Soil erosion, soil conservation and agricultural policy for arable land in the U.K.

co16-718Y89 $3.00 + 0.00 @ 1989 Pergamon Press plc

Geoforum, Vol. 20, No. 1, pp. ES92.1989 Printed m Great Britain

Soil Erosion, Soil Conservation and Agricultural Policy for Arable Land in the U.K.

D. A. ROBINSON*

and J. D. BLACKMAN,*

Brighton,

U.K.

Abstract: Reported occurrences of the erosion of arable land in the U.K. have increased in recent years. Erosion is concentrated in areas of sandy and silty textured soils with a low clay content. Much of the increased erosion has been by water rather than by wind, and has been associated with an extension in the area of arable cultivation and the intensification of production. In many areas, current rates of erosion are greater than rates of soil formation, and soil degradation is widespread. Runoff and erosion from arable land is also causing an increased incidence of flooding and nuisance to householders and local councils. Despite the widespread occurrence of erosion, there is no national soil conservation policy and no soil conservation service. However, large agricultural surpluses within the European Community are currently leading to changes in agricultural policy, with an increasing emphasis on environmental protection and conservation rather than agricultural output. These new policies are primarily directed towards biological conservation and safeguarding water quality, not the conservation of the soil, but resulting changes in land-use may lead to a reduction in erosion rates and improved.conservation of soil resources.

Introduction

this

is the

agricultural Erosion of arable land may be caused either by wind or rain. In the U.K., soil erosion has traditionally been accepted as a rare and minor hazard to farming (DAVIES et al., 1982; HUDSON, 1967; RODDA, 1970). Wind erosion was a localised problem in a few areas, but erosion by rainfall was considered negligible. However, in the past decade, there have been an increasing number of reports of erosion of farmland by water from many areas of the U.K. (REED, 1979; MORGAN, 1980,1986b; SPEIRS and FROST, 1987; FULLEN, 1985b; EVANS and COOK, 1986, 1987). In part, the increasing number of reports may be due to a greater awareness of soil erosion, but there are also good reasons for believing that the incidence of erosion has actually increased, and that

* Geography Laboratory, Brighton BN19QN, U.K.

University

of Sussex,

result

of changes

that

have occurred

in

practice.

The Soil Erosion Hazard

Erosion by wind Causes of wind erosion. In the Fens of eastern England, SNEESBY (1968) suggests that a free wind speed gusting to at least 10 m/s is required to initiate wind erosion. MORGAN (1985a) identifies a similar value of 9 m/s (measured at 10 m above the ground surface) as the minimum wind speed required to cause soil erosion throughout England and Wales, and says that all regions experience wind speeds greater than this threshold at least once every year. In a study of erosion in the Vale of York, WILSON and COOKE (1980) calculated 0.3 m/s as the threshold wind speed at the ground surface required to initiate erosion. No map of the erosion potential of wind over

Falmer,

83

84 the U.K. exists, but the greatest incidence of high wind speeds at low elevation occurs around southern and western coastal areas. However, these areas also receive the most frequent rainfall, which reduces the risks of wind erosion where arable cultivation occurs. Water increases the weight of soil particles and helps to bond them together. As a result, wind erosion is mostly confined to dry soils, although wet soils can occasionally be dried suf~ciently by a wind for erosion of the topsoil to be initiated. The soil surface must also contain soil particles sufficiently small and light to be entrained by the wind. Sand size particles are the largest that can be moved by the wind. The availability of transportable material depends on the parent material from which the soil has developed, the extent to which the soil particles are aggregated or disaggregated, and the presence or absence of a vegetation cover. Coarse textured, cloddy and well-aggregated soils are resistant to wind erosion; disaggregated, sand and silt-rich soils are highly erodible. Sand and coarse silt size material is transported close to the ground surface by creep and saltation. The wind speeds required to initiate these processes are greater than those required to sustain them, because impact by moving soil particles initiates the movement of further particles, creating an avalanche effect (DAVIES and HARROD, 1970). Fine silt and organic material are lifted from the soil surface to become suspended in the wind and create localised dust storms, or ‘blows’ (SPENCE, 1957). Geographical distribution. The Soil Survey of England and Wales estimates that about 7700 km2 of soils in lowland England and Wales have properties that make them potentially susceptible to wind erosion (SOIL SURVEY OF ENGLAND AND WALES, 1983). This is approximately 5% of the total land area and 14% of the total arable iand. Occurrences of wind erosion in England and Wales are concentrated in periods of exceptionally dry windy weather, and in areas of fine sandy, silty or peaty soils in the east of the country, notably the very flat regions of the Fens and the Vale of York (SNEESBY, 1953, 1968; SPENCE, 1955,1957; RADLEY and SIMMS, 1967; POLLARD and MILLAR, 1968; ROBINSON, 1969; WILKINSON et al., 1969; WILSON and COOKE, 1980). Wind erosion has also been reported from the drier parts of eastern Scotland with similar soils (PIDGEON and RAGG, 1979). Elsewhere, the damp oceanic climate. hilly terrain, hedged field boundaries and the predominance of pasture over arable cultivation limit the severity and incidence of

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erosion by wind. Nevertheless, localised blows do occur, especially during seed bed preparation in areas of sandy soils such as those developed on the New Red Sandstones (Permo-Triassic) of the West Midlands (FULLEN, 1985a) where, in some areas, up to 33% of soils may be affected [REED, 1979). Land drainage, hedgerow removal and the cultivation of crops such as carrots, sugar beet and leeks, which require fine tilth seedbeds and provide poor ground cover for much of the spring and early summer, are recognised as factors that increase the risk of wind erosion from susceptible areas. Erosion is almost entirely limited to fields with dry, friable surfaces in the period from March to June. During this period, many of the most vulnerable soils may suffer erosion sufficient to moderately or severely damage young crops one year in every two (EVANS and COOK. 1986). Measurement of wind erosion losses. There are very few data on soil loss by wind erosion, most reports consisting of descriptions of erosive events with 110 estimates of amoL~nts of soil eroded (BULLOCK, 1987). WILSON and COOK (1980) give details of losses of between 21 and 44 t/ha during a storm lasting 7-8 hr in the Vale of York. FULLEN (1985a) estimated that a 6-ha field of coarse loamy sand in the West Midlands lost 6-10 t/ha during a single storm in 1983 and calculated that the transporting power of the wind during erosive events varied from 0.27 tim’lhr to a maximum of 6.46 tim’lhr during gusts.

Erosion by water Causes of water erosion. Britain experiences a cool, temperate, western margin climate characterised by predominantly low-intensity, rainfall frequent, events. This led people to assume that erosion by water was a minor hazard to farming, because they believed most rainfall had insufficient energy to detach soil particles and fell at intensities too low to generate erosive runoff (KOHNKE and BERTRAND, 1959; HUDSON, 1967, 1971; DAVIES etaf., 1982). Thus, for example, HUDSON (1967) estimated that only 5% of British rainfall was erosive, because the remainder fell at intensities of less than 25 mmihr, which he believed to be the minimum intensity that possessed sufficient kinetic energy to cause erosion. However, it has since become apparent that erosion can be induced by much lower rainfall intensities. MORGAN (1980), suggested that, in a British context, rainfall intensities greater than 10 mm/hr are erosive, whilst REED

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(1979) has shown that intensities as low as 1 mm/hr can cause erosion of crusted and compacted agricultural soils, provided the rain persists for long enough to supply 10 mm or more of total rainfall. Similarly EVANS (1980a) noted that, if soils are saturated by antecedent rainfall, further lowmagnitude rainfatl may be sufficient to cause runoff and erosion. During the cool wet winters experienced in the British Isles, many soils remain at or close to field capacity for several months (ROBINSON and BOARDMAN, 1988) and are capable of absorbing very little heavy rainfall during this period. The likeIihood of runoff is accentuated if the infiltration capacity is reduced by surface crusting or capping. The reported occurrences of severe erosion are, however, usually associated with particularly intense storms and exceptionally heavy rainfall. Unfortunately, most observations post-date the erosive event, and it is often impossible to say whether it was rainfall intensity, rainfall volume, or a combination of the two, that triggered the erosion (BROWNE and ROBINSON, 1985). Rainfall intensities at an eroded site often have to be estimated from, or assumed similar to, those recorded by an autographic raingauge, or gauges up to 15 or 20 km away. There are also very few autographic rainfall stations with records for 20 years or more, which makes it difficult to assess the return periods of erosive rainfalls and therefore the likely recurrence interval of erosion risk (FULLEN, 1985b; BOARDMAN and ROBINSON, 198.5). Most erosion in areas of arable cultivation is recorded during the autumn, winter and earIy spring, although there are also records of erosive events occurring in late spring and early summer from fields of late sown market garden crops and sugar beet (FULLEN, 1985b). Erosion is concentrated on areas of bare or nearly bare soil, smooth seed beds being particularly vulnerable. Under traditional farming practices the majority of the land was sown in the spring and erosion was most prevelant at this time. However, over the past two decades autumn sowing, particularly of cereals, has greatly increased and this has led to increases in the incidence of erosion during the autumn and winter (EVANS and SKINNER, 1987; SPEIRS and FROST, 1987). Intrinsic properties of soils play a major part in determining erosion risk. Sandy and silty textured soils are most at risk because they lack the cohesive properties of finer textured soils and thus particles can be detached from the soil surface more easily.

85 They also tend to form less stable soil aggregates, leading to a flatter micro-relief and a tendency for the surface aggregates to disintegrate and form an impermeable crust, which decreases the infiltration capacity of the soil and increases runoff. EVANS (1980b) assessed the particle size distribution of known erodible soils in lowland England and found that they were characterised by their restricted clay content, with 87.5% containing between 9 and 35% clay. It has been estimated that erodible soils cover about one-third of Great Britain (MORGAN, 1980), but not all of these soils suffer from erosion, Soil organic matter content appears to be crucial in maintaining the aggregate stability of many of the soils. GREENLAND et al. (1975) suggested that a minimum of 2% organic carbon is required to give adequate structural stability to soils with a restricted clay content. When used repeatedly for arable cropping, the organic content of a soil decreases to a low level, especially when crop residues are removed or burnt. Soils which suffer erosion frequently have organic carbon contents at or below 2% (EVANS and NORTCLIFF, 1978; COLBORNE and STAINES, 1985; FULLEN, 1985b), but erosion has also been recorded on silt-rich soils with organic carbon contents above this threshold (BOARDMAN and ROBINSON, 1985). SPEIRS and FROST (1987) have questioned the importance of organic matter arguing that the low organic matter content of many eroded soils may be the result of erosion rather than the cause (FROST and SPEIRS, 1984), and that the recent increases in erosion have been far greater than can be explained solely by a lowering of soil organic content. Changes in land management practice appear to have accentuated the incidence of soil erosion in recent years. The increase in autumn sowing of cereals has been identified as a major factor (BOARDMAN and ROBINSON, 1985; ROBINSON and BOARDMAN, 1988). Autumn-sown cereals, especially late sown wheat, grow relatively slowly, and this exposes smooth soil surfaces with little or no vegetation cover to the heavy rainfalls of the autumn and winter, which is often the wettest period of the year. In addition to the increase in autumn sowing, other factors include the removal of field boundaries, especially hedgerows, to increase field sizes, increased compaction by heavier farm machinery, increased use of powered cultivation equipment which breaks the soils into a very smooth, fine “fluffy” tilth (SPEIRS and FROST, 1987), and across the contour, rather than

86 along the contour, cultivation of land. On sloping the removal of hedgerows frequently ground, increases slope length, thereby increasing the potential volume, depth and velocity of any runoff that may occur, and thus the likelihood of erosion. The increased power of machinery has enabled ever steeper land to be cultivated, and much of this steeply sloping land can only be safely worked across the contour. On parts of the South Downs, for example, slopes in excess of 20” are now used to grow winter cereals. Compaction along wheelings on such slopes greatly decreases the infiltration capacity of the soil and the wheelings frequently act as foci for rill development (REED, 1983,1986a; ROBINSON and WILLIAMS, 1987). In the West Midlands, FULLEN (1985~) has shown that infiltration along compacted wheelings can be as little as 0.04% of infiltration beneath grassland and 0.4% of the infiltration on crusted but uncompacted bare ground on the same soils. MARTIN (1979) has shown that one pass of a tractor increases soil loss from a wheeling by a factor of 15 times, and that additional passes further increase runoff and soil loss, but at a declining rate. Because of this, the use of ‘tramlines’, that is wheelings left bare of any crop cover along which tractors can pass as the crop grows, are a particular problem, especially where the tramlines run up and down the slope. Geographical distribution. In recent years, reports of soil erosion by water have been frequent and widespread. In England, for example, erosion has been reported from Bedfordshire (MORGAN, 1977; JACKSON, 1986), Derbyshire (BOARDMAN and SPIVEY, Kent (BOARDMAN and 1988)) HAZELDEN, 1986), Norfolk (EVANS and NORTCLIFF, 1978), Shropshire (REED, 1979. 1986b), Somerset (COLBORNE and STAINES. 1985), Surrey (BOARDMAN, 1983a), East Sussex (BOARDMAN and ROBINSON, 198.5; ROBINSON and WILLIAMS, 1987), West Sussex (BOARDMAN, 1983b), and Yorkshire (FOSTER, 1978); and in Scotland from Angus (SPEIRS and FROST, 1985; WATSON, 1985, 1986; DUCK and McMANUS 1987), East Lothian, Central Borders and Berwickshire (SPEIRS and FROST, 1985), Roxburghshire (FROST and SPEIRS, 1984) and Kincardineshire (WATSON, 1985,1986). Of the 296 Soil Associations in England and Wales identified by the SOIL SURVEY OF ENGLAND AND WALES (1983), 29 are considered to be susceptible to erosion by water (excluding upland peat soils that are of no value for arable cultivation). Some 14,200 km2 of these erodible soils are under arable

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cultivation (MORGAN, 1985a), comprising a little over 25% of the total area of arable land. EVANS and COOK (1986) have identified eroded fields on 153 of the 296 Soil Associations, indicating that potentially erodible soils are probably much more widespread than the Soil Survey suggest. However, only a small proportion of the land at risk erodes in any one year. The erosion is mostly confined to areas sloping at more than 3” (EVANS and COOK, 1986). The incision and development of rills and gullies tends to be particularly common where steep-slope convexities lie below broad, low-angled slope crests (EVANS and NORTCLIFF, 1978; JACKSON, 1986). Water collects on the crestal area and becomes erosive as it runs down the steeper slope below. Rill and gully erosion is also common along normally dry valley bottoms where water running off the slopes above becomes concentrated and erosive (BOARDMAN and ROBINSON, 1985; EVANS and COOK, 1986). Measurement of water erosion losses. There are few data on long-term rates of erosion from arable land in the U.K. Most reports of erosion concentrate on the development of rills and gullies because they are the most obviously visible results of erosion and are the features most easily mapped in the field and from air photographs. As a result, records of erosion rates mostly relate to extreme erosion events and are derived from estimates of soil losses obtained by measuring rill volumes or sediment accumulations after the erosion has occurred. It is thus the larger and more spectacular erosive events that are usually recorded whilst smaller, less obviously visible, but probably more widespread erosion receives little attention. The work of Morgan and co-workers (MORGAN, 1986a) suggests that up to 80% of erosion may occur by overland flow from inter-rill locations, and thus estimates derived from measuring rill volumes are probably a gross underestimate of the total amount of erosion that occurs during their development. Field scale erosion losses during short-period erosive events have reached 250 m3/ha on the South Downs of south-east England (ROBINSON and WILLIAMS, 1987), 150 m3/ha in East Anglia (EVANS and NORTCLIFF, 1978), 100 m’lha in the West Midlands (REED, 1979) and 66 m3/ha in Scotland (FROST and SPEIRS, 1984). Gullies formed during erosive storms have reached 4 m in depth in north-east England (MORRIS, 1942), 2 m

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in East Anglia and on the South Downs (EVANS and NORTCLIFF, 1978; ROBINSON and WILLIAMS, 1987), 1.7 m in Scotland (DUCK and McMANUS, 1987) and 1.5 m in the West Midlands (REED, 1979). Longer-term measurements of erosion have been carried out by MORGAN (1977) and FULLEN and REED (1986,1987). Morgan monitored erosion rates from variable sized plots laid out on an area of sloping sandy soils in mid-Bedfordshire during the period 1973-1975. Soil losses from bare soils reached 12.6 m3/ha/year, which were reduced to 1.7 m3/ha/ year under a grass cover, and 0.014 m3/ha/year under woodland. Most of the erosion was caused by runoff generated by infrequent heavy rainfall events, and very little erosion occurred during the far more prevelant low-intensity rainfall events. Fullen and Reed monitored erosion from 10 25-m’ plots, on slopes varying from 7 to 15”, in east Shropshire. The soils were slightly to moderately stony, loamy sands, and all plots were cultivated and maintained in a bare condition. Prolonged-duration low-intensity rainfall caused little erosion and most erosion occurred during brief summer convective storms with intensities >lO mm/hr. Erosion increased with slope angle, and was particularly pronounced on slopes > 13”. In 1982 the Soil Survey of England and Wales and the Ministry of Agriculture, Fisheries and Food (MAFF) set up a joint 5-year project designed to monitor erosion at 17 localities with a known high erosion risk. Monitoring commenced in the 1982-1983 farming year, and comprised an annual air photographic survey of each of the localities, with field verification and measurement of any erosion identified. The full results of the 5-year monitoring programme are not yet available, but interim reports (EVANS and COOK, 1986; SKINNER, 1986; EVANS and SKINNER, 1987) appear to confirm that silty and sandy soils have the highest erosion risk and clay soils the least. However, erosion rates for each soil type are very variable, especially those for the more easily eroded soils. Land management, and the chance coincidence of heavy storms occurring over bare soils appear to be the two most important factors that determine the pattern of erosion from year to year within the areas of erodible soils. Thus, for example, both the highest and lowest rates of erosion (42.5 and 0.4 m3/ha, respectively) monitored in 1982-1983 occurred on the light sandy loams of the West Midlands (EVANS and COOK, 1986). A national survey of soil erosion has also been initiated by the Soil Association. This organisation

promotes organic farming methods and has taken soil erosion as a cause ctkbre. In association with the Political Ecology Research Group, the Soil Association produced a review of soil erosion in Britain (HODGES and ARDEN-CLARKE, 1986) which concluded that soil erosion in Britain was increasing, that this was largely due to agricultural intensification, and that the adoption of organic farming methods would largely remove the problem. However, they recognise that existing reports of erosion are rather haphazard and possibly give a misleading picture of the distribution and severity of erosion in Britain. They have therefore launched a ‘Soilwatch’ campaign, asking their members to record and inform the Association of any erosion they observe. From this it is hoped that a clearer picture of the extent of the soil erosion problem in Britain may emerge. With around 4000 members spread throughout the country, the survey may provide a far more comprehensive coverage than has been obtained to date, although there will be problems resulting from nonspecialists providing data.

Implications

of Erosion

It can be argued that erosion is only serious if it results in a net loss of soil material and a reduction in soil fertility. Rates of soil formation in Britain are low, of the order of 0.025-0.1 mm/year, which is approximately equivalent to 0.3-1.3 t/ha/year (EVANS, 1985b). 1980; FULLEN, 1981; KIRKBY, MORGAN (1985b) suggests that the rate may be as low as 0.1 t/ha/year. Many of the measured rates of soil erosion from arable land are of a magnitude greater than this, and soil degradation is clearly occurring in such areas. The most frequently quoted threshold for the level of soil loss that should be considered acceptable from arable land is 2 t/ha/year (MORGAN, 1980), but several workers have suggested that the threshold of tolerable erosion should be much lower than this because rates of soil formation are less, and limiting soil losses even to 2 t/ha/year would still mean that farmers were managing a diminishing resource (STOCKING, 1978; FULLEN, 1985b). However it must be recognised that nearly all estimates of erosion rates are from individual fields, and that not all of the eroded soil is actually ‘lost’. Much of the soil is simply redistributed within the fields. In the case of wind erosion, this tends to occur along windbreaks, field boundaries and in ditches. With water erosion, soil is often deposited on gentle

88 footslopes (BOARDMAN, 1983; BOARDMAN and ROBINSON, 1985)) against field boundaries (SPEIRS and FROST, 1987)) or on flood plains lower down river valleys. Unfortunately, soil is usually lost from topographic locations where soil is already thin and is redeposited in zones where soils are thick. The thinning of soils has been shown to reduce crop growth and yield, especially where soils are well drained and overlie porous parent materials (EVANS and NORTCLIFF, 1978; EVANS, 1981; FROST and SPEIRS, 1984). Soil loss by wind erosion is very selective: it is the smaller, lighter particles that are lost. Organic matter is particularly susceptible to erosion and may form an aerosol which can be transported very long distances. FULLEN (1985a) has shown that this organic component may be extremely nutrient-rich, leading to a disproportionate decrease in fertility for the volume of soil lost. Similarly with water erosion, a substantial amount of fertiliser may be lost in runoff water, resulting in pollution and eutrophication of watercourses (SPEIRS and FROST, 1987). In recent years, the off-farm consequences of erosion have been a cause of increasing concern (BOARDMAN, 1988). Much of the increased runoff from arable land, along with soil and other debris eroded from fields, flows off the farmland onto adjacent highways, and sometimes results in localised flooding (BOARDMAN and STAMMERS, 1984). This is a particular problem on the South Downs where roads and housing on the urban periphery occupy the dry valley floors, whilst the steep valleyside slopes and interfluves have remained as farmland. Flooding of houses in the valley bottoms by soil-laden water flowing off arable farmland above has become a regular event during periods of high rainfall over the past 15 years. In the worst incidence, more than 60 houses in Rottingdean, a suburb of Brighton, were flooded by mud-laden water up to a depth of 1 m on 7 October 1987 (ROBINSON and WILLIAMS, 1987). The flood was generated by runoff from 120 ha of recently sown winter cereals in a small headwater valley from which more than 5000 m3 of soil was eroded. Estimates of the off-farm costs to householders vary between f250,OOO and fl ,OOO,OOO(FUNNELL and BLACKMAN, 1987). It also cost the local authority several tens of thousand pounds to clear roads and establish temporary flood protection works. Elsewhere, off-farm flooding has been reported at Lewes, East Sussex, in 1982 (BOARDMAN and

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ROBINSON, 1985), Ashford-in-the-Water and Ednaston, West Derbyshire, in 1983 (BOARDMAN and SPIVEY, 1988)) and in Kent, Somerset, parts of the Midlands, East Anglia and eastern Scotland (EVANS and SKINNER, 1987). Occurrences of minor flooding are widespread, and the overall cost to local authorities is thought to be considerable, although no figures are available. The flooding of households is causing considerable conflict between urban residents and farmers in a number of localities. Some householders have begun to examine the possibility of recovering the costs of flood damage through the courts. on the basis that a farmer should be considered criminally negligent if he fails to take precautionary measures to protect local property and inhabitants from the consequences of any erosion and flooding that may result from his farming practice.

Soil Conservation

and Agricultural

Policy

There is no soil conservation service in the U.K. and post-war agricultural policy has concentrated on encouraging farmers to maximise yields from their land. Advice on how to increase crop yields and farm profits by improved management, cropping practice and cultivation techniques has been available for free from the government-sponsored Agricultural Development and Advisory Service (ADAS). However, because increased rates of soil loss rarely have an immediate effect on farm yields, the possibility that the changes in land-use and farming practice recommended by ADAS might lead to accelerated rates of erosion was largely overlooked. Concern first arose over the loss of top-quality soil by wind erosion from areas such as the East Anglian Fens. In these areas, many measures designed to reduce the risk of wind erosion were introduced by farmers from an early date, and further work on the effectiveness of various conservation measures was carried out on ADAS Experimental Husbandry Farms from the 1950s onwards. Conservation measures used include shelterbelts, guard crops and strip cropping, mulching and straw planting, soil stabilizers, the use of rough seed beds, and land imprinting or pressing (HODGE and SEALE, 1966; DAVIES and HARROD, 1970; MORGAN, 1985b). Up to the mid 197Os, a government grant of 25% was available for the removal of hedges and, because of this, the enlargement of fields was widespread. Today, however, local authorities help in the provision of trees and saplings for hedge replanting. The development of specific gramicides in the late 1970s

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has led to the widespread use of barley as a cover crop on fields destined for crops, such as sugar beet, that present a high risk of erosion. The widespread occurrence of accelerated erosion by water from farmland in England and Wales, and the need for the introduction of soil conservation measures, were first highlighted by EVANS (1971), but neither MAFF nor ADAS accepted that there was a serious erosion problem at that date. The first brief advisory leaflet for farmers on soil erosion by water was published by ADAS in 1984 (MAFF, 1984), and this can be taken as the first official recognition that there was cause for concern about erosion rates. As part of the survey of water erosion carried out jointly by MAFF and the Soil Survey (EVANS and COOK, 1986; SKINNER, 1986), farmers with eroded fields were asked whether they considered erosion a problem, and what precautions, if any, they took to minimise erosion from their land. Sixty per cent of the farmers considered erosion to be a negligible or minor problem, 17% considered it a moderate problem and 23% a major problem. However, in Nottinghamshire, where erosion was most severe, 55% of farmers considered erosion to be a major problem. Fifty-five per cent of all farmers also said they took precautions to reduce the risk of erosion. The remainder either considered erosion to be a negligible problem, or considered there was little they could do to reduce its occurrence. Methods used by farmers to reduce erosion included sowing crops early, cultivating along the contours, leaving coarse seedbeds, subsoiling and installing drains to improve soil permeability, organic manuring to improve soil structure, and the reduction of effective downslope length by ditching, hedge planting, grass stripping, or the placing of straw-bales along the contours at downslope intervals. Surprisingly, the growing of winter cereals in place of spring cereals was also quoted as a method of reducing erosion. This is contrary to the results of most recent research work on erosion by water (BOARDMAN and ROBINSON, 1985; COLBORNE and STAINES, 1985, 1986; EVANS and SKINNER, 1986; SPEIRS and FROST, 1987), but would reduce the risk of erosion by wind in the spring. In the 198Os, the post-war agricultural policy of maximising yields in order to maintain a reasonable level of self-sufficiency in basic foodstuffs has been overtaken by a problem of food surpluses within the European Community (EC). This is leading to

89 changes in policy and governmental recognition that intensive farming can have adverse environmental consequences, including unacceptably high rates of erosion. Some of the more vulnerable areas have been designated Environmentally Sensitive Areas (ESAs) and financial inducements are being offered to farmers in these areas to adopt less intensive and more environmentally acceptable methods of production. However, the main thrust of this policy has been towards the conservation of biologically vulnerable environments, such as wetlands, rather than the conservation of soil in areas of high erosion risk. Of the nine areas in the U.K. initially designated as ESAs under the provisions of the Agriculture Act of 1986, only one, the eastern South Downs, covered an area in which erosion was known to be a serious problem. Even here, the impetus for its inclusion as an ESA was a concern over the loss of the rich flora and fauna of traditional chalk downland turf, much of which has been improved or converted to arable cultivation in recent years, and the loss of valuable sites of high archaeological or landscape value, rather than a concern over increased rates of soil erosion. Within an ESA, farmers can receive payment for converting arable land to pasture. Payment is at a set rate, and is intended to compensate the farmer for the reduction in profit that will ensue from not using the land for intensive arable cropping. If some of the land converted under this policy is land with a high erosion risk, then the policy will help to conserve the soil. It has yet to be seen whether this policy will be a success, and doubts have been expressed as to whether the size of the compensatory payments are sufficient. Nevertheless, in the first year of the scheme, farmers within the South Downs ESA signed agreements to convert some 570 ha of arable land to grass (ALLEN, 1988) and in the second year a considerable increase is expected (ALLEN, personal communication), thereby reversing, for the first time in 40 years, the trend to extend the area of arable land. The scheme is currently being expanded, with eight further areas being designated as ESAs, including an extension of the South Downs ESA to cover the whole of the South Downs, not just the area lying to the east of the River Adur. Other areas prone to erosion that have now been given ESA status include the Suffolk Breckland and the Shropshire Borders. In a further attempt to reduce agricultural surpluses within the EC, an extensification scheme for arable crops is being introduced in Britain and other member countries of the Community from 1988 onwards (EC Regulation 1760/87). Extensification is defined as “a

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90 reduction in a farmer’s output of a surplus product by at least 20% without other surplus production capacity being increased” (MAFF, 1987). The aims of the scheme include freeing some land from intensive agricultural production, and fostering a changed pattern of land-use in the countryside so as to improve and enhance landscape and environment. This is to be achieved by offering farmers financial inducements to reduce their arable acreages by at least 20%. Arable land taken out of production (i.e. ‘set-aside’), may be left as vegetated fallow, planted with trees, or used for permitted non-agricultural purposes such as farm-based industry, farm shops, accommodation, tourist and educational facilities; or the provision of livery and the hire of horses and ponies (MAFF, 1988). At the moment there is no way of knowing how many farmers will enter the scheme. As with ESA agreements, farmers will enter on a voluntary basis, but the scheme will be available to all farmers throughout the U.K., not just to those in designated areas, although farmers in less-favoured areas will receive lower payments than those elsewhere. Farmers receiving payments will have to remain within the scheme for at least 5 years. It is likely that many farmers may choose to set-aside some of their more marginal land, some of which may suffer from high rates of erosion. All the set-aside land will not have to be individual fields, but some could be strips of land, provided they are at least 15 m wide. Thus farmers could use the scheme to reduce the erosion hazard associated with arable cultivation by establishing grass strips on steep slopes or grassing areas particularly prone to erosion, such as some dry valley floors for example. However, the scheme is not being officially recommended for use as a soil conservation measure in this way, although advice is available on how to prevent erosion on set-aside land (MAFF, 1988). Thus any reduction in the erosion hazard that accompanies extensification of arable cultivation in the U.K. will be a chance by-product of the set-aside policy rather than a deliberate use of the policy to achieve soil conservation. An alternative way for a farmer to reduce yields would be to switch from intensive, high-input farming to organic farming. The possibility of using the money within the Extensification Scheme to encourage farmers to change to organic production methods was recognised by MAFF (1987), but has not been implemented (MAFF, 1988). Such a switch could be expected to reduce yields by more than 20% without requiring land to be taken out of production. This

20 Number 111989

would undoubtedly lessen the risk of erosion from areas of arable land by increasing the organic content and thereby the structural strength and erosion resistance of the soil (GREENLAND et al., 1975).

Conclusion

Erosion of arable land in the U.K. is both widespread and increasing. Over a third of the arable land is liable to erode and it is estimated that 16% of the land in England and Wales is vulnerable to erosion even when it is farmed in accordance with its recommended land-use capability (MORGAN, 1985a). Within the areas susceptible to erosion, topography and detailed soil characteristics make some fields more likely than others to suffer erosion, but which of the many fields susceptible to erosion erode in any particular year depends upon which are in a vulnerable state of ground preparation and crop growth when erosive wind or rainfall events occur. Annual variation in the frequency and intensity of erosive climatic events results in the severity of erosion and the distribution of eroded fields varying from year to year within the areas susceptible to erosion. Climatic variability over the U.K. also results in regional variation in the distribution of erosion from year to year. Erosion rates recorded from many areas are far greater than rates of soil formation and, as a result, degradation of the soil resources of the U.K. is widespread. Only recently has the erosion hazard posed by the intensification and expansion of arable cropping in the U.K. received any official recognition. Problems posed by wind erosion were the first to be recognised (MAFF, 1970), and in areas such as the East Anglian Fens, that are very susceptible to wind erosion, the adoption of conservation measures are widespread. However, erosion still occurs, and soil loss is unacceptably high. Widespread reports and expressions of concern over erosion by water have been more recent. Some official recognition of the problem has now occurred, but, even in the areas where erosion is occurring, less than a quarter of farmers believe that water erosion is a serious hazard. Despite this, over 50% of farmers in these areas take some precautions to lower the risks of erosion from their land. There is no soil conservation service and no coherent national conservation policy in the U.K. Decisions regarding cultivation practice, land-use, and soil conservation are left to the discretion of individual farmers. Farmers now have to pay for advice on farm management from the government advisory service

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(ADAS) or from other advisors, and this may or may not include assessment of erosion risks and soil conservation. However, food surpluses with the EC are creating a change in policy from intensification to ‘extensification’ of agricultural production. This could be an opportunity for much of the land with high erosion risk to be taken out of production, or for it to be managed in a manner which would decrease the likelihood of erosion occurring. This is not currently being proposed. The emphasis in extensification schemes is on the conservation of wildlife and water quality, not the conservation of soil resources. Any decreases in erosion and reduction in the area of land at risk will be a by-product of extensification rather than an official aim. Nevertheless, the proposed reduction in arable output will probably reduce the area of farmland at risk from erosion, and the high point of the present increase in soil erosion may have been reached. Acknowledgement-This

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