Terrestrial nematodes in a changing environment

Increasing awareness of the nature and extent of soil pollution on soil biota and their role in soil processes has resulted in exploring the possibilities of biological assessment systems to indicate the ecological condition of soils and to predict the ecological efficacy of e.g. policy measures. The research presented in this thesis is part of a project in which the possibilities of nematodes as bioindicator organisms are studied. The objectives of the study were to investigate i. the use of the nematode fauna to assess soil quality, and ii. the prospect of the nematode fauna to contributing to an ecological soil classification which can serve as a reference to assess soil quality. An ecological soil classification is based on a description of soils consisting of a set of both biotic and abiotic parameters.Besides the effects of certain pesticides on the occurrence of nematodes, many studies within the last decades showed changes in the composition of the nematode fauna due to e.g. heavy metals and other pollutants, fertilization and acidification. To assess soil quality by means of analyzing the composition of the nematode fauna, an effective and reliable instrument is needed. In Chapter 2 an assessment method based on life strategies of nematodes is described. Nematode taxa. can be classified from colonisers (r-strategists in the loose sense) to persisters (K-strategists sensu lato ) on a c-p scale. This c-p scale was divided into three classes, and of any soil sample the proportion of the nematode fauna belonging to each of these three classes was calculated. C-P triangles were used to visualize the distribution of the three c-p classes within a sample. It was shown that c-p triangles could be used to describe patterns in the composition of the nematode fauna which were found to be related to certain disturbances such as acute toxic compounds (arrow 2 Fig. 2.4) or those resulting in an increased availability of easily decomposable organic compounds (arrow 1 Fig. 2.4).In Chapter 3, c-p triangles were applied to study changes in the composition of the nematode fauna of a Scots pine forest, resulting from the application of lime, additional nutrients and organic manure to restore nutrient availability for tree growth. Soil samples were taken three and four years after the first applications, and in both years the occurrence of nematodes was significantly effected by liming. Analyses of patterns within the c-p triangles based on our own data and on a selection of literature data originating from locations with different nematode faunae showed that following liming, colonizers increased proportionally. This increase became manifest months later and could be demonstrated several years later. Application of urea also resulted in an increased abundance of colonizers. However, the effects of urea were stronger, appeared within a few weeks of application, but seemed to last for only a few months.In experimental studies like those described in Chapter 3, control treatments usually are available. In general, however, the assessment of the pollution or disturbance of soils lacks such controls. A reference system (e.g. ecological soil classification) or an analysis of changes in the composition of the nematode fauna using a time sequence, can then be used to assess the nematode fauna of that soil.Development of a reference system depends upon, among other things, knowledge of the ecological relationships of nematodes to their biotic and abiotic environment. Relationships between soil characteristics, vegetation and composition of the nematode fauna are described in Chapter 4, where the nematode fauna of >200 soil samples taken from a variety of habitats differing in vegetation (forest, shrubs, heathland, grassland) and soil type (clay, loam, sand) was studied. Using multivariate analysis techniques (clustering, correspondence analyses), the nematode fauna of these sites was classified in "Sample Groups". Seven Sample Groups could be distinguished, and these could also be described by soil characteristics in combination with vegetation. Gradual changes in the composition of the nematode fauna were observed in the sequence sandy, loamy sandy, sandy loam, loam soils. However, the nematode fauna of clay soils differed significantly from the former. In soils with comparable physical and chemical characteristics, subdivision was found to he related to vegetation, as was shown for the sandy soils. In sandy soils both the forests and the forest gaps, shrubs and grasslands had their characteristic nematode fauna. Methodological aspects as date of sampling and sampling strategy did not affect the Sample Group classification. It was concluded that the nematode fauna can contribute to a reference system such as an ecological soil classification.Assessment of changes in the composition of the nematode fauna in monitoring studies requires knowledge of the development of nematode faunae in natural habitats. Long-term changes in the composition of the nematode fauna were studied in a natural primary vegetation succession of blown-out areas in a drift sand landscape (Chapters 5 and 6). The successional stages studied were bare drift sand, Spergulo-Corynephoretum, Scots pine ( Pinus sylvestris L.) forests of respectively 3-5, 25-30, 45-50, 80-90 and 105 years old and an early variant of Betulo- Quercetum. Nematode samples were taken from the 0-10 cm mineral soil, and in the forested stages also from the litter, fermentation and humus horizons.The occurrence of nematodes depended on the stage of succession, the vegetation type (drift sand, Spergulo-Corynephoretum, forest) and the soil horizon, and could be related to microclimatological characteristics, soil texture and food availability. Relatively large differences in the composition of the nematode fauna were observed when going from drift sand to Spergulo-Corynephoretum, and subsequently to Scots pine forest. Changes in the composition of the nematode fauna during forest development appeared more gradual.Analyses of the nematode fauna of the forested sites showed a higher similarity between the nematode faunae of comparable soil horizons than between different horizons within the same profile. Within each soil horizon, c-p triangles showed patterns in nematode fauna development which could be related to vegetation succession and which differed per horizon. In the 0-10 cm mineral soil and in the fermentation and humnus horizons of the forested soils nematode development followed patterns as indicated by arrow 4 in Fig. 2.4: an initial dominance of taxa belonging to c-p group 2, followed by a relative increase of persisters (c-p group 3-5). However, in the litter horizons such development of persisters, could not be observed. In all successional stages of the litter horizon, the nematode fauna was composed mainly of colonizers (c-p groups 1 and 2), and here the most extreme colonizers (c-p group 1), could be found in relative high numbers.Finally, the nematode fauna in the natural vegetation succession of the blown-out areas in the drift sand landscape was compared with the Sample Group classification of Chapter 4 (Fig. 5.7). Projection of the nematode samples taken from the vegetation succession onto the correspondence analysis graph of the Sample Group data, showed that the position of the successional samples coincided with the Sample Groups composed of samples with related habitat types. These similarities between nematode fauna structure and habitat type as found in both investigations, support a classification of soils based on the composition of the nematode fauna as presented in Chapter 4. Moreover, with reference to an ecological soil classification, this comparison showed that developmental changes of the nematode fauna as a result of natural environmental changes in habitat structure can cross boundaries between "classes" or "types"

On-farm impact of cattle slurry manure management on biological soil quality

The effects of dairy cattle slurry management on soil biota, soil respiration and nitrogen (N) mineralization were evaluated in a farm trial across 12 farms and a field experiment on 2 farms located in a dairy farming area in the north of the Netherlands. The slurry management consisted of slit injection or surface application of slurry; the use or no use of additives [Euromestmix® (MX) and Effective Microbes® (EM)] and the type and level of inorganic N fertilization. Slit injection negatively affected epigeic earthworms whereas its effect on anecic and endogeic earthworms was absent or even positive. Enchytraeids were not affected in a consistent way, whereas numbers of nematodes indicative of nutrient- enriched conditions increased. Inorganic N fertilizer had similar effects. Bacterial diversity was not different among the treatments. Nitrifier diversity, however, was high at one of the farms in the field experiment, and was negatively affected by inorganic N fertilizer. The use of MX was usually associated with higher numbers of earthworms. EM affected numbers of earthworms and numbers of bacterial and plant-feeding nematodes, but only in specific combinations of field history, slurry type and slurry application method. We found no effects of EM on the composition of the microbial community. Soil respiration was increased when slurry was surface-applied. The calculated N mineralization by earthworms was in the order of 70–200 kg N ha −¹ year −¹. It was highest under farm-characteristic surface application of slurry with MX and lowest under farm-characteristic slit injection of slurry without additives. Compared with the N mineralization by earthworms, that by enchytraeids and nematodes was quantitatively insignificant. Negative treatment effects on earthworms led to corresponding reductions in calculated N mineralization

On-farm impact of cattle slurry manure management on biological soil quality

The effects of dairy cattle slurry management on soil biota, soil respiration and nitrogen (N) mineralization were evaluated in a farm trial across 12 farms and a field experiment on 2 farms located in a dairy farming area in the north of the Netherlands. The slurry management consisted of slit injection or surface application of slurry; the use or no use of additives [Euromestmix® (MX) and Effective Microbes® (EM)] and the type and level of inorganic N fertilization. Slit injection negatively affected epigeic earthworms whereas its effect on anecic and endogeic earthworms was absent or even positive. Enchytraeids were not affected in a consistent way, whereas numbers of nematodes indicative of nutrient- enriched conditions increased. Inorganic N fertilizer had similar effects. Bacterial diversity was not different among the treatments. Nitrifier diversity, however, was high at one of the farms in the field experiment, and was negatively affected by inorganic N fertilizer. The use of MX was usually associated with higher numbers of earthworms. EM affected numbers of earthworms and numbers of bacterial and plant-feeding nematodes, but only in specific combinations of field history, slurry type and slurry application method. We found no effects of EM on the composition of the microbial community. Soil respiration was increased when slurry was surface-applied. The calculated N mineralization by earthworms was in the order of 70–200 kg N ha -¹ year -¹. It was highest under farm-characteristic surface application of slurry with MX and lowest under farm-characteristic slit injection of slurry without additives. Compared with the N mineralization by earthworms, that by enchytraeids and nematodes was quantitatively insignificant. Negative treatment effects on earthworms led to corresponding reductions in calculated N mineralization

Soil biological quality of grassland fertilized with adjusted cattle manure slurries in comparison with organic and inorganic fertilizers

We studied the effect of five fertilizers (including two adjusted manure slurries) and an untreated control on soil biota and explored the effect on the ecosystem services they provided. Our results suggest that the available N (NO3- and NH4+) in the soil plays a central role in the effect of fertilizers on nematodes and microorganisms. Microorganisms are affected directly through nutrient availability and indirectly through grass root mass. Nematodes are affected indirectly through microbial biomass and grass root mass. A lower amount of available N in the treatment with inorganic fertilizer was linked to a higher root mass and a higher abundance and proportion of herbivorous nematodes. A higher amount of available N in the organic fertilizer treatments resulted in a twofold higher bacterial activity (measured as bacterial growth rate, viz. thymidine incorporation), a higher proportion of bacterivorous nematodes, a 30% higher potential N mineralization (aerobic incubation), and 25–50% more potentially mineralizable N (anaerobic incubation). Compared to inorganic fertilizer, organic fertilization increased the C total, the N total, the activity of decomposers, and the supply of nutrients via the soil food web. Within the group of organic fertilizers, there was no significant difference in C total, abundances of soil biota, and the potential N mineralization rate. There were no indications that farmyard manure or the adjusted manure slurries provided the ecosystem service “supply of nutrients” better than normal manure slurry. Normal manure slurry provided the highest bacterial activity and the highest amount of mineralizable N and it was the only fertilizer resulting in a positive trend in grass yield over the years 2000–2005. The number of earthworm burrows was higher in the treatments with organic fertilizers compared to the one with the inorganic fertilizer, which suggests that organic fertilizers stimulate the ecosystem service of water regulation more than inorganic fertilizer. The trend towards higher epigeic earthworm numbers with application of farmyard manure and one of the adjusted manure slurries, combined with the negative relation between epigeic earthworms and bulk density and a significantly lower penetration resistance in the same fertilizer types, is preliminary evidence that these two organic fertilizer types contribute more to the service of soil structure maintenance than inorganic fertilize

De schoonheid van een duurzaam beheerde bodem: Leidt biologische landbouw tot een gezondere bodem?

Grondgebonden landbouw is afhankelijk van de ecosysteemdiensten die het natuurlijk kapitaal van de bodem levert. Een gezonde bodem maakt voedingsstoffen vrij, geeft water door, heeft een goede bodemstructuur en het vermogen om ziekten en plagen te onderdrukken. Door gebruik te maken van deze diensten kunnen boeren een aanzienlijke agrarische productie realiseren van een goede kwaliteit. Het bodemleven vormt hierbij een belangrijke spil. We hebben gegevens van 137 melkveehouderijbedrijven onderzocht op de vraag hoe het is gesteld met de bodemgezondheid onder verschillende typen bedrijven

Effects of GM potato Modena on soil microbial activity and litter decomposition fall within the range of effects found for two conventional cultivars

Plant roots have a profound effect on soil microbial activity, particularly in the rhizosphere. Hence, it is important to understand the potential effects of genetically modified (GM) crops on soil microbial activity and related processes such as litter decomposition. In this study, we compared the effects of GM potato Modena on soil microbial activity and carbon (C) and nitrogen (N) mineralization to effects induced by Modena’s parental isoline (Karnico) and a conventional potato cultivar (Aventra). A field experiment was conducted at two sites to assess microbial catabolic diversity (using MicroRespTM) in the rhizosphere and in bulk soil, during flowering and senescence of the potato plants. In a laboratory experiment with soil and potato litter from the field experiment, we investigated whether the cultivars had modified the activity of soil microbial communities to such an extent that this affected C and N mineralization. Results of the field experiment showed no GM-induced effects on microbial catabolic diversity, while effects of field site location and sampling date were significant. Multivariate analysis including plant traits and soil characteristics revealed that microbial catabolic activities in rhizosphere soil were strongly correlated with soil organic matter and tuber sucrose content, whereas in bulk soil, they were primarily correlated with soil moisture. In the laboratory experiment, we found that Modena induced a "home-field advantage" in N mineralization, yet this effect was inconsistent across locations and was also observed for other cultivars. Based on our data and results from previous studies, we conclude that the effects of GM cultivar Modena on soil microbial activity and litter decomposition fall within the normal range of effects found for conventional potato cultivars

Effectiviteit van het "Alternatieve Spoor" in de Noordelijke Friese Wouden

Bij een deel van de melkveehouderijbedrijven in de Noordelijke Friese Wouden (NFW) leeft de wens om mest bovengronds te mogen uitrijden. Een aantal bedrijven volgt daartoe een zogeheten alternatief spoor. Deze strategie bestaat uit een combinatie van maatregelen als een verlaging van de kunstmestgift en het voeren van een eiwitarm en structuurrijk rantsoen. De hoofdvraag binnen dit onderzoek is of toepassing van het alternatieve spoor, inclusief het bovengronds aanwenden van mest, een even lage ammoniakemissie oplevert in vergelijking met bedrijven die dit spoor niet volgen en mest emissiearm aanwenden

Soil Quality - a critical review

Sampling and analysis or visual examination of soil to assess its status and use potential is widely practiced from plot to national scales. However, the choice of relevant soil attributes and interpretation of measurements are not straightforward, because of the complexity and site-specificity of soils, legacy effects of previous land use, and trade-offs between ecosystem services. Here we review soil quality and related concepts, in terms of definition, assessment approaches, and indicator selection and interpretation. We identify the most frequently used soil quality indicators under agricultural land use. We find that explicit evaluation of soil quality with respect to specific soil threats, soil functions and ecosystem services has rarely been implemented, and few approaches provide clear interpretation schemes of measured indicator values. This limits their adoption by land managers as well as policy. We also consider novel indicators that address currently neglected though important soil properties and processes, and we list the crucial steps in the development of a soil quality assessment procedure that is scientifically sound and supports management and policy decisions that account for the multi-functionality of soil. This requires the involvement of the pertinent actors, stakeholders and end-users to a much larger degree than practiced to date