Vegetable Production Under Protective Structures

Manuel C. Palada, Visiting ScientistProgram 2: Year-Round Vegetable Production SystemsAVRDC, Shanhua, Tainan, Taiwan

Off-season vegetable production under protective structures

Outline of topics and subtopicsIntroductionGlobal status of protective cultivationTypes of protective structuresComponents of protective structuresConstruction of protective structuresOrientation of structure

Outline of topics and subtopicsCooling systemMicro-climate and environmental determinantsProblems and prospectsYield of vegetables under protective structuresCosts and returns

Protective structures

Facilities that provide protection to vegetable cropsagainst biotic and abiotic stresses during the off-season.

Covered with materials such as plastic films, glassand nylon nets

Benefits of protective structures

Protection against the impact of heavy rainfallProvide protection against temperature extremesProtection against biotic stresses due to pests and diseases

Global statusPredominantly common in temperate regionsLeading countries are Japan and South KoreaVegetable crops occupy a major portion of protective cultivationPlastic houses are most common structures.

Global status

Protective cultivation for off-season vegetable production under hot, wet climate in the tropicsis becoming important and popular.

Types of protective structures

GreenhousesPlastic housesScreen housesRain sheltersTunnels

GreenhousesStructure made of steel or aluminum frames covered with transparent rigid platesGreenhouse roof or covering is made of rigid plastic plates such as fiberglass, acrylic plate or polycarbonate plate

Conventional glass greenhouse at AVRDC

Types of greenhouses

Modern type greenhouse in Silou area, Taiwan

Plastic house

A plastic house is a relatively simple structure madeof iron pipes or wooden frames covered with softplastic films or plastic nets. Characteristics which distinguish a plastic house from a greenhouse areflexible plastic covering materials on the structurewithout overall footing.

Simple qounset (arch) type plastic house at AVRDC

Vegetables under plastic houses

Screen house/net house

Similar to a plastic house, however, plastic film is replaced by a nylon net for top and side covers.The net comes in several mesh-sizes. The net actsas a physical barrier for most insect pests.

A screen house at AVRDC

Leafy vegetables grown under screen house at AVRDC

Leafy vegetable production under screen or net houses

Pai tsai production under net house in Silou, Taiwan

Leafy vegetable production under net house in Thailand

Rain shelter

Simple plastic houses are built using iron pipes, bamboo or wooden frames. Rain shelters are almost similar to high plastic tunnels, sometimes called hoop houses.

Single bed rain shelters at AVRDC

Types of simple single bed rain shelters

Double bed A type rain shelters

Tunnels

A tunnel refers to an arched structure figured byinserting both ends of the rod into the ground.It is the simplest structure to support the coveringmaterials.

Nylon netting single bed tunnels

Types of nylon netting tunnels

Components of protective structures

StructuralCovering materialsConnecting accessories

StructuralPillarsFramesPipesSide braces

Arch top pipe

Foot iron pipeTop and side iron linkage pipes

Structural components of simple plastic rain shelter

Structural components of simple single bed rain shelter

Strengthen side pipes Steel clips

Foot iron pipe Skeleton

Covering materialsPolyethylene film (PE)Polyvinyl chloride (PVC)Polyolefine (PO)Nylon netting

Plastic film Plastic film covering

Nylon nettingCovering materials for single bed rain shelters

Connecting and fastening accessories

Fastening pinsHooksClipsPlastic belts

Connecting and fastening accessoriesPlastic belt PE clips

PE clips

Construction of protective structures

Main point to consider in the construction of protectivestructures is strength. Structure should withstand againststrength of heavy rainfall or wind.

Construction of simple single bed rain shelter

Orientation of structureOrientation with respect to angle, solar radiation, andlatitude is an important factor to be considered in theconstruction of protective structures. Generally, east-west direction is more preferable than north-south direction for lighting as the latitude becomeshigher, and single structure is more suitable for light penetration than multiple ride and furrow structure.

Cooling systemHigh temperature in the summer is one of the majorconstrains in vegetable production under protectivestructures. Temperature inside a greenhouse or enclosed plastic net house can go up to more than 40 oCin the summer. The passive measure for cooling the protective structure is by shading. The active measure is by the use of pad and fan system or by mist cooling system.

Pad and fan cooling systemThe principle of this system is the latent heat loss when the liquid water changes its phase into vapor (latent heatloss is 540 cal/g of water). One side of the structure ispadded with dripping water and the ventilating fan on the other side of the wall does the suction of air insidethe structure. As the water flows with air movement, itchanges to vapor robbing latent hat. This systems workseffectively during daytime when dynamic evaporationoccurs.

Fog and fan (mist) cooling system

The principle involved in this system is similar to thatof the pad and fan system. Mist is generated from theposition of duct and the fan on the other side sucks theair in the greenhouse. Ventilation fan turned on at 8:00 a.m.and turned off at 6:00 p.m. with mist generated at 10:00 a.m.can bring temperature down to as much as 2oC initiallyand 4oC finally.

Cooling system for protective structures

Microclimate and environmental determinants

Solar radiationTemperatureWaterWindCarbon dioxide

Problems and prospects of vegetable production under protected structures

Design of protective structure suitable for the tropics.High cost of structures and covering materials.Running cost is high and the need for saving resources and energy input.Uncertainty of market prices for vegetables and expected profit.

Problems and prospects:

Adaptability of production system to market demands.Technology improvement to enhance yield and quality.Proper disposal of waste materials, especially plastic films.

Yield of vegetables under protective structures

TomatoHot peppersLeafy vegetablesCucumberSnow peasOkraYardlong bean

Fig. 1. Yield of two tomato cultivars grown in bag andsoil culture under open and protected rain shelters.

Table 1. Main effects of rain shelter, raised beds and bed width on fruit yields (t/ha) of tomato planted at end of summer season in Taiwan (AVRDC 1993).

Rain shelter Bed height Bed width

With 51.2 20 cm 61.2 1.0 m 58.3Without 68.1 40 cm 58.1 1.5 m 60.9

SED (23 df) 3.4 NS NS

Table 2. Effects of cultural practices on the pest and disease incidence and yield of tomato grown under protective structures. AVRDC 1998

Leaf Bacterial TYLCV Gray MktableTreatment miner spot (%) mold yield

(t/ha)Main plot Chemical spray 0.08 a 0.00 b 8.34 b 0.42 a 63.39 a No chemical spray 1.58 a 1.92 a 12.50 a 0.83 a 35.96 a

Subplot No netting (ck) 1.75 a 1.25 a 6.23 ab 0.00 51.71 a House netting 0.25 b 0.75 ab 10.43 ab 1.75 a 52.84 a House open 1.50 a 1.00 ab 18.75 a 0.25 b 47.07 a Tunnel netting 0.25 b 1.00 ab 0.00 b 1.25 a 53.96 a Tunnel open 0.75 b 1.25 a 8.35 ab 0.25 b 47.98 a Direct netting 0.50 b 0.50 b 18.78 a 0.25 b 44.49 a

Pest and disease incidence rating at last harvest: 0=none; 1=light; 2=medium; 3=severeMean separation in columns by Duncan's multiple range test (P=0.05)Seed sown: 22 Sept 1997Date transplanted: 20 Oct 1997Date harvested: 6 Jan-23 Feb 1998

Table 3. Effect of cultural practices on fruit yield of tomato under protective structure. AVRDC, 1998

Fertilizer Netting Pesticide Fruit no. Mktable Mktable(no/12m2) yield fruit (%)

(t/ha)

Organic - - 606 52 bc 87Inorganic - - 528 46 c 90Organic + - 619 42 c 70Inorganic + - 756 57 bc 86Organic - + 748 70 ab 91Inorganic - + 830 72 ab 91Organic + + 864 79 a 97Inorganic + + 876 85 a 98

Mean separation in columns by Duncan's multiple range test (P=0.05)

Table 4. Effects of rain shelters and grafting on yield of tomatoes transplanted in late summer 1999, AVRDC headquarters (AVRDC 1999).

Marketable yield (t/ha)Grafting (G) Rain shelter

No shelter Open-side Closed-side G-Mean

Non-grafted 61.8 66.6 63.8 64.1 bGrafted onto tomato, H7996 79.6 71.5 75.1 75.4 aGrafted onto eggplant, EG203 59.0 57.3 61.5 59.2 b

S-Mean 66.8 a 65.1 a 66.8 aIn a row or column, means followed by the same letter are not significantly differentat P<0.05 by least significant difference.

Off-season tomato trial under rain shelters

Off-season tomato trial under rain shelters

Table 5. Effects of grafting and rain shelters on plant survival and yield summer tomato transplanted 15 July 2000 (AVRDC 2001).

Plant survival* (%) Marketable yield** (t/ha)Rootstock Shelter No shelter Shelter No shelter

Non-grafted 7.5 c 63.3 ab 3.5 c 7.6 cHawaii 7996 3.3 c 26.7 bc 0.8 c 2.1 cEG203 90.0 a 65.0 ab 26.2 a 6.0 c

*Outliers excluded from analysis: trt4 (rep 1)**Outliers excluded from analysis: trt3 (rep 1), trt4 (rep 1)Mean separation in a row and column at P<0.05 by Duncan's multiple range test.

Off Season Tomato Trial Under Rain Shelters

Flooding and water logging after heavy rainfall

Flooding and water logging after heavy rainfall

CL5915 Non-grafted, RS CL5915 Grafted, RS

Growth of tomato one week after flooding and water logging

CL5915 Grafted, Open CL5915 Non-grafted, Open

Tomato plants one week after flooding and water logging

CHT501 Non-grafted, Open

CHT501 Grafted, RS

CHT501 Grafted, Open

CHT501 Non-grafted, RS

CHT501 Non-grafted RS+Net CHT501 Grafted, RS+Net

CL5915 Grafted, RS+NetCL5915 Non-grafted, RS+Net

Table 6. Effects of grafting and rain shelters on plant survival and yield of summer tomato transplanted 12 August 2000 (AVRDC 2001).

Plant survival* (%) Marketable yield (t/ha)Rootstock Shelter No shelter Shelter No shelter

Non-grafted 36.7 b 51.7 ab 7.2 b 5.5 bHawaii 7996 50.0 ab 20.0 b 10.9 b 4.4 bEG203 95.0 a 96.7 a 28.8 a 25.4 a

*Outliers excluded from analysis: trt4 (rep 1)Mean separation in a row and column at P<0.05 by Duncan's multiple range test.

Leafy vegetables under net house

Table 7. Effects of cultural practices on pest incidence and yield of Pai-tsai grown under protective structures. AVRDC 1998.

Diamond Cabbage Flea YieldTreatment back moth worm beetle (t/ha)

Main plot Chemical spray 1.58 a 1.67 a 1.92 a 13.8 b No chemical spray 0.92 b 2.58 a 1.50 a 15.8 a

Subplot No netting (ck) 2.50 a 1.25 b 3.00 a 13.2 b House netting 1.00 bc 2.25 a 1.25 c 14.7 ab House open 1.75 ab 2.50 a 1.50 bc 13.3 b Tunnel netting 0.25 c 2.25 a 1.25 c 15.3 ab Tunnel open 2.00 ab 2.25 a 2.50 ab 12.9 b Direct netting 0.00 c 2.25 a 0.75 c 19.5 a

Pest indidence: 0=none; 1=light; 2=medium; 3=severeMean separation in columns by Duncan's multiple range test (P=0.05)Seed sown: 11 Nov 1997Date transplanted: 27 Nov 1997Date harvested: 23 Dec 1997

Leafy vegetables in open field and net house

Table 8. Yields (t/ha) of leafy vegetables under open field and net house from different field (AVRDC 2001)

Hot Dry Season Cool Dry Season Hot Wet SeasonLeafy Vegetable No. of Sept. 1999 Nov. 1999 Open Sept. 1999 Feb. 2000 July, 2000

Acc. Open Open Field Nethouse Open Nethouse Open NethouseField Field Mean (32-mesh) Field (32-mesh) Field (32-mesh)

NH Chinese cabbage 17 37.6 38.1 37.5 30.6 36.9 32.7 15.6 18.9

Pak-choi 17 36.3 37.6 36.9 32.5 58.0 54.7 24.8 18.9

Choy sum 19 34.8 36.8 35.8 28.8 47.2 31.5 14.7 15.6

Chinese kale 18 24.8 31.7 28.3 17.3 30.0 26.9 13.7 10.1

Indian mustard 19 31.7 36.2 33.9 28.4 38.4 33.6 28.3 16.4

Mean 33 36.1 34.5 27.5 42.1 35.9 19.4 15.9

Table 9. Yield of Chinese kale and lettuce under double bed rain shelters and open field with drip and furrow irrigation. Cool-dry season, AVRDC 2000-2001.

Chinese kale LettuceShelter Irrigation Marketable Total plant wt Marketable

yield (kg/plot) (kg/plot) yield (kg/plot)

Rainshelter Drip 23.25 45.37 23.72 (RS) Furrow 27.01 47.07 29.82

RS mean 25.13 46.22 26.77

Open field Drip 29.60 43.43 22.63 (OF) Furrow 27.93 39.87 21.05

OF mean 28.77 41.65 21.84

Drip mean 26.55 44.40 23.18Furrow mean 27.47 43.47 25.44

Chinese kale and lettuce under open field and double bed rain shelter

Table 10. Yield of cucumber and snow peas under double bed rain shelters and open field with drip and furrow irrigation. Cool-dry season, AVRDC 2000-2001.

Cucumber SnowpeasShelter Irrigation Total no. of Total wt of Wt of 20 Total pod

fruits/plot fruits (kg/plot) pods (g) wt (kg/plot)

Rainshelter Drip 568 54.38 341.3 4.68 (RS) Furrow 594 58.53 375.3 6.57

RS mean 581 56.36 358.3 5.63

Open field Drip 595 56.29 412.1 8.5 (OF) Furrow 599 58.53 440.7 8.05

OF mean 597 57.11 426.4 8.28

Drip mean 582 55.34 376.7 6.59Furrow mean 597 58.53 408.0 7.31

Cucumber and snow pea under double bed rain shelter

Table 11. Yield of okra and yardlong bean in high and low bed under rain shelters a open field. AVRDC 2001.

Okra Yardlong beanBed Shelter Total no. Total wt of No. of mktWt of mktble

of fruits fruits (kg) pods pods (kg)

30 cmRS 768 8.02 1187 32.1RS+N 994 11.65 1567 44.2Open 853 9.36 1513 39.6

Bed mean 872 9.68 1422 38.6

45 cmRS 780 10.17 967 25.9RS+N 1060 14.24 1286 34.7Open 879 9.71 1181 34.7

Bed mean 906 11.37 1151 31.8

Shelter mean

RS 774 9.10 1077 29.0RS+N 1087 12.95 1427 39.5Open 866 9.53 1347 37.2

RS=Rainshelter; RS+N=Rainshelter+Net

Okra and yard long bean trial under rain shelters

Grafted tomato under rain shelter, Philippines

Table 1. Cost and return per 1,000 sq.m. for off-season grafted tomato under rain shelter, CLSU site, wet season 2000.

ITEM QUANTITY VALUE (P)

Gross IncomeSales P2,260kga/ 90,400

Total CostLabor costMaterial inputs and irrigation costRain shelter materialsb/

Grafting and hardening chamberc/

Total ExpensesNet Income

15,249.607,118.858,887.271,612.25

32,867.9657,532.04

Financial RatiosBreakeven volume (kg)d/

Breakeven price (P) e/

Return on total expenses f/

821.7014.541.75

a/ Price/kg is P40.00b/ Cost is distributed over the life span of the materials, e.g. net is for 6 cropping, GI pipe frame is for 20 croppings, etc.c/ P 19,347 last for 12 yearsd/ BEV = total expenses/price per kge/ BEP = total expenses/yieldf/ RTE – net income/total expenses

SummaryVegetable production under protective structures is gaining importance in the lowland tropics of Southeast Asia.Protective structures provide protection to vegetable crops against biotic and abioticstresses.Vegetable production under protective structures insures year-round supply of vegetables and helps stabilize market price.

SummaryProtective structures include greenhouses, plastic houses, net or screen houses, tunnels and plastic rain shelters.Main benefit of protective structures is protection against the impact of heavy rainfall and strong winds in the tropics.Yields of vegetables such as tomatoes have been improved under protective structures during the off-season.

SummaryYield responses of other vegetables grown under protective structures vary depending on species, season and environmental conditions. Economic benefits from vegetable production production under protective structures are not well defined and studied.There is a great challenge for more research to address the problems of vegetable production under protective structures.

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