Soil Fauna in Sustainable Agriculture: Results of an ... - Science Direct

Agriculture, Ecosystems and Environment, 27 (1989) 561-572

561

Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands

R e g i o n a l Projects

Soil Fauna in Sustainable Agriculture: Results of an Integrated Farming System at Lautenbach, F.R.G. EL TITI, A. and U. IPACH

Landesanstalt fiir Pflanzenschutz, Reinsburgstrafle 107, 7000 Stuttgart I (F.R.G.) (Accepted for publication 19 April 1989)

ABSTRACT E1 Titi, A. and Ipach, U., 1989. Soil fauna in sustainable agriculture: Results of an integrated farming system at Lautenbach, F.R.G. Agric. Ecosystems Environ., 27: 561-572. A comparison of a low-input farming system (integrated) with a "conventional" one was initiated in 1978 at the estate of Lautenbach, F.R.G. This paper describes the effects of both farming systems on some components of the soil fauna. The results indicate a significant influence of the farming system on the indicator groups monitored. Lumbricidae, mainly Lumbricus terrestris L., are most prevalent on the integrated fields. Both numbers and biomass of earthworms are up to six-fold higher than in the conventionally treated field sections. This is true of predatory mites (Gamasina, Mesostigmata). More gamasid mites of higher species diversity are extracted from the integrated farmed plots. Nematode populations show a wide range of variations from field to field. Significant differences however, occur among the herbivores, the saprophytic (including bacteriovores and mycovores ) and predatory nematodes (Mononchidae). The population density of the plant parasitic species Heterodera avenae (Wollweber) and Ditylenchus dipsaci (Filipjev), is mostly lower in the integrated system, whereas that of the saprophytic and predatory nematodes is higher.

INTRODUCTION

There are many different reasons why low-input agricultural systems are urgently needed in both developing and developed countries (Diercks, 1983; Pimentel et al., 1983). In the latter, the intensive use of mineral fertilizers and pesticides is increasingly polluting ground water (Cohen et al., 1987), endangering wildlife ( Heydemann, 1983; Kohler, 1986) and contributing to a declining farm income, in spite of increasing yields. Helpful strategies will be those able to decrease the energy input, aiming at being self-sustainable. This will be possible if natural regulation components are deliberately used as substitutes for synthetic input. The "integrated" concept relies greatly upon making the best possible use of such natural regulation elements. Supporting the an0167-8809/89/$03.50

© 1989 Elsevier Science Publishers B.V.

562 TABLE 1 Differences between "integrated" and "conventional" farming systems in Lautenbach

Soil tillage Sowing technique

Fertilization N, P, K, and Ca

Organic manure Undersowing Plant protection Weeds Diseases Insects

Integrated

Conventional

Broadshare cultivator Double rows 6 cm within 24 between

Reversible plough Drilling 16 cm between

Soil analysis N-min and other methods Suboptimal amount/slow acting 20 t h a - 1 every third year Clover in cereals or catch crop

Optimal amount high soluble Catch crop every 4 year Chemical

Mechanical or chemical Chemical, high tolerance Selective or in reduced dosage, economic thresholds

tagonistic agents, for example, would help to control pest species and consequently to substitute "pesticides", at least partially. With these aims, the Lautenbach Project started in 1978 on the 245-ha farm of Lautenbach. The project is designed to compare the productivity and the ecological impacts of two farming systems; "integrated" and "conventional" (Table 1 ) (Steiner et al., 1986). Both systems are run on a commercial base comparing incidence of pest attacks, diseases (El Titi and Richter, 1987), weeds (Wahl and Hurle, 1988), agrochemical inputs, labour demands and financial returns (Zeddies et al., 1986). Changes within the agroecosystems are recorded by monitoring some selected bioindicators on fixed plots within both farming systems. This contribution reports results on soil fauna under both farming regimes. METHODS AND MATERIAL

Experimental design There are six plots of 0.5 ha for monitoring soil fauna in each of the farming systems (Fig. 1 ). The plot pairs are located on field sections of the same soil type and topography. Single strips of at least 5 X 100 m are used for assessing the population density, species diversity and activity of the bioindicators. A large number of methods dealing with sampling and extraction of soil faunal groups is described (Koehler, 1984). The methods used in these studies are generally recommended techniques. They are indeed a compromise between accuracy generally required and labour available. It is to be pointed out that

563

•

W

?

[ ] Integrated

500

lOOjOm

• tp:::n~et:::t: on,

Fig. 1. Experimental design and location of the monitoring plots of soil fauna within integrated and conventionalfarmed fields in the Lautenbach Project. the purpose of these assessments is to compare the effects of the farming systems. Earthworms To estimate earthworm populations, different techniques are available (Edwards and Lofty, 1977). In our studies a formalin method slightly modified after Raw (1959) is used. To extract lumbricids 80 1 m -2 of a diluted formalin solution (0.15%) are used. Eight metal rings (replicants) of 1/8 m 2 each, randomised within three strips of 5 × 100 m in each monitoring plot of both farming systems build the basis for assessment on each occasion. Both number and fresh weight of the extracted worms are recorded. Acari and Collembola Only euedaphic species are considered in these studies. Sampling and extraction techniques as well as corer design are described elsewhere (El Titi, 1984; Bieri et al., 1978). Ten soil samples (5.6 cm diameter; 10 cm deep) are taken on every sampling occasion and system from each field. A modified Tullgren apparatus is used for the extraction. The extraction time is 1 week. Nema~des Free-living nematodes from soil samples are extracted according to LScher (1965) (250 ml soil sample-1 are sieved after being added to 250 ml H202 saturated water). Samples are "mixed samples" consisting of 50 soil corers each, taken up to 25 cm deep, on three occasions annually. A Retsch-vibration-

564 sieve extractor, equipped with 6 sieves of 50-/~m mesh is used. Only sieve residues are transfered to a Baermann funnel and kept for 48 h, to enable nematodes to move into water. To extract cyst nematodes, 200 cm 3 dry soil (30°C) are washed in Retschvibration-sieve extractor equipped with two sieves of 200-/tin and 300-/~m mesh. Sieve residues are used for examination and identification. RESULTS

Earthworms The extracted earthworms on fields of both farming systems are adults and juveniles, mostly ofLumbricus terrestris L. A very few specimens are identified as Allolobophora caliginosa (Savigny) and Octolasium lacteum (Oerley). Biomass and number of earthworms are only considered for comparison if assessments have been carried out under the same weather and crop conditions. The results obtained indicate a highly significant ( P < 0.01 ) difference in the biomass and population density between integrated and conventional systems. More earthworms are present in the integrated system (on average 29 individuals of 24.9 g m -2) than in the conventional (8.9 individuals of 6.3 g m -2) (Fig. 2).

Acari and Collembola A m o n g the soil-inhabitingmicroarthropods mites and springtailsdominate over many other groups. They make up more than 60% of the soil fauna, as illustratedin Fig. 3. There are many general trophic categoriesof below-ground arthropods. Predators are assumed to play an important role within the soil ecosystem. Mesostigmatic mites are even considered to be the "key factor" in the natural mortality of some pest species (Sharma, 1971; Karg, 1983; Karg L. T E R R E S T R I S integrated

~" E

50

o E ._o

20

m

tO

J~]

conventional

0 1980

1981 1982 r 1983 = 1984 = 1985 [ 1986

1987

Fig. 2. Biomassof Lumbricidaein integratedand conventionalfarmingsystemsbetween1980and 1987.

565

integrated

conventional

m

Pouropoda

I~

m

Acari

[~1 Diplopoda ~ Others

Symphylo

Collembolo

Fig. 3. Distribution and population size (circled area-surface) of the different faunal groups inhabiting the soils of integrated and conventional farming systems at Lautenbach {modified after Gottfriedsen, 1987). 807060T -

~

I~Rhodacacaradae

[ •Integrated [ ~ Conventional

5040-

Co 3 0 2010O'

1980

81

82

83

84

85

Year

86

Fig. 4. The annual mean of predatory mites (Gamasina, Mesostigmata) on average 6 fields in integrated and conventional farming at Lautenbach. and Grosse, 1983). About 65 gamasid species occur at Lautenbach (El Titi, 1984). Gamasid mites were found to be most abundant in the integrated farmed soils (Fig. 4). In addition, the number of species represented was also higher, on average 5-10 species (Gottfriedsen, 1987). Only subterranean springtails are included here. Onychiuridae and Isotomidae are dominant in the soils of both farming systems. More Collembola occur in soil samples from integrated than from conventional systems. In Lautenbach, 26 species of 5 families are recorded (Matt, 1986). The average number of extracted Collembola varied greatly from field to field in relation to sampling time.

566

Nematodes Nematodes were sampled three times annually: in spring, summer and autumn. Extracted nematodes are grouped into three trophic categories. These are herbivores, saprophytic (including bacterivores, mycovores) and predatory nematodes (Mononchidae). Significant responses to farming intensity are recorded by all three categories. Herbivores show great differences in single cases. Ditylenchus dipsaci (au%

40-

30~

20-

•9 2

®

o

IN"

10-

Fig. 5. Comparison of different nematode groups in integrated [] and conventional [] farming systems, indicating the percent frequency of soil samples with higher nematode densities over a 4-year period. DITYLENCHUS "~ ~

Field 160

o

V conventional

........

o~3

DIPSACl

integrated

120

8o E

•

•

4O

1979 Sugar Beet

1984 Winter Wheat

1985 Oat

1986 Winter Wheat

Fig. 6. The average density of Ditylenchus dipsaci in soil samples from integrated and conventional farmed plots between 1979 and 1986. Differences are highly significant (Wilcoxon test, P=99% ) from 1984 onwards.

567

HETERODERA o

AVENAE

(EGGS + LARVAE)

conventional

integrated

600-

03

E

o O u3 t~4

500-

hold 400-

"o O

E

300-

==

iiit O"

~79

1~4

19"85

Sugar Beet

Winter Wheat

Oat

Fig. 7. Incidence of infestation by H e t e r o d e r a a v e n a e in integrated and conventional systems expressed as the mean number of eggs + larvae per 250 cm ~ soil. Differences are highly significant, according to Wilcoxon test ( P = 9 6 % ) from 1984 onwards,

t u m n samples) is recorded on two of the six field pairs at Lautenbach. Frequency of occurrence in soil samples and incidence of infestation are found to be much lower in integrated soil. Out of 384 samples examined between 1984 and 1987, higher infestation in integrated soil was recorded only in 14 cases, and in 29 cases in conventional soil. The corresponding figures for a second serious pest, namely Heterodera avenae are 43 vs. 70 (Fig. 5). Ditylenchus dipsaci, known to be a serious pest to a wide range of arable crops, is less abundant in the integrated farmed soils. The average number of nematodes assessed in the autumn soil samples, as free-living stages, is significantly lower in integrated soil compared with conventional soil (Fig. 6). Similar effects of the farming systems are observed by oat-cyst-nematode Heterodera avenae. Samples of the conventional sections contain more eggs + larvae than those of integrated soil (Fig. 7). DISCUSSION

The integrated farming approach is generally accepted as a realistic alternative to the current intensive type of land use (Vereijken et al., 1986; Brussard et al., 1988). It offers the framework for pest management. It also emphasizes the implicit need to decrease the use of pesticides and fertilizers, cutting down environmental pollution. However, any ad hoc reduction or exclusion of such essential inputs without substitutions would probably not be able to maintain

568 yields and income at the present levels. This is why integrated farming is focusing on "input-substitutions", mainly through adoption of renewable natural resources. A deliberate supporting of specific natural enemies of a particular pest, for instance, can make routine use of pesticides unnecessary and substitute to some extent for "chemical control". Consequently, if this is the case, habitat and food demands of the natural control agents are to be considered as indispensable components of the farming system. In a similar way natural regulation could be utilised to replace fertilizers. Legumes in the crop rotation, as major crop or as "undersowings" do contribute significantly to nitrogen fixation. Decomposing legume residues will provide subsequent crops with nitrogen. This would cover at least a part of the fertilizer requirements. On the other hand, cropping non-legumes on harvested fields is an efficient instrument in nutrient management. Catch crops contribute to decreasing nutrient losses, for example, by leaching. Meanwhile, green manure limits erosion and supports soil fauna and microflora. However the achievement of these goals makes manipulation of farming techniques necessary. This includes adjustment of farming methods, timing of field operations, considering some particular farm machinery on the one hand, and diversifying the vegetation on the field (crops/weeds) in surroundings and landscape, on the other. In the Lautenbach Project soil tillage, sowing techniques, fertilization and greenmanure regime have been adjusted in the integrated farming system to suit these aims. The measures changed are assumed to have great effects on the agroecosystem. However, agroecosystem, i.e. man-managed ecosystems, generally have low biotic diversity and are of low levels of internal interaction and feedback mechanisms (Freckman and Caswell, 1985). But in contrast to above soil, below-ground ecosystems still maintain a wide range of biotic diversity with close interactions between the various trophic groups. A thorough understanding of the fundamental mechanisms of such relationships and particularly their relation to nutrient cycles and population dynamics of pest species are needed, if farming systems are to be made sustainable. Earthworms are generally considered as important "regulators" in the soil ecosystem {Edwards and Lofty, 1977). The species composition of earthworms in our experiments was almost completely similar in both systems. Lumbricus terrestris is the dominant species in all assessments. It would be surprising if technical changes on the same growing site and under the same cropping conditions induced a significant change in the species diversity of earthworms. However, the population size in the integrated-fields was considerably larger. On all experimental fields, more earthworms are present in the "integrated" plots. The biomass and the number of adults and juveniles are higher in the integrated-sections, reaching the 6-fold number of the conventional plots. However, this improvement cannot be related to a single farming component, but to the whole system. Soil-type can be excluded, since this is the same in every single field pair.

569 Mechanical damage during cultivation of the conventional fields can induce significant reduction in earthworm populations. This might be responsible for the recorded differences. The minimized tillage regime practised in the integrated system has obviously caused less damage to earthworms compared with ploughing in the conventional system. The most important factor, which affects control of the earthworm population in arable land, is the amount of organic matter that is available as food. About 30% of crop residues are usually left on the surface of the integrated plots. This seems to suit the feeding habits of L. terrestris better. Teotia et al. (1950) reported that there were up to five times more earthworm in sub-tilled and stubble-mulched plots than in ploughed ones. Graft (1969) pointed out that mulching favours the deposition of casts on the surface. These results support our data on earthworms. Integrated farming has basically contributed to establish a considerable earthworm population. Many different additional improvements of soil physical properties can be related to these changes. Earthworm burrows are known to contribute immensely in decreasing soil erodability (Arden-Clark and Hodges, 1987), improving water permeability and water-holding capacity. Positive changes in turn-over of organic matter are not only caused by earthworm activity but by that of other Annelida. Enchytraeidae have responded positively to the integrated farming system as well. A second group of soil organisms known to be of great importance for soil ecosystems is that of microarthropods. Edaphic mites and Collembola play different roles within the soil community. Gamasid mites for example feed on nematodes, springtails, Enchytraeidae, immature Diptera etc. Mesostigmatic mites are more abundant in the integrated farmed fields than in the conventionally treated ones. Higher densities in integrated systems were recorded regularly on the six fields over the 8 years. Density differences occur among the various families. Rhodacaridae and Eviphididae responded positively in almost all cases to the integrated farming, whereas Parasitidae, Pachylaelaptidae, Veigaiidae and Ascidae are not always more abundant there. Furthermore the species diversity of the gamasids is found to be higher in "integrated" systems. According to Gottfriedsen (1987), the index of similarity (Jaccard, Evness and Elton-Pyramid) refers to a higher number of species in the integrated system. The key factor responsible for these differences is assumed to be soil tillage (El Titi, 1984). Loosing deeper soil layers without turning them upside-down in the tillage regime used in the integrated system seems to favour various gamasid groups, particularly the Rhodacaridae. Some species such as Rhodacarus agrestis (Karg), Alliphis siculus (Oudemans) and Pachyseius humeralis (Berlese) are found only in the unploughed soils of integrated systems. Keeping these minute mites within their natural habitat in deeper layers seems to improve the rate of increase. There is also evidence that potential prey are more numerous in integrated systems. These are, as previously mentioned, Enchytraeidae and Collembola. An increase in the population density of the

570

edaphic Collembola species, mainly Onychiuridae and Isotomidae, shows positive responses of springtails to the alternative farming system. Onychiurus armatus (Tullberg) and TuUbergia densi (Bagnall) are most abundant there. In complete contrast to our expectations ( higher damage on sugar-beet seedlings by Onychiurus armatus) seedling emergence is significantly improved on the integrated fields (El Titi and Richter, 1987). Predatory mites have succeeded in establishing a kind of natural balance preventing a sudden outbreak of the Collembola population and serious damage. A third group of soil organisms (of different trophic categories: plant parasites, prey and predators) are nematodes. Free-living species, saprophytic nematodes are more abundant in the integrated system. This is a source of prey for the mesostigmatic mites, contributing to maintain a population of beneficials. Surprisingly, some of the herbivore nematodes occurred in much lower density in the integrated fields. Ditylenchus dipsaci, a nematode species attacking a wide range of host plants, of great economic importance, occurs on two of the six field pairs at Lautenbach. Both frequency of occurrence and population density of the stem eelworm are significantly lower in integrated systems. It is clearly extremely difficult to relate this difference to any single component of the pedoecosystem. But crop plant effects, which are commonly known to affect the rate of increase of D. dipsaci (Decker, 1969), can be excluded. Thus, both integrated and conventional systems are cropped with the same host plant. Similar responses to farming systems were assessed on oat cyst nematode, Heterodera avenae. The number of eggs plus larvae in soil samples taken from integrated systems is lower than those of conventional systems. Nematophagous fungi, reported to be an important natural control agent of cyst nematodes (Tribe, 1980; Kerry et al., 1982; Knuth, 1986) can be involved in this phenomenon. Again there is no evidence for the responsibility of any single ecosystemcomponent on its own. Probably it is the total sum of effects of various antagonistic agents. The mesostigmatic mites, as already mentioned, particularly the nematophagous species tend to play an important role in the natural mortality of cyst nematodes. Karg (1962) reported density dependent effects of Rh. rosae on potato cyst nematode (Globodera rostochiensis). Sharma (1971) related 85% of the mortality of Tylenchorynchus dubius to the activity of the same mite. According to Inserra and Davis (1983), the role of the mesostigmatic mite in the natural mortality of nematodes is still underestimated. It can be assumed that the higher population density of the predatory mites in the integrated sections is responsible, or mainly responsible, for the differences in the densities of the two pest species mentioned. This might be supported by predatory nematodes (Monochidae), since these were numerous in integrated systems as well. Integrated farming as it is practised at Lautenbach provides a fundamental base for the survival of natural control agents. They have succeeded in controlling major pest species and accordingly substitute the use of nematicide.

571 There are many options offered in sustainable agriculture strategies, which can be used in the same way.

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