BlackwellScience

Primrose McConnell’s

The Agricultural Notebook

20th Edition

Edited by

Richard J. SoffeSeale-Hayne

University of PlymouthUK

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iii

Contents

Preface to the 20th Edition ix

Primrose McConnell: a brief biographical sketch xi

Contributors xiii

Part 1 Crops 1

1 Soil management and crop nutrition 3Introduction 3Soil physical properties 3Agricultural land drainage 12Soil biological properties 19Soil classification 23Soil chemical properties and crop nutrition 25Soil sampling and analysis 36Nutrient sources: manures 38Nutrient sources: inorganic fertilizers 42Nutrient sources: organic fertilizers 46Forms of fertilizer and application methods 47Liming 50Fertilizer recommendations 53Soil management, crop nutrition and sustainable production 60

2 Crop physiology 63Fundamental physiological processes 63Growth 65Crop development cycle 66Environmental influences on growth and development 69Competition 73Modification of crops by growth regulators and breeding 76

3 Arable cropping 77Introduction 77Arable crop planning and production practice 78Choice of arable crop 78Choice of cropping system 80Enterprise planning 82

Arable crop enterprises 85Combinable crops 85Root and vegetable crops 106Fodder crops 123Fibre, fuel and other non-food crops 128

4 Grassland 131Introduction 131Rough grazing 131Permanent grassland 133Rotational grass 133Distribution and purpose of grassland in the UK 134Grassland improvement for agricultural production 134Characteristics of agricultural grasses 139Herbage legumes 141Herbage seed production 143Fertilizers for grassland 144Patterns of grassland production 149Expression of grassland output on the farm 150Grass digestibility 152Output from grazing animals 153Grazing systems 154Conservation of grass 158Grassland farming and the environment 168Glossary of grassland terms 172

5 Farm woodland management 177Introduction 177Setting management objectives 177Forest products and markets 177Silvicultural options for existing woodlands 178Improvement of neglected woodland 181Forest measurement 182Thinning 184Harvesting 186New farm woodlands 187Establishment 194Aftercare 200Forest protection 203Landscape design for farm woodlands 206Forest management for non-timber uses 207Forest investment 209Integration of agriculture and forestry 209Grants 210

6 Crop health – responding to weeds, diseases and pests 213Introduction 213Abiotic challenges to crop growth 213Biotic challenges to crop growth 213Invasion 215Infestation 216

iv Contents

Causes of crop losses 216Impact 217Interactions 218Intervention 219Weeds 222Diseases 224Pests 225Integrated crop management 228Decision support systems 229Conclusions 229Ten tips 229

7 Grain preservation and storage 231Introduction 231Conditions for the safe storage of grain 231Grain moisture content and its measurement 233Drying grain 233Grain cleaners and graders 240Handling grain 241Management of grain in store 243Alternatives to grain drying 245

Part 2 Management 247

8 The Common Agricultural Policy of the European Union 249Background, institutions and the legislative process 249Formation and development of the CAP 253The CAP in practice 257

9 A marketing perspective on diversification 266Introduction 266What do we mean by diversification? 268Small business management 272What do we mean by marketing? 272The application of marketing to diversified enterprises 277Conclusion 280

10 Farming and wildlife 282Introduction 282The emerging forces 282The process of farming for wildlife 284Managing for wildlife 285

11 Organic farming 288Definitions and historical perspectives 288Organic farming in practice 290Organic farming as a business 294Organic farming and society 297Organic farming and agricultural policy 299Future potential for organic farming 300

Contents v

12 Farm business management 304What is business management? 304Setting primary objectives 304Planning to achieve primary objectives 305Information for financial management 306Sources of capital 322Coping with risk and uncertainty 324

13 Farm staff management 327Introduction 327Job analysis and job design 327Recruitment and pay 329Interviewing and discrimination 331Control, guidance and negotiation 334Training and development 338Maintaining and increasing performance 340The employment environment 343Glossary of key terms used 344

14 Agricultural law 346Introduction 346The English legal system 346Legal aspects of ownership, possession and occupation of agricultural land 348Access to the countryside and public rights of way 353Legal constraints on the development of land 355Nature conservation and production methods 357Pesticides and pollution 358Conclusions 358

15 Health and safety in agriculture 360Introduction 360The Health and Safety at Work etc. Act 1974 (HSW Act) 361Basic statutory requirements of the HSW Act 362The effect of European Directives 364Other significant Regulations 365Food and Environment Protection Act 1985 (FEPA) 366Conclusions 367

Part 3 Animal Production 369

16 Animal physiology and nutrition 371Introduction 371Regulation of body function 371Chemical composition of the animal and its food 375Digestion 381Metabolism 387Voluntary food intake 400Reproduction 403Lactation 417Growth 423Environmental physiology 428

vi Contents

17 Animal welfare 431Introduction 431Background 431What is welfare? 432How do we assess welfare? 437What is an acceptable level of welfare? 440

18 Applied animal nutrition 443Introduction 443Nutrient evaluation of feeds 443Raw materials for diet and ration formulation 451Nutrient requirements 465

19 Cattle 473Introduction 473Health scares of cattle 473Grassland Management 475Milk production 475Definitions of common cattle terminology 478Ageing 478Calf rearing 478Management of breeding stock replacements 482Beef production 485Dairying 491Cattle breeding 498

20 Sheep and goats 500Sheep 500Goats 517Appendix 1: Body condition scores 521Appendix 2: Calendar for frequent-lambing flock 521

21 Pig meat production 522Introduction 522Trends in the global market for pig meat 522Structure and performance of the UK pig industry 528Pig housing and animal welfare 530Genetics and pig improvement 534Sow and gilt reproduction 537The suckling pig 544The newly weaned pig 545Growing-finishing pigs 546

22 Poultry 555Introduction 555World poultry information 555Meat production in the UK and Europe 555The broiler industry 556Anticoccidials and antimicrobials 557Neutraceuticals 558The broiler breeding industry 558Commercial egg production 558

Contents vii

Welfare legislation 561Feeding programmes for laying birds 563Feed restriction for replacement pullets 563Turkeys and water fowl 563Geese 564Micro-nutrients 564

23 Animal health 566Introduction 566Factors influencing the incidence of disease 567Disease and immunity 572Medicines 573Signs of health and disease 574Animal welfare and animal health 575Disease legislation 576The health of cattle 576The health of pigs 592The health of sheep 598

Part 4 Farm Equipment 603

24 Farm machinery 605Introduction 605The agricultural tractor 605Cultivation equipment 610Fertilizer application equipment 615Sowing and planting machines 618Crop sprayers 624Irrigation 627Forage harvesting 634Grain harvesting 641Root harvesting 645Feed preparation and feeding equipment 646Milking equipment 650Manure handling and spreading 652

25 Farm buildings 656Design criteria (BS 5502, Part 21, refers) 656Planning and construction design 661Stages in constructing a building (BS 5502, Parts 21 and 22, refer) 666Building materials and techniques (BS 5502, Part 21, refers) 670Water pollution control (BS 5502, Part 50, refers) 689Functional design of specific purpose buildings 692

Index 724

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ix

Preface to the 20th Edition

This new edition takes The Agricultural Notebook intoits third century. The first edition appeared in 1883. Itwas compiled by Primrose McConnell, a tenant farmerof Ongar Park Hall, Essex. As a student of ProfessorWilson at Edinburgh University, he found ‘a great wantof a book containing all the data associated with thebusiness of farming’.

The editor is very grateful to the team that has con-tributed to the new edition; also to a wider group of col-leagues and friends who have helped guide the contentof this edition. The challenge of the changing ruralscene is evident in the range of conferences currently onoffer considering the future of rural areas. The editormust take a balanced view regarding which sectionsshould be added, and which should be replaced. Thirty

contributors across the rural spectrum from Scotland toDevon and Norfolk to Wales are included. We hope thisreflects developments within the rural sector. New sec-tions added include (1) a marketing perspective ondiversification, (2) organic farming and (3) farming andwildlife.

Our primary aim has been to meet the needs of stu-dents studying a range of agricultural, food and ruralsubjects. We have received many useful comments fromuniversities and schools across the world who have beenusing The Agricultural Notebook to teach geography anda host of related subjects – please keep in contact withus and send in your suggestions. We additionally hopeit will be of value to farmers, landowners and advisorsin their many roles.

xi

‘I wish I had not been born for a hundred years to come,for there will be so many things found out after I amdone with . . .’, wrote Primrose McConnell in the springof 1906. It was typical of him: always fascinated by thelatest discoveries and inventions, but concerned to test them against his own extensive knowledge and experience.

McConnell was born at Lesnessock Farm, nearOchiltree in Ayrshire, on 11 April 1856, the son andgrandson of tenant farmers. After leaving Ayr Academy

he was apprenticed to a Glasgow engineering firm, butsubsequently, in the 1870s, went to the University ofEdinburgh, which did not then offer degrees in agricul-ture but prepared students for the diploma examinationsof the Highland and Agricultural Society. McConnellpassed in 1878, and a little later also passed the certifi-cate examinations of the Royal Agricultural Society ofEngland. When Edinburgh eventually introduced adegree, he returned, and was the second student to beawarded the BSc in Agriculture in 1886.

The Notebook is his lasting memorial, but his writingwas based on the foundation of his other activities, asfarmer, scientist, engineer and inventor, traveller, lec-turer and all-round man of agricultural affairs. Farmingformed the foundation of his life. He first rented the636-acre Ongar Park Hall Farm, about 20 miles fromLondon, near Epping in Essex, initially in partnershipwith his father. When he began farming, half of the landwas in arable, but this was in 1883, when cheap grainfrom the new world was beginning to make life difficultfor corn producers on stiff London clays. He thereforegrassed down about 200 acres and based his farmingupon dairying (he had about 60 cows in milk at any onetime) and feeding bullocks, heifers and sheep. In 1905he moved. Why? ‘For the very good reason that I waslosing more money than I could afford’, he wrote soonafterwards, ‘but also for various other reasons’, which infact centred on a dispute with his landlord over how hewas to be compensated for capital invested in buildings.The case went to court, and McConnell had the betterof the legal arguments, but he was left with a jaundicedview of landlords. He was the owner-occupier of his newfarm, North Wycke, 500 acres of land ‘as flat as a table’near Southminster in Essex, between the Crouch andBlackwater estuaries, with ‘nothing higher than a tree ora house between me and the Ural Mountains’. When hebegan to farm there, it was half arable and half grass,

Primrose McConnell: a brief biographical sketch

P.W. Brassley

and he kept 80 cows, nine work horses, a pony, two dogs,three tomcats and ‘135 head of poultry of all breedsunder the sun, including those that do not lay in winter’.He was understocked, he knew, but he was too short ofcapital to buy any more. He continued to farm thereuntil he died in 1931.

McConnell farmed to make money, but not only tomake money. Fascinated by the scientific and technicalproblems involved, he attempted to deal with them pro-fessionally, as befitted an agricultural graduate. He triedmachine milking, found that it resulted in decreasedyields, and so went back to hand milking. Then, afterconsidering his experiences for a year or so, he wrote adetailed article for the Agricultural Gazette setting outthe costs, technical details, yield changes and probableexplanations, before concluding that ‘It is rather a dan-gerous thing to prophesy as to future inventions, and wedo not know what mankind may accomplish in anothergeneration. We may, therefore, still see a successfulmilking machine, but it has not arrived yet.’ He was anearly advocate of milk recording and kept a Gerber fattesting machine in his dairy. He experimented withsilage and he designed his own elevator. The string-binder, he thought, was the greatest invention of thenineteenth century. He had ‘an outfit of every possiblekind of tool in my workshop on the farm that is likelyto be of use’, and was ‘never . . . happier than when atthe bench or vice’. When he wanted to try out a newplough, he would use it himself for a day, with adynamometer between the horses and the plough. Notsurprisingly, the shortcomings of farm machinery provoked some of his more vitriolic comments.

McConnell also led a busy life away from the farm.He lectured, at various times, at the Glasgow VeterinaryCollege (where he was appointed Professor of Agricul-ture at the age of 24) and Oxford and Edinburgh uni-versities and the Essex Winter School of Agriculture(the forerunner of Writtle College), and examined atReading, Wye and the Royal Agricultural College. Hewas a Fellow of the Geological Society. He was on theCouncil of the Dairy Show and a milking judge there,and involved with the British Dairy Farmers’ Associa-tion and the Eastern Counties Co-operative DairyFarmers’ Association. He visited farms in Holland in1899 and made at least two trips to North America, in1890 and 1893, on one occasion meeting some of theSioux who had taken part in the Custer massacre in1876. He was also one of the pioneers in the migrationof farmers from Scotland to Essex in the late nineteenthcentury. No sooner had he found his farm at Ongar Park

xii Primrose McConnell: a brief biographical sketch

Hall than he was writing articles about the potential ofEssex farms for the North British Agriculturalist.

And it is as a writer that he is now best remembered.‘I began to write to the farm papers at the age of eigh-teen, when first learning to hold the plough’, he recalled,and he produced eleven editions of the Notebookbetween 1883, when he was 27, and 1930, the year beforehis death at the age of 75. He also wrote The Elementsof Farming (1896), an elementary textbook, The Elementsof Agricultural Geology (1902), The Diary of a WorkingFarmer (1906) and The Complete Farmer (1908), in addi-tion to articles in the journals of the Royal AgriculturalSociety of England and the Bath and West Society.Later he spent many years as dairy editor of the Agri-cultural Gazette and editor of Farm Life.

Thus he was academically successful, and he clearlyenjoyed writing. But it is also evident from his diary thathe enjoyed physical work too: he writes enthusiasticallyof making his own cheese, digging, ploughing and broad-casting, and stooking even though the sheaves aredrawing blood from his forearms. He was a teetotallerand a dissenting churchman (his wife Katherine was thedaughter of a Free Church minister) who took a five-daystudy tour with the British Dairy Farmers’ Associationas his annual holidays. He took an unsentimental atti-tude to landscape: ‘in a level district you get a great widesky, and the sun shines longer’. But if this suggests thestereotypical dour Scot, then his irascibility, his sense ofhumour and his benevolent interest in the world aroundhim keep breaking through, as does his pride in hisfamily, when he mentions that his daughter Ann is anaccredited dairymaid, and prints a photograph of hissons Archibald and Primrose (who was to be killed in the last days of the First World War). Farming, andthinking and writing about farming, provided him withstimulation and satisfaction. Fortunately, there wasalways something new to learn: ‘Agriculture is a verywide subject, and no one can master it all within thelimits of an ordinary lifetime’.

Sources

Most of the material used here is taken fromMcConnell’s The Diary of a Working Farmer (1906) andfrom his obituary, published in the [Essex] Weekly Newsof Friday, 10 July 1931. For the latter, an enormousamount of other biographical material on McConnell,and many perceptive editorial comments, the author isindebted to Elizabeth Sellers of Chelmsford.

Paul Brassley, BSc (Hons), BLitt., PhD.

Present appointment: Senior Lecturer Agricultural Eco-nomics, Faculty of Land, Food and Leisure, Seale-Hayne,University of Plymouth.

After reading agriculture and agricultural economics atthe University of Newcastle-upon-Tyne went on toresearch in agricultural history at Oxford. Since hisappointment to his present post at Seale-Hayne hastaught agricultural economics and policy and re-searched agricultural history from the seventeenth tothe twentieth centuries.

Peter Brooks, BSc (Hons), PhD.

Present appointment: Professor of Animal Production andHead of Research, Faculty of Land, Food and Leisure,Seale-Hayne, University of Plymouth

Obtained degree in Animal Production and PhD from Nottingham University. Was Head of Agricultureat Seale-Hayne College (subsequently University of Plymouth) for 18 years before becoming the faculty’sHead of Research. Has researched and published extensively on the production, behaviour, manage-ment and nutrition of pigs. Current research focussedon the development of liquid feeding systems for pigs.

Adam Carter, BSc (Hons), MSc.

Previously: Lecturer in Rural Resource Management,Faculty of Land, Food and Leisure, Seale-Hayne, Univer-sity of Plymouth.

Graduated in Rural Environment Studies at WyeCollege, University of London, before completing an MSc in Forestry at the Oxford Forestry Institute,University of Oxford. Previous experience in British

xiii

silviculture and forestry extension work in NorthernSudan with Voluntary Services Overseas. Currentresearch interests in forest ecology, silviculture andmedicinal uses of forest products.

Richard Coates, FRICS, MRAC.

Present appointments: Buildings officer to the AnglicanChurch Schools of Papua New GuineaWas Sole Principal of Rural Design Consultancy, LempriceFarm, Budleigh Salterton, Devon. (now rtd)

Chartered Building Surveyor and Land Agent with aspecial interest in design in the countryside – both inagricultural, construction and other rural building projects. Forty years’ experience in field including 18years as Resident Building Surveyor to Clinton DevonEstates. Only designer to have won the coveted CLAFarm Buildings Award four times. Principal contributorof articles in Countryside Building, the journal of theRural Design and Building Association (Chairman2000–2001).

R.A. Cooper, CDA (Hons), NDA, MSc, PhD.

Present appointment: Principal Lecturer, Animal Produc-tion, Faculty of Land, Food and Leisure, Seale-Hayne,University of Plymouth.

Taught animal production at Shropshire Farm Institutebefore moving to University of Malawi as lecturer inanimal husbandry and assistant farms director. JoinedSeale-Hayne in 1974 following MSc at Reading University and completed PhD on interactions betweengrowth promoters and reproductive physiology in ewelambs in 1982. Main research interests in aspects of goatproduction, particularly in milking does, and in waterintake studies.

Contributors

John Eddison, BSc, PhD, CBiol, MIBiol.

Present appointment: Principal Lecturer, Applied Ethology,Faculty of Land, Food and Leisure, Seale-Hayne, Univer-sity of Plymouth.

Graduated in Zoology from Leeds University and then conducted PhD research at Aberdeen Universityinto the effect of environmental variation on ecologi-cal communities. Post-doctoral research followed at the Edinburgh School of Agriculture investigating the grazing behaviour and ecology of hill sheep. Tookup his position in 1983 and now has a number ofresearch projects on the behaviour and welfare of farmanimals.

Tim Felton, LLb (Hons) of the Middle Temple, Barrister at Law.

Present appointment: Senior Lecturer, Law and BusinessManagement, Faculty of Land, Food and Leisure, Seale-Hayne, University of Plymouth.

After reading law at Leeds University was called to theBar of the Middle Temple. Following a period of legalpractice he took up a career in practical farming and obtained a Diploma in Farm Management fromSeale-Hayne. Prior to taking his present position he wasshare farming a mixed dairy, arable and beef farm atTiverton, Devon of 185 hectares. Particular interestsinclude access to the countryside and employment lawissues in the rural environment.

David Fuller

Present appointment: Agriculture Colleges Liaison Officer,Royal Society for the Protection of Birds (RSPB), Sandy,Bedfordshire.

Has held the above post since its creation in 1997. Prior to working for the RSPB he spent over 33 years in theMinistry of Agriculture, Fisheries and Food (MAFF),administering many of the grant and subsidy schemesin East Anglia, Yorkshire and Lancashire. He also spentseveral years in Whitehall on policy work and in par-ticular the development of the Environmentally Sensi-tive Areas (ESAs) scheme. He is a keen ornithologist andlicenced bird ringer and carries out bird survey work onfarmland in his local area of Norfolk.

Michael P. Fuller, BSc, PhD.

Present appointment: Reader in Crop Improvement andActing Head of Department, Department of Agricultureand Food Studies, Faculty of Land, Food and Leisure,Seale-Hayne, University of Plymouth.

xiv Contributors

Graduated from Leicester University and then com-pleted a PhD at the Welsh Plant Breeding Station,Aberystwyth (now IGER) on Frost Resistance inGrasses. Previous appointments: Leeds University andSports Turf Research Institute; was visiting Professorto Angers University and is a Visiting Fellow of ExeterUniversity. Current research interests include ice nucle-ation and resistance to frost; growth and development ofcauliflowers and plant tissue culture.

Anita J. Jellings, BSc (Hons), PhD (Cantab).

Present appointment: Principal Lecturer, Faculty of Land,Food and Leisure, Seale-Hayne, University of Plymouth.

Read Applied Biology at the University of Bath andcompleted a PhD at the University of Cambridge beforetaking up a research fellowship at the University of Yorkinvestigating constraints on photosynthetic capacity.Current interests are centred on sustainable agriculturalsystems.

J.A. Kirk, BSc, PhD.

Present appointment: Principal Lecturer, Animal Produc-tion, Faculty of Land, Food and Leisure, Seale-Hayne,University of Plymouth.

Spent nine years farming before reading agriculturewith agricultural economics at the University College ofNorth Wales, Bangor. Postgraduate research on thegrowth and development of Welsh Mountain lambs ledto a PhD. Current research interests are the growth anddevelopment of animals and the improvement of meatquality.

Nicolas H. Lampkin, BSc (Hons), PhD.

Present appointment: Senior lecturer, Agricultural Eco-nomics, Institute of Rural Studies, University of Wales,Aberystwyth.

Graduated in agricultural economics from University ofWales, Aberystwyth, followed by PhD research on theeconomics of conversion to organic farming. Subse-quent research has focused on the financial performanceof organic farming and the role of organic farming inthe development of the Common Agricultural Policy.Currently co-ordinator of organic agriculture teachingand research at IRS and director of Organic Centre Wales.Author/editor of Organic Farming (Farming Press) andthe Organic Farm Management Handbook (UWA/EFRC).

A. Langley, BSc, MSc, HNC (Building), NDAgrE,MIAgrE.

Present appointment: Lecturer, SAC, Edinburgh.

After two years involvement with potato cultivationinvestigations at the National Institute of AgriculturalEngineering (Scottish Station), joined SAC in 1974 as aMechanisation Adviser, covering all aspects of mecha-nisation and specialising in cultivations, irrigation and crop storage. Focused on lecturing from 1990 andcovered a range of topics including crop storage andprocessing, field production equipment and waste man-agement. Also involved in organising and co-ordinatingnational machinery field demonstrations.

Tony G. Marangos, BSc (Hons), PhD, CBiol, MIBiol,RNutr.

Present appointment: Principal, Nutrition Solutions, Con-sultant Nutritionist, Burnham House, Fairfield Road,Shawford, Winchester, Hampshire, SO21 2DA

Educated at Reading and London Universities where hegained a PhD. Since then has held senior technical(nutrition) and marketing positions in the animal feedand supply industry. In 2000, after 25 years, began his ownindependent nutrition consultancy, Nutrition Solutions,and now advises national and international organisations.

D.J. Mattey, MIAgrE, MIOSH, MWeldI.

Present appointment: Consultant, International LabourOrganisation (ILO) Training Centre (Turin); and TheInternational Social Security Association (Geneva)Former HM Chief Inspector of Agriculture for HSE, andRegional Director (Midlands)

Robert E.L. Naylor, BSc (Hons), PhD, DSc, CBiol,FIBiol.

Present appointment: Partner in Trelareg Consultants specializing in crops and environment and Honorary Pro-fessor in Crop Science and Protection at the University ofAberdeen.

Spent 30 years at Aberdeen University teaching cropphysiology, weed science, seed science and rural bio-diversity and researching in specialist areas of thesetopics. On Board of Editors of Seed Science and Tech-nology and Crop Protection. Senior Editor for Journalof Agricultural Science. Edited a new edition of the WeedManagement Handbook for the British Crop ProtectionCouncil. Author of over 100 research papers and bookchapters.

R.M. Orr, BSc, PhD, MIBiol.

Present appointment: Senior Lecturer, Faculty of Land,Food and Leisure, Seale-Hayne, University of Plymouth.

Contributors xv

Read agriculture with animal science at the Universityof Aberdeen. Postgraduate research at Edinburgh University on appetite regulation led to a PhD. Teach-ing and research interests include food quality andnutrition.

H.E. Palmer

Formerly Farm Woodland Consultant, Scottish Agricul-tural College

Graduated in Agriculture from the University ofReading and completed an MSc in Forestry and its relation to land use at the Oxford Forestry Institute,University of Oxford. Wide experience in temperateforestry and farm woodland management, and hasworked as a woodlands adviser and consultant on farmsand estates in Scotland for 12 years. Member of theInstitute of Chartered Foresters.

Robert Parkinson, BSc (Hons), MSc, PhD, MILT.

Present appointment: Principal Lecturer, Soil Science,Faculty of Land, Food and Leisure, Seale-Hayne, Univer-sity of Plymouth.

Studied at Leeds and Reading Universities before takingup a post as Research Officer at Birkbeck College, University of London, working on soil water dynamicsand agricultural drainage. This research subsequentlyled to the award of PhD. Current research interests in-clude nutrient management in agricultural systems, bio-waste recycling and composting, and soil/hydrologicalcontrols on the reconstruction of species-rich grassland.

John I. Portsmouth, NCP, NDP, DipPoult, NDR,FPH.

Present appointment: Managing Director, JP Enterprises,Consultant Nutritionist, Tremaen, Maenporth Hill, Falmouth, Cornwall.

Began his own private consulting service in 1991 fol-lowing some 30 years in animal nutrition and animalhealth industry. Author of several books and many tech-nical articles on poultry nutrition and management.Specialist subjects are calcium metabolism in layinghens and micro-nutrient requirements of poultry. In1988 given a distinguished service award for services innutrition to the UK poultry industry.

David Sainsbury, MA, PhD, BSc, MRCVS, FRSH,CBiol, FIBiol.

Present appointment: Director of The Cambridge Centre for Animal Health and Welfare, 101 Madingley Road,Cambridge.

After a period of research and lecturing at the Depart-ment of Veterinary Hygiene, Royal Veterinary College,London, until 1993 worked at the Department of Clini-cal Veterinary Medicine, University of Cambridge inthe Division of Animal Health. Main interests have beenconcerned with the health and well-being of farm live-stock especially under intensively managed conditions.Author of five textbooks and some 130 scientific papers.

R.W. Slee, MA, PhD, Dip Land Economy.

Present appointment: Senior Lecturer Rural Economics,Department of Agriculture, University of Aberdeen.

Before moving to Aberdeen in 1989, spent over 10 yearsas a lecturer at Seal-Hayne Faculty, University ofPlymouth. Has written widely on rural economic change,including contributions to The Changing Countryside (eds J. Blunden and N. Curry, Croom Helm, 1985) and A Future for Our Countryside (eds J. Blunden and N.Curry, Blackwells, 1988) Author of Alternative FarmEnterprises (2nd edn, Farming Press, 1989). Currentresearch interests include agrienvironmental policyquestions and the economic impact of rural tourism.

Richard J. Soffe, MPhil, MCIM, M Inst M, ARAgS.

Present appointment: Senior Lecturer, Farm Business Mana-gement, Faculty of Land, Food and Leisure, Seale-Hayne,University of Plymouth.

Previous appointments have included a lectureship atSparsholt College, Winchester, and assistant farmmanager of a large estate in Hampshire. Research inter-ests include rural leadership management and market-ing. Course Director of the innovative and wellrespected Challenge of Rural Leadership at the Univer-sity of Plymouth. He was co-editor of the eighteenthedition, editor of the nineteenth edition of The Agricul-tural Notebook and is editor of the current edition.

Mark A.H. Stone BA (Hons), MSc (Econ), MCIPD.

Present appointment: University of Plymouth TeachingFellow and Principal Lecturer in People Management andElectronically Supported Open and Distance Learning.

After reading economics and politics at the Universityof Central Lancashire he went on to a masters degree inEmployment Studies at University College Cardiff. Hespent five years working in industry, during which timehe achieved membership status within the CharteredInstitute of Personnel and Development. He is involvedin People Management and Information Technologyteaching. He along with Dr Neil Witt formed the Communication and Learning Technology Group in

xvi Contributors

1997 to facilitate cross-faculty research and develop-ment in this area. He is currently leading an HEFCETDTL Project into Student Progression and Transfer.

M.A. Varley, BSc, PhD, MIBiol, CBiol.

Present appointment: Lecturer, Department of AnimalPhysiology and Nutrition, University of Leeds.

Before his present position, spent 4 years as a lecturerin animal science at Seale-Hayne Faculty, University ofPlymouth, and then moved to the Rowett ResearchInstitute where he was a Senior Scientific officer for 6 years. Research interests include reproductive phys-iology of the sow, neonatal immunology and animalbehaviour and welfare.

Martyn Warren, BSc, MSc, FIAgM, FRSA MILT.

Present appointment: Head of Land Use and Rural Management Department, Faculty of Land, Food andLeisure, Seale-Hayne, University of Plymouth.

Martyn Warren was educated at Newcastle and ReadingUniversities, and since 1994 has been Head of Land Useand Rural Management at the University of Plymouth,at its Seale-Hayne campus. He is author of FinancialManagement for Farmers and Rural Managers, in its 4th

edition after nearly 20 years in print, and is Editor ofFarm Management, the journal of the Institute of Agri-cultural Management. His main research interest is inthe role of information and communication technologiesin rural businesses and communities.

R.J. Wilkins, BSc, PhD, DSc, FIBiol, CBiol, FRAgrS.

Present appointment: Visiting Professor, Faculty of Land,Food and Leisure, Seale-Hayne, University of Plymouth;Visiting Professor, Department of Agriculture, Universityof Reading; Research Associate, Institute of Grassland andEnvironmental Research; Academician, Russian Academyof Agricultural Science.

After completing a PhD at University of New England,Australia, he was appointed to the Grassland ResearchInstitute, Hurley, in 1966. Held a series of posts in thatInstitute and its successor, the Institute of Grassland andEnvironmental Research, until retirement in 2000 frompositions including Institute Deputy Director, Head ofthe North Wyke Research Station, Devon, and Head ofthe Soils and Agroecology Department. Research inter-ests include the production and utilisation of grasslandand the environmental implications of grasslandfarming. Recipient of the RASE Research Medal and theBritish Grassland Society Award; President of BritishGrassland Society, 1986–7 and 1995–6.

Part 1

Crops

Introduction

Fertile soil is essential for sustained agricultural pro-duction, and has been exploited as a growing mediumsince animals and plants were domesticated. Cultivationof soils in order to create improved conditions for thesowing of crops can be dated back to at least 6000

(Goudie, 2000). Primitive farmers exploited the naturalbuildup of soil fertility by growing crops on land thatwas allowed to remain uncultivated for several yearsafter the previous crop was harvested. The inten-sification that followed the enclosure of land and theadoption of sequential cropping patterns in rotation has ultimately lead to greater demands being placed on the soil to supply the needs of the growing crop andto allow machinery access over much of the croppingyear.

Today, it is possible to grow some crops continuouslyon many soils, with the addition of fertilizers for plantnutrition and agrochemicals to control weeds, pests anddiseases. Over the centuries, crop yields have increaseddramatically, but our understanding of basic soil prop-erties has not always increased proportionately. Duringthe 1970s and 1980s evidence began to accumulatewhich indicated that soil fertility could decline underintensive agricultural use, mainly due to modificationsof physical properties that had not previously been con-sidered important. These changes were highlighted bythe Houghton Report on The Sustainable Use of Soil(Cm 3165, 1996). Soil erosion and enhanced leachinglosses of nutrients became more common on arable land,particularly under continuous winter cereal cropping.The challenge for farmers in the twenty-first century isto manage the soil to optimize yields while reducingunnecessary applications of fertilizers and other agro-chemicals. Managing soil in a sustainable manner can

1

Soil management and crop nutritionR.J. Parkinson

only be done with a full appreciation of soil physical,chemical and biological properties. In this chapter theprinciples of soil management and crop nutrition arediscussed.

Soil physical properties

Soil components

Soils are a complex mixture of mineral materials and organic matter that evolved over long periods oftime, in some cases thousands of years, as a result ofinteractions between parent materials, soil organismsand climate. Analysis and understanding of the physi-cal properties of soils and the way they respond when cultivated demands a detailed knowledge of thebasic soil components, and how these components are arranged. A fertile soil will contain a mixture ofmineral particles, organic matter and void spaces. Thesevoids may be occupied by air or water. In Fig. 1.1 theproportion of these components is given for a well-managed topsoil. The properties of most agriculturalsoils are dominated by weathered mineral material. Theprimary components comprise the texture of a soil.Some soils, such as peats, are composed mostly oforganic matter, in which case a texture description,based on the mineral fraction, is not appropriate. Thecombination of primary components with organicmatter forms the structure of soils. In this section the agricultural significance of texture and structure will be described, followed by other important soil physical properties, most of which are controlled bytexture or structure, and may be modified by agricul-tural practices.

3

Texture

Mineral particles in soil range widely in size from largestones to minute clay fragments. The proportion ofvarious sized particles has a major impact on soil physical, chemical and biological properties. Hence thedescription and characterization of soil texture is ofprimary importance to farmers and growers. Texturedetermination can be carried out approximately, butrapidly, by hand texturing in the field, or quantitativelyby laboratory analysis.

Field determinationHand texturing is a rapid but relatively crude method ofdetermining soil texture. A soil sample is moistened inthe fingers and rubbed in order to break down anynatural structures that exist. Coarse sand grains can beseen with the naked eye, and will make the sample feel‘gritty’. Fine sand and silt feel smooth, and can make thesample ‘slippery’. Clay binds soils together, and impartsa sticky feel. A description of these different size com-ponents is given in Table 1.1. More detailed descriptionof the determination of soil texture in the field can befound in Rowell (1994). Accurate hand texturingrequires technical skill and years of practice. Care mustbe taken when hand texturing, as some organic matterfractions feel slippery or soapy, similar to silt-sized par-ticles. Mineral soils with high organic matter levels canfeel finer in texture than is actually the case.

4 Part 1 Crops

Laboratory determinationLaboratory determination of texture or particle size dis-tribution by a process known as mechanical analysis istime consuming and is only carried out when detailedinformation is required. The procedure is based uponsieving and sedimentation in water after thorough disaggregation. MAFF (1986) describes a three-phaseprocess. Firstly, the soil sample is passed through a 2-mm sieve to remove stones. The analysis continues onthe fine earth fraction that passes through the sieve. Secondly, the soil is dispersed using hydrogen peroxide(which destroys organic matter) and sodium hydroxide(which separates individual particles). Finally, the sus-pension of soil and water is passed through a series ofsieves or a process of controlled sedimentation is carriedout, so that the precise proportion of different sizedmineral particles can be determined following dryweighing. The equivalent diameters of sand, silt andclay particles are shown in Table 1.1. This is the systememployed in the UK (see Rowell, 1994); in other coun-tries different size classes are used. The results of a par-ticle size analysis can be plotted on a graph that has beensubdivided into named texture classes (Fig. 1.2). A plotof percentage clay versus sand includes the silt compo-nent by difference, as the total must add up to 100%.For example, a soil containing 40% sand and 30% clay(and hence 30% silt) would be described as a clay loam.Having defined texture in a quantitative manner, it ispossible to predict more accurately the behaviour of thesoil in specific management situations.

Mineral materialsThe mineral components of soils derive primarily fromthe underlying parent material. Hence the character ofa soil will depend intimately on the type of rock fromwhich the soil has been formed. In simple terms, soilscomposed of coarse particles derived from rocks such as

Figure 1.1 Components of a well-managed topsoil,expressed on a volume basis.

Table 1.1 Range of particle size and properties formineral components of soil

Particle Diameter (mm) Characteristic properties

Gravel or >2.0 —stones

Coarse sand 0.2–2.0 Coarse builder’s sand or beach sand, particles clearly visible

Fine sand 0.06–0.2 Egg timer sand, just visible with naked eye

Silt 0.002–0.06 Flour, visible with hand lensClay <0.002 Plasticine or putty, visible

using electron microscope

sandstone and granite will produce coarse-textured,sandy soils. Mudstones and slates will produce fine-textured soils. The chemical character of a soil is alsorelated to the size and origin of the mineral components.Sand and silt-sized particles tend to be dominated byonly a few primary, rock-forming minerals, of whichquartz (silicon dioxide) is the most common. Quartz ischemically unreactive, and therefore plays no part innutrient retention by soils. In contrast, the clay fractionis dominated by clay minerals that have a varied chemi-cal composition and can be chemically and physicallyvery reactive. The potential for soil mineral particles to be physically and chemically reactive is partiallyexplained by the increasing surface area with decreasingparticle size. Table 1.2 shows the theoretical relationshipbetween particle diameter and surface area. Clay miner-als that have an expanding lattice structure, such asmontmorillonite, exhibit large surface areas that allowwater and nutrients to be retained, while sandy soilspossess a small surface area and tend to be chemicallyinert. Silt is intermediate in behaviour, and does not

Soil management and crop nutrition 5

have the large surface area possessed by clay, nor does ithave the often beneficial properties attributed to sand(see next section for more details). In practice, soils area mixture of all three mineral components, although onemay dominate and hence control soil behaviour in thefield.

Texture and soil managementTexture exerts a profound influence on soil manage-ment. Ultimately the choice and flexibility of cropping,

Figure 1.2 Soil texture classification as used in the UK (after Mullins, 1991).

Table 1.2 Relationship between particle size andsurface area

Surface area (m2 g-1)

Fine sand 0.1Silt 1.0Kaolinite clay 15–20Montmorillonite clay 700–800

as well as potential yields, all depend on soil texture.Detailed knowledge of texture variations within andbetween fields can help farmers to manage soils andinputs such as fertilizers and manures effectively. Themost important impacts of texture are given below.Many of these relationships are discussed further inother sections of this chapter, and in more detail byDavies et al. (1993).

Drainage statusClay-rich soils retain water against gravity and thereforehave high water contents during the winter months. Atsuch a time a clay loam might hold 50–60% water, incomparison with a sandy loam which may hold only25–30%. High water contents lead to reduced oxygenlevels and poor plant growth as well as risk of soildamage by vehicles and livestock (see ‘Agricultural landdrainage’ for more discussion of the consequences ofpoor drainage).

Water availability to plantsWhile finer textured soils retain more water than coarsersoils, much of it is held so strongly (by capillary forces)that crop plants cannot extract the water. Consequently,silt soils tend to have the highest reserves of plant-available water, and are the most drought tolerant.Sandy soils tend to be very droughty due to the smallvolume of stored water.

Workability and trafficabilityAccess to land in the critical autumn and spring monthscan be controlled by soil texture. Sandy, well-drainedsoils have few access restrictions, making them suitablefor the growth of a wide range of arable crops. Clay tex-tured soils are often difficult to cultivate, being too hardwhen dry and too soft when wet, and frequently cannotsupport the weight of agricultural machinery during thewinter. Cultivation operations must be timed very care-fully in order to minimize the risk of soil damage due tocultivation when too wet.

Nutrient retentionClay-sized particles retain nutrients very effectively,while sandy soils are often described as ‘hungry’, that isnutrients need to be added frequently but in small dosesin order to supply the requirements of crop plants (see‘Nutrient retention – cation and anion exchange’ forfurther discussion).

Soil texture describes the fine earth fraction (particles<2 mm). Stones and gravel are therefore excluded fromthis discussion, but quite clearly the presence of sig-nificant proportions of stone-sized material can have amajor influence on the growth of root crops and culti-

6 Part 1 Crops

vation operations. Many of the glacially derived soils ofnorthern Britain and the flinty chalk-derived soils ofsouthern Britain contain significant quantities of stonesthat limit the choice of crops. No hard and fast rule canbe given as to the amount of stones that will restrict cropchoice or influence cultivations, as stone type and dis-tribution are equally important. Soil organic matter caninfluence many of the properties listed above. Highlevels of organic matter can increase nutrient retention,increase water retention and make soils more workable(see ‘Soil organic matter and the carbon cycle’ forfurther discussion).

Structure

Formation of soil structureAs soils develop, mineral particles of sand, silt and clayare mixed with organic matter by soil organisms. Thismixing process creates stable aggregates and hence thesoil structures. Immature soils, such as might be foundon a river flood plain or sand dune, tend to show littleevidence of structure development, but most soils inagricultural use are well structured. Stable soil structuredevelops over long periods of time, as soils shrink andswell throughout the year, and as organic residues arecombined with mineral particles, often through theaction of soil organisms. A simplistic representation ofsoil structural components is given in Fig. 1.3, whichhelps to explain the important process of structure

Figure 1.3 Detailed representation of soil structure formation.

formation by the intermixing of soil mineral and organiccomponents. Certain soil characteristics aid structuredevelopment, namely organic matter (most important),clay, calcium carbonate and iron oxide (least important).A well-structured soil will display fine, even-sized struc-tures in the topsoil, with progressively larger aggregatesin the lower horizons of the soil. Figure 1.4 shows severalexample soil profiles broken down into structure types.

Importance of soil structureWell-structure soils display high porosity, low density,adequate water storage, free drainage and movement ofair within the soil profile. Plant roots are able to exploitthe whole soil volume, and will display a fine fibrous rootsystem. The fine stable aggregates near the soil surfacewill be resistant to collapse and therefore will allow freepassage of water and air through the surface layers.Roots will extract water and nutrients from within theaggregates, while excess water will drain away throughgaps between the aggregates, resulting in no prolongedperiods of waterlogging. The importance of structurecannot be underestimated in agricultural productionsystems, although assessment of soil structure is a diffi-cult task. Experience can be gained by frequent field soilexamination, particularly of soil profile pit faces thathave been allowed to weather naturally for a few days,after which time natural structure patterns becomemore visible.

Soil management and crop nutrition 7

Modification of soil structureMany agricultural practices modify soil structure andthe stability of soil aggregates; the creation of a seed-bed by ploughing and secondary cultivation, forexample, is direct modification of soil structuredesigned to suit the needs of the seed to be sown. Unliketexture, structure is not permanent. Soil aggregate stability can be changed by the cultivation and intensiveuse of soils. Serious structure breakdown can lead to soil compaction and soil erosion. Many soils in the UKhave suffered from problems relating to modification ofstructure by farming practices. The intensification ofagricultural activity in the latter part of the twentiethcentury has lead to some deterioration of soil structure.Most notably, arable cropping has caused organic matterlevels in some soils to decline, due to the removal of cropproducts, such as grain and straw. This reduction hasbecome critical for many sandy soils that tend to havenaturally low organic matter contents. Rates of organicmatter decline are variable, but soils with organic matterlevels of less than 5% are susceptible to compaction andsoil erosion.

Tilth is the term applied to the finely structuredsurface soil that has been worked down by cultivationimplements to create ideal conditions for the germina-tion and growth of crops. Unfortunately the repeatedcultivation of soils destroys natural, stable aggregates,resulting in weaker, finer structures that ultimately may

Figure 1.4 Some examples of soil structure types under good and poor management (after Davies et al., 1993).

collapse, hence leading to deterioration in the soil physical environment. It is therefore important that soilis not overcultivated, particularly for autumn-sowncrops where soils are exposed to the full force of thewinter weather with minimal protection from a growingcrop.

Soil structure can be improved by a number of agri-cultural practices: use of (long) grass leys in rotations,adding manures and other organic materials, addinglime, and the use of deep-rooting green manure crops.All these will help to stabilize the soil and maintain fertility.

Soil density

Figure 1.1 gave a typical breakdown of soil componentsfor a well-structured topsoil, which is made up of 50%solids and 50% pore space. As the structural propertiesof a soil change under agricultural management, so willthe density and pore space. As roots need to access waterand air held in these pore spaces, an understanding ofsuch changes is important.

Bulk densityBulk density is defined as the mass of oven-dry soil perunit volume, and depends on the densities of the con-stituent soil particles and, most importantly, how theseconstituents are packed together. Bulk density is usuallydetermined by extracting a soil core of known volume,oven drying at 105°C for 24 hours to remove the soilwater and then weighing the core. Values of bulk densityrange widely, as shown in Table 1.3. In general, rootaccess to soil pore spaces becomes difficult above a bulkdensity of 1.5–1.6 t m-3. Soil compaction results in anincrease in bulk density. In Fig. 1.5 some example bulkdensity profiles are given for a soil that has suffered

8 Part 1 Crops

surface compaction due to excessive animal grazing(Profile B) and a soil that has been compacted at ploughdepth due to repeated cultivation when soil conditionswere too wet, resulting in smearing and structuredestruction (Profile C).

Under good management, bulk density will tend toreduce until an equilibrium value is reached for a givensoil and cropping situation. Bulk density is simply anindication of the general status of the soil in physicalterms – to understand the effect on crop plants, it is necessary to describe pore space changes associated withincreases in bulk density.

Given bulk density, it is possible to calculate the massof soil in a given area. For example, assuming a bulkdensity of 1.0 t m-3, 1 ha of soil down to plough depth(200 mm) will have a mass of 2000 t. This represents aconsiderable mass of material that is moved every timethe soil is ploughed.

Particle densityIt is necessary to know the density of mineral particles(or when unweathered, solid rock) in order to calculatethe pore space in a soil. Particle density is defined as the mass per unit volume of mineral particles in soil,and does not include air spaces or water. Typical valuesfor particle density range from 2.50–2.70 t m-3. Forexample, a 1 m3 solid granite block weighs approximately2.65 t. A value of 2.65 t m-3 can be assumed for quartz-dominated mineral material in British soils. Organicmatter weighs considerably less than mineral material;values of 1.20–1.50 t m-3 are common for organic mate-rial. Given this difference, it is important to state the

Table 1.3 Bulk density and total pore space foragricultural soils

Bulk density Pore space Description(t m-3) (%)

0.5–0.8 >70 Loose, uncompactedtopsoils. Peats and organicsoils

�1.0 60–65 Permanent pasture,woodland soils, wellstructured

�1.5 45 Compacted, root penetrationdifficult

�2.0 25 Dense, no root growth

Figure 1.5 Example bulk density profiles. A Uncom-pacted soil; B heavily grazed soil showing surface com-paction; C cultivated soil showing compaction at ploughdepth.

organic matter content of a mineral soil when describ-ing pore space of soils.

Pore space

The size, shape and arrangement of soil aggregatescontrol not only the density but also the total porosityof a soil. When density changes as a result of soil management practices, porosity also changes. Total porespace is defined as the volume of pores expressed as afraction of the total soil volume, and is usually deter-mined by measuring the bulk density and assuming aparticle density of 2.65 t m-3.

% Pore space = [1 - (bulk density/particle density)]¥ 100

For the example given in Fig. 1.1, the total pore spaceis 50%. By substitution into the equation above, thisequates to a bulk density of 1.32 t m-3. A well-structuredtopsoil under permanent grass with a bulk density of1.0 t m-3 would have a total pore space of 62%; i.e.greater than half the soil is pore space. Increases in bulkdensity, which are associated with compaction, lead toreductions in pore space. Further examples of increas-ing bulk density and decreasing pore space are given inTable 1.3.

Total porosity does not provide any direct informa-tion about the size of the individual pores, or their func-tion. It is simply an expression of the total volume of asoil that may act as a store of air or water.

Water retention

Water occupies pore space in soil. The mechanisms bywhich water is held in soils, and then released to plantsor allowed to drain out of the profile, depend upon thesize of the pores. Pores can be classed as having variousfunctions according to their approximate diameter. Thelarger pores (termed macropores, >60 mm in diameter),for example drying cracks and earthworm burrows,allow excess water to drain out of the soil, as gravita-tional forces exceed the low capillary forces in such large pores. These voids are very important during the winter months when heavy textured soils are prone towaterlogging. Macropores tend to be the first to be lostwhen soils are compacted, hence leading to drainageproblems. In addition, these pores allow air to enter thesoil profile.

The smaller pores (<60 mm in diameter) store wateragainst gravity, due to capillary forces. These forces

Soil management and crop nutrition 9

become stronger the smaller the pore diameter. Eventu-ally a point is reached where the pore is so small thatplants cannot overcome the capillary force, and so anywater contained in that pore is considered to be unavail-able. Figure 1.6 displays the relationship between soiltexture and the quantity of water, expressed as a per-centage of the soil volume, that is available (held inmesopores between 0.2 and 60 mm in diameter) orunavailable (held in micropores <0.2 mm in diameter).These differences are of vital importance in croppingsystems; sandy soils may have only 5–10% availablewater, while at the other end of the range, silty soils maycontain more than 20% available water. In a dry summerthese differences may lead to crop failure or poor yieldson sandy soils, while heavier textured soils may be ableto maintain crop growth throughout a drought period.

As well as soil texture, the depth of a soil exerts a con-trolling influence over the total amount of water that isavailable to plants in the soil profile. The total availablewater that is stored in three example soils is given inTable 1.4. Soil A is coarse textured, but deep, while soils

Available water

Unavailable water

40

30

20

10

0Sandyloam

Sandyclayloam

Siltloam

Clayloam

Soil

wat

er c

onte

nt (%

)

Figure 1.6 Soil texture and available water capacity.

Table 1.4 Total plant-available water for three examplesoil types

Soil depth Available water (mm)(mm)

A B CSandy loam Silt loam Silt loam

(0.5 m deep)

0–200 40 80 80200–500 21 45 45500–1000 25 50 —

Total 86 175 125

B and C are fine textured, although soil C is only 0.5 mdeep, below which weathered rock is encountered. Theimpact that texture and soil depth have on the amountof water available to a plant is clearly seen in thisexample. The need for irrigation is dependent upon soiltexture and hence available water capacity, as well as theclimate and weather patterns in a given area.

Aeration

Soil air differs from the free atmosphere above the soilsurface in being enriched in carbon dioxide and some-times depleted in oxygen. A steady supply of oxygen is needed in soils for root respiration and to supportaerobic bacteria that carry out important functions inthe soil (see ‘Micro-organisms’). If the volume ofmacropores that allow drainage and aeration falls below10%, it is likely that there will be insufficient air for rootrespiration. Any practice that increases the volume ofair-filled pore space, such as soil loosening, is to beencouraged.

The consequences of poor aeration are that soil con-ditions change to the detriment of most crop plants,although the susceptibility to poor drainage varies fromcrop to crop. Breakdown of organic matter in anaerobicconditions can lead to the production of organic acidsand ethylene (C2H4), both of which inhibit root exten-sion. Nitrate may be denitrified to gaseous nitrous oxide(N2O) or dinitrogen (N2), and lost from the soil system.

Soil strength and cultivation

Careful management of soils will lead to continued highproductivity and few physical problems. However, it isnot always possible to cultivate under optimum condi-tions, and it is sometimes necessary to keep animals outon the land when high soil water contents will lead todamage occurring. The ability of a soil to resist defor-mation and damage depends upon the relationshipbetween water content and strength. This relationshipis unique for each soil type. In general, high soil watercontents lead to low strength, and hence greater sus-ceptibility to potential damage under applied load, forexample a tractor tyre or an animal hoof. Figure 1.7 dis-plays this general relationship for a well-structured soil.Optimum conditions for cultivation occur when the soilwill fail in a brittle, friable manner, as indicated by theasterisked arrow in Fig. 1.7.

Various problems can ensue if trafficking or animaltrampling (‘poaching’) occurs when the soil is at a highwater content such that deformation occurs in a plastic

10 Part 1 Crops

rather than a brittle manner. Some of these problems aredescribed below, and are discussed in more detail inDavies et al. (2001).

Cultivation pansA cultivation pan or plough layer will form followingrepeated cultivation under conditions that are too wet.Structural aggregates will be destroyed and a compactedsmeared layer will be formed (see Fig. 1.5). Such panscan occur in soils of any texture, but they are mostcommon in heavy textured soils that tend to have higherwater contents. The presence of a pan will lead to tem-porary waterlogging, even in better drained soils, as wellas higher bulk density, both of which will restrict rootdevelopment. Alleviation of the problem is usually bysoil loosening to below the depth of the pan under dryconditions, when brittle failure will occur.

Surface compactionSurface compaction may be due to machinery access orlivestock grazing of land that is too wet, resulting inplastic deformation, smearing and compaction of thesurface layer (see Fig. 1.5). In consequence, aeration will be restricted and surface run-off may occur. Giventhe opportunity, soils will naturally ‘restructure’ at thesurface, as a result of wetting and drying cycles thatoccur in all soils during the year. Removing the cause ofthe initial damage and allowing the soil to recover natu-rally is often all that is needed in such circumstances.

‘Puffy’ seedbedsOvercultivation of soils with high sand and silt contentscan lead to structure breakdown with very light, puffy

Figure 1.7 Relationship between soil strength and watercontent. A Soil aggregate; B whole soil, if well structured.

seedbeds. In such cases rolling may be necessary toensure good soil : seed contact following drilling. Failureto roll may result in uneven germination and poor establishment.

Machinery work days

Autumn and spring are the critical periods of the yearwhen soil damage is possible due to high water contentsat times when essential cultivations need to be carriedout. The concept of machinery work days describes thepotential cultivation opportunities that exist for givensoil types. These opportunities are measured during themain autumn and spring periods, and describe thoseoccasions when harvesting, tillage and drilling opera-tions can be conducted without risk of structuraldamage to the soil. Soil Survey regional bulletins (see‘Further reading’) contain a detailed description of thesystem employed in England and Wales. These descrip-tions form a basis for the discrimination of soils accord-ing to their flexibility of management at those criticaltimes of the year when access to the land is necessary inorder to be able to establish and then harvest arablecrops. Table 1.5 lists the machinery work days for threesoil types that occur in south-west England. Texture canbe seen to exert a strong influence on the number ofmachinery work days.

Soil erosion

Erosion is a natural process, but changes in soil prop-erties caused by intensive use of land can lead to accel-erated rates of soil loss. On a global scale, there are many examples of severe erosion, often associated withthe removal of protective vegetation cover in areas sub-jected to intense rainfall or high winds. The ‘Dust-Bowl’of the mid-west United States and severe gullying in thefootslopes of the Himalayas demonstrate the importanceof protecting vulnerable soils. In the UK, accelerated

Soil management and crop nutrition 11

rates of erosion are associated most frequently withwinter cereals, and to a lesser extent potatoes, sugar beetand oilseed rape (MAFF, 1999a). The Houghton Reporton The Sustainable Use of Soil (Cm 3165, 1996) notedthat up to 15% of arable land was at risk of erosion inany one year. Erosion not only results in the loss of valu-able topsoil, hence leading to potential yield reductions,but also causes significant pollution of water courses.Examples include sediment clogging gravel-bottomedrivers and nutrients (such as nitrogen and phosphorus)contributing to eutrophication. Erosion can also occurin grassland and moorland, mainly due to overgrazingwhich in upland areas has been found to contribute toaccelerated erosion.

Water erosion is the most common process of soil loss in the UK. First, rainsplash detaches soil particles.Various factors, summarized in Table 1.6, increase therisk of splash detachment occurring, such as soil aggre-gate stability and the soil surface protection or cover.Declining organic matter content and the increased areaof winter cereals are the main factors leading to watererosion in the UK. Losses in excess of 10 t ha-1 year-1 arebecoming more common. Strategies to control watererosion must be based on awareness of the problem.MAFF (1999a) details steps that should be taken; thekey elements are summarized in Table 1.6, with main-tenance of a rough seedbed with some stubble or othersurface cover being essential. The principles of Inte-grated Crop Management include many of these strat-egies. If these are unsuccessful, then it will be necessaryto revert to more grass in the rotation to allow the soilto recover naturally.

Erosion by wind is a problem in some eastern counties of England, notably the Fenland and the Vale of York, where vulnerable soils (peats and finesands/silts) are intensively cropped with sugar beet and potatoes. Fine seedbeds produced in the spring can be vulnerable to ‘windblow’ if dry weather followsdrilling. The establishment of windbreaks at fieldboundaries and use of non-cultivated strips within thefield can help to reduce the risk of soil and crop loss bywind erosion.

Table 1.5 Machinery work days for three example soils in south-west England (after Findlay et al., 1984)

Location Soil association and texture Machinery work days

Autumn Spring(1 Sept–31 Dec) (1 Mar–30 Apr)

Bridgnorth Loamy sand 86 29Frilsham Sandy clay loam 73 18Hodnet Silty loam/clay loam 32 3

Agricultural land drainage

Drainage needs and benefits

Why drain?The removal of excess water from soil by an artificialdrainage system can reduce soil management problemsand increase crop yields. The need for drainage in theUK arises either from heavy textured soils retainingexcess winter water, or from a high water table, forexample on a river floodplain. Heavy textured soils havean ability to retain nutrients and provide the waterneeded to satisfy the requirements of demanding crops,and hence are capable of producing high yields, particu-larly of cereals and grass. For example, the majority of10 t ha-1 wheat crops have been obtained from clay loamor clay textured soils, but only with efficient drainagesystems to remove excess winter water from the soil.The move in recent years to lower-input farmingsystems puts more emphasis on the need to ensure thatsoil physical conditions are optimal; in addition, theincreased variability in weather patterns associated withglobal warming is predicted to result in increased rain-fall in north-west Europe. Both these factors demon-strate the need to ensure that drainage systems functioneffectively.

Annual patterns of water loss and gain are very vari-able across the UK. As a result of higher rainfall andless sunshine, the soils in western Britain tend to posemore drainage problems than do those in the east. Thisdoes not mean that the arable soils in eastern Britain donot need drainage. The greater demands placed on soilsin arable cropping systems have lead to the need for

12 Part 1 Crops

increased flexibility of soil management in arable situa-tions, and hence many soils in eastern Britain have beendrained prior to being cropped intensively.

The first drainage systems date from Roman times,but it was only after the large-scale enclosure ofcommon lands in the eighteenth century that drainagebecame widespread. Techniques used varied widely,with most systems relying on stones, straw or otherbulky material to form and stabilize a channel to removeexcess water. The mechanical production of clay tiles inthe mid-nineteenth century led to dramatic improve-ments in the quality of drainpipes, and 100-year-oldsystems can still be found that are working well today.Estimates of areas drained in the nineteenth and earlytwentieth centuries suggest that up to 50% of the agri-cultural land in southern England was drained, all byhand. Mechanical drain installation became the norm bythe middle part of the twentieth century, when 50 000–100 000 ha were drained annually. The current rate of drainage is very much less, in the region of 10 000 hayear-1, due to the progressive reduction in grants fordrainage schemes and changes in the economics ofarable crop production in the 1980s and 1990s. In addi-tion, the conservation value of wetland habitats is nowmore appreciated than formerly, such that decisions to drain areas of land are no longer based solely on considerations of likely yield increases after drainage.The conservation value of species-rich grasslands, forexample, may depend on land remaining undrained. In some cases grants are now available to encouragefarmers to choose this option (e.g. Countryside Stewardship Scheme). The following discussion refersonly to land of little conservation value where drainageis needed to improve soil management and raise yields.

Table 1.6 Soil erosion: high-risk situations and control strategies

Factors leading to high risk of erosion Erosion control strategies

WaterSandy or fine silty texture Survey farm to identify vulnerable soils and sites where erosion has Valley features which concentrate run-off occurred in the pastSteep slopes (10%) Use field margins as buffer zones to detain run-offLong unbroken slopes Replace or add field boundaries, cultivate across slopeLow organic matter content Reduce frequency of cultivation, add organic manuresCompacted soils Adjust timing and intensity of cultivation to avoid compaction and leaveFine seedbeds seedbed roughLack of surface protection, e.g. stubble Leave stubble on surface; use non-inversion tillage

WindSilty texture or peaty soils Identify soils at riskFine seedbeds, particularly in late spring Avoid overcultivation, leave seedbed roughLarge, flat fields, few hedges Plant windbreaks, subdivide field, plant different crops

Drainage benefitsLowering soil water contents by drainage results inseveral changes in the crop rooting environment, all ofwhich are beneficial to the crop and soil management(Parkinson, 1988). These benefits are summarizedbelow.

Duration of waterloggingAutumn-sown crops rely on efficient water table controlto allow development of a root system. Failure to controlwaterlogging in the late autumn/winter/early springperiod will result in a stunted root system unable toexploit deeper-seated water and nutrient reserves duringthe following summer.

Soil workability and trafficabilityA reduction in water content will increase soil strength.Successful cultivation usually depends on the soil watercontent being below the lower plastic limit. Drainagelowers the water content of the topsoil, resulting inincreased cultivation opportunities during the criticalautumn and spring months. In grazing systems, the ben-efits from drainage will come from the increased numberof days that livestock can graze a sward without risk ofdamage to the soil structure.

Soil temperatureDrainage reduces soil specific heat capacity and there-fore can lead to higher temperatures. Castle et al. (1984)noted a 2°C elevation in spring soil temperatures on aclay soil in eastern England compared to when under-drained. Such an increase may lead to the more rapidgermination and emergence of spring-sown crops, andmay accelerate the development of winter-sown crops.It must be noted, however, that soil temperature doesnot always rise following drainage. In some field exper-iments no benefits have been found.

Efficiency of fertilizer useMore aerobic, warmer soil conditions will lead to moreefficient use of applied fertilizers, particularly nitrogentop dressings. Growing roots will absorb nutrients more readily and less will be lost by leaching or denitrification.

Arable crop yield benefitsThe benefit obtained as a result of installing a drainagesystem can be most easily measured in terms of cropyield, but the variability of the British climate often pro-duces a wide range of yield benefits from year to year.The yield advantage for most crops when comparingdrained and undrained soils is 10–25%. For example,average winter wheat yields can be increased by up to

Soil management and crop nutrition 13

1.0 t ha-1. In wet years, however, efficient drainage canmake the difference between crop failure and success.

Grassland/livestock benefitsIn the wetter regions of the UK, drainage is essential inorder to maximize grass utilization. The benefits can beexpressed in terms of dry matter yield or liveweightgain. For example, Tyson et al. (1992) reported thatdrainage of a clay soil in Devon resulted in a 5-daylonger growing season and an increase of 11% in beefcattle liveweight gain compared to the undrained soil.Drainage can alter the composition of the sward,increasing the proportion of productive grasses at theexpense of weed species, as well as increasing theresponse to nitrogen. In addition to liveweight gain,other benefits in a livestock production system caninclude a reduction in the incidence of liver fluke andfoot problems.

Drainage systems

Land can be drained by a system of ditches or pipes laidin the soil, or a combination of both. In the case of pipedrainage, additional short-lived measures, such as moledraining, can be carried out to increase the effectivenessof the drainage system. Both permanent and temporarysystems serve specific purposes and must be installedfollowing recommended guidelines (see Castle et al.,1984). The principles and some of the practical pointsare outlined here.

Open ditch drainageMost drainage systems find outlets into an open ditchthat usually leads to a larger watercourse. These ditchesare a vital component of a drainage system, and in somecases may be the sole method of water removal. Carefuldesign, construction and maintenance are therefore veryimportant. Ditches allow direct access for water, have alarge capacity to carry storm flows and are easily main-tained. However, they can hinder cultivations, they needfencing to exclude livestock and are susceptible to wallcollapse and blockage by vegetation.

Ditch specificationsDesign standards require that ditches must be of suffi-cient capacity for the catchment area drained. Theo-retical capacity can be calculated given catchment sizeand design rainfall rate (see, for example, Farr and Henderson, 1986, p. 131). Ditch width and depth willdepend upon soil and geology. The more stable the soil,the steeper the permissible slope. Some examples are givenin Table 1.7. Ditches dug in sandy materials must have

lower slopes than those in more stable finer-texturedsoil. Ditch floor gradient will in practice depend uponlocal topography. The gradient should be uniform andnot too steep (leading to channel erosion) or too shallow(leading to silting). A gradient of 0.5–1.0% is generallyconsidered to be adequate. Ditch sidewall collapse canbe minimized by guarding against water erosion andlivestock damage. Pipe drain outfalls should be fittedwith splash plates, ditches should be fenced and, in areaswith highly erodible soils, the sidewalls should begrassed down. Ditches must be piped under roads andfarm tracks. The pipes used, normally concrete, must belarge enough to carry anticipated peak flows. The designflow can be calculated (see MAFF, 1982), but theminimum recommended pipe diameter is 225 mm. Thissize of pipe will serve a catchment area of up to approx-imately 12 ha.

Pipe drainagePipe drains remove excess water without reducing thearea of land cropped or interfering with field operations.Installing a permanent system of clay tiles or plasticpipes to carry water below plough depth can solvedrainage problems efficiently and can be a worthwhileinvestment. It is particularly important that the princi-ples of operation, design, installation and maintenanceare all understood and followed, as a buried drainagescheme is difficult to inspect and maintain onceinstalled. The successful operation of a drainage pipesystem depends upon the flow of water from the soilsurface into the drain itself.

Water flow in soil depends upon the hydraulic con-ductivity. In a uniformly permeable material, such as asandy textured soil that is underdrained because of ahigh regional water table, as, for example, would befound on a river floodplain near sea level, water move-ment takes place through the whole soil (see Fig. 1.8a).In heavy textured soils with low rates of water move-ment, particularly in the subsoil, water tends to move in

14 Part 1 Crops

the topsoil and into the trench created by the drain-laying operation (see Fig. 1.8b). The bulk of the subsoilplays little part in the disposal of excess water. Rates ofwater movement depend on soil texture. Table 1.8 givesexamples of water flow rates, class descriptions and soiltypes that are used in drainage design (MAFF, 1982).Water flow rates in coarse textured soils can be 100 or1000 times more rapid than in clay soils, hence rein-forcing the need for drainage of many heavy soils.

Drain materialsSeveral choices need to be made when installing adrainage system. Drains may be clay or plastic. Clay tilesare normally cylindrical and 250 mm in length. Tiles aresupplied in a palletized form, which allows for easymechanical handling. The most common sizes are 75,100 or 150 mm internal diameter. Good-quality tiles areessential, as the failure of one tile can cause the failureof a complete lateral. The tiles are laid in the trench tobutt up to one another, but with a gap of 0.5–2.0 mmresulting from the uneven ends of successive pipes.Plastic pipes have largely superseded clay tiles. Theformer have several advantages, being easier and lighterto handle, and more suited for mechanical laying. Inaddition, disjointed drain runs are unlikely. However,the rough interior surface of a plastic pipe results in alower hydraulic carrying capacity, and the material isinherently weaker. Slots run the length of plastic pipesso water entry is relatively unrestricted. Standard jointsand junctions are available for both plastic and claypipes, so that laterals can be led into main drains. Plasticpipes are available prewrapped with a filter, which maybe necessary in silty soils to prevent blockage of the slotsby sediment.

Some form of gravel is placed over pipes in about halfof field drainage systems installed in England and Wales.As permeable fill may account for 50% of total installa-tion costs, it is important to justify its use. Permeable fillacts as a connector to allow water movement from thetopsoil to the drainpipe. In addition, backfill forms apermeable surround, to improve water entry to the pipe,and acts as a filter to prevent soil particles entering thedrain. Washed gravel with a mean particle diameter of20–50 mm is the most suitable permeable fill material.The use of permeable fill is not recommended formedium and coarse textured soils.

Where a pipe discharges directly into a ditch, the first1.5 m of the pipe should be sealed, rigid and frost resis-tant. The pipe should be able to discharge freely – there-fore the invert of the pipe should be at least 150 mmabove the normal ditch water level. Where the ditchsides are unstable the pipe should be supported by a con-

Table 1.7 Ditch channel side slope ratios (horizontal :vertical) and soil type (after Castle et al., 1984)

Channel side slope ratio

Channel Channel<1.3 m deep >1.3 m deep

Fen peat Vertical 0.5 : 1Heavy clay 0.5 : 1 .1 : 1Clay loam or silt loam 1 : 1 1.5 : 1Sandy loam 1.5 : 1 2 : 1Sand 2 : 1 3 : 1