Comparison of soil arthropods and earthworms from conventional and no-tillage agroecosystems

Soil

& Tillage

Research,

5

Elsevier Science Publishers

(1985) 351-360 B.V., Amsterdam

351 -Printed

in The Netherlands

COMPARISON OF SOIL ARTHROPODS AND EARTHWORMS CONVENTIONAL AND NO-TILLAGE AGROECOSYSTEMS

GARFIELD

J. HOUSE

Department 2 7695-7613

of Entomology,

ROBERT Institute

(Accepted

North

Carolina

State

University,

Athens,

GA

Box

7613,

FROM

Raleigh,

NC

(U.S.A.)

W. PARMELEE of Ecology, 4 March

University

of Georgia,

30602

(U.S.A.)

1985)

ABSTRACT House, G.J. and Parmelee, R.W., 1985. Comparison of soil arthropods and earthworms from conventional and no-tillage agroecosystems. Soil Tillage Res., 5: 351-360. Soil-arthropod and earthworm densities (number m-2) were higher (P < 0.05) under no-tillage than conventional tillage practices. Enchytraeid worms were higher in conventional tillage. Two predaceous groups, ground beetles (Carabidae: Coleoptera) and spiders (Araneae), comprised more than one-half of all soil macroarthropods collected. All major microarthropod suborders (Oribatids, Prostigmatids, Mesostigmatids, and the order Collembola) were higher (P < 0.01) under no-tillage than conventional tillage. High soil-arthropod and earthworm densities under no-tillage systems suggest an expanded and beneficial involvement for these soil fauna in crop-residue-deco?nposition processes.

INTRODUCTION

No-tillage cropping practices generate soil-litter conditions very different from conventionally-plowed systems (Gregory and Musick, 1976). The absence of tillage leaves the soil surface covered with the previous crop’s residue if it is not removed or burnt, promoting environmental conditions conducive to the proliferation of a robust soil fauna (House and Stinner, 1983). A significant feature of continuous no-tillage cropping practices is that they enhance the predatory and saprophagous soil-arthropod community as well as that of crop-damaging herbivores. Ground beetles (Coleoptera: Carabidae) (House and All, 1981), spiders (Blumberg and Crossley, 1983) and decomposer fauna such as earthworms (Edwards, 1975; Barnes and Ellis, 1979), have been found to occur in higher numbers in no-tillage than in conventionally-plowed systems. Continuous no-tillage has effects on chemical and physical soil properties, such as increasing organic matter and concentrating nutrients at shallow

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352

depths (Juo and Lal, 1979; Hargrove et al., 1982; Blevins et al., 1983; Stinner et al., 1983). The level of involvement of arthropods and earthworms in influencing these no-tillage soil-property changes is not well understood. Although soil arthropods and earthworms comprise only a small fraction of the total soil-decomposer biomass, we hypothesize that the densities of these organisms occurring under continuous no-tillage are sufficient to influence surface crop-residue-decomposition processes. The notillage soil fauna, by virtue of their large numbers, probably play an important indirect catalytic role in the crop-residue breakdown and mineralization process in agroecosystems, as in other natural terrestrial ecosystems (Petersen and Luxton, 1982; Anderson et al., 1983; Seastedt, 1984; Seastedt and Crossley, 1984). As no-tillage area increases, knowledge of these and other indirect influences of soil fauna1 activities, such as nutrient transfer and turnover, will become increasingly important to agroecosystem management (Broadbent and Tomlin, 1982; House et al., 1984). This paper reports and compares the effect of conventional tillage and continuous no-tillage on the densities of 3 major soil faunal groups: (1) microarthropods and mites); (2) macroarthropods (e.g., beetles and (e.g., collembolans spiders); (3) earthworms and enchytraeids. The potential significance of the increased abundance of these no-tillage soil faunal groups is discussed in relation to decomposition processes. METHODS

Field research was conducted at the University of Georgia’s Horseshoe Bend Experimental Area near Athens, a site representative of the Southern Piedmont. The agricultural plots are relatively flat (slopes < 3%) and are considered prime farmland of moderately high fertility for the Southern Piedmont. The soil is classified as a Hiwassee loam (Typic Rodudults, a welldrained, moderately acidic sandy-clay loam). The no-tillage plots had not been moldboard plowed, disked or cultivated since 1966. Thus, these systems represent the most extreme form of conservation tillage (Crosson, 1981: Mannering and Fenster, 1983). In November 1983, 6 cropping seasons, 4 years of sorghum, Sorghum bicolor (L.) Moench (1978-79 and 1982-83) and 2 years of soybean, Glycine max (L.) Merr. (1980-81) were completed. Rye grain, Secale cereale L. or crimson clover, Trifolium incarna turn L., were grown each year as a winter cover crop following sorghum or soybean. These rotations are typical for the Southern Piedmont (Langdale et al., 1978). Prior to 1978, the land was fallow and undergoing succession. No insecticides had been applied to the agricultural plots since 1966. The present study was initiated in the spring of 1983. On 10 May 1983, 8 replicate 0.03-ha conventional-tillage (CT) plots were moldboard plowed once, disk plowed 3 times and rotary tilled twice. Eight replicate 0.03-ha no-tillage plots were left undisturbed. Rye cover crop plots only were

353

fertilized with ammonium nitrate (150 kg N ha-‘), and all plots received 45 kg P ha-’ and 135 kg K ha-’ on 12 May 1983. The herbicide glyphosate (6.5 kg ha-‘) was applied to all vegetation on 24 May 1983, and sorghum (44 kg seed ha-‘) was planted in 75-cm rows on 25 May 1983. Microarthropods were sampled using a 5-cm diameter by 5-cm deep soil core on 8 dates from 5 May to 18 December 1983. One core was removed from the center of each plot. In the laboratory, microarthropods were extracted into 95% alcohol on modified high-gradient Tullgren funnels (Merchant and Crossley, 1970) for 7 days and identified to the following acarine suborders: oribatids, mesostigmatids, prostigmatids, plus the order Collembola and micro-insects. On 4 dates from 28 April to 17 June 1983, macroarthropods were collected from l/4 m2 quadrat samples (House and Stinner, 1983). Sieves were/used to separate macroarthropods from litter and the top 2 cm of excavated soil. Earthworms were sampled on 5 dates from 12 January 1983 to 25 April 1984, using 15-cm deep by lo-cm diameter soil cores. Three cores were removed at random from each plot. Earthworm adults, juveniles, and cocoons were removed by hand from soil cores under running water. Only juvenile and adult earthworms were enumerated on 25 April 1984. Enchytraeids were sampled once on 25 April 1984 and sorted as described for earthworms. RESULTS

The elimination of tillage had a major impact on the soil fauna in these Soil macroarthropod densities were greater experimental agroecosystems. under no-tillage, regardless of the type of winter cover crop. Table I shows the mean number of individuals of ground beetles, spiders and other soil TABLE

I

Number of ground beetles (Carabidae: Coleoptera), spiders (Araneae), and other macroarthropods per m2 from conventional (CT) and no-tillage (NT) sorghum/rye and sorghum/ clover cropping systems. Means and one standard error are shown (n = 16)

A

B

C

*All

CT

NT

7.2 + 1.6 1.6 i 1.2

32.8 f 8.4 48.8 f 20.0

Spiders (Araneae) Sorghum/rye Sorghum/clover

0.8 + 0.4 3.6 f 1.2

16.8 A 3.6 16.0 zt 5.6

Other macroarthropods Sorghum/rye Sorghum/clover

6.0 i 2.4 7.2 2 4.0

28.0 f 46.0 +

Ground beetles (Carabidae: Sorghum/rye Sorghum/clover

tillage treatment

Coleoptera)

pairs (i.e., CT and NT) significantly

different

6.0 7.6

(P < 0.05).

354

macroarthropods from 4 cropping systems: no-tillage sorghum/rye, notillage sorghum/clover, conventional-tillage sorghum/rye, and conventionaltillage sorghum/clover. The 2 predaceous groups, ground beetles and spiders, comprised more than one-half of the soil macroarthropods collected. Other arthropods (Table I) included detritivores such as dipteran larvae and important herbivorous insects such as immature Japanese beetles (Scarabaeidae), cutworms (Noctuidae), and wireworms (Elateridae), none of which were collected in large numbers. The number of earthworms from these same 4 ag-roecosystems is shown in Table II. Earthworm densities were higher under no-tillage than conventional tillage, but the type of winter cover crop also influenced these values: more earthworms were collected from the sorghum/rye rotation than from the sorghum/clover. Two earthworm species predominated, Aporrectodea turgida (Lumbricidae) and Lumbricus rubellus (Lumbricidae). Enchytraeid worm density was higher in conventional tillage than no-tillage systems (Table III). Figures 1 and 2 show the seasonal dynamics of the microarthropod community in sorghum/clover and sorghum/rye cropping systems. Throughout the season, the number of microarthropods in all groups was higher in no-tillage than in conventionally-tilled systems (Figs. 1 and 2). The aggregated mean number of microarthropods shows highly significant differences between conventional and no-tillage systems (Table IV). TABLE

II

Number of earthworms including adults, juveniles and cocoons per m* from conventional (CT) and no-Wage (NT) sorghum/rye and sorghum/clover cropping systems. Means and one standard error are shown (n = 16) Cropping

system

Sorghum/rye Sorghum/clover

CT*

NT

631 + 140 a 191k 51a

2202 2 38 b 1210 2 127 b

*Treatment pairs (i.e., CT vs. NT) ference (P < 0.05). TABLE

followed

by different

letters

indicate

statistical

dif-

III

(CT) and no-tillage Number of enchytraeids and earthworms per m * from conventional (NT) sorghum/clover and sorghum/rye systems. Means and one standard error are shown (n = 4) Sorghum/clover

Enchytraeids Earthworms

Sorghum/rye

CT

NT

CT

NT

4108 + 892 276 f 159

935 f 329 860 f 175

1837 f 866 149 f 22

520 + 206 967 + 51

355 TABLE

IV

Aggregated mean number per m’ of microarthropods over 8 collection dates from conventional (CT) and no-tiliage (NT) sorghum/rye (S/R) and sorghum/clover (S/C) agroecosystems Sorghum/clover

Sorghum/rye

CT*

NT

CT

NT

2645 25978 5097 3486

6799 63859 33272 97

2054 23318 14990 719

8639 32523 36809 285

Collembola

7721

12487

6244

14684

Insects

1070

2594

2105

2548

46004

119107

49424

96584

Acarina Mesostigmatids Prostigmatids Oribatids Astigmatids

Total All tillage treatment

24 22 20

pairs (except-insects)

significantly

different

(P < 0.01).

(A) TOTAL tdk%CMRm 22

(6) MSOSTKNATA

I

Fig. 1. Seasonal dynamics of (A) total microarthropods and 3 acarine suborders; (B) mesostigmatids; (C) oribatids, (D) prostigmatids from conventional (CT) and no-tillage (NT) sorghum/clover agroecosystems. Mean number of microarthropods and standard error bars are shown (n = 4).

356

2:. In. I8

iA1 TOTAL MICRXRTHR)P(1OS

12

I

(Cl CfWATlDS

Fig. 2. Seasonal dynamics of (A) total microarthropods and 3 acarine suborders; (B) mesostigmatids; (C) oribatids; (D) prostigmatids from conventional (CT) and no-tilllge Mean number of microarthropods and standard (NT) sorghum/rye agroecosystems. error bars are shown (n = 4). DISCUSSION

Although the soil fauna of natural terrestrial ecosystems influences organic matter decomposition, and mineralization processes such as nutrient release rates (Crossley, 1977; Petersen and Luxton, 1982; Seastedt, 1984), this catalytic role has not been demonstrated for the soil fauna of agricultural systems. However, under conditions of continuous no-tillage, we speculate that earthworms and microarthropods will assume a more dominant role in organic-matter decomposition, and, therefore, nutrient flux patterns through and within these agroecosystems. Elimination of soil disturbance and stratification of organic matter contributed to the higher densities of soil arthropods and earthworms under no-tillage. No-tillage provides a more favorable environment for soil- and surface-residue-dwelling organisms by reducing moisture loss, ameliorating temperature extremes and fluctuations atid supplying a relatively cdntinuous substrate for decomposers (House and All, 1981; Crossley et al., 1984). Figure 3 conceptualizes and contrasts some of the major physical and

357

biological differences in soil between conventional and no-tillage decomposition processes. Continuous no-tillage stratifies the soil, concentrating organic matter, nutrients and microbial activity near the surface (Doran, 1980). In contrast, conventional tillage, through implement mixing and cutting, increases contact between crop residues and soil and generates more homogeneous conditions (Coleman, 1983; House et al., 1984; Odum, 1984). Under no-tillage, we expect soil fauna1 interactions to be more pronounced, and the rate of decomposition and nutrient release to be controlled by a complex of soil fauna (Fig. 3). Tillage substitutes mechanical energy for the biotic activity of the soil fauna (i.e., earthworm tunneling and redistribution of organic matter and microarthropod comminution of crop residues). Tillage indirectly accelerates decomposition of organic matter by stimulating microbial activity and lowering the diversity of the soil fauna community (Fig. 3). The decomposer community may also shift to organisms with a higher metabolic rate as indicated by the higher density of enchytraeids in conventional tillage (Table III). Although these may contribute less to biomass than earthworms, they have a much higher respiration rate, thereby indirectly increasing the rate of organic matter mineralization (Golebiowska and Ryszkowski, 1977). Earthworms have long been associated with the maintenance of soil fertility through their degradation of organic matter and its incorporation

CONVENTIONAL TILLAGE

CONTINUOUS NO-TILLAGE Decompositionand Mineralization of Crop Residue f

\ Soil Biota -insects

Fig. 3. Conceptualization of the major physical and biological differences occurring between conventional and no-tillage soils. Continuous no-tillage practices stratify the soil, concentrating nutrients and organic matter at and near the soil surface. Crop residue decomposition occurs almost exclusively through the activity of a diverse community of soil biota, mimicking the decomposition processes of natural terrestrial ecosystems. Organic-matter breakdown and mineralization in conventionally-tilled soil occurs more rapidly, with fewer steps, fewer types of organisms (primarily the microflora), and over a deeper area of soil.

358

into the soil, These activities are recognized as improving soil structure, aeration and drainage. Edwards and Lofty (1978, 1980) found that barley seedling emergence, heights of plants and root weights were all greater in no-tillage soils with arthropods and earthworms than in those without these animals. Since fertilizers and lime are generally placed on the soil surface in continuously no-tilled fields, earthworms, which mix soil vertically, may provide a biological method of incorporating these crop amendments. In a recent field study, Springett (1983) found that Allolobophoru Zongu, an abundant lumbricid earthworm, increased the vertical mixing of lime in a ryegrass clover pasture. Earthworms may also play an important role in the nutrient cycles of notillage systems. Surface crop residues such as rye contain as much as 40 kg N ha-’ and over 5000 kg ha-’ dry matter. Such crop tissues have a high C:N ratio which earthworm feeding lowers by carbon utilization during respiration. Nitrogen, mineralized by the activities of earthworms, has been estimated to be as high as 100 kg N ha-’ (Edwards and Lofty, 1977). Clearly, as no-tillage acreage increases, more research on the role of earthworms in the nutrient dynamics of these systems will be required. Many soil microarthropods such as oribatid mites and Collembola have well developed mouthparts, capable of fragmenting organic matter while feeding on bacteria and fungi adhering to plant residues (Wallwork, 1976, 1981). The fragmentation of plant material increases its surface area and thus accelerates microbial activity, which in turn enhances organic matter breakdown and mineralization (Seastedt and Crossley, 1980; Seastedt, 1984). Furthermore, microarthropods have been found to inoculate plant residue with fungal spores (Santos and Whitford, 1981). In no-tillage systems, such feeding and dispersal activities of soil microarthropods would alter the nutrient content of organic matter as well as influence its decomposition rate. We conclude that these soil fauna are a beneficial component of continuous no-tillage agroecosystems in that they have an indirect catalytic role in surface crop-residue decomposition. Tillage accelerates crop-residue decomposition by generating homogeneous soil-litter conditions and increasing soil-litter contact, both of which stimulate microbial activity. Therefore, mineralization rates in tilled systems may, during certain periods, exceed the nutrient uptake ability of crop plants. In contrast, under notillage, nutrients are immobilized within surface crop residue and their associated microflora and fauna for a longer period. Nutrient release is more gradual and perhaps more efficient in terms of nutrient recycling over a period of several years. Once the sequence and extent of involvement of the soil fauna in crop-residue-decomposition processes are understood, they can be incorporated into no-tillage management programs as biotic regulators of nutrient release and turnover.

359 ACKNOWLEDGMENTS

We gratefully acknowledge the welcomed contributions of our colleagues in the Institute of Ecology, especially D.A. Crossley, Jr., E.P. Odum, Paul Hendrix and Peter Groffman. Earthworms were identified by John W. Reynolds. This research was supported by an NSF grant (DEB 82077206) to E.P. Odum and D.A. Crossley, Jr. REFERENCES Anderson, J.M., Ineson, P. and Huish, S.A., 1983. Nitrogen and cation mobilization by soil fauna feeding on leaf litter and soil organic matter from deciduous woodlands. Soil Biol. Biochem., 15: 463-467. Barnes, B.T. and Ellis, F.B., 1979. Effects of different methods of cultivation and direct drilling, and dispersal of straw residues, on populations of earthworms. J. Soil Sci., 30: 669-679. Blevins, R.L., Thomas, G.W., Smith, M.S., Frye, W.W. and Cornelius, P.L., 1983. Changes in soil properties after 10 years of continuous non-tilled and conventionally tilled corn. Soil Tillage Res., 3: 135-146. Blumberg, A.Y. and Crossley, DA., Jr., 1983. Comparison of soil surface arthropod populations in conventional tillage, no-tillage and old field systems. Agro-Ecosysterns, 8: 247-253. Broadbent, A.B. and Tomlin, A.D., 1982. Comparison of two methods for assessing the effects of carbofuran on soil and animal decomposers in cornfields. Environ. Entomol., 11: 1036-1042. Coleman, D.C., 1983. The impacts of acid deposition on soil biota and C-cycling. Environ. Exp. Bot., 23: 225-233. Crosson, P., 1981. Conservation tillage and conventional tillage: a comparative assessment. Soil Conserv. Sot. Am., Ankeny, IA. Crossley, D.A., Jr., 1977. The roles of terrestrial saprophagous arthropods in forest soils: current status of concepts. In: W.J. Mattson (Editor), The role of arthropods in forest ecosystems. Springer-Verlag, New York, pp. 49-56. Crossley, D.A., Jr., House, G.J., Snider, R.M., Snider, R.J. and Stinner, B.R., 1984. The positive interactions in agroecosystems. In: R:R. Lowrance, B.R. Stinner and G.J. House (Editors), Agricultural ecosystems: unifying concepts. Wiley, New York, pp. 73-81. Doran, J.W., 1980. Soil microbial and biochemical changes associated with reduced tillage. Soil Sci. Sot. Am. J., 44: 765-771. Edwards, C.A., 1975. Effects of direct drilling on the soil fauna. Outlook Agric., 8: 243-244. Edwards, C.A. and Lofty, J.R., 1977. Biology of earthworms. Second Edition. Wiley, New York, 333 pp. Edwards, C.A. and Lofty, J.R., 1978. The influence of arthropods and earthworms upon root growth of direct drilled cereals. J. Appl. Ecol., 15: 789-795. Edwards, C.A. and Lofty, J.R., 1980. Effects of earthworm inoculation upon the root growth of direct drilled cereals. J. Appl. Ecol., 17 : 533-543. Golebiowska, J. and Ryszkowski, L., 1977. Energy and carbon fluxes in soil compartments of agroecosystems. In: U. Lohm and T. Perrson (Editors), Soil Organisms as Components of Ecosystems. Ecol. Bull. (Stockholm), 25, 274-283. Gregory, W.W. and Musick, G.J., 1976. Insect management in reduced tillage systems. Bull. Entomol. Sot. Am., 22: 302-304.

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