Plaggic Anthrosols are the result of historical forms of land management in
cultural landscapes on chemically poor sandy substrates. Application of
plaggic manure was responsible for the development of the plaggic horizons of
these agricultural soils. Pollen diagrams reflect aspects of the
environmental development but the interpretation of the pollen spectra is
complicated due to the mix of the aeolian pollen influx of crop species and
species in the surroundings, and of pollen occurring in the used stable
fillings. Pollen diagrams and radiocarbon dates of plaggic Anthrosols
suggested a development period of more than a millennium.
Plaggic Anthrosols occur in cultural landscapes, developed on cover sands. These chemical poor Late-glacial aeolian sand deposits dominate the surface geology of an extensive area in northwestern Europe. Plaggic Anthrosols are the characteristic soils that developed on ancient arable fields, fertilized with plaggic stable manure. Plaggic Anthrosols have a complex genesis and are valuable records of environmental and agricultural history (van Mourik et al., 2011).
In previous paleopedological studies of such soil records in The Netherlands
(van Mourik et al., 2011, 2012a, b), information was unlocked by application
of pollen analysis, radiocarbon (
The use of ectorganic matter from forest soils in the Dutch cover sand area must have been strongly reduced in the 11–13th century, due to commercial forest clear cuttings as recorded in archived documents (Vera, 2011). This deforestation resulted in a regional extension of sand drifting and the managers of the heaths had to protect their valuable ecotopes against this “historical environmental catastrophe” (Vera, 2011).
Heaths were already present in the Late Paleolithic landscape (Doorenbosch, 2013) and played a ceremonial role in the society of our ancestors. People already had the knowledge to manage the heath as sustainable grazing areas for cattle (Doorenbosch, 2013).
The use of heath for sheep grazing and other purposes as honey and oil production could continue until the middle of the 18th century (Vera, 2011). In the southeastern Netherlands sustainable use of the heaths was promoted by many management rules and laws (van Mourik, 1987; Vera, 2011). Over the course of the 18th century, the population growth resulted in an increasing food demand. In the course of the 18th century, the deep stable economy was introduced and the booming demand for manure resulted in intensification of manure production. Farmers started with the use of heath sods as (additional) stable filling (Spek, 2004). This caused heath degradation and initiated the second extension of sand drifting. The use of sods finished at the end of the 19th century after the introduction of chemical fertilizers (Spek, 2004).
Through the combination of OSL and
The goal of the present study was to further explore the applicability of biomarker analysis as part of a multi-proxy reconstruction aimed at unraveling the sources of stable fillings used for the production of plaggic manure in the context of the historic development of the plaggic agriculture ecosystem. For this, we applied biomarker analysis on three previous investigated plaggic Anthrosol.
The distribution area of plaggic Anthrosols in northwestern Europe is indicated in Fig. 1. Pape (1972) published the first map of the distribution of plaggic agriculture in northwestern Europe. Bastiaens and van Mourik (1995) found traces of intensification and extension of this area in Vlaanderen (Belgium) while van Mourik (1999b) also reported plaggic Anthrosols in Schleswig (Germany). Beside this area with “real” plaggic Anthrosols, Spek (2004, p. 724) summarized information about the occurrence of soils with some evidence of application of plaggic manure in the Atlantic coastal zones of Norway, Denmark, France, Galicia, Scotland and Ireland (soil classification according to ISRIC-FAO, 2006).
For this pilot study we selected three previously investigated plaggic
Anthrosols in the Netherlands with an undisturbed plaggic horizon:
Valenakker, Nabbegat and Posteles (Fig. 2). Pollen diagrams,
Valenakker (van Mourik et al., 2012b) is situated southwest of the city Weert
(middle Limburg) on the sport fields of a former college. As a result, during
the 20th century the soil has never been ploughed or subjected to land
consolidation. This profile has never been affected by roots of
The location of sampled profiles Valenakker, Nabbegat and Posteles in the distribution area of plaggic agriculture.
The plaggic Anthrosols Valenakker, Nabbegat and Posteles. The location of the OSL samples are indicated in the white circles (depth in cm); the locations of the profiles are indicated in Fig. 1.
Nabbegat (van Mourik et al., 2012a) is situated on the Maashorst (eastern North-Brabant). The plaggic deposits were buried by drift sand around AD 1800. Consequently, the plaggic deposits have perfectly been protected against damage by land consolidation or pollution afterwards (van Mourik et al., 2012a). The site is now vegetated by oak and birch trees. Roots of these trees may have caused input of organic matter by decomposed roots in the upper part of the plaggic horizon (Fig. 3).
Cross-section of a (living) tree root in the thin section of the 2
Aan of Nabbegat (70–80
Posteles (van Mourik et al., 2011) is situated in Twente (eastern
Overijssel). The landowner informed us that during the last three generations
this land was never subjected to deep ploughing or land consolidation but
since 1960
Pollen diagrams of plaggic Anthrosols provide paleoecological information about plant species, present on site and in the region during the formation of the plaggic horizon. Previous research showed that pollen grains, infiltrated in soils and incorporated in plaggic deposits, are well preserved in the anaerobic and acid microenvironment of excremental aggregates (van Mourik, 1999a, 2001) (Figs. 4, 5).
Distribution pattern of organic aggregates in a thin section of the
Aan of Valenakker (40–50
Samples for pollen extraction were collected in 10 mL tubes in profile pits. For a correct matching of pollen and biomarker spectra of the plaggic deposits, the same samples were treated for both pollen and biomarker extraction and analysis. The pollen extractions were carried out using the tufa extraction method (Moore et al., 1991, p. 50). For the identification of pollen grains, the pollen key of Moore et al. (1991, p. 83–166) was applied. Pollen scores were based on the total pollen sum of arboreal and non-arboreal plant species. For the estimation of the pollen concentrations of the various soil horizons, the exotic marker grain method was applied (Moore et al., 1991, p. 53).
The determination of the age of plaggic deposits is subjected to various
complications (Spek, 2004). Pollen stratification is disturbed by
bioturbation and ploughing. Besides, the pollen content is a mix of the
regular pollen influx and pollen in stable fillings, used for the production
of stable manure (van Mourik et al., 2011). The ages of humic horizons of
buried Podzols cannot be correctly determined by
Pollen grains, visible in a welded aggregate of the same thin sections. Pollen grains in thin sections are observable as opaque, empty spheroidal objects. The palynological characteristics as sculpture and aperture are not visible without the chemical treatments during pollen extraction.
Conventional radiocarbon dating of humin and humic acids showed in presented diagrams, extracted from plaggic deposits, was performed in the CIO (Centre for Isotope Research of the University of Groningen).
OSL dates provide reliable information about the moment of fossilization of plaggic material under the rising furrow because the quartz grain were perfectly bleached during active ploughing (Bokhorst et al., 2005). OSL dating of quartz grains, extracted from plaggic deposits, was performed in the NCL (Netherland Centre for Luminesce Dating, Wageningen University).
A detailed description of the biomarker approach using the VERHIB method is
presented in our previous publications (Jansen et al., 2010, 2013; van Mourik
and Jansen, 2013). Briefly, the basis of the method lies in the unraveling of
the preserved concentration patterns of C
The second group concerned crop species. Close to the educational Field Study
Centre Orvelte (Drenthe) is a traditional plaggic field where they continued
with the cultivation of traditional crop species. There we sampled
The concentration patterns of the
Flow diagram of the methodology of biomarker analysis.
The n-alkane biomarker distribution in leaves and/or roots of species sampled, for the reference base of this pilot study.
A second parameter that must be considered in the application of VERHIB is
input of leaf and root material. VERHIB considers the species-specific
n-alkane patterns in plant roots separately from the patterns in plant
leaves, and uses this to deal with the input of young root material at depth
(Jansen et al., 2010). A first selection criterion here concerns whether or
not leaf and root material can be expected to have entered the soil at all.
For the deciduous forest soil material potentially used as stable fillings
(
Figure 6 shows a flow diagram that illustrates the functioning of the VERHIB modeling as well as the selection of parameters and reference base species as described above.
Approximately 0.1
Figure 7 presents the n-alkane biomarker distribution in the leaves and/or roots of the species, inserted in the reference base. The results show the odd-over-even chain-length predominance typical of higher plants (Kolattukudy et al., 1976). The observed variation in patterns and concentrations is in line with the variation found in other species in previous work (e.g. Jansen et al., 2006).
Pollen diagram Valenakker. Pollen density in
Profile Valenakker is a plaggic Anthrosol (Aan), overlying a ploughed umbric
Podzol (2ABp, 2Bs). The pollen diagram (Fig. 8) and the absolute dates
(Table 1) reflect a soil development of
The post sedimentary pollen spectra in the 2BS show percentages of tree
species as
Micromorphological observations (Figs. 4, 5) of the plaggic deposits show the complexity of soil organic matter. There are various sources of organic carbon as plant roots, tissue of table fillings and sods. Also the composition of pollen spectra is complex: it is a mix of the regular pollen influx of plants on the fields and in the surrounding areas infiltrating into the soil and pollen, and also the pollen present in various stable fillings.
Biomarker diagram Valenakker.
Pollen diagram Nabbegat. Log
In previous studies the origin of stable fillings, used in plaggic
agriculture, was reconstructed on the basis of pollen diagrams (Spek, 2004;
van Mourik et al., 2012a, b). The pollen spectra of the Aan horizon show very
low scores of arboreal trees but reasonable scores of Ericaceae and Poaceae.
Ericaceae pollen may indicate the use of heath sods, Poaceae pollen the use
of grassland sods, the combination of sods from degrading heath and the rise
of the land surface by plaggic manure is caused by the mineral fraction in
such sods. However, the rise of the plaggic horizon of
The biomarker spectrum of the base is dominated by
Profile Nabbegat is a haplic Arenosol (with Mormoder humus form), overlying a
plaggic Anthrosol, overlying a ploughed umbric Podzol. The pollen diagram
(Fig. 10) and the absolute dates (Table 2) reflect a soil development of
The post sedimentary pollen spectra of the 3ABp reflect the start of
agriculture (increase of Cerealia) on a former heath (decrease of
The radiocarbon ages indicate that the farmers used organic matter with very
little mineral “contamination” for a long time. The OSL ages indicate that
the rise of the plaggic horizon started
Figure 11 shows the results of biomarker analysis. Biomarkers of
Profile Posteles is a plaggic Anthrosol, overlying a ploughed umbric Podzol. The pollen diagram (Fig. 12) and the absolute dates (Table 3) reflect a soil development of at least 1200 years.
The pollen content of the buried ploughed Podzol (2Ap, 2B) is
post-sedimentary infiltrated in Late-Glacial cover sand by bioturbation and
agriculture. Characteristic is the sharp decrease of pollen concentrations
with depth, shown by the pollen density curve. The spectra of the 2B horizon
already reflect evidence of agriculture (Cerealia) in a deforested landscape
(low percentages of
The radiocarbon age of the base of the plaggic deposits (95
The actual Ap horizon (the active plough horizon) is palynologically
characterized by peak percentages of Cerealia, a slight extension of
Biomarker diagram Nabbegat.
The lowest spectrum (80) is dominated by the crop species
The spectra 10, 20, 40, 60 are dominated by biomarkers from roots of
Pollen diagrams of plaggic Anthrosols provide valuable paleoecological information to reconstruct the soil dynamics during the plaggic agriculture. However, interpretation of pollen diagrams is complicated. Pollen grains, extracted from plaggic deposits, may originate from two sources (van Mourik et al., 2011). The first source concerns the regional pollen influx from flowering species and local flowering crop species. Pollen grains precipitate on the soil surface and may infiltrate into the Anthrosols by ploughing and bioturbation. This pollen influx will be mixed with the pollen content of materials, used as stable filling to produce manure.
Pollen diagram Posteles; pollen density in
Pollen will be preserved in plaggic deposits in the anaerobic and acid micro environment of humic aggregates, produced by worms and micro arthropods (van Mourik, 1999b, 2001). In general it is not possible to make a clear separation between pollen grains originating from the regular pollen influx or from materials as sods. Therefore, the identification of the various sources of stall fillings cannot be based on pollen analysis alone. Additional information, acquired by biomarker analysis proved very useful for this purpose.
In the pollen diagrams
The radiocarbon ages of plaggic deposits are much older. This is caused by (1) older organic carbon, present in the applied stable fillings (as forest litter) for the manure production and (2) accumulation of hardly decomposable organic carbon during active soil formation. Consequently, the radiocarbon dates overestimate the ages of the plaggic sediments, but approach the age of the introduction of agricultural soil management (van Mourik et al., 1995, 2011, 2012a, b). Manuring of infertile soils already came in use in the Bronze Age and also the Celtic fields are an example of a prehistorical agricultural system based on manure management (Spek, 2004).
The mineral component of stable manure, applied on the fields, was
responsible for the thickening of the plaggic horizon. Ploughing of the
furrow will bleach the OSL signal of the mineral grains until the moment that
the grains are no longer part of the active soil furrow. For that reason, OSL
dating of the plaggic horizon provides reliable ages of the plaggic deposits
(Bockhorst et al., 2005). The OSL dates of the profiles Valenakker, Nabbegat
and Posteles indicate a start of the thickening
It was not possible to determine the sources of stable fillings palynologically. Possible stable fillings were forest litter, sods from moist grass lands and heat sods. But in almost all spectra of the pollen diagrams Ericaceae, Poaceae and arboreal pollen occur. Biomarkers extracted from plaggic deposits originate from two sources. The first source concerns biomarkers from decomposed roots of crop species, the second source of organic material as straw and sods, used as stable filling for manure production.
Biomarker diagram Posteles.
In the three diagrams we find
Only in the top of the Aan horizon markers of Calluna are present, indicating the use of heath sods as stable filling. Based on the results of the biomarker analysis we can conclude that heaths sods were used as stable filling only in the 18th and 19th century. This fits with the observations about the use of heaths in historical archives (Vera, 2011).
So the question rises about heath management before the introduction of the
deep stable economy. Some researchers point to careful heath management
before the 19th century. In interviews with farmers born before 1950, Burny
(1999) collected essential information about historical heaths management in
the Belgian Kempen. A historical study of land use in the Campina also
indicated careful maintenance and sustainable use of valuable common fields
(de Keyzer, 2014). Before the 19th century, heath sods were never dug on the
dry
An important factor may be the presence of pollen and biomarkers in sheep
droppings. According to Simpson et al. (1999) biomarkers survive the
congestion process and stay in the manure. But what do sheep consume? Grazing
sheep are very selective in collecting food (Oom et al., 2008; Smits and
Noordijk, 2013). They prefer grasses (
If it is true that
According to Smits and Noordijk (2013) there are several sources of minerals. Firstly, a small amount of mineral grains will be incorporated in the manure during emptying out of the manure of the stable. Secondly, farmers had the knowledge that the addition of sand could improve the fertility of the soil. Not the leached and acid sand from heath sods but not leached sand, dug on sheep walks and in blown out depressions in nearby drift sand landscapes.
The vertical zoning of biomarkers and pollen in plaggic horizons are
different. Palynologically, the plaggic horizon is a homogenous, the
biomarker diagrams show differentiation. We can identify various stable fillings used based on the vertical
distribution of biomarkers. The biomarker spectra of the base layer of the plaggic horizon are
dominated by biomarkers of deciduous trees litter (dominated by
The biomarker spectra of the middle part of the plaggic deposits are
dominated by crop species ( Only the top spectra of the plaggic horizons are dominated by Profile Posteles shows the impact of the contribution of biomarkers of
roots of The negligible percentages of
We would like to thank Jap Smits (State Forestry) for his information about historical heath management and agriculture. We are grateful to Annemarie Philip (IBED, University of Amsterdam) for the preparation of the pollen slides, Hans van der Plicht (CIO, University Groningen) for production of the radiocarbon dates and Jakob Wallinga (NCL, Wageningen University) for the realization of the OSL dates. The digital illustrations were produced by Jan van Arkel (IBED, University of Amsterdam).
We thank Jakob Wallinga and an anonymous reviewer for their constructive remarks. Edited by: S. Kluiving