Effects of organic matter content on earthworms and nitrogen mineralization in grassland soils

Available online at www.sciencedirect.com

European Journal of Soil Biology 43 (2007) S222eS229 http://www.elsevier.com/locate/ejsobi

Original article

Effects of organic matter content on earthworms and nitrogen mineralization in grassland soils P.C.J. van Vliet*, B. van der Stelt, P.I. Rietberg, R.G.M. de Goede Department of Soil Quality, Wageningen University, PO Box 8005, 6700 EC Wageningen, Netherlands Available online 2 October 2007

Abstract Earthworms play an important role in the nitrogen cycle in the soil. Through their activities they affect the mineralization of organic matter directly and indirectly. However, the presence of organic matter also affects earthworm abundances. For this study, we selected 2 grasslands differing in organic matter content at nine dairy farms on sandy soils in the Noordelijke Friese Wouden (NFW) in the Netherlands. We expected a larger number of earthworms and a higher mineralization rate in grasslands with a higher organic matter content. We also expected a positive relationship between earthworm abundance and nitrogen mineralization. At each farm the grassland with the highest organic matter content contained the largest number of earthworms (up to 858 worms m2), (r ¼ 0.286 (p ¼ 0.036)). These grasslands also had the highest root biomass (r ¼ 0.504 (p ¼ 0.0001). With an increase in organic matter in the soil (from 5 to 10.2%), potential nitrogen mineralization increased from 138 to 310 kg N1 ha 6 months1. No relationships between the calculated amount of nitrogen mineralized by earthworms and the potential and actual nitrogen mineralization were found. Nitrogen mineralization due to earthworm activities, calculated using production ecological formulas, ranged from 4 to 24 kg N ha1 month1. Ó 2007 Elsevier Masson SAS. All rights reserved. Keywords: Earthworms; Grassland; Organic matter; Nitrogen; Mineralization

1. Introduction To comply with European legislation, Dutch farmers are allowed to fertilize their grasslands with animal slurry manure to a maximum of 250 kg N ha1 year1 [1], and nitrate concentrations in the upper groundwater should not exceed 50 mg L1 [2]. To satisfy environmental regulations while at the same time maintain grass production, farmers have to adopt a fertilization * Corresponding author. Tel.: þ31 317 482344; fax: þ31 317 483766. E-mail address: [email protected] (P.C.J. van Vliet).

regime in which N-uptake by plants is maximized while N-losses to the environment are minimized. One way farmers address this issue is by producing manure slurry with a higher C-to-N ratio (raised from 6 to 10) and a lower Nmineral-to-Ntotal ratio (reduced to < 0.5). By using this type of manure slurry, farmers become more dependent on soil biological processes that play a role in the decomposition of the manure slurry. An important role in the mineralization of nitrogen from organic matter is played by earthworms. De Goede et al. [3] estimated that earthworms contribute 85 or 170 kg N ha1 year1 to gross N mineralization in grasslands which are fertilized either with inorganic

1164-5563/$ - see front matter Ó 2007 Elsevier Masson SAS. All rights reserved. doi:10.1016/j.ejsobi.2007.08.052

P.C.J. van Vliet et al. / European Journal of Soil Biology 43 (2007) S222eS229

N or with cattle manure slurry. Furthermore, earthworms also affect soil physical properties as they ingest and excrete soil; they construct burrows and produce excrement, which is partly deposited on the soil surface. Earthworm abundances in soils are affected by soil type, hydrology, cultivation and organic matter management [4]. Minimizing physical disturbance of the soil and increasing food supply through organic amendments promote earthworm activity. Organic matter, whether in the form of living plant biomass, surfacedeposited residues or incorporated residues into the soil, is one of the main factors determining earthworm abundances [5]. In general, the organic matter content of grassland soils, which is affected by field management and plant species, increases with usage time of the grassland [6e8]. An increase in soil organic matter (SOM) seems to favor the abundance of earthworms, which will then affect N mineralization and hence plant nutrition. However, the risk that part of the mineralized N will be leached, as a result of an increased macro-pore flow through the (extra) constructed burrows, will also increase [9e11]. A modeling study by Sonneveld and Bouma [7] indicated that older grasslands in the northern part of the Netherlands were at a higher risk of NO 3 levels exceeding the environmental threshold of 50 mg L1 in the upper groundwater, than younger grasslands. In this field study we determined the consequences of differences in soil organic matter content for earthworm populations and nitrogen mineralization. We expected a larger number of earthworms (hypothesis 1) and a higher mineralization rate (hypothesis 2) in grasslands with a higher organic matter content. Because earthworms contribute considerably to N mineralization, we expected higher mineralization rates to be related to higher earthworm abundances (hypothesis 3). 2. Materials and methods 2.1. Field experiment We selected nine dairy farms located on sandy soils in the northern part of the Netherlands. At each farm, two grasslands which differed in organic matter content were selected. Clay and silt content ranged from 2.5 to 6.8 (average 4.9%) and 11.0 to 19% (average 15.1%), respectively. The average pH measured in 0.01 M CaCl2 was 5.0 (range 4.5e5.4); carbon and nitrogen content ranged from 3.3 to 6.0 (avg. 4.7%), and from 0.3 to 0.5 (avg. 0.4%), respectively. Soil samples for determination of the organic matter (OM) content

S223

(loss-on-ignition method [12]) in the 0e10 cm layer were taken in spring 2004. In each grassland, a plot of 250 m2 was laid out and a grass cage was placed to prevent grass consumption by animals. Triplicate pits of 20  20  20 cm were sampled for earthworms in each plot in April, June and September 2004. Five hundred milliliters of 0.2% formaldehyde was poured into each pit to recover earthworms occurring below 20 cm. All earthworms were weighed (fresh weight without emptying gut) and identified to species. The species were allocated to the categories anecic, epigeic or endogeic [13]. At the three sampling dates aboveground grass production was determined by clipping a 0.25 m2 area located in the grass cage. Root biomass was determined by taking 8 soil samples (7.6 cm diameter) to a depth of 15 cm from which roots (and earthworm cocoons) were washed using a 1 mm mesh sieve. Grass and roots were dried for 48 h at 70  C and weighed. Throughout the plot, 40 soil samples were taken to a depth of 10 cm for soil chemical analyses and for the determination of potential and actual mineralization rates. Prior to soil chemical analyses, part of the soil was dried at 40  C for 24 h and sieved through a 2 mm sieve. Total C and N contents were determined using a Fisons Instruments EA 1108 CHN-analyzer. Soil pH and nutrient content of the soil were determined after extraction with 0.01 M CaCl2 [14]. Concentrations  of N-NHþ 4 , N-NO3 , and soluble Ntotal were measured using a Skalar Segmented Flow Analyzer. All results were expressed on a m2 basis. 2.2. Measured nitrogen mineralization Potential N mineralization was determined by rewetting dried sieved soil to 60% of the water holding capacity and incubating this soil with a constant soil moisture at 20  C for 12 weeks. The difference in mineral nitrogen content after 2, 6 and 12 weeks of incubation was taken as a measure for the potential mineralization rate of the soil. The actual nitrogen mineralization rate was determined by incubating field moist sieved (<5 mm) soil for 6 weeks at the soil temperature and moisture content when the soil samples were taken. Incubation temperatures were calculated using the equation Xb ¼ 0.7Xa þ 3.5 [15] in which Xb corresponds to the soil temperature in the 10 cm soil layer below the soil surface. The air temperature (Xa) was obtained from a nearby weather station [16]. The calculated soil temperatures at the sampling times in April, June and September were 8, 14 and 15  C, respectively. The

S224

P.C.J. van Vliet et al. / European Journal of Soil Biology 43 (2007) S222eS229

moisture content of the soils sampled during the April, June and September sampling dates, was on average 37%, 19% and 33%, respectively. 2.3. Estimated nitrogen mineralization by earthworms Nitrogen mineralization due to earthworm activities was estimated using production ecological formulas [17]. Respiration was calculated according to Persson et al. [18]: Q ¼ a*Wb, where Q is the amount of O2 consumed (mm3 individual1 h1), a and b are species-specific parameters and W is the body weight (gram fresh weight). Since, the parameters a and b are temperature-dependent, Q is corrected for temperature using a Q10 value of 2. After respiration is calculated, assimilation, consumption, excretion and production can be derived using assimilation and production efficiencies [19, 20]. These are then recalculated from carbon into nitrogen, thereby assuming that the production C to production N ratio and the consumption C to consumption N ratio were similar to the C:N rations in the earthworms and food sources, respectively [21]. We also assumed that the food of the earthworms consisted mainly of dead organic matter (e.g. [22]) and that the quality of the food of endogeic earthworms is of lower quality (higher C:N) than that of anecic and epigeic worms [13, 23] Hence, we assumed that the food of endogeic earthworms consisted of detritus and dead roots resulting in a food C:N ratio of 12.4. Since anecic earthworms feed partly on litter, but live in the soil in burrows, we assumed that their food consisted of detritus, roots, fungi and bacteria with a final C:N ratio of 11.8. Epigeic earthworms feed mainly on fresh organic material and bacteria and fungi associated with it [23], resulting in a C:N ratio of 8.8. In Table 1 the basis for the calculations of these food C:N ratios is shown. All

Table 1 Food preferences (percentage) for the different ecological groups of earthworms Food source

Anecic

Endogeic

Roots (C:N ¼ 7.5) Bacteria (C:N ¼ 8) Fungi (C:N ¼ 10) Detritus (C:N ¼ 15) Protozoa (C:N ¼ 7) Fresh organic matter (C:N ¼ 7.5) C:N food

10 10 30 50

30

70

Epigeic 20 20 10 50

11.8

12.4

8.8

The food C:N ratio is calculated by multiplying the food preference divided by 100 with the C:N ratio of the food source. The C:N food is based on these calculations.

other parameters used for the production ecological calculations are shown in Table 2. Soil temperatures for the respiration calculations were recalculated from air temperatures as mentioned above. To calculate mineralization by earthworms in the 6 month period from April until September, we estimated monthly densities by linear extrapolation of the known abundances in April, June and September to abundances in May, July and August. 2.4. Statistical analysis SAS/STAT version 9.1 was used for statistical analysis of the data. Within farm results were analyzed using paired t-tests (low organic matter versus high organic matter content). Regression and correlation analyses were used to determine relationships between earthworms and the chemical measurements (soil organic matter content, N mineralization). 3. Results The organic matter content of the 18 grasslands ranged from 5.0 to 10.2% with a mean of 8.0%. With an increase in organic matter content, earthworm abundances increased (Fig. 1), although this relationship was not significant in April. At each farm the grassland with the highest organic matter content had the highest root biomass (Table 3) (paired t-test, p ¼ 0.038). These grasslands also contained the largest abundances of earthworms (paired t-test, p ¼ 0.002) and had the highest numbers of cocoons (paired t-test, p ¼ 0.002). Aboveground biomass in the different grasslands was not affected by organic matter content. Also, no relationship between aboveground biomass and earthworm abundances or biomass was observed. Nine species of earthworms were found in the different plots (Table 3). Endogeic species were the most abundant; abundances ranged from 17 m2 in a low organic matter plot to 716 m2 in a high organic matter plot. The most abundant endogeic species was Aporrectodea caliginosa. Also for epigeic species, higher abundances were present in the high organic matter plots. In contrast, abundances of anecic species were higher in the low organic matter plots. This difference is primarily caused by Lumbricus terrestris which was more abundant in low organic matter plots (Table 3). Potential nitrogen mineralization rates ranged from 118 to 310 kg N ha1 for a 6 month period (Table 4). Potential N mineralization was positively correlated with the soil OM content (Pearson r ¼ 0.516, p ¼ 0.029).

P.C.J. van Vliet et al. / European Journal of Soil Biology 43 (2007) S222eS229

S225

Table 2 Parameter values used for the production ecological calculations Parameter

Anecic

Endogeic

Epigeic

Reference

Individual weight (full gut) Gut contents correction Individual weight (g) Fresh/dry wt C-contents (% of dw) C/N ratio earthworm A B Q10 Base temperature Assimilation efficiency C Production efficiency C Assimilation efficiency N Production efficiency N Gross production efficiency C/N food

2.17 10% 1.95 5.5 50 5 81 0.90 2 19 0.21 0.2 0.30 0.33 0.10 11.8

0.45 15% 0.38 5.5 50 5 78 0.91 2 19 0.03 0.1 0.14 0.05 0.01 12.4

0.68 10% 0.61 5.5 50 5 93 0.84 2 19 0.10 0.2 0.20 0.18 0.04 8.8

Derived from dataset [24]

A/C P/A

Actual mineralization rates ranged from 10 to 47 kg N ha1 month1. The mineralization rate in June correlated well with the potential N mineralization rate (Pearson r ¼ 0.596, p ¼ 0.009). Actual mineralization rates on the other 2 sampling dates did not correlate with the potential nitrogen mineralization rate. Actual mineralization rates did not correlate either with the organic matter content of the different plots. Nitrogen mineralization due to earthworm activities, calculated using production ecological formulas, ranged from 4 to 24 kg N ha1 month1. Since endogeic earthworms were the most abundant in the different plots, their contribution to the calculated N mineralization was highest in all plots, ranging from 21 to 92% of the total N amount mineralized by earthworms (Fig. 2). The contribution of anecic and epigeic

[24] [17] [17] [17, 24] [17, 24] [24] [24] [24, 26] [27e29] [30e32] Calculated [33]

earthworms to the total N amount mineralized was much smaller, ranging from 0 to 48%, and 0 to 52%, respectively. In a period of 6 months (April to September) earthworms mineralized on average 51 kg N ha1 in the low organic matter plots and 69 kg N ha1 in high organic matter plots. Earthworm abundances and biomass did not correlate with potential mineralization rates. Also no correlation between the calculated amount of nitrogen mineralized by earthworms in the period of April to September and the potential nitrogen mineralization was found (Fig. 3). Correlations between the calculated nitrogen mineralization by epigeic, endogeic and anecic earthworms and the potential nitrogen mineralization or actual mineralization rates were not significant, either. 4. Discussion

1000 April 2004 June 2004 Sept. 2004

900

Number m-2

800 700 600 500 400 300 200 100 0 5

6

7

8

9

10

11

% OM

Fig 1. Relationship between organic matter percentage (% OM) and the number of earthworms for the 3 sampling periods. Equations: April, n.s.; June, y ¼ 25.84x 21.00, r2 ¼ 0.2658, p ¼ 0.0285; Sept, y ¼ 65.26x þ 2.34, r2 ¼ 0.2366, p ¼ 0.0407.

Due to differences in abiotic conditions (mainly soil moisture and temperature) during the season, abundances of earthworms and fractions of epigeic, endogeic and anecic earthworms varied during the growing season. However, our first hypothesis, that numbers of earthworms would be higher in the high organic matter plots than the low organic matter plots, can be accepted. Our results corroborate the findings of Hendrix et al. [34], who found higher earthworm abundances with an increasing soil organic carbon content. In our study, the grasslands with a higher OM content were left undisturbed and were fertilized with slurry manure for a longer time, apparently resulting in more food sources and/or better habitats for earthworms. De Goede et al. [3] found similar densities ranging from 59 (summer) to 830 m2 (autumn) in the

P.C.J. van Vliet et al. / European Journal of Soil Biology 43 (2007) S222eS229

S226

Table 3 Averages and minimum-maximum ranges of variables determined in the low (low OM) and high organic matter (high OM) grasslands Unit

OM-effect

Low OM Avg

High OM (minemax)

Avg

(minemax)

Endogeic species Allolobophora chlorotica Aporrectodea caliginosa A. rosea A. limicola Anecic species A. longa Lumbricus terrestris Epigeic species L. rubellus L. castaneus Satchellius mammalis

Number Number Number Number Number Number Number Number Number Number Number Number

2

m m2 m2 m2 m2 m2 m2 m2 m2 m2 m2 m2

LH ns L>H L
209 15 182 9 2 54 38 16 48 29 16 4

(17e527) (0e83) (17e488) (0e34) (0e57) (0e150) (0e142) (0e59) (0e150) (0e73) (0e98) (0e57)

307 39 246 16 6 33 26 8 88 50 23 14

(75e716) (0e252) (35e682) (0e51) (0e84) (0e93) (0e76) (0e25) (25e228) (0e157) (0e101) (0e169)

Earthworm cocoons Earthworm numbers Earthworm biomass

Number m2 Number m2 g fw m2

L
926 310 183

(174e2213) (67e608) (33e436)

1404 421 192

(522e3059) (125e858) (50e355)

Root biomass Aboveground biomass

g m2 kg ha1

L
647 1463

(346e898) (279e2776)

715 1470

(391e1130) (587e3045)

Potential N mineralisation Actual N mineralisation

kg N ha1 6 months1 kg N ha1 month1

L  H (p ¼ 0.097) ns

189 26.4

(118e278) (15.9e44.9)

226 25.4

(158e310) (10.0e47.1)

Results of paired t-tests (p < 0.05) (unless shown otherwise) are shown in the column OM-effect. L, Low organic matter content; H, high organic matter content; ns, not significant.

same region of the Netherlands. Variations in earthworm densities were also similar: low in summer (our June data) and much higher in autumn (our September data). Lower earthworm densities were reported by Edwards [35] Table 4 Potential nitrogen mineralization (kg N ha1 6 months1) and the actual nitrogen mineralization (kg N ha1 month1) in high and low organic matter plots on 9 farms Farm

1 1 2 2 3 3 4 4 5 5 6 6 7 7 8 8 9 9

%OM

9.27 9.99 5.06 6.65 6.99 8.82 6.94 8.61 7.02 9.92 7.80 8.58 5.96 7.35 8.17 10.16 7.35 9.32

Pot Nmin (kg N ha1 6 months1)

April

June

Sept

208.7 223.9 183.3 157.6 190.3 268.4 193.7 309.8 171.0 185.2 221.4 239.5 118.3 201.1 137.7 235.8 278.1 217.9

21.5 30.0 25.1 21.0 22.9 26.6 26.3 22.0 21.0 10.0 22.9 26.6 20.5 29.2 31.6 18.6 34.0 36.1

31.7 30.7 33.3 19.9 28.9 21.0 27.5 47.1 21.5 28.6 25.7 36.2 27.3 31.1 23.0 14.1 44.9 27.4

20.9 26.4 31.4 20.7 27.0 22.6 15.9 25.6 22.7 24.8 25.0 30.2 25.1 22.1 27.3 17.4 27.7 20.9

Actual Nmin (kg N ha1 month1)

(average 255 worms m2) and Curry [4] (<400 worms m2), which may be related to regularly ploughing of grasslands, which reduces earthworm abundances [9, 36, 37]. In contrast, the grasslands in this study were not roughed up for at least 5 years. In our study we found a higher potential nitrogen mineralization rate as the organic matter content of the grassland increased, which confirms our second hypothesis. Haynes [38] has shown that older pastures have a higher total C and N content, higher water soluble C and N and a higher light fraction C content, than younger pastures. Apparently, in our high organic matter grassland soils sufficient nitrogen was present, which in combination with a high amount of labile carbon resulted in higher potential mineralization rates than in the low organic matter grasslands. The estimated nitrogen mineralization due to earthworms (51e69 kg N ha1 6 months1) is in accordance with the estimates by De Goede et al. [3] (85e170 kg N ha1 year1). Several other studies have estimated N mineralization due to earthworms ranging from 10 to 74 kg N ha1 year1 (e.g., [33]). Estimates in our study are larger, which is mainly due to the fact that our study contained undisturbed grasslands with high abundances of earthworms. We observed no relationships between the calculated nitrogen mineralization by earthworms and potential

P.C.J. van Vliet et al. / European Journal of Soil Biology 43 (2007) S222eS229 epigeic: ns endogeic: L < H p = 0.007 anecic: ns total earthworms: L < H p = 0.03

90 April 2004

kg N ha-1 month-1

25 epigeic endogeic anecic

20 15 10 5 0

1L 1H 2L 2H 3L 3H 4L 4H 5L 5H 6L 6H 7L 7H 8L 8H 9L 9H

Code

B

epigeic: L < H p = 0.003 endogeic: ns anecic: ns total earthworms: ns

June 2004

kg N ha-1 month-1

25

15 10 5

1L 1H 2L 2H 3L 3H 4L 4H 5L 5H 6L 6H 7L 7H 8L 8H 9L 9H

Code epigeic: L < H p = 0.074 endogeic: ns anecic: L > H, p = 0.076 total earthworms: ns

Sept 2004

25

kg N ha-1 month-1

5-6% OM 6-7% OM 7-8% OM 8-9% OM 9-10% >10%

80 70 60 50 40 30 100

150

200

250

300

350

Pot Nmin (kg N ha-1 6 months-1) Fig. 3. The relationship between the calculated N mineralization by earthworms (kg N ha1 6 months1) and the potential N mineralization (Pot Nmin) (kg N ha1 6 months1). Symbols refer to categories of soil organic matter content.

20

0

C

Calculated earthworm (Nmin kg N ha-1 6 months-1)

A

S227

20 15 10 5 0 1L 1H 2L 2H 3L 3H 4L 4H 5L 5H 6L 6H 7L 7H 8L 8H 9L 9H

Code Fig. 2. Calculated N mineralization (kg N ha1 month1) by the three earthworm ecological groups for the different plots at the different farms in April (A), June (B) and September 2004 (C). In ‘‘code’’ the number refers to the farm, while the L and H refer to the low- and high-organic matter plot, respectively. Statistical results (paired t-test) of the effect of OM on the N mineralization by the different earthworm ecological types are shown.

and actual nitrogen mineralization rates, so we reject hypothesis 3. Potential and actual mineralization rates were determined in root-free, sieved soil during a standard period of time (12 or 6 weeks, respectively). During the 6 months period, earthworm abundances varied considerably due to the abiotic circumstances. These

variations had considerable effect on the calculated N-mineralization and might explain the lack of relationship between the potential and actual N mineralization estimates and the calculated estimates. The most abundant earthworm species in the grasslands were A. longa, A. caliginosa and L. rubellus. The latter two species were also the most common in an earthworm study in the Netherlands by Didden [39]. L. rubellus is an epigeic species which occurs mostly in the top layer of the soil, which in the Netherlands is often not disturbed and is rich in food sources due to the application of slurry manure several times during the growing season. A. caliginosa is an endogeic species, which occurs mainly in the mineral layer of the soil. In Dutch grasslands, this layer contains a large amount of roots, hereby creating an environment conducive to these earthworms. Endogeic earthworms have due to their low food quality (detritus C:N ratio 15) low assimilation and production efficiencies [25]. Large abundances of endogeic worms found in the grassland plots resulted in a high contribution to the total amount of nitrogen mineralized. Anecic worms select higher quality food sources, resulting in higher assimilation and production efficiencies [40]. However, they were present in much lower numbers than the endogeic worms. Their contribution to the total amount of nitrogen mineralized was similar to the contribution by epigeic worms. The estimated nitrogen mineralization by earthworms using production ecological formulas corresponds to the direct contribution of earthworms. Indirect contributions, for instance the mixing of organic matter into the soil which makes the material more easy to decompose by microorganisms, are not included in this calculation. We

S228

P.C.J. van Vliet et al. / European Journal of Soil Biology 43 (2007) S222eS229

therefore expect the calculated mineralization to be a minimum estimate; the contribution of earthworms in the field may be much larger. To fertilize agricultural fields efficiently, it is important to estimate the amount of nitrogen that can be mineralized from the applied slurry manure and the soil during the growing season. The potential nitrogen mineralization method is often used to estimate the N supply capacity of the soil [41]. However, this method does not include stimulatory effects of roots and soil fauna on nitrogen mineralization. We found no relationship of this parameter with the calculated N mineralization by earthworms. For more efficient fertilization, effects of soil fauna and plants on nitrogen mineralization have to be taken into account. Field experiments that include these factors and also encompass variable abiotic conditions are a route to a better understanding of the role of plants and soil biota in nitrogen mineralization and hence, a basis for an improved estimation of nitrogen mineralization in the field. Acknowledgements We thank all farmers for allowing us to perform our research on their grasslands. We thank all people that have aided in the collection of the earthworms and soil samples. Thanks are also due to Tamas Salanki for identifying all earthworms and to Lijbert Brussaard and two anonymous reviewers for their constructive comments on an earlier version of the manuscript. This study was funded by a grant from the Foundation for Soil Knowledge Development and Transfer (SKB) and Wageningen University and Research Center. References [1] Anonymous, COMMISSION DECISION of 8 December 2005 granting a derogation requested by the Netherlands pursuant to Council Directive 91/676/EEC concerning the protection of waters against pollution caused by nitrates from agricultural sources (notified under document number C(2005) 4778) (2005/880/EC), Official Journal of the European Union, 2005. [2] P. de Clercq, A.C. Gersis, G. Hofman, S.C. Jarvis, J.J. Neeteson, F. Sinabell, Nutrient management legislation in European countries, Wageningen Pers, Wageningen, The Netherlands, 2001. [3] R.G.M. de Goede, L. Brussaard, A.D.L. Akkermans, On-farm impact of cattle slurry manure management on biological soil quality, Neth. J. Agr. Sci. 51 (2003) 103e133. [4] J.P. Curry, The composition of the invertebrate fauna, Grassland Invertebrates, Ecology, influence on soil fertility and effects on plant growth, Chapman & Hall, London, 1994, pp. 33e123. [5] J. Scown, G. Baker, The influence of livestock dung on the abundance of exotic and native earthworms in a grassland in south-eastern Australia, Eur. J. Soil Biol 42 (2006) S310eS315.

[6] B. Christensen, A.E. Johnston, Soil organic matter and soil quality lessons learned from long-term experiments at Askov and Rothamsted, in: E.G. Gregorich, M.R. Carter (Eds.), Soil Quality for Crop Production and Agroecosystem Health, Developments in Soil Science 25, Elsevier, Amsterdam, 1997. [7] M.P.W. Sonneveld, J. Bouma, Effects of different combinations of land use history and nitrogen application on nitrate concentration in the groundwater, Neth. J. Agr. Sci 51 (2003) 135e146. [8] M.M. Pulleman, J. Bouma, E.A. van Essen, E.W. Meijles, Soil organic matter content as a function of different land use history, Soil Sci. Soc. Am. J 64 (2000) 689e693. [9] J. Domı´nguez, P.J. Bohlen, R.W. Parmelee, Earthworms increase nitrogen leaching to greater soil depths in row crop agroecosystems, Ecosystems 7 (2004) 672e685. [10] W.D. Shuster, M.J. Shipitalo, S. Subler, S. Aref, E.L. McCoy, Earthworm additions affect leachate production and nitrogen losses in typical Midwestern agroecosystems, J. Environ. Qual 32 (2003) 2132e2139. [11] X. Wang, F. Hu, H.-X. Li, Contribution of earthworm activity to the infiltration of nitrogen in a wheat agroecosystem, Biol. Fertil. Soils 41 (2005) 284e287. [12] V.J.G. Houba, J.J. van der Lee, I. Novozamsky, Soil Analysis Procedures, Other procedures (Soil and Plant Analysis, part 5B), Wageningen University, Wageningen, 1997. [13] M.B. Bouche´, Strategies lombriciennes, in: U. Lohm, T. Persson (Eds.), Soil Organisms as Components of Ecosystems, Ecological Bulletins 25, 1977, pp. 122e132. [14] V.J.G. Houba, E.J.M. Temminghoff, G.A. Gaikhorst, W. van Vark, Extraction with 0.01 M CaCl2, Wageningen University, Wageningen, 1999. [15] B.C. Verschoor, R.G.M.d Goede, F.W.d Vries, L. Brussaard, Changes in the composition of the plant-feeding nematode community in grasslands after cessation of fertilizer application, Appl. Soil Ecol 17 (2001) 1e17. [16] Anonymous, Climatic data Royal Netherlands Meteorological Institute, 2004. [17] W.A.M. Didden, J.C.Y. Marinissen, M.J. Vreeken-Buijs, S.L.G.E. Burgers, R.d Fluiter, M. Geurs, L. Brussaard, Soil meso- and macrofauna in two agricultural systems: factors affecting population dynamics and evaluation of their role in carbon and nitrogen dynamics, Agric. Ecosyst. Environ 51 (1994) 171e186. [18] T. Persson, E. Ba˚a˚th, M. Clarholm, H. Lundkvist, B.E. So¨derstro¨m, B. Sohlenius, Throphic structure, biomass dynamics and carbon metabolism of soil organisms in a Scots pine forest, in: T. Persson (Ed.), Structure and Function of Northern Forestsd An Ecosystem Study, Ecological Bulletins 32, 1980, pp. 419e459. [19] H.W. Hunt, D.C. Coleman, E.R. Ingham, R.E. Ingham, E.T. Elliott, J.C. Moore, S.L. Rose, C.P.P. Reid, C.R. Morley, The detrital food web in a shortgrass prairie, Biol. Fertil. Soils 3 (1987) 57e68. [20] P.C. de Ruiter, J. Bloem, L.A. Bouwman, W.A.M. Didden, G.H.J. Hoenderboom, G. Lebbink, J.C.Y. Marinissen, J.A.d Vos, M.J. Vreeken-Buijs, K.B. Zwart, L. Brussaard, Simulation of dynamics in nitrogen mineralization in the belowground food webs of two arable farming systems, Agric. Ecosyst. Environ 51 (1994) 199e208. [21] T. Persson, Influence of soil animals on nitrogen mineralisation in a northern Scots pine forest, New trends in Soil Biology, Proceedings of the VIII Intl. Colloquium of Soil Zoology, 1983, pp. 117e126.

P.C.J. van Vliet et al. / European Journal of Soil Biology 43 (2007) S222eS229 [22] P. Lavelle, F. Charpentier, C. Villenave, J.-P. Rossie, L. Derouard, B. Pashanasi, J. Andre, J.-F. Ponge, N. Bernier, Effects of earthworms on soil organic matter and nutrient dynamics at a landscape scale over decades, in: C.A. Edwards (Ed.), Earthworm Ecology, CRC Press, Boca Raton, 2004, pp. 145e160. [23] P. Lavelle, Earthworm activities and the soil system, Biol. Fertil. Soils 6 (1998) 237e251. [24] T. Persson, U. Lohm, Enchytraeidae/ Lumbricidae, in: T. Rosswall (Ed.), Energetical Significance of the Annelids and Arthropods in a Swedish Grassland soil, Ecological Bulletins No. 23, Swedish Natural Science Research Council, Stockholm, 1977, pp. 34e47, 167-194. [25] P.J. Bolton, J. Phillipson, Burrowing, feeding, egestion and energy budgets of Allolobophora rosea (Savigny) (Lumbricidae), Oecologia 23 (1976) 225e245. [26] A. Martin, A. Mariotti, J. Balesdent, P. Lavelle, Soil organic matter assimilation by a geophagous tropical earthworm based on d13C measurements, Ecology 73 (1992) 118e128. [27] H. Petersen, M. Luxton, A comparative analysis of soil fauna populations and their role in decomposition processes, Oikos 39 (1982) 288e388. [28] J.B. Byzova, Comparative rate of respiration in some earthworms, Revue D’Ecologie et de Biologie du Sol 2 (1965) 207e216. [29] U. Bo¨strom, Earthworm population dynamics and flows of carbon and nitrogen through Aporrectodea caliginosa (Lumbricidae) in four cropping systems, Swedish University of Agricultural Sciences, Uppsala, 1988. [30] F. Binet, P. Trehen, Experimental microcosm study of the role of Lumbricus terrestris (Oligochaeta: Lumbricidae) on nitrogen dynamics in cultivated soils, Soil Biol. Biochem 24 (1992) 1501e1506. [31] M.B. Bouche´, F. Al-Addan, J. Cortez, R. Hammed, J.-C. Heidet, G. Ferriere, D. Mazaud, M. Samih, Role of earthworms in the

[32]

[33]

[34]

[35]

[36]

[37] [38]

[39] [40]

[41]

S229

N cycle: a falsifiable assessment (5th International Symposium on Earthworm Ecology), Soil Biol. Biochem 29 (1997) 375e380. J.K. Whalen, R.W. Parmelee, Quantification of nitrogen assimilation efficiences and their use to estimate organic matter consumption by the earthworms Aporrectodea tuberculata (Eisen) and Lumbricus terrestris L, Appl. Soil Ecol 13 (1999) 199e208. J.K. Whalen, R.W. Parmelee, Earthworm secondary production and N flux in agroecosystems: a comparison of two approaches, Oecologia 124 (2000) 561e573. P.F. Hendrix, B.R. Mueller, R.R. Bruce, G.W. Langdale, R.W. Parmelee, Abundance and distribution of earthworms in relation to landscape factors on the Georgia piedmont, USA, Soil Biol. Biochem 24 (1992) 1357e1361. C.A. Edwards, The importance of earthworms as key representatives of the soil fauna, in: C.A. Edwards (Ed.), Earthworm Ecology, CRC Press, Boca Raton, 2004, pp. 3e11. G.H. Baker, Managing earthworms as a resource in Australian pastures, in: C.A. Edwards (Ed.), Earthworm Ecology, CRC Press, Boca Raton, 2004, pp. 263e286. D.C. Coleman, D.A.J. Crossley Jr., P.F. Hendrix, Fundamentals of soil ecology, second ed. Elsevier, Burlington, 2004. R.J. Haynes, Labile organic matter as an indicator of organic matter quality in arable and pastoral soils in New Zealand, Soil Biol. Biochem 32 (2000) 211e219. W.A.M. Didden, Earthworm communities in grasslands and horticultural soils, Biol. Fertil. Soils 33 (2001) 111e117. O. Daniel, Leaf-litter consumption and assimilation by juveniles of Lumbricus terrestris L. (Oligochaeta, Lumbricidae) under different environmental conditions, Biol. Fertil. Soils 12 (1991) 202e208. G.L. Velthof, O. Oenema, J.A. Nelemans, Vergelijking van indicatoren voor stikstofmineralisatie in bouwland, Meststoffen 2000 (2000) 45e52.