issn: 0889-3144 rapra review reports rapra review …€¦ · rapra review reports a rapra review...

Expert overviews covering the science and technology of rubber and plastics

ISSN: 0889-3144

Volume 15, Number 2, 2004

R.P. Brown

Polymers in Agriculture and Horticulture

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RAPRA REVIEW REPORTS

A Rapra Review Report comprises three sections, as follows:

1. A commissioned expert review, discussing a key topic of current interest, and referring to the References andAbstracts section. Reference numbers in brackets refer to item numbers from the References and Abstractssection. Where it has been necessary for completeness to cite sources outside the scope of the Rapra Abstractsdatabase, these are listed at the end of the review, and cited in the text as a.1, a.2, etc.

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Item 1Macromolecules

33, No.6, 21st March 2000, p.2171-83EFFECT OF THERMAL HISTORY ON THE RHEOLOGICALBEHAVIOR OF THERMOPLASTIC POLYURETHANESPil Joong Yoon; Chang Dae HanAkron,University

The effect of thermal history on the rheological behaviour of ester- andether-based commercial thermoplastic PUs (Estane 5701, 5707 and 5714from B.F.Goodrich) was investigated. It was found that the injectionmoulding temp. used for specimen preparation had a marked effect on thevariations of dynamic storage and loss moduli of specimens with timeobserved during isothermal annealing. Analysis of FTIR spectra indicatedthat variations in hydrogen bonding with time during isothermal annealingvery much resembled variations of dynamic storage modulus with timeduring isothermal annealing. Isochronal dynamic temp. sweep experimentsindicated that the thermoplastic PUs exhibited a hysteresis effect in theheating and cooling processes. It was concluded that the microphaseseparation transition or order-disorder transition in thermoplastic PUs couldnot be determined from the isochronal dynamic temp. sweep experiment.The plots of log dynamic storage modulus versus log loss modulus variedwith temp. over the entire range of temps. (110-190C) investigated. 57 refs.

GOODRICH B.F.USA

Accession no.771897

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Previous Titles Still AvailableVolume 1Report 3 Advanced Composites, D.K. Thomas, RAE, Farnborough.

Report 4 Liquid Crystal Polymers, M.K. Cox, ICI, Wilton.

Report 5 CAD/CAM in the Polymer Industry, N.W. Sandlandand M.J. Sebborn, Cambridge Applied Technology.

Report 8 Engineering Thermoplastics, I.T. Barrie, Consultant.

Report 11 Communications Applications of Polymers,R. Spratling, British Telecom.

Report 12 Process Control in the Plastics Industry,R.F. Evans, Engelmann & Buckham Ancillaries.

Volume 2Report 13 Injection Moulding of Engineering Thermoplastics,

A.F. Whelan, London School of Polymer Technology.

Report 14 Polymers and Their Uses in the Sports and LeisureIndustries, A.L. Cox and R.P. Brown, RapraTechnology Ltd.

Report 15 Polyurethane, Materials, Processing andApplications, G. Woods, Consultant.

Report 16 Polyetheretherketone, D.J. Kemmish, ICI, Wilton.

Report 17 Extrusion, G.M. Gale, Rapra Technology Ltd.

Report 18 Agricultural and Horticultural Applications ofPolymers, J.C. Garnaud, International Committee forPlastics in Agriculture.

Report 19 Recycling and Disposal of Plastics Packaging,R.C. Fox, Plas/Tech Ltd.

Report 20 Pultrusion, L. Hollaway, University of Surrey.

Report 21 Materials Handling in the Polymer Industry,H. Hardy, Chronos Richardson Ltd.

Report 22 Electronics Applications of Polymers, M.T.Goosey,Plessey Research (Caswell) Ltd.

Report 23 Offshore Applications of Polymers, J.W.Brockbank,Avon Industrial Polymers Ltd.

Report 24 Recent Developments in Materials for FoodPackaging, R.A. Roberts, Pira Packaging Division.

Volume 3Report 25 Foams and Blowing Agents, J.M. Methven, Cellcom

Technology Associates.

Report 26 Polymers and Structural Composites in CivilEngineering, L. Hollaway, University of Surrey.

Report 27 Injection Moulding of Rubber, M.A. Wheelans,Consultant.

Report 28 Adhesives for Structural and EngineeringApplications, C. O’Reilly, Loctite (Ireland) Ltd.

Report 29 Polymers in Marine Applications, C.F.Britton,Corrosion Monitoring Consultancy.

Report 30 Non-destructive Testing of Polymers, W.N. Reynolds,National NDT Centre, Harwell.

Report 31 Silicone Rubbers, B.R. Trego and H.W.Winnan,Dow Corning Ltd.

Report 32 Fluoroelastomers - Properties and Applications,D. Cook and M. Lynn, 3M United Kingdom Plc and3M Belgium SA.

Report 33 Polyamides, R.S. Williams and T. Daniels,T & N Technology Ltd. and BIP Chemicals Ltd.

Report 34 Extrusion of Rubber, J.G.A. Lovegrove, NovaPetrochemicals Inc.

Report 35 Polymers in Household Electrical Goods, D.Alvey,Hotpoint Ltd.

Report 36 Developments in Additives to Meet Health andEnvironmental Concerns, M.J. Forrest, RapraTechnology Ltd.

Volume 4Report 37 Polymers in Aerospace Applications, W.W. Wright,

University of Surrey.

Report 39 Polymers in Chemically Resistant Applications,D. Cattell, Cattell Consultancy Services.

Report 41 Failure of Plastics, S. Turner, Queen Mary College.

Report 42 Polycarbonates, R. Pakull, U. Grigo, D. Freitag, BayerAG.

Report 43 Polymeric Materials from Renewable Resources,J.M. Methven, UMIST.

Report 44 Flammability and Flame Retardants in Plastics,J. Green, FMC Corp.

Report 45 Composites - Tooling and Component Processing,N.G. Brain, Tooltex.

Report 46 Quality Today in Polymer Processing, S.H. Coulson,J.A. Cousans, Exxon Chemical International Marketing.

Report 47 Chemical Analysis of Polymers, G. Lawson, LeicesterPolytechnic.

Volume 5Report 49 Blends and Alloys of Engineering Thermoplastics,

H.T. van de Grampel, General Electric Plastics BV.

Report 50 Automotive Applications of Polymers II,A.N.A. Elliott, Consultant.

Report 51 Biomedical Applications of Polymers, C.G. Gebelein,Youngstown State University / Florida Atlantic University.

Report 52 Polymer Supported Chemical Reactions, P. Hodge,University of Manchester.

Report 53 Weathering of Polymers, S.M. Halliwell, BuildingResearch Establishment.

Report 54 Health and Safety in the Rubber Industry, A.R. Nutt,Arnold Nutt & Co. and J. Wade.

Report 55 Computer Modelling of Polymer Processing,E. Andreassen, Å. Larsen and E.L. Hinrichsen, Senter forIndustriforskning, Norway.

Report 56 Plastics in High Temperature Applications,J. Maxwell, Consultant.

Report 57 Joining of Plastics, K.W. Allen, City University.

Report 58 Physical Testing of Rubber, R.P. Brown, RapraTechnology Ltd.

Report 59 Polyimides - Materials, Processing and Applications,A.J. Kirby, Du Pont (U.K.) Ltd.

Report 60 Physical Testing of Thermoplastics, S.W. Hawley,Rapra Technology Ltd.

Volume 6Report 61 Food Contact Polymeric Materials, J.A. Sidwell,

Rapra Technology Ltd.

Report 62 Coextrusion, D. Djordjevic, Klöckner ER-WE-PA GmbH.

Report 63 Conductive Polymers II, R.H. Friend, University ofCambridge, Cavendish Laboratory.

Report 64 Designing with Plastics, P.R. Lewis, The Open University.

Report 65 Decorating and Coating of Plastics, P.J. Robinson,International Automotive Design.

Report 66 Reinforced Thermoplastics - Composition, Processingand Applications, P.G. Kelleher, New Jersey PolymerExtension Center at Stevens Institute of Technology.

Report 67 Plastics in Thermal and Acoustic Building Insulation,V.L. Kefford, MRM Engineering Consultancy.

Report 68 Cure Assessment by Physical and ChemicalTechniques, B.G. Willoughby, Rapra Technology Ltd.

Report 69 Toxicity of Plastics and Rubber in Fire, P.J. Fardell,Building Research Establishment, Fire Research Station.

Report 70 Acrylonitrile-Butadiene-Styrene Polymers,M.E. Adams, D.J. Buckley, R.E. Colborn, W.P. Englandand D.N. Schissel, General Electric Corporate Researchand Development Center.

Report 71 Rotational Moulding, R.J. Crawford, The Queen’sUniversity of Belfast.

Report 72 Advances in Injection Moulding, C.A. Maier,Econology Ltd.

Volume 7

Report 73 Reactive Processing of Polymers, M.W.R. Brown,P.D. Coates and A.F. Johnson, IRC in Polymer Scienceand Technology, University of Bradford.

Report 74 Speciality Rubbers, J.A. Brydson.

Report 75 Plastics and the Environment, I. Boustead, BousteadConsulting Ltd.

Report 76 Polymeric Precursors for Ceramic Materials,R.C.P. Cubbon.

Report 77 Advances in Tyre Mechanics, R.A. Ridha, M. Theves,Goodyear Technical Center.

Report 78 PVC - Compounds, Processing and Applications,J.Leadbitter, J.A. Day, J.L. Ryan, Hydro Polymers Ltd.

Report 79 Rubber Compounding Ingredients - Need, Theoryand Innovation, Part I: Vulcanising Systems,Antidegradants and Particulate Fillers for GeneralPurpose Rubbers, C. Hepburn, University of Ulster.

Report 80 Anti-Corrosion Polymers: PEEK, PEKK and OtherPolyaryls, G. Pritchard, Kingston University.

Report 81 Thermoplastic Elastomers - Properties and Applications,J.A. Brydson.

Report 82 Advances in Blow Moulding Process Optimization,Andres Garcia-Rejon,Industrial Materials Institute,National Research Council Canada.

Report 83 Molecular Weight Characterisation of SyntheticPolymers, S.R. Holding and E. Meehan, RapraTechnology Ltd. and Polymer Laboratories Ltd.

Report 84 Rheology and its Role in Plastics Processing,P. Prentice, The Nottingham Trent University.

Volume 8

Report 85 Ring Opening Polymerisation, N. Spassky, UniversitéPierre et Marie Curie.

Report 86 High Performance Engineering Plastics,D.J. Kemmish, Victrex Ltd.

Report 87 Rubber to Metal Bonding, B.G. Crowther, RapraTechnology Ltd.

Report 88 Plasticisers - Selection, Applications and Implications,A.S. Wilson.

Report 89 Polymer Membranes - Materials, Structures andSeparation Performance, T. deV. Naylor, The SmartChemical Company.

Report 90 Rubber Mixing, P.R. Wood.

Report 91 Recent Developments in Epoxy Resins, I. Hamerton,University of Surrey.

Report 92 Continuous Vulcanisation of Elastomer Profiles,A. Hill, Meteor Gummiwerke.

Report 93 Advances in Thermoforming, J.L. Throne, SherwoodTechnologies Inc.

Report 94 Compressive Behaviour of Composites,C. Soutis, Imperial College of Science, Technologyand Medicine.

Report 95 Thermal Analysis of Polymers, M. P. Sepe, Dickten &Masch Manufacturing Co.

Report 96 Polymeric Seals and Sealing Technology, J.A. Hickman,St Clair (Polymers) Ltd.

Volume 9

Report 97 Rubber Compounding Ingredients - Need, Theoryand Innovation, Part II: Processing, Bonding, FireRetardants, C. Hepburn, University of Ulster.

Report 98 Advances in Biodegradable Polymers, G.F. Moore &S.M. Saunders, Rapra Technology Ltd.

Report 99 Recycling of Rubber, H.J. Manuel and W. Dierkes,Vredestein Rubber Recycling B.V.

Report 100 Photoinitiated Polymerisation - Theory andApplications, J.P. Fouassier, Ecole Nationale Supérieurede Chimie, Mulhouse.

Report 101 Solvent-Free Adhesives, T.E. Rolando, H.B. FullerCompany.

Report 102 Plastics in Pressure Pipes, T. Stafford, RapraTechnology Ltd.

Report 103 Gas Assisted Moulding, T.C. Pearson, Gas Injection Ltd.

Report 104 Plastics Profile Extrusion, R.J. Kent, TangramTechnology Ltd.

Report 105 Rubber Extrusion Theory and Development,B.G. Crowther.

Report 106 Properties and Applications of ElastomericPolysulfides, T.C.P. Lee, Oxford Brookes University.

Report 107 High Performance Polymer Fibres, P.R. Lewis,The Open University.

Report 108 Chemical Characterisation of Polyurethanes,M.J. Forrest, Rapra Technology Ltd.

Volume 10

Report 109 Rubber Injection Moulding - A Practical Guide,J.A. Lindsay.

Report 110 Long-Term and Accelerated Ageing Tests on Rubbers,R.P. Brown, M.J. Forrest and G. Soulagnet,Rapra Technology Ltd.

Report 111 Polymer Product Failure, P.R. Lewis,The Open University.

Report 112 Polystyrene - Synthesis, Production and Applications,J.R. Wünsch, BASF AG.

Report 113 Rubber-Modified Thermoplastics, H. Keskkula,University of Texas at Austin.

Report 114 Developments in Polyacetylene - Nanopolyacetylene,V.M. Kobryanskii, Russian Academy of Sciences.

Report 115 Metallocene-Catalysed Polymerisation, W. Kaminsky,University of Hamburg.

Report 116 Compounding in Co-rotating Twin-Screw Extruders,Y. Wang, Tunghai University.

Report 117 Rapid Prototyping, Tooling and Manufacturing,R.J.M. Hague and P.E. Reeves, Edward MackenzieConsulting.

Report 118 Liquid Crystal Polymers - Synthesis, Properties andApplications, D. Coates, CRL Ltd.

Report 119 Rubbers in Contact with Food, M.J. Forrest andJ.A. Sidwell, Rapra Technology Ltd.

Report 120 Electronics Applications of Polymers II, M.T. Goosey,Shipley Ronal.

Volume 11

Report 121 Polyamides as Engineering Thermoplastic Materials,I.B. Page, BIP Ltd.

Report 122 Flexible Packaging - Adhesives, Coatings andProcesses, T.E. Rolando, H.B. Fuller Company.

Report 123 Polymer Blends, L.A. Utracki, National ResearchCouncil Canada.

Report 124 Sorting of Waste Plastics for Recycling, R.D. Pascoe,University of Exeter.

Report 125 Structural Studies of Polymers by Solution NMR,H.N. Cheng, Hercules Incorporated.

Report 126 Composites for Automotive Applications, C.D. Rudd,University of Nottingham.

Report 127 Polymers in Medical Applications, B.J. Lambert andF.-W. Tang, Guidant Corp., and W.J. Rogers, Consultant.

Report 128 Solid State NMR of Polymers, P.A. Mirau,Lucent Technologies.

Report 129 Failure of Polymer Products Due to Photo-oxidation,D.C. Wright.

Report 130 Failure of Polymer Products Due to Chemical Attack,D.C. Wright.

Report 131 Failure of Polymer Products Due to Thermo-oxidation,D.C. Wright.

Report 132 Stabilisers for Polyolefins, C. Kröhnke and F. Werner,Clariant Huningue SA.

Volume 12

Report 133 Advances in Automation for Plastics InjectionMoulding, J. Mallon, Yushin Inc.

Report 134 Infrared and Raman Spectroscopy of Polymers,J.L. Koenig, Case Western Reserve University.

Report 135 Polymers in Sport and Leisure, R.P. Brown.

Report 136 Radiation Curing, R.S. Davidson, DavRad Services.

Report 137 Silicone Elastomers, P. Jerschow, Wacker-Chemie GmbH.

Report 138 Health and Safety in the Rubber Industry, N. Chaiear,Khon Kaen University.

Report 139 Rubber Analysis - Polymers, Compounds andProducts, M.J. Forrest, Rapra Technology Ltd.

Report 140 Tyre Compounding for Improved Performance,M.S. Evans, Kumho European Technical Centre.

Report 141 Particulate Fillers for Polymers, Professor R.N.Rothon, Rothon Consultants and ManchesterMetropolitan University.

Report 142 Blowing Agents for Polyurethane Foams, S.N. Singh,Huntsman Polyurethanes.

Report 143 Adhesion and Bonding to Polyolefins, D.M. Brewisand I. Mathieson, Institute of Surface Science &Technology, Loughborough University.

Report 144 Rubber Curing Systems, R.N. Datta, Flexsys BV.

Volume 13

Report 145 Multi-Material Injection Moulding, V. Goodship andJ.C. Love, The University of Warwick.

Report 146 In-Mould Decoration of Plastics, J.C. Love andV. Goodship, The University of Warwick

Report 147 Rubber Product Failure, Roger P. Brown

Report 148 Plastics Waste – Feedstock Recycling, ChemicalRecycling and Incineration, A. Tukker, TNO

Report 149 Analysis of Plastics, Martin J. Forrest, RapraTechnology Ltd.

Report 150 Mould Sticking, Fouling and Cleaning, D.E. Packham,Materials Research Centre, University of Bath

Report 151 Rigid Plastics Packaging - Materials, Processes andApplications, F. Hannay, Nampak Group Research &Development

Report 152 Natural and Wood Fibre Reinforcement in Polymers,A.K. Bledzki, V.E. Sperber and O. Faruk, University ofKassel

Report 153 Polymers in Telecommunication Devices, G.H. Cross,University of Durham

Report 154 Polymers in Building and Construction, S.M.Halliwell, BRE

Report 155 Styrenic Copolymers, Andreas Chrisochoou andDaniel Dufour, Bayer AG

Report 156 Life Cycle Assessment and Environmental Impact ofPolymeric Products, T.J. O’Neill, PolymeronConsultancy Network

Volume 14

Report 157 Developments in Colorants for Plastics,Ian N. Christensen

Report 158 Geosynthetics, D.I. Cook

Report 159 Biopolymers, R.M. Johnson, L.Y. Mwaikambo andN. Tucker, Warwick Manufacturing Group

Report 160 Emulsion Polymerisation and Applications ofLatex, C.D. Anderson and E.S. Daniels, EmulsionPolymers Institute

Report 161 Emissions from Plastics, C. Henneuse-Boxus andT. Pacaray, Certech

Report 162 Analysis of Thermoset Materials, Precursors andProducts, Martin J. Forrest, Rapra Technology Limited

Report 163 Polymer/Layered Silicate Nanocomposites, MasamiOkamoto, Toyota Technological Institute

Report 164 Cure Monitoring for Composites and Adhesives,David R. Mulligan, NPL

Report 165 Polymer Enhancement of Technical Textiles,Roy W. Buckley

Report 166 Developments in Thermoplastic Elastomers,K.E. Kear

Report 167 Polyolefin Foams, N.J. Mills, Metallurgy and Materials,University of Birmingham

Report 168 Plastic Flame Retardants: Technology and CurrentDevelopments, J. Innes and A. Innes

Report 169 Engineering and Structural Adhesives, David J. Dunn,FLD Enterprises Inc.

ISBN 1-85957-460-2

Polymers in Agricultureand Horticulture

Roger Brown


1

Contents

1. Introduction .............................................................................................................................................. 3

2. The Market ............................................................................................................................................... 3

3. Materials ................................................................................................................................................... 6

4. Crop Protection ........................................................................................................................................ 7

4.1 Greenhouses/Large Tunnels ............................................................................................................ 7

4.2 Low Tunnels ................................................................................................................................... 9

4.3 Direct Covers ................................................................................................................................ 10

4.4 Windbreaks ................................................................................................................................... 10

4.5 Shading ......................................................................................................................................... 10

4.6 Protection Against Pests ................................................................................................................11

5. Soil Conditioning ....................................................................................................................................11

5.1 Mulching ........................................................................................................................................11

5.2 Soil Improvement ......................................................................................................................... 12

6. Water Management ............................................................................................................................... 12

6.1 Collection, Storage and Transport of Water ................................................................................. 13

6.2 Irrigation ....................................................................................................................................... 13

6.3 Water Holding ............................................................................................................................... 14

6.4 Drainage ........................................................................................................................................ 14

7. Harvesting and Crop Storage ............................................................................................................... 14

8. Buildings ................................................................................................................................................. 15

9. Machinery and Equipment ................................................................................................................... 15

10. Containers and Packaging .................................................................................................................... 16

11. Miscellaneous Applications ................................................................................................................... 17

11.1 Identification Tags ........................................................................................................................ 17

11.2 Clothing and Footwear ................................................................................................................. 17

11.3 Controlled Release of Fertilisers, etc. ........................................................................................... 17

11.4 Garden Ponds ................................................................................................................................ 17

11.5 Greenhouse Sundries .................................................................................................................... 17

11.6 Labels ............................................................................................................................................ 18

11.7 Seed Coatings ............................................................................................................................... 18

11.8 Soil Less Cultivation ..................................................................................................................... 18

11.9 Ties and Grafting Bands ............................................................................................................... 18

11.10 Twine ............................................................................................................................................. 18

11.11 Others ............................................................................................................................................ 18


2

The views and opinions expressed by authors in Rapra Review Reports do not necessarily reflect those ofRapra Technology Limited or the editor. The series is published on the basis that no responsibility orliability of any nature shall attach to Rapra Technology Limited arising out of or in connection with anyutilisation in any form of any material contained therein.

12. Standards and Testing ........................................................................................................................... 18

13. Disposal and Recycling .......................................................................................................................... 19

Additional References ................................................................................................................................... 20

Abbreviations and Acronyms ....................................................................................................................... 20

Abstracts from the Polymer Library Database .......................................................................................... 21

Subject Index ................................................................................................................................................. 75

Company Index .............................................................................................................................................. 89


3

1 Introduction

The origins of polymers in horticulture are said to datefrom 1948 (113) when Professor E.M. Emmert had nomoney to buy a glasshouse and had the idea of coveringa wooden structure with cellulose paper, which hereplaced with polyethylene film when it becameavailable. This inventive gentleman is also creditedwith inventing plastic mulch and row covers.

The use of polymers in agriculture and horticulture ona significant scale started as far back as the early 1950swhen low density polyethylene (LDPE) was used intrials to replace paper for mulching vegetables. Theoptical properties of plastic films were also investigatedas a replacement for glass with the cladding of framesand greenhouses in mind. The plastics industry itselfwas then young and, being hungry for more outlets,was quick to co-operate with agricultural andhorticultural organisations to support research and fieldtrials and to generally promote plastics to the farmer.

It must have been clear that there was tremendouspotential for polymers in agriculture and horticulturewhich warranted considerable resources to be appliedto developing suitable materials and demonstrating theirperformance. The largest scale application was coveringsfor greenhouse structures but another example is thedevelopment of technology that led to the first dripirrigation system in the open field in Israel in the late1950s. The potential was significant enough that the termplasticulture was coined and in 1964 the InternationalCommittee for Plastics in Agriculture (CIPA) wasformed. Plasticulture is not now found in all dictionariesbut the subject is very much alive and there is still theimportant journal Plasticulture. This publication hasdefined plasticulture as a set of advanced technologieswhich take form as the multiple uses of plastics inagriculture. The CIPA, which interestingly was institutedfor 99 years, is still alive and information can be foundat www.plasticulture.com.

In 1973 Keveren (282) wrote a staggeringlycomprehensive review of plastics in horticulturalstructures. By that time, the use of polyethylene andother polymer tunnels was well established incommercial horticulture in a number of countries.Interestingly, a gardening book for amateurs publishedat that time makes only a passing reference to plasticwith no distinction between different materials andgives the impression that the author did not approve ofsuch things. At grass roots, amateurs were notcompletely dismissive as in 1978 Keveren and thepresent author gave a talk to a local gardening clubwith the title Plastics in Horticulture.

Farmers and gardeners are sometimes considered to berather cautious and traditional so that even in the 1970sthere would have been many people, amateur andprofessional, still highly suspicious of ‘new fangled’plastics getting near their plants or animals. Now wewould be surprised to see a commercial tunnel coveredin glass, clay pots are museum pieces and large blackpolyethylene covered bales are commonly seen in fields.

A cautious approach to adopting polymers waswarranted. Early experiments with film coveredstructures were not successful and the first polyethylenefilms lasted not much more than a year in the UK.Generally, there was a rush into making all manner ofgoods from plastics with scant regard for whether thechosen material or the design was really suitable, whichled to plastics being associated with cheap and nastyproducts – poor substitutes for the real thing. Earlypolystyrene seed trays demonstrated that horticulturedid not escape this problem.

Subsequently, the great success of polymers inagricultural and horticultural applications reflects thetrend in many industries where traditional materialshave been increasingly replaced on cost, and perhapsmore importantly, on performance grounds. Wood,natural fibres, glass, ceramic and metal have all beenreplaced in products as diverse as working clothes, partsof tools, machinery components, plant containers,packaging and mulches. However, it has not only beena matter of polymers replacing traditional materialsbecause use of polymers has allowed the introductionof many new products such as drip irrigation and directcovering materials. Certainly, use of polymers has madean enormous contribution to increased yields, earlierproduction and efficiency.

Polymers now pervade all aspects of agriculture andhorticulture and the range and variety of products isenormous. The object of this review is to give an outlineof the roles polymers play in this spectrum ofapplications. Classifying the range of products intodifferent groups is not easy so that the section headingsused here are rather inexact. For example, mulchingcould be water management or soil conditioning andall crop protection conditions soil.

2 The Market

It has been made clear in the introduction that themarket for polymers in the agriculture and horticultureindustry is extremely diverse; it started in the early days


4

of the plastics industry and grew very rapidly to becomeof major importance. A history can be found inPlasticulture (113). Although there is vast diversity,the mainstream of plasticulture is said to be thetechnologies around the greenhouse industries and thevolume statistics confirm this.

Reliable and systematic figures for the size of thesector are somewhat scarce. As indication of growth,Keveren (282) quoted figures for Japan (the largestuser of plastics in agriculture at the time) as 8,000tons excluding irrigation, drainage and packagingapplications growing to 37,000 tons in 1965 and110,000 tons in 1970. Another estimate gave 254,000tons including tubes and packaging of which 164 tonswas polyvinyl chloride (PVC), 74,000 polyethyleneand 14,000 polypropylene. The split of polymersillustrates the greater use of PVC coverings in Japancompared to most other countries. In the UK in 1956the split was 60% polyethylene and 40% PVC andother polymers.

A previous review report (281) published in 1988 givesa global consumption of plastics in agricultural use asapproaching 3 million tonnes. PVC film was said toaccount for 200,000 tonnes and polyethylene between680,000 tonnes and 845,000 tonnes excludingpackaging. Other uses were much smaller but far frominsignificant with France requiring 35,000 tonnes forfertiliser bags, Algeria using 6,000 tonnes for packagingfresh produce and 20,000 tonnes of polypropylene (PP)twine was consumed by French farmers. The variationof estimates of consumption is such that the total marketfor plastics in the agricultural sector was reported in1994 to be about 2 million tons (13). About 50% ofthis was used for protected cultivation in greenhouses,tunnels, mulching and temporary structures for fruittrees, etc. A figure quoted in 2000 gives the worldwideconsumption as 2,250,000 tonnes (119).

Estimates published in 2000 (114) state that greenhousesare mainly concentrated in two geographical areas: theFar East (especially China, Japan and Korea) with almost60% and the Mediterranean basin with about 30% ofthe world’s greenhouse covered area. By continent, Asiahad 63%, Europe 27%, Africa 5% and America 5%. Thearea covered by greenhouses has been steadily increasingat something like 20% per year from ~100,000 ha in1980 to more than 485,000 ha in 2000. The mostdramatic increase was in China from 6,500 ha in 1980to more than 200,000 ha in 2000.

Although the statistics for polymers in agriculture arevery impressive, the sector is actually relatively small.Current estimates for Europe (a.1) give agricultural

consumption as 695,000 tonnes representing 2% of thetotal (packaging is given separately and is the largestsector), being even lower than leisure/sport. Film forgreenhouses and tunnels was estimated at 500,000tonnes with 50% of the total consumption forgreenhouse and tunnel film and 25% each for silageand mulch films (119). LDPE is the most importantpolymer, accounting for 55% of consumption in Francefor example, followed by high density polyethylene(HDPE), with considerable quantities of PVC used inpiping. The total LDPE film was given as 350,000tonnes of which transparent crop covering filmaccounts for 160,000 tonnes, black silage film 148,000tonnes, transparent mulch films 60,000 tonnes andstretch films 33,000 tonnes.

The largest use of rubber is in tyres and, interestingly,the agricultural sector accounts for 3% worldwide(bigger share than for plastics) which is worth £1.5billion (89).

The difficulty of obtaining accurate statistics isdiscussed by Jouet (70) with problems due tocontradictory estimates and different definitions usedin different countries. He gives the worldwide totalplastics consumption in agriculture (1999) as 2,800,000tonnes, this being a 60% increase since 1990. Thisfigure excludes materials used indirectly before andafter production, such as bottles, packaging, machineryand animal hygiene, which accounts for about 14 billionEuros.

Jouet gives comparative data for 1985, 1991 and 1999with breakdown into major applications, see Figure 1.Mulching consumes the greatest quantity at 650,000tonnes followed by micro-irrigation, silage andglasshouses/large tunnels, twine, low tunnels,miscellaneous, direct covers and hydroponics in thatorder. A table gives a breakdown by country for areacovered by greenhouses and large tunnels whichconfirms the dominance of use in Asia and the relativelyminute amount in North America (see Table 1). Thereare also tables for area of low tunnels, direct coversand mulch plus tables for the use of silage andwrapping, hydroponic systems, irrigation and twine.

The concentration in all these figures is for arable cropsrather than animals. Getting reliable figures forpolymers in animal production is more difficult (112),probably because of the diverse products and materialsthat are involved.

It is evident from the figures quoted previously, that thedistribution of plasticulture geographically is extremelyuneven. In fact it can vary from a few percent of total


5

national plastics consumption to 25% or more. A detailedanalysis of the reasons for the diverse levels ofagricultural polymer use has not been found but it isclearly a function of the importance of agriculture/horticulture in a region and economic/practical pressures.The early use of plastics in agriculture was inindustrialised countries, northern Europe, Japan and USAwith economic incentives. There was then a very rapidrise in use in Mediterranean countries which later spreadto China and South-East Asia. It is fairly obvious that adry country such as Israel could benefit enormously fromdevelopment of efficient irrigation systems, whereasthere was relatively little incentive in the UK.Greenhouses and tunnels in Mediterranean countrieshave increased performance and efficiency whereagriculture was important and the climate was alreadyfavourable. The growth of mulching in China is probablylargely associated with combating soil erosion.

Achon (53) reports that Spain uses more agriculturalfilm than any other country in Europe. An agricultural

economy is traditionally seen as a poor one andAlmeria in south-east Spain was once one of thepoorest regions. Now it has the largest concentrationof greenhouses in the world (54% of its total surfaceis covered) and is one of Spain’s most profitableregions. Coupled with the greenhouse concentration,a large amount of black LDPE is used for liningreservoirs to supply water. Film accounts for 42% ofagricultural plastics consumption in Spain with 33%in tubing, 15% in twine and nets and 6% in reservoirlining (119). Further details for Spain are given inSpanish only (20). Spain is clearly a leader inplasticulture and the only book found on the subjectis Plastics Films in Agricultural Production,published by the Spanish company Repsol YPF.

Developments in plasticulture in Latin America havebeen described in some detail (40) with accountsbeing given of the situation in six countries. Theeconomy in these countries is mostly based onagriculture and it is understandable that modern

A: Low tunnels, B: Mulching, C: Direct covers, D: Greenhouses & large plastic tunnels, E: Silage, F: PP twine,G: Hydroponic systems, H: Micro-irrigation, I: Others (nets, plastic bags except fertilizing bags)

Figure 1

World consumption of plastics in agriculture in 1999 (tons) (70)

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6

methods are being rapidly adopted and even beingdeveloped. Argentina has some 2,500 plasticscompanies, mostly small and medium sized, andgreenhouse area grew 20% between 1999 and 2001.The challenge in Venezuela which can only be metby plastics is to extend the agricultural coverage tothe tropical regions. Cuba has similar climaticproblems and growth in many areas of plastics inagriculture is being seen. Important crops in Ecuadorare bananas, which use about 28,000 tonnes ofpolyethylene per year, and flowers which use plasticsin many applications, and for which the market isgrowing at 10% per year. Plastics usage is relativelymodest in Guatemala and small in El Salvador.

The use of plastics covered greenhouses for theprotected cultivation of fruit trees in Japan wasexamined and developments in environmentalstrategies and cost reduction discussed (191).

Plasticulture is now a very international business. InNepal cucumbers are grown in PE tunnels to enableproduction out of season (71). India has a large areaunder drip irrigation and has a significant productioncapability which exports nearly 20 million pieces ofdrippers per year (93). Biodegradable films formulching have been studied at an agriculturalimprovement station in Taiwan (120). Thedevelopment of strawberry production has beenexamined (143) and there have been reviews ofplasticulture in Israel (181) and in Egypt (188).

It is clearly a misconception that plastics are for therich countries (a.2). It is also obvious that plasticulturecan be very important in developing countries butwhether the funds for its use are available is anotherquestion. Although it is theoretically true thatplasticulture enables vegetables to be grown incountries where they were a luxury, and hencenutrition and health can be improved, again, such fineideas depend on investment.

The foregoing essentially addresses commercialagriculture/horticulture, which is where the bulk useof polymers lies. However, there is a significantamateur gardener market which will also be considered.

3 Materials

The vast majority of polymer used in agriculture is inthe form of plastic film used in plant protection, coversand mulching. Low density polyethylene is the

dominant film material being used in all forms ofmulch and cover. Polyethylene (PE) is also used innets, hydroponics pipes and containers. Most PE filmis clear or translucent but large amounts of blackmaterial are used for silage and reservoir linings.Opaque white outer and black inner is also used forsilage. Much smaller amounts of white and colouredfilm are used for specialist applications. PVC film isalso extensively used in mulching and covers andbecame particularly popular compared topolyethylene in Japan. PVC is also used in pipe.Linear low density polyethylene (LLDPE) andethylene vinyl acetate (EVA) films are also used inquantity. Over the years there have been manydevelopments in the formulation of the polymercompounds to improve performance and theintroduction of coextruded films having as many asfive layers to optimise required properties.

A chapter on the application of plastics film inagriculture (13) is somewhat vague but does give anoutline review of film stabilisation, factors affectingstability of greenhouse films, ageing resistance andrecycling. A brief review of several applications ofplastics in agriculture is given by Kumar and Singh (47).

Polypropylene is used extensively in nets, twine, pipesand containers, while some polycarbonate andpolymethyl methacrylate (PMMA) is used in glazing.The natural and synthetic rubbers used in tyres alsoconstitute an important volume of polymer used inagriculture.

The dominance in tonnage terms of the main filmmaterials rather overshadows the fact that the vastdiversity of products used in agriculture involves theapplication of the widest possible range of polymers.In fact it is difficult to think of a material that has notfound some agricultural use: polychloroprene rubberin milking liners, fibre reinforced plastics tanks, variousengineering plastics in machinery parts, fibres inclothing, foam insulation for buildings and so on.Consequently, there are opportunities in agriculture forjust about all sectors of the polymer industry. A list ofplastics used in agriculture by type is given in Table 2.

One interesting link of agriculture with polymerproduction is the increasing use of vegetable-basedfillers and fibres to replace the more traditionalinorganic fillers and glass fibre. It is in principle a win-win situation because the vegetable products areotherwise waste and the plastics industry can gain oncost and perhaps aid biodegradability.


7

4 Crop Protection

Crop protection is defined here as the use of coversplaced over plants whilst they are growing. Hence, itcomprises greenhouses/large tunnels, small tunnels anddirect covers, but excludes mulch.

The purpose of providing protection is to increase the yieldand/or to extend the cropping season. The basic and mainform of protection is achieved through regulating thetemperature and moisture levels, and eliminating windand possible damage from heavy rain, hail or snow. Suchprotection can also modify the spectrum of light reachingthe plants which modifies their growth. The mechanicsof this type of protection primarily involves a covering offilm, but netting is sometimes used when shading isrequired to reduce temperature. Windbreaks are apermeable wall rather than a covering. Secondaryadvantages of greenhouses and large tunnels is that theyadditionally provide shelter for the workforce.

The other form of protection is to prevent pests reachingthe plants, which is generally achieved with netting or

mesh. Whilst in principle a film covering could protectagainst pests, in practice the conditions are such thatproblems are usually made worse because theenvironment created suits the pest as well as the crop.

The largest use of protection is for vegetables but is alsoused for fruit, flowers, mushrooms and nursery stock.

Protection could be thought of as an acceleratingprocess for yield, and the acceleration is relative.Hence, covering can be effectively applied not only ina relatively cold climate where cropping may not evenbe possible without protection, but can be even moreeffective and important (especially in economic terms)in improving the already good results obtainable in arelatively warm climate.

4.1 Greenhouses/Large Tunnels

A greenhouse is defined as a large structure in which itis possible to stand and work. A large tunnel is simplya particular form of construction. In such a structure ahigh level of control of temperature, moisture,ventilation, shading, etc., can be achieved and tallgrowing species accommodated. Traditionally, agreenhouse was a wooden or metal frame with glass,or later rigid plastic, panes and that form is still thenorm for amateur use and where aesthetics areimportant. Much cheaper tunnel structures can be madewith simple tubular metal framing and a flexible filmcovering and this has been the most popular commercialapproach. However, a great variety of constructionshave been developed including inflated double skinroof, multi-span houses and the use of rigid or semi-rigid plastics end covering.

A quite detailed discussion of the design andconstruction of plastic film greenhouses has been givenby von Zabeltitz (72). The design of a greenhouseinvolves consideration of the imposed forces generatedby outside weather conditions of storm, rain, hail andsnow as well as crop and structure loads. A Europeanstandard, EN 13031 (a.3) exists for the design of plasticfilm covered greenhouses which it is said could formthe basis for use in countries outside of Europe. Thisstandard gives rules for structural design, includingrequirements for mechanical resistance and stability,serviceability and durability, and the scope extends tocover the foundations.

The article outlines different requirements in differentclimates and for different crops, and discusses practicalconstruction details such as the need to isolate the film

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8

covering from metal supports to avoid locallyoverheating it, the need to avoid anything that hindersthe run off of water droplets and the ratio of ventilationarea to floor area. Comparison is made between thesimplicity of the single span tunnel and the advantages,but higher cost, of multi-span gutter-connectedconstructions in terms of space utilisation, efficiencyof ventilation and prevention of dripping. Someexamples are given to demonstrate different factors.

Inherent limitations of greenhouse films are theirmodest strength and working lifetimes, althoughconsiderable improvements have been made over theyears. A combination of choice of film and the frameconstruction needs to be made to ensure satisfactoryperformance in the given situations. The continuedincrease in the use of film covered structures indicatesthat even modest lifetimes compared to many productareas is economically satisfactory.

An outline of the properties of the covering is givenwith some figures for a polyethylene cover. The lighttransmittance between 400-760 nm wavelengths was86.2% when new but fell to 78.8% at one year old anddirty or 85.2% when cleaned. After three years thefigures were 56% dirty and 85.2% cleaned, illustratingthe good ageing performance of the film but theconsiderable penalty in loss of light if cleaning wasnot undertaken.

Most consideration of greenhouses is directed towardsthe Mediterranean and temperate climates but simplecheap wooden frames with film or net coverings havebeen developed in the Seychelles (173).

Rigid plastic sheet has the advantage of strength but isan expensive option and much less often used than film.However, it has considerable popularity for amateurgreenhouses because of safety compared to glass.Corrugated and plain PVC, horticultural grade acrylic(PMMA) and more recently styrene acrylonitrile (SAN)are available. The other option is twin or triple wallpolycarbonate which offers exceptional energy savingwhere the greenhouse is heated. This is also used forthe ends of large commercial greenhouses because ofits structural integrity and thermal efficiency (a.4).

Plastic films for greenhouse covering act as a filter,selectively allowing radiation of different wavelengthsto go through. The visible light region from about 380-760 nm roughly covers the photosynthetically activeregion (PAR) of the spectrum which is essential forthe development of plants. When other requirementsof water, temperature, CO2 and nutrients are satisfied,growth will depend on light received. In sunny

conditions the covering needs to diffuse the light sinceshadows are reduced and the light is more efficientlyused, plus scorching is prevented.

Some transmission figures (114) show that 0.2 mmthick LDPE has total transmission in the 87-89% regionbut different materials range from 80% down to 48%for direct transmission. EVA is given as 90-92% totaland between 60 and 91% direct, and PVC as 87% totaland 78% direct. A retail supplier’s catalogue quotestransmissions of 92% for horticultural acrylic and 90%of the transmission of glass for Twinwall polycarbonate(although highly diffuse).

At night, the longer wavelength infrared light isemitted by plants and soil and causes the cooling ofthe greenhouse. The lower the transmission ofinfrared radiation through the covering the better isthe heat retention, and the greater the ‘greenhouseeffect’. Thermic films are defined in the EN 13206standard (a.5) as those that let through less than 20%of the radiation in the wavelength range 7-13 μm.Thermic films are also good diffusers of light. Asan example (114), an experiment using a thermic filmgave an 8% increase in yield with a 16% saving inheating fuel. A detailed consideration of thermalfilms has been given in spanish (80). A modificationof the ratio of red to far red light transmitted by afilm can prevent plants becoming ‘leggy’ (92). In adifferent context, an infrared blocking film helps tokeep the temperature down in conventionalglasshouses (101).

If fluorescent or phosphorescent molecules are addedto a film covering, certain wavelengths may beabsorbed and re-emitted at more photosyntheticallyefficient wavelengths, and the film is said to bephotoselective (53). Russian tests (63) havedemonstrated the value of UV absorbing luminophoresbased on europium compounds to shorten maturationtime, accelerate growth and increase yield by up to100%. The effect of both photochromic andthermochromic additives in a range of greenhouse filmson photodegradation was investigated by followingmechanical property changes in both natural andaccelerated ageing (143).

Coloured film coverings can block particularwavelengths and hence affect growth. One case ofphoto-selective film is filtering out far red light toproduce shorter stemmed plants as an alternative tochemical growth regulators (a.6). Like the use ofcoloured mulches discussed later, there is considerablescope for experimentation and potential applicationsare extensive and exciting.


9

Water condensing in droplet form on the inside of thegreenhouse covering reduces light transmission, dropsfalling onto the plants can encourage disease and, inextreme cases, the drops act as lenses and causescorching. Films having anti-dripping properties havelowered surface tension so that water tends to form afilm rather than drops and such materials are clearlyadvantageous. However, a disadvantage of anti-dripping films can be the attraction of dust in dryweather, but this can be alleviated in multi-layer filmsby having the one with anti-dripping characteristics onthe inside. The magnitude of the effect (178) was foundto be a decrease in transmission of up to 16% for dropscompared to dry conditions, but moisture filmformation increased transmission by 2.6%.

Ultraviolet radiation is at the other end of the spectrumto infrared and has several effects relevant to plants(114). It can stimulate the germination of some seeds,cause the death of plant tissue, is responsible for theblackening of rose petals, helps formation/activation/deactivation of certain plant pigments, some insectsneed it for vision and it is necessary for the sporulationof certain fungi. Films can be formulated to filter outcertain UV wavelengths and reduce some of theseeffects, although field results are said to be limited. Inone experiment UV filtering reduced the incidence ofwhiteflies by about one-third but care is necessarybecause, for example, reduction of other insects suchas bees could reduce pollination. A study has also beenmade on the effect of UV blocking PVC netting andPE and PVC films on insect populations in thecultivation of tomatoes and cucumbers (180).

The limitation of what can be achieved with a singlelayer film can be overcome by using multi-layeredconstruction. For example, in a three layer film thecentre layer could give the main optical and thermalproperties whilst the outer layers optimised abrasionresistance and anti-dripping characteristics. Withcombinations of different materials, films with a rangeof properties to suit different crops and circumstancescan be produced. It is reported (69) than one Israelicompany marketed 30 types of agricultural plastic.

An outline of co-extruded films for greenhouse coveringhas been given by Trujillo and Garcia (33). The conceptis not new as dual layer products were produced in the1960s but the sophisticated procedures for multi-layeragricultural films is much more recent. Tables are givenwith examples of different materials and possible co-extrusions to give particular characteristics.

A discussion of effects that can be achieved by additivesto film covers a broad spectrum of properties that can

be introduced/modified (31). A combination of anti-fogging and UV stabiliser was reported to be under trial(73). The effectiveness of UV stabilisers and theinteraction with the effects of absorbing UV is discussed(95) together with the effect of pesticides on stabilisation.

To reduce heating costs in a greenhouse means eithergrowing a crop that will require lower temperatures orimproving the heat loss through the covering. Doublepolyethylene glazing is very popular in the USA (a.4)and a conservative estimate of energy saving is 33%.With newer infrared barrier films this could reach 45%.Bubble insulation material made from triple laminatedfilm is available for attachment to the inside ofgreenhouses to provide insulation in winter.

Leonidopoulos (104) has published calculationmethods to give the greenhouse temperature as afunction of size, shape, time and outside temperatureand also a study (105) on the relation of sun intensityand temperature. The heterogeneity of climate andairflow pattern in a plastic tunnel was investigated andcrop transpiration was found to vary by up to 30% (44).

4.2 Low Tunnels

Low tunnels or row covers could be thought of as adevelopment from the glass cloche or Dutch frametraditionally used in market gardening, over which theyare much more efficient. In fact, it was the availabilityof polyethylene film that made economic row coveron a large scale possible.

Small tunnels are much less expensive thangreenhouses (although more expensive than directcovers) but essentially do the same job. There areobvious restrictions and disadvantages compared togreenhouses but they are very effective in the rightcircumstances, for example for short-term cover of lowgrowing crops.

Construction varies but essentially a simple frame ofhoops stakes and wire supports a film covering to givea typical cross section of 40-50 cm high and about 120cm wide. The edges of the film may be buried in soilor pinned down. The restricted volume and accessmeans that care has to be taken with ventilation to avoidoverheating and high humidity by opening the tunnelwhen necessary. Consideration also has to be given toproviding the plants with sufficient water. Obviously,the small size restricts the material that can be grownand very often the tunnel does not remain in place forthe whole growing period of taller species.


10

The film covering is usually polyethylene, essentiallythe same as used for larger tunnels. However, in theMiddle East it is common for non-woven fleececoverings (see Section 4.3) to be used stretched over aframe (77).

For amateur use, similar tunnels on a smaller scale aresold but there are also cloches and frames with rigid orsemi-rigid plastic construction. Cold frames are alsoquite popular with amateurs and can also still be seenin nurseries. Plastics used include PVC and twin wallpolycarbonate.

4.3 Direct Covers

These can be considered as frameless low tunnels, hencethe term unsupported row cover. Interestingly, directcovers were developed later than tunnels indicating thatit took time to realise that plants can thrive whilst holdingup their protecting cover, although in reality it neededto wait for the introduction of perforated films and nonwoven fleece. The film or fleece is generally severalmetres wide and is laid very loosely with the edges helddown with earth. The covering will then float in the windand expand as plants grow, hence the other name offloating cover. The growth in the use of direct covershas been rapid, no doubt influenced by the low cost.

The covering is generally either perforatedpolyethylene or non-woven cloth or fleece because itneeds to be lightweight and to allow the passage ofwater for irrigation and air for ventilation. The coversprovide the same functions as low tunnels in that theyact to conserve heat, prevent excessive transpiration,protect from wind and heavy rain and exclude pests,but the level of protection is different because of theintrinsic ventilation and the absence of a frame. If thecover is made of a very fine mesh it will be particularlyeffective for excluding pests such as carrot fly but allowgood ventilation and passage of water.

Non-woven fleece cover in Europe (77) is typically inthe weight range 17-20 g/m2 and several rolls ofmaterial may be joined with adhesive to give a totalwidth of up to 16 m. Experience showed thatimprovements in durability of the fleece withoutincrease in fabric weight were desirable and onemanufacturer initiated a development programme incooperation with the polypropylene supplier and theScottish Crop Research Institute. This led to productionof an in situ formed bi-component filament whichresulted in improved strength properties which weresubsequently proven in the field.

The effectiveness of non-woven covers alone and incombination with black/white and brownpolyethylene mulch on growth of squashes wasinvestigated (136). Trials in Mexico (137) evaluatedthe effects of different combinations of spun bondedfabric covers, perforated and non-perforatedpolyethylene micro-tunnels and black polyethylenemulch on growth and yield of muskmelons, insectpopulations and soil temperatures.

4.4 Windbreaks

In exposed areas a windbreak can have a significanteffect on cropping. An artificial windbreak has theobvious advantages over natural materials of consistentpermeability, does not compete for water and nutrients,does not harbour pests and is moveable, although itdoes carry a cost premium.

Plastic windbreaks are essentially a mesh or grid ofpolyethylene or polypropylene supported on fenceposts. Clearly, adequate strength and stabilisationagainst UV light are very important.

4.5 Shading

Shading is mostly important in very hot countries toprevent plants from becoming overheated. The use ofmesh with a porosity of the order of 50-60% in tropicalconditions can extend the type and season of vegetablethat can be grown. It has also been used to help establishnewly planted areas in parks in tropical areas of theFar East. In climates like those of Israel or Florida,nurseries without natural shade can protect their stockwith shade netting. Such artificial shading material hasthe same advantages over natural shading as given forwindbreaks, and it is also possible for it to be temporaryaccording to season.

Even in temperate climates protection is needed forshade loving plants such as ferns and rhododendronsin nurseries. Greenhouses may be shaded with ‘paints’or the use made of netting or various blinds.

By the use of different percentage coverage of thenetting and also different colours it is possible to caterfor different conditions and even different plants. Onecommercial range (39) of polyethylene shading nettingand fabrics gives coverage from 30-90% with a largevariety of colours and is treated to prevent rotting andto repel insects.


11

4.6 Protection Against Pests

The use of fine mesh direct covers to exclude flyingpests has been mentioned and can be very effective.All the types of cover give protection against birds butgenerally insect pests can readily populate greenhousesand low tunnels. In fact one of the problems of usingplastics for protection is that the climate that suits theplants also suits the pests. Consequently, as an example,red spider and whitefly are usually much more of aproblem under cover than in the open. On the otherhand, the closed environment of a greenhouse is helpfulwhen applying pest control measures.

The effect of mulches in repelling insects will bediscussed in Section 5.1.

Netting is widely used to protect fruit, particularlysoft fruit, from birds. The polyolefin netting withsuitably small mesh is usually attached to a frameforming a cage. A very wide mesh netting can be usedto cover brassica plants against the attack of pigeonsbut this is probably only used on a small scale. Nettingis also used on a small scale to protect fish in pondsfrom herons.

Very fine mesh is used to keep out pests such as carrotfly. Spun-bonded fleece used as wind and frost protectioncan also be effective in keeping insects out. EVA ‘cottoncandy’ is said to have potential in preventing insect attackby interfering with insect behaviour (56).

Effective tree guards can be made from recycled PVCand it was reported that 20,000 have been donated bythe PVC Tree Protector Campaign to tree planting andwildlife groups in the UK (85).

An unusual application of polyethylene sheet is to putit as a sleeve around mango trees to prevent mealy bugsclimbing up (47).

5 Soil Conditioning

Soil conditioning is taken here to cover mulching, i.e.,covering the soil rather than the plants, and the additionof materials into the soil. Covers for plant protection,particularly direct covers, achieve some of the aims ofmulching but they have been dealt with in the previoussection. Conversely, it can be said that mulches give ameasure of plant protection by warming the soil,preventing weeds and, with reflecting films, increasinglight and warding off aphids.

5.1 Mulching

Traditional mulching was the application of loosematerial such as composts, straw and grass cuttingsaround plants. The main objectives were to conservemoisture, maintain the surface soil structure and toprotect it from erosion and the leaching of nutrients.In winter a mulch would act as thermal insulation forthe roots in cold climates. Such mulches alsoimproved soil structure after being incorporated bysubsequent cultivation.

Plastic film used as a mulch has the advantages of lightweight and is much easier to handle as volume forvolume it covers a much greater area than naturalmulches and, being in rolls, is amenable to mechanisedinstallation and, hence, has a cost advantage. Also, itshould not introduce pests or chemical residues whichare possible with natural materials.

Films for mulching can be distinguished by colour.Transparent materials enable rapid heating of the soil(through the greenhouse effect) as well as conservingmoisture and protecting the soil, whereas blackmaterials are effective at preventing weed growth.Reflective films, opaque white or metallised, can beused in low light conditions to concentrate sunlight ontothe plants to increase photosynthesis.

Coloured mulches have been shown to be effective fora range of vegetables including cucumbers, melons,peppers, cabbages and corn (a.7) but a single colourwas not suited to all crops nor effective against all pests.For example, red plastic gave best results for tomatoesfor growth whilst silver mulch controlled whitefly.Similarly, coloured mulch has reduced thrips on leeks.Apparently, it is the UV light reflected by the silvermulch that repels the insects whilst a plant may bestimulated by the coloured light reflected giving theimpression of there being competitive plants nearby.Blue mulch produced the best results for peppers inMexico (148) due to the reflection of photosyntheticallyactive wavelengths and raised soil temperature, whilstblack mulch on inclined beds gave considerableimprovement of pineapple yield and sugar content(164). Yellow/brown films delayed the incidence oftomato yellow leaf curl (179). An example of the useof a black mulch in a temperate climate is theadvantages found for asparagus cultivation in southernGermany (192).

The quality and thickness of film will vary with the cropto be treated. For short-term crops, which includes mostvegetables, the period is in the 3-6 month region andstandard thin film will be satisfactory. However, for long-


12

term service in situations such as in vineyards andorchards several years life will be expected and the filmswill be upwards of 50 μm with high mechanicalproperties and high protection against degradation.

Normal films could not be incorporated into the soilby subsequent cultivation, and for mechanicalharvesting may need to be removed in advance toensure that they do not block or damage machinery.However, films made of photo/biodegradable materialswill break down with time and this time can beprogrammed to suit crop requirements and the amountof sunlight available (latitude). See Section 13 forinformation about degradable materials.

Woven HDPE or polypropylene fabric is used aspermeable ground cover that prevents weeds andprovides a clean and good looking surface for thedisplay of plants in nurseries. It commonly has linesmarked to aid with pot spacing.

Black spun bonded polypropylene mulching film forsuppressing weeds has pre-cut cross holes for plantingindividual plants through.

Bark is widely used where a decorative mulch isrequired but this can be replaced with a coloured mulchbased on rubber from recycled tyres which avoids theneed for relatively frequent replacement (45, 86).

A short-term use for a covering of film is in thedisinfection of soil when the film helps to raisetemperature and/or to retain chemicals. In hot regionsthe temperature under the cover can be sufficientlyraised through the greenhouse effect to cause solardisinfection without the need for chemical treatment.The traditional use of methyl bromide is being phasedout (42) but other chemicals to replace it will need aplastic covering.

5.2 Soil Improvement

Natural soils vary considerably in their compositionand structure and most can be improved by theincorporation of organic matter and in some cases fromaddition of inert materials. Hence, the addition ofmanure, etc., has been practiced since timeimmemorial. Very much more recently polymericmaterials have been used for soil improvement.

The main applications have been in sports turf andamenity areas where the intention was to increase thestrength and resistance to wear of the turf rather than

to improve soil in the classical sense. One basicapproach is the incorporation of geotextile materialsas a grid or mesh which then acts as a mechanicalbinder. Another approach is to add shredded rubberwaste from tyres, an example of which is reported fora softball field (48).

One of the main improvements given by traditionalmaterials is the improvement of water holding abilityand consideration has been given to the use of scrappolymer foam which would hold water as well as altermechanical structure. For the use of water holdingpolymers see Section 6.3.

The Russian Academy of Sciences has developed amethod to help soil recover from the effect of themining industry (36). A water-based emulsion is appliedto the freshly seeded soil surface and forms a permeablefilm which binds the soil particles ensuring that thetop surface stays in place. The film is air and waterpermeable and plants can readily grow through it. Itstays in place for several years before biodegrading.

The breakdown of biodegradable plastic mulches willresult in residue being incorporated into the soil andinvestigation is needed of the long-term effects onsoil quality.

6 Water Management

The simple fact is that the geographic and seasonaldistribution of rainfall is extremely variable and inmany areas there are periods when the amount isinsufficient for growing crops. Furthermore, thedemand for water is increasing and the extra is notavailable. In many cases agriculture is the mainconsumer of water (49) and it has been estimated thatonly 40% of water used in agriculture actually reachesthe plants. In consequence, there is a huge requirementfor the management of water for agricultural andhorticultural use. Clearly, the need is greatest in aridregions but it can also be a limiting factor in temperateregions and to use less water would reduce costs.

A general discussion of the use of plastic materials forthe management of irrigation water is given by Losada(111) which makes the point that plastics havecontributed to a real revolution in irrigation in manyways, from the irrigation equipment to the control ofwater by mulching. A suggestion is made as to whatirrigation would have been like without plastics for thelast 50 years.


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In complete contradiction, there are circumstances wherethere is too much water and land has to be drained tomake it viable for cultivation. Here again, plastics havebeen fundamental in important innovations.

6.1 Collection, Storage and Transport of Water

The great majority of systems for the collection andstorage of water are shared by industry, domestic andagriculture needs but there are boreholes, wells andreservoirs which specifically serve agriculturalpurposes.

Plastics are present at the start of the process – PVCpipes are used to transport water from bore holes andfilm or sheet can be used in channels to divert water tostorage positions.

Water is efficiently stored in reservoirs created byexcavation which are lined with a polymeric sheet toprevent loss by seepage. PVC, EVA, HDPE, LDPE,ethylene-propylene diene monomer (EPDM) and butylrubber have been used and enormous structures arepossible with thick polyethylene sheet. The use of PVCsheeting for agricultural reservoirs has been described(110). An additional use of polymers can be in waterstorage through the geotextiles used to protect thereservoir lining. The rainfall in Spain is inconsistentwhich encourages the building of irrigation reservoirs(53). HDPE, LDPE, EPDM and butyl rubber have beenused and the average size is said to be 50,000 m2 withan exceptional reservoir in the crater of a volcano inthe Canary Islands of 4,000,000 m2.

A novel type of dam (a.8) uses two polyethylene linerscontained within a single woven outer tube. The twoliners are filled with water and they then form a stablenon-rolling dam barrier.

Transport of water from the storage facility can be bypipe or open channel but pipe clearly has theadvantage of no contamination or loss. The materialsgenerally used are polyethylene, PVC or glassreinforced plastic (GRP).

6.2 Irrigation

Simplistically, irrigation systems can be categorisedas flooding, above surface spraying or sprinkling anddrip irrigation, and they could be ranked in that orderfor increasing efficiency.

A great quantity of PVC pipe is used to carry waterfor irrigation to the field and for permanentunderground networks in sports facilities.Polyethylene pipe is widely used in surface networks(which may or may not be intended to be moveable)to feed spray and sprinkler heads. PVC sprayline pipecan be pre-drilled at intervals for attachment of outlets.Similar networks, although on a smaller scale, providemist systems in greenhouses and sprinkler systemsfor nursery stock. Additionally, there are the mouldedpipe connectors and, often, the spray or mist headsare made from moulded plastics components.

Drip irrigation or micro-irrigation systems are one ofthe great success stories of the effect of plastics onhorticulture. This approach only became feasiblewhen small bore flexible plastic pipe with mouldedconnectors and drip or mini-spray heads wasavailable. The idea was conceived in Britain in theearly 1950s for greenhouse use and at first used rubbertubing (113). It was exported to Denmark forgreenhouse use and then to Israel where it wasdeveloped for use in the open field. Drip systems areefficient because water is delivered exactly where itis needed and nowhere else, and loss by evaporation(very high in spray systems) is minimised. Also, thepressures needed are very low. The only disadvantageis the relatively high installation costs but the longerterm economics are very favourable. Despite theefficiency, less than 1% of arable land is irrigated inthis way (49). Probably it needs the incentives of waterbeing in short supply and/or expensive to justify theinvestment, which would explain its high use incountries such as Israel but relatively little in the openin the wetter climate of the UK.

There is a variety of systems with various degrees ofsophistication including simple perforated pipe hose(which can be buried) and self-regulating drippers.Commonly, a drip irrigation installation will becoupled with a plastic film mulch to further preventevaporation losses.

The productivity of making pipes with drippers hasimproved greatly in the last 2-3 years throughimproved technology which should reduce costs (49)and perhaps aid the adoption of this approach toirrigation.

Sprinkler systems are widely used by amateurgardeners but they are also increasingly turning todrip systems, particularly is such countries as Israeland the hotter States of North America, and also inthe UK. One attraction is the possibility of automatic/timed systems.


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A different type of irrigation is found in capillarymatting made from non-woven polyester fibres andused in greenhouses. In addition to the mat itself thereis likely to be a polyethylene sheet beneath it and aperforated sheet above to reduce evaporation.

6.3 Water Holding

Water is held in soil by the organic content but this canbe augmented to cover dry periods by the introductionof artificial water holding materials. Hydrophilic gelsare generically known as hydrogels and there are anumber of trade names. They have the ability to holdmany times their own weight (300-1500 depending onthe product) and to release it as the environmentbecomes dry (a.9). These polymers have been availablefor 20 years but interest has varied.

Starch-based hydrogels have a very limited life butpolyacrylamides and polyacrylates are much more stable,remaining active for two years or more. The gels areclaimed to increase available water, improve aeration,reduce compaction, improve drainage and increase plantsurvival and growth. It appears that enthusiastic claimsare made about the improvements that these productscan make but research results have been conflicting andcontroversial. The author of (a.9) gives a fine exampleof how marketing blurb has a turned a complete failureinto a magnificent success for the product.

A pioneering hydrogel material is Broadleaf P4, thebenefits of which are outlined on the web site of themanufacturers (a.10). Other materials are calledStockosorb (a.11) and Erisorb (a.12). The makers ofErisorb also produce a flocculent material based onpolyacrylamide called Eribond which is said to bondsoils to prevent erosion. There are some potentialenvironmental issues relating to polyacrylamide use.Polyacrylamide is designed to be resistant tobiodegradation, thus there is the possibility of long-term accumulation, but this fear is unfounded ifpolyacrylamide is used at low concentrations. Themonomer used to synthesise polyacrylamide is aneurotoxin. However the polyacrylamide is suppliedalmost devoid of monomer, so the presence of themonomer in the environment should be minimal.Possible alternative natural polymers have also beenconsidered (121).

In principle, polymeric foams could be incorporatedinto soil to absorb water but this does not appear tohave been adopted. Simple trials by the author withpolyurethane foam were inconclusive.

An investigation of the feasibility of the application ofpolymers to facilitate the growth of plants in arid lands(11) is looking at whether a polymer can be synthesisedto encourage precipitation of moisture in the air and atpolymers that absorb water through crystallisation.

6.4 Drainage

The majority of plants do not like waterlogged soilbecause of the lack of oxygen, and it can result inreduced yield or, in the worst case, death of the plants.Excess water will also restrict access to crops oranimals. Consequently, there are many instances wheredrainage is essential to reclaim land for agriculture oris desirable to improve yield.

Traditionally, the only methods were ditches, runs ofcoarse aggregates and clay pipes. Clay pipes are brittle,heavy and the laying process is labour intensive.Ditches became blocked, requiring perhaps annualmaintenance, and waste land. The introduction ofplastics pipes allowed a dramatic improvement in theease and efficiency of field drainage.

Originally, rigid perforated PVC pipes developed byWavin in 1956 were used but they were not totallysatisfactory for strength and flexibility. Flexiblecorrugated pipe in long lengths was introduced in 1962.Such pipe can be machine laid very rapidly and its useis much more efficient. Pipe may be made frompolyethylene, polypropylene or PVC, with PVC havingthe best strength and stiffness to weight ratio, butpolyethylene is good at low temperatures.

The design of a drainage system is a specialisedprocess. Consideration has to be given to soil loadingto ensure pipes will not fracture and it may be necessaryto include non-woven geotextile layers to preventclogging of the pipe.

7 Harvesting and Crop Storage

Polymers contribute to the harvesting of crops in theform of containers such as nets, bags and crates. Theadvantages over more traditional materials include lightweight and ease of cleaning/disinfecting. Plastic cratescan be moulded to particular forms to suit the crop andare reusable. The containers used at harvest are in manycases suitable for transporting the crop to store ormarket without damage.


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Film can be used in several ways for the storage ofgrain – to line existing pits or silos, cover sacks stackedon a damp free base or to directly produce storagecontainers. In all cases the low permeability to air andmoisture and low cost are attractive. Probably, the useof film as a covering for sacks in the open is expedientin times of exceptional harvest.

In the last few years there has been a large increase inthe use of polyethylene bags for grain storage inArgentina (41). The bags are essentially tubes ofbetween 60 and 75 metres in length and the largestdiameter size used carries about 220 tonnes of wheator 200 tonnes of soya or maize. They can be storedoutside and alleviate the problem of limited on-farmstorage at low cost.

The trend for plastics to replace metals applies toconventional grain silos and here consideration has tobe given to the electrical insulating nature of mostpolymers and the danger of dust explosions.

Ensilage is the process of storing and fermenting greenfodder in a silo, or the fodder thus preserved (commonlycalled silage in the UK). The object is to produce amaterial when a crop is plentiful that can be stored forfeeding in the winter when food is scarce. Ensilage isan anaerobic fermentation process that requires air-tightcontainment. Until the 1950s this could only beprovided by steel or concrete structures which made ita rather difficult or expensive process. The othermethod of preserving fodder is by making hay whichis seriously reliant on the weather and one presumesthat it was the revolution of introducing plastic filmcontainment for silage that caused it to have largelyreplaced hay making. Haylage is made by essentiallythe same process as for silage but the grass has beenallowed to dry before being baled. It is wrapped in thesame manner as silage.

Initially, large bags were used but stretch wrappingwas invented in Australia and use of it in Britainstarted in 1986, and quickly spread to the rest ofEurope (113). This process produces the large balesnow commonly seen.

Polyethylene film is most commonly used and it hasrelatively low air permeability. However, co-extrudedmaterials can improve this further. The colour is usuallyblack but sometimes white or a black/white bi-extrusionis used, particularly in sunny climates. A white filmoutwards reflects light and helps avoid extreme heatingof the fodder. Another important property of the filmis its resistance to acidic conditions.

8 Buildings

Agricultural buildings can incorporate plastics in anumber of ways which include polyethylene dampproof course material, PVC cladding, rain water goods,PVC window frames and polyurethane foam insulation.Plastic wall linings are easily cleaned and non-absorbent and hence hygienic for wall linings inmilking parlours, etc.

PVC profiles have been found to be a practical andcheap option for flooring in pig breeding and fatteningunits (112) because of corrosion resistance, strength,not causing damage to stock and ease of cleaning anddisinfecting. A similar approach is used for poultry.Foam mats from recycled polyolefin with a watertightcover were tested by the Dutch state agriculturalinstitute HAS and it was shown that cows having floorslined with the mats gave more milk than those withoutsuch creature comforts (99).

PVC boards have also been shown to resist beingkicked when used as separating walls in horse stablesand again are hygienic.

9 Machinery and Equipment

The range of plastics and rubber-based componentsused in agricultural machinery is legion and includespolyamide gear wheels and bearings, polypropyleneand GRP covers, electrical wiring and various syntheticrubber seals.

The biggest use of rubber in agricultural is for tyres.The 3% of total world market held by agricultural tyresis worth £1.5 billion. Tractors have large tyres and asthe engine power has increased even larger tyresbecome the norm, said to be now 520/70 R38 (89).This has meant that, coupled with the trend to radialfrom cross ply tyres over recent years, the tonnage oftyres sold has increased even although in unit termssales have decreased. Although radial tyres are makingheadway it is reported that in the USA the large farmtyre segment remains a bias stronghold (23).

There has been consolidation of tyre manufacturers andmarket is dominated by Pirelli, Goodyear and Michelin/Kleber. Consolidation is also expected in theagricultural tyre dealers because of increased call forvery specialised service and bespoke tailoring of tyresto particular operations in the field that smaller dealers


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cannot provide. The replacement tyre market is lessdominated by the leaders and this is particularly so forthe tyres for implements.

It is forecast (84) that, according to current trends,rubber tracks as opposed to tyres will be the choice forhigh powered agricultural tractors. The article considersthe advantages and disadvantages of tracks and notesthat dealers will need the expertise to advise on thealternative products.

Polymers are extensively used in dairy equipmentincluding hoses, storage tanks and rubber liners.

High impact polypropylene is successfully used in lawnmowers, for example, as an under deck to improve grasscollection and reduce noise (30).

Spraying equipment uses polypropylene tanks, rubberseals and many components are moulded plastics.Polymers are prevalent in tools; polypropylene has evenreplaced steel for the trays and wheels of somewheelbarrows with the obvious advantages of strengthto weight ratio and no rusting.

A review of lawn and garden injection mouldedproducts (194) noted that plastics were increasinglyreplacing metals in engines of garden machines andthat polyamide was being used in handles.

10 Containers and Packaging

This section covers a wide and varied range ofapplications:

• Plant and seed containers• Troughs, pans, and buckets• Packaging for fertilisers and chemicals• Packaging of food stuffs• Tanks and pits

It is easy to forget that plastics produced a revolutionin containers and packaging. The variety of materialsand the ease of producing complicated shapes alloweda freedom in design and performance probably not evendreamed of previously. The revolution has applied inagriculture as much as in other areas.

Injection moulded and vacuum formed polypropyleneplant pots come in a large range of sizes, are manytimes lighter than clay pots and have much more

efficient drainage. Their low cost and convenienceenabled the huge market that has developed forcontainerised plants that can be marketed andtransported at any time of the year. Complementaryto plastic pots are the carrying, shuttle and markettray systems for transporting and display, whichthrough clever design have rigidity but low materialusage. There are also specialised containers for therelatively new market of plug and baby plants by mailorder. Simple seed trays have been augmented/replaced with multi-cell plug trays and tray insertsystems that cater for all possible plant raising needs.For the consumer market, plant containers are madein a variety of designs and sizes and have enabledcontainer gardening for those with little space verycheaply. Specialist containers have been developed,for example strawberry towers, hanging baskets, pondplanting baskets and even a polypropylene potatogrowing container.

Simple plastic buckets are used in most industries andgalvanised steel has long since gone. The same appliesto a variety of troughs, pans and drink and feeddispensers needed in animal husbandry. In domesticuse, blow moulded polyolefin compost bins and waterbutts are popular, and watering cans are very widelyfound useful. Large carrying bags, variously ofpolypropylene or polyethylene, are used forhorticultural rubbish such as hedge trimmings.

Polyethylene bags are universally used to packagefertilisers, composts, soil improvers, lawn sand, etc.,providing efficient handling with good protection atlow cost. Additionally, there are the compost filledgrowbags used for tomatoes, cucumbers, etc., thatoffer a pest and disease free starting environment. Allmanner of chemicals come in plastic bottles and drumswith sizes from 1 to 25 litres or more. Almosteverything nowadays comes packaged, including theshrink wrapped film that encases the pallets of bagsof potting or seed compost and the polystyrene foamthat protects machinery parts or the farm computerduring transit.

Perhaps not strictly part of the agriculture industrybut certainly a result of it, the produce after anyprocessing will in most cases be packaged when itgoes to the retail market. Food packaging is now verysophisticated with multi-layer films developed withselective gas and moisture permeabilities to suit therequirements for preserving the particular product.Milk sold in shops and supermarkets is no longer inglass bottles and produce such as vegetable oils andfruit juices are usually in plastic bottles. Perhapsupsetting to the purist, plastics corks are used for


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sealing wine bottles and it is demonstrated that screwtops with a plastic element will be even more efficient.As an indication of the care taken with packaging, atrial found that polyethylene was the best option formaintaining the taste and quality of Sweetheartcherries (8).

Animal waste can be channelled from buildings andcontained in GRP tanks or polymer lined pits/pondsconstructed in the same manner as reservoirs.

Tanks 1.5 m wide, 0.7 m deep and between 3 and 9 mlong made of plastic fibre (possibly made of GRP?)and lined with PVC can be used on fish farms (112),one advantage over conventional installations beingthe saving of space if the tanks are arranged in two orthree levels.

11 Miscellaneous Applications

This section serves as a vehicle to list applicationswhich for whatever reason have not fitted into othercategories.

11.1 Identification Tags

Animal identification tags are normally injectionmouldings used externally. A novel ‘moo-tag’ is fedto cows and sits in the stomach as a permanent meansof electronic identification (85).

11.2 Clothing and Footwear

Fabrics and sheet materials used in work andprotective clothing are very often polymeric. Thisincludes polychloroprene aprons and nitrile gauntletsfor chemical resistance and polycarbonate face masksand goggles. Wellington boots were originally naturalrubber but are now more likely to be PVC.

11.3 Controlled Release of Fertilisers, etc.

Controlled release technology has attracted a lot ofattention in recent years. There is a clear advantage ifone dose of a drug, fertiliser, pesticide, etc., can beeffective over a long time period without there beingan overdose at the beginning which trails off to

underdose. In horticulture, controlled releasefertilisers such as Sincrocell and Osmocote areprobably most widely known examples of thetechnology, but it is also applied to pesticides,pheromones and biomaterials.

A variety of polymers are used as the carrier for theactive ingredient, both natural and synthetic. A list ofthose used to give controlled release of agriculturalfertilisers is given in (47). The method of holding theactive ingredient can be by physical coating/embedding or by chemical combination with thecarrier. In the first case the coating membrane providesbarrier properties to control the release whilst in thesecond there is a gradual breakdown of the chemicallinkage. A detailed review is given by Dave and Mehta(129). They also give a list of some commercialfertiliser products which does not include Sincrocell.This product appears to be relatively new to the marketand is said to use an advanced polyurethane carrier.

The use of natural rubber and styrene-butadienerubber (SBR) as a carrier for slow release of a traceelement, zinc, was recently studied in detail anddemonstrated the effect of temperature and pH (32).A nanoprecipitation technique for encapsulation ofan insecticide for cotton plants enhanced thepenetration of the insecticide but did not givecontrolled release (9). Another approach is based onthe intercalation of polymers containing metribuzininto montmorillonite (37). Polymeric formulations ofdichlorobenzaldehyde (DCBA) by modification ofboth linear and crosslinked polyglycidyl methacrylatehave been studied for release of the DCBA as afunction of temperature and crosslinking (74).

11.4 Garden Ponds

Rigid ponds are constructed in quite large sizes fromGRP, and flexible liners are produced in PVC at thecheaper end and EPDM and butyl rubber at the higherquality end. The most recent material is a polypropylenematerial called Xavan sold as Pondtex liner. It is madeof layers of filaments formed into a multidirectionalweb and heat bonded at the crossover points. Pondtexis said to be at least as strong as butyl rubber.

11.5 Greenhouse Sundries

These include foam sealing strip, climate screenaccessories such as clips and polyamide vent guidesand fan components.


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11.6 Labels

It was interesting to see in one horticultural merchant’scatalogue a reference to ‘traditional plastic pot labels’.The market is now so mature that plastics aretraditional. Computer generated labels are now usedby most larger nurseries.

11.7 Seed Coatings

Encapsulation of seeds makes for easier and moreaccurate sowing. Treatment of seed with a polymercontaining the hormone kinetin is said to result insignificant increases in germination (58).

11.8 Soil Less Cultivation

Cultivation on inert natural or artificial substrates wasdeveloped in the 1970s and relies on plastics in theform of membranes, troughs, pipes and tanks, etc. Truehydroponic systems are used on a relatively small scalebut usage has doubled since 1991 (70).

11.9 Ties and Grafting Bands

A variety of ties are made from plastics and rubbers.Velcro tree ties are a newer introduction that can becut off the roll and repositioned as the tree grows.

11.10 Twine

Despite having a one line entry under miscellaneous,the market for agricultural twine is very large as notedin Section 2.

11.11 Others

Other uses for plastics include: hanging basket liners,lawn edging strip, netting for plant support, polyamidemonofilament for strimmers, sealing tape and pegs forfixing ground cover, plastic coated training wires andplant supports.

No doubt there are farmyard toys made of plastics, butif farmers want to go one better for their children thereare miniature garden kits complete with automaticirrigation (118).

12 Standards and Testing

Standards have been established at national andinternational level for a number of polymer productsfor agricultural use, notably plastic films and pipe, inresponse to the need for consistent and adequatequality. The web sites/catalogues of ISO, CEN andnational standards bodies can be consulted foravailable documents. Spanish standards related toagriculture are examined by Ruiz (83). Generally, thetest methods used to demonstrate quality andperformance of polymers for agricultural use are thesame as used for polymers in general (12, a.13)although there will be emphasis on particularproperties and some special requirements.

In a discussion of applications of plastic film inagriculture (13), analytical methods for determinationof the presence and compatibility of additives such asantioxidants and UV stabilisers are outlined togetherwith factors affecting the stability of greenhouse films,from temperature to the effect of pesticides. The ageingresistance of films is also briefly considered.

For polyethylene film for greenhouse covering, therehave been extensive studies of test methods to establishthe European specification. Dilara and Briassoulis(154) gave a critical evaluation of existing test methodsand suggested that additional methods were needed forthe particular circumstances of this application. Laterin the work, Briassoulis and Aristopoulou (42) gave adetailed account of the adaptation and harmonisationof test methods to be used in a specification forgreenhouse films. In the measurement of basicmechanical properties a particular problem indetermination of strain of the horticultural film wasencountered using standard strain gauges (50) becauseof the low film thickness.

In comparison with many areas, the lifetime ofagricultural products are at extremes. Undergroundpiping is expected to have a working life of severaldecades whilst mulch film may last for only one season.Greenhouse cover film lasts only a few seasons, but morethan earlier materials, and its resistance to UV light,temperature and chemicals is a very important factor.

In situ exposure of greenhouse films with continuousmonitoring of the spectral absorption has been used toestimate lifetime and models fitted to allow predictionof deterioration at a given time (21). A method forevaluating polymer films for agricultural applicationsby optical characterisation is proposed and results forbiodegradable materials compared to conventional films.


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A test chamber has been constructed for testing theeffect of agrochemicals on greenhouse film anddemonstrated that sulfur vapour had a serious effecton condensation and mechanical properties in a matterof weeks (10).

A comprehensive study of ageing of polypropylenecords showed that chemicals such as pesticides andfungicides could practically neutralise the benefits ofUV stabiliser (132), as noted for films in Section 13.

A method for checking on whether biomass fromdegraded materials has been bio-assimilated that shouldappeal to farmers, is to weigh at intervals a populationof starved earthworms (22).

13 Disposal and Recycling

The quantity of polymer waste generated now gives riseto very serious environmental concerns. On quickreflection it is obvious that the great success of polymersin agriculture will mean an enormous amount ofdiscarded material which contributes to this problem.The volume of fertiliser bags and used plant pots mustbe intimidating but would pale against the quantity ofdiscarded mulching film and silage wrapping. Anextremely attractive way to alleviate the problem is formuch of the material to be environmentally degradable.

An overview of environmentally degradablepolymeric materials in agricultural applications hasbeen given by Chiellini and co-workers (27). Studiesof photo/biodegradable films for mulching have beencarried out in Taiwan (120). Not only the performanceof films for the current crop, but also the effect onsubsequent crops, including the presence of heavymetals, was considered.

What was claimed to be the first totally biodegradablepolyethylene, known as Symphony, has been described(152). It is said that it can be engineered to degrade in aslittle as 60 days or as long as 5-6 years either incomposting conditions or through photo and thermaldegradation. At about the same time a family of totallydegradable materials based on polyethylene was reportedto have been successfully developed and commercialised(125). A comparison of the weathering of a degradablecopolyester and HDPE films was carried out to see ifthe former could replace the latter (28).

Systematic collection of polymer waste is expensive andlimited. Agricultural waste from mulch and crop cover

film, irrigation tubes and packaging has an added problemof often being contaminated with soil and chemicals andhas been categorised as ‘special waste’ in an EuropeanCommunity classification, which means it needs specialtreatment. Apart from alleviating the waste disposalproblem there could be cost savings from avoiding theexpense of removing and sorting the discarded productsif they could be photo-thermally or biologically degraded.

The large amounts of film used with homogeneouscomposition should in principle make collection andrecycling operations easy (13) but this is ignoring practicalproblems such as the contamination levels. Apparently,pesticide residues can reduce the efficiency of stabiliserswith implications for the stability of the recycled product.Also, the film after use outdoors for long periods is infact considerably degraded before recycling and is furtherdegraded by the reprocessing. To alleviate this problem,trials were made by adding Irganox antioxidant duringthe reclamation (55) and it was concluded that it shouldbe added at each step of the process. The levels ofpesticides in waste film has been investigated (132). Thereuse of recycled LDPE with the incorporation of EPDMmodifier was investigated and the effect of naturalweathering measured (34).

Initiatives for recycling include a partnership inOntario, Canada between the Environmental andPlastics Industry Council, the Ontario Ministry ofAgriculture and the Ontario Soil and CropImprovement Association (62). The first phase of aCanadian project was reported as completed (75) andthe next step was to pilot different methods ofcollection. Brief details are given of recycling projectsin the UK for agricultural plastic waste; recycling inWales, a composting plant near Bridlington and anincinerator in Huddersfield (126). The Cumbria PlasticsRecycling Scheme (16) is an example of the sort ofscheme that UK farmers will need to become familiarwith when legislation on waste management is appliedto agricultural waste in 2004. The scheme is supportedby several very notable bodies and expects to recycle600 tonnes of agricultural film this year.

An advanced methodology for recycling called SolidState Shear Pulverisation (46) does not need sorting ofthe waste film either by type or colour and is claimedto produce high quality blown film with particularlyhigh elongation at break.

The complete cycle of reuse could come about fromexperiments to recycle waste cellulosic material fromplants into electrospun nanofibres, one possible use ofwhich could be mats for controlled release of fertilisers,pesticides, etc., (a.14).


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Used tyres are now a large scale problem and mucheffort has been put into reclaiming, recycling and useas fuel. Agriculture is putting its minor, but neverthelessvery significant, input to this problem. One slightlyunusual way of recycling is to use the tyres asconstruction elements (a.15). They can be directly usedto build bank protection, breakwaters and artificial reefsor compressed into baled blocks for bank protection ordam construction. One restriction is the release of heavymetals, but it would seem appropriate if tractor tyrescould become the home of fish that are subsequentlydestined to be food.

A very novel use of recycled tyres is as a wateringstation for livestock (64).

Additional References

a.1 European Plastics Converters, http://www.eupc.org/markets/agri.htm

a.2 CIPA-CIDAPA, http://www.plasticulture.com

a.3 EN 13031-1, Greenhouses – Design andConstruction, Part 1: Commercial ProductionGreenhouses, 2001.

a.4 W.J. Roberts, Plasticulture, 2001, 2, 120, 70.

a.5 EN 13206, Covering Thermoplastic Films foruse in Agriculture and Horticulture, 2001.

a.6 University of Florida News,www.napa.ufl.edu/2001news/plastics.htm

a.7 Floraculture International, http://www.floracultureintl.com/display.asp?ArticleID=590

a.8 Aqua Dam, http://www.aquadam.com

a.9 Horticulture Digest, http://www2.ctahr.hawaii.edu/depart/tpss/digest/hd99/hd99_5.html

a.10 Agricultural Polymers International, http://www. agripol.co.uk

a.11 Stockhausen Inc., Stockosorb, http://www.stockhausen-inc.com

a.12 Eridan Co. Ltd., http://www.eridan-asia.com

a.13 Handbook of Polymer Test Methods, Ed.,R.P. Brown, Marcel Dekker, New York, NY,USA, 1999.

a.14 Netcomposites, http://www.netcomposites.com/news.asp?1802

a.15 R.A. Fenner and K. Clarke, Water andEnvironmental Management Journal, 2003,17, 2, 99.

Abbreviations and Acronyms

CIPA International Committee for Plastics inAgriculture

DCBA dichlorobenzaldehyde

EPDM ethylene-propylene diene monomer

EVA ethyl vinyl acetate

GRP glass reinforced plastic

HDPE high density polyethylene

LDPE low density polyethylene

LLDPE linear low density polyethylene

PAR photosynthetically active region

PE polyethylene

PMMA polymethylmethacrylate

PP polypropylene

PVC polyvinyl chloride

SAN styrene-acrylonitrile

SBR styrene-butadiene rubber

UV ultraviolet