W-TP2 25 WORLD BANK TECHNICAL PAPER NUMBER 253 April I 95 Protected Agriculture A Global Review Merle H. Jensen and Alan J. Malter P r .I _ . . . s t, ''- /4^ o Ss I s te X # .~~~~~~~~.. *li -- l] . @' S~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~d . s t v '- 8'w' -S''' ' jJ~~~~~~~~~~~A RECENT WORLD BANK TECHNICAL PAPERS No. 183 Najera, Liese, and Hammer, Malaria: New Patterns and Perspectives No. 184 Crosson and Anderson, Resources and Global Food Prospects: Supply and Demandfor Cereals to 2030 No. 185 Frederiksen, Drought Planning and Water Efficiency Implications in Water Resources Management No. 186 Guislain, Divestiture of State Enterprises: An Overview of the Legal Framework No. 187 De Geyndt, Zhao, and Liu, From Barefoot Doctor to Village Doctor in Rural China No. 188 Silverman, Public Sector Decentralization: Economic Policy and Sector Investment Programs No. 189 Frederick, Balancing Water Demanids with Supplies: The Role of Management in a World of Increasing Scarcity No. 190 Macklin, Agricultural Extension in India No. 191 Frederiksen, Water Resources Institutions: Some Principles and Practices No. 192 McMillan, Painter, and Scudder, Settlement and Development in the River Blindness Control Zone No. 193 Braatz, Conserving Biological Diversity: A Strategyfor Protected Areas in the Asia-Pacific Region No. 194 Saint, Universities in Africa: Strategiesfor Stabilization and Revitalization No. 195 Ochs and Bishay, Drainage Guidelines No. 196 Mabogunje, Perspective on Urban Land and Land Management Policies in Sub-Saharan Africa No. 197 Zymelman, editor, Assessing Engineering Education in Sub-Saharan Africa No. 198 Teerink and Nakashima, Water Allocation, Rights, and Pricing: Examplesfrom Japan and the United States No. 199 Hussi, Murphy, Lindberg, and Brenneman, The Development of Cooperatives and Other Rural Organizations: The Role of the World Bank No. 200 McMillan, Nana, and Savadogo, Settlement and Development in the River Blindness Control Zone: Case Study Burkina Faso No. 201 Van Tuiji, Improving Water Use in Agriculture: Experiences in the Middle East and North Africa No. 202 Vergara, The Materials Revolution: What Does It Meanfor Developing Asia? 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Jensen and Alan J. Malter The World Bank Washington, D.C. Copyright © 1995 The International Bank for Reconstruction and Development/THE WORLD BANK 1818 H Street, N.W. Washington, D.C. 20433, U.S.A. All rights reserved Manufactured in the United States of America First printing April 1995 Technical Papers are published to communicate the results of the Bank's work to the development community with the least possible delay The typescript of this paper therefore has not been prepared in accordance with the procedures appropriate to formal printed texts, and the World Bank accepts no responsibility for errors. Some sources cited in this paper may be informal documents that are not readily available. The findings, interpretations, and conclusions expressed in this paper are entirely those of the author(s) and should not be attributed in any manner to the World Bank, to its affiliated organizations, or to members of its Board of Executive Directors or the countries they represent. 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The complete backlist of publications from the World Bank is shown in the annual Index of Publications, which contains an alphabetical title list (with full ordering information) and indexes of subjects, authors, and countries and regions. The latest edition is available free of charge from the Distribution Unit, Office of the Publisher, The World Bank, 1818 H Street, N.W., Washington, D.C. 20433, U.S.A., or from Publications, The World Bank, 66, avenue d'I6na, 75116 Paris, France. ISSN: 0253-7494 Merle H. Jensen is professor of Plant Sciences at the University of Arizona. At the time this paper was prepared, Alan J. Malter was a market researcher for the Ministry of Agriculture in Israel. Library of Congress Cataloging-in-Publication Data Jensen, Merle H. Protected agriculture: a global review / Merle H. Jensen and Alan J. Malter. p. cm. - (World Bank technical paper, ISSN 0253-7494 ; no. 253) Includes bibliographical references (p. ). ISBN 0-8213-2930-8 1. Greenhouse management. 2. Plants, Protection of. 3. Floriculture. 4. Truck farming. I. Malter, Alan J. II. Title. III. Series. SB415.J46 1994 635'.0483-dc2O 94-24839 CIP TABLE OF CONTENTS FOREWORD vii ABSTRACT ix ACKNOWLEDGEMENTS xi PART I BACKGROUND CHAPTER I INTRODUCTION 2 Definition of Terms .....2....................................2 Economic Relationships .........................................3 Geographic Considerations .........................................4 CHAPTER 2 HISTORY 5 Early Development and Status of Protected Agriculture ...................................... 5 PART 2 PROTECTING MATERIALS AND STRUCTURES CHAPTER 3 COVERING MATERIALS 10 Mulches ............... 10 Row Covers ...... ......... 14 CHAPTER 4 GREENHOUSES 25 Basic Characteristics ............... 25 Site Selection ............... 26 Structural Design ............... 26 Environmental Control ............... 30 iii PART 3 PRODUCTION ASPECTS CHAPTER 5 GROWING SYSTEMS IN GREENHOUSES 44 Tissue C ulture ......................................... 44 Transplant and Plug Mixture Production ......................................... 45 Greenhouse Vegetables ......................................... 47 Hydroponic/Soilless Culture ......................................... 48 Closed Systems ......................................... 59 CHAPTER 6 FLORICULTURE CROPS 60 Growing Media and Mixing ......................................... 60 Cut Flower Production ......................................... 61 Potted Plant Production ......................................... 61 Bedding Plant Production ......................................... 63 CHAPTER 7 WATER SUPPLY, WATER QUALITY AND MINERAL NUTRITION 65 W ater Supply ......................................... 65 Water Quality .......................................... 65 Mineral Nutrition ......................................... . 66 CHAPTER 8 DRIP IRRIGATION 70 Field Layout ......................................... 71 Chemical and Fertilizer Injection Equipment ......................................... 71 Filters ..........................................72 Pressure Regulators ......................................... 72 Mainlines ......................................... 73 Drip Emitters and Tape/Tube ......................................... 73 Drip Irrigation Schedules ......................................... 73 Increase in Crop Yield ......................................... 73 Drip Irrigation Used in Combination with Plastic Mulch and Row Covers ......................................... 74 CHAPTER 9 DISEASE AND INSECT CONTROL 75 Root D iseases ......................................... 75 Foliage Diseases and Insects ......................................... 75 Integrated Pest Management (IPM) ......................................... 75 CHAPTER 10 PROPAGATION AND CULTIVAR SELECTION 77 Vegetable Crops ......................................... 77 Floriculture and Nursery Crops .......................................... 78 iv PART 4 ECONOMIC FACTORS CHAPTER I I ECONOMICS OF PROTECTED AGRICULTURE 82 Land Use Factors ...................................... 82 Yields ................... 84 Labor Requirements and Skills ...................................... 86 Capital Requirements and Economics of Production ...................................... 87 CHAPTER 12 MARKETING AND DISTRIBUTION 95 Intra-national Competition ...................................... 95 International Competition ...................................... 97 CHAPTER 13 TECHNOLOGY TRANSFER BETWEEN NATIONS 100 The A m ericas ...................................... 100 Western Europe ........................................ 102 Eastern Europe ........................................ 105 Africa and the Middle East . ...................................... 106 Asia and Oceania ....................................... 107 CHAPTER 14 DEVELOPMENT CONSTRAINTS, RESEARCH NEEDS AND THE FUTURE OF PROTECTED AGRICULTURE 110 Development Constraints ...................................... 110 Research Needs ......................................Il I The Future of Protected Agriculture ...................................... 1 12 REFERENCES 113 GLOSSARY I 17 ANNEX MARKETING AND DISTRIBUTION OF PROTECTED CROPS 127 v FOREWORD As land and water resources become increasingly conistrained for agriculture in Amany parts of the world and in the urban areas in particular, there has been a rapid upsurge in the production of high value crops under plastic and glass. The removal of trade barriers, coupled with growing consumer demand for quality pro- duce all year round, has further stimulated this move towards high value, intensive forms of horticultural production. Importantly, protected cultivation, while requir- ing farmers to have a more comprehensive knowledge of agronomic and crop mani- agement principles than for traditional agriculture, is well adapted to both small and large scale commercial operations. The success of protected agriculture is very much dependent on the level and quality of applied technology and on factors such as the local climate, the buy- ing power of the consumer, transport organization, market intelligence and access to local and international markets. An important aspect for succesful exports is the time of the year that fresh vegetables and( flowers canl be made available to fit in a niche in the overseas markets at a time when local production is not sufficient or absent altogether. Producers in arid and cool climates in the Southern hemllisphere and the Middle East have therefore an advantage in dealing witlh Northernl mar- kets. In response to the need to be better informed of the technical develop- mnents in protected cultivation and their application through W' Norld Bank support- ed projects, the Agriculture and Natural Resources Departmnent has prepared this technical publication, primarily for use by World Bank staff and those responsible for implementing such projects. The paper draws together globally applied tech- nologies, best practices and international markets experience as reflected in the special annex to this paper. Alexander F. McCalla Director Agriculture and Natural Resources Department vii ABSTRACT T1his Paper, "Protected Agriculture, A Global Review", gives a broad overview of the three main protective methods of plant coverage and related technologies for cliimate control and production techlniques, includinig drip irrigation in vegeta- bles and floriculture. The three protective methods are by using mulches, row cov- ers and green houses. The Paper also addresses some relevant economlic and pol- icy aspects in protected agriculture. Because of the overriding importance of the sector, a special ANNEX on modern marketing has been included to highlight world wide marketing issues and trends from centers in Europe, North America, the Middle East, to Latin America. The Paper is generously illustrated and written specifically for WNorld Bank's operational staff and national counterparts in devel- oping countries. The Paper is organized in four PARTS and a special ANNEX on Marketing. PART I gives the Background in Chapters 1 and 2, PART II deals with the Protective Materials and Structures in Chapters 3 and 4, PART III discusses the main Production Aspects in Chapters 5 to 10, while PART IV highlights the Economic Considerations in the remaining Chapters 11 to 14. The ANNEX on Marketing has been written by a different author and can be read seperately from Chapter 12 on Marketing and Distribution in PART IV of the document. However because of the complementarity of the contents, it is highly recommended to read both the ANNEX and Chapter 12. ix ACKNOWLEDGEMENTS The publication of this Technical Paper, "Protected Agriculture, A Global Review" was made possible under an AGR Study, which was initially managed by Hamdv Eisa, Principle Agriculturist. The need to address the subject is based on the Bank's increased attention to agricultural intensification and diversification issues, and particularly to high value crop production under glass and plastic bv smalliolders in arid and cool climates. The main author is Merle H. Jensen, whvile a special Annex on Marketing was written by Alan J. Malter. Dr. Merle H-. Jensen is Professor of Plant Sciences, Associate Director of the Agricultural Experiment Station and Assistant Dean for Sponsored Researclh in the College of Agriculture at the University of Arizona. He is a world authority on protected agriculture and has written many research ancd technical papers on the subject. Mr. Alan J. Malter is a market researcher for horticultural products in the Market Research Departmenit of the Ministry of Agriculture, Israel. His conitribution to the Paper deals with the marketing and distribution of protected crops. It exam- ines the broad trends in the USA, European and Japanese consumption and tradle in fresh vegetables and cut flowers, noting the opportunities for "off-season", developing country suppliers. The first draft reports produced were reviewed and edlited by external reviewers and their comments incorporated. Final editing was done bv World Bank staff Steven Jaffee, Agro-business Specialist and Johannes ter Vrugt, Senior Agronomist. The layout aiid design was carried out by Peter WViant. graphic consultanit. xi PART ONE BACKGROUND CHAPTERS I - 2 1 INTRODUCTION Protected atriculture is tihe modification of thie nattiu-al cinvi- farmling tech ni(qtles, which incorporate Idevelop)ments in irrigai- ronment to achievc optimum plant growxth. Nodifications caii tion, fertilizers, pestici(les, herbicides and genetics have aLlrea(dy be made to othl thle aerial an(l root environments to increase increased prodiuction. Nlore disease-resistant crop culltivars crop yields, extend( the gro\ing season and( permit plant (Trowth have been bLredl wvhich are responsive to suc h i farm inpits as fer- c(luring perio(ds of the year not commonly iised to grow open tilizer and plant density. The well-known Green Revolution is fielcd crops. 'rotectecd agricilttire maV' also inclicate compre- an) example of' how minodlerin teclnolog l has sil)stantially hlensive systems of contiolledl environmental agrict titure (CEA) increased yielis in somce developing cot intries with severe in which all aspects oftthe natiral environment are moldified fotr food/popilation prolblens. For mich of' the world, climatic maximum plant growth anld econlomi1ic return. Control may be conditions have prohibited year-arouid farming with crop pro- imlposedl on air and root temperatures. light, water, humidit,v dtiction ofteni limnitedl to onlys one season. Protected agricuiltulre carbon dioxicle and plant iitritioll, along wkiti coilliplete climat- Call providle new alteriniatives anid econiomic opporttiunities in ic protectioni and may' ultimately make it possible to gt'row crops Crop produetion to feecl a huInry woricl. on a luiniar lbase or anothier planet. This publicatioti describes the potential atid applicationi of Protected agricul- protected agricti lire ttire has enabled fo ulIse in developing miant comintries to 0 eotirities. It details greatly extend their- techtnological advantces foodl prodLuction tise-I1 throughouit the capability. Until now, Wotldl to increase crop suich systems of agri- vields, to impromve cuiltule have been (_tuality antd to permnit larigely concentrated early ail otut-of-season in developed coitin- cropping of foocl and( tries, hut recent ornaniLenital crops. research dlevelop-'it tuents have tna(le it DEFINITION possible to extetidc OF TERMS the benefits of this Many imethiodis of pro- technolog\: to less tectedc agricnltuire are aif'fluieint regions of misedl to modify the thie wiorkl. Plastic.' environitlmenit. Sonie gireenihouises, row _I ar e(Llite siniple and covers, and mulel- m inexpensive; others at-e ing systems were fiirst 7wo hectare greenlcumsefiacilitj in United Arab Emiirate.s alloced p)rLl(ldttiioi of coniplex aii(l costly. u1sed w idlele in huortiecimltm,ro crops udecr severe elimutic eondition.s. Ideally, crol) prodiic- Souithierin E.nrope, tioti \vonkl take place Japan. and the ill an araea not requir- Unite(d States: t iey are niow found in other areas sUutc as the ing protected atriictiltuire systems. ati ai'ea with year-ariond People's Republic of China, Soutih Korea. Miiddle East ani(l (rrowing teinperatuires. Because such t-egiotis are rare, and often North Africa. comipletely lacking in im(ost couintries. iiiethio(s hiave been Protected ag-icultur e will pla\ an impoirtant role in meeting devised to protect crops agai nst the hiarshi climilatic extremes. the vorild's food proCluction rer1mi-emetnts for tlhe year 2025. It is estimated that, by that yeari 8 5 billioti people will have to be Mulching. MNilehing is thf piacti( e of covering the soil arolilld fed - all additioni of' olme thian 3 billion people to the \vorld pop- plants with an org anic ot syinthe tic material to make e oditions ulation in ]990. In the dceveloping wvorld aloiie, the popiilatio i more favorable for plait t row th developmient and cropi pro- is expected to reach 5 billion bv the year 202.5. Alrea(lv, about (Iiictioin (Hopen and Oebker 1976) half' of' the Thir(d Wor ld is 16i ve ars of' atge or youinger Byv the yeaflr 2000, it is estimated that half the xodld's poptilatioti will Bov Covers. A row cover is at piece of elcr plastic stretched live in cities. Of the 24 cities expecte(d to exceedl 10 tillion over low hoops anid secictecl along the sidles of'the plant row b inihabitants, 18 will be in the less developed comititries. bmiring thi ecs alkcl ends with soil Floating NAV covers are It is clear that if we are to increase thie spply of food d(uliing wide sheets of clear, perforatedl. polvethy lente or noi-wvoNen the niext centhir. we must increase the output of the land. Nc'w porcoits plastic. niot snpported by hoops btw b! the plait itself. 2 INTRODUCTION High Tunnel. A greenhouse-like uinit but , .L, xVitlholt 1meC(hlallica1l ventilation or a periw a- - *.- , nienlt heating svstemi. Intensive Agriculture. This is based on -i cropping systeins that miay re(quire laree alnionllts of lahor and capital per innit area ofa ho id per year aitil normnalIN involves Cl'ops of highi %ale (Dalrymple 197:3). SIulci agri- -W f,r t_ cultural endeavors usuallv involve the Vo' . extelnsioll of tile growing seasoiii v iymeans of'p)rotected agriciilture. Muiltiple cropping, ; the rrowvinr ofg miore than one ecrop per unit of't lad( per year. is coni imlon_. Greenhouses. A greenbouse is a fham/ed or- inflated striuctiure, ecivered by a transpr- ent or translucent material that permits optimi imiil lighit transmission for planiit pr(- 7. dUctioll and pr-otects againist adverse climnat- Cucu-mbers grown in a sand culture system with drip irrigation in Anzona. Cucumber- yieids in ic conditions. Snielh a strnietiire enahles a this system exceeded 700 MTlho. person to work inside: anl iimayjo i v mates were le'velopedl oiilv>i as a sloping roof. at the samie time. Of Later in the century '' these mulc hes, only glass w,as usecl on both those made of polvetil- siles. This glass-house v lene are still usedl \as iused ftor fruit crops - toclav in the aricultur- siuchl as melons, grapes, r - _ al inclustry. The pre- peaches, amid strawber- ferrecl colors are clear ries and onily rarelv for t- p- anscd 1lack, althouglhiL a vegetahle procduction s- -ide vrietv of shacles (IDal rympile 1973). It a -' ii adc olors are used for svotlld seem tlhatt tle W K _ specific reasonis in the developers of this new - - ' o - prodUcHution of foocd technology kept mar-ket IL crops Significant profitahilitv in mind: Clear polyethylene muilch, in combination with drp irrigation, is used extensively in advances in the uise of tliey prodiuced cr-ops Southern California, to produce hitgh quality strawberres. milchies occurred (hir- wshich appealed to the ing the eariv 1960's wealth> and privileged, the only people sVho could(I afford the with mechanization, tire invention of mulch applicators and( luxurv of fi-esh fruiit prodiuced ouit of'season in greenlilouses. transplanters w\hich wotildl plant directly thl-ouighl the miilch. Protectedc agric'ultiire was fully established witli the introduic- Infraredl transmitting I (IRT) muilclhes wvhich transimiit most of tiomi of polvethlene after XX'orld \N'ar 11. The first rise of pol v- the solar heatt portioin of liglht radiation but absorb most of the etihylene as a gi'eenbomise coser wats in 1948, xlheni Piofessor visible portion, have recentlv heen introditicedl to the rimarket Emery MNIers Emimlert at the Unix'ersitv of Kentucky, usedl the (Los, et al. 1989). IIT MIulches provide weed conitr-ol as dloes less expensive material in place of too-e expensive glass. black mulch hut incr-ease the soil temperature, as with clear Pm'ofessor- Emimie't is considered the fathier of plastics in tile plastic mullelh Unfortunatclvl. lahor re(qiuiremnents to remove U.S.. becauLse he developed manyILV principles of plastic techlnol- plastic mulch fromil the field after the gr'owiin seasoi c'llI he ogv for agric'ultclmmal puripioses through hiis research oi green- high. New bio- andc pIhoto-degradlable polyethylene anml combi- houses, mulches anild row co\ers, nations of' polvethylene-paper andl polyethyllene-starch show pm'omiise in eliminating the neecl for mulch removal. EARLY DEVELOPMENT AND STATUS OF Today, millionis ofi'hectares are planted to plastic mulch. In PROTECTED AGRICULTURE the People's Republic of' China alone, over 2,867(000 ha, of mulch was uisedl in 1989 a plienomilenial increase oser- the 44 hia. Mulches. Natural mulches stichi as leases, straw. sawdust, peat in 1979, The a'ea andl tonnag1,e nsecl in each region of' the worldl nioss,andl compost hiave been usecl for centiuries to contiol ai'e listedl in Table 1 5 BACKGROUND Table 1. Estimated world use of plastic mulch (1987-1989) Area (ha) Tonnage (mt) Region Min. Max. Min. Max. Western Europe 150,000 200,000 40,000 50,000 Eastern Europe 8,000 0,000 2,000 2,500 Africa and the Middle East 8,000 10,000 2,000 2,500 Americas 180,000 200,000 45,000 50,000 Asia and Oceania 3,000,000 3,329,000 330,000 366,190(*) World Total 3,346,000 3,749,000 419,000 471,190 'its tlss C, c/c/c c li7s'p/c!/si c ( lutistf,,>,,,,e,, cist jt icss 5.,,,ly/ (5., is,tt,Isc It, . .,,, tile /lctts,Sc,i lc I,,, tc it ,, i f./, isis Ji/scc c S ./f cit/si tlscsis( tic,, th/ cs 8 i. jl ts t-/1, ,> 1ic ,,, s/. cc/i css .sc s i,,, l.st rli, .aticwiscsl (Iohiciitt ci Plastic, its Aticis/si'' (II'A I. 19.5/i9 rA 19S / a7) emd /iisis'. Pla,tic 'sislc11i l1s-ccc, " 1/, Ass,cc ]HiS /l,ltc 1 c)c)9 Row Covers. Rowv covers, or plastic tunnels, protect erops for the extrusion-blowin pr-ocess of mak-inig polvetIlenec niiih f'romi ftrost and create favorable conditions for plants to achieve less capital intenisive than the PVC equitipiment, and therefore early production. Befor-e the introduction of polvethl'lenie. earl)' selected polyethivlene for use as row covers. spr-inig crops suchl as cicunilmhers were started and grown in In the lUnite(d States, the first uise of polyethllene row covers miuslin-coverecd wooden bhox frames measuring,: approximatelv for ear-lv erop produtictioni was for a iLcuictiml)er planiting in 17 mleter-s sqiiare at 0.3 mneters in height. This was a costly hut California in 1958. With careftil venting acdjustimienits (or weath- ef'fective method of' producinig earuly fruit fronm 19:3.5 to 1945 er changes. plastic row covers prodhicecd a mnargill for maivrketilng (Hall 196:3). In the mlicd-forties a niethocl otsinl,g tvo separate of four to five weeks over that of'thie two paper cover methio(ds paper- caps replaced the woodeni h)ox frame. A small cap, 28 cmll. andCI produced good yields as well (Hall 196:3). in diamneter andl 14 em. in height. was usedl to start the plants. For 25 vears tiere was steady} growth in the uise of' )lastic row A second. larger. tent-ty-pe papier cover- was installe(d whieni the covers. However, no significant inic-ease has occurred in recent plarnt fille(d the smaller cap. This secondl cap miieasur-ed :35 cil x years (Tal)e 2). with the exception of'tlhe People's Repuhlic of 28 cn x 21 cim in heighit. This tent cap wits constructed so that C(hina where there are approximatelY 80,000 lha. ind(ler- cover at one or b)oth encis couiil h)e openecl. Usutally it was the leeward the present time and( expectations of greatly expandledl use in side xchicih was openie(d and the plants were trainled in that the near- fuiture. direction,. Tle paper tent thiis actecl as a wiTicl bregk. The earho Tu]-ol]giotit the world, a total of'souine 70.00(0 la. are covered fruit coumldc develop wlhile the plant had partial protectioll dur- with PVC film: 60-62,000 )ha. in Japani, 4.000 ha. in Franice and( ina adverse weather. The double cap produced f-uit as earlv as 1,500 ha. in Italy. Low clensity polyethylene tilm on the otlel- the wooded fiamce mietho(d but was less costil. Paper covers are hanid, is used ont ahout 195.000 hla. of wvlich over 80,0()0 ha. are still usedl today in somie parts of the world. Paper covers haLive locatedI in the People's RepulNic of China ( Huang 1989). In one serionis liaility: while thev help protect planits froim earlx 1988, the ctareage iiceeased over u30()()0 ita. in (ilina itlone. spring f'rost and wind, they also reduce the arnoitnt of liglht The total woorld tonnaage amiotunts to about 74,000)-76,000 ni) t of reaclhing the plant. wvith the resuilt that planits may h)e succuilent polyethylene uisedl for tuininels. and \veak. In Japanl miore tranislucenit miateriails suchi as Xinvl ol polyethylene film are substituting paper as platint covexis or hiot- Table 2. Estimated world use of plastic r-ow covers caps. Suchi hotcaps not onIv protect against light fhost hut also (1987-88) proxidle extra heat andl protection against chilling vindscl blow- ReBion Area (ha) ing sandl andl soil particles. Plastic row covers wer-e initiallY usecl in EUrope and the ULnsited Western Europe 60,000 States, and especially iil japari. In f'act, in 1959, Frtiiec ancd the Eastern Europe 20,000 U.S.A. totaled less than 4(00 ha. undce plastic; Japan ihad itore Africa and the Middle East 10,000 thian 8,0(30 lia. (Bliiclot 1966). Since thien this itiethiocl of pr-o- Americas 10,000 tected agriculture has h)ecoie coinmon thirou glowit tlte world. Asia and Oceania 165,000 Today, as in 1959. Japan uises mostI -polvymvinlchloicle (PVC) film for Irow c'cvers. In othier coimntm ies polyetthlene predlomi- World Total 265,000 nates. Tlhere are lhistorical as well as econolmiic measonis for the selectionis of' (lifferreit materials fot' the same taxsk IP\C filmis s Ic lstusscilus c nnistcsttcc fw IP/mics isl Awicsltii c( IPA 1957c Alct. N tib7 liave aL h)etter Iheat-rmetaining (inf rar'edl i'adiatioti) capac ity thall c f/is (:/iisc'0 Pl/tic1ts/i h' l/ RcctA'/-c . J§59 iHisnt I]/sI polvetlrleine but they are also m)ore expensive EarlY in the developmient of row covers it was not possible to produce PVC The simplest atnci most economnical forml of row covemrs is tIle shieets wider tItan 1.6 meters, althouglt polvethslene dilms of 2- direct, or floatingr covers Nith inO suistainingo wvire or canle itoops. 12 inieteis in width were available. With governnicnit finianciail Fir'st inticicrloced in Gerniany in 1970(, floating(y covers theni were support, Japain was the first country to dtevelop wide PVC shieets adopted b)y neighbtring cotilitries. Perforatecl )ol\ etlvlene film v (2-3 meters): as a ritsult, Japan selectedl this inaterial as the p(re- 50 mnm thickl, generally with 50) holes per m- /i.e. 4%' ventila- cloiinant tle of filn. France aiid ltalv toll]d the e(qilipimielit tiOni, 46 g/m2) nlow conlipetes with nioni-woveni/sl)nilhonicle(l falb- 6 HISTORY rjc materials (PP. PA, polVester), which are porous an(I m1UchI lighter (1(-.5 g/r). - These latter m11aterials haL[ve been particular- r - -' I, suiccessfilI in Franllce (2.,800 ha. out of - _ 4,500 lha., andcl in Japan (1C lOO of 4,000 hla.). ,- Accordingy to the International Commllittee for Plastics in Agrriculiture (CIPA). the 1986 . xvoi-ld estinu1(ltes are: -Perforated PE film: 15,00.( ha. x 0.4.5 . . MT/hIa. = 62750 NT M . -Non-woven veils: 10,000 lha. x 0.2 ' MT/Ih. = 2,000 MT Since the non-woven covers are (qiuite nexv in agrici litUre. man' grower an(l university- experiments are cuirrenitly unlderwav .1* - throughout Nortlh America, Eur-ope and JTapanii to unlderstandl the effectiveness of this - nexv generation of plastics in modliRing the . -b. micro-enxvir-onment in crol) procli ction. For i - . > instanice, scientists att the University of New In the People's Republic of China, production of cucurbit crops under plastic row covers for liaimpshiire are studying the use of non1- early market has increased dramatically. woven covers in produtictioll of a number of crops: inicluding vegetables, simiall fi-uits. flowers. oriiamilenitals, with i total world tonnage of abotit 224.000-24.5,000 MT/vear. tree see(illings in nuti-series, tUtf an(d the overAvinter-ingc of vegeta- In Japan. the area covered bx' plastic filmn greenilouises bles, perennials anidl nursery stock (Vells and Lox' 1985). increased :35,000 ha. in just 20 vears (196.5-8.5). In Korea. these greenilouses increasedl 6.3 times, from :3,099 ha. in 197.5 to Greenhouses. The total xvorld area ofglasshouses over the last 21(061 hia. in 1986. The Peoples Republic of China soiowed 10-1.5 ears has been estimated at :30,000 ha. (Anon. 1987): with equally dramatic grox'th: 5,:3:30 ha. in 1978 to 34,000 )ha. in most of these fouiind in niorthiwester-ni Europe. 1988. The combined growvth for both areenlioises andl ro\v nov- In conitr-ast to glasshiouses, plastic greenhouses have been ers, in Chinia exceedlecd 96.000 ha. in just ten vears. rea(lilv adopted oni all five continents, especially in the Undicloubtedly, Chinia is one of the largest user-s of agricultural Mediterranieani region, (hinia andl Japani. Most plastic greeni- plastics in the world, where over one billion people - 20 per'ent houises operate on a seasonal basis, rather thani year round, as is of the xvorld7s populatiou4 - are being fedl f'romil onlk 5 percent of the case with most glaisshiouises. The estimiiatedl areit of plastic the earthi's cultivated lan(l. greenhouses is shown in Table :3. Sinice 1960, the greenhouse lias evolved into milore than a plant protector: it is now better unidlerstoodI as a svstem of Table 3. Estimated world use of plastic greenhouses Controlled Environiment Agriculture (CEA), \ith precise con- (1987-1988) trol over air and root temperature. water, humidity, plant nutitri- tion, carbon dlioxide ancl even light. The greenhouses of today Region Area (ha) caln best be seen as plant or veg etable factories. Almlost ever Min. Max. aspect of the production systemii is auitomattel, witli the artificial environment and growincy svstem 1iniilder nlealylv total computer Western Europe 55,000 58,000 contiol. In a research setting. suchi at totally eciCloserI systelm, Eastern Europe 16,000 18,000 \ith artificial light, is called a growthi chambier or a phvtot-oll. Africa and the Middle East 15,000 17,000 In the Uniited States and Japan. suichl systemns miax cover larae Americas 8,000 10,000 areas. Asia and Oceania 91,000 95,000 Controlled emnironment agrriculture has gained in hiorticuil- tiural imiportanice inot onlY ill \egetable and ornamental crol) World Total 185,000 198,000 production but also in the prodIuiction of plant see(lings, either fromi seedl or throm igh tissiue culti ire proce(llires. sini 0' )ii Il ('a,l,iit,', f al,ri> Yi. ii .Agi co'I1.A, 19Yj i.A?)i . 19S-, , flu In the last 1.5 vears tl ei'e lhas been inucreasing interest in the (l/ai, Pla'ta .Xl lJc R, H, A'.', . I099 Haaiq 1 a,S wl) al in S, ,inmar a, it, Dd'l/na of P'la.,, -a Agr, . 19',7 (Park. 1.5'1. use of soilless or1 li(droponic techniques fOr producing green- hotise hor-ticulturral crops. The futire grs uvxth of greenlrihose or1 PVC( filim ftor greenhlioutses is still dominant in Asia. especiall\ conitiolle(d exvironi imenit agriculture, where hydroponics is uise(d in Japan (35..200 ha)l. an1d( low xdensity polxethylene is also uise(d for vegetable prouclticinu w ill depend greatti! on the develop- in Italy (.500 Ia) anildC Greece. LDPE films cover at total of niciot of pro(luction sYstemis that are competitive, in terims of 149,000-162,000( ha; the averagre coiisurinptinni is 1.5 MT/ha/year, costs. with openi fieldl agrlicllture. 7 0 F LU a- 8 = D I 'L~~~~~a U) m z 3 COVERING MATERIALS The financial return for producing early crops can be higih, hut. gationi usually wets the soil miore thani necessary; this results in so is the risk. Protectecl agriculture cani reduce this risk. the leaching of nutrients ancl a dIrol) in soil temilperature. As a Off-season crop produietioni means miore thiani just early consequence. plant development is retarded and the earliness spuing cr-oppinig; it inlcludes produiction (lurinig times of adverse of' yield is aff'ected. Over-lhead irrigation also requires careful climatic or econiomilic condlitionis, suich as may occu-r in sulimillelr monitorinig of proper rates of water application to prevent clam<- Or' xwinter. For exaniple. off-season productioni of greenilouse age firom ice forimiation. This occurs whieni excessive water, \vith meloni crops in the United States is not profitable due to com- large droplets, accumulates, folloxved by a prolonged periodl of petition fromii mnelonis grown in Mexico. The slightly warmer freezing. temperatures in Mexico obviate the neecl for protectedl agric ul- Indivicdtial plant covers, or hot caps, made of paper have been ture, except perhaps for row covers, while in the United States used for manyv years to protect plants and hills of seeds or planits the mnore expensive methods of greenhouse agricultuire are still in the field, bult are not used extensively today. In Michigan. needled to produice a similar crop. This weathier advantage - andl beginning in the 1920's, covers madfe of paraf'fined or oilecd lower labor costs - gives Mexico the econoimic advantage in pro- brown paper made it possible to fieldl plant approximatel' two ducing off-season wvinter and earlyv spring meloll crops, despite weeks earlier than usual. Althouah these covers helped to pro- the high costs of shiipping the crop northi. tect plants fi-om the earilv sprinig fiosts and winds, it was found Of prime importance in offsetting the additional cost of pro- that the brown paper used, reduced the lighit to the plan)ts andl tectedl agriculttiu-e is a good yield. To this end, manly methlodis tended to make them more succulenit and spindily in growth. have been devised to protect crops against the cold and frost. Similar growth occuired when other miaterials wvere used, sulch Ideally, agricultiral productioni wotild he located in areats that as celluloid, alassinie. paper parcmliileuit, andl brown wrappiiig are fr-ost-free; however, in many' countries, suchi locations are paper. After the paper covers were removed, the plants wver-e rare or even absent. In addlition, increased capital ancd trans- easily damagecd by a cold wind or a light frost because of their portation costs, as well as excise duties on imports, often miake soft, succtilenit growth (Hibhard 1926). it uniprofitable for farmers to produce horticultural crlops in Plant covers of vinyl or polyethiylene film are still used in anotier count-y for exportation back to the hoie country. Japani. Framedl with xwire or split bamboo sticks, withi certaini Farmers have devised manly methiods of protecting agricul- cr'ops, they' produce an earlier marketable product witil highier tore, with varving degrees of effectiveness. These include total yields. smoke, wind machliines, wettina agents. chiemilical fogs, bacterial The "brushindrg" methodis of crop protection consists of lean- spraving, sprinkling, hot caps, an(l brushinig. Smoke, which has ing shieldts of brown kraft wrapping paper over the plants. been used by somie vegetable growers in the United States to These shieldls are attached to a firainework of brush, lath, or prodiuce a clolid cover duiring cold peliods1, h1as comie into con- wire andl placed againist supports on the northi side of the east- flict with environmental pollution laws and( policies. Wk7inld west rows. XVith this, a mibcro-climnate is formed and earliness of machliiies prevent frost by moxing air over the endangeredI yield can be accomplished. A similar systei, using paln fioids, plants. In fielcl trials, a wind miaelinle in the 100 h.p. class lhas is eimployedl in the Middle East during the early fall monithis to been shown to proiide protection of 20C or nmore for anl area of protect horticuiltural crops from h(:ot windis and cli-ect sunlight. :3-3.5 hectares on a clear, c;dlim nighit. Suehi systemils are com- This method is not feasible for extensive areas since it requires mnonily used in fruit orchards in the LJUnitedl States. Wetting large amioints of plant imiaterial, wiici is ofteni not i-eadil avail- agents an(l chemilic-al fogs have demonistiatedl their effectiveness able. Suchi methiodis of crol) protection are r arelv tisecl today, in protecting plants during experimnenits but are rarely used in especially sinee the introductioni of agriCultural plastics. coininercial prodclution because of cost and lack of protection While wind machines are qjuite comimoni in fi-uit orchiards, dluu-ing times of slighlt air movement. Bacteria sprayed onto especially in citrus procduction), none of the above systems of plants give a small degree of frost protectioni; however, govern- protectecl aaTirtilture is as comimioni as mulching, row ]enital a'sencies have been slow in granting permlissioni to use covers/low tuLinnels, andl greenhouse agriculture. sucih bio-controls because of uncertainty about the imJpact of these bacteria on the overall ecology. MULCHES The sprinklinig of wxtter- - ovehlieadl irrigationi - at the time of NMulch svstems are primarily used to inicrease soil temperature, frost is often used to prevenit dlamilage but has serious disadlvan- reduce compaction, prevenit weel agrowtli and conserve soil tages. Water tuininig to ice releases heat energy. therefore, the moistire. All of these inic-ease erop growtvh and production of latent heat of freezing water keeps the plant tissue at 0(2C; anc saleable product and, in some cases, promilote earliness. even offers good protection to several clegrees below 0()C. However, coverinig a large area at once with a sprinkler irriga- Organic Mulches. These tyj)es of mulches are not usedl to tion systemil can be prohibitively expensive because of the cost increase the earlinless of crop productioin. with the exception of of pumping and sprinkler equipment. In addition. spririkler irri- pet roleum m ulches. Straw is somiletiimes placed over low-gr-ow- I0 COVERING MATERIALS in( crops silch ias strawiberries to aive pro- tectioni atgainst t'reezinga, wiinter windls that - ' m c! (lessicate the strawberrv pltants. somie- timiies causing severe daniage. In Chinia. - -- melon crops are ci o nlv grown il the stiilhli of sinll] girin erojIs. This place- Ililient pCermits fltlit ti (y)\v ilow (ad iii titie o1) a bet] of straw muilchl. svhich keeps it fromi elotact sVith soil-hor(me ftilngi is, lessenint , _ the incidence of (LUl'in]iin fung.al diseases. C - Petroletim Mulches. Since the early - - 1 9.50's. petroletium iililichles. somietinies r (leal oif attention. Tese wter emlsionls f peti'oleuimii resins are forimilated for spray- in, bN zidIiicr yd in aprpiro iate solxeiit an(ti _a_ si it h)le s tiurictanit thitt is eii Isif et I iillto - - svater. 'The formnlation plrodilices a gel-like until tlhat is sprayed onto the suirface of the in Kuwait. strowvbemes ore grow,,n !n polyethylene greenhouses on .!'ost!c mulch. greot!lv soil. Yielcl increases of as imuch as 50 per- reducing ecoaoration of dnp orrigatea ,^ater punL-fied by desolnotnn. cenit hIae beeni reported wvitlh petroleum midilc oin carrots, OnioIIs, lettuce, tuiirns ipiand ra(lisises (Miliier reduces or climiniates wveed probliems, as (lo otht r 196:3). milcies whici bhlock the traLlsni1ission(I of 1iost of tile Most of tlie value received frioim petroleum mulci is derived phiotosntlieticall\ active ratliatioi. in the first fewv veeks after plaiting dtim-ing tie period of ger- Becai ise clea- plastic allows nearly t'ill liglht transinis- min atio n anid earls grovtli. Petroleuium iuldl i is nrm'elv used ill sioil - eedl gowthi canin e a serions prolblemin: for this agriculture hecatUse o(f its tvo sti'oiig' dlisadvantages: it cloes niot reiason, black is sometimes preferrecl. Applic'ltioil of contiol sveedls and it is ai ser\ iv ess\ milateriial to milix and appl. helerbicides to eli iiiate sveed prohblemis is hecominig iicreaLsinlMv c'onsttioned bN environmentadl ('ililcerils Plastic Mlulehes. Svmlthetic mnilc'les such as those miade o(f ail le(islatioln. Grey plastic' iicldi providles somlle polvethivlleie utre noxw comiiluino tli'rmuigh ioimt the sorll. Plastie advanta",e iii weecl control. The giey color t m'insmnits a mu]Ilch is avalil Ilble in shieets of' vi'iOiis sv%idtlhs colors, amid thiick- limited amioutnt of liglit hot still eniioitig to promi' ote nesses. The vidth l most comiunlon uise(d is 1:3 meters, with a sveed grosvtlh. Nevertheless, since miuchli of thie infi'r'ed thiickiness ot :37.5 iiiicroiis. Black is the minost common color of raliatioln is stopj)ecl at tile sulrface of this plastic' fill, polkethlMenie mimlc1. Hoswever, thiere lhas heen inc'ieasing inter- the surtface heat is sift'flcienit to i-ibrn xveeds \vieii tles\ est in thie uise of cleiar plastic sinice its clarith imIcreases tile soil touch thle filiii. \'itli less veedl growtl utnder the gre>' temlpem'ttiii'e~ therebyN- pi'oinotinig earlier (growVth andli lhigher filma there is less loss of feritilizer miimt'ienits andl less vield thian hblaick plistic. water loss from the soil. Siice imor-e infrared i rad(liation Plastic mulch prox'ides the hollosvinig ad(vatages (Lamonit permeates the grey plastic thani the black, imore heaLt 1991): reiaces the soil, resultin"c, in an earlier barvest. 1. Eamlier crops. By i'aisingc tile soil teniperiture in the 4. Reduces nutrielnt leinCigi(f. NitroCgen ind potaissium aie plantin bed, pletilt gri'owtl is accelematecl. piodi icing ear- easilv lecied wvitliout plastic mulchliin lier Vields. Black plastic miuiieli can resi it in 7-14 &iy's 5. Reduced soil compaction. Soil unilder tiie plastic iimulchli e'arlierI hrivest while clear plastic ac'cele'ates hmarvest by riemimains loose f'r'iable, and( wvell-aeratel. 21 das's i mans codii(litions. Citiin iilist he taken ill 6. Root priniigl.> eliminated. (Cl:lti\vaLol is eliiLntecl. lusing plastic niiilc'h inl hot deselt regions, especiailly xith except for the areat betNveen the munilci strips. crops sucli as peppers. that do iiot shadle tue mlulx ch later 7. Cleaner vegetable piroduct. The eclible product doe s iiot into the siuimiiier. This i'esuilts in excessiv- temperatllre come into direct conttaLt withi the soil. svhic'l resuilts in a hibiufl-iip in the soil, wvilic' encouriges certain f'iingal cleatiner product w1itli less i-ot ami(l fruit llemilisiies. Time pathlogens suichi as P1tIlhimo spp to thrive mudl ofteli cleaner prodhic't retquiires less ttCentiol in gradl(lillmg pack- dlestroiv the ci'op. White or- white-oii-lAlac'k 1)1lcl creatcs ing, ant] pocessi ig. a1 cioler soil tempei'atire tlhant titlher icleair Or hlick. This S. Aids fumigyation. Mulchies inc'i'ease tile effectiveness of m(ill i is prefe'rec! for estatblislingi crops sli it as idll chemicalts applied as soil fumli(gants. toiilatoes uii lei' liot sunlimie c'oli(litiouis. 9. Red u'eu iatei-l ogginig of' c'iil). \\'ate' is sli'l fioiti tlie 2. Reduced eviaporation. Miiilc'h reduices soil water ioss. row area 1)N the raised, taip'ecled iecl althiouig,h ilot all Bec'aise mi ori IfiniOrm soil mioistiure is nmjiiuiti nc'i ctli plastic iiiiclich is u sedl oillY oli rilised bedIs. frequency of irrigation ii iav le r'ecluc'e'l. 10. Nssist ill insect nmianagetnemit strategies. Use if' mefler tive :3. FeNver seed] prouldems. Black amidlvliite-oi-bLick plastic mulICh 11elps toi m'p' insec't sectors of\virius diseases. IIl PROTECTING MATERIALS AND STRUCTURES In the mid-1980's, a plastic mulclh callel "Infrared cent more total yield (Loy 1991). Clear mulclh produced nearly Transmitting", or IRT mulch. was placedl on the m arket. IRT 13 percenit inore earlv yield than IRT but produced slightly occupies a niche between black and clear iutlchi, affording lower total yield due to weed problemiis under the clear mulchi. weed control as vith black mulch and increasinig soil tempera- Melon plants growving on the IRT and clear mulch did not ture as with clear mulch (Loy and Wells 1989). exhibit cold injury as did those on black mulch. In the first IRT absorbs (or blocks) most of the visible radiation, that part month, vine growth was double that obtained on vines growing of the solar spectrum which supports photosynthesis and the on black mulch. growth of weecls. In areas where either purslane (PortWlaca No doubt plastic mulch can increase vield and improve prod- oleracea L) or grass species cause serious weed problems under uct quality by modifying soil temperature and controllinig soil clear plastic (without herbicide treatmenit) there is little or no moisture. A mulch can facilitate fertilizer placemenit and weed growth under the IRT mulches. Weeds will germinate reduce the loss of nutrients throughl leachinig. Mulches can also under IRT mulch and will either continue to grow slowly dur- provide a barrier to soil pathogenis. ing cool weather or will be largely killed by hiigh temperature Reflective mulches have been shown to repel certain insects under the mulch surface \vhen daytime ambient temperatures such as aphids (Aphis gossypii). The reductioni of aphidls and are higher thani approximatelv 27°C. otlher vectors can greatly r educe the incidence of virus cliseases. If properly managed, plastic mulch can produce significant In tests conducted by Dudley et al. (1980) muskmelons were vield increases. Plastic mulch has increased yields in several grown on four synthetic mulches: aluminiiumil foil on paper. ali- crops, such as tomatoes, peppers, eggplant, muskuiielons, sum- minuin on black polyethylene, black polyethylene and white on mer squash. cucumbers, watermelons, and strawberries, even black polvethvlenie. All mulches produced lower aphiid counts doubling production in some cases (Geraldson 1962; Nettles than unlmllelhed plots with the aluminium foil oni paper hiaving 1963). the lowest overall count. The soil temperatures were hiiglhest Carolus (1962) has demonistrated that a polyethylene mulch under the black mulch and lowest under the aluminum foil on increased the early yield of plantedl tomatoes by 50 p)ercent with paper. The largest early yield and the greatest total yield was a 300 percenit increase in growth. In a cool season, muskmiieloni from the black mulch treatment. varieties increased in yield from 40 to 20.3 percent. The yield of These trials were conducted in the spring when aphids num- early cucuiiibers was increased by 130 percent and the total bers were low. During late summer when the aphid populations yield by :30 percent. Woodbury (196:3), in Idaho, comparedc may be hiigh in some areas, the incidenlce of virus may reduce black plastic mulch with. non-mulch production awil got a yieldl yields bv as much as one-half (Dudlley et al. 1980). Using black of 8,733 muskmelons on the black plastic treatments versus mulch in the late suinmer. during a time of already high soil 2.994 melons without plastic. The mulchl advanced peak pro- temperature. may heat the soil excessively, thereby damaginog ductiori by 1-2 weeks. plant growvth rather tlhani promoting it. as happens during cool- Lamont (1991) lists possible vield achievemenits using plastic er periods of the year. Reflective muleles offer the advantage muleh systems with drip i-rigation: of not overheating the soil at a time wheni they are needed to At the University of New Hampslhire. research comparisons repel insect vectors of severe virus diseases. Their use has betveen IRT, clear and black plastic mulch showeed that IRT therefore shown promnise in tropical regions where insect pop- doubled early' meloni yields over black mulel with over 33 per- ulationis are high year-around. Earlv researclh results with colored mulches, testing the effect oni plant grow\lth. yield, aiicl insect populationis (Decoteami. et al. 1986: Kaplan 1991) look promising. While too early to recomllmenid, this new _developmiienit is the first major applicatioin to comne fromi the scienitific discovery of phvtochrome. Despite the obvious advantages, the high cost of synlthetic mullclhes has limllited their uise in c-ommiierc-ial production. At pr-esenit. synthetic mnulches are ilsed for crops wVith _higlh valuie per uinit area. However, plastic muitlchi is increasingly uisedI for- the prodiic- tion) of cottoni in Israel and( miaize in France, ~~ * ~~~~aih a~~-s well ais fruiit trees ituul vine crops. it |In Chiniia, plastic mu1ilc-h aidIs in the pr-o- ( (IlictioI of fortv (lifferenit crops. inielmudin cotton. corn, I-ice transplants. T'fruit trees. _ -. tobacco. sugar caiie, peaIuts, and vegreta- ~~ / t ~ ~ bles, and the Cihinese ha\ e conduclctedI Fruit decay and blemishes are reduced when piastic mulch is used to prevent direct contact research oni the uise of mloulch vith niiore of fruit writh the soil. than 90c diftfer-ent crops. The total area of 12 COVERING MATERIALS Imlchl in ChIiina has reaclhecl 2.87 millioni hectares, witlh 65 per- Figure 1. Crops grown on plastic mulch in China cent in the nortlh and the rest in the soutil. Figure 1 shows the breakdown of c rops growni on plastic mulcl. The cost of muleih has been reduced because the mullel used - is a verv thin film rather thani the thicker film used in other counitries. The material being usedl for mulclh film is mostly low density- polyethylene (LDPE) but some LLDPE (extra low dlensity) and /' \ higil density polyethylenie (LIDPE) is also used. Generally, 0 ,hers LDPE film is 0.014 mm; however, film made of LLDPE. Oh lIDPE and LDPE mixed with HDPE along with LLDPE 1' - mixed with HDPE is only 0.008 to 0.01 mm thick. The very thiniT , films are very popular with the growers, sincie the growth ben- C? , " / efits of the thin muleh are the same as the 0.014 nmn ones and cost :30 percent less. Most of the imliichl films are clear althouglh some silver, black, and wlhite films are used. Herbicide films and pbotodegradable films are being studied and tested. Disposal. The disposal of' waste imliichl is of great concern as authlorizedl system is allowed, although disposal of stulch large landlfills become overburdened with waste plastic. large amount is not recommenidecl. More detailed and Polyethylene mulch does not decoimpose and must be remiioved thor-ouglh approaclhes are needed, both technically and from the field or it will interfere with fututre tillage. administratively. In Japan. the handlinlg of waste plastic is one of the biggest Recycling of plastics in Finiland (Cornwell 1989) is a major problems yet to be solved. Plastic consumptioni has increased businiess for a private company' producing heavy-duty plastic dramatically in Japan in recent years (Takakura 1988). In 1985, sacks, agricultural films, and constructioni grade films. The the total amouint of waste exceeded 165,892 tons, whliel includ- company collects used films from the comimunith and returnis to ecl waste materials from greenhouses and row covers, as well as the plant to process them. The film is separated by type, plastic mulhlles. Since 1970, Japan has treated plastic waste wlhether clear, colored, or printed; it is then wasled, dried, and uiicler the law of industrial wastes Growers are themselves repelletized for feedback into the cycle. Sinee reproeessed resin responsible for halalling the wvastes and, in the process, must is not of the quality of virgin resin, only 15 percent, or less, not pr-odtuce any air or water pollution. It is illegal to carelessly reprocessed plastic is used with virgin raw material. Except for tliscard the waste plastic in a maniner that uiglht create obsta- medical or food packaging, injection moldlecl plastic processors cles inl rivers andl other public places. use half reprocessed plastic and hialf virgin material for prod- The three methods usedl in Japan to discard plastic waste are: ucts such as furniture and tovs. (1) reeycling. (2) burial, and (3) incineration. Takakul-a (1988) Degradable plastic mulchles are currently receivinog much explains the metlhods as follows: attention, especially the photodegradable mulcl. These plastic Recycling. Five types of recycling are used. a) mutlches have many attribtutes of standard polyethylene mulcl: Generation of pellets and fluff. Collected waste plas- they are easy to lay altil provide the usual benefits associated tics. mostly PVC, are first graded and foreignl matter is Withi mutlch. The major difference is that photodegradable removecl After rotigh crushinig, theyv are washecd wvith milchles decompose after the film has received a predeter- \vater. finely cruslhed anti tlrietl. The repr-oduiction miniedl alm1oun1lt of tTV light. The clhemiiical composition of the ratio of nsetl materials is approximatelv 5OWr for PVC. film cletermnines the amount of light requtiredl to initiate break- The products are half-materials for plastic tiles, mats, tdown. sandlals and fillers. h) Collectetl waste plastics. either XVhen the degradable nudlc has received sulfficient light it PVC, or PE are crulslhe(d andl theni mleltecl \vithout becomiies brittle andl tlevelops cracks, tears. ani( holes. Small wasbing. Plastic exUtlation makes final plastic prodI- sectitins of nitilchl (uisuially less thani 5-6 square cmii may be ncts.) C'ollecte(d waste PE is crIsIietil antld mijxetI with tornl off anc blown aOvwavy by the w\ind. The ftilm finally disinlte- sawtlust or rice hullls to make solitI fuels wlhose calorif- grates into small flakes antl disappears into the soil. The edges ict valtes vary friom 5,630 to 10.050 kcal',g which are of the mutlch covered by soil vill retaini their- strengtlh anlI t'qikialent to those of coals andl cokes. c) Waste PVC decoimupose very slowly (Garrisoni 1990). To tacilitate quicker aLL(l PE Ctan be treated to make hyvlrophlobic materials breaktlown of that mtulchl buried in the soil, soil coverini,g the for drainage. e) Oil or g7as can be recycled by pylrolsis etlges sholdlC be removetl before final harvest, or as sooII after of wasted PE. harvest as possible. Exposinig the coveretl edges to lighlt will Burial. WN7aste plastics which are not suitable for- initiate the breakdown process. sooi enoumghi it is hopetl, to reproduction llst be buried according to the law reg- facilitate sul'licient decomposition l)elore fieldl prel)arationi the ulating plastic wtaste tlispositl. The place ancl metlhodl of' following spr ing. burial and pre-treatment iae regildated by the la.v Each miateriial respotllcs differently to conditions \ithin a IncWinerationi. Incineratioii is also regulated lv the given gromving region. Ther-e are regional ViariationIs in light law. Inmcineration amLlotulnts up to l(( kiav bv an intensitv air andsoil temiper-aittire. amicl soil tN-pe. Slatlimig of tlle 13 PROTECTING MATERIALS AND STRUCTURES muilclh andicl the amotint of lialbt affects the tiuine of' breakdownil. loniger seasonis. Othiei fmictois that ilihIieTCe the timile of bireakdlown are: plant * a shortage of planlt niltients, re(Tiirinig mor-e efficienit fertil- gro\tlh lial)it (vine ori uprigit), the timile of year the fillm is laid ize r uise. (early Spriiig oT 1 siOil imner), the tiune b)et-ween la0ing the plastic * the nieedl for non-chemnical pest and wveed control, and filiti and plantliea the crop vis 0ro aLid the use of docible or sinl- * sanIitatioll regula;6tions fOr 'freshl proI0dIce Which re(lIuirethle gle rows (Garrison 199)1. The milost imiipor-taniLt factor- affecting crop to be kept away from the soil surface. brecakdowsit is thie Oriinulttioll of'tile mIuLICI - siucil as Nwliethier it Resear'ch hLIs alr-eadls deImonIstraLted the degree of iillpro\e- is a sh ort, iuite ieloeiate oi a lone -lasting film. Becaiise of thiese inieiit that VaLiouIs lullllches miake oni pliat procliuctixity. Future onlsiderations it is b)est to expcriment with the various optionis reseairch will probably concentrate on1 iunderstandincg the ii icro- and im anuifac tretris of filmnl befoire a specific photodegradable climate pro\ided 1wy the differenit mulches, with thle goal of' miulcli is selected for large-scale app)licaLtionI. deter ,ininin liowv eacinicocliniate c IC l)e reauilated to pro- Biodegradlable nii1ilci es are still in tIc experimiieltaUl stage. vile opti miin) conclitions for specific plant species. Research onlI begam in the iiiid-1970's (Otev and \Westoff The suggested plant spaceing for vegetables onl plastic tilc'iel) 198()). The i oost promising film fliormuilatiouis contain abouit 40 is listedl in Table 4. Sui(rgestions on clouiible-cropping of' egcta- percenlt starel anld :30 percenit eaelh of' polx' ethvlene-co-ac'rvlic Hles oi plastic iiitilchl is listed in Table 5. aci(l) anti poilveth0leiie. In researchl at tihe Arorgouine National Lalorator, \wastes of potato statircli and chieese w Yic'v are beiln ROW COVERS piit th'rouloWh a fi( rioentitZti0iii pr-occss: the elni proilduct. lactic Since the inid-19t 50's0 rows co\ei-s hiaxe b ecom li a en ifilpor-talilt acid, appears to he a viable candidate f'or conversion to envi- oilethiotl of' protected a-riciiltue. ialy wolrk in Japaii ronmentally safe d-grladable plastics ( Bonsignllor-e et al 1990). (Slinmokaswa and Oino 19.54) shosved thiat the cise of' s%ins1 flii \\ihen g iroo I)iodegradahle inilolices come onto the miarket a tuInnels pe rmittedl cuctiml)ers to lie plaited ill Api il insteacd of' °ireat breakthrou ighl will havc b)een iiade in reducing tile cost of earls Mlax, adlxancing the h)arvesting 1) a perio(d of 1() clas ad plastic riei i oval f'0i ii thle field adl eli l iinatillg the pi'oblcil of illC'rieasii ig the NiClld of 175 per'ceii t. Early woirk hy \ o(ial (1963 plastic disposal. found that the har'vesting of' spriiig. cIops of carl-ots. lettuice. Snvitlhetic' miui lehes xwill coni 1tinuiie to ile isecl. pI;irticilarkl\1 ill cai iliflowe'' kolrlkl-l)i-'inid rhuil)hari'b wsas adv anced li)v ai av enitge the intensive c'iltivatioin oif valiiable crops. Certaini coii(litioius of tso to six weiks '1( cive'ring the plants with plastic tililiiels accelerate the spreadtI oIfsviiltetic imilch cuiltur, lotahlv: for a shiort perniodl in tie spring. With these paIrticiLlar ciop)s htC * wateri shiortagrCs in ari'd aili seni i-ari't regiolis. fbounid that whiile t'OW civets acld\iflcetd hiarvesti ng, tle- IIad lit- * tlie Tiee( f'or incri'easedl pr)crtidition. ini limlitecd spate and o\c'r tle effect on total Yieldls. Table 4. Suggested plant spacing for vegetables grown on plastic (Laniont 1991) In-row Spacgng Between row Single row Double row Spacing cm cm cm Cucumbers (slicers) 30-45 22-45 30-35 Cucumbers (pickles 30-45 22-45 30-35 Eggplant 45-61 45-76 35-40 Honeydew 45-76 Lettuce (leaf)l 15-22 22-30 (3 rows) Muskmelon 45-76 Okra 30-45 45 35-40 Pepper 30 22-30 30-45 Pumpkin 61-121 Squash (summer) 30-40 40-61 5-40 Squash (winter) 45-121 Tomato 45-61 Watermelon 61-1 21 Broccoli 20-30 22-30 Cabbage 22-30 30-40 Cauliflower 45 45-61 35-45 Chinese cabbage 30 22-30 30-35 Collard 22-30 30-45 30-45 Corn (sweet) 15 15-30 30-45 Greens 15-30 22-30 (2-3 rows) Onion 10-I 5 10-25 (3-6 rows) 14 COVERING MATERIALS Table 5. Suggestions for double-cropping vegetables using plastic mulches (Lamont 1991) Crop Plonted 1st Crop Plonted 2nd Peppers Summer squash, cucumbers, or cole crops Tomatoes Cucumbers, summer squash or cole crops Summer squash Pumpkins, tomatoes, or cole crops Eggplant Summer squash Cucumbers Tomatoes, pumpkins, or summer squash Muskmelons Tomatoes Watermelons Tomatoes Honeydews Tomatoes Broccoli Summer squash, pumpkins, muskmelons, tomatoes Cabbage Summer squash, pumpkins, muskmelons, tomatoes Cauliflower Summer squash, pumpkins, muskmelons, tomatoes Lettuce Summer squash, pumpkins, muskmelons, tomatoes Snap Beans Summer squash, pumpkins, muskmelons, tomatoes Sweet corn Summer squash, tomatoes, okra or cucumbers Onions Tomatoes, snap beans or cucumbers Herbs Broccoli, cabbage, cauliflower, Chinese cabbage Strawberries Tomatoes, summer squash, cucumbers, muskmelon, pumpkins, okra There are manay divfferent methodIs of using row covers. The thickniess and is clear. following are systems that hiave proven Niable for those iegionis For tomato proclictioin. the plastic toinnels are formied in the of the world whiere row covers are cuirenitly in use. same maninler as foir ecumber prodluctioni except that the woorleni stakes are two mleters in lengthi, placed 1-1.2 in apart California Svstem. In California (Roche 1964) several methi- dowin the plant row. Two wires are stapled on alterinate sides of ods are used to form the plastic tunnels over rows of food crops. each stake at a heighit of 50-55 cim from the grounid. Wire hoops For cuctimber produtictionl. two sheets of 90 cm polyethylene are set at alternate stakes in forimling the tuninel shape. filim are formedl into the sides of the tuninel. Growers in Sani Clothespinis are used to hold the tvo 1 nieter sheets to the two Diego, California tested various types of hioops (Hall andl top wires. Besemer 1972), deciding on 9-gatige, aalvanlizedl ire, ctit in Veentinig is one of the most critical featiires in usinig plastic 17.5 cim lengthis to support the tvo sheets of polvethylene in the row covers. In ventinig the above menitioniedI tuninels, the plastic formiationi of tunnels. The wire is bent into an oval shalpe (or is opened as needled ancl seclire(l to the wire hoops and top hoop) spanninig 70 to 80 cm., with the heighit of' hoop estab- wires wvithi clothespinis. lishe(d at 337.5 to 40 cim. The hoops are spaced 1.66 to 2.3 in In Southierin California, all of'the early cucumber and tomato apart. The row covers are reinifoicecl by 2.5 x 2.5 x 70 cmil wood- plantings started in Januiary and early' Februarv are grown en stakes driveni into the grounid below the center of' the wire uncler row covers. Cticurmbers planted as transplants in earl> hoops at spacings of .3.5 to 5 ni downi the plant row'. The hoops, February normally begini producinig in mid-April, continuing in tuii, are f'astene(d to the stakes and wire to give stability in strong winds. Soil is uised l to hiold the bo'ttomi edges of eachl polvethsvl- 3 ;' ene sheet. A 16-gaLlUe wire stapled to the l top of the stakes is the coninectinig fulcrumir for the tvo plastic sheets. Ordinary spring - ,, grip clothiespinis secure the two plastic , i 11 ~ ~ ~ ~ ~ ~ ~ _ sheets to the top wnire. In areas of high , - winds, a secon(l wire hoop is loijiblerl over the top of' the plastic at evern secondl or - r tliir-l lioop. This is especiallv imiportant ii =t r w hen the plastic covers are pulle(l back (lur- ina tirdes of ventilatiosi. Wes ei veatilatiora is . desired, the plastic is simply slid dlown one side of' the tube between the wire hoops: . . and it is either fastened there bv the clothiespinis or hield( in place by the corn- bined force of the hoops. The top hoop secures the plastic between the hloops and . ' redutices the flapping that may loosen and The 'Califomia System'" of row covers using perforated plastic are common for growing early damage it. The filml use(d is :38 micronis in market tomatoes. As shown, the covers are closed dunng cool penods. I5 PROTECTING MATERIALS AND STRUCTURES toO1n to allow' nomnal pollination. Clear plas- tic nnilch is nearlv alwavs tiseci in conillina- _ tion xwitlh the row covers. Mlulech unidlerL a plastic tutnnel will increase the dav and night temperatuires ol the soil, at a depth of a cmii. by 7- l0(C and( 2-.50C respectively (Tarak-anoxy LaindI Rozov 1962). The Fernthurst Svstem. This svstem wvas first developedi for strawherry' production h_bt is 11se(I throtughlout Europe and( the Middle East for otlher crops as well, suicl as i_meloins, cucnimbers, peppers. andl eggplant. The polyethyleene sheet, 1:30 cm in wi(dt and 38 inicron in thickiness, is spleadi over wire hoops that are placed at intervals of 60-90 cnm in the plant riow. It is n1ot advis- able to increase the distance behteen hoops since sinow v loadin(lLc max' rlistor-t or flatten During warm days, the covers are opened for ventilation. As p/ants progress into the tuinnels, perllitting w\n(ls to remove the the warmer vweather, covers are left open and vines trained to wooden stakes. plastic cover. The hoops. 1S( ciii in length. are made of S gauge galvaxnized wire. Each through June. Tomatoes transplanted in litte January will be hoop has tvo eves made in the wire by a simple jig made On1 the readv for the first harvest in late Ma' alind continue to procluce farm. Each eye has a diaineter of appiroxilm]attelx .L8 ci and the throulygh mid-JuIx'. length of each "leg" is 20 cm. Cleair plastic mu11lclh is tised in combination with the rowv cov- Once the pol yethylene is p)ut over the hoops, the end( of eachi ers. wlhere wee(d control is economnicallv accomiiplislhe(d thrlouighl row hals an additional hoop fo-r extria sta bilits and the end( of the the uise of soil fumigation. The cost and clilturiall operations poly sheetinig is buried in a trenclh. associated witlh clear plastic have heen a liniitinao, factor. Lengths of polvp)opylenle baler twine are cuit 1.50 cni long Fumnigation withi metlivi bromiide anid chloropicrin hiLas given and loops are tie(i at eaehi end. These are slippecl ox-er the eves good weed, disease, and pest conitrol (lall and Beseimer 197 2). of the hoops to hold the slieetinacT ill place. After securing the Today, nexv foodl and dnig regulations in the U.S.A. prohibit the sheetiig. the eyes of the hoops are pushed inito thc ground1(d so uise of man' chiemlical filmi,ganits, therefore alteniatives suclh as tlhalt there is n1o yap between the polyethlwene and( the soil (Figure soil solarizationi are emp)loyed. In soil solarizatiorm, clear plastic 3). tarps or muielch are placei over the soil stiufaee for it period tip t V Ventilation1 of tuninlels is easily achieve(l byv liftiin one edge of 90 day's dturinig a summi1i1er fallow period to allow the soil tempera- the filimi away fi-onil the soil level andl puslhing it towardls the top ture to rise approximately 1(0) above bare soil at a depth of 5 c'ml. of the hoop. It moves easily betveen the wir e annd the t-vine, but Suchl solarization procedures have significauitiv reduced the illci- because it is sectirely tensioniedI at all times, it remiiainis firmly in dence of disease (Katan 1981). position) even wvhen the tinnels are opene(d (Ficrure 4) In another row cover metlhodI in Californlia, a single 150 cm sheet of clear ' plastic is centered over tall stakes and t '1 force(d downward. The stakes poke holes -- throughi the plastic. wlieh ricdes down to about the 50 cim level, wlhere a lengthwise -wire forms a tent ridge. Wire hoops ofteni are uised betveen the tomato stakes to form - _ rounded tuinnels, givinig the plants more air space. This type of row cover is often tised for i'ain protection. Bow covers are not commonly uised in strawberry productioni in California, except for earily january thl-oulgh April prioduction when eariv produic'tionI biings higher prices. Row covers also proxide important rain pro- tectioI. The c{over conlsists of one sheet that is secmim'ed between thvo galvanized wvire hoops with the aid of clothespilis. For The "Femhurst System" is commonly used throughout the worid for ctops not commonly strawberries, the tutininel is open at the bot- trained upright to a trellis system or wooden stakes and string. 16 COVERING MATERIALS Figure 2. The Fernhurst hoop system The hoops are spreod to a width of 60 cm over the crop, r-eady for covenng with polyethylene. The hoops are spoced 75 crn (0") apaot with each "leg" pushed into the soil to a depth of 20 cm (8"). Figure 3. Side view of tunnel SUPPORTING HOOP RETAINING TWINE POLYTHENE UNDER POLYTHENE OVER -POLYTHENE tI t Son, F ron, Bri,i,, \X insq,uc, (191] | Securing the polyethylene (Polythene) sheetinu is essentiol in order to avoid any possible displacement by the wind. The securing twine must be fixed to the eves in the hoops. Figure 4. Ventilation of the tunniel THE POLYTHENE LIFTED FROM SOIL LEVEL S,'1,,,-, Finn,, Iz-iri,Ii \',,,i,.,, en 1971,. g I I U Ventilation can either be provided ot inten'ols along the row, or the whole of-one edge can be lifted a few inches above soil level. 17 PROTECTING MATERIALS AND STRUCTURES Figure 5. Wire hoops and ventilation slits plastic tuinnels are less labor- intensive: soli(l plastic tunlilels recluire consi(lerable tinie to sectire ample ventilationi in the Wire hoop #8 or #9 galvanized wire morning and( evening duiing an eighit week period. Little con- 63 inches long center heigh:: \ ,,/ >ldenisationi occuirs tin(ler the perforated ftilmi. Ettiiicre- (1964). in 14 to 16 irchesV 5 leet between hoops Israel, lemonistr atedl that perforated plastic shieets reducedl tiln- /nel temperatures by 5-6(C in comparison to univenitilate(l solidl Slits in /olyethytenI plastic tiuninels anil that the perfrTatioln in the plastic reclticed for ventilation the need for man nal ventilation. 5 inches long }/ \ / Perforationi can be pr-odlticed by dIrillinig the polyethylen)e. 1/4 inch /w lhile it is still on the roll, with a low speed twist (irill, aiminig the apart Y / drill at the center of the core. Excessively rapicd drilling melts and( Soil covering fuses the film. The perforations are approximately 0.62.5 cm in t a / / edge of cover (liamileter. spaced 8cm on center- in each direction. /og ~Bu ried edge / . < of ccver Slitted Row Covers. Slitted row covers have a series of cross- polyelhylene fulch \ise slits wlvicli provi(le venitilattioni on1 suninyv days. Withiout Wire/hoopobred hen sol these slits, pliastic covers would have to be maniuially openie(d and( Z ~~~Wire hoop buried 6 inches in soil Black polyelhylene mulch closed to provicle ventilationi during the datv and cold protection at nighlt. This metlhod of ventilationi was first (levelopeti at the University of New Ilamipshlire in the earlv 1970's (Wells and The wire hoops are 158 cm (63 in.) long, installed at a height of 35- L . U Lov 1985). Usii1cy r-eseai-c-il oni inuskiiieloiis, tlhev shiowecl that 40 cm (1 4-16 in.) in the plant row. The slits for ventilation ore 12.7 melons with covers plus black polyethylene mulch produced (5 in.) long and 1.9 cm (.75 in) apart. yields thr-ee timies tlhat of bare soil, having no mulch or row cover, andl about two times areater than with black mtulchl alone For spraying against pests and diseases, the tuninlels are (Lox and Wells 1974). Row covers an(d muileh together opene(d bv lifting both edges of the sheetinig to the tops of the increasecd fi-uit maturity by :3-9 days xvitlh comimiilercial hybrids hoops. To prevelnt the sheetinig fromil slipping, it can be heldl in andl 12-13 days with experimental hiybrids over those gronil oil position by temporarily releasinig some of the lengths of black polyethylene alone. polypropylene twine, which are wouncd once aroundl the In New Hampshire, row covers were initi,ally patternied after bunched film andl resectired to the eye of the hoop. the California svstem: however,the tvo piece conistruictioni was At blossomil time, the tuninels are ventilated on onie sicle by fountd to be very labolious and( also sublject to severe clamage by lifting an edge of the sheetinig about 330 cm every fifth hoop. In winid gusts (Wells and( Lov 1985). England, irriaationi bv overheadi spray line has been nsedl to While perforatedl Iow cover provicled reasonably effective protect crops under the polyethylene from frost. ventilation writhout appreciably sacrificing temperature increas- The twine is usedl insteadl ofan additional wire tha,t wvas once es, (Dubois 1978) perforate(d row covers were not put on the coniiiionl) placed over the top of the tuninels in order to secure commercial market in the UnitedI States as thev were in Eyvope them d(uring w,ind conditions. The polypropylene twine is much andl the Middle East. To achieve ventilationi, Irow covers in New lower- in cost andl does not cut or damage the polyethylenie as HamIpshire wer-e conistirictedl fromil a single sheet of plastic. 1.5 wire might. In wide, :38 micron thick, with two) Iows of continuous slits, 1.9 For general guidance. the wkider the tuininel the better will be cin apart and 12.7 cim long. Figure 5 shows the desigin of wire the temperattire cond(litionis prevailing in the ear-ly part of the hoops together with installation institictionis for the slittedl rowv year. However, as the widthi of the tuninlel increiases, so cloes the covers. likelilhood of xwindl damage. For certaini low crops, particullarly In the New Hamipshiire trials, tht slitted, one-piece row cov- radlish and lettuce, the base hoops can be spread out to give a ers showedl about an 80% reduction in installationi labor, were flatter andl lower- tuniniel. A low tiuninel offers less wind resis- self-ventilating, eliminiating (laily manual openiing andiclosinga of tance. Tender crops can be starter1 verv early unilder- tuninels and( the covers and wvere able to withistand very gustv winds (W ells part of the polyethylene can be cut away later to alloxv the crop et. al. 197 7). to emier-ge. This tecihiniquie is particularly stuitable for ninner In addition to li]eloiis. other crops sucih as cuctimbers, toniia- beans, squiashi and sweet corin. toes and( peppers are grown with the slittecl plastic miuilchl. Since the weedis wel-e conlitrolled thirougih the use of black plastic Perforated Plastic Tunnels. High winids remain a problemn mulch, the slitted row covers were care-free froml the time of witih everv' method of ventilation tried. A techniiiqute has been installation until the timne of removal, :3-6 weeks later, depend- develope(d in Franice whereby the plastic is perfor-ated in orrler ing on the c'iop anid the weather. Wlhenl ambient temilperiattire to facilitate ventilationi (MaMaire. 1964) insteald of the conven- reaelhes the range of:30-32'C, either the covers are remilove(d or tional miethio(d of openinig and( closing the tuniniels dailv. extra slits ar-e made for tomiatoes anid peppers. For vine crops, Ther-e is a slight differenice between temperatures - mini- the covers are left on uintil the appearance of the first feimale Illtilli and Illxililmlllu - withi the perforated and( the non-perfo- blossoms or u tntil the vines reachi the edge of thie covei-s (WVells ratedl tuninlel. They procilice similar mesuilts in earliniess of har- and( Lov 198.5). vest, and yield. Froim a practical point ofview, the perfor-attedl Frost protection with the slitte(d covers is similar to that with 18 COVERING MATERIALS Figuire 6. Structur-e for air-suppor-ted row cvr Air I'Flow Furnace -- '. Fan '0 4% 4 tru c tu re C harmbe r opening to pla(A,c row cover the perforated i)olvetlmlene covers 1)1it is itif'erior- to .sid cit](IX-- sidle temlperattire. Oni onie occaisioni the ot itdloij (Ir c teiipetra- ers. The ntliaxiion increase ill tenmperatuire is only 1 1) to 2.0f)(C tore reachled at high of :36oC. Bv hilly opening tile' VittilatiOnl ablovx (e oiti field tem iperatures whler-eas with solid covers, frlost doors, tilt' tempieratuire att the end (Iof the ttn iels 51) Inl in p)ro tection of 2l5i1 to 40_C iln b e aehieved. In view of the aivls-a- letigatl ireadhed at high of onlyN 4OoC. Teinperatores of, appr-oxi- ta(Tes of the slittedI titi iiels lIver ti e sollitI, thte Llse (If slittedi roIv linatei thte saime tdc,rce were miain taiined in thet \\ ire-si ipported c eoves iS a reasionadble tcmpon 1 m11ise I etwev ii a\imat (111 fri-ost iove rS, WhiCh hadl( 0peii slits aLt the ti p] (If'the ti tiie! foi- ventila- p r(otec-tioln atiid a saving in labor. How, covers shioti( ild ot he ti oti. E arlv iil thle ti im ati trials a h0 iw t(100tdi Ilir igt teminpe ratuitre viewed mierelv as a frost prolte'tio n svstenii hot as a g~rowth- of nilitiiis 3oC(' was reeiIrded. Tlhois plaints tm lo-e the \\ire-solp- ii teilsikfl-t igsvstemndiigc 1(11) spi tig, weather. Tlierefi re. it is pi irtetl riiv covers, with nio addl dliei ett \were eomnplctclv iioit atlkisabile toi plant very earlI-. hliphiti t(o protect these early destroyed bv the fi-ceze. Those pllants tindier- tlic air-soipported plantings against beasv froSt. Anl earlier planthiti (late If If) tlaVs tiunntels wvere saved with thle aipplicathion i IF1 iat. to two wveeks XvoiiiCI lie mior-e reasonahle (\\clls and LoxN 198O). \Vlien) heat Was Stipphied tIl the tidieS the temiperattire- Ac-cording to W'ells and Lox (1980>- late spring frosts arie proh- decreased \\xstll the lemth ofgtlI(Fte tubte. It wvas mo1(st imipiortant Iti abl\ niot the higgest restraint tio earilx cutltur I fii ii of iskmcllons and have ai sniiall opening at tIe ci it oF the air-supp1ortedl tithe; thlis oItle1- S i I]e ertips. C0(io SPHiI( SOg i S Isinaik-ec INI inthihit gli0iwthI, openincog all0wedh soilmot-, air 1 m Xt'11eit ill the row55 tiover. ei] soil ii g water, and notrtientt uptake h\voSilt to sec(llitig(s or- transpianits. that the lieat ci iteringi time tot itels xxvi tld he dlistilibutetd tio the cutd. Row- cvet-rs in combiiiatiou ii th 1blaek plastic mouilt-h., will uisuail- fnisett and disease c-onitrol Was aecciompllishled ILv injectiilg at lv itlerease sioil tem peratuires bYPv til 4.,5ilC. Utmf0ttoiatelx. row dotst iitto the flit intake, which prodUced an cxcii' distrihbutioti tovers \viII not prolte't \itie t_rips. especkia>N melo CiroIls. tIli-otgli"llott the plantilng. If the air suippoIrted r(ow c(Ivers were agansttheefec-s o eteiclei piids f fveor- motre lv (If, kept rigrid, thiex withistoodt tIme weitrht of'snow better thanl those t'otttlv c-ool weather. Wijth suc'l wveather patteols, tlie sol tei]i- sttppoIrtedtb Nvwire: however any si](iXWFall overI ClitE especially peratutre driops. therebiy pr-ev-eitiigt the uiptake (If xwater I)v the wvet snilxw, woutild colllapse the p)lastic totnumels. tiherehx calisinua plants. Cntlst'qoetlvd\ wheit'i stum]tY weather (lilts retort.Ii tlit plhttt 1breakage. It wvas alsio imp] jortant to keep thte t'over-s rigid xoIlwti xSitl Wit'er astraillSIi ratiotl t'Ct't'IS w oe ptatke. (tloiiiig lug1l witits sotlott tliex wouhd tnot swax ant il i-th pliolits otitller CO\t'r. Air-Suipportedi Row Covet's. It] an atteillipt to at-iiie\t' a Tvp)icall. munskmtitltons will tilatliii-e 9-1:3 datvs earlier Xwitht irt'ater degree of co('11 protectio~n. Jenmse'n atid Sheldi'ake (t965S) Xvire-stipp(ortedl ril\ t'OX'rs iii c'tbinationiii wxitli plaistic- iiuiilchl atppli etl ititi ficial h1 at ini platsti c tun t ll's5l ti i-tiert to p rovidte Fri ost tha tai51th Illat'k plais tiet ai loit. itI ti e airi-sitppoIrtetd triiaths. dli IC tio protit'ttiot I to] C'r'(ps gi'oXincg ini the iliirte titoltlieri-l lattitudes of' the cam-lier thian i In0 ll1tl pIlantitflg iniiler- t'iiers s1 ippoIl'tetl Xitll the Uitiitetl States (Figuriie 6). \vi-e, the nitiiskuieiloti harvest xvas 2(0-2-5 davs ecirilier- thallti tu ToillatoeS, (,c'mit biiers riitcl iilliskiiieloins wvere groivi titller- titormall first harvest date of imiisknlcon 1t5 ot raisetd tinnier Ci I` roxV c-iixers supporteti by air p~ressur-e I't-oIti I lt iti i locatedi t olte ers. Toma~toes wxere 1harvested 15-52(0 tiaYs cad-litr th atn the i iir- et]dI ilf ti]e totiiiels. Tue speeud of air tmovemeiCnt tihiiiuigb the titti- ilial oltit-oIf-dooilr platntiiig tielS Was I-C'UhtCdttt I\ adjjuistitlg1 a St1 l t1,100tl oirtpethingr at the While tlier-e is uistitlI till signific-amnt tliFt'rieiic-e in earls tttmai- opptosite ('lIt of theI tititiiel - Diiri-igc periodls of hilt weather. veti- tol priltlit-tioit] ]etX\veet]jttt ii pa tic ltl [ ttd i tlld ill tilt'1]C tihitre iS ti 1 jtti on o- airil iovemte ut thro'uI gii ti e ti totiel wals iiit'm-eiisedI ]lX i]o liii] t]lv it notaibIc~ tliff'relitee iii t le earlitness (If citet ii be r atndt t'htu speed aitii('or b\ Cenlargitig the o]peninlg at the ent](Iof thle ttti- m]luskmielon] prtltltit-tiil I - ll trials t'OM]iU C-tetl 1 Je-ilSet t andi tiel. Diiritiaic titiles oif' fr-ost. lieiett ~xas addetd tio tilt air sticauti SheIdratke ( 1967) v\ it're ai r su pported roxw tiovers wet-c tIlsed ill tihrttltigh the ton niels - The smal~lleri the do(1r op (lit'il i t tl te cid c( ombin h ation Xwitl i plastic- imiu-lit, c- itito 1mlet atd mi tliskilelo llt of tle tIC itItiC1e, tieless'5 the air mii(iemte t thri-iltgIh tihe tuti elt's, criiops grtwni oIii pla5 tit-tn imItll- prolduci-etid itt-li higihICr eatrl c-itutsitigc a temlperatture bunild-op ii isitdt thit' totitiels tlt l-jilig wxarmi, v-ieltds tiiaii tibose w\ith io ti tiltclth (Tab lt's 6 anid 7). Today,. if' soniivI (hits's. Tile larger thit iopt'nint ig t tile Ciii] ill the tithe. the groWe is itt- goillg to the addtedi expen~se atnd ef'fort of' tist t ig i-iw faster thle aitril m yt'tmt'lt or Ittiri'tdationi, tbiiebii loxweritlg the covers il ('illb iiltaitii li with p lIastie tmiiut-h. they shiotiut1 c-nider5iC 19 PROTECTING MATERIALS AND STRUCTURES Polvethvlenie is stretchled over a trench in the grounld. The hot- Table 6. Effect of plastic mulch on marketable yields of ton; of' the trenclh is approxillmately 18 cm below the plastic. In early cucumbers, USA, summer 1965 the second method, plastic is laidl across tvo soil ridges 40 cim in heiglht. A mechanical mulch laver is used wlheni the polveth- Treatment Cucumber var. Triumph vlene was appliecd over trenches. (Na.Iha) Yield (kg/ha) Weedl control is essential under such systemls of protected agiiculture, and is noinlllalv accomplislhed througlh the use of Clear plastic mulch 161,637 37,569 chemical herbicides. The polyethiylenie is remiloved froml the Black plastic mulch 148,592 33,336 trenches wheni the plants first touch the plastic. With tomatoes. No plastic mulch 115,507 26,043 the trenches are filled and the beds levelecl bv cultivationl with- in two weeks after the remioval of the plastic. P.laff 1jpopulatitrl. 13,610 ha. Tomatoes procdtuced unider this metlhod wouild come into pro- F'niif hlainr cf JIn Se 2.9 - Ang ts? 6 Sais rc] I seae andl S/l, hrake. 19i67 ductioni approximately 1:3 davs before thtose seeded in the open fielcl. A similar svstem is presentlv used in California and Arizona Table 7. Effect of plastic mulch on marketable yields of to grow early cantaloupe andi watermelons. In regions wlhei-e early muskmelons, USA, summer 1965 there is geothermal activitv, frost protection is effectedl by applicationi of warmn water through dlrip irrigation lines installed Treatment Muskmelon var. Harper Hybrid under the polyethvlenie. This systeml has saved imelon plantinigs (No./ha) Yield (kg/ha) clon to a temperature of -4.5°C. A plastic-covered trenchl svstenm is feasible wlhere low tem- Clear plastic mulch 13,230 13,362 peratures limit early growth, where the dcanger of frost increas- Black plastic mulch 8,315 9,786 es the risk of early planitinig, and where higher prices are No plastic mulch 755 911 received for early prodUCtion (CGan-ison 1973). While plastic covered trenches mav not give the aclded Plant ppibtionts: 6,N0,5/hea agrowthi response andl earlinless of yield in compparisoni to that of .s ,it harvs'fs Jilri 19 t, Assgst iti 16 Soars,: Jensen an /d Sh/dhrake. 1967 rOW covers usecl in combinationi ith plastic mulclhes, this svs- tem is far less expensive and becoming qtiite commiion in the Again, row covers are tuse(d in combinationi with plastic mulch desert regions of the United States, Mexico and Israel. only wheni the goal is to gain an advantage in earlier fruit pro- duction over crops plantecl only tlhrouglh plastic mulch. While Floating Row Covers. Floating row covers can offer protec- row covers will increase both labor and expense, thevx will raise tion to both cool and( warm season crops. The simplest form of both the air andl soil temperature. provide some fiost protec- row cover is the fabric or floating row cover, without x,ire or tion, and therel)b incr-ease earliness and yield. cane hoops. First introdutced in Germ-lanyv in 1970, thie technlol- While earlier yields of up to two weeks can be achlieved in ogy was soon ado1)te(l by neighlborinog counltries. By 1987. more tunnllels where heat is applied, the capital costs in fan andl heat- thani 15,00() hectar-es of' floating covers were in uise, mostlv in ing eqLuipmiienit can be quite higl. Operatinig costs for electric- Austria, England, Frntice, Ger-iian, Spain, and Italy (1 oag itv and propane canl be expensive as well. The plastic row cover 1988). Their potenitial in North Africa ancl the Eastern and mulchlinlg rmater-ial mxav cost tip to $1,750-2,500/ha.; the capital cost of the f:anI anlI furlnace is approxi niately $1,500- 2,000/hla.; andl energy costs for fuiel anid electricitv imavx reach $2,000-2,500/lha. These addedl expenises mulst be offset by higher return-ls in the imiarket. UInless tlhev are, th en proclucing a product earlier does not justify the added cost of air-sUpported row covers. This WaLs the experience in Newv Jersey xvlmere commiiiiercial uise of air- supported rowv covers was dliscontiiiued after the first vear tlue to the high cost of operation and maintenance. Plastic Covered Trench Svstem. In 196), Garrison (191:3) of Ruitgers _ E iiversitv. Nexv Jersey, UISA. develo)ped a _ sxvstenii of crop protectioni that permitted early seeding, promoted early planit devel- Muskmelons, in Ithaca, New York, tro-nsplanted directly to the field on Moy 5. Gs opmienit. and(I prokided fIrost protection, they oppeared on June 5. 20 COVERING MATERIALS Mediterraneain is being examined. They were first used in the United States in 1980, b' Wells and Loy at the University of Newv Hampslhire. Currenit use in the United States is estimate(d at 4,00(l ha. (Mansour 1991). Floating row covers are made of spunbond(led or non-woven ftabrics: polyp)ropylene (PP), polyamide (PA) or polyester. Polypropylene an(l polyester are __ _ the two fabrics most coinmonly available. These covers are made by melting the appropriate plastic, or combination of plas- 7 tics. They are sprayed as fine filamienits onto C a nmoving belt which conveys themil to a bonding roller. The roller presses and fuses the filaments together. This process is rapid anid creates fabrics that are strong, light- weight, economlical, and porous, ranging in weight froim 10-50 g/rI12. Fabric durabilit: is dependenit on its weighit, the type of plas- In the southwestem part of the United States, plastic covered trenches are becoming tic, the additives an d the method of bond- increasingly popular for the production of muskmelons for early market. ing. Fabric can be madle into very, ide pieces. ranging from one meter to about 10 meter-s in wridth: is left on a crop for only a short period of five weeks or less. The narrower wvidths maay reach a length of 850 meters. By special lightest weight fabrics are seldomil reused (Mansour 1991). order, fabrics of over 20 meters in width can be accommodated. The lightest covers, those around 10 g./sq.rn are use(d as Th-e covers can be applied over a single row (Figur-e 7) either insect barriers. Tlhe offer protection against viruses and feed- bv hand or by using a modified mulch applicator (Wells an(d ing (lamage from insects such as aphids, loopers, and beetles loy 1985), or over a number of planit rows with one large cover. (Mlansour 1991, NWleatley 1991). They also prevent or discomir- When covering a single row, the material must not be stretched age feeding by birds ancd small animials. However, these fabrics tiglitlv but left with slack in the center to allow for expansioni as are easily damaged by livestock, dogs, and other animals. Thev the crop develops. The edges should be securely buried. espe- have minimal effect on temperature and light transmissioni. cially wheni usingc lightweight covers, w hich inay requtire According to Miansouir (1991), those covers of about 17 weights. in additionl to soil, to secure thiemii. The wind will bloxv g/sq.m are, by far, the most commonly available. Thev have the through the material. Using a combinationi mechanical/imanual same applications as supported row tunnels or unheated green- method of applying the widlest covers to a field, a team of three houses: All these protectedl systems of agriculture are used to people can cover nearly a half hectare in 40 miiitites. enhance early maturity, increase early yield and total yields. Heavier fabrics can be reuse(d one or miore timies. Even the improve quality ancd to extendc the growing season or miake pos- 17 g/sq.n] material can be reused once if handled properl, if it sible the growing of crops in areas where thiey are not coin- i_monily grown. -. ,,<<; .- lHeavier covers, those greater thain 30 -g/sq. in. are usedl primarily fo(r frost andc f,reeze protection, andl in situations reqiir- ; '* ' ',S,- ' , - > ti + . _@ =.'rE j(ing extr-a imechlianiical strength and durabili- X5 J U N E 8 tt to extend the growing season, adill rense -I ~t-MEEL of n;iitterials. Somce maniflicturers claiml =_r ,. ,f"'_'~ s k t >t [lieavier fabrics will give fiost pro- F n- g te tion doI vn to -:3.3oC. Polyester pirovides ~~~ '- / ~ ~ ~ ~ ~ ~ ~~~~12C, fost protection: polypropylene Pro- *8r ,, I/)i_l 22 COVERING MATERIALS Table 9. The effect of slitted polyethylene and polyester row covers on early and total Nields (kg/ha) of 'Goldstar' muskmelon over a 4-year period Test year Treatment 1981 1982z 1983 1984 Avg. Early yield Black poly mulch 3466aY Oa 370a 672a 1127 Polyester & mulch 20,929b 1453b 1 7,473b 6451 b 11,577 Slitted & mulch 21,377b 2560c 15,681 b 6182b 11,450 Total yield Black poly mulch 50,099a 4574a 40,024a 27,507a 30.551 Polyester & mulch 67,433b 9453b 40,322a 29,478a 36,672 Slitted & mulch 65,978b 13,377b 52,420b 21,504a 38,320 t'ieltl rt'tlIitiont ItI till duetit' tlilt in'atnui t it- ilit. Y,11cti,* ephlar-ition withi cl umn-1E1e;^s by! D),i,,can,, . ntiltip)le ranige t.ht, 5%7 /,t,'t' S. Wnr elt'' ls Ut/i im Ly 195.5 2. The covers modifyi moisture by raising the relative ers over a four yeair period. They fotiund that muskimielois, a humlidity, and redlucinig water losses by transpirationi or cro0) sensitive to low soil and air temiperatures but tolerant to evaporaltion. Thtis, they enhance seed geriniiationi by biah teimperattires, responids well to row cover culture maintaining higher soil moisttire at the surface, andcl Table 9). prevent crrusting. Their- research also illustrated yield increases wvith pepper 3. The covers can modify gas conicenitiationis arounid (Table 10). Tomato yield increases were not as dIramiatic, espe- the plant. They may increase C02 levels wlienl decomi- cialls. during one year whieni tomato vields uni(ler covers were posing organic miatter is available in the soil. drastically re(Itice(d cdue to higli ambienit temperature con(li- 4. They modifv light. thereby influenicing p)hotosyn- tions. thesis, flowering an(d plant growth (Friend( 1990). Other crops. whieni grow'n udicler covers, have showna vield Spunibonlded field covers do the above things at a increases as well, suchi as sweet corni eclible po)0 peas, carrots, miucil lower cost for labor and installation than row cabbage, leafy' lettice, green beans, squasi, cucumbers, water- tuLinels or plastic greenilouses. thereby providing flex- meloni and root crops suchi as ra(lishes (Table 11). The covers ibilit to the annual row crops grower who imav choose have proveni to be especially effective in controlling cabbage to grow a protected crop one year but inot the next. maggots on radlish andl in re(ucing flea beetle damiage. as shown Research at Oregona State Universitv (Hemnphill et at] 1987) i