Septembre 2007 .

CONTENTS

Introduction

The Hydroponic Nutrient Solution

Nutrient Solution Management

(i) Electrical Conductivity (E.C.)

• How to measure E.C. of the nutrient solution

• Recommended values of E.C.

• Tips for accurate E.C. measuring using a portableE. C. meter

(ii) pH

• How to measure pH of the nutrient solution

• Recommended values of pH

• Tips for accurate pH measuring

How to get the desired E.C and pH values.

Adjusting for pH values of hydroponic nutrient solution.

Introduction

Hydroponics is the science of growing plants in medium other thansoil. The plants grown in hydroponics are fed with a nutrient solutionwhich consists of water into which are dissolved all the essentialelements needed for their growth and development.

The Hydroponic Nutrient Solution

Plants require 16 essential nutrient elements in proper proportions fortheir optimum growth and development. These essential elements aredivided into macro elements (required in relatively larger quantities)and micro elements (required in smaller quantities).The macro elements are carbon, hydrogen, oxygen, nitrogen,phosphorus, potassium, calcium, magnesium and sulphur and themicro elements consist of iron, chlorine, boron, manganese, copper,zinc and molybdenum. In hydroponics, all nutrients are supplied to theplants in the nutrient solution.

Nutrient Solution Management

Proper management of the nutrient solution is the key to success inhydroponic gardening. The grower can adjust the concentration of thenutrient solution to suit the plant growth stage and at the same time,provide the essential nutrient elements in balanced amounts. Thenutrient solution is prepared by dissolving exact amounts of inorganicfertilizers given in the' recommended formulation. This will ensurethat the plants are getting the right balance of essential elements.

While optimum nutrition is easy to achieve in hydroponics, incorrectmanagement of the nutrient solution may hamper plant growth andlead to poor yield. To ensure that the nutrient solution is providing the

right balance of fertilizer, its E.C. (Electrical Conductivity) and pH(acidity) should be measured and monitored.

(i) Electrical Conductivity (E.C.)

When inorganic fertilizers aredissolved in water, theydissociate into ions whichconduct electricity. This abilityof the solution to conductelectricity gives its ElectricalConductivity (E.C.) whichindicates the concentration offertilizers III the nutrientsolution. Portable pHIEC meter

Although a measure of electrical conductivity does not give anyindication of which specificnutrient ions are pre ent or anyinformation about undissolvednutrients, it gives a usefulmeasure of the total concentrationof nutrient elements.

E.C. is most commonly expressedin microSiemens per centimetre (S/cm) or milliSiemens percentimetre (mS/cm).

How to measure E.C. of thenutrient solution

• From one dripper, collect aPortable EC meter

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small amount ( 20-30cc) of hydroponic nutrient solution in a smallclean container

• Remove the protective cap of the E.C. Meter and switch on thelatter.

• Immerse the tip of the E.C. meter in the nutrient solution collected,taking care to completely immerse the electrodes in the solution.

• Allow to stabilize for a few seconds.• Read the displayed E.C. value.• Remove the E.C. meter from the nutrient solution.• Switch off the E.C. meter.• Rinse the tip of the E.C. meter with water.• Replace the protective cap.

Recommended values

Recommended values of E.C. for hydroponic nutrient solution for thedifferent crops at different crop stages are as follows:

At One week Flowering / End of crop Adjustment for season

transplanting after Fruiting cycle (Winter)transplantingto first flower

Flowering / End ofFruiting crop

cycle

Tomato 1.2 1.2-1.5 1.8-2.0 2.0 2.0-2.2 2.2

Cucumber 1.2 1.2-1.5 1.8 1.8 2.0 2.0

Melon* 1.2 1.2-1.5 1.8 2.0-2.8 2.0 2.2-2.8

Sweet 1.2 1.2-1.5 1.2-2.2 2.2-2.4 2.0-2.4 2.4-2.8Pepper

Lettuce 1.2 l.2 1.2 1.2 1.2 1.2

* For melon it is important to adjust the E.C. to a higher level at theend of the crop cycle to increase the brix content of the fruit so that thefruit is sweeter.

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+

Note:

Adjustment in winter is made with respect to evapotranspiration inplants.

Bench type and portable E.C. meter are available commercially formeasuring the E.C. of the nutrient solution.

Tips for accurate E.C. measuring using a portable E. C. meter

• Calibrate the E.C. meter regularly using standard solutionsavailable commercially.

• Check the battery status; low batteries in portable E.C. meters oftencauses error.

• Do not immerse the E.C. meter above the immersion level.

• Always take measurements at the same time each day; this willallow easier interpretation of the result.

• When not in use, switch off the meter and replace the protective capas per recommendation of the supplier

• Store the E. C. meter in a cool and dry place.

(ii) pH

The pH is a measure of the concentration of hydrogen ions (H+) in asolution. pH ranges from 1 to 14 and a pH of 7 is neutral, below 7 isacid and above 7 is alkaline. Pure water has a pH of 7, i.e it is neutral.pH is an important measure of nutrient solution and media as itstrongly affects absorption of certain nutrients or elements(particularly the micronutrients) by the plant. Most plants grow at theirbest in a nutrient solution having a pH between 5.5 and 6.5.

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When pH rises above 6.5 some ofthe micro-nutrients (includingiron, manganese, copper, zinc andboron) begin to precipitate out ofsolution and are no longeravailable to the plants. At low pH,

•.. excessive uptake of certainelements can be stimulated andthe solubility of elements likecalcium and manganese dropssharply.Therefore, careful control of thepH is important in order to keepall the essential elements insolution and to prevent toxicitydue to excessive uptake. Portable pH meter

The pH of a nutrient solution is measured using a pH meter.

How to measure pH of the nutrient solution

• Collect a small amount of the hydroponic nutrient solution in asmall container, made of plastic or glass, from the drippers.

• Remove the protective cap.• Switch on the pH meter.• Immerse the tip of the pH meter in the nutrient solution collected,taking care to completely immerse the electrodes in the solution.

• Allow to stabilize for a few seconds.• Read the displayed pH value.• Remove the pH meter from the nutrient solution.• Switch off the pH meter.• Rinse the tip of the pH meter with water.• Replace the protective cap.

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Recommended values

Recommended values of pH for hydroponic nutrient solution for thedifferent crops are as follows:

Tomato 5.5-6.5

Sweet Pepper5.8-6.0Cucumber5.5-6.5

Lettuce 6.0-6.5

Tips for accurate pH measuring

• Calibrate the pH meter regularly using standard solutions.• Check the battery status; low batteries in portable pH meters areoften a cause of error.

• Crystals may appear around the cap. This condition is normal.The crystals will dissolve when rinsed with water.

• After use, rinse the electrode with water to minimize contamination.• Always ensure the pH probe is immersed in a few drops of storagesolution or pH 7 solution in the protective cap.

• Always replace the protective cap after use.• Store the meter in a cool dry place.

How to get the desired E.C and pH values.

Concentrated hydroponic nutrient solution (or stock solution) can beobtained as follows:

1. Already prepared mixtures of nutrient solution A and B separatelyobtained from Chemco Ltd.

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2. Individual fertilizer salts which are mixed in different proportionsto prepare the nutrient solution A and B using the CIRADformulation.

Once the concentrated hydroponic nutrient solutions A and B havebeen prepared, these have to be diluted before being fed to the plants.This is achieved by adjusting the pump injector to the recommendedlevel which is 0.6% for the CIRAD formulation and 1.0% for theChemco solution.

At these settings of the injector pump, the nutrient solution at thedripper will have an E.C. of around 1.8- 2.0 mS/cm and a pH around5.8- 6.2. If a lower E.C. value is required, the injector pump iscalibrated at a lower value while a higher E.C. value is obtained withthe injector pump set at higher values.

As for the pH, if the nutrient solution is too acidic it will give a lowpH and then it is recommended to adjust the pump injector of theconcentrated solution B (which is more acidic) to a lower percentage.

Plate 4:Injection pumps

Plate 5:Adjusting injection pump at 0.6%

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Adjusting for pH values of hydroponic nutrient solution.

Please note that:

(i) The pH of the hydroponic nutrient solution can be adjustedusing either an acid (phosphoric acid) or an alkali (sodiumhydroxide) only if the pH of the water being used to preparethe nutrient solution is found to be alkaline or acidic respectively.

(ii) The pH of the diluted nutrient solution may also not fall in therecommended range due to irregular functioning of thefertilizer injector pumps or they have not been properlycalibrated. It is recommended to ensure that the fertilizerinjector pumps are in good working conditions.

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LIST OF SUPPLIERS

1. Ducray Lenoir Ltd.19 Poivre StreetPort LouisPhone No. 212 2890, 208 2098

211 1397(Mr. Bernard Lirn)

2. Biswal Trading Co. Ltd.Monte SPetite RivierePhone No. 233 5166,233 1355

233 1072(Mf. Walia Ajit, Mf. Nasser)

3. Hanna Insturment (Mauritius) Ltd.C/o. Danieleti Mauritius Ltd.MIDA Industrial BuildingPhase 2Beau VallonPhone No. 631 2700Fax No. 631 9327

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