The cost of soil degradation in England and Wales

Appendix I: Cost of organic matter loss

Introduction Soil organic carbon levels in soils depend on the relative rates of organic carbon inputs from net primary production and organic matter decomposition. Thus there is a direct relationship between organic carbon change and the threat of organic matter decline. The lower extent of the range of organic carbon contents in agricultural soil in England and Wales is bounded by clay content 1 and there is a less distinct upper boundary controlled by texture and mean annual precipitation 2. Bellamy et al (2005)3 reported an overall decline in the level of soil organic carbon in soil in England and Wales, based on repeated sampling of the National Soil Inventory (NSI). Other studies4 have not been able to corroborate this finding and there has been no repeated sampling. Nonetheless, based on similar reports for other regions (e.g. Belgium), it is more likely than not that there is an overall decline in soil organic carbon in England and Wales. Importantly, Bellamy et al (2005) 5 reported that rates of loss of soil organic carbon varied between land use types. Specifically, losses in arable soils were found to be limited, while much higher rates were reported for humose grassland soils. It is likely that the lower rates for arable soils reflects their long past cultivation, so that levels have fallen well towards the lower boundary controlled by their clay content. The rates of loss reported by Bellamy et al (2005)6 for different land use categories are likely to be the best available data on which to base an economic valuation of soil organic carbon loss due to soil organic matter decline. In theory, peat should not be treated similarly to the other groups mineral and organo-mineral soils, since a decline in soil organic matter content cannot be interpreted to provide an accurate estimate of soil organic carbon change. This is due to loss of bulk volume being the dominant factor driving loss rather than a concentration reduction.

Losses of soil organic carbon also occur due to water and wind erosion. In both cases, however, the eroded soil may be substantially deposited back to soil surfaces so there is only a re-distribution of soil organic carbon and no loss from the soil environmental compartment to others, such as surface waters and eventual transport to the ocean. Information appears to be unavailable on the extent of re- distribution of soil organic carbon by water and wind erosion relative to that of actual loss from soil. Therefore although an estimate might be made of the quantity of soil organic carbon contained in eroded soil, it would be misleading to assume that this quantity is actually lost to soil resources.

There is no well-organised information about the changes in soil organic matter stocks that accompany transfer of land in to the built environment. Destruction and degradation of soil by excavation may cause a loss of soil organic carbon, but the overall change may be to a higher total level rather than decrease. Firstly, when soil is sealed at its surface and disconnected from the atmosphere and the hydrological cycle, the processes of soil organic matter decomposition are slowed especially if the soil remains wet. Consequently, losses of soil organic carbon do not necessarily follow transfer in to the built environment. Secondly, excavated soil is often re-distributed

1 Loveland, P., and J. Webb. (2003). Is there a critical level of organic matter in the agricultural soils of temperate regions: a review. Soil & Tillage Research 70: 1–18

2 Verheijen, F.G.A., P.H. Bellamy, M.G. Kibblewhite and J.L. Gaunt (2005). Organic carbon ranges in arable soils of England and Wales. Soil Use and Management. Volume 21, Issue 1, pages 2–9, March 2005

3 Bellamy, P.H. & Loveland, P.J. & Bradley, R.I. & Lark, M.R. & Kirk, G.J.D. (2005) "Carbon losses from all soils across England and Wales 1978-2003." , Nature, vol. 437, page 245-248

4 Countryside Survey (2010). Soils Report from 2007. www.countrysidesurvey.org.uk

5 Bellamy, P.H. & Loveland, P.J. & Bradley, R.I. & Lark, M.R. & Kirk, G.J.D. (2005) "Carbon losses from all soils across England and Wales 1978-2003." , Nature, vol. 437, page 245-248

6 Bellamy, P.H. & Loveland, P.J. & Bradley, R.I. & Lark, M.R. & Kirk, G.J.D. (2005) "Carbon losses from all soils across England and Wales 1978-2003." , Nature, vol. 437, page 245-248

Draft report Page 1 Cranfield University The cost of soil degradation in England and Wales on site or moved to another site to augment its soil resources, so there is no loss and only a redistribution of soil organic carbon. Thirdly, where the creation of a built environment is accompanied by permanent planting of ornamental crops, turf areas and trees, the primary productivity per unit area may be similar or even higher than for the previous agricultural use. For these reasons it is not possible to assess with confidence whether soil sealing is a cause of soil organic carbon loss.

Soil organic carbon is both a product and a substrate for the soil biota. Intuitively, it appears likely that a loss of soil biodiversity should affect soil organic carbon levels. Counter intuitively, they may increase if the input from net primary production is not affected, due to an absence of some communities and disruption of food chains. However, current knowledge appears inadequate to inform a reliable assessment of the actual influence of changes in soil biodiversity on soil organic carbon levels.

The effects of soil organic matter decline on soil properties Maintenance of soil physical structure is important to soil health7. The creation and preservation of pores of varying size and with connectivity provides a network that modulates the soil atmosphere and water regimes and within which the biota live. Especially the maintenance of this network and its resilience to physical degradation by compaction and tillage is supported by soil organic matter which binds and ties mineral particles to each other. Various studies have explored relationships between soil organic matter levels and soil physical properties leading to an accepted conclusion that these are positively affected by soil organic matter. In addition to better bulk mechanical properties, soils with higher organic matter generally have a higher water holding capacity. Less certain, however, is how these benefits translate quantitatively to improved delivery of goods and services.

The economic costs and benefits associated with altered soil organic matter levels

The most important impacts of soil organic matter losses appear to be linked to provisioning and regulating services.

Provisioning services Food production: Defra project SPO3108 and KeySoils9 have reported on studies of gross margin improvements that may be achievable through management to optimise soil organic matter levels in agricultural soils. Net benefits in the order of between £30 to £100 per hectare per year were estimated, derived from a variety of benefits including improved nutrient cycling and improved soil structure, after 2 to 5 years of application. The benefits arise from lower costs of substitution for soil processes that are degraded by a decline in soil organic matter, namely: nutrient additions for nutrient cycling and tillage for soil structure maintenance. A further non-quantified benefit could be less prevalence of soil-borne diseases leading to lower pesticide requirements and costs.

Timber and biomass: Organic matter additions are sometimes made to support establishment of perennial biomass and timber crops on land restored following mining and other industrial activities. However, these additions are probably rare on agricultural or forested land. Furthermore, once established, substantial increases in below-ground organic carbon are expected from a higher root mass.

Water supply: Reduced soil organic matter and peat in soils across a catchment are expected to decrease its holding capacity and increase the potential need for reservoirs to sustain supplies during drought periods. Such changes are likely to be catchment specific and it appears that no generic data is available for quantitative assessment in relation to mineral and organo-mineral soils.

7 Kibblewhite, M.G., Ritz, K. and Swift R.S. (2008) Soil health in agricultural systems Phil. Trans. R. Soc Lond B Biol Sci 363 685-701

8 Defra project SP0310. To develop a robust indicator of soil organic matter status

9 KeySoils: http://www.keysoil.com/

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Regulating services

Climate Change (GWP): Bellamy et al. (2005)10 provide the best estimated of losses of soil organic carbon from soils in England and Wales. For mineral and organo-mineral soils, a reasonable approximation would be that all these losses are to the atmosphere. Therefore the rates of loss reported by Bellamy et al (2005)11 could be used to estimate mass emissions. However, more investigation of the literature is needed to assess the emissions from peat soils.

Water Quality: Degradation of organic soils and peats leads to increased levels of dissolved organic matter in raw water supplies necessitating additional treatment prior to supply and higher costs. The proportion of organic carbon lost from soils and peats via dissolution / suspension is probably rather less than one tenth of the amount lost to the atmosphere as carbon dioxide. Nonetheless this represents a very large quantity of organic matter and treatment costs are also substantial.

Estimating the cost of soil degradation The annual loss of organic matter from the soils in England and Wales was estimated using data from the NSI database described and developed by Bellamy et al. (2005) 12. The measurements span two periods of time, a first set of measurements between 1978 and 1983 and a subset of about 40% of the same sites that were measured between 12 and 25 years later. Between 1994 and 1995, 853 of the original 2,578 sites on arable land and rotational grassland were sampled; between 1995 and 1996, 771 of the original 1,579 sites in permanent grassland areas were resampled, and in 2003, 555 of the original 1505 sites in bogs, rough grazing, woodland and other non-agricultural sites were resampled.

Bellamy et al. (2005)13 then calculated the rates of change in the soil sample, assuming that change between the two time periods was linear. A regression model was fitted to the resulting data and used to express the rate of change in terms of the original C content of the soil (Organic Cchange = 0.6 –

0.0187 x Organic Coriginal) where both Organic Cchange and Organic Coriginal were in units of: g of C per kg soil per yr. This was then used to predict the rate of change in C for sites where no second sampled had been taken. These data were then combined with the original data to provide a national rate of change (g C kg-1 soil yr-1) for different total soil organic carbon contents (Table 1).

Table 1 Estimated cost of soil compaction in England and Wales – all soilscapes

Topsoil C content (0-15cm) Rate of change in topsoil C content (0-15cm) (g kg-1 soil C) (g C kg-1 soil yr-1) >0, <=20 0.34 >20, <=30 0.13 >30, <=50 -0.10 >50, <=100 -0.68 >100, <=200 -2.18 >200, <=300 -4.00 >300 -7.37

As noted in Appendix D, these NSI topsoil data were intersected with the spatial landuse/soil type dataset and the mean total carbon content of the soils calculated for each of the land use/soil type

10 Bellamy, P.H. & Loveland, P.J. & Bradley, R.I. & Lark, M.R. & Kirk, G.J.D. (2005) "Carbon losses from all soils across England and Wales 1978-2003." , Nature, vol. 437, page 245-248

11 Bellamy, P.H. & Loveland, P.J. & Bradley, R.I. & Lark, M.R. & Kirk, G.J.D. (2005) "Carbon losses from all soils across England and Wales 1978-2003." , Nature, vol. 437, page 245-248

12 Bellamy, P.H. & Loveland, P.J. & Bradley, R.I. & Lark, M.R. & Kirk, G.J.D. (2005) "Carbon losses from all soils across England and Wales 1978-2003." , Nature, vol. 437, page 245-248

13 Bellamy, P.H. & Loveland, P.J. & Bradley, R.I. & Lark, M.R. & Kirk, G.J.D. (2005) "Carbon losses from all soils across England and Wales 1978-2003." , Nature, vol. 437, page 245-248

Draft report Page 3 Cranfield University The cost of soil degradation in England and Wales categories. The mean rate of change (Table 2) was then calculated for each of the land use/soil type categories using the relationship between topsoil C content (g kg -1 soil C) and the rate of change (g C kg-1 soil yr-1) data provided in Bellamy et al14 (Table 1). This on the whole showed that C loss was greater on a per weight basis in peat soils.

The quantity of soil in the top 15 centimetres (the depth measured in the samples) of the soil profile was then calculated using the bulk densities developed for each land use/soil type category in Appendix C (Table 3). This was then used to quantify the rate of change per hectare in the top 15 cm of each landuse/soil type category (Table 4). This was multiplied by the unsealed area of each land use/soil type category to derive the total soil organic C lost (Table 5), after subtracting the portion of C that is removed from the parent soil due to enrichment of eroded material (Appendix H). Using this approach, the total C lost from the soil each year in England and Wales is 5.3 Mt yr -1 most of it from peats and clays. This is rather more than the 4.4Mt yr-1 reported by Bellamy et al. (2005)15 and may be due either to the simplification of the landscape into different landuse/soil type categories, the different bulk density relationship used here (see Appendix D), or the need, as suggested above, to estimate loss of SOM from peat differently from mineral and organo-mineral soils.

Table 2. The estimated mean loss of organic matter (g C kg-1 soil yr-1) in each land use/soil type category Predicted change in Organic Carbon (g C/ kg soil) Soilscapes Land use Clay Silt Sand Peat Urban -0.10 -0.10 -0.10 -2.18 Horticulture -0.10 -0.10 0.13 -2.18 Arable intensive -0.10 -0.10 0.13 -2.18 Arable extensive -0.10 -0.10 -0.10 -2.18 Grassland improved -0.10 -0.10 -0.10 -2.18 Grassland unimproved -0.68 -0.10 -0.68 -4.00 Rough grassland -0.68 -0.68 -0.68 -2.18 Forestry -0.68 -0.10 -0.68 -2.18 Woodland -0.10 -0.10 -0.10 -2.18 Wildscape -0.68 -0.68 -0.68 -4.00

Table 3. The estimated quantify of soil (t) in each hectare for each land use/soil type category

Soil per hectare (t) in top 15 cm Soilscapes Land use Clay Silt Sand Peat Urban 1395 1530 1446 644 Horticulture 1561 1462 1730 512 Arable intensive 1502 1411 1706 575 Arable extensive 1552 1518 1637 707 Grassland improved 1335 1493 1363 801 Grassland unimproved 1101 1349 1023 494 Rough grassland 1138 1269 1234 644 Forestry 1072 1405 1266 534 Woodland 1361 1518 1363 703 Wildscape 904 1297 864 441

Table 4. The estimated loss of C (kg C t-1 soil) per hectare for each land use/soil type category

Estimated C change per hectare (kg C/t soil) in top 15 cm Soilscapes Land use Clay Silt Sand Peat

14 Bellamy, P.H. & Loveland, P.J. & Bradley, R.I. & Lark, M.R. & Kirk, G.J.D. (2005) "Carbon losses from all soils across England and Wales 1978-2003." , Nature, vol. 437, page 245-248

15 Bellamy, P.H. & Loveland, P.J. & Bradley, R.I. & Lark, M.R. & Kirk, G.J.D. (2005) "Carbon losses from all soils across England and Wales 1978-2003." , Nature, vol. 437, page 245-248

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Urban -0.14 -0.15 -0.14 -1.40 Horticulture -0.16 -0.15 0.22 -1.12 Arable intensive -0.15 -0.14 0.22 -1.25 Arable extensive -0.16 -0.15 -0.16 -1.54 Grassland improved -0.13 -0.15 -0.14 -1.75 Grassland unimproved -0.75 -0.13 -0.70 -1.97 Rough grassland -0.77 -0.86 -0.84 -1.40 Forestry -0.73 -0.14 -0.86 -1.16 Woodland -0.14 -0.15 -0.14 -1.53 Wildscape -0.62 -0.88 -0.59 -1.76

Table 5. The estimated loss of C (t) in each landuse/soil type across England and Wales

Total rate of soil C change (t) per hectare in top 15 cm of soil layer Soilscapes Land use Clay Silt Sand Peat Urban -78,721 -15,663 -36,961 -24,810 Horticulture -3,859 -1,238 3,652 -1,067 Arable intensive -24,723 -3,905 27,667 -7,719 Arable extensive -412,501 -69,932 -118,498 -66,916 Grassland improved -305,990 -66,792 -76,286 -222,846 Grassland unimproved -548,272 -16,490 -145,496 -1,044,539 Rough grassland -268,200 -63,449 -135,300 -120,560 Forestry -109,299 -4,238 -86,692 -145,129 Woodland -92,609 -24,070 -32,204 -82,073 Wildscape -85,107 -31,611 -48,363 -670,075 Results The loss of soil C has both on-site implications and off-site implications for global warming.

Soil organic matter, for which soil organic C is a proxy, is critical for good soil structure. From this, there are numerous benefits, such as improved workability of the soil, crop germination, water holding capacity, resistance to compaction, increased crop productivity have been reported 16. Using typical assumed application rates of 40 t ha-1 FYM applications, the annual net benefit from a range of case studies was assessed and use to derived a per tonne soil C (£ t C yr-1) (Table 6). The annual cost of the loss of organic matter as a soil amendment in the soil, as measured by loss of soil organic C, was calculated to be £3.5 million per year.

Table 6. The estimated impact of soil C loss (£) in each landuse/soil type across England and Wales Total cost of fertiliser value of C stock loss (t) in top cm Soilscapes Land use Clay Silt Sand Peat Urban -52,481 -10,442 -24,641 -16,540 Horticulture -2,573 -826 2,435 -712 Arable intensive -16,482 -2,603 18,445 -5,146 Arable extensive -275,001 -46,621 -78,999 -44,610 Grassland improved -203,993 -44,528 -50,858 -148,564 Grassland unimproved -365,515 -10,994 -96,997 -696,360 Rough grassland -178,800 -42,299 -90,200 -80,374 Forestry -72,866 -2,825 -57,795 -96,752 Woodland -61,740 -16,047 -21,469 -54,715 Wildscape -56,738 -21,074 -32,242 -446,717 -1,286,188 -198,259 -432,321 -1,590,489

The off-site cost in terms of GHG emission was much more significant. Whilst the ratio of soil C to CO2 in the atmosphere is 1 to 3.67, assuming all the soil organic matter degrades, here a degradation

16 KeySoils: http://www.keysoil.com/

Draft report Page 5 Cranfield University The cost of soil degradation in England and Wales co-efficient of 80% of the cellulose and hemi-cellulose and 30% for lignins was assumed as suggested by Abad et al (2002)17 and personal communication (Dr A. Williams, Cranfield University). The rest it was assumed would move to deeper soil layers or into water bodies. Using these degradation co-efficients, a ratio of 1 to 2.11 for soil C to CO2 was used as a general coefficient to represent the loss of soil organic C to the atmosphere. The cost of this loss of C, assuming a CO 2 value of £51 t CO2 was then estimated to be £566 million, mostly associated with clay and peat soils (Table 8).

Table 7. The estimated impact on CO2 emissions to the atmosphere (t CO2) in each landuse/soil type across England and Wales

Total E&W CO2 (t) emitted to the atmosphere from the top 15 cm Soilscapes Land use Clay Silt Sand Peat Urban -166,102 -33,050 -77,987 -52,349 Horticulture -8,143 -2,613 7,706 -2,252 Arable intensive -52,165 -8,239 58,378 -16,286 Arable extensive -870,377 -147,557 -250,032 -141,192 Grassland improved -645,639 -140,931 -160,964 -470,204 Grassland unimproved -1,156,854 -34,795 -306,996 -2,203,978 Rough grassland -565,902 -133,878 -285,483 -254,382 Forestry -230,621 -8,942 -182,920 -306,222 Woodland -195,406 -50,788 -67,950 -173,174 Wildscape -179,575 -66,699 -102,046 -1,413,859 -4,070,784 -627,490 -1,368,295 -5,033,899

Table 8. The estimated impact on CO2 emissions to the atmosphere (£) in each landuse/soil type across England and Wales

Total cost of C stock loss (t) in top 15 cm Soilscapes Land use Clay Silt Sand Peat Urban -8,471,197 -1,685,533 -3,977,347 -2,669,822 Horticulture -415,274 -133,255 392,991 -114,870 Arable intensive -2,660,434 -420,165 2,977,270 -830,592 Arable extensive -44,389,228 -7,525,397 -12,751,615 -7,200,784 Grassland improved -32,927,569 -7,187,477 -8,209,172 -23,980,417 Grassland unimproved -58,999,575 -1,774,529 -15,656,809 -112,402,894 Rough grassland -28,861,006 -6,827,756 -14,559,653 -12,973,489 Forestry -11,761,665 -456,051 -9,328,935 -15,617,301 Woodland -9,965,686 -2,590,211 -3,465,443 -8,831,889 Wildscape -9,158,336 -3,401,641 -5,204,345 -72,106,795 -207,609,969 -32,002,015 -69,783,057 -256,728,853

The cost of GHG emissions induced by changes in soil organic content are very high in comparison with other degradation effects. It is noted that all the parameters in the estimate are liable to large estimation errors, namely: rates of loss, bulk density, the fate of emissions, and the unit price of carbon (measured here at the cost of GHG abatement). For this reason the estimate needs to be treated cautiously.

Table 9. The estimated cost of loss of soil organic C in England and Wales

17 Abad, M, Patricia Noguera, Rosa Puchades, Angel Maquieira and Vicente Noguera (2002). Physico-chemical and chemical properties of some coconut coir dusts for use as a peat substitute for containerised ornamental plants. Bioresource Technology, Volume 82, Issue 3 Pages 241-245

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Physical data Soil C loss (t yr-1) 5,260,886 On-site costs £,000 Total E&W C loss cost due to erosion (£) - 3,507

Off-site costs £,000 GHG cost of soil C loss (£) - 566,124

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