Soil Management for Potatoes updated 2013

Soil managementfor potatoesUpdated 2013S o i l m a n a g e m e n t f o r p o t a t o e S2

ContentsIntroduction.....................................................................................................................................................2Threats to Soils ................................................................................................................................................2123Section 1 Soil Assessment.....................................................................................4Soil profile.........................................................................................................................................................4Texture..............................................................................................................................................................4Structure...........................................................................................................................................................4Porosity.............................................................................................................................................................4Soil Organic Matter...........................................................................................................................................5Soil water movement........................................................................................................................................6Section 2 Soil-related problems...........................................................................7Erosion............................................................................................................................................................7Wind erosion.....................................................................................................................................................7Water erosion....................................................................................................................................................8Diffuse pollution................................................................................................................................................9Slopes and water run-off..................................................................................................................................10Capping............................................................................................................................................................10Irrigation............................................................................................................................................................10Compaction....................................................................................................................................................11Areas where soil problems can be found in potato crops................................................................................11Potato rooting and sensitivity to compaction...................................................................................................12Potato diseases particularly affected by waterlogging.....................................................................................13Field operations and position of possible compaction.....................................................................................13Section 3 Addressing the issues..........................................................................14Field selection................................................................................................................................................14Field layout........................................................................................................................................................14Checklist for the autumn before planting potatoes..........................................................................................14Cultivations.....................................................................................................................................................15Ploughing problems..........................................................................................................................................15Pre-ridging cultivation.......................................................................................................................................15Deep ridging / bed opener................................................................................................................................15Deep bed-tiller..................................................................................................................................................16Separator..........................................................................................................................................................16Planter...............................................................................................................................................................16Subsoiling post-planting...................................................................................................................................17Spray lines / irrigation lines...............................................................................................................................17Harvesting.........................................................................................................................................................1745Section 4 Legislation.................................................................................................18Codes of Good Agricultural Practice................................................................................................................18Water Framework Directive...............................................................................................................................18Soil Framework Directive..................................................................................................................................19Section 5 Environmental Planning checklist....................................................20S o i l m a n a g e m e n t f o r p o t a t o e s3

1 Soil assessmentSoil profileYou can learn a lot from studying the soil profile. Choosewhere to dig carefully, prepare the profile, then examineeach layer of soil.Look at the root growth.The pattern of roots inthe growing crop can beused as an indicationSoil surfaceof any suspect layerin the soil. Look at theposition, quantity andvigour of roots in theCultivated layersubsoil – they show upthe effects of many soilproperties. The drynessof zones in the soil maySubsoilalso shed light on rootactivity.Potatoes are particularly sensitive to compaction. Severepanning may show as a web of roots on the upper surfaceof the pan with only a few penetrating below.Texture and structureTexture – the relative amounts of the primary particlessand, silt, clay and organic matter.Structure – the arrangement and packing of particlesresulting in their grouping into aggregates.Soil texture is fixed, while soil structure is changed bymany agricultural activities including cultivation andmachinery traffic.TextureA soil’s texture determines almost all aspects of soilbehaviour, including use of certain herbicides, drainagecharacteristics, porosity, cultivation needs and availablewater reserves.Marked changes in texture can occur within a vertical soilprofile. These can have a considerable influence on watermovement and root growth.StructureSoil structure is the architecture of the soil and describesthe size, shape and stability of units in which the individualparticles of the soil are held together. The only opportunityfor growers to modify soil structure is the period betweencrops. The effect on structure depends on the nature ofcultivation and state of the soil.A hardened layer can form in the subsoil wherequantities of calcium carbonate, silica or iron,manganese and aluminium compounds cause particlesto bind together tightly in a discrete layer. They areusually linked to a fluctuating water table.Aggregates – individual mineral particles of the soil areheld together.Pores – spaces between the aggregates that play a keyrole in good soil husbandry.Bonds – organic matter, clay and, in some soils, calciumand iron compounds that bind the larger particlestogether. The strength of the bonds determines thestability of the soil and its potential to withstand wind andwater erosion.PorosityPores are essential to thedynamics of the soil profile as theyallow movement of water, air andnutrients within the soil.The role of air spacesHealthy crop roots and beneficial soil organisms needoxygen. Low oxygen concentration in the soil slowsroot function, tuber development and skin set. This canprolong the period of susceptibility to surface diseasessuch as powdery scab and black dot.Large pores, called macropores, allow the free movementof water and air. In sandy soils they can be the spacesbetween grains. In other textures they are usually cracksand fissures between soil structures and worm or oldroot channels. Such pores are very prone to closure bycompaction. Water movement out of soils replenishes thesoil gas environment.How water affects structureAs it gets wetter, soil becomes softer and is more easilydeformed and will reach a phase called plastic. Above itsplastic limit a soil that is compressed, through mechanicalSevere damage can result from travelling on or working soils that areexcessively wet4S o i l m a n a g e m e n t f o r p o t a t o e S

1 Soil assessmentcultivations for example, will retain the compressed form.The greatest risk of structural damage occurs when a soilis at or near field capacity (see soil water status conditionson page 6).How cultivations affect structureThe mechanical mixing of the soil compacts and shearsaggregates, fills pore spaces and speeds up the decayand oxidation of organic matter. The amount of damagecaused depends both on the type and force of cultivationand the conditions of the soil – whether wet or dry, hard,soft or loose. A feature of this is that over-worked soilscan be more prone to slumping and capping, particularlyif the soil has high silt content. Continued cultivation andwheel traffic also causes compaction.The benefits growers notice from SOMOver-working a soil can damage its structure. Consider ways to reducecultivationsFurther ReadingThere are several good guides to examining soils suchas A Guide to Better Soil Structure (NSRI, Cranfield)and Visual Soil Assessment (SMI/Vaderstad).The problem for arable soilsThere is concern that intensive arable farming is causingthe Soil Organic Matter (SOM) content of soils to fall tounacceptable levels. SOM plays an important, yet oftenpoorly understood role in sustaining soil functions.Long-term arable soil contains less organic matter thanadjacent grassland soil. Arable total SOM content isdifficult to increase and there is no easy way to measureany change. But soil loss from erosion does decreasemarkedly as SOM content increases.Soil organic matter (SOM)What organic matter does• Holds soil particles together, reducing erosion• Improves structure, making the soil more friable andeasier to work• Helps maintain an open structure, aiding root growthand penetration• Increases porosity for air and water infiltration, reducingrun-off• Stores and supplies nutrients• Retains carbon from the atmosphere and other sources• Provides a food source for soil microbes• Cultivation: Easier cultivation (faster forward speeds,less implement wear), less subsoiling needed, easier toproduce a suitable tilth for planting, more flexibility in orgreater window of opportunity for mechanical operations• Soil structure: Better moisture retention, less capping,improved tilth, less susceptibility to compaction anderosion• Soil biota (life): Increased earthworm and insect activity• Fertiliser: Less inorganic fertiliser needed to optimiseyield• Drought resistance: Yield affected less in droughtyears, lower irrigation requirementImportance of SOMThere’s growing evidence that suggests the ‘active’fraction of SOM – up to 10% of the total SOM – is moreimportant to soil physical properties than total SOM. Thisconsists mainly of recent additions of crop residues andorganic manures. Under arable cropping, annual returnsof crop residues to the soil are the major source of theseactive substances.CompostThe UK potato industry is a potentially large marketthat could benefit from quality composts, with potatoesplanted on 121,800ha of agricultural land in the UK in2012. If compost was applied to a quarter of this area atan application rate of 30t/ha, just under a million tonnes ofquality organic matter would be beneficially recycled.Compost should be applied prior to potato planting andincorporated into the soil. It is recommended that PAS(Publicly Available Specification) 100 composts are usedfor potato production for the benefits to the soil, crop andthe environment. These benefits include:• Enhancing water retention• Improving heavy land• Reducing compaction• Reducing production costs• Supplying nutrients, especially P and KS o i l m a n a g e m e n t f o r p o t a t o e s5

1 Soil assessmentSoil water movementSoil is constantly wetting and drying throughout the layersof its profile. These are rarely at the same soil moisturestate, and much depends on texture – water movesrelatively slowly through clay soils, or clay layers in a soil,and through compacted layers. This means the topsoilmay hold water that exceeds its plastic limit before drainsstart to run, and the soil is prone to damage.The three soil water status conditionsSaturationAll the pores are filled with water and there is no air inthe soil. Potatoes are highly sensitive to waterlogging.Damage includes Blackheart, erupted lenticels andplants may die. Roots will be affected after even ashort time, leading to premature root death and cropsenescence.Field capacityReached when a soil has drained for about 48 hoursfollowing heavy rain, air has re-entered the soil andno more water is lost through gravitational drainage.Soils usually change from being at field capacity orgreater during winter to being in soil moisture deficitin summer.Permanent wilting pointSoil dries progressively until only the smallest porescontain water. Roots are unable to draw on thiscausing leaves to wilt. Plants may recover at night, butwhen damage is permanent, the soil has dried to thepermanent wilting point.Generally soils with larger pores, such as sands, willdrain more quickly and retain less water. However if waterrunning through the profile encounters a layer of coarsematerial, it often stops until the soil above it becomesnearly saturated. This is because the water cannot enterthe sand layer until the large pores can pull water into it.So a soil that becomes sandier with depth holds morewater than its texture would suggest.Capillary action is responsible for moving water from wetareas of the soil to dry areas. It describes the attraction ofwater molecules to soil particles. Smaller pores pull watertowards the centre of the pore with more force than largerpores, rather like small or large tubes. It is easy to removewater from larger tubes, but it takes a lot of suction toremove water from the smallest tubes. So a plant mustexert considerable suction to remove water from smallpores in the soil.Hydraulic conductivity describes how easily water canmove through the soil. It depends on the permeabilityof the soil (pore size, fissures and compaction) and themoisture content of the soil. The infiltration rate can onlybe maintained if the system of coarse pores is maintained.The zone where this system is most likely to collapse isthe soil surface. Wet soil aggregates are weak and caneasily be broken by the impact of rain drops. This causessoil particles to become detached and block the coarsersurface pores.Infiltration is the process by which water on the groundsurface enters the soil. Large cracks and macroporesallow a rapid infiltration. Smaller pores take longer to filland rely on capillary forces as well as gravity.Drainage rates are a combination of hydraulicconductivity and infiltration. In most soils, the subsoildrainage rate will control the whole profile.The availability of water to potato rootsThe moisture content of a soil between field capacityand permanent wilting point is available to crops and isknown as the Available Water Capacity (AWC). If morewater is removed by evaporation and plant transpiration(evapotranspiration) than added through rainfall orirrigation then soil moisture content reduces creating asoil moisture deficit (SMD). Potato crops are sensitive torelatively low levels of water stress and it is important tokeep the soil moisture deficit below a threshold that couldlimit growth. A large component of increased sensitivityto water stress in potatoes is the lack of accessibility tosoil water owing to the inability to root in even moderatelycompacted soils.Content (per cent)100806040200C ZC ZCL CL SCL ZL SZL SL LS SSoil TextureSolidmaterialAir (at fieldcapacity)AvailableWaterCapacityUnavailablewaterKnowing the water content of the soil aloneis not enough, for example if the soil is at29% water content then:• Sand is wetter than field capacity anddrainage will still be taking place• Sandy silt loam is in an ideal condition forplant growth• Clay is at permanent wilting point.C = ClayZC = Silty clayZCL = Siltly clay loamCL = Clay loamSCL = Sandy clay loamZL = Silt loamSZL = Sandy silt loamSL = Sandy loamLS = Loamy sandS = Sand6S o i l m a n a g e m e n t f o r p o t a t o e s

2 Soil-related problemsErosionWind and water are the weather-related factors that causesoil to erode. Soil erosion is the relocation and movementof soil within fields and into other parts of the landscapeincluding roads, buildings, streams and rivers.Light sands and peaty soils are mainly affected by winderosion. Water erosion occurs on all soils but is mostdramatic on unstable sands and silts.are growing crops such as sugar beet and fine-seededvegetables, erosion is more likely to take place. Butflattening of potato ridges can occur.The lighter and less dense the particles, the more they arelikely to erode. So fine sands or relatively large particleson peaty soils (around 1mm) are most likely to be liftedby the wind. Increasing organic matter helps bind sandparticles.Soil erosion problems• Loss of fertile topsoil• Systematic reduction in overall soil quality• Reduction in agricultural productivity• Loss of important nutrients, in particular phosphorus• Eroded soil particles become sediment particles,moving from land towards river systems to spoil fishspawning grounds• Affects other people – soil on road, or blockingstreams and drains• Destruction of wildlife habitats and wildlife• Pollution• Potential legal actionWind erosionSome of the most common soils for growing potatoesare those most likely to suffer – the non-cohesive sands(where individual particles are only weakly, if at all, heldtogether), light loams and peats. On these soils, if youDamage• Young foliage sand-blasted• Potato ridges flattened, exposing tubers• Crops smothered by deposited soil• Ditches filled in• Dune-like appearance on roadsHow to reduce wind erosion• Establish windbreaks (e.g. hedges, lines of trees) butthis may take many years and they are only effectiveover short distances• Create a vegetative cover, surface trash or leave a roughsoil surface• Align potato ridges across the normal wind direction• Fleece or polythene covers give very good short termcover• Increase soil organic matter content throughapplying slurry or manure (check NVZ rules and croprequirements)• Increase the cohesiveness of the soil particles by usingsoil stickers• Dampen the soil using irrigationS o i l m a n a g e m e n t f o r p o t a t o e s7

2 Soil-related problems• Vegetation cover stabilises the soil• Tillage lines and wheelings- Consider running a tine through to improve infiltration- Break up long runs with buffer zones (either cultivatedor grass strips)• Slope characteristics – break up long slopes andconsider taking steep areas out of cultivationThe signs of erosion and run-offSource: Highways AgencyWater erosionWater erosion is a natural process that removes topsoil.When soil loss exceeds regeneration of soil by weathering,soil fertility decreases and crop yields are reduced.Rain or irrigation that falls at a rate faster than the soil canabsorb it will form surface water-ponding and run-off. Thiscan occur where capping or compaction is present. If thewater flow increases or speeds up, shallow channels (rills)may be formed. Additional water volumes will turn the rillsinto deeper gullies. Any evidence of rilling should be takenas an indication that significant erosion is occurring.Water erosion facts• Land that floods is susceptible to erosion andrun-off, particularly when under cultivation• Areas that flood at least one year in three shouldnot be cultivated for potatoes.• Since the 1970s it has increased• The rise in winter cereal acreage is a contributoryfactor• More intensive cultivations have reducedstructural stability• Research at Silsoe College has recorded lossesup to 4.5kg per sqm on sandy loam soils• Soil renewal is at best only 0.1kg per sqm per year• A soil loss of 1mm over 1ha is equivalent to11-16 tonnesSoil erosion is most likely to occur in winter and spring,when soils are saturated. Potatoes are very vulnerable justafter planting, and irrigation can compound the problem,as growers try to keep the field close to field capacity forcommon scab control. On sloping sites water will run off,carrying soil particles with it.Factors that determine extent of run-offand resulting damage• Soil texture – sands, silts and those with a low SOMare vulnerable• Soil compaction – pans and compacted areas limitinfiltrationSource: Cranfield UniversityDuring run-off, soil particles of all sizes may be moved.When flow is checked, these start to settle. Stonesand gravel settle out first, followed by sand, which cancommonly be seen as depositional fans where rills runonto level or vegetated ground. Silt-sized particles, andespecially clay-sized particles and organic matter, staysuspended much longer, and can more readily reachdrains and watercourses. Every time a local stream orditch is seen running brown it is as a result of soil erosion.The unseen effectsSmall deposits of coarse sand at the foot of a fieldshould not give false reassurance that the eroded soil hasstayed within the field. The fine material, together withnutrients and pesticides will have travelled much farther.Where they finish up depends on the farm and landscapefeatures, such as roads and tracks, and natural slopes.The erosive power of rain will be reduced if the soilsurface is covered by a growing crop (stubble or trashafter cereals).8S o i l m a n a g e m e n t f o r p o t a t o e s

2 Soil-related problemsDiffuse pollutionThe Environment Agency has estimated that highphosphate levels in around half of England’s total riverlength and a quarter of its lakes mean that they may notachieve Water Framework Directive objectives by 2015(see Legislation, page 18).High levels of nitrogen and phosphorus can causepollution in rivers or lakes and impact on biodiversity andwater quality. These nutrients are lost from agriculturalland through a combination of land managementpractices, land vulnerability and climatic factors.They are key contributors to the pollution of surfaceand ground waters. Water flowing over the soil surfacecan carry particulate and water soluble phosphate withit, for example. According to Defra’s Water Strategy 2008,25% of phosphorus in UK water bodies comes fromagriculture.The scourge of brown waterBrown water carried into watercourses takes nutrients with it. Thisphoto sequence shows how longit takes for brown water runningoff a field to settle out in a bottle. Itindicates just how much suspendedsolids remain in water run-off evenafter a full 48 hours period.2 mins 2 hours 24 hours 48 hoursEutrophicationWhen a surface body of water is enriched with nutrients,this accelerates algal or plant growth that leads toundesirable changes in water quality and disturbance ofthe ecology within the water body.• Leave the soil surface protected with stubble or a covercrop for as long as possible before cultivating the land• On fields where erosion risk has been identified considergrowing an earlier variety, which may allow you toestablish an autumn crop after harvest• Following harvest, where conditions are dry enough,carry out a tined cultivation to break up the surface ifyou are not establishing an autumn-sown crop- This has the added advantage that the operation willleave groundkeepers close to the surface andtherefore more likely to frost- Carry out the operation as early as possible afterharvest to allow water to infiltrate the soil and reducethe risk of erosion from bare and rutted surfacesSteps growers can take toavoid eutrophication• Try to prevent soil erosion taking place and avoidapplying animal manures, especially slurries, towaterlogged or very dry soil when rain is imminent• Maintain soil phosphate levels at the optimum point forpotato crop production and soil type (refer to RB209)• Keep records of phosphorus balance for each fieldand check a near neutral balance is maintained by soilsampling and analysis every 4-5 years• Adjust fertiliser application to allow for the phosphorusin organic manures• Be aware of compaction if overworking the soilS o i l m a n a g e m e n t f o r p o t a t o e s9

2 Soil-related problemsSlopes and water run-offSteep sloping fields are often prone to erosion of drills,resulting in soil, fertiliser and pesticide loss and green ordiseased potatoes. Water will run off the slope if the rateit falls is greater than the rate it can enter the soil – theinfiltration rate. Maintaining a high soil infiltration rate willreduce surface run-off. This can vary within a field as wellas between fields.CappingSoil aggregates are susceptible to breakdown into smalleraggregates when relatively dry soil is suddenly wetted bywater. This is known as slaking. Soil particles can alsoseparate from one another in water, known as dispersion.The two processes, separately, or together, can lead tosurface capping and interrupt the movement of water andair into the potato ridge.Reduction in infiltration rate with slopeSlope Degrees Reduction in infiltration rate %2-3 103-4 205-7 407-11 60Above 11 75Reference adapted from Bill Basford Potato Council Workshop 2002Factors that influence infiltration rate• Soil texture, structure (compaction), porosity and bulkdensity• Groundcover• Slope and dispersion (separation by water of soilparticles)• Depth – subsoil infiltration rate is often lower• Capping after heavy rain, making free-draining soilssusceptible to run-off• Fields with long, uninterrupted slopesWhat growers can do to reduce run-off• Retain more surface cover• Increase the organic matter content in the topsoil• Improve soil structure through increasing solublecarbohydrates in the soil, the ‘active SOM’• Relieve compaction• Break up surface capping• Break up impermeable layers by subsoil cultivation, ifappropriateCapping can prevent the emergence of developing stems,or the collar of hard soil can restrict or damage emergingstems. If not recognised, a large number of seed tuberscan die. Adding fresh organic matter can reduce the riskof slaking.IrrigationRain guns can discharge largedroplets of water, which candamage the soil or crop foliage.The biggest single fault observedwith rain guns is running them attoo low a pressure. Maintainingthe correct rain gun pressure ensures correct atomisation(typically 4-5 Bar pressure at the gun for 72m lanespacing). Using the appropriate nozzle ring minimises theimpact energy of the water droplets. Too low a pressurealso results in poor distribution and shorter throw of wateracross the working width.Boom irrigators produce finer droplets and so reduceerosion risk. The wetted front of the watering patternfrom a boom is narrower than from a rain gun, so the soilinfiltration rate needs to be higher.Growing crops in flat-topped orcentre-dished beds together withthe use of the Simba Aqueel(see photo above) allows thewater to remain near the surfacewithout run-off for longer. Thismeans less erosion risk and morewater infiltrating into the soil.Irrigation application rates should bereduced if:• Use tied ridges in furrow bottoms• Use a Simba Aqueel on ridge or bed tops (see photo)• Divide long slopes with grass buffer strips or unplantedcultivated areas• Soil shows visual signs of erosion or where soilis bare• Slope is more than 3 degrees (a commonly usedmaximum infiltration rate on steeper slopes is10mm per hour)See also Managing the risk of Common Scab PCL 2010 and CommonScab Cost Benefit Analysis 201110S o i l m a n a g e m e n t f o r p o t a t o e s

2 Soil-related problemsCompactionSoil compaction is the increase in bulk density usuallycaused by pressure on the soil. Pore space reducesas the air or water is squeezed out. The load applied,through a tractor wheel, for example, is greater than thesoil structure can stand. The soil deforms and thetractor sinks.Near the surface, compacted layers of dense soil formedunderneath the ridge are often attributed to using heavymachinery and cultivating the soil when wet.At depth, compacted layers may be a result of heavyharvesting machinery or trailers from previous crops,at times when the soil was too wet to support the highaxle loads. The need to plant crops within a limitedtime window increases the risk of working the soil in aninappropriate condition.Some degree of soil consolidation is needed for cropgrowth – good contact with the soil helps root anchorageand allows water uptake. If there is not enoughconsolidation of the soil around the tuber at planting timecrop emergence is delayed. The ridge will slump with apotential increase in some tuber skin diseases such aspowdery scab and black dot. It is only when the degreeof soil compaction prevents optimum crop growth that itbecomes a problem.Areas where soil problems can be found in potato crops1. Compaction pan below plough depth, resulting from ploughing the soil when wet or from previous croppingoperations2. Compaction pan caused by bed tiller or separator just above plough depth3. Compaction in wheelings is normal, but should not extend under the bed. The further it does, the greater waterrun-off and the less water that is available for the crop4. Compaction at the base of the ridge will prevent water that has been shed by the drill profile entering the soil5. Opening coulters on the planter can cause localised compaction below the tuber6. Ridge-capping can occur from very fine soil particles that ‘cement’ together sealing the ridge. The lack of air leadsto high death rates of seedS o i l m a n a g e m e n t f o r p o t a t o e s11

2 Soil-related problemsPotato rooting and sensitivityto compactionThe shallow rooting of potatoes is often due to thefact that they are more sensitive to unfavourable soilconditions than other crops. Potatoes extract less waterfrom each soil layer and have about half the effectiverooting depth of cereals. This makes the crop’s leafgrowth rate and canopy development unusually sensitiveto low soil moisture.Symptoms of compaction in potatoes• Uneven and/or delayed emergence• Stunted plants with delayed canopy cover• Reduced rate and density of rooting- Reduced availability of soil water- Increased irrigation requirement- Increased fertiliser requirement• Premature senescence• Wilting leaves on hot days even though the soilis moist• Slight or severe yield reduction• Increasing tuber deformities, such as cracking,secondary growth, powdery scab, lenticel eruption• Waterlogged soils• Water erosion• Harvesting problems- Share penetration in hard soil- Clods- Waterlogging• It restricts the extent of the root system, reducing aplant’s capacity to uptake nutrients• It reduces the movement of nutrients through the soil,which lowers nutrient availability• Compacted soil in wet conditions can result in:- A 30% reduction in mineralisation of nitrogen inorganic matter to nitrate- A 20% increase in loss of nitrogen by denitrification offertiliser nitrogenVarietyThe determinacy of the variety (a measure of thecrop’s capacity to maintain leaf production after thefirst appearance of flowers) will affect rooting depths.Indeterminate varieties such as Cara or Maris Piper willhave deeper roots than determinate varieties such asEstima or Lady Rosetta.Sandy soilsThese are generally regarded as not prone to compaction.But sandy soils can and do compact, often quite severely.Unlike other soils they will not recover with time as theydo not shrink and crack when drying out.Their low available water capacity means the presenceof a pan in a sandy soil can have larger effects on cropgrowth than in other soil types. So it is important toexamine sandy soils and treat them appropriately toensure optimum rooting depth.Early growth stagesPotato roots are most sensitive to compaction during thefirst 3-4 weeks after emergence when growth rates ofroots are most rapid. Shallow compaction immediatelybelow the seed is more damaging than deep compactionsince it is encountered when roots are growing mostrapidly.Nutrient uptakeAbout 85% of total nitrogen uptake occurs by 45-65 daysafter emergence; so restricting early root growth can haveserious consequences. Compaction reduces nutrientuptake in a number of ways:Factors that can contribute to soilcompaction• Water content of soil during cultivations (damageoften occurs when surface is dry but soil is wetbelow)• Ground pressure/draft force exerted on soil• Tyre characteristics and weight supported• Number of passes of wheels/machinery• Soil cultivation equipment12S o i l m a n a g e m e n t f o r p o t a t o e s

2 Soil-related problemsTravelling on soilsTo keep compaction to a minimum, soils must be drierthan the plastic limit when you travel on or cultivate them.Heavy machinery with a small soil contact area (on narrowwheels, for example) will apply a high ground pressure.Driven wheels or tracks from machinery that produceshigh draft forces (pulling) cause additional problems.The soil can shear in a plane at an angle to the surface,rather than vertically downward as a normal load.Reducing the risk• Reduce the weight of the machine• Try to spread the load over a wider area. Care is needed as reducing the weight on a driven wheel can lead toincreased wheel slip. This can increase compaction and smearing, rather than reduce it• Spread the load over a larger area by selecting radial tyres that have a larger footprint than cross-ply tyres• Reduce the tyre pressure to that recommended by the manufacturer for fieldwork. Often tractors can be foundworking in fields with tyres at high pressures used for roadwork. High pressure reduces the contact area of the tyreand increases compaction and wheel slipPotato diseases particularly affected by waterloggingBlackleg(Pectobacteriumcarotovorum subsp.atrosepticum)Occasionally serious, particularly in wet seasons, irrigatedcrops and on poorly drained land. During crop growthinfected seed tubers rot, release bacteria, and infect progenytubers. In poorly drained, waterlogged soils the seed tuberrots earlier and the risk of tuber infection is greater.Rubbery rot(Geotrichum candidum)Pink rot(Phytophthoraerythroseptica)Watery wound rot(Pythium ultimum)Powdery scab(Spongosporasubterranea)Outbreaks are invariably associated with heavy irrigation orfollowing rain within three weeks of lifting, especially in warmweather in panned, poorly drained soils.Usually confined to patches in crops where the drainage ispoor. Control relies on maintaining good drainage and a widerotation.It is important to improve drainage and not to grow potatoes infields with a history of the disease.Risk depends on factors such as soil type (moisture retention),drainage (avoid poorly drained fields), and previous history ofpowdery scab.Source: Potato Council Research review, Soil compaction and potato crops 2005, www.potato.org.uk/publications/r260-review-soil-compaction-andpotato-cropsField operations and position of possible compactionPositionWheelings Under the bedPlough ✘ ✘Deep Tine ✘ ✘Bed Former ✘ -Bed Tiller ✘ ✘Fert. Broadcast ✘ -Separator ✘ ✘Planter ✘ ✘Sprayer ✘ -Irrigation ✘ -Flail ✘ -Harvester ✘ ✘Trailers ✘ ✘S o i l m a n a g e m e n t f o r p o t a t o e s13

3 Addressing the issuesField selectionFor healthy roots and good crop growth, potatoes needsoil that is:• well aggregated• stable• aerated• free-draining• biologically activeTarget market and variety should be considered. The tablebelow shows field situations that should be avoided.Variety trait/market requirementSensitive to cold soilsBright skin finishDrought-sensitiveSalad cropsEarly marketField historyPotatoes are grown in rotation, so the use andmanagement of the field in years prior to potatoproduction is important. Previous crops may have abearing on soil structure, contribute to compactionproblems or cause tuber damage at harvest. Forexample:• Trash and divots from fields previously in grass willpresent problems for separators• The late harvest of sugar beet could leave seriouscompaction problemsAvoidHeavy soils that are wetAbrasive sandy soilsSandy soilsSoils with high stone contentHeavy, cold soilsField layoutThere are a number of factors to consider when decidingthe best way to plant a field:• Water run-off from slopes and irrigation lines• Soil type should be consistent along the row for easierharvesting and agronomy• Drill wheelings need to match other machinery –starting harvest can be a problem if trailer track widthsdon’t line up• Aim for straight drill lines to ease machinery set-up• The headland warrants special attention• Consider leaving it unplanted as this is where mostbruising occurs- If sown with a grass margin mixture, it will providea water intercept and result in lower soil compactionproblems- If planted, allow ample room for turning and spraytramlines – the ends of drills can become flattened bytyres, causing tuber damageChecklist for the autumn beforeplanting potatoesInspect the field and examine the soil to a depth of atleast 500mm and preferably 700mm in several areas ofthe field. Look for and identify any problems with:• Soil structure• Compaction pans• Potential water run-off• Soil texture• Drainage problemsBuffer strip ©ADASSubsoilingSerious compaction problems are usually caused byprevious cropping activities that had not been rectifiedbefore planting potatoes.• Check to identify if it occurs all over the field or onlyin local areas that can be individually treated• Decide if or when soil conditions are suitable torectify the problem• Try to subsoil at right angles to the direction ofproposed drill linesThe late summer or autumn, if dry, is generally the besttime to carry out subsoiling.• The previous crop will have removed water at depth,drying the subsoil• This allows satisfactory shattering of the subsoil• Avoid subsoiling when the soil is wet and in a plasticstate as this could make conditions worse• Sandy soils, which are never plastic, can besubsoiled during most of the year and should besubsoiled as close to planting as possible to reducethe effects of re-compaction14S o i l m a n a g e m e n t f o r p o t a t o e s

3 Addressing the issuesCultivationsManaging residue and trashDifficulties can occur where there is heavy trash residueespecially with stone/clod separation. Excessive trash willpass over the separator and fill the furrow bottom.Farmyard manure (FYM) can also cause problems forseparators if not well broken down by planting time.Ensure that FYM is spread evenly and there are nolarge lumps. More information on nutrient analysis canbe found at www.ahdb.org.uk/projects/documents/AHDBImprovedanalysisofsolidmanuresandslurries.pdf• You can reduce compaction if the tractor wheels arekept on the surface when using high-powered tractors(on top as opposed to in-furrow)• The plough share can also cause localised smearing ofthe soil when wetPre-ridging cultivationThe benefits of deep tine cultivation• Pre-ridging work helps to loosen stiff soil at around250-350mm and allow the deep ridger to work correctly– stiff soil at this depth will prevent the deep ridgerpenetrating the ground properly• Stiff soil can easily pull the tractor off-line, making it hardto maintain a straight line• Pre-ridging work also helps the soil to dry out bybringing wet soil to surface• Avoid adding subsoiler tines to bed-formers unlessworking in sandy soils as the soil at depth will mostlikely be plastic and exacerbate any existing compactionTips for success• Check soil conditions by digging down to 300-350mm; if it is easy (don’t have to stand on spade), nopre-ridging work is required• Watch for operators going too fast and the tinesriding up out of the ground• Check working depthPloughing and soil moisture• A field that has been ploughed and left for severalmonths will have formed natural drainage channelsand wormholes, allowing easier water movement• This means it is quicker to dry out in the spring• It is often drier than a soil that has been ploughed foronly a few weeks• A field ploughed immediately before planting willbe drier (if not rained on after ploughing) than oneploughed a few weeks previously and rained onManaging constraints of the weatherWorking the soil speeds up drying. But worked soil thatis rained on will hold more water than unworked soil.Soils with high silt and clay contents need very carefultiming of operations. Either too dry or too wet can makeit impossible to achieve a satisfactory tilth. This increasesclod formation and compaction.Ploughing problemsSevere soil structure problems can be created if ploughingis carried out when the soil is wet.• If the soil surface is already compacted from previouscropping and inverted when wet there is a tendencyfor it to go over as a continuous lump that can form ananaerobic layer at the plough share depth• If the tractor wheel is run in the base of the furrowsevere compaction can be created by wheel slip, whichis greater in wet conditions or with high draft forcesProblems• Wheelings if wet• Smearing under the tineDeep ridging / bed openerDeep ridging will bring a considerable quantity of wet‘raw’ material to the surface.• Leave this material to dry out for 1-2 hours beforebed-tilling or separating but not for prolonged periodsas clods become more stable and may requireexcessive extra cultivation to break downProblems• Smearing at the base of the furrow – often the startof a serious problem for water movement, resultingin run-off• Smearing on the side of the ridge will dry and formhard clodsS o i l m a n a g e m e n t f o r p o t a t o e s15

3 Addressing the issuesDeep bed-tiller• For optimum output match separator and bed tillerwork rates and only bed-form as deep as required forthe de-stoning operation• A good operator can alter the forward speed dependingon soil conditions: faster when soil is easy to work andslower in cloddy/sticky areas• Check the discharge – there should be no usable soilin the furrow base• There is little benefit in producing de-stoned bedsdeeper than 25cm on any soil. This depth of bedallows sufficient soil to plant and harvest tuberswithout damage• Soils with moderate (20-30%) clay content willfrequently be in a plastic state below 25cm at plantingand cultivating deeper will result in compaction whichwill reduce yield• Separating soils shallower than the normal 30-38cmdepth will speed up the operation allowing more timelycultivation, reduce fuel and labour costs and decreasemachinery wear and breakdown timeDifference in yield depth from standard depth (t/ha)Problems• Pan, created by action of blades at base ofcultivation depth. Some types of machines canproduce very serious pans. Extent of problemdepends on:- blade type- rotor speed and forward speed• Excessive tilth at this stage produces fine soilparticles that can lead to increased capping andridge slumping• An increased risk of soil erosion by wind and bywater on sloping sitesSeparatorDo you need one?Difference in yield depth from standard depth (t/ha)Problems• Compaction pan created by share• Compaction at side of bed from separator tyres if notcorrectly aligned or when travelling across slopes• While needed for stones, clods will break down to acertain extent during the growing seasonDifference • Widespread in destoning use depth of Dalhman-type from standard depth cleaning (cm) units on Planterharvesters ensure clods now present fewer problems-15 -10 -5 05 10 15 SlopesOperate at the 10 right depth• The high centre of gravity of the hopper can often• Go too deep with 8 the separator and too much wetcause the planter to skew down a slope, making thematerial comes over 6 the machine that cannot be broken tractor slip off the stone windrows on to soft soil ofdown and is discharged 4 to the wheelingthe next bed20Destoning shallower than the typicalDifference in destoning depth from standard depth (cm)-2depth used by growers (30-38cm) can-15 -10 -5 0 5 10 15result in higher -4yields on soils with higherclay content and -6 have no detrimental10effect on yield -8on sandy soils.8-106Figure: Effect of destoning depth on yield42011-20122Loamy sands and sandy loams0Sandy clay loams and clay loams-2-4-6-8-10(Source: CUF 2013)16S o i l m a n a g e m e n t f o r p o t a t o e s

3 Addressing the issues• Wheel steerage on the planter can help but the wheelsmay produce a rut or compact the adjacent drill• If using quad planting and/or covering hoods check tosee that there are no compaction issues arising fromtheir useProblems• Planter weight with full hopper on the small tyre sizecausing compaction• Operation on side slopes can result in compaction onadjacent drills• Localised compaction from opening coulters aroundwhere tubers are placed• Covering bodies and hoods causing smearing thatcan later cap and impede crop emergence and causeanaerobic conditionsSubsoiling post-plantingConditions are rarely favourable for subsoiling to beeffective after planting, although some growers areconvinced that the crop has benefited from undertakingthis operation.Is it needed?• First examine the field or area where you think there maybe a problem• Confirm that there is a problem and gauge its extent• Check if the soil is dry enough at the depth of proposedoperations• Subsoiling after planting should only be considered onfragile sandy soilsLoosening compaction on the shoulder of the ridge using tinesmounted on the front of a rotary hiller also allows greater water infiltrationand crop rooting.Spray lines / irrigation linesProblems• Compaction and ruts in wheelings lead to watercollection and rill formation• Problem made worse through:- Narrow tyre sizes supporting heavy equipment- High number of passes in season- Timing and number of blight sprays irrespective ofsoil moistureSolutions• Try creating an extra wide area for the wheels atthe spray line only, which allows wider tyres to beused on the sprayer• Use a wider wheelbase width- Pull the ridges in closer together under the spraytramlines- Try both measures- Use a wide sprayer (36m) which fits in withthe irrigation lines (72m) to reduce the numberof spray lines and associated crop losses at thespray lineHarvestingProblems• Subsoiling the centre of the wheelings can lift orpush buried stones back into the ridges• Tractor wheels sink into the aperture during sprayingand harvesting operationsAlternative solutions• Consider using a ‘tied ridger’ type system to reducerun-off in wheelings• Check for compaction and alleviate any found at thebase of the drill edge, at the side of the wheelings(see photo top right)Problems• Weight of harvester – historically the greatest threatof compaction to soils• Weight of trailers – now the size is such they oftenhave highest ground pressure• Double or triple axles of some trailers can maketurning on soft ground require a lot of power that canresult in excessive tractor wheel slip• High number of passes on headlandsComplianceResolving any compaction problems soon after harvestis not only good for your soils – there are legislativerequirements when harvesting wet fieldsS o i l m a n a g e m e n t f o r p o t a t o e s17

4 LegislationCode of Good Agricultural Practicefor Farmers, Growers and LandManagers: Protecting our Water,Soil and AirIt is the responsibility of every grower to have available themost up-to-date version of the Code of practice togetherwith cross compliance requirements.ContentThe code of practice covers all aspects of agriculturalproduction, particularly as it interacts with theenvironment, including soil management. The guidediscusses in detail most soil issues, including key actionsthat can be taken to protect and enhance the quality ofthe soil apart from the nutritional and pesticide aspects.Guidance on nutrition can be found in Potato Council’sCrop Nutrition for Potatoes and DEFRA RB209 –Fertilisers for Arable and Horticultural Crops. More onpesticide usage can be found in the Code of Practicefor Using Plant Protection Products – DEFRA and Welshassembly. The Scottish Executive has published a Coderelevant to Scotland.WalesGrowers in Wales are encouraged to grow grass leys oneyear in five or incorporate bulky organic manures. This isprobably not possible in the more intensive arable areas ofthe UK because of lack of availability of organic manures.ScotlandThe Farm Soils Plan provides a similar function toEngland’s Soil Protection Review, but is not a requirementunder GAEC (Good Agricultural and EnvironmentalConditions).The Prevention of Environmental Pollution fromAgricultural Activity (PEPFAA) code only briefly addressesthese issues, and needs to be supplemented by landmanagement information.Soil strategyThe Environment Agency in England and Wales alreadyhas one and the EU is developing its own. The latter isexpected to cover many of the points made in this guideas well as the restoration of soils following industrialactivity and the need to prevent ‘soil sealing’ – i.e. beingbuilt on.Cross ComplianceSoil Protection ReviewThe purpose of the Soil Protection Review (SPR) is totackle degradation threats to soil. Anyone who receivessupport under Single Payment Scheme (SPS) must meetthe GAEC standards for soil management and protection,as well as all the other relevant standards that are setout in The Guide to Cross Compliance in England. Thisincludes new entrants to the SPS and/or Schemes suchas Entry Level Stewardship (ELS).The revised SPR incorporates all four soil GAECs whichwere previously applicable to soil:• Soil Protection Review (GAEC 1)• Post-harvest management of land (GAEC 2)• Waterlogged Soil (GAEC 3)• Crop residue burning restrictions (GAEC 4)Water Framework Directive (WFD)This is one of the most important soil and water relatedpieces of legislation that will have a particular impact onland use and management. The main approaches adoptedby the government to implement farming elements of theWFD requirements is to use:• The Catchment Sensitive Farming Delivery Initiative• Single Farm Payment• Environmental Stewardship schemesThe WFD came into force in the UK on December 22,2000. It sets out a timetable for member states totranspose the directive into laws. It also stipulates whenrequirements should be implemented. The key issuesrelating to the WFD are:• That it applies to all waters• It aims to tackle diffuse source pollution (e.g. fromagricultural and urban run-off)• It introduces ecological water quality for the first timeand this includes hydro morphological aspects – thechanges in depth, structure and flow of water bodies• It demands cost effective measures and full costrecoveryThe impact of the WFD on current activities is dependent,for each water body (river, lake, aquifer, etc.), on its currentwater quality status and on what ‘good status’ will mean.The first requirement is to ensure no deterioration and thesecond is to achieve ‘good status’.Good Agricultural and EnvironmentalCondition (GAEC) main requirements• Do not work or travel on waterlogged land unlessthere is a need to improve drainage• Leave the land in stubble or rough cultivated overwinter to allow excess rainfall to infiltrate into the soil• Do not create the final seedbed for spring-growncrops until it is really needed, the objective being toreduce the potential for soil erosion by water overwinter• (England) Produce a Soil Protection Review andreview it annually- List problems, such as erosion and compaction- Action to alleviate them18S o i l m a n a g e m e n t f o r p o t a t o e s

4 LegislationSoil Framework Directive (SFD)The EC adopted the Thematic Strategy for Soil Protectionon 22 September 2006. This contains a Communication,a Soil Framework Directive (SFD) and an ImpactAssessment. The proposed SFD was blocked in a vote byEuropean ministers in late 2007, but it is likely to be reintroduced,either in whole or in part.The SFD duty of care requires:• The restoration and remediation of degraded soil to alevel of functionality consistent at least with current orapproved future use• Member states shall ensure that any land user whoseaction affects soil in a way that can reasonably beexpected to hamper significantly the soil functions isobligated to take precautions to prevent or minimisesuch adverse affectsOther DirectivesThose that are having or will have an impact on land useand farming include:• Habitats Directive• Pollution and Prevention Control Directive• Environmental Liability Directive• Sludge Directive• Waste Framework DirectiveSources of informationLegislation, guides and codesof practiceDefra publications• Code of Good Agricultural Practice for Farmers, Growersand Land Managers (Defra 2009)• Cross Compliance Guidance for Soil Management2010 Edition (Defra)• Cross Compliance Soil Protection Review (Defra 2010)• Irrigation Best Practice, Water Management for Potatoesa Guide for Growers• Code of Practice for Using Plant Protection Products(Defra 2006)• RB209 – Fertilisers for Arable and Horticultural Crops8th Edition (Defra 2010)Scottish Executive publications• The Prevention of Environmental Pollution fromAgricultural Activity Code, 2005• Farm Soils Plan Protecting Soils and Income in Scotland• Code of Practice for Using Plant Protection Products inScotlandDepartment of Agriculture and RuralDevelopment (Northern Ireland)• Code of Good Agricultural Practice for the Prevention ofPollution of Water, Air and Soil, 2003Potato Council publications• Applied Research Forum Soils Information Gateway• Research review: Effects of Soil Compaction on PotatoGrowth and its Removal by Cultivation, 2005• Compost use in agriculture, 2004• Soil, water and other legislation: impacts on Scottishpotato production, 2008• Soil water and other legislation: impacts on UK potatoproduction, 2007• PCL Research Review – Soil compaction and potatocrops, 2005• Review of non-water control measures for potatocommon scab, 2005Technical notes and otherpublicationsStalham, M. A., Allen, E. J., Rosenfield, A. B. & Herry,F. X. (2007). Effects of soil compaction in potato(Solanum tuberosum) crops. Journal of AgriculturalScience. Cambridge 145, 295-312.Critical Levels of Soil Organic Matter MAFF Project CodeSP0306Hatley, D. L. J. Garwood, T. W. D. & Johnson P. A. 2002The Impact of Changing Farming Practices on SoilOrganic Matter and Soil Structural Stability of Fen SiltSoils Proceedings BSSS conference Edinburgh 2002Sustainable Management of Soil Organic Matter, editedby RM Rees, B.C.Ball, C.D. Campbell and C.A.Watson,CABI Publishing 2001Greenland et al, (1975) Determination of the StructuralStability Class of English and Welsh Soils. Journal of SoilScience 26, 294-303Updating the Estimate of Sources of Phosphorus in UKWaters, Defra-funded project WT0701CSFPhosphorus in Agriculture in Relation to Water Quality,AE Johnston and CJ Dawson, Agricultural IndustriesConfederation, Nov 2005Plant Roots – Growth, Activity and Interaction with Soils,Peter Gregory, Blackwell Publishing 2006MAFF Technical Bulletin 29, Soil Physical Conditions andCrop Production, 1975A Guide to Better Soil Structure, National Soil ResourcesInstitute, Cranfield University, 2002Visual Soil Assessment, Soil Management Initiative andVäderstadSoil Husbandry – A Guide to the Use and Managementof Soils, Tom Batey, published by Soil and Land UseConsultants, 1998Irrigated Crops and Their Management, Roger Bailey,Farming Press Books, 1990Russell’s Soil Conditions and Plant Growth 11th Edition –Edited by Alan Wild, Longman Publishing Group, 1998Soil Survey of England and Wales Regional Bulletins,National Soil Resource Institute Cranfield 1984Soil Survey of Scotland, The Macaulay Institute for SoilResearch 198219S o i l m a n a g e m e n t f o r p o t a t o e s

ShelterbeltEarth bankSterile areaDitchField marginsSubjectDelete asappropriateYourresponseActionMeeting regulationsSoil Protection Review (SPR)This ismandatoryCheck the Soil Protection Review and ensurethe land use measures are implemented.Review the success of these measures andupdate the SPR accordingly. Record anyplanned post harvest management measures.Nitrate Vulnerable ZonesThis ismandatoryCheck the location of land in respect ofNVZ designation: www.magic.gov.ukUtilise the latest version of RB209 to calculatecrop nitrogen requirements and ensureappropriate records relating to fertiliser andorganic manure applications are maintained.Agriculture waste: are wastepotatoes deposited on farm?Yes/No Yes Apply to the Environment Agency forappropriate licenses or exemptions.www.environment-agency.gov.uk/business/topics/waste/default.aspxEnsure any waste potato disposals take placein accordance with EA licence conditions.Resource Management PlanningAre all fertilisers applied as part ofa recognized farm plan prepared bya FACTS accredited advisor?Are all manures applied as partof a recognized farm plan?Does the farm have a CropProtection ManagementPlan prepared by a BASISaccredited advisor.Have you prepared anenvironmental assessmentfor the abstraction zone?Yes/No No Prepare a Nutrient Management Plan.Refer to guidance on PLANETwww.planet4farmers.co.uk or ‘Tried and Tested’www.nutrientmanagement.orgYes/No No Prepare a Manure Management Plan.Yes/No No Contact the Voluntary Initiative:www.voluntaryinitiative.org.ukYes/No No Contact EA/CSF on how to prepare a plan.www.naturalengland.org.uk/ourwork/farming/csf/default.aspxSource: Environmental guidance for Potato Production – PCL. CSF and FWAG 2010S o i l m a n a g e m e n t f o r p o t a t o e S21

Potato CouncilAgriculture and Horticulture Development BoardStoneleigh ParkKenilworthWarwickshireCV8 2TLTel: 0247 669 2051Web: www.potato.org.ukWritten by:Eric Anderson, Scottish AgronomyPaddy Johnson, SMIFraser MilneReviewed in 2012 by:Eric Anderson, Scottish AgronomyMark Stalham, CUFChris Steele, Potato CouncilWhile the Agriculture and Horticulture Development Board, operating through its Potato Council division, seeks to ensure that the informationcontained within this document is accurate at the time of printing, no warranty is given in respect thereof and, to the maximum extent permittedby law, the Agriculture and Horticulture Development Board accepts no liability for loss, damage or injury howsoever caused (including thatcaused by negligence) or suffered directly or indirectly in relation to information and opinions contained in or omitted from this document.© Agriculture and Horticulture Development Board 2013. All rights reserved. Potato Council is a division of AHDB. Registered in England andWales No 6410734. Registered Office: Agriculture and Horticulture Development Board, Stoneleigh Park, Kenilworth, Warwickshire, CV8 2TL.S o i l m a n a g e m e n t f o r p o t a t o e swww.loudgroup.com1