Growing Greenhouse Tomatoes in Soil and in Soilless Media

8/8/2019 Growing Greenhouse Tomatoes in Soil and in Soilless Media

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Growing greenhouse

tomatoes in soil and *in soilless mediaAX P a p a d o p o u l o sResearch StationHarrow, Ontario

Cover i l lus t r a t ionPhoto by Faye Clack Associates, courtesy ofOnt.ario Greenhouse Veget.able Producers Marketing Board

Ag r i c u l t u r e Ca n a d a P u b l ic a t i o n 1865 /Eavailable fromCommunicat,ions Branch, Agriculture CanadaOttawa. Ont. KIA OC7

3Minister of Supply and Services Canada 1991Cat. No. A53-186511991E ISBN O-662-18859-4Printed 1991 5M-lo:91Produced by Research Program Service

kgalement disponible en fransaissous le titreLa culture des tomntes en serre 6-w sol et sans sol


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Conten t s

I n t r o d u c t io n 6

C h a p t e r 1 . T h e t o m a t o p l a n t 6Origin 6Determinate versus indeterminate 6Plant improvement 7Seed germination 7Initial growth and development 9The flower 9The fruit 13

C h a p t e r 2 . E n v ir o n m e n t a l r e q u i r e m e n t s 13

Temperature 13Light 14Relative humidity 14Carbon dioxide 15Air movement 15

C h a p t e r 3. N u t r i t io n a l r e q u i r e m e n t s 15

Soil-plant relationships 15Vegetativeness versus reproductiveness 21Nutrient requirements and effects 21

C h a p t e r 4. G e n e r a l c u lt u r a l p r a c t i ce s 24

Crop scheduling 24Cultivar selection 25Plant propagation 26Plant spacing 35

Pruning and training 35Pollination and cluster pruning 39Harvesting and storage 40

C h a p t e r 5. C o n v en t ion a l c r o p p in g in s o i l 40

What type of soil to look for 41Drainage 41Flooding and leaching 42Organic matter 42Control of pH 43Preplant fertilizer application 45Cultivating 45Watering 46Scheduling the application of fertilizer 46Mulching 46

C h a p t e r 6 . Cropp ing in soi l w i th d r ip i r r iga t ion 48

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Ch a p t er 7. Cr o p pin g in p e a t m oss a n d ot h e r or g a n icm e d i a 5 1

The trough system 51Peat bags 55The Harrow peat-bag system 59Cropping in sawdust 59 .C h a p t e r 8 . C r o p p i n g in r o c k w o o l a n d o th e r in e r t m e d ia 6 2C h a p t e r 9 . T h e n u t r i e n t film t e c h n iq u e a n d o t h e r h y d r o p o n i c

s y s t e m s 6 8

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In t roduc t ion

Tomatoes are the most important greenhouse vegetable crop in Canada.They are grown in spring or fall, with conditions and problems varying forthe two seasons. The spring crop is normally seeded in the first or secondweek of November, set in the greenhouse the first week of January, andharvested from mid March to July, with some plantings extended to the fall.Because of the short and dull days of winter, this crop gets a slow start anddemands superior handling from the grower, who must ensure maximumuse of available light and minimum waste of available photosynthates.Failing to maintain a good balance between vegetative and reproductive

growth during the first 2-3 months of this crop results in either excessivegrowth with little fruit-setting or in overbearing offruit on hardened plantsthat grow very slowly. Longer and brighter days that occur later in theseason cannot compensate for lost early, premium-priced production,resulting in an uneconomical crop for the grower. Despite its difficulties,the spring crop has always been the most important of the two because ofhigher prices received and the longer season. The fall crop, on the otherhand, is seeded around the end of June, set in the greenhouse during thefirst week of August, and harvested from the beginning of October to themiddle of December. Fall tomatoes, in contrast to the spring crop, get anexcellent start under the bright and relatively long days of August andSeptember, but they mature during the short days of late fall and winter:

Ch a p t e r 1. Th e t om a t o p la n t

Origin

The genusLycopersicon of the family Solanaceae is believed to originate inthe coastal strip of western South America, from the equator to about 30latitude south; the greatest genetic diversity is found here. The genus isdivided into two subgenera, Eulycopersicon and Eriopersicon, of which theformer contains the species L ycopersicon pim pin ell i fol iu m and

Lycopersicon esculentum. Lycopersicon pimpinellifolium, often known asthe red currant tomato, has exceedingly small fruit (less than 10 mm).

Lycopersicon esculentu m contains large-fruited types that grow wild or aregrown in cultivation as annuals or perennials. Plants of those species

allocated to the subgenus Eriopersicon are generally found in the wild asperennials, with hairy and whitish green fruit that is most unattractive inappearance and flavor.

D et e rmi n a t e v e r s u s i n d e t e rmi n a t e

Based on plant habit and vigor the cultivated tomato is divided into twotypes: indeterminate (or vine), whose plants are trained to single stemswith the side shoots removed, as is done in greenhouse tomatoes; and

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determinate (or bush), which are used for field cropping where all sideshoots are left on the plants to terminate in a cluster (Fig. 11. Theoreticallyall indeterminate types are perennial plants, whereas all determinate typesare annuals.

Plant improvement

Traditionally, the oldest and simplest way to improve tomatoes was to saveseed from plants that had desirable characters, e.g., high yield, good flavor.This approach leads to crop improvement only when there is geneticdiversity to begin with and the plants breed true (i.e., desirable charactersare transferred unaltered from generation to generation). In recent years

the cultivated tomato has been improved greatly by many cross-breedingtechniques. Most frequently, new Fi hybrids are created by crossingpreexisting cultivars or pure lines bred for that purpose (Fig. 2). Thismethod is based on the breeders skill in selecting the parents that shouldbe crossed in order to produce a good hybrid and provides a convenient wayof obtaining desirable combinations of characters from the parents.However, F, hybrids do not breed true, and so each crop must be raisedfrom fresh hybrid seed produced every year from the parental lines. Thus,the seed company that has the parents has a monopoly on the seed supply ofthe hybrid. It is hopeless for the grower to try and economize by saving theseed of a tomato hybrid, as such seed is useless.

Seed germination

The tomato seed, 3-5 mm in size, has a silky appearance and contains alarge coiled embryo surrounded by a small amount of endosperm; itnevertheless retains its viability for many years after harvesting. Well over90% germination is possible after 10 years when the seed is stored undercool dry conditions. The first sign of germination is the appearance of thesmall white root (radicle) (Fig. 3). As the radicle pushes downward into thegrowing substrate, the hypocotyl (primitive stem part) takes on acrook-like form known as the plumular hook. The plumular hook grows tothe soil surface, where in response to light it begins to straighten and turnsgreen. When the seed is firmly anchored in the soil and the plumular hook isstraight, the colyledons (seed leaves) are pulled out of the seed coat (testa),which remains in the soil. However, when the growing medium is too loose

the colyledons cannot separate from the testa, and sometimes the seedlingis distorted (Fig. 3). Tomatoes have a well-defined taproot, with anabundance of lateral fibrous roots. It is possible to encourage thedevelopment of more fibrous roots by pruning the taproot, as happenswhen a seedling is pricked out from a seeding tray and transplanted into apot. The plant readily forms adventitious (aerial) roots on the stem, whichis of great value if the roots become diseased or damaged; a layer of moistsoil or peat (the latter is preferable) at the stem base encourages new rootsto form at this point. Once the cotyledons are fully grown the true leaves

soon appear at the growing point.


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Determinate type

Indeterminate type

Vine &e%see) type

Fig.1 Twotypea~ftomatogravth.

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In i t i a l g rowth and deve lopment

After several leaves have formed (7-12) the growing point changes fromvegetative to reproductive, and a cluster of flower buds are formed thatultimately develop into the first flower cluster or truss. Vegetative growthcontinues in the form of a side shoot growing from the axil of the last leaf.This side shoot forms a small number of leaves (2-4) and thendifferentiates to form the second flower truss along with a new vegetativegrowing point. Thus, the greenhouse tomato develops as a succession ofside shoots; this process is known as a sympodial, or indeterminate, growth(Fig. 4). A peculiar thing happens every time the plant turns vegetative anda new growth starts to develop from the axil of the last leaf: this last leaf,

which is formed before flower initiation, is carried up on its axillary growthand ultimately appears at a higher position than the truss.The final result is that the stem appears continuous and the trusses

seem to arise at internodal positions, whereas in fact they are growing outof the axil of the first leaf above them. Occasionally, strong side-shootsdevelop from several leaves, resulting in confusion as to which shoot is theleader and which shoots should be removed by pruning. To be certain thatthe leader is not accidentally removed, always pull out the side shootsarising from the leaf immediately below each truss, thus allowing the main

growing point of each plant to remain intact. The number of leaves thatform before the first flower truss varies from cultivar to cultivar but is alsoinfluenced by environmental conditions. Most cultivars produce aminimum of seven leaves before the first flower truss and thereafterusually three leaves between trusses.

The f lower

The tomato truss is composed of a succession of axils, each bearing a singleflower (Fig. 5). The main stem of the truss (peduncle) is capable ofbranching one or more times; such branched (or double) trusses can beencouraged by low-temperature treatment, a procedure discussed later.Branching is desirable because it usually increases the number of flowersper truss and allows the number of flowers on each branch to remain fairlyconstant, irrespective of the degree of branching (Fig. 5). Thecharacteristically bright yellow flowers of the cultivated tomato usuallyhave five sepals (constituting the calyx) and five petals (constituting thecorolla) although six or more such segments are possible (Fig. 6).

The stamens (male organs) are composed of short filaments andenlarged anthers, which are united in the form of a narrow-necked cylinder(anther tube). The style, which is part of the pistil (female organ), is usuallyshorter than the anther tube, and therefore the pollen-receptive stigma isenclosed within the anther tube. This ensures self-pollination because thepollen is shed from inside the anther tube (Fig. 6). The importance ofself-pollination is exemplified by the fact that when light is at low levels andthe style becomes longer than the anther tube, fruit set is greatly reduced.

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F i g. 2 C r o ss p o lli n a t io n o f t w o t o m a t o p a r e n t li n e s fo r t h e p r o d u c t i on o f F 1h y b r i d s e e d .

Cr o s s p o ll in a t i o n r e q u i r e s t h e r e m o v a l of t h e a n th e r s o f p a r e n t X b e fo r e p o l le n i sr e l e a s e d .

Th e Y p a r e n t s a n th e r t u b e i s o p e n e d w h e n p o l le n i s p r e s e n t . Th e p o ll e n i s p i ck e du p w i t h a s o ft b r u s h .

T h e p o l le n i s d e p o s i t e d o n t h e s t i gm a o f p a r e n t X. T h e s e e d s fr o m t h e r e s u l t in gt o m a t o h a v e c h a r a c t e r i st i c s of b o t h X a n d Y.

(3.5 mm)

F ig. 3 G e r m i n a t i on o f t h e t o m a t o s e e d .

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Main growing point

Third cluster

(flowers) \

t----Second burst of

vegetative

growth

T --__First burst ofvegetativegrowth-

W15mm

Actual stem

thickness

F i g . 4 T h e s y m p o d i a l t y p e o f g r o w t h o f t h e i n d e t e r m i n a t e t o m a t o g r o w n

c o m m o n l y i n g r e e n h o u s e s .

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1 Typical flower cluster Branched fruit cluster

F ig . 5 T h e flo w er c lu s t er o f t om a t o .

Standard polllnatlon

abscission layer

Fig. 6 T h e f lo w e r o f t h e t o m a t o a n d i t s p o l li n a t i on .To m a to f l o w e r s a r e c o m p le t e , w i th b o th m a le a n d f e m a le o r g a n s , a n d a r e m o s t l yse l f - fe r t i l i z ing . When f ru i t f a i l s to se t , b lossoms sepa ra te a t the absc i s s ion laye ra n d t h e n d r o p .

P o ll in a t i o n : P o ll e n g r a in s a r e r e l e a s e d b y t h e a n th e r s . So m e f a ll or f lo a t i n t h e a i rt o t h e s t i gm a , u s u a l ly o f t h e s a m e f lo w e r , w h e r e t h e y a d h e r e t o t h e s t i c k y s u r fa c e .

Fe r t i l i z a t i o n : Th e f r u i t i s s e t w h e n p o l l e n g r a in s g e r m in a t e a n d s e n d t u b e s w i thth e p o l l e n t u b e n u c l e u s ( s p e r m ) d o w n th e s t y l e . Th e r e t h e y u n i t e w i th t h e o v u le s ,i n t h e o va r y .

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Fruit core, Mesocaro .

Bilocular fruitFig. 7 The tomato fruit.

The fr u i t

The tomato fruit, which is classified as a berry, is an enlarged ovary of two

or more chambers (locules) containing the seeds (fertilized ovules), whichare imbeded in a gelatin-like placenta (Fig. 71.

C h a p t e r 2 . E n v i r o n m e n t a l r e q u i r e m e n t s

The greenhouse environment has a profound effect on crop productivityand profitability. In this chapter, environment is taken in its narrow

meaning and includes_ only temperature, light, relative humidity, carbondioxide, and air movement. Other related subjects, such as water andnutrients, are discussed elsewhere.

T e m p e r a t u r e

Air temperature is the main environmental component influencingvegetative growth, cluster development, fruit setting, fruit development,fruit ripening, and fruit quality The average 24-h temperature is believed

to be responsible for the growth rate of the crop-the higher the average airtemperature the faster the growth. It is also believed that the larger thevariation in day-night air temperature, the taller the plant and the smallerthe leaf size. Although maximum growth is known to occur at a day andnight temperature of approximately 25C, maximum fruit production isachieved with a night temperature of 18C and a day temperature of 20 C.The recommended temperatures that follow are therefore a compromiseand are designed for sustained, high fruit productivity combined withmodest crop growth throughout the growing season.

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Recommended air temperatures

Night minimumDay minimumVentilation

Low light High light

17C 18C19C 21C21C 24C

With carbon dioxide

18C21C26C

Note

l When growing cold-tolerant, cultivars such as Vendor, air temperatures can be l-2Clower than t,hose indicated. However, when growing vigorous cult,ivars such as OhioCR-6, the indicated temperatures are the absolute minimum.

l During very bright weather, temperatures higher than 26C do not harm the plants; but,above 29C, blossoms of most cultivars sustain injury (Ohio CR-6 is an exception).

l A minimum soil temperature of 14C is recommended.

Light

Light is a prerequisite of plant growth. Plant matter is produced by theprocess of photosynthesis, which takes place only when light is absorbed bythe chlorophyll (green pigment) in the green parts of the plant, mostly inthe leaves. In the process of photosynthesis the energy of light is used in

fixing atmospheric carbon dioxide with water in the plant to produce suchcarbohydrates as sugars and starch. Generally, the rate ofphotosynthesis isrelated to light intensity, but not proportionally. The importance of light intomato production is greatest in the winter, when it is in short supply. In theshort dull days of late fall, winter, and early spring, flower bud developmentis arrested and clusters fail to produce flowers and fruit. This failure is dueto the low daily levels of radiant energy, which result in insufficientcarbohydrate production. Not only do the poor light conditions limitphotosynthetic productivity but the limited carbohydrates produced

during the day are expended by the respiring plant so that it can survivethrough the long nights. A fully grown tomato crop benefits from anyincrease in natural light intensity, provided the plants are well suppliedwith water, nutrients, and carbon dioxide, and the air temperature isprevented from becoming too high.

Relative humidity

The effects of relative humidity on crop performance are not well

understood. The crop can withstand a wide range of relative humidity, fromvery low to very high, as long as the changes are not drastic or frequent. Atlow relative humidity, irrigation becomes critical, whereas at high relativehumidity diseases can manifest themselves. Growth in general is favoredby high relative humidity; high relative humidity during the day can alsoimprove fruit setting. However, high relative humidity, when not managedproperly, can easily lead to water condensation on the plants and thedevelopment of serious diseases.

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C a r b o n d i o x i d e

In cold weather, with no ventilation, a minimum carbon dioxideconcentration of 1000 vpm (~1000 ppml is recommended during the day.In the summer, with ventilation, the application of supplemental carbondioxide at a concentration up to 400 ppm has been found economicallyuseful in other countries, but this technique is too new in Canada to supportdefinite recommendation. Regions with a moderate (sea) climate, such asBritish Columbia, are more likely to benefit from carbon dioxide applied inthe summer. But in regions with a continental climate, such assouthwestern Ontario, the need to ventilate the greenhouse activelythroughout the hot summer probably renders the practice uneconomical.

Air movement

Horizontal air movement is beneficial for several reasons. An approximateair speed of 1 m/s, which causes leaves to move slightly, isrecommended. Horizontal air movement helps minimize air temperaturegradients in the greenhouse, removes moisture from the lower part of thegreenhouse (under the foliage), distributes moisture in the rest of thegreenhouse, helps the carbon dioxide from the top of the greenhouse to

travel into the leaf canopy where it is taken up and fixed in photosynthesis,and may even assist pollination. As a result of modest air movement in thegreenhouse the uniformity of the greenhouse environment is improved,which is generally beneficial to crop productivity and energy conservation.

C h a p t e r 3 . N u t r i t i o n a l r e q u i r e m e n t s

Soi l -p lan t r e l a t ionsh ipsPlants in their natural environment have lived, with almost no exception,in association with soil, an association known as the soil-plantrelationship. Soil provides four basic needs of plants: water, nutrients,oxygen, and support. With the advancement of science and technology,humans have provided for these needs in an artificial way and havesuccessfully grown plants without soil. All the various methods andtechniques developed for growing plants without soil are collectively called

soilless methods of plant culture. These methods include a great diversity of systems, from the purely hydroponic, which are based on water andnutrients only (e.g., nutrient film technique, or NFT), to those based onartificial mixes that contain various rates of soil. In between theseextremes lie a great number of soilless methods that make use of some sortof growing medium, either inert (e.g., rockwool slabs, polyurethanechunks, and perlitel or not inert (e.g., gravel culture, sand culture, and peatbags).

1 metre per second

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Soil as a growth medium

Soil consists of mineral matter, organic matter, water, and air. An averagesoil in optimum condition for plant growth might consist of 45% mineral

matter, 5% organic matter, 25% water, and 25% air space. The mineralmatter is made up of a great diversity of small rock fragments. The organicmatter of a soil is derived from plant and animal remains and is a mixture ofthese materials at various stages of decomposition. In the process ofdecomposition, some of the organic entities are oxidized to theirend-products and others to an intermediate product called humus. Boththe type and the relative quantity of the mineral and organic constituentsofa soil determine its chemical properties. Chemical properties of a soil arethe amounts of the various essential elements present and their forms of

combination, as well as the degree of acidity or alkalinity, known as PH.~The extent of nutrient availability to the plants depends not only on thechemical properties of the soil but also on its physical properties.

Soil structure and texture

The physical properties of a soil describe its texture, i.e., the sizedistribution of its mineral constituents, expressed as a percentage ofcontent of sand, silt, and clay (Fig. 81, and its structure, i.e., the type andextent of formation of the various mineral and organic constituents intocrumb-like soil aggregates. The organic matter of a soil plays an importantrole in soil structure because of the diversity in the size of its componentsbut, even more importantly, because of the role of humus in cementingtogether the various soil constituents into crumb-like aggregates.

Soil structure in turn plays an important role in soil fertility (the abilityof soil to sustain good plant growth and high yields) because it determines,to a great extent, the water-holding capacity and aeration of a soil. Thewater held within the soil pores, together with the salts dissolved in it,

make up the soil solution that is so important as a medium for supplyingnutrients and water to growing plants. The air located in the soil poressupplies oxygen for the respiration of root and soil microorganisms andremoves the carbon dioxide and other gases produced by them. Plantnutrients exist in soil as either complex (organic or inorganic). compoundsthat are unavailable to plants or in simple forms that are usually soluble inwater and are therefore readily available to plants. The complex forms,which are too numerous to mention, must first be broken down throughdecomposition to simple soluble forms to be available and therefore useful

to plants (Fig. 9). The available forms of all essential nutrients for plantgrowth are summarized in Ta.ble 1.

* Th e pH value of a s olut ion is t he n egat ive logar ith m of its h ydrogen ion concent ra tion(pH = -log[H + I). ApH of 7 indicates neutral conditions; values lower than 7 indicate anacid environment ; an d values higher t ha n 7 indicat e an alkaline environment .

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Increasing clay

sandy clayloam

clay i(~0.002 mm)clay loam

+

Iloam

silty clayloam

et y loamandy loamsand(0.05-2.00 mm) silt(0.002-0.05 mm)Increasing sand Increasing siltFig. 8 Classi f icat ion of soi l s a c c o r d i n g to t e x t u r e .

Soil reaction (pH)The reaction of the soil solution (pH1 also affects the solubility of thevarious nutrients and thus their availability to plants; this process isillustrated in Fig. 10.

In acid soils (pH


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MINERAL MATTER

ISand. P,,,. clayl

1 /,!$$~&,I 1 HU M U S I I WATE R I I AIR I IFERTILIZER~

HUMUS-CLAY

EARTH

VIRGINSOIL

.

CULTIVATED

SOIL

CULTIVATED

SOIL

SOIL

SOLUTION

Fig. 9 The processes of mineralization, soluhilization, cation exchange, andnutrient absorption.

a storehouse for certain essential ions (cations). The negatively chargedions (anions), such as nitrates (NO;1, phosphates (HPO:?, sulfates WI-I,and chlorides (Cl-), are found almost exclusively in the soil solution and cantherefore be leached away easily with overwatering. The roots and roothairs are in intimate contact with the soil colloidal surfaces, which arebathed in the soil solution, and therefore nutrient uptake can take placeeither from the soil solution or directly from the colloidal surfaces (cation

exchange).The soil solution is the most important source of nutrients, but since itis very dilute its nutrients are easily depleted and must be replenished fromsoil particles. The solid phase of the soil, acting as a reservoir of nutrients,slowly releases them into the soil solution by the solubilization of soilminerals and organics, by the solution of soluble salts, and by cationexchange. A more dramatic increase in the nutrient content of the soilsolution takes place with the addition of commercial fertilizers.

As plants absorb nutrients (ions) they exchange them for other ions.

For example, for the uptake of one potassium (K+) ion or one ammonium

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Table 1 Essential elements for the growth of most cultivated plants

Element SymbolAtomicweight

Availableform

Organic elements (obtained from the air and water)

Hydrogen H 1.00Carbon C 12.00Oxygen 0 16.00

Macronutrients (needed in large quantities)

Nitrogen N 14.00

Potassium K 39.10Calcium Ca 40.08Magnesium Mg 24.32Phosphorus P 30.92Sulfur S 32.07

M icron utr ients (needed in small quantities)Iron

Fe 55.85Manganese Mn 54.94Copper c u 63.54Boron B 10.82Zinc Zn 65.38Molybdenum MO 95.95

NO; , NH:K+Ca2+Mg2+H,PO;, HPO;-so:-

Fe3+ Fe2+Mn2cl?+ cu+BO:;B,O;-Zn+MOO; +

(NH:) ion, one hydrogen (H+) ion is released into the soil solution ordirectly into the soil colloids by the process of cation exchange. Similarly,for the uptake of one calcium (Ca2+) or one magnesium (Mg2+) ion, twohydrogen (H+) ions are released by the root. Thus, as the plant absorbsthese essential cations, the soil solution and the colloidal particles containmore and more hydrogen (H+) ions, which explains why the removal ofcations (ammonium (NH ;I nitrogen is a good example) by crops tends tomake soils acidic, i.e., having a low pH. Also, as the plant absorbs essentialanions such as nitrates (NO ;1 and phosphates (HP0 4), the soil solution isenriched with more and more hydroxyl groups (OH-1 and bicarbonates(HCO; 1, which explains why the removal ofanions (nitrate (NO;1 nitrogenis a good example1 by crops tends to make soils alkaline, i.e., having a highPH.

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v)EaaKjE

-._ii0=_s:

= :

a

Fig. 10 How so i l p H a f f ec t s av a i l ab i l i t y o f p l an t n u t r i en t s ( d i ag r am co u r t e sy o f P l a n t P r o d u c t s L t d . ) .

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Vegeta t iveness versus reproduct iveness

Growing a successful tomato crop depends on the growers ability tomaintain an optimum balance between vegetativeness and reproduc-

tiveness. Long, sustained fruit production is accomplished only underoptimum environmental conditions and by timely application of water andnutrients. A well-balanced plant is judged by its thick stem, dark greenleaves, and large, closely spaced, readily setting flower clusters. A properlynourished plant should have a stem 1 cm thick at a point 15 cm below thegrowingpoint. Thicker stems are an indication of overvegetativeness andare usually associated with poor fruit set and low productivity. Thinnerstems are an indication of overproductiveness, which leads intocarbohydrate starvation, slow growth, and ultimately low productivity.

Regulating the nitrogen and the water supply is the most common andeffective technique for controlling crop growth. The water supply can beregulated directly, by adjusting the irrigation, or indirectly, by adjusting therelative humidity in the greenhouse and the electrical conductivity of theirrigation water. Light irrigation, low relative humidity, and high electricalconductivity in the irrigation water tend to make water less available to theplants and result in hard plants and slow growth. Of the three approaches,the regulation of electrical conductivity is the most preferred because ofitssimplicity, effectiveness, and dependability. The nitrogen supply can also be

regulated directly, by adjusting the nitrogen fertilization, or indirectly, byvarying the supply of other nutrients, e.g., potassium. Maintaining a highpotassium-to-nitrogen ratio in the fertilizer feed is a technique that, is usedby some growers to reduce the rate of growth.

Nut r i en t r equ i remen t s and e f fec t s

Although only 1% of the total plant weight is made up of inorganicnutrients, fertilizer application is critical; it influences greatly the growth

and development of the crop, as well as the quantity and quality of the fruit.A tomato crop absorbs the major nutrients at the following average rates:nitrogen, 370 kg/ha; phosphorus, 50 kg/ha; potassium, 680 kg/ha;magnesium, 290 kg/ha; and calcium, 45 kg/ha.

Over a season a grower should apparently apply twice as muchpotassium as nitrogen and almost as much magnesium as nitrogen to fulfillthe plants needs. However, that interpretation is too simplistic. In fact,fertilizer feeding programs are adjusted regularly throughout the produc-tion season to suit the changing nutritional needs of the crop according to

crop and environmental conditions. Furthermore, the fertilizer feed is usedas a tool to control crop growth and fruit quality.The role of each nutrient in the growth and productivity of tomatoes is

described in the sections that follow.

N i t rogen

This nutrient contributes more toward the vegetative components (leavesand stems) of the plant than the reproductive components (fruit). High

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rates of nitrogen induce vigorous vegetative growth to the detriment offruit production. However, under hot and bright conditions, the nitrogenlevel must be increased to enable the plant to continue growing and torealize the maximum production potential of the fruit.

An excess of nitrogen is marked by strong thick stems, curled leaves inthe head of the plant, large clusters and flowers, and poor fruit set. Adeficiency of nitrogen expresses itself in hard plants with thin heads, lightgreen foliage, and pale yellow flowers.

P o t a s s i u m

Potassium has a great influence on fruit quality and is effective in

hardening growth at high rates. Potassium levels are particularlyimportant at planting time for growth control and later for the preventionof ripening disorders. The ratio between potassium and nitrogen is alsoimportant in growth control-the higher the ratio the slower the growth.Problems with fruit quality, such as blotchy ripening, boxy fruit, and evento some extent, greenback, are associated with low levels of potassium andin most cases can be counteracted with high-potassium feeds. The propermanagement of irrigaton and a stable salt content of the soil solution arealso factors in avoiding blotchy ripening.

P h o s p h o r u s

Although phosphorus is used in much smaller quantities than nitrogen andpotassium, its presence is needed continuously Initially, phosphorus isimportant for early root growth, especially under cool soil conditions, but italso has a profound effect on both vegetative growth and fruit setthroughout the crop. Symptoms of deficiency include a characteristicpurple color of the veins and stem, thin growth, and poor clusterdevelopment. Phosphorus toxicity is uncommon. Phosphorus is stored wellin soil but is easily leached in peat media. It is therefore imperative thatphosphorus always be included in the feed of peat-grown crops.

M a g n e s i u m

Although magnesium deficiency is common, it rarely results in yieldreduction. However, its presence might offer entry points for botrytic and

other diseases. The deficiency usually exists only in the plant, not in thesoil, and is related to high-potassium feeds or poor root development. Boththese make it difficult for the plant to take in sufficient magnesium,thereby forcing the plant to move magnesium from the old leaves to thenew. Magnesium, being a vital part of chlorophyll, is easy to monitorbecause its absence is made obvious by the absence of chlorophyll. Amagnesium deficiency is easily corrected with Epsom Salts, in a 2%solution spray. In fact, some growers provide most of the magnesiumrequirements of a crop in frequent sprays.

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Calc ium

Calcium deficiency is usually expressed as blossom-end rot of the fruit andas dieback of the growing tips. In most cases the calcium deficiency is not inthe soil but is induced. The most likely cause is water stress on the plantresulting from inadequate or uneven watering, frequent and largevariations in relative humidity, or a high level of salts. Sprays of calciumnitrate or calcium chloride, in a 2% solution, help correct a calciumdeficiency, but improving the water balance in the plant is a more practicalsolution to the problem.

Calcium, magnesium, and potassium are believed to compete with eachother, with a varying degree of success, for the same sites of absorption by

the plant; it is useful to remember that increasing one of them affects theother two.

Su l fu r

This element is rarely a problem because it is present in many fertilizers asa carrying element and because it is a commonplace pollutant. However,high sulfur levels can become sources of excessively high salts and couldalso be detrimental to the uptake of molybdenum.

I ro n

Iron deficiency, a frequent problem, is usually expressed in chlorotic youngleaves. Similar to calcium deficiency, iron deficiency is, in most cases,induced. Indirect causes of iron deficiency may be soil pH that is too high, amanganese level that is too high, and poor root growth or poor anaerobicsoil conditions resulting from overwatering. In many cases, improved soilaeration or drying out the soil or peat corrects the problems. Soilapplications and foliar sprays of iron salts or iron chelates are helpful, butas usual the most recommended action is the elimination of the source ofthe problem.

M a n g a n e s e

Manganese deficiency is frequently confused with iron deficiency and isoften an expression of iron toxicity. Manganese toxicity is a more seriousproblem, encountered when steaming is not well controlled and is notfollowed by leaching.

C o p p e r

Peat media may occasionally be deficient in copper, but the widespread useof copper plumbing ensures an adequate copper supply in most cases.

B o ro n

Boron deficiency is expressed as brittleness of leaves, premature wilting,

and, in acute form, as dieback of the growing tips. This deficiency can be

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corrected easily with foliar sprays of a Borax solution, but the rate ofapplication must be monitored carefully because boron toxicity can causesevere plant damage.

Zinc

This element is rarely in deficiency. Toxicity is a potential problem inrecirculating hydroponic systems, as there is always some zinc releasedfrom galvanized pipes.

M o l y b d e n u m

A molybdenum deficiency can be induced by acid soil conditions or highsulfur levels. Although symptoms of molybdenum deficiency are not easilydistinguishable, leaf tissue analysis is a dependable diagnostic tool.

Ch a p t er 4. Ge n e r a l cu lt u r a l p r a ct ice s

Crop schedu l ing

E a r l y s p r i n g t o m a t o e s

l Sow seed 25 October-25 Novemberl Set plants in permanent bed 1 January-15 Januaryl Harvest April to Julyl Remove plants 1 July-20 Julyl Sterilize soil 1 July-25 July

F a l l t o m a t o e sl S o w seed 15 June-15 Julyl Set plants in permanent bed 20 July-15 Augustl Harvest October to Decemberl Remove plants 15 December-l Januaryl Sterilize soil 16 December-l January

The early-spring tomato crop is usually replaced by a late-springtomato crop in old single plastic houses where light transmission is poorand heating costs are high.

L a t e -s p r i n g t o m a t o e s

l Sow seed 15 December-15 Januaryl Set plants in permanent bed 1 February-l Marchl Harvest May to Julyl Remove crop 20 July-25 July

Sometimes the spring crop of tomatoes is extended to the followingNovember if plants are healthy. The replacement of the spring crop of

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tomatoes by a spring crop of cucumbers and the fall crop of tomatoes by afall crop of cucumbers or two fall crops of lettuce are variations to thestandard scheduling of one spring and one fall crop of tomatoes per year.

Cult ivar se lect ion

The first decision that must be made is whether to grow a red-fruited or apink-fruited cultivar This decision is normally based on market conditions,but it could also be influenced by the growing conditions and by theavailability of cultivars. In general, the selection of red-fruited cultivars isgreater than that of pink-fruited cultivars. However, a shortage ofred-fruited cultivars with resistance to fusarium crown and root rot disease

is often encountered. Canadian farmers have grown the followingcultivars,which have received commercial acceptance.

R e d -fr u i t e d c u l t iv a r s

Michigan-Ohio hybrid

This cultivar produces medium-size fruit. It is very vigorous andoccasionally difficult to pollinate. The Michigan-Ohio hybrid is not

recommended for fall production or production under plastic and issusceptible to leaf mold. Once widely grown, this cultivar is nowcommercially insignificant, although seed is still commerically available.

Vendor

This cultivar ripens uniformly Its fruit size is small, mainly because fruit isset readily, which results in overloading. Fertilizing should start earlierthan for other recommended cultivars. Vendor is recommended as a springor a fall crop under glass but can be especially valuable as a short springcrop under plastic. This cultivar produces excellent-quality fruit, evenunder slightly cooler greenhouse conditions than normal, but unfortu-nately its usefulness has been limited by its susceptibility to leaf mold andits lack of resistance to tomato mosaic virus (TMV) and to fusarium crownand root rot disease.

Dombito

This large-fruited cultivar has vigorous growth and high fruit production.It has good general disease resistance but lacks resistance to fusariumcrown and root rot disease.

Caruso

Although large-fruited, Caruso is not as vigorous as Dombito; however, itsfruit production is as good or better. This cultivar has good general disease

resistance but lacks resistance to fusarium crown and root rot disease.

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Dombito and Caruso were the most important red-fruited cultivars at timeof writing. New red-fruited cultivars with resistance to fusarium crown androot rot disease have been introduced and tested recently with somesuccess. Although their development is still being pursued actively byseveral seed companies, the cultivar Trend has already gained considerablecommercial acceptance.

P in k - f ru i t e d c u l t i v a r s

Ohio MR-13

This cultivar ripens uniformly, producing medium to large fruit. It resists

cracking and requires heavy feeding after fruit set is well under way. OhioMR-13 is relatively free from blotchy ripening but is susceptible to leafmold and blossom-end rot. It can be grown as a spring or fall crop when leafmold is kept under control. This cultivar is TMV-resistant. Once widelygrown in Ontario and Ohio, its usefulness and cropping fell drasticallywhen fusarium crown and root rot became a problem.

Ohio CR-6

This large-fruited cultivar, with resistance to fusarium crown and root rotdisease, has extremely vigorous growth requiring delicate nutritional andenvironment control to ensure fruit set. Fruit on first clusters has a roughshape. Some improvement in fruit quality is normally achieved by raisingthe air temperature and feeding low nitrogen. Ohio CR-6 produces fruit aweek later than most other cultivars, with the first cluster appearing toohigh on the main stem.

KS1 5 and KR-381These two closely related cultivars have resistance to fusarium crown androot rot disease.

Ohio CR-6 was the most important pink-fruited cultivar for some timeprevious to writing, but after extensive testing, the KR lines are nowreceiving wider commercial acceptance. As the development and testing ofnew red and pink cultivars are continuing research activities, consult thelocal adviser on horticultural crops for the latest cultivar recommenda-tions before starting a crop.

Pl a n t p ropa ga t i on

Most greenhouse operators in Canada grow their own transplants. This is adesirable practice because it reduces the possibility of importing diseasesand insects. However, transplant raising in other countries has been

practiced successfully by specialized nurseries that ensure a reliable supply

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of low-cost high-quality transplants to local growers through theapplication of modern technology. Plant propagation is a vitally importantstage in greenhouse vegetable production. The success of a crop depends

largely on the attention paid to detail and the care taken during plantraising. Moreover, with early spring crops, propagation must take place inthe winter, when natural light is limited. To make the best use of availablelight, other factors such as spacing, temperature, irrigation, and nutritionmust be subject to close and accurate control. Artificial light is now usedwidely to enhance transplant growth when natural radiation is limited,with the result that the performance of early-planted spring crops hasimproved significantly.

P r o p a g a t i o n s c h e d u l e s

In deciding when to seed, the desired harvesttime should be considered. Itusually takes 5 months from seed to first pick in a normal spring crop butonly 4 months in a normal fall crop. A spring crop that comes intoproduction in the beginning of April requires seeding to take place in thelatter part of November. In recent years, an increasing number of growersare planting a late spring crop in plastic houses. In that case, seeding takesplace in January and planting in-house in March. Harvest is in May, June,

July, and later. The late spring crop is easier and less expensive to grow butcomes into production when prices are relatively low.

S e e d s o w i n g

Each gram contains about 300 seeds. Assuming a planting density of 25 000plants per hectare, a germination rate of 80%, and a safety margin of anadditional 100/o, seed should be sown at approximately 120 g/ha.

The most common approach is as follows. Fill a plastic tray (55 x27 cm) with a soilless mix, such as a commercial peat mix, and strike it offlevel. Press the medium down evenly with a wooden board to about 1.5 cmfrom the top. Broadcast the seed or sow it in rows, as evenly as possible, at arate of 500-600 seeds per tray. Cover the seed with 0.5 cm of fine-gradegrowth medium to assist the prompt shedding of the seed coat, thusreducing the risk of transmitting tomato mosaic virus and of distorting theseed leaves. After sowing, cover seed trays with glass or paper, whichconserves moisture; no further watering is needed before germination.Place the seed trays in a small greenhouse or special propagation room (no

light is needed at this stage) at a day and night temperature of 24C untildaily inspection shows seedlings to be breaking the surface of the growthmedium; the higher the air temperature of the propagation room duringgermination the faster and more uniform the germination will be. However,seedling growth is fast at high temperatures, which makes the use of a highgermination temperature risky because a delay of a few hours in removingthe seed tray cover can result in excessive elongation of the seedling stemsand carbohydrate depletion. Once seedling emergence is well under way,remove the seed tray covers, reduce the day and night air temperature to

20C and supply as much light as possible. Maintain these conditions for2 7


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Fig. 11 T y p i ca l s t ag es o f seed l i n g g r o w t h fr eq u en t l y used a s m a r k e r s o f t h e i d e a lt i m e f or i n i t i a t i n g (p l a n t A) a n d t e r m i n a t i n g (p l a n t B ) t h e c ol d t r e a t m e n t .

2-3 days to allow all seedlings to emerge and become photosyntheticallyactive and to prevent excessive elongation.

C old t r e a t m e n t

Under a cold treatment regimen, place young tomato seedlings in a day andnight air temperature of lo-13C for approximately 2 weeks, whileproviding as much light as possible for 9-12 h. Seedlings should besubjected to cold treatment just after the seed leaves (cotyledons1 unfoldand the first true leaves start to appear (Fig. 11). Shoots kept at lowtemperatures at this stage of growth produce a small number of leavesbelow the first cluster and therefore flower earlier; roots kept at low

temperatures cause branched clusters, i.e., many flowers in the first andpossibly the second cluster. Cold temperatures during both day and nightare effective. The cold treatment increases the number of flowers but doesnot influence the setting of fruit. If later conditions for fruit setting areright, a greater number of flowers will set fruit because of the increasednumber of blossoms. If, however, the temperature for fruit set remains lessthan ideal, the pollen does not germinate and grow normally resulting inpoor fruit set and cat-faced fruit. When the cold treatment is used, seedlo-14 days earlier than usual to compensate for the slow growth rateduring the cold treatment. The growth medium in the seedling trays mustbe sterile, because when plants are grown at relatively low temperature thedanger of damping-off is increased.

T r a n s p l a n t i n g i n t o p o t s ( p r i c k i n g o u t )

The best time to prick out tomato seedlings is at cotyledon expansion, justafter the cold treatment. Seedlings are too hard to handle before this timeand if pricking out is delayed further, the transplanting shock will be

greater because more roots are broken. Transplants are grown in 7.5cm or

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lo-cm plastic pots or in soil blocks. In addition to good topsoil, peat mixesare used extensively as growth media but always after proper sterilization.Growers should avoid modifications to recommended mixtures, as the

results could be disastrous.A

worldwide trend toward peat-based mixturesis replacing those containing loam, because loam of desirable specificationsis difficult to obtain. However, greenhouse soil that has good texture andstructure is a valuable asset as a growth medium for transplant raising,provided it is sterilized effectively before use. Heavy leaching following soilsterilization is also highly recommended. This treatment ensures theremoval of excess salt, which can be harmful to young seedlings and resultsin low nutrient levels, especially nitrogen, in the growth medium. Lownutrient levels allow for better control of plant growth through the

manipulation of liquid feeding.Do not change frequently the substrate used for raising transplantsbecause seedlings respond differently to different substrates, and theexperience gained over the years on one substrate is not entirelytransferable to other substrates.

Although larger pots (10 cm) appear to increase the cost of producingplants, they are, in fact, the best choice because they allow growers to holdtheir plants longer in the propagation house, which is much less expensiveto heat than the entire greenhouse. Furthermore, an extended propagation

time results in greater use of artificial light whenever available. Finally, theuse of large pots for transplant raising has frequently been associated withincreased early yields. Pots can, of course, be used again the followingseason, but they should first be washed and soaked in a bleach (10%)solution, or any other approved disinfectant.

Watering and nutrition

Immediately after pricking out the seedlings, water them thoroughly to

bring the growth medium to field capacity and to settle it around the roots.Careful watering is necessary during the propagation period. Keep theyoung plants well supplied with water without depleting the growthmedium of its oxygen by overwatering. Because it is difficult to judge themoisture content of growth media in plastic pots, pull out two or threeplants regularly and make sure that the medium at the bottom of the pots iskept moist but not too wet. Transplants raised in lo-cm pots requirewatering daily in good weather; in very bright weather, more than onewatering a day may be necessary; in dull winter weather, watering as

infrequently as once every 3 days may be adequate. The use of smaller potsrequires more frequent watering. A deliberately short water supply in thepropagation pots restricts growth and helps produce hard, stocky, darkgreen plants. However, this type of growth control invariably results inexcessive hardening of the transplants because of the difficulty ofregulating the water supply, resulting in yield losses early in the productionseason when prices are best. In recent years, research has identified moredependable means of growth control. Fertilizer is now fed continuously atevery watering, with the fertilizer concentration in the solution used as an

osmoticurn in regulating water availability to the plants (Table 21. The

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recommended fertilizer concentration in the irrigation water, measured asits electrical conductivity (EC), varies according to the environmentalconditions. For transplants raised during the winter, complete nutrient

solutions of an EC that ranges between 3000 and 6000 kS/cm have beenused with good results (Table 3). Higher conductivities now appear saferwhen the potassium-to-nitrogen ratio in the nutrient solution is higherthan 4:l (Plate 1).

Also, the supply of artificial light allows the use of higher ECs thannormal, but not when artificial light results in overheating the transplantsand in drier conditions in the greenhouse.

The individual nutrient concentration in the final solution variesaccording to EC, but in the standard case, where 1 L of each stock solution

is diluted in 100 L of water(1:lOO

mixing ratio), the concentration ofnutrients is as described in Table 4.Transplants of similarly good quality can also be raised when

commercial mixes of fertilizer such as those commonly known as startersare used at appropriate rates. A simple solution of starter fertilizer (3 g of10-52-10 per litre of water) with an approximate EC of 4000 $Ycm used incontinuous feeding produces transplants acceptable to most growers in asimple and safe way Alternativeb, commercial fertilizer mixes that containall nutrients except calcium and that offer a potassium-to-nitrogen ratio ofabout 51 can be used safely with acceptable results at ECs up to5000 wS/cm.

Table 2 Stock solutions required for the preparation of completefertilizer solutions with a varying potassium-to-nitrogen ratio

Fertilizers(kg)Potassium-to-nitrogen ratio

2:l 4:l 6:lStock A, 1000 L

Calcium nitratePotassium nitrate

Stock B, 1000 LPotassium sulfate

Stock C, 1000 L

Monopotassium phosphateMagnesium sulfateIron chelate (13% iron)Micronutrient mix (STEM)

67.0 70.0 70.074.0 9.5 9.5

13.5 92.5 150.0

22.5 22.0 22.050.0 50.0 50.0

0.6 0.6 0.60.8 0.8 0.8

l The stock solutions described can be used, as shown in Table 3, to produce fertilize1

solut ions of var ious ECs for r aising tr an splant s.l A typical m icronut rient mix, e.g. Peters soluble tr ace elemen t mix (STEM), cont ains

1.45% boron, 3.2% copper, 7.5% iron, 8.15% manganese, 0.046% molybdenum and 4.5%

zinc.

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Pla t e 1 Ef fec t on cu l t i va r Oh io CR-6 o f t he po ta s s ium- to -n i t rogen

r a t i o a n d E C (@/cm ) o f t h e f e r t i l i z e r s o l u t i o n a p p l i e d o n t o m a t ot r a n s p l a n t s . No t e t h e e x c e l l e n t q u a l i t y o f t r a n s p l a n t s p r o d u c e d w i t h

nu t r i en t so lu t ions o f modera t e ly h igh EC ( i . e . , 3000-6000@) w h e n t h epo ta s s ium -to -n i t rogen r a t io i s a l so h igh (i .e ., 4:l or 6:l).

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Table 3 Amount of each stock solution (in litres) required to produce100 L of final nutrient solution with varying EC

EC($Ycm)Potassium-to-nitrogen ratio

2 : l 4 : l 6 : l

1 0 0 0 0 . 3 7 5 0 . 3 7 5 0 . 2 7 5

3 0 0 0 1 . 4 5 0 1 . 4 5 0 0 . 8 7 5

6 0 0 0 3 . 3 5 0 3 . 1 5 0 2 . 4 0 0

Table 4 Nutrient concentration in final nutrient solution*

Potassium-to-nitrogen ratio

Nutrients 2:l 4:l 6:l

Nitrogen, nitrate (NOi-1 1 9 3 . 0 0Nitrogen, ammonia (NH:) 7 . 0 0Phosphorus 5 0 . 0 0

Potassium 4 0 0 . 0 0

Calcium 1 2 7 . 0 0

Magnesium 5 0 . 0 0

Iron 8 . 0 0

Zinc 0 . 0 7

Copper0 . 0 7

Boron 0 . 3 0

Manganese 2 . 0 0

Molybdenum 0 . 0 5

wm1 1 3 . 0 0 1 1 3 . 0 0

7 . 0 0 7 . 0 0

5 0 . 0 0 5 0 . 0 0

4 8 0 . 0 0 7 2 0 . 0 0

1 3 3 . 0 0 1 2 7 . 0 0

5 0 . 0 0 5 0 . 0 0

8 . 0 0 8 . 0 0

0 . 0 7 0 . 0 7

0 . 0 7 0 . 0 7

0 . 3 0 0 . 3 0

2 . 0 0 2 . 0 0

0 . 0 5 0 . 0 5

* St ocks described in Table 2 ar e diluted with a fert ilizer injector h aving a 1:lOO mixingratio.

Artificial light

Artificial light, as mentioned earlier, is first used immediately aftergermination. A relatively small installation is needed at this stage, and highlight intensity is economically feasible. Both fluorescent (ideally in mixturewith some incandescent) and high pressure sodium (HPS) lamps areacceptable and are widely used to generate a minimum light intensity of100 pmol/s per square metre (equivalent to 20 W/m2 or 8000 Lux or 760 fclin growing rooms. The fluorescent lamps produce slightly shorter plants

with a deeper green bluish color than HPS lamps, but the latter are the

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most economical to install and operate. During the first few days afterpricking off, when the pots can be arranged close together, it is stilleconomical to maintain a high light intensity (75-100 pmol/s per squaremetre) for approximately 16-18 hours daily. However, as plants grow theyare spaced progressively to avoid crowding and becoming spindly, makingthe use of high light intensity less and less cost effective. For the rest of thetime, while the plants are in the propagation house, provide supplementallight (artificial light in addition to natural light) at a light intensity of about50 kmolis per square metre. Obviously, whenever cost is not a factor, thehighest light intensity available should be provided for a maximum of 18 hdaily, as this treatment results in shorter propagation time and heavier,stronger, sturdier transplants. There is no advantage in using low-intensityincandescent light on tomato plants in midwinter to extend the daylight

period.

T e m p e r a t u r e c o n t r o l

Recommended temperatures for transplant raising, along with thosementioned earlier for seed germination and cold treatment, aresummarized in Table 5.

Table 5 Recommended temperatures for tomato transplant raising

Air temperature in CGrowth stage Light conditions Day Night

Seed germination Not critical 24 24

For 2 weeks after Maximum available

cotyledon expansion light intensity 10-13 10-13(i.e., cold treatment) for 9-12 h daily

After pricking out Good light 21* 18(i.e., while in pots) conditions

After pricking out Poor light 19 17(i.e., while in pots) conditions

* When growing cold-toleran t cultivars su ch a s Vendor, air tem pera tu res can be l-2Clower t ha n t hose indicat ed. However, when growing vigorous cultivar s such a s OhioCR-6, a similar r eduction in a ir t emper at ur e result s in poor-quality, cat -faced fru it.

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C a r b o n d i o x i d e e n r i c h m e n t

During propagation an atmosphere enriched with carbon dioxide at anominal concentration of 1000 vpm (~1000 ppml increases plant vigor andearly fruit set and may partly compensate for poor light conditions. Thebeneficial effects of carbon dioxide enrichment are more evident when airtemperatures are on the high side and are proportional to the duration ofenrichment. Apply carbon dioxide during the day or any part of the nightwhen artificial light is supplied. Because raising transplants occupies only asmall area, it is economically feasible and highly advisable to use liquidcarbon dioxide (carbon dioxide gas liquefied under pressure) because of itsguaranteed purity and amenity to accurate concentration control. Liquidcarbon dioxide is also preferred because burning natural gas or propane to

generate carbon dioxide increases the risk of plant injury from gaseouspollutants.

Graf t ing

Grafting is a useful technique when soil sterilization is not available orwhen certain diseases, e.g., fusarium crown and root rot, cannot becontrolled by soil steaming. Wild species closely related to the tomato, oreven tomato cultivars with resistance to a number of diseases, are used asrootstocks. Rootstocks are currently available with resistance to corkyroot rot, fusarium and verticillium wilt, root knot nematode, and fusariumcrown and root rot. Figure 12 shows various grafting methods suitable fortomatoes.

All types of grafting require a sharp knife and a clean working surfaceso that cuts are not contaminated with soil; a razor blade or scalpel are idealtools for grafting. Type A grafting is the fastest but is associated with themost check in the growth of the transplant. Type B grafting is also fast andresults in a stable grafting union, but some check in the growth of the

transplants can be found. Type C grafting is the slowest but is usuallyassociated with the greatest success in grafting.Because the germination of rootstock seed is slow and nonuniform,

sow rootstock seed before the scion cultivar so that by grafting time bothscion and rootstock are of similar size and stem thickness.

If the diseases to be controlled include fusarium wilt or verticilliumwilt, remove the scion root system by cutting through the stem of thecultivar below the graft union. Gradually extend the cut through the stemof the scion over a period of 1 week, to minimize the wilting of the grafted

plants; some misting during this time may also be needed to aid recovery.Although grafting can be very helpful in saving soil sterilization costsand in allowing the cropping of cultivars that are productive but devoid ofadequate disease resistance, it poses its own problems. The graft union isan inherited obstacle in the movement of water and nutrients from theroots to the top of plant and of photoassimilates from the top of the plant tothe root. Grafting is therefore a potential limiting factor in maximizingyield.

Grafting also requires skilled labor, which is either expensive or not

readily available. The difference in vigor between scion and rootstock can

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Fig. 12 Types o f g r a f t ing fo r t om a t oes ; R , roo t s tock ; S , s c ion ( c o n t i n u e d ) . 1

T yp e A. B a r e -r o ot e d p la n t s (b e n c h g r a ft ).

S t e p 1S e le c t a r o ot s t o ck a n d a s c io n p l a n t o f s im i la r s iz e. M a k e a n u p w a r d c u t i n t h es t em o f o n e a n d a d o w n a r d c u t i n t h e s t e m o f t h e o t h e r .

Istep 2J o in t h e t w o st e m s , w h i ch a r e t h e n h e ld t o g e t h e r by t h e f la p s o f t i s s u e .s t e p 3B in d b o t h p l a n t s t og et h e r w i t h a d h e s iv e t a p e a n d p la n t t h e m in a p o t w i t h t h egraf t un ion wel l above so i l l eve l .

S t e p 4R e m o v e t h e t o p o f t h e r o ot s t o ck a n d t h e a d h e s i ve t a p e w h e n t h e g r a ft u n i on h a sh e a l e d .

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F ig. 12 Types of g raf t ing for tomatoes ; R, roo ts tock; S, sc ion (cont inued) .

Type B . Roo t s tock and sc ion -p l an t s g rown in same po t ; immed ia t e de topp ingo f t h e r o o t s t o c k .

step 1M a k e a n u p wa r d c u t i n t h e s c i o n a n d r e m o v e t h e r o o t s t o c k t o p w i t h a d i a g o n a lc u t .

S t e p 2P l a c e t h e t o p o f t h e r o o t s t o ck s t e m i n t o t h e c u t o f t h e s c i on s t e m .

S t ep 3R e m o v e ob s t r u c t in g l e a ve s a n d b i n d t h e t wo p l a n t s t o g e t h e r w i t h a d h e s iv e t a p e .

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F ig. 12 Types o f g ra ft ing fo r t om a toes ; R , r oots tock ; S , scion ( c o n c l u d e d ) .

T y p e C . R o o t s t o c k a n d s c i o n p l a n t s g r o w n t o g e t h e r i n s a m e p o t ; d e l a y e dd e t o p p i n g o f t h e r o o t s t o c k .

s t e p 1P l a n t s c io n a n d r o o t st o ck 1 0 m m a p a r t i n t h e s a m e p o t a n d g r o w t h e m u n t i l t h e ya r e ready for g r a f t i n g . M a k e a n u p w a r d c u t i n t h e s c i o n a n d a d o w n w a r d c u t i n t h e

r o o t s t o c k .

step 2J o i n t h e t w o s t e m s , w h i ch a r e t h e n h e l d t o ge t h e r b y t h e fl a p s o f t i s su e .

S t e p 3B i n d b o t h p l a n t s t o g e t h e r w i t h a d h e s i v e t a p e .

S t e p 4R e m o v e t h e t o p o f t h e r o o t s t o c k a n d t h e a d h e s i v e t a p e wh e n t h e g r a f t u n i o n h a sh e a l e d .

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P o l l i na t i on a nd c lu s t e r p run ing

Once a flower bud has been initiated, four additional processes must becompleted before a healthy tomato fruit is set: the anthers must produce

viable pollen; the anthers must release pollen to the stigma; the pollengrams must germinate on the stigma; and the pollen tubes must grow downthe stigma, resulting in fertilization of the ovules in the ovary. Adversetemperature, light, and nutritional conditions can cause these processes tofail, resulting in poor fruit set and poor fruit quality Day air temperatureundoubtedly plays an important role in fruit set, and once flowering starts,it should not fall below 18C. Other potential causes of poor fruit setinclude excessive growth, poor light, incorrect nutrition, and any kind ofcrop stress. During late fall, winter, and early spring, flowers of most

cultivars grow with a slightly different shape, making natural pollinationdifficult. This change in shape appears to be the result of low night-airtemperature and is occasionally aggravated by high nitrogen availabilityTo assist flower pollination, vibrate all flower clusters with open flowers atleast every other day Use electric vibrators, known as electric bees, tovibrate flower clusters, preferably between 11 a.m. and 3 p.m., whenflowers are moderately dry and pollen is shedding. As alternatives to thelabor-intensive electric bee, the tapping of the strings supporting theplants and the use of coarse water sprays have been tried, but the results

were not satisfactory Hormone sprays were also used when pollinationfailed, but the quality of the resulting fruit was not acceptable for NorthAmerican markets. Lately, bumblebees have been used for tomato flowerpollination, with reasonable success. The bees are already commerciallyavailable, and growers experience with them in the past has been good.Problems of fruit quality related to inadequate pollination are invariablythe result of poor and uneven seed set within the fruit, which is known tocause hollow, misshapen fruit.

Overbearing can sometimes become a problem. To prevent exhaustionof the plants and to improve fruit size, control the number of the flowersper cluster through the recently developed technique of cluster pruning.This is a powerful technique and therefore must be applied with greatcaution. Prune the first two clusters to three marketable fruits and laterclusters to four fruits. However, the optimum number of fruits per clustervaries with the cultivar and even more with the growing conditions.Although, a limited number of fruits per cluster invariably results inpremium-priced large fruit, there is always a risk that a grower,underestimating the potential of the crop or failing to forecast goodweather, might decide to remove too many fruits and thus unnecessarilylimit production. Cluster pruning is undoubtedly most useful in the handsof an experienced grower who can use it to maximize financial return.Obviously, fruit to be pruned must be removed as soon as it can be handled,before it is too large.

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Harvesting and storage

After all the effort and money invested in production, it is essential thatfruit be handled well at harvesting and transportation to the market.

Most growers pick twice and even three times a week, in hot weather.Pick fruit carefully and place in rigid, padded containers to avoid bruisingand damage. The color of the fruit should be as uniform as possible to speedup grading in the packing house and to enable uniform treatment of all fruitin storage. It is critical that every effort be made to minimize a loss in fruitquality while the produce is in transit.

Maturity of the fruit at harvest time is important. Fruit harvestedbefore it is fully developed is more susceptible to handling injury because ofinadequate development of the protective waxy layer. Tomato fruit is

sometimes harvested with the calyx so as to identify it as a greenhouseproduct. Take care to ensure that the calyx does not puncture the fruit.Overfilling the crate or stacking the produce too high may damage thebottom layer.

Harvest fruit in the early morning, when it is cool and when fruittemperature is not too high. Move produce out of direct sunlight and intocool, shaded, and ventilated areas immediately after harvest so that fruittemperature is not increased.

Use a covered vehicle to transport the produce to the packing shed,

thus protecting the fruit from direct sunlight and exposure to the dryingeffect of air. Do not park a loaded truck in direct sunlight for any length oftime. During transportation, minimize heat gain and place produce in coldstorage (12C) as soon as it arrives at its destination, Stacking the cratestoo high or too tight does not allow the crates in the middle to cool downadequately when the product is stored in a cooler.

Packing and storing produce in the same place as active ethyleneproducers, such as apples, accelerates ripening and results in overripeproduce. When the fruit is removed from cold storage, do not allowwater tocondense on it. Prevent condensation by keeping the environment drythrough ventilation or by raising the storage temperature gradually beforethe fruit is removed. O n c e t h e f r u i t is h a r v e s t e d i t s q u a li t y ca n o n lyb e p r e s e r v e d , n o t i n c r e a s e d .

Ch a p t e r 5. Con ven t ion a l cr o p pin g in soil

Conventional cropping in soil is the simplest cropping system and involvesthe planting and raising of a crop as would be done outdoors. The actualplanting is an important stage in the growth of the crop. First, dig a trenchat least 10 cm deep and 15 cm wide. Then place the plants in soil blocks orpeat pots in the trench and heel in with 0.25 L of starter fertilizer solution(5 g of 10-52-17 per litre of water) per plant; pull only a little soil aroundthem. Spot-water plants as needed for 2 weeks after transplanting. Oncethe plants are established, general watering usually is not needed for 4-6

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weeks, depending on soil type and light intensity On light soils generalirrigation begins sooner than on the heavier soil.

Wh a t typ e o f so i l to look fo rTo achieve maximum production, greenhouse vegetables in general need awell-aerated soil with a high water-holding capacity, rich in nutrients andfree from pathogens. Although greenhouse tomatoes can be grown on awide variety of soils, the most suitable are those classified as loams, sandyloams, and some silty loams, all with a high organic-matter content, ifpossible (see Fig. 8). Other types of soils can be used, but they are moredifficult and expensive to manage. For example, coarse sandy soils have low

water-holding capacity, poor nutrient retention, and poor cone formationwhen drip-irrigated; silty soils have an unstable structure that breaks downwith heavy watering; and clay loams are poorly drained, difficult to leach,and their structure is damaged by cultivation when wet. Propermanagement can render almost any soil suitable for greenhouseproduction. For example, both light and heavy soils can be improved byadding organic matter. If natural drainage is poor, as in most clay, silty clay,and sandy clay loams, a tile or pipe drainage system is necessary. The mainpurpose of the soil is to provide a medium in which there is a proper balance

between air, water, and nutrients. If this balance is ensured, the roots caneasily obtain water and nutrients, resulting in rapid growth.

D r a i n a g e

Install tile drainage in ground beds to ensure that all excess water is carriedaway. For drainage, use perforated or nonperforated clay tiles, 10 cm indiameter, and lay them with a small space between them to allow forexpansion; a few 7.5cm tiles make effective slip joints for lo-cm tiles. Toimprove the effectiveness of drainage, cover the tile lines with glass fibermatting made for this purpose or with 2-cm gravel. Set tiles at a depth thatprevents their being broken by rototilling or other cultural practices. Placetiles 35 cm deep and 45 cm apart, with a slope of 10 cm for every 150 m oflo-cm clay tiles. The same tiles, with perforations on the bottom or thesides, are also used for steam sterilization. Loop adjacent rows of tiletogether at the ends, with elbows and tees for more equalized steamingfrom line to line. Introduce steam into the rows of tile through a header.

This header, with a 50-cm capped riser on each end for steam input, extendsacross the width of the house and is equipped with nipples 2-3 cm indiameter and about 25 cm long; one nipple corresponds to, and is cementedinto, each row of tile. Both the header and the rows of tile should be nolonger than 15 m because beyond that length steam condenses into waterand sterilization is poor.

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Table 6 Leaching requirements after steaming

Electrical conductivity Q_&cm) Water required (L/m21Saturated-paste I:2 Watermethod extract Sandy soils Other soilsup to 1.5 up to 0.5 15 251.5-3.0 0.5-1.0 30 503.0-5.0 1.0-1.5 70 100

Over 5 Over 1.5 100 150

The numbers suggested for litres per square metre of required water also indicateequivalent r at es of ra in in millimetr es.

The rates apply to leaching and are added to the requirement for bringing the soil to fieldcapa city (usu ally 20-50 L/m2).The rates apply to use of overhead sprinklers at intervals over 2-5 days.

It is difficult to leach sa lts from h eavy-textu red soils, especially if no effor t is m ade t oimprove their structure.

If the condu ctivity before leaching is higher th an th e recomm ended ra nge, it m ust bechecked again after leaching and before planting.

Flooding reduces nitrates and conductivity markedly, and may reduce potassium

reserves slightly, but it produces little change in other nutrient levels.

Flooding and leaching

To achieve the best results with steam sterilization, the soil is firstcultivated and its water content is brought to field capacity. The amount ofwater required varies with the original moisture content of the soil and thesoil type, but it is generally between 20 and 50 L/m2.

Steam sterilization, particularly oversteaming, often releases toxicamounts of ammonium and manganese. Other elements, such aspotassium, iron, and zinc, may also be increased. Water leaching is usuallynecessary to remove an excess of these substances, as well as an excess ofother soluble salts, and to cool the soil following steam sterilization. Whensoil analysis shows an undesirable excess of soluble salts in the rootingmedium, leach the soil with much greater quantities of water. The amountsgiven in Table 6 can be used as a guide.

Organic matter

A high level of organic matter helps to maintain a stable soil structure andimproves the water-holding capacity of the soil. In the past, growers used tosteam sterilize greenhouse soils and then add well-rotted manure aftersterilization. This procedure reduced the release of ammonia and othertoxic substances, and it also helped to reinoculate the soil with beneficialorganisms. However, the danger of introducing disease organisms andweed seeds always remained. An additional complication in the use of

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manure or muck soil as a source of organic matter is the inherent potentialfor contaminating the greenhouse soil with herbicide residues. Therecommended amounts of manure varied from 45 to 225 t/ha, depending onthe kind of manure and the soil conditions. For example, spent mushroom

compost has a high nutrient content and can cause soil conductivityproblems, whereas uncomposed straw may induce nitrogen deficiency.

In recent years the addition of organic matter has increasingly beenviewed as a means of improving the soil condition (structure) and not somuch as a means of increasing the nutrient content of the soil. In fact, thenutrient content of most manures and other nonstandardized sources oforganic matter is considered a liability rather than an asset because of itsextreme variability and the unpredictable effects the various nutrients canhave on the crop to follow. At present, coarse peat is the most satisfactory

material as a source of organic matter. This type of peat is acid, with a pH ofabout 4, and therefore has the added benefit of reducing the pH ofcalcareous soils; where the soil is noncalcareous, add ground limestone toloose peat at an approximate rate of 5 kg/m3 to neutralize the peats acidityWhen used to improve the soil conditions, e.g., on new sites, apply peatgenerously at rates of up to 500 m3/ha. When the soil reaches the desiredcondition, reduce the rate; the need for an annual dressing remains becausesoil organic matter decomposes under glass rapidly. Apply loose peat to soilat a yearly rate of 100 m3/ha.

Broadcast peat and lime before the main cultivation and incorporatethem into the top 30 cm of the soil.

C on t r o l o f p HGreenhouse vegetables in general grow quite well in a wide range of soil pH(5.5-7.51, but a pH of 6.0-6.5 for mineral soils and a pH of 5.0-5.5 fororganic soils are generally accepted as optimum. When the pH is too low,add ground calcitic limestone, or equal amounts of dolomitic limestone

when the magnesium level in the soil is low, to raise it to a desirable level.The rates given in Table 7 should be used only as a guide; the actual limerequirement is best assessed by an appropriate laboratory test. When thepH is too high, as is usually the case in most greenhouse mineral soils, takesteps to reduce the pH to within the optimum pH range (6.0-6.5 for mineralsoils).

A simple, though temporary, solution to a high pH problem is to addpeat, without neutralizing its acidity with limestone. Peat also helps tomaintain a good soil structure, but it must be added yearly to make up for

loss through decomposition. If additional calcium is needed, supply iteither as calcium sulfate (gypsum), which has no affect on soil pH, or insoluble form, with each irrigation. Adding elemental sulfur, i.e., flowers ofsulfur, provides a more long-term solution to a high pH soil. No definiterecommendations can be made regarding the amount of sulfur that shouldbe applied, because it depends on the buffering (cation exchange) capacityand original pH of the soil, both of which are variable from one soil to thenext. In general, apply flowers of sulfur at a rate of 50-500 kg/ha.Theoretically, 320 kg of elemental sulfur could neutralize 1000 kg of

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Table 7 Lime requirements (in tonnes per hectare1 for soil pH correctionto 6.5

Soil pHSandy Loam,

loam silty loam

Clay loam,

organic

6.0 3.0 4.5 6.0

5.5 6.0 9.0 12.0

5.0 9.0 12.0 18.0

4.5 12.0 15.0 24.0

4.0 15.0 18.0 30.0

N o t e : The rates of lime suggested are for the top 15 cm of soil. If acidity has to be correctedto a greater soil depth, the rates should be increased accordingly.

limestone, but this equation assumes that all sulfur is converted to sulfuricacid instantly. However, the conversion of sulfur to sulfuric acid isperformed by soil microorganisms (ZhiobaciZZusl over time and is morerapid in moist, warm, well-aerated soils. Broadcast and thoroughly mixordinary ground sulfur with the top 15-30 cm of soil several weeks beforeplanting the crop because the initial velocity of the reaction may be slow incold soils.

Iron sulfate can also be applied to soils for acidification. When this saltis hydrolyzed it releases sulfuric acid, which drastically lowers the pH andliberates some of the iron already present in the soil. At the same time,soluble, i.e., available, iron is being added. However, on a weight basis, iron(ferrous) sulfate is four to five times less effective than sulfur and is usuallymore expensive. Sulfuric acid can be added directly to the soil, but it isunpleasant and dangerous to work with and requires the use of specialacid-resistant equipment. In some areas it can be applied by customsuppliers who have the equipment necessary for handling it. Sulfuric acidhas the advantage of reacting quickly with the soil.

Under most conditions it may be advisable to acidify only a zone nearthe plant roots, in which case much smaller amounts of chemicals arerequired. This method is particularly applicable when drip irrigation isused, which results in the root systems occupying a restricted, well-definedarea of soil. Injecting phosphoric or nitric acid, appropriately diluted forconvenience and safety, offers an attractive alternative for lowering the pHof the soil near the plants; furthermore, these acids prevent saltprecipitation and clogging of the irrigation lines and add useful nutrients tothe plants. To determine the rate of acid to be injected, add a knownamount of acid to a known volume of water until the desirable pH isobtained. Alternatively, start injecting small amounts of acid into theirrigation line while checking the pH with an in-line pH meter; graduallyincrease the amount of acid injected until the desired water pH is obtained.When other conditions allow, try to select the regularly applied fertilizers

on the basis of their ability to lower or increase the soil pH according to44


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Watering

Irrigation is usually the flood type, although some automated equipmentmight be used. The objective of watering is to maintain a fully adequate

supply ofwater to the plant roots without wetting the soil to the extent thatair cannot get to the roots. Waiting until the plants start to wilt is notrecommended. A good practice is to reach down into the soil and judge howmuch water is left before starting the next irrigation.

Regular watering on the same day of the week is unwise. The waterrequirement of the plants changes daily and seasonally. Water young plantsplanted in the greenhouse in January or February only once every 10 daysor 2 weeks, and then only enough to soak 15-20 cm of the soil. Similarplants growing in June may need five to ten times as much water.

Each producer of greenhouse tomatoes should know how much waterto add to the soil at each application. With this information and byexamining the soil before watering and several hours thereafter, theeffectiveness of the water application can be determined.

Scheduling the application of fertilizer

In addition to preplant fertilizer application, fertilizers must also be added

regularly thoughout the production season. When applied to a growingcrop, fertilizers are in dry form, as with base fertilizers, and are broadcaston most or all the cropped greenhouse soil. Recommended rates are listedin Table 9.

Mulching

The soil should be mulched when tomato plants are about 0.5 m high. Straw

is the most common mulch material, but ground corn cobs are alsoacceptable. The mulch reduces evaporation and soil compaction. Also,when mulch is present, little soil is splashed onto plants during watering,thus avoiding dust in the greenhouse. Furthermore, mulch releases aconsiderable amount of carbon dioxide as it breaks down, which helps plantgrowth. Mulch also turns into useful organic matter after it is incorporatedinto the soil at the end of the cropping season. However, mulching withorganic by-products gives rise to the well-known problems associated withthe addition ofany organic matter to intensely cultivated soils, as discussedearlier. In recent years, mulching has not been practiced widely; instead, awhite polyethylene film is used to cover the ground whenever the irrigationmethod permits it. This mulchingalternative has several advantages and isbest practiced in conjuction with drip irrigation.

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Table 9 Recommended fertilizer application rates (kg/ha)Stock solution 1 St ock solut ion 2

W e e k from 10-52-10 Magnesium P ot assium Calcium Am on iu m

planting s t a r t e r 20-5-30 sulfate n it r a t e n it r a t e n it r a t e

1 1 0 0

2

3 Z84 1 0 0

5 100 1 0 0 50 50

6 10 0 50

7 10 0 1 0 0 50 1 0 0

8 1 0 0 509 1 0 0 1 0 0 100 10 0

10 1 0 0 100

11 10 0 1 0 0 10 0

1 2 10 0 1 0 0 1 0 0

1 3 100 1 0 0 10 0

14 1 00 100

15 10 0 1 0 0 1 0 0 1 0 0 0.5

1 6 100 1 0 0

1 7 1 00 1 0 0 100 0.5

18 1 0 0 1 0 0 1 0 0

19 1 0 0 1 0 0 100 0.520 1 00 100

21 1 00 100 1 0 0 1 0 0 0.5

2 2 1 0 0 100

2 3 100 100 10 0 0.5

24 1 00 1 0 0

2 5 1 50

26 15 0

Choose soluble fertilizer formulations that are as free as possible of chlorides, sulfates,and carbonates.

For a spring crop do not vary the schedule.For a low-fertility soil or early setting cultivars (e.g., Vendor) omit, weeks 3 and 4 andproceed immediately to week 5 after week 2.

For a fall crop omit weeks 2, 3, and 4 and proceed immediately to week 5 after week 1.

Caution : If fertilizers are first mixed in thick stock solutions before they are applied tothe crop, they should be grouped as indicated. Do not mix in the same concentratedsolution a fertilizer containing calcium and one containing sulfate or phosphate, as sucha m ixtu re results in a th ick suspension t hat can plug wat ering equipment.

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Ch a p t er 6. Cr op p in g in soil w it h d r ipi r r iga t ion

The drip irrigation cropping system is similar to but better than theconventional soil cropping system because it can be used to control cropgrowth through a regulated supply of water and nutrients. In addition, thesystem allows reduced relative humidity in the greenhouse because not allthe soil is irrigated and because it is compatible with the use of whitepolyethylene film as a light-reflecting mulch. Resources, including energy,are thus used more efficiently with this system.

Irrigate the crop up to four times a day, and use the irrigation system to

apply fertilizer to the crop. Fertigation is the application of fertilizerthrough the irrigation system and is a popular method of fertilizinggreenhouse vegetables. Fertilizers are either dissolved in a large holdingtank and the solution is pumped to the crop or they are mixed inconcentrated stock solutions, which are then incorporated, with fertilizerinjectors, into the irrigation water

Several makes and models of fertilizer injectors are available atvarying costs and offer varying degrees of fertigation control. Asophisticated fertilizer injection system capable of meeting the nutrient

Documents

Growing Greenhouse Tomatoes in Soil and in Soilless Media