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The Management of Arable Land from Prehistory to the Present: Case Studies from the Northern Isles of Scotland Erika B. Guttmann,1,* Ian A. Simpson,2 Donald A. Davidson,2 and Stephen J. Dockrill3 1

Department of Engineering, Centre for Sustainable Development, University of Cambridge, Trumpington Street, Cambridge CB2 1PZ, United Kingdom 2 Department of Biological and Environmental Sciences, University of Stirling, Stirling FK9 4LA, United Kingdom 3 Department of Archaeological Sciences, University of Bradford, West Yorkshire BD7 1DP, United Kingdom

The arable soils from two multiperiod settlements were analyzed to identify changes in agricultural methods over time. The settlement middens were also analyzed to determine whether potential fertilizers were discarded unused. Results suggest that in the Neolithic period (~4000–2000 B.C. in the UK) the arable soils at Tofts Ness, Orkney, and Old Scatness, Shetland, were created by flattening and cultivating the settlements’ midden heaps in situ. The arable area at Tofts Ness was expanded in the Bronze Age (~2000–700 B.C. in the UK), and the new land was improved by the addition of ash, nightsoil, and domestic waste. Cultivation continued briefly after the fields were buried in windblown sand in the Late Bronze Age or Early Iron Age, but by the Early Iron Age cultivation ceased and organic-rich material was allowed to accumulate within the settlement. By contrast, at Old Scatness, arable production was increased in the Iron Age (~700 B.C.–A.D. 550 in Scotland) by the intensive use of animal manures. The results indicate that during the lifespan of the two settlements the arable soils were fertilized to increase production, which was intensified over time. © 2006 Wiley Periodicals, Inc.

INTRODUCTION The difficulty of producing adequate food supplies for a growing population has been a fundamental problem since the beginnings of agriculture. It can be addressed by either increasing arable production by the expansion of arable land, or by intensifying production on land already under cultivation (Boserup, 1965). Production can be increased by fertilizing the soil, or by improving the type of fertilizers which are applied. A wide range of fertilizers can be used to improve soil quality, but the materials which are actually available will depend on the local environment and whether or not domestic livestock are kept. The available fertilizers are not always used, whether from ignorance or indifference, and the agricultural survey of Britain

*Corresponding author; E-mail: [email protected]. Geoarchaeology: An International Journal, Vol. 21, No. 1, 61–92 (2006) © 2006 Wiley Periodicals, Inc. Published online in Wiley Interscience (www.interscience.wiley.com). DOI:10.1002/gea.20089

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in 1793–1817 cited many cases of wasted materials, including vast heaps of farmyard manure that were never applied to the fields (Woodward, 1994). There was a radical change in British agriculture in the 17th and 18th centuries, when a number of agricultural innovations were introduced, referred to by historians as “the Improvements.” This research is an investigation into the development of fertilizing techniques on two multiperiod settlements, and is founded on the hypothesis that there were “Improvements” in agricultural practices in prehistory, as well as in the recent past. In the Middle Ages an intensive land-management system was developed in northern Europe, which involved stripping turves of peat for use as animal bedding and later spreading this material onto the fields as fertilizer (Pape, 1970; van de Westeringh, 1988; Spek, 1992; Smeerdijk et al., 1995; Stoklund, 1999; Dercon et al., in press). Over time, this process enriched and aggraded the arable topsoils to depths of over a meter. These distinctive soils are known as plaggen soils, from the German plagge or sod. The term has been broadened to include soils aggraded by the addition of shell sand, which is applied to neutralize acidic soils; this system was used in the 12th century in Devon and Cornwall (Staines, 1979) and during the 13th century in Ireland (Conry and Mitchell, 1971). Plaggen soils also occur in Scotland (Davidson and Simpson, 1984; Davidson and Carter, 1998), and place name evidence, radiocarbon dating, and soil analysis in the Northern Isles have suggested that the system dates back to at least as early as the late Norse period (12th–13th century; Simpson, 1993). The plaggen system in Shetland was used on the more remote islands until the 1960s, and the soils created by this system have characteristics similar to the plaggen soils in Germany and the Netherlands: The soils reach depths of over 1 m and the phosphate levels are markedly enhanced. Unlike the continental soils, many of the Scottish plaggen soils are still exceptionally rich even today (Davidson and Smout, 1996). In the 1980s, deep topsoils were discovered in Scotland that predate the late Norse plaggen soils (Simpson et al., 1998a). Neolithic, Bronze Age, and Iron Age soils were discovered, some of which have depths of over 40 or 50 cm. The specific aim of the project reported here was to investigate the methods by which the prehistoric soils were fertilized, to determine whether they too were produced by the complex plaggen system used from the late Norse period until the 1960s. The analysis of the soils was complemented by analysis of the settlement middens to identify differences in the materials that accumulated in the settlements, which might indicate that certain materials were selected for use as fertilizers while other materials were discarded. GEOLOGICAL AND ARCHAEOLOGICAL SETTING The multiperiod sites of Tofts Ness (Sanday, Orkney) and Old Scatness (Shetland) were selected as study sites because both had distinct, multiple phases of activity, including multiple buried arable soils. Preliminary archaeological excavations (Dockrill, 1993; Nicholson and Dockrill, 1998) had established the chronology of some of the soils and midden deposits, so a sampling strategy could be planned that would include a representative range of soils and contemporary middens. 62

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MANAGEMENT OF ARABLE LAND

Figure 1. Location of the sites.

Tofts Ness is the northernmost peninsula on Sanday, Orkney (Figure 1). The solid geology is Middle Old Red Sandstone and the drift deposit is till, with about a third of the island (including the Tofts Ness Peninsula) covered by calcareous windblown sand. The soils of the peninsula are calcareous gleys, brown calcareous soils, and DOI: 10.1002/GEA


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Figure 2. Tofts Ness: Excavated areas on Mound 11.

regosols of the Fraserburgh Association, formed on shelly windblown sand (Dry and Robertson, 1982). The soils are coarse textured, with a weak structure and low organic matter. The Tofts Ness peninsula is used for today grazing. Seven large mounds and over 300 smaller mounds and cairns have been recorded in this area. Excavations of some of the mounds in the 19th century uncovered stone structures, some of which contained human remains (Traill & Smelli, 1845). One of the larger mounds, known as Mound 11 (NGR HY 756 464), was partially excavated between 1985 and 1988 (Dockrill, 1993; Hunter et al., in press). This site was reexcavated in 1999 to carry out geoarchaeological analyses on the soils and middens. Two test pits on the edge of the mound were reopened (Test Pits 1 and 2; Figure 2), and two transects of test pits (3–5 and 6–9) were excavated to establish the extent of the different buried soils (Figure 2). Six phases of activity were identified in the original excavation, including five archaeological phases and an episode of sand blow (Dockrill, 1993) (Table I). A radiocarbon date (GU2210 4480 70 yr B.P., 3360-2920 cal B.C., 95.4% probability) from a bone in the middens in Area A (Figures 2 and 3) established the Neolithic date for the deposits and a terminus ante quem for the soil that they sealed (Hunter et al., in press). An OSL date from the lower sand layer (5069) in Test Pit 6 (Figure 2) produced a date of 2980 710 B.C., which established a 64


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MANAGEMENT OF ARABLE LAND Table I. Tofts Ness phasing and bulk sample list (does not include thin-section samples). Period

Description

Samples

Neolithic Neolithic and Neolithic to Early Bronze Age

One Neolithic stone structure & one Neolithic to EBA 200, 217–227, 234, structure. Neolithic midden deposits and buried soil. Ard 243, 243, 248, 249 marks under the Neolithic soil in Area A. Elsewhere the basal (Neolithic) soil is sealed by a thin layer of blown sand.

Bronze Age

Deepened arable soil up to ~30 cm, containing large amounts of nightsoil. One EBA stone structure and two dating to LBA.

201, 202, 204, 229, 231, 233, 236–239, 242, 250, 251

Late Bronze Age to Early Iron Age1

Blown sand in all areas. No structures.

228, 232, 240, 241, 245, 246

Late Bronze Age to Early Iron Age2

Roundhouse structure, arable soils with ard marks cut into the Phase 5 sand. Midden deposits.

205–207, 209–214, 216

Modern control

Pasture soil

215

Figure 3. Tofts Ness: Section, Area A (Test Pit 2).

Neolithic terminus ante quem for the basal horizon (Sommerville et al., 2001). The lower sand layer (Phase 1) was used as a marker horizon to date the basal soil in Test Pits 7 and 8 to the Neolithic. The sand layer was absent from Test Pits J, 3, and 4, but the absence or minimal amount of shell in the basal layers suggests that these are also Neolithic, and that the sand layer which sealed them was incorporated into the much sandier Bronze Age soils above. Radiocarbon samples were DOI: 10.1002/GEA


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GUTTMANN ET AL. Table II. Old-Scatness phasing and bulk sample list (does not include thin-section samples). Period

Description

Neolithic–Iron Age Anthropogenic soil containing Neolithic pottery developed on quartz sand. Ard marks cut into the underlying sand. OSL dates from 2108: 4621 312 to 2752 202 yr B.P. (Burbidge et al., 2001)

Samples 10121, 10122

Middle Iron Age1

Broch constructed, surrounded by a ditch. Middens. Anthropogenic soil.

Middle Iron Age2

Roundhouse 12 constructed, with 5 or 6 abutting structures. Broch refurbished. Roundhouse went out of use and middens were deposited within. Anthropogenic soil. AMS dates 42 B.C.–216 A.D. and 86 B.C.–127 A.D. (from middens infilling Structure 12)

Midden deposits in Structure 12: 10115–10119 (Iron Age deposits, Area H: 10124–10127

Late Iron Age

Pictish structure cutting earlier midden.

10105, 10108

Norse

Anthropogenic soil.

Post-Medieval

Anthropogenic soil. A.D. 1800 (Provisional OSL date)

10129–10130

Modern controls

Pasture soils on differing geologies

Three samples

taken from the top (SRR 5256: 2665 40 yr B.P.) (900–790 cal B.C., 95.4% probability) and bottom (SRR 5247: 3140 40 yr B.P.) (1520–1310 cal B.C., 95.4% probability) of the Bronze Age soil above the lower sand in a test pit excavated in the 1990s (Simpson et al., 1998a). Old Scatness is a multiperiod settlement mound located at the southern tip of Mainland Shetland, to the west of Sumburgh airport (Dockrill, 1998). The solid geology is Middle Devonian Old Red Sandstone, and the site is located on a low-lying area of blown sands upon which calcareous regosols, brown calcareous soils, and calcareous gleys of the Fraserburgh Association have formed (Dry and Robertson, 1982). To the north and south are areas of drift derived from sandstone, upon which peat, peaty gleys, noncalcareous gleys, and saline gleys of the Skelberry Association have formed (Dry and Robertson, 1982). The 5-m-high settlement mound was formed by the accumulation of rubbish and structural debris that built up as a result of building and rebuilding on the same plot of land over the course of millennia (Table II). The phases include Neolithic and Bronze Age settlements, and in the Middle Iron Age a broch was constructed; brochs are substantial stone-built circular towers standing up to 13 m high, which are found on the northwest coast of Scotland and the Northern and Western Isles. An Iron Age village then grew up around the broch, with stone structures continuing to be built in the Late Iron Age or Pictish period. The land surrounding the settlement mound has also been aggraded, partly through the addition of fertilizing materials to the fields around the settlement and partly through the deposition of windblown sand (Simpson et al., 1998b). The settlement at Old Scatness was even more long66


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Figure 4. Old Scatness: Section, Area H.

lived than Tofts Ness, having been occupied for ~5000 years (although not necessarily continuously). The samples from Old Scatness were taken from a test pit (Area H) located on the western edge of the mound (Figure 4) and from Middle and Late Iron Age middens within the settlement. Samples taken in an earlier study are also discussed; these were from a transect of test pits through the anthropogenic soil to the east of the broch (Simpson et al., 1998b). DOI: 10.1002/GEA


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METHODS Sampling Strategy The specific objective on both prehistoric sites was to sample a series of prehistoric soils together with the contemporary midden deposits. The chronologies were inevitably rather broad, some of the soils having been in use over long periods of time, but by analyzing two multiperiod sites the results could be compared and contrasted. The conclusions drawn from the study can then be tested on other sites in the Northern Isles. The analytical methods used in this study were initially tested on the soils of a farm on Papa Stour, Shetland, which was cultivated from the Norse period until 1967 using the plaggen system. The farmer was able to describe exactly how each area on the farm was used and what materials (peat ash, food residues, and peat turves used as animal bedding) were added to the soil, and in what quantities. A reference collection of the material described was collected and thin-sectioned to assist in the identifications. In this way the characteristic signatures of the plaggen soils were identified and the methods used to study the prehistoric soils were validated (Guttmann, 2001). Control was an important aspect of the overall study, and samples from pasture soil in the vicinity of each site were taken to determine the level of enhancement of the archaeological soils. The modern control soils cannot be called undisturbed, but provided the nearest possible analogues to the prehistoric soils. Samples were taken from soils formed on all the different geologies around each site, including soils on blown shell sand (Tofts Ness and Scatness) and on till (Scatness and Papa Stour). Statistical Analyses The differences between the different areas and phases were tested using analyses of variance (ANOVA) in SPSS. A range of different post hoc tests were applied; post hoc tests identify which variables differ significantly, with differing degrees of rigorousness. The critical significance level used was p 0.05 (95% confidence interval [C.I.]). The data was normalized using log scales to transform positively skewed data, or by squaring or cubing to transform negatively skewed data. Correlations were carried out using Pearson’s correlation on normalized data in SPSS. The P values are given in the text. Thin-Section Micromorphology Thin-section analysis was used to identify the anthropogenic materials that were added to the soil. Studies of modern, medieval, and prehistoric agricultural soils in Scotland have demonstrated the potential of soil micromorphology in identifying fertilizing materials, such as peat fragments, animal manures, and fuel-ash residues in arable soils (Simpson, 1997; Davidson and Carter, 1998; Simpson et al., 1998a, 1998b). The quantities of added material can be estimated using thin-section 68


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analysis, while complementary analytical techniques can further assist in assessing the levels of enhancement. Thin sections of undisturbed soil samples and control materials were prepared at the Micromorphology Laboratory, University of Stirling, based on the standard procedures of Murphy (1986). The thin sections were examined using a polarizing microscope and described using the International System for soil thin-section description (Bullock et al., 1985). A range of magnifications (10–400x) were used. Light sources included plane polarized (PPL), cross- polarized (XPL), and oblique incident (OIL). Interpretations were based on FitzPatrick (1993) and Courty et al. (1989). Phosphate Analysis The soil phosphate levels were analyzed in order to asses the quantity of added organic manures and domestic waste; thin-section micromorphology assisted in distinguishing between the different sources of phosphate-rich materials. The samples were air dried and sieved at 2 mm, and were then heated in a furnace at 550°C for 1 hr to transform the organic P fraction into inorganic P. This provided an estimate of the total phosphate content of the sample, excluding the phosphate bound in silicate structures; the sulfuric acid extraction method followed Mikkelsen (1997). Colorimetry was carried out using an ammonium molybdate reagent. The analytical error for Scatness, based on 10 replicate samples, was 743 78 mg P/100 g soil (Mean SD); for Tofts Ness it was 254 17 mg. The phosphate values from Old Scatness were compared to the levels found in the soils by Simpson et al. (1998b). Different processes of acid extraction were used in the two studies, but the results were compared adding Simpson’s control samples to the control group in the later study and running an ANOVA comparing the controls, midden, and soils. This demonstrated that the variation between the groups (controls, middens, and soils) was greater than the variation within the groups (95% certainty). To further establish the comparability of the methods, the Iron Age midden samples and control samples from this study were reanalyzed using Simpson’s NaOH fusion method (Smith and Bain, 1982). An ANOVA demonstrated that there was no significant difference between samples analyzed by the two methods (p 0.000). Particle-Size Distribution Particle-size distribution was used to characterize the different deposit types, which can have distinct textures, depending on their origins. Used together with thin-section micromorphology, this method is particularly useful in the very windy environment of the Northern Isles, where blown sand is evident in differing quantities in the different phases of activity. The specific aim of the particle-size characterization was to identify the formation processes of the different deposit types and, if possible, to find links between deposit types to determine how different materials (particularly, midden materials) were distributed on the sites. The particle size was estimated using the standard methods of the Department of Environmental Science at the University of Stirling. The particle size was established DOI: 10.1002/GEA


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using a laser Coulter Counter (model LS230) following standard procedures (Coulter Corporation, 1994). The samples were prepared by sieving to 500 mm, as the counter does not work well on material with a larger grain size. This removed the coarse sand fraction, as defined by Bullock et al. (1985), and the coarse sand fraction and part of the medium sand fraction by the definition of the Soil Survey of England and Wales. The samples were then ignited in a furnace at 425°C for 41/2 hours. Ten milliliters of dispersant (comprising of 33 g sodium hexametaphosphate and 7 g sodium carbonate dissolved in 1 L of distilled water) was added to 50 mL of suspension. Subsamples were agitated on a mechanical shaker for 1 hr to ensure complete dispersion of the particles throughout the suspension. To ensure that the particles in the prepared suspensions remained dispersed throughout the liquid during counting, each suspension was continually mixed with a magnetic stirrer and a modified Pasteur pipette as it was fed into the counter. The mean and median particle sizes for each sample were produced by the laser counter, and do not include the 500 µm fraction. RESULTS AND INTERPRETATIONS Reference Material To bring objectivity to the micromorphological interpretations, reference slides were made of the different types of fertilizing materials that were described in the ethnographic and historical literature, and which could potentially appear in the prehistoric soils. Samples were taken from the Shetland Croft Museum, which functioned as a traditional farm until the 1930s, and from the Corrigall Farm Museum on Mainland Orkney. The samples included: •

•

• •

•

Dried peat from the peat stack at the Shetland Croft Museum. This was a distinctive fibrous red material (PPL) with very rare ( 0.5%) fungal sclerotia (Figure 5). Samples from the packed earth between the stone flags of the Croft Museum’s byre floor and drain. This material contained diatoms and fungal sclerotia; the porosity was high at 40–50%, and fragments of fibrous red material (peat) made up 5–10% of the slide. Other plant tissues made up 5–10%, with ~2% charcoal (Figure 6). Peat ash from a peat fire in an open hearth from the Corrigall Farm Museum. This was pale yellow in OIL, and contained fragments of charred peat. Sheep dung (Corrigall Farm Museum). This sample contained large amounts of parenchymatic tissues and dendritic phytoliths. Calcitic spherulites were also present. Cattle dung and straw bedding from a modern muckheap at Sumburgh Farm, near Scatness. This was also highly organic and contained calcitic spherulites.

A reference slide for coal ash was kindly provided by M. Canti of English Heritage. Some processing was also undertaken to create further reference slides for peat ash. Peaty turf samples were taken from differing geologies on Papa Stour, Shetland, and from Hestingott, to the north of Old Scatness. The samples were burned at 400°C 70


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Figure 5. Dried peat (magnification 25).

Figure 6. Byre floor, Shetland Croft Museum (magnification 20).

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(the temperature of an open fire) and 800°C (the temperature achieved in iron smelting) in a furnace. The flow of air through the furnace (for extraction of smoke and fumes) is believed to be similar to the flow of air through an open fire (Johan Linderholm, personal communication, Feb. 1998). Three of the four samples burnt at 800°C were bright orange-red in OIL, and one was white. Three of the samples burnt at 400°C were brown in OIL, and one was bright orange-red; the bright orange colored ash sample was taken from low-lying boggy ground on Papa Stour, Shetland. Tofts Ness Neolithic Soils Ard marks below the Neolithic soil were apparent in only one test pit, Area A, where they were found cut into the till below the soil; these were not recorded in the original excavation, when the base of the test pit was below the water table. The soil contained 0.5–5% charred peat/turf fragments, and four of the samples contained rare (0.5–2%) and very rare ( 0.5%) fragments of woody charcoal (Table III). Phytoliths were very rare or absent, apart from the sample from Area A, where they made up 2–5% of the slide. The soil microstructure was mostly spongy and contained porous to dense excremental fabric, indicating biological activity. The Neolithic soils were enhanced in phosphate (Table IV; Figure 7), but the concentration in Area A was particularly high, at 5.5 times the level of the modern pasture topsoil (this is the outlier in the Neolithic soil, Figure 7). Neolithic Middens The Neolithic middens contained 2–5% charred peat/turf fragments, and two out of the four contexts investigated contained very rare ( 0.5%) woody charcoal. The fine fabric of the middens in OIL was 5YR 7/6 and 10YR 6/8 and brighter, showing a similar range of colors to the reference samples taken from the open peat fire at the Corrigall Farm Museum. This also suggests that peat ash may be a component of the middens. The median particle size of the Neolithic middens was significantly finer than that of the Early Iron Age, Bronze Age, and Neolithic soils (p 0.000), apart from the Neolithic soil in Area A (Table V). The mean particle size of the Neolithic soil in Area A was also significantly finer than that of the other Neolithic soils, the Bronze Age soils, and the Late Bronze Age–Early Iron Age soils (p 0.002–0.016) but was similar to the Neolithic and Early Iron-Age middens. The similarities in particle size, phosphate concentration, and thin-section characteristics between the Neolithic soil in Area A and the overlying middens suggest that the soil has not simply had midden material added, but appears to be a midden which has been flattened out and cultivated. This is a different process from that which formed the Bronze Age soils. Bronze Age Soils The test pit transects established that the Bronze Age soil was up to 35 cm thick and extended for some 36 m to the east of the mound. Beyond this point, the original land surface sloped down into a hollow in which the soils became peaty and the 72


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(continued)

+ Very Rare (0.5%); ++ Rare (0.5–2%); +++Very Few (2–5%); • Few (5–15%); •• Frequent (15–30%); ••• Common (30–50%); •••• Dominant/Very Dominant; ? possible (i.e., an uncertain identification); ? very rare to few; ?? frequent, etc.

Table III. Tofts Ness soil micromorphology


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MANAGEMENT OF ARABLE LAND Table IV. Phosphate ranges, Tofts Ness (mg total P per 100 g soil). Phase and deposit type Neolithic soil (excluding Area A) Neolithic soil, Area A Neolithic middens Bronze Age soil LBA-EIA soil EIA middens Control (modern pasture topsoil)

Range of P values

Average P

92–329 858 493–1028 71–272 82–96 102–785 157

300 858 763 178 89 377 157

Figure 7. Tofts Ness: Total phosphate (the stars represent outliers).

blown sand that sealed the soils was much deeper. The thin-section analysis demonstrates that sand was blown onto the site throughout the Bronze Age. The sand may have accumulated steadily, or may have accumulated in single episodes during storms, after which the sand layers were reworked and mixed into the soil by Bronze Age ploughing. DOI: 10.1002/GEA


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GUTTMANN ET AL. Table V. Particle-size distribution, Tofts Ness (µm).

Neolithic soil (excluding area A) Neolithic soil, area A Neolithic middens Bronze Age soil LBA-EIA soil EIA middens Control (modern pasture topsoil)

Range of means

Average mean

102–227 73–77 44–132 53–301 235–246 58–123 234–252

171 75 79 190 245 94 244

Median range 68–215 35–38 12–75 23–294 229–257 25–74 234–241

Median average 140 37 37 160 243 49 237

The Bronze Age soils contained peat ash ( 0.5–15%) and woody charcoal (0–2%). The soils contained a higher concentration of shell sand than the Neolithic soils, based on estimates from the thin-section analysis, and, in places, a thin band of shell sand separated the Neolithic from the Bronze Age soils. The Bronze Age soil was, as a result, higher in pH than the Neolithic soil. The Bronze Age soils were analyzed in an earlier study (Bond, 1994a; Simpson et al., 1998a), which demonstrated that they contained fuel-ash slag, burnt seaweed (Fucus/Ascophyllum), and burnt root and stem fragments including alder, willow, heather, and crowberry leaves (Bond, 1994a). Stable isotope ratios indicate that the organics within the soil were predominantly from terrestrial sources, with a small input from marine sources (Simpson et al., 1998a). Analysis of the soil lipids suggested a large input of grasses, based on the high C31 component (an n-alkane common in temperate grasses; Simpson et al., 1998a). The analysis of the 5β-stanol ratio and the associated bile acids indicated that human fecal matter had been added to the soil (Simpson et al., 1998a). Late Bronze Age–Early Iron Age Soil In the Late Bronze Age or Early Iron Age, a layer of sand was deposited on top of the Bronze Age soil. Sand-filled ard marks cut the darker, Bronze Age soil below the sand layer, indicating that the sand deposit was cultivated (Figure 8). The sand-filled ard marks were traced to a distance of 14 m east of the mound. The sandy soil contained charred peat (0.5–5%) and wood charcoal ( 0.5%). The presence of calcitic spherulites indicate the addition of herbivore dung (Canti, 1997), but the phosphate concentration was very low (Table IV; Figure 7). Early Iron Age Middens The Early Iron Age midden deposits (Figure 9) were distinct from the Neolithic middens in that they contained larger amounts of charred peat (5–30%) and woody charcoal (0.5–2%). These deposits were the only contexts to contain wood ash, which was identified in thin section. The survival of the ash crystals may, however, be a taphonomic factor due to the level of the middens above the water table (the calcium carbonate druses that form ash crystals are water soluble; Canti, 2003). The Early Iron Age middens had lower P concentrations than the Neolithic middens but higher levels than the Late Bronze Age–Early Iron Age soil (Figure 7). This suggests that although organic 78


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Figure 8. Late Bronze Age–Early Iron Age ard marks. Photo: Alan Duffy.

waste was used to fertilize the fields (demonstrated by the presence of calcitic spherulites) it was also allowed to accumulate in middens within the settlement. Old Scatness Neolithic–Iron Age Soils The Neolithic–Iron Age soils were dated by the presence of Neolithic pottery and by optically stimulated luminescence (OSL) dating (Burbidge et al., 2001). The soils were reddish-brown to dark reddish-brown (5YR 3/3 and 4/3), and removal of the layers exposed ard marks cutting into the sand below; the ard marks were filled by the same distinctive reddish-brown soil. Both horizons of the Neolithic–Iron Age soil (Contexts 2108 and 2109) contained 2–5% bone (Table VI). Charcoal from burnt peat or turf occurred in small amounts throughout the sequence, but the largest amount (5–15%) occurred in the upper horizon of the Neolithic–Iron Age soil (2108). Wood charcoal occurred in both Neolithic–Iron Age horizons. The color of the Neolithic–Iron Age soil in thin section in OIL was a striking, bright orange that was well beyond the scale of the Munsell chart. This color was identical to the Iron Age midden and the bright orange reference samples. The upper horizon of the Neolithic–Iron Age soil had a DOI: 10.1002/GEA


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Figure 9. Tofts Ness: Section, Area J (Test Pit 1).

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+ Very Rare (0.5%); ++ Rare (0.5–2%); +++Very Few (2–5%); • Few (5–15%); •• Frequent (15–30%); ••• Common (30–50%); •••• Dominant/Very Dominant.

Table VI. Old Scatness micromorphology, Area H.


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MANAGEMENT OF ARABLE LAND Table VII. Particle-size distribution, Old Scatness (µm). Range of means

Average mean

104–166 131–201 58–175 80–114 198–234

135 176 107 97 221

Neolithic–Iron Age soils Iron Age deposits 2105 and 2106 Middle Iron Age middens Late Iron Age middens 18th–20th century soils

Median range 113–60 50–191 20–122 32–27 193–249

Median average 87 130 51 29 229

Table VIII. Phosphate ranges, Old Scatness (mg total P per 100 g soil). Description

Range of P values

Neolithic–Iron Age soils Iron Age soils (Simpson et al., 1998b) Iron Age Deposit 2105 Iron Age Deposit 2106 Middle Iron Age middens Late Iron Age middens 18th–20th century soils Controls

691–1516 1125–1782 215 560–797 279–402 863–1072 103–271 15–52

Average total P 1151 1583 215 696 329 968 182 28

median particle size in the very fine sand range, which was very distinct from the much coarser sand that dominated all of the other soils and sediments in Area H (Table VII). The Iron Age midden samples, by contrast, were dominated by silt, very fine sand, and fine sand. The similar color, particle-size distribution, and charred peat content suggest that the Neolithic–Iron Age soil is, in fact, midden material which has been subject to cultivation. The Neolithic–Iron Age horizons (2108 and 2109) contained between 691-802 mg P per 100g soil (Table VIII). These levels were between 13 and 38 times the levels of the controls from local pasture soils at Scat Ness, Toab, and Hestingott. Iron Age Soils The two Iron Age layers that were recorded in Area H had very different sedimentary characteristics. Deposit 2106, provisionally OSL dated to A.D. 399 235, had a close porphyric-related distribution, whereas 2105 had a chitonic-related distribution and was described in the field as blown sand. The dominant fabric of layer 2105 was blown quartz sand with no shell. Within the sand were two channels 5–6 mm wide, interpreted as earthworm channels, and biological activity was also demonstrated by the presence of porous and dense excremental fabric. The deposit contained 0.5% bone and 0.5% rubified mineral material. The organic matter in the soil included 0.5–2% charred peat/turf fragments and 0.5% fibrous red material interpreted as unburned peat. Phytoliths were also very rare ( 0.5%). The fabric of 2106 was biologically reworked to form a total excremental fabric of intergrain microaggregates with denser areas of spongy porphyric fabric. Shell sand made up 0.5%. Cultural material included 2–15% bone, 2–5% charred peat/turf, 0.5% unburned peat, and 0.5% phytoliths, diatoms, and fungal spores. DOI: 10.1002/GEA


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The inclusions of cultural material indicates that domestic waste was incorporated into these deposits, but it was not clear whether the deposits were soils or middens. They contained lower quantities of peat/turf ash than the midden deposits described below but had larger amounts of bone. There were no ard marks to unequivocally show that these layers were cultivated soils. The samples from the transect to the east of the broch may be more representative of the Iron Age arable soils. Iron Age Soils to the East of the Broch The soils to the east of the broch were sampled in a transect of test pits, and Iron Age deposits were identified within the sequence (Simpson et al., 1998b). The earlier Iron Age soils contained fine mineral material that was red in oblique incident light, and had inclusions of fine charcoals, heated (rubified) stone, and animal bone. The Later Iron Age soils were characterized by reddish-brown to brown fine material in oblique incident light, with porphyric to enaulic-related distributions. There were higher frequencies of coarse lignified tissue and finely fragmented amorphous organic material. Much of this material had been bioturbated. Fragments of fibrous red material, interpreted as unburned peat or turf, were also recorded. Fine fishbone fragments and animal bone were recorded, and also phytoliths and relict irondepletion pedofeatures. The total phosphorus values for the Iron Age soils ranged from 1125 to 1782 mg /100 g soil, higher than values from the earlier soils (Table VIII). The mean particle-size distribution of the 500 mm fraction ranged from 258 to 296 µm, finer than the values evident in the earlier soils. It is also noteworthy that the Iron Age midden deposits had even finer values of 191 µm and 216 µm. Such characteristics suggest that while domestic wastes and ash continued to be used as soil amendments during the Iron Age, organic material became an integral part of the manuring strategy once the Iron Age period was well established. An increase in organics is suggested by the finely fragmented nature of the fine and coarse organic material, frequently observed in animal manures. The quantities of bone in both the Later Iron Age and the preceding phases was recorded as “few” (Simpson et al., 1998b); because this source of phosphate appears to have been constant, it is suggested that the enhanced phosphate level in the Later Iron Age may be attributed to an increase in organic material. Silty clay textural pedofeatures in the later Iron Age soil horizons suggest soil disturbance, possibly the result of more intensive cultivation of the arable areas (Macphail et al., 1987; Simpson, 1997), although their absence from the earlier soils could be due to reworking. An increase in animal manures suggests that the relationship between arable and livestock husbandry was changing, with a greater organization of the resources required for agriculture. Iron Age Middens The middens considered as a whole were very low in organic material. Only two samples contained unburned peat, which, in each case, made up 0.5% of the slide (Table IX). Phytoliths were very rare (6 samples) or absent (5 samples), and fungal spores were only found in one sample. The distinguishing characteristics of the 84


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Table IX. Old-Scatness soil micromorphology, middens.



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Figure 10. Phosphate levels, Tofts Ness and Old Scatness.

midden samples were the large proportion of charred peat (2–5% in three samples, 5–15% of five samples, and 15–30% of three samples) and the bright orange and light red colors of the fine fabric in OIL, indicating a high proportion of peat ash. The phosphate range in the Middle Iron Age was 279–402 mg/100 g soil, rising to 863–1072 in the Late Iron Age (Table VIII). There is a striking difference between the phosphate levels in the Iron Age middens and soils at Old Scatness. Figure 10 shows the phosphate in the controls, Iron Age middens, and Iron Age soils at Scatness, together with the middens from Tofts Ness (for comparison). The graph shows the low level of enhancement in the Middle Iron Age middens at Scatness as compared to the very high levels in the Iron Age soils. The Scatness middens are also distinct from those at Tofts Ness in that the Iron Age middens at Tofts Ness show a much broader range and demonstrate the greater quantity of phosphate-rich waste (bone and organics) that was allowed to accumulate within the settlement. The Neolithic middens at Tofts Ness are even higher in phosphate, but, since they were being cultivated, the material was not wasted. 86


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Post-Medieval Soils in Area H Fibrous red material, interpreted as unburnt peat, made up 0.5–5% of the 18th century and later slides in Area H. This is interpreted as material brought in by the plaggening system, which recycles byre bedding as fertilizer in the fields. Unburned peat has been found in large quantities on farms which used the plaggen system up until the 1960s (Davidson and Carter, 1998; Guttmann, 2001). Earthworm/slug granules were present, indicating biological activity. Shell sand made up 5–30% of the 18th century to modern soils, which ties in with historical records for major sandstorms at this time. DISCUSSION The earliest prehistoric soils at Tofts Ness and Old Scatness were probably created by flattening and cultivating the middens, rather than by bringing midden material out onto the surrounding arable areas. The Neolithic middens at Tofts Ness were composed of peat ash, animal bone, and organic material (i.e., they were composed of domestic waste and possibly also of organic manures). The thin-section analysis, phosphate analysis, and particle-size analysis suggested that at Tofts Ness the arable soils were composed of the same material as the midden heaps and were not simply soils with added midden material, although such soils occurred in the later phases. At Scatness there were no uncultivated Neolithic midden deposits with which to compare the earliest soil, but the bright orange-red color of this soil, both in the field and in thin section, was identical to that of the Iron Age middens. The striking color suggests that the earliest soil was composed almost entirely of peat ash. The particle-size distribution of the Neolithic–Iron Age soil was distinctly finer than that of the later soils and was similar to the silt-size material that made up the Iron Age midden deposits. The ard marks below the earliest soils on both sites indicate that the deposits were cultivated. In the Bronze Age there was an expansion in the arable area at Tofts Ness, and the soils were aggraded and enriched by the addition of domestic waste. The arable soils were enhanced in phosphate, and soil lipid analysis in an earlier study has demonstrated that this enhancement is due largely to the addition of nightsoil (Simpson et al., 1998a). The fertility of this soil is demonstrated by the large size of the barley grains recovered from this phase, which were comparable to the grains grown in the Norse period at the nearby site of Pool (Bond, 1994b). The most significant difference between the Neolithic and Bronze Age soils was one of scale; in the Neolithic the midden was used as an arable plot and was surrounded by amended but not especially deepened soils, while the Bronze Age soil was deeper and more extensive than the Neolithic. In the Iron Age the arable soils at Scatness were enriched and deepened by the addition of organic manures and domestic waste. The middens which accumulated on the site at this time were predominantly composed of peat ash and had lower phosphate levels than the contemporary soils, which suggests that most of the organic waste produced in the settlement was being used as fertilizer. This was not the case in the Early Iron Age at Tofts Ness, where the middens were not only high in phosDOI: 10.1002/GEA


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phate, but calcitic spherulites indicative of animal dung were also found within them. Organic material was not used selectively as fertilizer on the thin, sandy soil of this last phase of activity. It may be that the inhabitants of the contemporary roundhouse were no longer depending on arable produce when the middens were formed, but obtained their grain through trade. It is suggested here that there was an intensification of arable production in the Iron Age at Old Scatness, demonstrated by the intensive fertilization of the arable fields. The practice differed from the earlier method of cultivating the middens in situ. The Iron Age horizons in Area H and the eastern transect contained very rare fragments of unburned peat, which occurred more commonly (0.5–5%) in the 18th century and later deposits. The occurrence of peat fragments in arable soils in this region is generally linked with the plaggen soil system (Davidson and Carter, 1998; Guttmann et al., 2003). This suggests that the plaggening system known to have been used in the 18th century and later may have had its origins in the Iron Age. Furthermore, waste materials may have been used selectively in the Iron Age at Old Scatness, with the more organic-rich materials being favored as fertilizer above the poorer quality peat ash. At Tofts Ness this transformation did not occur, and occupation ceased in the Early Iron Age. Production was never intensified, but was abandoned altogether. Evidence from the Iron Age site of Dun Vulan, South Uist has also produced results that contrast with Scatness. As at Tofts Ness, organic material rich in phosphate was allowed to accumulate around the settlement rather than being used as fertilizer. The excavators suggested that the midden may have had a symbolic meaning, possibly linked with fertility (Parker Pearson et al., 1996), but an alternative interpretation was made by Smith (1994), who suggested that the accumulation of midden material on a number of Iron Age sites was simply due to less intensive manuring in the Iron Age than in subsequent periods. The accumulation of unused midden material may simply demonstrate that agriculture in prehistory was less efficient than in later periods. If there were no trade opportunities, arable production was probably only as intensive as it needed to be to support the population. The differences in the intensity of arable production on different sites in the Iron Age may relate to the development of a trade in subsistence goods. Old Scatness is located in a low-lying area with a large concentration of broch sites. An auger survey around the nearby brochs of Jarlshof and Eastshore has shown that these sites also have artificially deepened topsoils which may date to the Iron Age, but a broch located on the higher ground to the north of Old Scatness produced contrasting results (Guttmann and Simpson, unpublished data). Clevigarth is a broch ~3 km NNE of Old Scatness, and an auger survey around the site demonstrated that, unlike the sites to the south, there were no deepened soils associated with it, and the soils were poor and thin. It may be that the brochs on the poorer quality soils of the Shetland uplands were trading in subsistence goods with the broch sites on the better-quality lands. This may also explain why some Iron Age sites, such as Tofts Ness and Dun Vulan, did not make use of the available fertilizing materials; they may have been unable to compete with sites that had better soils, which were more successful in producing grain for trade. 88


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The evidence from Old Scatness suggests that the plaggen manuring system may have developed in the Iron Age. Whether or not this is the case, by the Norse period it was probably widespread in Orkney, where deep topsoils surround a number of farms with Norse place names and where radiocarbon dating has confirmed the Norse date of one plaggen soil (Simpson, 1993). Plaggen soils also surround farms with Norse place names on the island of Papa Stour, Shetland. The development of the Norse plaggen soils coincides with increases in fishing (Bigelow, 1992), including deepwater fishing (Barrett et al., 1999), both of which may be linked with an international trade. This argument is further supported by historical and archaeological evidence for the production of dried fish in the 13th–14th centuries (Barrett et al., 1999), and by the late 14th century the Shetland fish trade was a major industry controlled by the Hanseatic League (Nicholson, 1998). The development of plaggen soils in the late Norse period may be linked with increased opportunities for trade at this time. Arable production in the UK was further intensified in the Improvements of the post-medieval period. A survey of the agricultural methods used between 1793–1817 listed “yard muck” as the most common fertilizer, but many 18th century sources describe how manure heaps were left unused; some farmers even placed their manure heaps by the river so they would be swept away in the floods (Woodward, 1994). An 18th-century visitor to the Western Isles was horrified to find that although seaweed and shell sand were widely available, they were not used to fertilize the soils (McKay, 1980). The agricultural improvers set out to increase productivity in farming and to educate farmers about the use of fertilizers and crop rotation. The drive to increase the productivity in agriculture reached the Northern Isles in the 19th century, and the changes introduced included drainage, liming, and the expansion of agricultural land (Fenton, 1978). The historical and ethnographic research on land management in the Northern Isles describes a post-Improvement system in which little was wasted. Kitchen refuse, nightsoil, byre waste, and fuel ash were deposited together in middens, which were subsequently spread onto the fields, and potential fertilizer was not allowed to accumulate within the settlements. This system continued to be used on the more remote Scottish islands until the 1960s, but is today regarded as too labor intensive. The deep anthropogenic soils on Orkney are mapped as the deepened phase of the Bilbster series, and it is worth noting that even now they remain rich, fertile soils. The land around Old Scatness was subject to major sand blows in the 18th and 19th centuries, which made this area unviable for agriculture. An 18th-century traveler described the area as “An Arabian desert in miniature,” with “clouds of sand flying as far as the eye can reach” (Low, 1779). Around the beginning of the 20th century, the coastal dunes were stabilized by planting Marram grass (Ammophila arenaria) but not before several crofts to the north of Old Scatness were buried in blown sand. CONCLUSIONS This study has demonstrated that were changes in both the methods and the intensity of prehistoric arable land-management practices over time. At both sites, the Neolithic middens were flattened and cultivated in situ to create what may have been DOI: 10.1002/GEA


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small, garden-sized plots, a practice that continued into the earlier Iron Age at Old Scatness. This is a new development in the study of prehistoric agriculture in Europe, and it suggests that early cereal cultivation on the study sites took place in plots more like gardens than fields. In the Bronze Age, the arable area at Tofts Ness was expanded and artificially deepened by the addition of domestic waste and organic matter, including nightsoil (Simpson et al., 1998a; Guttmann, 2001). The Neolithic and Bronze Age agricultural soils were not, strictly speaking, plaggen soils; although they are artificially deepened, they represent a much less labor-intensive agricultural regime than the plaggen system of the Middle Ages in Scotland and northern continental Europe. The first notable “Improvement” can be seen in the Iron Age at Old Scatness, when animal manures were added to the soil and a plaggen system may potentially have been in use. In the Iron Age at Tofts Ness, the sandy soils were fertilized with animal manure (demonstrated by the presence of calcitic spherulites), fuel ash residues (peat/turf and wood), and kitchen waste (demonstrated by animal bone fragments), but these materials were also allowed to accumulate within the settlement where their fertility was wasted. At Old Scatness, by contrast, the Iron Age arable soils were higher in phosphate than the middens, which suggests that organicrich material was used selectively as fertilizer. This indicates an increased efficiency in manuring that would have increased arable production. The intensified arable production evident in the Iron Age may have been necessary to feed a growing population, or a surplus may have been grown for trade. These findings are supported by the archaeological evidence for this region: The Iron Age in the Northern Isles of Scotland is characterized by larger, more densely populated settlements quite unlike the scattered farmsteads of earlier prehistory. This suggests that there were major social changes taking place at the time of these early agricultural improvements. This paper is based on Erika Guttmann’s doctoral thesis. E. Guttmann’s research was funded by NERC with support from AOC Archaeology. The reexcavation of Tofts Ness was funded by a grant from Historic Scotland.

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Received October 20, 2002 Accepted for publication December 15, 2004

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