °C, precipitation 650–750 mm and no marked seasonal pattern of rainfall. Mean monthly temperatures typically range from 4 °C in December–January to 16–18 °C in July–August. The field had been under Italian ryegrass (Lolium multiflorum var. italicum) for 3 years prior to the establishment in 1994 of two adjacent 1 ha plots for conventional winter and wheat drilled directly into a permanent white clover base. Details of crop establishment and management up to autumn 1997 are given in Schmidt and Curry [10]. Following the 1997 harvest, both plots received similar management to the rest of the field. The stubble was grubbed in late autumn, and the field was ploughed to 30 cm and tilled for a potato crop in spring 1998. The soil was grubbed twice, then ridged, bed-tilled, ridged again, destoned and ridged again for potato planting. Compound fertilizer (10:10:20 NPK) was applied at 1 t ha–1; one broad-spectrum herbicidal application was made for weed control, and 13 fungicidal foliar sprays were applied throughout the growing season for the control of late blight. The potato crop was harvested in late autumn using an automatic harvester. The field was deep grubbed, ploughed and tilled the following spring, and barley was sown in
Fig. 1. Impact of cultivation on earthworm populations (means ± S.E.).
March 1999. It was ploughed and harrowed twice in spring 2000 and again sown with barley. Earthworm populations were sampled in April, June and October 1998, in February, May and October 1999, and in February and May 2000 (Fig. 1). Eight to twelve 25 × 25 × 25 cm soil samples were taken from each of the former plots and hand sorted in the laboratory on each sampling date, except in February 1999, when five samples per plot were hand sorted in the field. Earthworms were weighed live (with gut contents) and fixed in 4% formalin, and adults were determined to species level [11].
3. Results A marked increase in earthworm population density and biomass had occurred under the wheat–clover crop while populations had remained relatively stable under conventional wheat [10]. These trends were most pronounced during the third cropping cycle (November 1996–September 1997), when the mean population density ranged from 968 to 1347 individuals m–2 and the biomass from 140 to 200 g m–2 under wheat–clover, compared to 216–435 individuals m–2 and 31–78 g m–2 under conventional wheat.
J.P. Curry et al. / Eur. J. Soil Biol. 38 (2002) 127–130
129
Table 1 Population densities (individuals m–2) of earthworm species in the third year of winter wheat and wheat–clover cropping and in the three following years
Adults Allolobophora chlorotica Aporrectodea caliginosa A. longa A. rosea Lumbricus castaneus L. festivus L. terrestris Murchieona minuscula Satchellius mammalis Juveniles Lumbricus spp. Others Total no. m–2 Numbers of species Total numbers of samples (n)
November 1996–September 1997
April 1998
June–October February–October February–May 1998 1999 2000
Wheat/Clover
Wheat
Fallow
Potatoes
90.7 49.8 21.3 36.4 30.2 3.6 1.8 45.8 25.3
54.2 19.1 6.2 8.0 1.8 0.9 1.8 25.8 3.6
14.0 2.7 0.7 4.7 2.7
1.0 2.4 0.5 0.5
1.4 3.4 8.7
1.0 1.2
3.5
143.1 709.7
3.6 191.5
14.0 156.2
0.8 47.0
1.0 39.0
316 9 36
208 8 24
54 6 32
47 5 48
1158 9 36
The population difference between the former wheat and wheat–clover plots had disappeared by April 1999 following late autumn stubble grubbing and spring ploughing (Fig. 1). In both cases, there was a substantial decline in numbers and biomass compared with September 1997 levels, the decline being more marked (78% for numbers, 67% for biomass) in the wheat–clover plot than in the conventional wheat plot (54% for numbers, 53% for biomass). Earthworms had virtually disappeared from both areas by June 1998 following late spring cultivation for potatoes. Populations recovered slightly in autumn 1998, but no earthworm was found in the 16 samples sorted in May 1999, following late autumn potato harvesting and spring cultivation for barley. Populations remained at barely detectable levels (less than one individual per sample on average) under successive spring barley crops (Fig. 1). Table 1 gives the abundance of the earthworm species recorded. The decline in total earthworm abundance under potato cropping and subsequent spring barley crops was accompanied by a drastic decrease in species richness—from nine under wheat and wheat–clover crops in 1996–1997 to six under potatoes in 1998, five under barley in 1999 and just one under barley in spring 2000. The epigeic and anecic species Satchellius mammalis (Savigny, 1826), Lumbricus spp. and Aporrectodea longa (Ude, 1885) were least tolerant of cultivation, while the endogeics Allolobophora chlorotica (Savigny, 1826), Aporrectodea caliginosa (Savigny, 1826) and A. rosea (Savigny, 1826) were somewhat more tolerant, but only Murchieona minuscula (Rosa, 1906) appears to have survived the effects of continuous cultivation.
Barley
Barley
0.5 0.5 2.5
4.2
4 1 26
4. Discussion While earthworm populations generally decline over time with continuous arable cropping [6,8,9], this tendency tends to be more pronounced under root crops than under cereals. Thus, earthworms were twice as abundant in plots under continuous wheat for 136 years at Rothamsted Experimental Station than in plots growing wheat and root crops [5]. These trends are thought to reflect differences in food supply, with crop residue inputs in the form of dead roots and straw being much greater under cereal crops than under root crops, where most of the organic matter is harvested. However, in view of the previous cropping history of the field, it is unlikely that the decline in earthworm populations under potato cultivation at Lyons can be attributed to food shortage. Some fungicides, notably benomyl and related compounds, are known to be toxic to earthworms [12], but there is no evidence to suggest that the materials applied for blight control in the present case (metalaxyl + mancozeb, fluazinam, fentin hydroxide) could have any appreciable adverse effects. The decline appears to have been caused directly by the very drastic cultivation prior to sowing the potato crop in spring, and again in late autumn during mechanical harvesting. Destoning is likely to have been particularly detrimental as this process involves lifting, agitating and sieving the topsoil in order to remove stones. Automatic harvesting involves essentially similar and equally severe soil disturbance. The lack of population recovery during the two succeeding years under cereal crops is particularly alarming and suggests that the capacity of the
130
J.P. Curry et al. / Eur. J. Soil Biol. 38 (2002) 127–130
population to recover from perturbation may have been fatally compromised.
[6]
C.A. Edwards, J.R. Lofty, The effect of direct drilling and minimal cultivation on earthworm populations, J. Appl. Ecol. 19 (1982) 723–734.
[7]
A.C. Evans, J.W.McL. Guild, Studies on the relationships between earthworms and soil fertility. V. Field populations, Ann. Appl. Biol. 35 (1948) 485–493.
[8]
P.M. Fraser, P.H. Williams, R.J. Haynes, Earthworm species, population size and biomass under different cropping systems across the Canterbury Plains, New Zealand, Appl. Soil Ecol. 3 (1996) 49–57.
[9]
A.D. Rovira, K.R.J. Smettem, K.E. Lee, Effect of rotation and conservation tillage on earthworms in a red-brown earth under wheat, Aust. J. Agric. Res. 38 (1987) 829–834.
References [1]
[2]
[3]
[4]
[5]
U. Boström, Ecology of earthworms in arable land. Population dynamics and activity in four cropping systems, Report 34, Department of Ecology and Environmental Research, Swedish University of Agricultural Sciences, Uppsala, 1988. J.C. Buckerfield, D.M. Wiseman, Earthworm populations recover after potato cropping, Soil Biol. Biochem. 29 (1997) 609–612. G. Cuendet, Predation on earthworms by the black-headed gull (Larus ridibundus L.), in: J.E. Satchell (Ed.), Earthworm Ecology. From Darwin to Vermiculture, Chapman and Hall, London, 1983, pp. 415–424. J.P. Curry, D. Byrne, K.E. Boyle, The earthworm population of a winter cereal field and its effects on soil and nitrogen turnover, Biol. Fertil. Soils 19 (1995) 166–172. C.A. Edwards, Earthworm ecology in cultivated soils, in: J.E. Satchell (Ed.), Earthworm Ecology. From Darwin to Vermiculture, Chapman and Hall, London, 1983, pp. 123–137.
[10] O. Schmidt, J.P. Curry, Population dynamics of earthworms (Lumbricidae) and their role in nitrogen turnover in wheat and wheat–clover cropping systems, Pedobiologia 45 (2001) 174–187. [11]
R.W. Sims, B.M. Gerard, Earthworms, Synopses of the British Fauna (New Series) No. 31, The Linnean Society of London and the Estuarine and Brackish-Water Sciences Association, London, 1985.
[12] A. Stringer, M.A. Wright, The toxicity of benomyl and some related 2-substituted benzimidazoles to the earthworm Lumbricus terrestris, Pestic. Sci. 7 (1976) 459–464.