Impact of five different tillage systems on soil organic ...

European Journal of Soil Biology 45 (2009) 247–251

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European Journal of Soil Biology journal homepage: http://www.elsevier.com/locate/ejsobi

Original article

Impact of five different tillage systems on soil organic carbon content and the density, biomass, and community composition of earthworms after a ten year period Gregor Ernst*, Christoph Emmerling ¨t Trier, FB VI, Bodenkunde, Campus II, Behringstraße, D – 54286 Trier, Germany Universita

a r t i c l e i n f o

a b s t r a c t

Article history: Received 27 November 2008 Accepted 10 February 2009 Available online 25 February 2009 Handling editor: Stefan Schrader

To assess the impact of different types of soil tillage on the density, biomass, and community composition of earthworms, a long-term field study was performed in which soils were tilled in different ways for ten years. This study included five different types of tillage: (i) plough, (ii) grubber, (iii) disc harrow, (iv) mulch sowing, and (v) direct sowing. At the end of the experiment the earthworm density, biomass, and community composition, and the SOC (soil organic carbon) content were determined. The results show that density, biomass, and community composition of earthworm populations varied in relation to the type of soil tillage used. The density of anecic earthworm species decreased when soils were managed by conventional ploughing, relative to reduced tillage practices, whereas conversely the density of endogeic species increased. Additionally, the varying types of soil tillage influenced the abundance and biomass of different earthworm species in different ways. The density of Aporrectodea caliginosa was positively influenced by ploughing, whereas Aporrectodea longa, Lumbricus castaneus, and Satchellius mammalis showed a positive relationship to the grubber and Allolobophora chlorotica to direct sowing. We attribute these changes to modifications in the vertical distribution of SOC and varying potentials for mechanical damage of earthworms by tillage. A decrease in tillage intensity modified the vertical SOC distribution in the topsoil and consequently revealed positive effects on earthworm biodiversity, thus sustaining soil functioning. Ó 2009 Elsevier Masson SAS. All rights reserved.

Keywords: Reduced tillage Earthworms Community composition SOC Redundancy analysis

1. Introduction Earthworms play a major role in ecosystem functioning. In agricultural ecosystems they enhance the turnover of organic residues [1,3,4,21], increase the microbial activity [2,11,30,32] and therefore contribute to an enhanced mineralisation and nutrient availability in soil. Their burrowing and feeding activity modify the soil structure [18,20] and several soil water characteristics [12,26]. Their impact on soil properties differ between species, functional groups [12,15,25], and varying levels of biodiversity [24]. Thus, in agricultural ecosystems the loss in earthworm biodiversity might negatively effect soil functioning. It is generally acknowledged, that soil tillage can modify the density and community structure of earthworms. However, many studies concerning the impact of conventional tillage practice on the density of earthworm populations showed conflicting results

* Corresponding author. Tel.: þ49 (0)651 201 2254; fax: þ49 (0)651 201 3809. E-mail address: [email protected] (G. Ernst). 1164-5563/$ – see front matter Ó 2009 Elsevier Masson SAS. All rights reserved. doi:10.1016/j.ejsobi.2009.02.002

[7,31]. House [16], Rovira et al. [23], Springett [28], and Francis and Knight [13] observed a decrease in earthworm number when soils were tilled by conventional plough, relative to no-tilled soils. In contrast, Edwards and Lofty [9] and Bostro¨m [5] reported an increase in earthworm numbers when soils were tilled conventionally. Furthermore, studies of Gerard and Hay [14], Wyss et al. [33], and Emmerling [10] gave evidence that also earthworm community compositions may vary within different types of soil tillage. While the number of anecic earthworm species decreased in conventional tilled soils due to an enhanced mechanical damage of their bodies and disturbance of their burrows, higher abundances were found in reduced tilled soils [31,33]. Furthermore, evidence exists that the abundance of endogeic earthworms increases when soils were ploughed [5,33], probably due to a lower bulk density and an increased transport of organic matter in deeper soil layers in conventionally tilled soils. Additionally, the soil organic matter (SOM) might be improved in its palatability and accessibility for endogeic earthworms. The risk of a mechanical damage for generally smaller endogeic earthworms might be lower, relative to anecic species [33]. In a long-term field study Emmerling [10]

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G. Ernst, C. Emmerling / European Journal of Soil Biology 45 (2009) 247–251

reported a higher species richness in reduced tilled soils, compared to ploughed soils. In a variety of agroecosystems of increasing intensity, Decae¨ns and Jimeńez [8] observed decreasing diversity in earthworm populations with increasing tillage intensity. Despite this large amount of studies about the effects of soil tillage on earthworm populations, only few studies have focussed on earthworm density, biomass, and community composition between different types of reduced tillage. However, the loss of biodiversity, which could be due to an intensified agriculture, as well as its consequences for ecosystem functioning are of particular interest [6]. The aims of this study were to assess the impact of five different tillage practices (plough, grubber, disc harrow, mulch sowing, and direct sowing) on the amounts and distribution of soil organic carbon and on the density, biomass, and community composition of earthworms. Thus, a long-term field study was carried out where soils were tilled in different ways for 10 years. 2. Materials and methods 2.1. Research design This field study was performed to measure the impact of five different tillage treatments with varying intensity, as well as the soil organic carbon (SOC) concentrations as a co-variable, on the earthworm density, biomass, and community composition. The experimental site was situated near Welschbillig (49 510 N, 6 330 E), southern Eifel, Germany. Mean annual temperature is 8 C and annual precipitation varies between 600 and 800 mm. The study included five tillage treatments: (i) plough: conventional, soil turning down to 25 cm depth; (ii) grubber: field cultivator, noninversive loosening of the topsoil down to 15 cm depth; (iii) disc harrow: slightly soil loosening down to 15 cm depth; (iv) mulch sowing: a shallow grubber, organic residues remain on the soil surface; (v) direct sowing: without any soil tillage. Each treatment was replicated twice in the field and the area of each plot was 380 m 12 m. During ten years of annual tillage practices a fourcrop rotation schedule was performed including rape, winter wheat, winter barley, and spring barley. Soil tillage was performed in autumn, except for the year of spring barley cultivation, in which tillage was performed in spring. Samples were taken at the end of the experiment after ten years in spring 2008, when winter barley was cultivated. Weather conditions in the winter before the investigations were carried out were relatively warm and wet (mean temperature 3.9 C, total precipitation 222.7 mm; 2007-1221 until 2008-03-21).

between 1.35 0.11 g cm3 at 0–10 cm, 1.53 0.08 g cm3 at 10– 20 cm, and 1.60 0.06 g cm3 at 20–30 cm depth, without any significant differences. 2.3. Earthworm extraction In spring 2008, earthworms were extracted by a combination of hand-sorting from 30 cm deep plots with an area of 0.25 m2 and a subsequent extraction of the deeper living earthworms by applying 10 L of a 0.37% formaldehyde solution [17]. Each extraction was performed in three-fold replication per experimental plot, resulting in six replicates per tillage treatment. Earthworms were fixed in 3.7% formaldehyde solution and species identification followed Sims and Gerard [27]. 2.4. Bulk density and SOC analyses For determination of soil bulk density, eight 100 cm3 cores were taken from 0 to 10 cm, 10–20 cm, and 20–30 cm soil depth per plot. After a 24 h drying period at 105 C soil bulk density was calculated as the dry weight per unit volume of soil. Similar to bulk density, eight replicates of disturbed soil samples were taken for SOC analysis from each depth. Organic residues on soil surface were not included in the samples from 0 to 10 cm depth. SOC was determined by wet potassium dichromate digestion according to Nelson and Somers [22]. The total amount of SOC (kg m2) at 0–30 cm depth was calculated by considering the bulk density in soil. 2.5. Statistical analyses All results are presented as means S.D. Statistical comparison of the total amount of SOC and the earthworm abundance and biomass between the different tillage treatments was done by a one-way ANOVA followed by a post-hoc Tukey-B-test using the SPSS 15.0 software. The impact of the different types of soil tillage and total amount of SOC on the abundance and biomass of the different earthworm species was determined by multivariate ordination analysis using the Canoco version 4.5 software package. Detrended canonical correspondence analysis (DCCA) indicated the use of redundancy analysis (RDA) because of predominantly linear relationships within all data. Significance of the first and of all ordination axes was calculated by the Monte-Carlo significance test. The principle of an RDA is described in detail by Ter Braak and Smilauer [29]. 3. Results

2.2. Soil properties 3.1. SOC The soil at the experimental site was a Eutric Cambisol with a texture varying from silty loam in the topsoil and a clayey loam in the subsoil. The pH value (0.01 M CaCl2; 0–10 cm depth) ranged between 6.9 and 7.1 and the total amount of soil organic carbon (SOC) varied between 5.31 and 5.78 kg m2 at 0–30 cm depth (Table 1). Mean bulk density of all tillage treatments in soil varied

Highest total amounts of SOC in the topsoil (0–30 cm depth) were determined in the plough treatment and lowest in the mulch sowing treatment without any statistically significant differences between the treatments (Table 1). However, the different tillage practices significantly affected the vertical distribution of SOC.

Table 1 Means S.D. of SOC concentrations (mg g1) at different soil depths and the summarised amount of SOC at 0–30 cm depth (kg m2) in different tillage treatments. Different letters indicate significant differences between tillage treatments (ANOVA, Tukey-B-test, p ¼ 0.05 level).

0–10 cm (mg g1) 10–20 cm (mg g1) 20–30 cm (mg g1) Summarised amount of SOC at 0–30 cm (kg m2)

Plough

Grubber

Disc harrow

Mulch sowing

Direct sowing

15.63 0.91 a 15.24 0.43 b 8.73 0.73 a

17.91 1.01 ab 12.19 0.77 a 7.54 1.55 a

19.43 0.67 b 12.33 0.82 a 7.40 1.57 a

17.13 1.45 ab 11.42 0.58 a 6.81 0.69 a

17.50 1.64 ab 11.45 0.69 a 6.65 1.83 a

5.78 0.20 a

5.41 0.31 a

5.49 0.44 a

5.31 0.17 a

5.42 0.49 a


249

Table 2 Means S.D. of the abundance (No m2) of anecic, endogeic, epigeic (only adult), total juvenile, and of all earthworms (adult and juvenile; n ¼ 6) and occurrence of earthworm species in the different tillage treatments. Different letters indicate significant differences between tillage treatments (ANOVA, Tukey-B-test, p ¼ 0.05 level). Plough Anecic Endogeic Epigeic Juvenile Total

4.7 26.7 1.3 86.7 119.3

Earthworm speciesa

An: Lt, Al En: Aca, Ar Ep: Lr, Lc

5.3 a 8.3 c 2.1 a 20.9 a 23.2 a

Grubber

Disc harrow

Mulch sowing

Direct sowing

25.3 10.0 6.7 71.3 113.3

18.7 20.0 7.3 114.0 160.0

21.3 21.3 5.3 84.7 132.7

19.3 2.7 6.7 128.7 157.3

10.0 b 6.1 ab 7.4 a 26.9 a 21.5 a

An: Lt, Al En: Aca, Ar, Ach Ep: Lr, Lc, Sm

10.6 ab 10.1 bc 4.7 a 46.4 a 53.2 a

An: Lt, Al En: Aca, Ar, Ach, Oc Ep: Lr, Lc

10.3 b 9.7 bc 4.8 a 33.2 a 29.9 a

An: Lt, Al En: Aca, Ar, Oc Ep: Lr, Lc, Sm

9.9 ab 4.1 a 7.0 a 53.3 a 62.9 a

An: Lt, Al En: Aca, Ar, Ach Ep: Lr, Lc, Sm

a An ¼ Anecic, En ¼ Endogeic, Ep ¼ Epigeic, Lt ¼ Lumbricus terrestris, Al ¼ Aporrectodea longa, Aca ¼ Aporrectodea caliginosa, Ar ¼ Aporrectodea rosea, Ach ¼ Allolobophora chlorotica, Oc ¼ Octolasion cyaneum, Lr ¼ Lumbricus rubellus, Lc ¼ Lumbricus castaneus, Sm ¼ Satchellius mammalis.

In the plough treatment, the SOC concentrations were 15.63 0.91 mg g1 and 15.24 0.43 mg g1 at 0–10 cm and 10–20 cm depth, respectively. Soil tillage by the disc harrow affected a significant enrichment of SOC at 0–10 cm depth, and all reduced tillage practices led to significantly lower SOC concentrations at 10–20 cm depth, relative to the plough treatment. At 20–30 cm depth no significant differences in SOC concentrations were observed between the different tillage treatments (Table 1).

treatments with reduced tillage the biomass of anecic species was significantly higher relative to the plough treatment. Conversely, endogeic earthworms showed a significant higher biomass in the plough treatment, than in the grubber and the direct sowing treatment. The biomass of epigeic species did not differ significantly between the different tillage treatments (Table 3). 3.4. Relationships between soil tillage and earthworm species composition

3.2. Earthworm abundance At the experimental site in total nine earthworm species were found. In each reduced tillage treatment eight earthworm species were specified, whereas the plough treatment included only six earthworm species (Table 2). Total earthworm abundances varied between 119 23 individuals m2 in the plough treatment and 160 53 individuals m2 in the disc harrow treatment. The earthworm population was generally dominated by juvenile earthworms. The abundances of adult earthworms showed clear differences between the tillage treatments when regarding the different ecological groups. In the plough treatment we found significantly less anecic earthworms than in the grubber and mulch sowing treatments. Additionally, higher abundances of endogeic earthworms were observed in the plough treatment, relative to grubber and direct sowing treatment, especially due to a high density of Aporrectodea caliginosa (data not shown). The abundance of endogeic earthworms in the direct sowing treatment was significantly lower than in the disc harrow and the mulch sowing treatments. The abundances of epigeic species were relatively low, without any significant differences between the tillage treatments (Table 2). 3.3. Earthworm biomass Results of earthworm biomass showed a stronger variability between the treatments than the earthworm abundance. The total biomass was lowest in the plough treatment and significantly higher in the disc harrow treatment (Table 3), which can be attributed to the high number and biomass of anecic species. In all

Fig. 1A shows the ordination diagram of a redundancy analysis (RDA), which was calculated for the environmental variables (types of soil tillage and total amount of SOC) and the abundances of the different earthworm species (adult individuals) as species variables. Eigenvalues of the RDA indicated, that 37.9% of the total variance within the abundances of all earthworm species was explained by the 1st and 2nd ordination axis (Table 4). High species–environment relationships pointed out a strong relationship (species–environment correlation ¼ 0.77) between different soil tillage practices and earthworm species abundances. The abundance of A. caliginosa (Savigny, 1826) showed a positive relationship to the plough and that of Octolasion cyaneum (Savigny, 1826) to the total amount of SOC in the topsoil and the mulch sowing and disc harrow tillage (Fig. 1A). The abundance of Aporrectodea longa (Ude, 1885), Aporrectodea rosea (Savigny, 1826), Lumbricus castaneus (Savigny, 1826), Satchellius mammalis (Savigny, 1826) and Lumbricus terrestris (Linnaeus, 1758) showed a strong positive relationship to the grubber, whereas those of Lumbricus rubellus (Hoffmeister, 1843) and Allolobophora chlorotica (Savigny, 1826) were positively influenced by direct sowing. Particularly the two tillage practices grubber and plough differed considerably in their impact on the earthworm community composition (Fig. 1A). The results of the RDA showed furthermore, that 38.0% of the total variance within the biomass of the earthworm species was explained by the 1st and 2nd ordination axis (Table 4). High species–environment relationships pointed out a strong relationship (species–environment correlation ¼ 0.77) between different soil tillage practices and earthworm species biomass. The biomass of A. caliginosa showed a strong positive relationship to the plough,

Table 3 Means S.D. of the biomass (g fresh weight m2) of anecic, endogeic, epigeic (only adult), total juvenile, and of all earthworms (adult and juvenile) in different tillage treatments (n ¼ 6). Different letters indicate significant differences between tillage treatments (ANOVA, Tukey-B-test, p ¼ 0.05 level). Plough

Grubber

Anecic Endogeic Epigeic Juvenile

10.1 16.3 0.9 39.3

Total

66.7 19.2 a

13.4 a 6.7 c 1.8 a 12.1 a

78.7 4.3 1.9 24.9

Disc harrow 26.1 b 3.0 ab 2.0 a 8.6 a

109.8 20.7 ab

58.3 11.3 4.4 44.9

30.6 b 7.9 bc 4.9 a 20.7 a

118.8 27.7 b

Mulch sowing 53.2 23.6 3.7 29.8

14.8 b 42.8 bc 4.6 a 11.3 a

97.9 21.9 ab

Direct sowing 51.7 0.6 4.1 46.5

26.3 b 0.9 a 6.4 a 23.9 a

103.0 48.7 ab

250


A

0.6

direct sowing

plough

B

1.0

direct sowing

axis 2

axis 2

A. chlorotica

L. rubellus L. terrestris

A. rosea L. castaneus S. mammalis

L. terrestris

A. chlorotica

disc harrow S.mammalis L. castaneus O. cyaneum

A. caliginosa disc harrow

L. rubellus A. rosea

plough

O. cyaneum

A. longa

grubber

SOC grubber

SOC

A. longa

mulch sowing

-0.6 -0.8

0.8

axis 1

mulch sowing A. caliginosa

-0.6 -0.8

1.0

axis 1

Fig. 1. Ordination diagram of the RDA between earthworm abundance (A) and biomass (B) of the different earthworm species (species variables) and the different soil tillage factors and the total amount of SOC in topsoil (environmental variables).

that of A. longa and O. cyaneum to SOC concentrations and to grubber tillage, and that of L. castaneus and S. mammalis was strongly connected to soil tillage with the grubber and the disc harrow. The biomass of the three species A. chlorotica, A. rosea, and L. rubellus was strongly connected to direct sowing, whereas the biomass of L. terrestris was strongest influenced by the disc harrow tillage (Fig. 1B). 4. Discussion Generally, conventional tillage practice with a plough may decrease earthworm density in agricultural ecosystems [13,16,23,28]. In the present study total earthworm abundance was not significantly modified by the different tillage practices. However, the weather conditions in the winter before the investigations carried out were relatively warm and wet, and tillage effects might not be weaken by frost or drought. Joschko et al. [19] emphasized that earthworms react positively to tillage reduction especially in finer textured soils. Assumedly these contradictory results may depend on different soil texture. However, this study confirms results of several previous studies, which demonstrated that ploughing inhibits anecic and promotes endogeic earthworms [5,7,31,33]. Wyss et al. [33] assumed that anecic earthworms comprise a higher risk of mechanical damage, due to their high individual biomass and that the disturbance of their habitats is a relevant factor which could reduce their density. Endogeic earthworms might profit on lower bulk density and an increased transport of organic matter in deeper soil depths of conventionally tilled soils [33]. In this study, bulk density did not differ significantly between the different tillage treatments (data not shown), but SOC was significantly enriched at 10–20 cm depth in ploughed

Table 4 Results of redundancy analysis (RDA). Values for axes 1 and 2 plotted in the RDA diagram in Fig. 1. Axes

Abundance 1

Eigenvalues Species-environment correlations Cumulative percentage variance Species data Species–environment relation Monte-Carlo significance test F-value p-value

Biomass 2

0.291 0.767 29.1 75.6 9.835 0.004

0.088 0.471 37.9 98.4 All axes 3.001 0.004

1

2 0.309 0.774

30.9 79.3 10.738 0.004

0.071 0.559 38.0 97.4 All axes 3.070 0.002

soils. The palatability of the SOM, which generally increases with advanced stages of decomposition [21], and its accessibility in soil might be improved for endogeic earthworms, relative to those in reduced tilled soils. However, results from RDA indicated that the different endogeic earthworm species were affected by the varying tillage practices in different ways. A. caliginosa showed a strong positive relationship to the plough, whereas A. chlorotica was strongly connected to direct sowing and A. rosea to the grubber. After a reduction of the earthworm density by ploughing, A. caliginosa probably could return faster to higher density levels than other endogeic earthworm species, e.g. A. rosea, as observed by Bostro¨m [5]. Generally, A. chlorotica was described to be often found near the roots of plants [27], which might give evidence that a well developed rhizosphere in the direct sowing treatment (a no-tillage treatment) probably might promote the density of this species. Surprisingly, results from RDA indicated that soil tillage with the grubber had a stronger positive effect on the abundance of both anecic species (A. longa and L. terrestris) than the direct sowing and mulch sowing, although the use of the grubber was expected to have a higher risk for mechanical damage of anecic earthworms. In this study, the grubber used had a wide blade spacing, which might be a reason that mechanical damage was relatively low for anecic earthworms. A. longa showed a strong relationship to the total amount of SOC in topsoil. We assume that A. longa, as well as the two epigeic species L. castaneus and S. mammalis, might be promoted by the incorporation of residual organic matter in soil (0–15 cm depth) in the grubber treatment. Similar to anecic species, the grubber might have a relatively low disturbance potential also for L. castaneus and S. mammalis, relative to other types of tillage. The RDA results also indicated that the abundance and biomass of both L. castaneus and S. mammalis were influenced in the same way by the tillage practices. We assume that this might be due to an equal body size and a similar habitat of both species [27]. The abundance and biomass of L. rubellus was strongest connected to direct sowing, which was the treatment with the lowest tillage intensity in this study. The results of the earthworm community composition showed that all reduced tillage treatments comprised a higher species richness (eight species) than the conventional tilled soils (six species), which is in accordance to the results of several other studies. In a long-term field study Emmerling [10] reported a higher species richness in reduced tilled soils, relative to ploughed soils. Additionally, Decae¨ns and Jimeńez [8] observed in a variety of agroecosystems that the diversity of earthworm populations decreased when the intensity of soil tillage increased.


5. Conclusions This study demonstrated that different soil tillage modified the vertical gradient of SOC significantly in the way, that SOC was partly increased in the topsoil under reduced tillage compared to ploughing. Assumedly, both factors, soil tillage and vertical SOC distribution, considerably affected the density, biomass, and community composition of earthworm population. Despite this, it is suggested, that earthworms attended the redistribution of SOC within the soil profile. Earthworm biomass and species richness were generally higher in plough-less tillage systems, whereas little effects were found within the reduced tillage types. The conversion of formerly conventional tillage into reduced or conservation tillage will change SOC distribution in the topsoil and will positively effect earthworm biomass and biodiversity, and thus might be important to sustain soil conservation and plant production in agroecosystems. Acknowledgements The experiment was arranged by the Landwirtschaftskammer Rheinland-Pflalz. We like to thank Prof. Dr. Thomas Appel (University of Applied Sciences, Bingen, Germany) for providing SOC and bulk density data. References [1] J.A. Amador, J.H. Go¨rres, Role of the anecic earthworm Lumbricus terrestris L. in the distribution of plant residue nitrogen in a corn (Zea mays)–soil system, Appl. Soil Ecol. 30 (2005) 203–214. [2] P.J. Bohlen, C.A. Edwards, Earthworm effects on soil N dynamics and respiration in microcosms receiving organic and inorganic nutrients, Soil Biol. Biochem. 27 (1995) 341–348. [3] P.J. Bohlen, R.W. Parmelee, D.A. McCartney, C.A. Edwards, Earthworm effects on carbon and nitrogen dynamics of surface litter in corn agroecosystems, Ecol. Appl. 7 (1997) 1341–1349. [4] P.J. Bohlen, R.W. Parmelee, M.F. Allen, Q.M. Ketterings, Differential effects of earthworms on nitrogen cycling from various nitrogen-15-labeled substrates, Soil Sci. Soc. Am. J. 63 (1999) 882–890. [5] U. Bostro¨m, Earthworm populations (Lumbricidae) in ploughed and undisturbed leys, Soil Till. Res. 35 (1995) 125–133. [6] CBD, Multilateral Convention on Biological Diversity, No. 30619, Rio de Janeiro, 5 June 1992. [7] K.Y. Chan, An overview of some tillage impacts on earthworm population abundance and diversity – implications for functioning in soils, Soil Till Res. 57 (2001) 179–191. [8] T. Decae¨ns, J.J. Jimeńez, Earthworm communities under an agricultural intensification gradient in Colombia, Plant Soil 240 (2002) 133–143. [9] C.A. Edwards, J.R. Lofty, Effects of cultivations on earthworm populations, Report of Rothamsted Experiment Station for 1968, 1969, pp. 247–248. [10] C. Emmerling, Response of earthworm communities to different types of soil tillage, Appl. Soil Ecol. 17 (2001) 91–96. [11] G. Ernst, A. Mu¨ller, H. Go¨hler, C. Emmerling, C and N turnover of fermented residues from biogas plants in soil in the presence of three different earthworm species (Lumbricus terrestris, Aporrectodea longa, Aporrectodea caliginosa), Soil Biol. Biochem. 40 (2008) 1413–1420.

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