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LLM - Digital Humanities 16

ERROR: type should be string, got "https://doi.org/10.1016/j.chemosphere.2018.11.155\n0045-6535/© 2018 Elsevier Ltd. All rights reserved. a r t i c l e\ni n f o Annually, sand and gravel processing generates approximately 20 million tonnes of non-commercial by-\nproduct as fine silt particles (<63 mm) which constitutes approximately 20% of quarry production in the\nUK. This study is significant as it investigated the use of quarry silt as a sub-soil medium to partially\nsubstitute soil-forming materials whilst facilitating successful post-restoration crop establishment. In a\nglasshouse pot experiment, top-soil and sub-soil layering was simulated, generating an artificial sub-soil\nmedium by mixing two quarry non-commercial by-products, i.e. silt and overburden. These were\nblended in three ratios (100:0, 70:30, 50:50). Pots were packed to two bulk densities (1.3 and 1.5 g cm-3)\nand sown with three cover crops used in the early restoration process namely winter rye (Secale cereale),\nwhite mustard (Sinapis alba) and a grassland seed mixture (Lolium perenne, Phleum pratense, Poa\npratensis, Festuca rubra). Three weeks into growth, the first signs of nitrogen (N) deficiency were\nobserved in mustard plants, with phosphorus (P) and potassium (K) deficiencies observed at 35 days. Rye\nexhibited minor N deficiency symptoms four weeks into growth, whilst the grassland mixture showed\nno deficiency symptoms. The 70:30 silt:overburden sub-soil blend resulted in significantly higher Root\nMass Densities of grassland seed mixture and rye in the sub-soil layer as compared with the other blends. The innovation in this work is the detailed physical, chemical and biological characterisation of silt:o-\nverburden blends and effects on root development of plants commonly used in early restoration to bio-\nengineer soil structural improvements. 2018 El\ni\nL d All i h\nd Article history:\nReceived 30 August 2018\nReceived in revised form\n11 November 2018\nAccepted 23 November 2018\nAvailable online 1 December 2018 Article history:\nReceived 30 August 2018\nReceived in revised form\n11 November 2018\nAccepted 23 November 2018\nAvailable online 1 December 2018\nKeywords:\nQuarry silt\nCover crops\nRestoration\nRoot mass density\nNutrients Article history:\nReceived 30 August 2018\nReceived in revised form\n11 November 2018\nAccepted 23 November 2018\nAvailable online 1 December 2018 Keywords:\nQuarry silt\nCover crops\nRestoration\nRoot mass density\nNutrients © 2018 Elsevier Ltd. All rights reserved. h i g h l i g h t s \u0001 Silt is not fully utilised in quarries as a resource. \u0001 Silt is not fully utilised in quarries as a resource. \u0001 Root development of mustard tap roots was restricted compared to grass. \u0001 Quarry silt blended with growing medium is a suitable subsoil medium for grass and rye. \u0001 Root development of mustard tap roots was restricted compared to grass. \u0001 Quarry silt blended with growing medium is a suitable subsoil medium for grass and rye. Assessment of silt from sand and gravel processing as a suitable\nsub-soil material in land restoration: A glasshouse study Lucie Ma\u0001skov\u0003a a, Robert W. Simmons a, Sarah De Baets a, Enrique Moran Montero b,\nAude Delmer b, Ruben Sakrabani a, * a School of Water, Energy and Environment, Cranfield University, Building 52a, Cranfield Bedfordshire, MK43 0AL, UK\nb Tarmac Ltd., Panshanger Park, Hertford, Hertfordshire, SG14 2NA, UK * Corresponding author.\nE-mail address: r.sakrabani@cranfield.ac.uk (R. Sakrabani). Contents lists available at ScienceDirect Contents lists available at ScienceDirect * Corresponding author.\nE-mail address: r.sakrabani@cranfield Chemosphere 219 (2019) 58e65 Chemosphere 219 (2019) 58e65 E-mail address: r.sakrabani@cranfield.ac.uk (R. Sakrabani). * Corresponding author.\nE-mail address: r.sakrab © 2018 Elsevier Ltd. All rights reserved. 2.3. Winter rye The aim of this project was to determine the suitability of non-\ncommercial by-product such as quarry silt from mining lagoons in\ncombination with overburden as a replacement for sub-soil to\nfacilitate cover crop establishment on restoration sites and whole\nprofile bio-remediation of soil structure. Outcomes will inform\nrecommendations for the successful use of non-commercial by-\nproducts such as quarry silt and overburden in future restoration\nprojects by mineral operators. Seeding rates for Winter Rye depend on local climate conditions\nand seeding method being either drill or broadcast. Values as low as\n62e67 kg ha\u00041\n(Government\nof\nAlberta,\n2016)\nand\nup\nto\n56e224 kg ha\u00041 (Casey, 2012) can be used. Based on this, a seeding\nrate of 90 kg ha\u00041 was used, as an approximate average value for\nthis experiment. Winter Rye can germinate in temperatures as low as 1 \u0005C\nallowing seeding as late as September, the end of October, or even\nDecember (AGRAVIS, 2017; Rosenfeld and Rayns, 2011). It is the\nmost frost tolerant of all cereals (Oelke et al., 1990). It prefers well-\ndrained light loams and sandy soils, but can also be established on\nheavy clays (Bj€orkman and Shail, 2014; Oelke et al., 1990). It has a\ndense, fibrous branching root system that grows especially vigor-\nously in the upper 0.3 m of soil. 2.2. Experimental design In typical quarry restorations conducted by Tarmac Ltd, a 0.6 m\nlayer of sub-soil would be capped with a 0.3 m layer of top-soil\nstripped from the surface prior to sand and gravel extraction. This\nsubstrate layering ratio was also simulated in the pot experiment. As a sub-soil medium, 3 quarry silt:overburden blend ratios were\nselected, 100:0, 70:30 and 50:50, aiming for a high quarry silt\ncontent. Quarry restoration can result in spatial variation in sub-soil and\ntop-soil bulk densities (BD). Bulk density values normally vary from\n1.1 to 1.8 g cm\u00043, whilst in extreme conditions surface soil layers\nmay have BD as low as 0.5 g cm\u00043 and heavily compacted soils may\nexceed 2.0 g cm\u00043 (Cresswell and Hamilton, 2002). A value of\n1.3 g cm\u00043 was chosen for top-soil BD and the sub-soil materials\nwere packed at a BD of either 1.3 or 1.5 g cm\u00043 in order to represent\na low and a high degree of sub-soil compaction. Cover crops possess traits that can effectively remediate com-\npacted soils (Kirkegaard et al., 2008). Research has also demon-\nstrated that the generation of biopores through a ‘bio-drilling’\neffect of cover crops in compacted soils can result in increased yield\nof follow-on crops (Chen and Weil, 2010; Cresswell and Kirkegaard,\n1995; Kirkegaard et al., 2008). Plant roots engineer soil structure\ndirectly by penetrating and displacing soil, depositing adhesive\ncompounds which encourage aggregation, and indirectly via a\nrange of other root deposits which provide energy and nutrient\nsources for soil biota (White and Kirkegaard, 2010). 1.1. Quarry restorations At the end of the operating life of sand and gravel quarries, the\nresulting voids have to be levelled and graded to achieve landscape\nand landform objectives stated in restoration plans to allow agreed\nupon restoration objectives (CEMEX, 2014; DCLG, 2014). Quarry silt\nlagoons would normally be restored into wetland habitats, or\ncapped with a \u00031 m thick layer of overburden and planted with\nwillow rods (Tarmac Ltd., 2008). However, quarries often face a\nshortage of top-soil and sub-soil forming materials. Moreover, it is a\npriority to use materials available on-site to minimise the high\ntransport costs associated with importing materials (Tarmac Ltd.,\n2008). A possible solution would be the use of non-commercial\nby-product such as quarry silt and overburden as a partial\nreplacement for sub-soil in restorations. The suitability of quarry\nfor use in artificial soils was evaluated by (Mitchell et al., 2004) who\ninvestigated several types of quarry fine blends as a growing me-\ndium for grass species. However biomass was restricted primarily\ndue to nutrient deficiencies. Three restoration cover crops were evaluated in this study. These included white mustard (Sinapis alba) a tap rooted species;\nwinter rye (Secale cereale) as a cereal representative; and a grass-\nland seed mixture (Lolium perenne, Phleum pratense, Poa pratensis,\nFestuca rubra) as a reference crop already used in Tarmac Ltd res-\ntorations. No fertilizers were applied to simulate natural restoration\nprocesses. Each treatment was replicated in triplicate. 1. Introduction crushing and screening of the material to separate sand and gravel\naggregates from fines (<0.063 mm), which consist of silt, clay and\nother non-quartz particles (British Geological Survey, 2013). These\nfines are collected in water, giving rise to a suspension, which is\nthen pumped into lagoons and allowed to settle out (British\nGeological Survey, 2013). The resultant suspension remains in\nsemi-liquid, anaerobic state for many years, or even decades (Jarvis\nand Walton, 2010). This product is then usually referred to as\n‘quarry silt’. Quarry silt, which is generated during sand and gravel pro-\ncessing, is an un-avoidable and significant proportion of quarry\noutputs (Mitchell, 2007). The amount of quarry silt varies between\n5 and 30% of the total volume extracted, averaging around 10e15%\n(Harrison et al., 2001). Mineral processing involves washing, Quarry silt is currently defined as a non-commercial by-product\nas there is currently no market, nevertheless it should be noted that L. Ma\u0001skov\u0003a et al. / Chemosphere 219 (2019) 58e65 59 quarry silt is an inert and non-hazardous material (Mitchell, 2007). Overburden, which is a layer of material lying above the product to\nbe extracted, is also regarded as a non-commercial by-product. The\nneed to minimise the amount of quarry non-commercial by-\nproduct is driven by environmental and social considerations and\nregulatory compliances (Mitchell, 2007). Quarry silt production can\nexceed storage capacity on site and require excavation in order to\nincrease lagoon capacity, which causes both economical and\nlogistical problems to the quarry operators (Mitchell, 2007). Reduction of quarry non-commercial by-product production usu-\nally starts at source, with an optimisation audit of the processing\ntechnology where emphasis is usually placed on good practice and\nmodernization of the crushing plant (Mitchell, 2007). The main use\nof sand and gravel non-commercial by-products is as a backfill or\nsub-soil material in site landscaping and restoration (Harrison et al.,\n2001). Another possible use of quarry non-commercial by-products\naccording to Mitchell (2007) is as vegetated tips around the quarry\nsite to screen the workings. Reusing mineral non-commercial by-\nproducts such a quarry silt contributes to efficient use of resources,\nreduces environmental impacts, and improves sustainability for\nlocal communities (Mitchell et al., 2004). using excavators. Top-soil was sourced from a compacted vegetated\nbund lining Blashford Quarry using trowels. An 8-point 120 kg top-\nsoil (0e0.3 m depth) sample was collected. 2.1. Study area Materials for this study were obtained from two different\nquarries operated by Tarmac Ltd, where there was an excess pro-\nduction of quarry silt and overburden. Blashford Quarry was the\nsource of the quarry silt sub-soil material and top-soil, and\nMountsorrel Quarry provided overburden. Mountsorrel Quarry is a\ngranite quarry located between the villages of Mountsorrel and\nQuorn in Leicestershire. A total of 80 kg of overburden from this site\nwas collected from 10 randomly selected points. Blashford Quarry\nis located in Hampshire, south of Salisbury with an annual quarry\nsilt production of >20,000 m3. A 10 point 210 kg composite quarry\nsilt sample (0e0.3 m depth) was collected from two silt lagoons 2.6. Glasshouse experiment set-up For both pot experiment and laboratory analyses, growing me-\ndiums (top-soil, quarry silt and overburden) were air dried and\nsieved to <2 mm. It should be noted, that in order to minimise\nheterogeneity between experimental replicates, the coarse aggre-\ngate fraction >2 mm, was removed during sample preparation. Post\nair-drying, quarry silt and overburden were ground to <2 mm using\na mechanical sieved soil grinder. EC was determined on 1:5 soil:water extract, based on the\nBritish Standard BS 7755: Section 3.4:1995. SOM content was\nanalysed using the loss on ignition method following British\nStandard BS EN 13039:2000. Soil pH was determined on a 1:5\nsuspension of soil in water, based on the British Standard BS ISO\n10390:2005. PSD was measured using the sieving and sedimentation\nmethod based on the British Standard BS 7755 Section 5.4:1998. Soil\nmineral-N was measured using KCl extract based on MAFF\nReference Book RB427 (1986). Sub-soil medium was mixed to the desired ratios of 100:0, 70:30\nand 50:50 of quarry silt:overburden. To represent the restoration\nlayering ratio, the sub-soil layer was packed to a depth of 12 cm\nfrom the bottom of the pot, leaving the next 5 cm for the top-soil\nlayer. Sub-soil was packed at two bulk densities (BD), representing\nlow and\nhigh\ncompaction. The\nhighest\nBD\nachievable\nwas\n1.5 g cm\u00043, with the lower value set at 1.3 g cm\u00043. All pots were then\ncapped with a 5 cm layer of top-soil (previously acquired from\nBlashford Quarry) at a BD of 1.3 g cm\u00043 to reach a total pot volume\nof 2313 cm3. 2.8. Statistical analyses Results were analysed using the STATISTICA 12.0 software. Soil\nproperties were analysed using factorial analysis of variance\n(ANOVA) to determine the effects of multiple categorical variables,\nnamely bulk density (BD), quarry silt:overburden ratio (sub-soil\nblend T1, T2 and T3) and cover crop (CC) treatment. One-way and\ntwo-way ANOVA were used to analyse single categorical indepen-\ndent values for either BD or sub-soil blend, where significance for\nthe CC was not proved. Significant values were analysed following\npost-hoc Fisher LSD analysis to show differences between mean\nvalues. Normality was checked and significance was set at p \u0006 0.05. Spearman correlation was carried out on key parameters as shown\nin Table 4. Pots were placed in the Cranfield University Glasshouse in a\ncompletely randomised layout and wetted to field capacity from\nthe base via capillary rise. Cover crop seeds (winter rye, white\nmustard and grassland seed mixture) were broadcasted on the 16th\nof June 2017 (adopted from Tarmac Ltd seeding methods). However\ndue to unexpectedly hot weather (~30 \u0005C, seeds had to be incor-\nporated to a depth of <0.5 mm. Uniform pot watering was under-\ntaken approximately every two days, depending on weather\nconditions to assure crop survival. The experiment was terminated\napproximately 6 weeks after set-up. Pot layout was changed twice\nin order to randomize possible variation in growing conditions\nwithin the glasshouse. During the pot trial, mustard plants were\naffected by several insect species including aphids (Lipaphis ery-\nsimi), mustard leaf miner (Chromatomyia horticola) and large white\nbutterfly (Pieris brassicae). The rye and grass mixture treatments\nhad no pest infestation issues. in Table 4. 2.5. Grassland seed mixture A standard seed mixture for quarry restoration adopted by\nTarmac Ltd when restoring back to an agricultural end-use is a\ngrassland seed mixture. It is commonly used in the first 2e3 years\nwithin a mandatory 5-year aftercare period. Seeding is usually\ncarried out during MarcheApril or SeptembereOctober at a rate of\n34 kg ha\u00041 (Walnes Seeds, 2017). Mixtures containing the same or\nsimilar grass species (Table 1) are usually designed as a damage\nresistant paddock mixture for grazing and hay production (Walnes\nSeeds, 2017). RMD ¼ MD\nV\n\u0001\nkg m\u00043\u0003\n(1) RMD ¼ MD\nV\n\u0001\nkg m\u00043\u0003 (1) Prior to packing in pots a 6-point composite sub-sample of top-\nsoil was collected and analysed at the Cranfield University's Envi-\nronmental Analytics Facility, following Standard Operating Pro-\ncedures based on British Standard Methods. At termination, fresh\nsub-soil blends and top-soil samples were collected and analysed\nfor nitrate and ammonium as plant available nitrogen (N) in a\ncommercial external laboratory. Blended treatments T1-T3 and top-\nsoil was air dried, sieved to <2 mm and analysed for electrical\nconductivity (EC), soil organic matter (SOM), pH and particle size\ndistribution (PSD). has a tap rooting architecture and is frost sensitive. has a tap rooting architecture and is frost sensitive. has a tap rooting architecture and is frost sensitive. penetration through the top-soil and sub-soil layers. One quarter of\neach pot was the used to assess root development. Roots were\nextracted following the root washing method of De Baets et al. (2007). To determine the root mass density (RMD), roots had to\nbe oven-dried at 65 \u0005C for 24 h. Dry root mass (MD (kg)) was then\ndivided by the volume of the soil sample (V (m3)) (De Baets et al.,\n2007) to obtain RMD. 2.5. Grassland seed mixture 2.7. Laboratory analyses In accordance with BS 3882:2015 (BSI, 2015), the texture of the\ntop-soil derived from Blashford Quarry used in the pot experiment\nis classified as a silt loam. With a clay content of 17.9%, soil pH of\n5.7e6.7 and OM of 2.97% the top-soil is defined as a low fertility\ntop-soil (BSI, 2015) (Table 2; Table 4). At termination, the soil was carefully extruded intact from the\npots a cut in half using a palette knife to visually asses root Table 1\nTarmac's standard grassland seed mixture. Common name\nVariety\nScientific name\n%\nPerennial ryegrass\nTemprano\n(Lolium perenne L.)\n32\nPerennial ryegrass\nElital\n(Lolium perenne L.)\n29\nTimothy\nAlma\n(Phleum pratense L.)\n7\nSmooth stalk meadow grass\nPanduro\n(Poa pratensis L.)\n29\nCreeping red fescue\nReport strong\n(Festuca rubra L.)\n3 2.4. Mustard Mustard can be sown from March to September (Rosenfeld and\nRayns, 2011). It prefers fertile, loamy, well drained soils and does\nnot tolerate waterlogging and dry sandy soils (Oplinger et al., 1991). Seeding rates for mustard vary from 10 kg ha\u00041 (Bodner et al., 2010)\nup to 20 kg ha\u00041 (Rosenfeld and Rayns, 2011). A commercially\nadopted seeding rate of 20 kg ha\u00041 was used in this study. Mustard\nseedlings emerge rapidly but continue to grow slowly thereafter. It L. Ma\u0001skov\u0003a et al. / Chemosphere 219 (2019) 58e65 60 3.2.1. Available N Cover crops significantly influenced the amount of nitrate in\nboth TS and SS, and available N in TS. Different SS blends only had Fig. 1. Visual assessment of mustard root development (T3 (50:50), BD 1.5). Marked correlations are significant at p < 0.05. Table 4 Spearman correlation coefficients between key variables. RMD (kg m\u00043) is for root\nmass density, OM (%) is organic matter, EC (mS cm\u00041) is electrical conductivity, pH is\nsoil acidity, TS stands for topsoil and SS for subsoil. The most significant dependence was found for the TS:SS ratio\n(Table 6). Highest ratios, which indicate uneven root distribution,\nwere observed on mustard treatments. The lowest values for TS:SS\nratio were obtained on rye. RMD (kg\nm\u00043)\nOM (%)\nEC (mS cm\u00041)\nSoil pH\nTS:SS\nTS\nSS\nTS\nSS\nTS\nSS\nTS\nSS\nRMD TS\nRMD SS\n0.82\nOM TS\n\u00040.02\n0.02\nOM SS\n0.00\n\u00040.07\n0.76\nEC TS\n\u00040.17\n\u00040.18\n\u00040.22\n\u00040.33\nEC SS\n0.16\n0.29\n\u00040.56\n\u00040.78\n\u00040.04\npH TS\n0.29\n0.31\n0.37\n0.19\n\u00040.40\n\u00040.55\npH SS\n\u00040.20\n\u00040.13\n\u00040.19\n\u00040.52\n0.17\n0.25\n\u00040.06\nTS:SS\n\u00040.54\n\u00040.89\n\u00040.17\n0.01\n\u00040.01\n\u00040.25\n\u00040.34\n0.13\nBD\n\u00040.04\n\u00040.10\n0.03\n\u00040.02\n0.27\n0.32\n0.36\n\u00040.03\n0.10\nMarked correlations are significant at p < 0.05. Table 2\nMean (n of significant relationships was the SS blend. Root mass densities\nwere most affected by type of cover crop (CC) (Table 5). The RMD of\nSS was also significantly affected by BD. Further, the TS:SS RMD\nratio was significantly affected by CC type. Table 2\nMean (n ¼ 4) particle size distribution (PSD) of blended sub-soil treatments. Sand - 0.6 mm\n- 0.063 mm (%)\nSilt - 0.063 mm\n- 0.002 mm (%)\nClay <0.002\nmm (%)\nTop-soil\n6.66 (±0.90)\n75.4 (±0.66)\n17.9 (±0.49)\nT1\n5.39 (±0.62)\n33.7 (±0.73)\n61.0 (±0.92)\nT2\n6.26 (±0.95)\n46.5 (±0.93)\n47.3 (±0.98)\nT3\n5.08 (±1.01)\n55.1 (±1.26)\n39.8 (±0.75)\nT1 ¼ Sub-soil blend with 100% silt; T2 ¼ 70% silt and 30% overburden; T3 ¼ 50% silt\nand 50% overburden. Values in parentheses indicated ±1 SE. Table 2\nMean (n ¼ 4) particle size distribution (PSD) of blended sub-soil treatments. Correlation coefficients shown in the Table 4 indicate, that there\nis a high correlation between RMD TS/RMD SS and the TS:SS ratio. Also OM TS/SS correlates with EC SS, OM TS correlates with OM SS\nand pH SS correlates with OM SS. Sub-soil blend (quarry silt:overburden ratio) had a significant\neffect on all of the metrics measured. RMD of SS was significantly\nhigher\nin\nSS\nblend\nT2\n(0.1 kg m\u00043)\nas\ncompared\nwith\nT1\n(0.06 kg m\u00043) and T3 (0.06 kg m\u00043), which had comparable values\n(Table 4). 3.2. Soil-root interaction To quantify the root distribution between substrate layers,\nvalues for RMD were used to create a top-soil:sub-soil (TS:SS) ratio. To quantify the root distribution between substrate layers,\nvalues for RMD were used to create a top-soil:sub-soil (TS:SS) ratio. Low TS:SS values represent a balanced root distribution between\nthe TS and SS, high TS:SS ratio values correspond to few or no roots\nfound within the SS layer, hence root mass being mostly restricted\nto the TS layer. Low TS:SS values represent a balanced root distribution between\nthe TS and SS, high TS:SS ratio values correspond to few or no roots\nfound within the SS layer, hence root mass being mostly restricted\nto the TS layer. y\nSignificant relationships between soil and root properties are\nshown in Table 3. The categorical variable with the largest number Fig. 1. Visual assessment of mustard root development (T3 (50:50), BD 1.5). Table 3 Categorical significant responses for all three variables and their combinations. RMD\n(kg m¡3) is for root mass desity, OM (%) is organic matter, EC (mS cm\u00041) is electrical\nconductivity, pH is soil acidity, TS stands for topsoil and SS for subsoil. Cover crop significantly (p \u0006 0.001) influenced RMD in both the\nTS and SS layers (Table 3). A balanced root distribution (TS:SS) was\nnoted\nfor\nrye\ntreatments,\nfollowed\nby\nthe\ngrassland\nmix. Conversely, a significantly lower TS:SS was observed for the\nmustard cover crop treatments (Table 5). This corresponds with the\nvisual assessment of pots where in most cases, mustard roots did\nnot penetrate into the SS layer (Fig. 4). Bulk density significantly\ninfluenced the RMD of the SS (Table 5). RMD (kg\nm\u00043)\nOM (%)\nEC (mS\ncm\u00041)\nSoil pH\nTS:SS\nTS\nSS\nTS\nSS\nTS\nSS\nTS\nSS\nSub-soil blend\n**\n***\n***\n**\n***\nBD\n***\n*\nCC\n***\n***\n**\n***\n***\nBD*CC\n*\n**\n*\nSub-soil blend*BD*CC\n***\nMean values significant at *p \u0006 0.05, **p \u0006 0.01, ***p \u0006 0.001. The combination of CC and BD variables significantly influenced\nRMD of both TS and SS, which is reflected in the TS:SS (Table 6). Mustard had in general significantly lower RMDs as compared with\nrye and grassland cover crop treatments (Table 6). High BD\n(1.5 g cm\u00043) of the SS was associated with increased RMD of TS in\npots with mustard and rye as compared to the low BD treatments\n(1.3 g cm\u00043). High BD (1.5 g cm\u00043) of the SS in grassland mixture\ntreatments was conversely followed by decrease in RMD of TS. Table 1 In accordance with BS 2601:2013 (BSI, 2013), the texture of the\nT1 (100:0) sub-soil blend corresponds to a clay, while both the T2\n(70:30) and T3 (50:50) sub-soil blends are defined a s a silty clay. T1\nand T3 blends are, with pH values of 5.4e8.5 slightly below re-\nquirements (5.5e8.5) for multipurpose sub-soil (Table 4). The T2\nsub-soil blend with a pH of 7.9e8.0 falls within the calcareous sub-\nsoil category. L. Ma\u0001skov\u0003a et al. / Chemosphere 219 (2019) 58e65 61 Within the same column values followed by the same letter(s) are not significantly different following Factorial ANOVA and post-hoc Fisher LSD analysis. Values in parentheses\nindicated ±1 SE. Table 5 grassland mixture showed only minor signs of nutrient deficiency. At the time of termination of the pot trial, mustard plants were fully\nexhausted (Fig. 2). Fig. 3. Mustard plant showing N deficiency signs e stunned growth and chlorosis on\nolder leaves (27 days after sowing) (left) and possible P deficiency signs e purple\npetioles (35 days after sowing) (right) (Berry, 2006; Kumar and Sharma, 2013). 3.3. Plant response In general, roots avoided the sub-soil layer by growing in the\nspace between the soil and the pot. Mustard roots were almost\nalways unable to penetrate into the sub-soil (Fig. 1). 4.1. Cover crop treatment response an effect on the ammonium content (Table 7). In general, mustard\ntreatments were associated with significantly higher amounts of\navailable N in top-soil as compared to rye and grass mixture\ntreatments. Sub-soil blend T1 had the highest amounts of ammo-\nnium\nas\ncompared\nwith\nT2\nand\nT3\nirrespective\nof\nCC\ntreatment(Table 7). Cover crops are used as a temporary measure to facilitate the\nstabilisation and recover of soils and hydrology post restoration\n(BWSR, 2012). In a restoration context, a soil profile is re-created\nusing materials, which might have been kept under anaerobic\nconditions for years, such as quarry silts. Essential first steps for\neffective rehabilitation of restored soil profiles are improving the\nsoil structure and enhancing hydrological and gaseous connectivity\nbetween soil horizons. Planting a mixture of species can be ad-\nvantageous to ensure soil cover and increase organic matter\nthroughout the profile due to different root systems architectures\n(BWSR, 2012; Cresswell and Kirkegaard, 1995). Cover crops influ-\nence soil properties through the decomposition of crop residues\n(Radicetti et al., 2016). If used correctly, they can enhance soil\nproperties by capturing, fixing and recycling nutrients, increase\nSOM, improve soil structure, enhance soil microbiology, mitigate N-\nleaching and protect soil from erosion (Bodner et al., 2010). Table 5 Table 5\nMean (n ¼ 18) significant root mass densities (RMD, kg m\u00043) and soil physico-chemical characteristics between blended treatments. OM (%) is organic matter, EC (mS cm\u00041) is\nelectrical conductivity, pH is soil acidity, TS stands for topsoil and SS for subsoil. Table 5\nMean (n ¼ 18) significant root mass densities (RMD, kg m\u00043) and soil physico-chemical characteristics between blended treatments. OM (%) is organic matter, EC (mS cm\u00041) is\nelectrical conductivity, pH is soil acidity, TS stands for topsoil and SS for subsoil. RMD e SS (kg m\u00043)\nOM - SS (%)\npH - SS\nEC e TS (mS cm\u00041)\nEC e SS (mS cm\u00041)\nT1\n0.06a (±0.014.5)\n4.37b (±0.31)\n5.7b (±0.16)\n8.86a (±0.84)\n19.1a (±0.96)\nT2\n0.1b (±21.1)\n3.80ab (±0.31)\n8.0a (±0.01)\n10.3ab (±1.27)\n27.8a (±1.65)\nT3\n0.06a (±18.4)\n3.15a (±0.35)\n7.9a (±0.16)\n13.8b (±1.70)\n21.3b (±2.16)\nWithin the same column values followed by the same letter(s) are not significantly different following Factorial ANOVA and post-hoc Fisher LSD analysis. Values in parentheses\nindicated ±1 SE. Mean (n ¼ 18) significant root mass densities (RMD, kg m\u00043) and soil physico-chemical characteristics between blended treatments\nelectrical conductivity, pH is soil acidity, TS stands for topsoil and SS for subsoil. MD, kg m\u00043) and soil physico-chemical characteristics between blended treatments. OM (%) is organic matter, EC (mS cm\u00041) is\nnds for topsoil and SS for subsoil. RMD e SS (kg m\u00043)\nOM - SS (%)\npH - SS\nEC e TS (mS cm\u00041)\nEC e SS (mS cm\u00041)\nT1\n0.06a (±0.014.5)\n4.37b (±0.31)\n5.7b (±0.16)\n8.86a (±0.84)\n19.1a (±0.96)\nT2\n0.1b (±21.1)\n3.80ab (±0.31)\n8.0a (±0.01)\n10.3ab (±1.27)\n27.8a (±1.65)\nT3\n0.06a (±18.4)\n3.15a (±0.35)\n7.9a (±0.16)\n13.8b (±1.70)\n21.3b (±2.16) L. Ma\u0001skov\u0003a et al. / Chemosphere 219 (2019) 58e65 62 Fig. 2. Effects of nutrient deficiency on mustard plants 36 days (left) and 47 days\n(right) after sowing. Fig. 4. Mustard leaf showing possible K-deficiency symptoms (35 days after sowing)\n(Kumar and Sharma, 2013). Fig. 2. Effects of nutrient deficiency on mustard plants 36 days (left) and 47 days\n(right) after sowing. Fig. 3. Mustard plant showing N deficiency signs e stunned growth and chlorosis on\nolder leaves (27 days after sowing) (left) and possible P deficiency signs e purple\npetioles (35 days after sowing) (right) (Berry, 2006; Kumar and Sharma, 2013). Fig. 4. Mustard leaf showing possible K-deficiency symptoms (35 days after sowing)\n(Kumar and Sharma, 2013). Table 7 Another advantage of a rye-legume mixture is that rye holds\nN while improving soil structure and legumes fix N, making some\nof it available for rye (Kammermeyer, 2016). Rye can also be useful\nin restoration projects taking place in the autumn, as late seeding is\nrequired, owing to its ability to germinate at low temperatures and\nproduce sufficient soil cover for the winter (AGRAVIS, 2017; CEMEX,\n2014). root length and root anatomy of 7-day old cereals. Materechera\net al. (1991) grew seedlings of twenty-two plant species for 10\ndays and observed that soil compaction reduced root elongation by\n90% while increasing root diameters. Strongly compacted soils are\nusually only penetrated by roots through cracks and/or pre-existing\nbiopores (Gła̧b, 2008). This may in large part explain the RMD re-\nsults observed for rye treatments in this study. Nevertheless, it is\nimportant to note that in this pot study, rye roots avoided pene-\ntrating the SS mainly by growing through the macro-pore space at\nthe soil-pot interface. Evidence suggest that yields of some grasses\nmight be unaffected by compaction (Gła̧b, 2013, 2008). Vallance\nand Sonogan (1995) stated that fibrous roots of rye grow espe-\ncially well in the first 30 cm of soil, however, Chen and Weil (2010)\nclaim that rye roots are strongly affected by soil compaction. Scholefield and Hall (1985) claim that the ability of grasses to\npenetrate highly compacted soils by becoming constricted can be\nconsidered as a compensation of radial pressure. Growing rye may\nhowever be considered in mixtures with other grass species, or\nlegumes. According to Clark (2007), a rye-legume mixture is able to\nadjust to different N levels, meaning that in soils rich on N, rye\ntends to grow better while in soils poor on N, the legume grows\nbetter. Another advantage of a rye-legume mixture is that rye holds\nN while improving soil structure and legumes fix N, making some\nof it available for rye (Kammermeyer, 2016). Rye can also be useful\nin restoration projects taking place in the autumn, as late seeding is\nrequired, owing to its ability to germinate at low temperatures and\nproduce sufficient soil cover for the winter (AGRAVIS, 2017; CEMEX,\n2014). Adaptation for local environmental conditions and suitability\nfor the specific agro-ecological target are however essential\n(Bodner et al., 2010). Materechera et al. Table 7 (1991) have observed, that\nroots of larger diameters such as taproots of dicotyledonous plants\npenetrated soil more than those with smaller diameters. Perkons\net al. (2014) also found, that tap-root plant species create larger\nbiopores thus allow subsequent crop roots to penetrate to deeper\nsoil layers. Yu et al. (2016) claim, that especially for annual plants,\nroot thickness is very important for improving soil structure. Nonetheless, Cresswell and Kirkegaard (1995) suggest that tap\nrooted annual crops are unlikely to improve porosity of deeper,\ncompacted soil horizons. At the higher BD (1.5 g cm\u00043) of SS blends, RMD of rye in the TS\nincreased, with a corresponding decrease in RMD in the SS. This\ncould be explained by the inability of rye to penetrate into the\ncompacted SS, hence the root mass remained limited to the TS\nlayer. Root growth rate is minimally affected by BDs below\n1.4 g cm\u00043, however, values above together with the absence of pre-\nexisting biopores considerably decreases root elongation rate\n(Gaiser et al., 2013). Contrary to this, the TS:SS ratio of rye was\nsignificantly lower (low TS:SS ratio represents even root distribu-\ntion throughout the pot) as compared with mustard, which can be\nexplained by a proportion of the rye roots growing in the space\nbetween the pot and the soil, distorting the RMD ratio. 3.4. Nutrient deficiency Signs of N-deficiency were assessed by visual analysis against\nimages in Berry (2006), visible on mustard plants three weeks after\nsowing (Fig. 3). Four weeks into the experiment all mustard plants\nexhibited significant visible signs of N as well as potential phos-\nphorus (P) and potassium (K) deficiencies (Berry, 2006; Kumar and\nSharma, 2013), (Fig. 4). At four weeks, rye also started displaying N\nnutrient deficiency symptoms through yellowing leaf tips, the Cover crops encourage soil aggregation indirectly via root de-\nposits which provide energy and nutrient sources for soil biota\n(White and Kirkegaard, 2010). These biota improve the architecture\nof the soil by mechanisms including adhesion, kinetic restructuring\nand filamentous binding (Miransari, 2014). Herrera et al. (2017) also L. Ma\u0001skov\u0003a et al. / Chemosphere 219 (2019) 58e65 63 Table 6\nEffect of cover crop treatment and subsoil blend bulk density (BD) on topsoil (TS) and subsoil (SS) root mass densities (RMDs) and topsoil:subsoil ratio (TS:SS ratio). COVER CROP\nBD (g cm\u00043)\nRMD e TS (kg m\u00043)\nRMD e SS (kg m\u00043)\nTS:SS\nGrassland\nBD 1.3\n0.76bc (±121)\n0.08c (±10.7)\n10.5a (±1.76)\nGrassland\nBD 1.5\n0.56b (±70.3)\n0.04b (±5.55)\n18.5ab (±5.43)\nMustard\nBD 1.3\n0.17a (±22.7)\n0.01a (±1.05)\n45.9c (±9.00)\nMustard\nBD 1.5\n0.21a (±30.8)\n0.01ab (±5.51)\n29.8b (±5.55)\nRye\nBD 1.3\n0.86c (±82.9)\n0.19e (±24.6)\n5.24a (±1.57)\nRye\nBD 1.5\n1.13d (±169)\n0.14d (±14.3)\n8.94a (±1.90)\nWithin the same column values followed by the same letter(s) are not significantly different following Factorial ANOVA and post-hoc Fisher LSD analysis. Values in parentheses\nindicated ±1 SE. Table 6\nEffect of cover crop treatment and subsoil blend bulk density (BD) on topsoil (TS) and subsoil (SS) root mass densities (RMDs) and topsoil:subsoil ratio (TS:SS ratio). COVER CROP\nBD (g cm\u00043)\nRMD e TS (kg m\u00043)\nRMD e SS (kg m\u00043)\nTS:SS\nGrassland\nBD 1.3\n0.76bc (±121)\n0.08c (±10.7)\n10.5a (±1.76)\nGrassland\nBD 1.5\n0.56b (±70.3)\n0.04b (±5.55)\n18.5ab (±5.43)\nMustard\nBD 1.3\n0.17a (±22.7)\n0.01a (±1.05)\n45.9c (±9.00)\nMustard\nBD 1.5\n0.21a (±30.8)\n0.01ab (±5.51)\n29.8b (±5.55)\nRye\nBD 1.3\n0.86c (±82.9)\n0.19e (±24.6)\n5.24a (±1.57)\nRye\nBD 1.5\n1.13d (±169)\n0.14d (±14.3)\n8.94a (±1.90)\nWithin the same column values followed by the same letter(s) are not significantly different following Factorial ANOVA and post-hoc Fisher LSD analysis. Values in parentheses\nindicated ±1 SE. Table 7\nSoil N values, significantly dependent (p \u0006 0.05) on CC and sub-soil blends. Table 7 a The amount of soil N as kg ha\u00041 has been estimated assuming the standard Tarmac TS depth of 0.3 m for soil N profiling; Within the same column values followed by the\nsame letter(s) are not significantly different (p \u0006 0.05) following Factorial ANOVA and post-hoc Fisher LSD analysis. Values in parentheses indicated ±1 SE. a The amount of soil N as kg ha\u00041 has been estimated assuming the standard Tarmac TS depth of 0.3 m for soil N profiling; W\nsame letter(s) are not significantly different (p \u0006 0.05) following Factorial ANOVA and post-hoc Fisher LSD analysis. Values in observed that the choice of CC influences the C and N input into the\nsoil via root decomposition dynamics and variable root biomass\nproduction. Brennan and Acosta-Martinez (2017), observed that\nfrequent cover cropping can have more significant beneficial im-\npacts on soil microbiology than using compost. root length and root anatomy of 7-day old cereals. Materechera\net al. (1991) grew seedlings of twenty-two plant species for 10\ndays and observed that soil compaction reduced root elongation by\n90% while increasing root diameters. Strongly compacted soils are\nusually only penetrated by roots through cracks and/or pre-existing\nbiopores (Gła̧b, 2008). This may in large part explain the RMD re-\nsults observed for rye treatments in this study. Nevertheless, it is\nimportant to note that in this pot study, rye roots avoided pene-\ntrating the SS mainly by growing through the macro-pore space at\nthe soil-pot interface. Evidence suggest that yields of some grasses\nmight be unaffected by compaction (Gła̧b, 2013, 2008). Vallance\nand Sonogan (1995) stated that fibrous roots of rye grow espe-\ncially well in the first 30 cm of soil, however, Chen and Weil (2010)\nclaim that rye roots are strongly affected by soil compaction. Scholefield and Hall (1985) claim that the ability of grasses to\npenetrate highly compacted soils by becoming constricted can be\nconsidered as a compensation of radial pressure. Growing rye may\nhowever be considered in mixtures with other grass species, or\nlegumes. According to Clark (2007), a rye-legume mixture is able to\nadjust to different N levels, meaning that in soils rich on N, rye\ntends to grow better while in soils poor on N, the legume grows\nbetter. 3.4. Nutrient deficiency CC\nNitrate N (þ) (mg kg\u00041)\nAvailable N (þ) 30 cm profilea (kg N ha\u00041)\nSub-soil blend\nAmmonium (þ) (mg kg\u00041)\nTS\nSS\nTS\nSS\nGrassland\n0.58a (±0.50)\n0.19a (±0.00)\n5.22a (±1.82)\nT1\n0.90b (±0.05)\nRye\n1.56a (±0.35)\n0.07a (±0.10)\n8.12a (±1.44)\nT2\n0.50a (±0.15)\nMustard\n5.85b (±0.11)\n0.62b (±0.08)\n24.5b (±0.44)\nT3\n0.51a (±0.07)\na The amount of soil N as kg ha\u00041 has been estimated assuming the standard Tarmac TS depth of 0.3 m for soil N profiling; Within the same column values followed by the\nsame letter(s) are not significantly different (p \u0006 0.05) following Factorial ANOVA and post-hoc Fisher LSD analysis. Values in parentheses indicated ±1 SE. Table 6 Table 7\nSoil N values, significantly dependent (p \u0006 0.05) on CC and sub-soil blends. CC\nNitrate N (þ) (mg kg\u00041)\nAvailable N (þ) 30 cm profilea (kg N ha\u00041)\nSub-soil blend\nAmmonium (þ) (mg kg\u00041)\nTS\nSS\nTS\nSS\nGrassland\n0.58a (±0.50)\n0.19a (±0.00)\n5.22a (±1.82)\nT1\n0.90b (±0.05)\nRye\n1.56a (±0.35)\n0.07a (±0.10)\n8.12a (±1.44)\nT2\n0.50a (±0.15)\nMustard\n5.85b (±0.11)\n0.62b (±0.08)\n24.5b (±0.44)\nT3\n0.51a (±0.07)\na The amount of soil N as kg ha\u00041 has been estimated assuming the standard Tarmac TS depth of 0.3 m for soil N profiling; Within the same column values followed by the\nsame letter(s) are not significantly different (p \u0006 0.05) following Factorial ANOVA and post-hoc Fisher LSD analysis. Values in parentheses indicated ±1 SE. 5. Conclusions EC values for the T1-T3 treatments varied between 9 and\n28 mS cm\u00041, which is classified as non-saline and is typical for\nnormal surface soils (Hazelton and Murphy, 2007). To accelerate\nthe process of silt-water separation within silt lagoons, some\nquarries choose to use anionic flocculants such as iron (Fe) and\naluminium (Al) salts to accelerate water and silt separation. This\ncould influence EC values of quarry silt as well as be one of possible\ncauses of highly restricted mustard root development. Testing silt\nfor flocculants or other potentially phytotoxic elements is therefore\nrecommended. Across all cover crop types, the best preforming sub-soil blend\nwas the T2 (70:30) treatment in terms of significantly higher RMD\nin the sub-soil. Mustard with tap roots performed poorly in com-\nparison to the rye and grassland mix treatments which are asso-\nciate\nwith\ndense\nfine\nroots. Therefore,\nmustard\ncannot\nbe\nrecommended as a suitable cover crop for restoration projects\nwhere quarry silt is used in a blended sub-soil medium. Both the\ngrassland mixture and winter rye had significantly better perfor-\nmance, as compared to mustard with a different root type. It can be\nsuggested that improving top-soil/sub-soil connectivity could be\nachieved if rye and grasses were grown together in a mix, or in\nconjunction with legume species to facilitate successful biological\nand hydrological connectivity in restored soils. The results indicate\nthat quarry silt can be used for this purpose, nevertheless, due to its\nhigh clay content, blending quarry silt with overburden, or PAS 100\norganic compost is highly advisable. Soil pH may be used as an indicator for suitability for specific\ngrass or crop species (Hazelton and Murphy, 2007). Baize (1993)\nsuggests that optimum pH should be between 6.5 and 7.5. As\nsub-soil blends T2 and T3 resulted in a pH typical for alkaline soils\n(7.9 and 8.0, respectively), this should be approached with caution. Soil pH above 7 reduces bioavailability of trace metals such as Cu,\nZn and Ni, (Han, 2007). Nevertheless, according to Hazelton and\nMurphy (2007), pH values of the T1-T3 SS blends and TS used in\nthis study should not affect availability of N, P, K, S, Ca, or Mg as they\nwere always >5.0 and < 8.5, with the exception of availability of Fe\nbeing reduced in pH < 7.5, which applies for both T2 and T3. Acknowledgements The authors would like to express their gratitude and thanks to\nTarmac Ltd., for providing the funding and study materials. 4.3. Nutrient deficiency associated with experimental treatments N, P and K, also known as primary nutrients, are essential\nmacronutrients promoting growth, energy storage and higher\nplants cell wall strength (Kumar and Sharma, 2013). In restored\nsoils blended with quarry non-commercial by-product, a lack of\nnutrients should be expected (Mitchell et al., 2004). N-deficiency\nwas visible on mustard plants as early as 3 weeks into growth. The\nlack of N was noticeable through retarded growth and leaf symp-\ntoms. These symptoms were first observed in older leaves owing to\ntranslocation of N through the plant to younger tissues, leaving\nlower leaves yellow chlorotic and in later stages necrotic (Kumar\nand Sharma, 2013). This nutrient deficiency was aggravated by\nbuds being visible at week four. Typically in mustards, buds are\nusually visible after 5 weeks and flowers appear 7e10 days later\n(Oplinger et al., 1991). Early flowering of mustard results in short\nlived preservation of accumulated N, as stated by Herrera and\nLiedgens\n(2009). According\nto\nRosenfeld\nand\nRayns\n(2011),\nmustard will start to flower once its canopy reaches 0.5e0.7 m of\nheight and continues to grow even after that, exceeding 1 m. In this\nstudy, the average height of mustard plants in bloom was only\n0.38 m as a result of stunted growth induced by lack of essential\nnutrients. According to (Kumar and Sharma, 2013), lack of N is\nlikely to occur in waterlogged conditions, and soils with pH < 6.0 or\npH > 8.0. Most plants absorb N as ammonium (NH4þ) or nitrate\n(NO3\u0004), which is also soluble in water and therefore easily leachable\n(Hosier and Bradley, 1999). Laboratory results showed that pots\ntreated with mustard had significantly higher NO3\u0004 concentrations\nin both TS and SS as compared with other CC treatments. This\nsuggests that mustard is not effective in scavenging nutrients due\nto its root structure lacking fine roots. Phosphorus P deficiencies on\nmustard plants were also visible across all blended treatments as\npurple petioles, dwarfed plants (P promotes root development) and\nmarginal and interveinal chlorosis (Berry, 2006; Kumar and\nSharma, 2013). 4.2. Growing media characteristics Soil compaction does not only increase BD, resulting in greater\nmass per volume, it also changes soil properties, such as water\nretention, hydraulic conductivity, nutrient transport and uptake, N\nmineralization, soil gases movement etc. (Guaman et al., 2016;\nLipiec et al., 2003; Miransari et al., 2009; Wolkowski and Lowery,\n2008). Most importantly, soil compaction may alter root penetra-\ntion between restored soil layers, or even limit root growth to the\nTS only, thereby considerably reducing water and nutrient avail-\nability to plants, resulting in plant growth reduction (Lipiec et al.,\n2003; Miransari et al., 2009; Pabin et al., 2003; Wolkowski and\nLowery, 2008). According to results of the PSD, quarry silt contains a large\nproportion of clay sized particles. Clays tend to be chemically and\nphysically active, which means that their ability to hold water and\nnutrients is increased (Hazelton and Murphy, 2007). High clay\ncontent however increases susceptibility to compaction (Frost,\n1988). Critical BDs, which are likely to severely affect plant growth and\nroot penetration, are different for different soil textures. For clay\nloam and clay soils, the critical values are >1.6 and > 1.4 g cm\u00043\n(Hazelton and Murphy, 2007). This may in large part explain the\nobservation that for blends T1, T2 and T3, the higher SS BD Lipiec et al. (2012) observed that soil compaction (Soil pene-\ntration resistance exceeding 2 MPa at field capacity) directly affects L. Ma\u0001skov\u0003a et al. / Chemosphere 219 (2019) 58e65 64 significantly reduced RMD of rye. significantly reduced RMD of rye. used as sub-soil media. Results from the research project ‘Minerals\nfrom Waste’ suggest that quarry non-commercial by-products can\nbe successfully used; especially if mixed with a green waste\ncompost in order to prevent any possible nutrient depletion and\nimprove the initial soil structure (Mitchell et al., 2004). Quarry silt from Blashford Quarry contained not only fine par-\nticles, but also a coarse fraction of cobbles and boulders (>63 mm),\nwhich is not uncommon for a quarry silt (Harrison et al., 2001). Under field conditions, this may positively influence root penetra-\ntion by creating macro pores and voids within the substrate. References AGRAVIS, 2017. Winter Rye (Secale Cereale) [WWW Document]. URL. https://www. agravis.de/en/pflanzen/saatgut/getreide/winterroggen/index.html\n(accessed\n7.14.18). i\n1993 S il S i\nA\nl\nG id\nC\nil\nS Baize, D., 1993. Soil Science Analyses - a Guide to Current Use. Wiley, Surrey. Berry, W., 2006. Symptoms of deficiency in essential minerals. 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(2019) Assessment of silt from sand and gravel\nprocessing as a suitable sub-soil material in land restoration: A glasshouse study.\nChemosphere, Volume 219, March 2019, pp. 58-65\nhttps://doi.org/10.1016/j.chemosphere.2018.11.155\nDownloaded from CERES Research Repository, Cranfield University Cranfield University\nCERES Research Repository Cranfield University\nCERES Research Repository https://dspace.lib.cranfield.ac.uk/ School of Water, Energy and Environment (SWEE) Staff publications (SWEE) Mašková L, Simmons RW, De Baets S, et al. (2019) Assessment of silt from sand and gravel\nprocessing as a suitable sub-soil material in land restoration: A glasshouse study.\nChemosphere, Volume 219, March 2019, pp. 58-65\nhttps://doi.org/10.1016/j.chemosphere.2018.11.155\nDownloaded from CERES Research Repository, Cranfield University References Review of modelling crop growth, movement\nof water and chemicals in relation to topsoil and subsoil compaction. 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(2019) Assessment of silt from sand and gravel\nprocessing as a suitable sub-soil material in land restoration: A glasshouse study. Chemosphere, Volume 219, March 2019, pp. 58-65\nhttps://doi.org/10.1016/j.chemosphere.2018.11.155\nDownloaded from CERES Research Repository, Cranfield University"