Plant Nutrition, Water and Fertilizer Management

8/20/2019 Plant Nutrition, Water and Fertilizer Management

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Prepared for sharing with participants at the Waterand Fertilizer Workshop, SGGA Conference

Nov.8, 2013This publications has its roots in Alberta

Contact Information: Dr. Mohyuddin MirzaPhone: 780-463-0652, email: [email protected], www.agga.ca

PLANT NUTRITION AND FERTILIZERMANAGEMENT IN GREENHOUSE GROWN

CROPS


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CONTENTS

Fundamental Aspects of Plant Nutrition

Introduction 1Absorption of Nutrients 1

Essential Macro-Elements 3

Trace or Micro-Elements 5

Water Status and Quality for Crop Production

Introduction 7

Water Status 8

Water Potential 8

Water Quality 10

Water Treatments 13

Fertilizer Management

Introduction 14

What are the Essential Elements for Plant Growth? 14

What do these Numbers on Fertilizer Bags Mean? 15

What are Parts Per Million? 15

Any Formulas to Calculate PPM? 16

Solubilities of Fertilizers 18

Different Sources of Fertilizers 19Preparing a Fertilizer Program 20

Making Stock Solutions from Trace Elements 27

Principles of Mixing Fertilizers 27

pH, Your Water and Fertilizer? 27

What is Electrical Conductivity. . . 29

Sample Fertilizer Programs………30

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FUNDAMENTAL ASPECTS OF PLANT NUTRITION

INTRODUCTION

Plants require certain nutrients to grow properly. Sixteen elements are considered to be

essential for their growth and development. They are: carbon, hydrogen, oxygen,nitrogen, phosphorus, potassium, calcium, magnesium, sulfur, iron, manganese,copper, zinc, boron, molybdenum and chlorine.

Plants are non selective in absorbing nutrient elements from the growing medium. Thismeans that the presence of a particular element in a plant tissue does not indicate thatthe element is essential for growth. For example silicon, chromium and cobalt havebeen found in many plant species but it is not known if they are essential for growth.

Out of the 16 essential elements, carbon, hydrogen, oxygen, nitrogen, phosphorus,potassium, calcium, magnesium and sulfur are required in relatively large amounts and

that is why these elements are referred to as macro or major elements. The remainingseven elements in the above list are micro-nutrients. They are required in smallamounts to carry out different essential functions in the plant. Role of aluminum (Al),gallium (GA) and Silicon (Si) in the growth of some plant species is also known.

ABSORPTION OF NUTRIENTS

Plants use carbon, hydrogen and oxygen from the air and water in general from thegrowing medium to make simple foods by the process of photosynthesis. Thesesubstances are needed to make amino acids, proteins and protoplasm. Other elementsare taken up by plants through the roots. Moderate amounts are also absorbed through

the leaves and stem tissues. Quite often trace element deficiencies can be correctedthrough foliar feeding.

Absorption through roots is the major route of nutrient uptake. If the root system isdamaged by disease, insects or higher levels of soluble salts in the growing medium,the nutrient uptake is reduced.

Roots can absorb organic salts or ions, which are formed as a result of interactionbetween root respiration and soil water. Inorganic salts applied as fertilizers are brokenapart by a chemical process called dissociation.

At any time, both molecules and separate ions of the salt are present. A moleculeconsists of two or more ions. For example, potassium chloride (KCl) supplied as afertilizer is dissociated in the soil solution into potassium (K+) and chloride (Cl-) ions.Ions with positive (+) charges are called cations. Ions with negative (-) charges arecalled anions . The ions are then absorbed by the roots through a special membrane.This semi permeable membrane surrounds each cell within the root and allows the ionicexchange..


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Cation-Exchange Capacity

The actual process of nutrient uptake by plants is controlled by the cation-exchangecapacity (CEC) of the growing medium. This action is associated with the clay particlesof a mineral soil. Organic materials such as peat moss also have a cation exchange

capacity. The clay particle has a negative (-) surface charge and attracts cations (+charge). Hydrogen ions are released when carbonic acid is formed from thecombination of hydrogen from the soil water and the carbon dioxide resulting from rootrespiration. These hydrogen ions, which have a positive charge, exchange theirpositions in the soil solution for positively charged cations held on the surface of the clayparticles. These cations are then absorbed by the roots.

The cations are calcium, potassium, magnesium, sodium, and ammonium ions. Theroots have to release a hydrogen ion to take up one ion of potassium, magnesium,sodium and ammonium while two hydrogen ions will be required to obtain one calciumbecause of its two positive charges.

Anion-Exchange Capacity

Plants also need anions for good growth. Nitrates (NO3-), chlorides (Cl-) and sulfates

(SO4-) are examples of anions. Negatively charged anions are not attracted by the

negative charge of the clay particles. Thus, they are not held like cations. They remainin solution unless absorbed by the plant or lost through leaching. If leaching is notadequate, anions can build up in the soil solutions and cause an increase in theelectrical conductivity of the root zone medium. The practical implications are thatnitrates are easy to leach with over watering and thus deficiency in plants can occurrather quickly.

pH Effect on Nutrient Absorption

Uptake of nutrients is strongly affected by the pH of the growing medium. Ourexperience is that the pH of the growing mix should be between 5.5 and 6.5. Below thatvalue the uptake of manganese, iron and boron increases considerable and can causetip burning and toxicity problems. Enough dolomite lime should be added to raise thepH to around 5.5. Dolomite lime can be replaced with potassium bicarbonate becausecalcium is supplied through calcium nitrate and magnesium through magnesium sulfate.

Many growers have reported difficulties with pH adjustments while plant seedlings arebeing grown. It takes a long time to change pH from a lower to a higher value or viceversa. Since the pH scale is based on logarithms, a growing medium with a pH of 6 is10 times more acidic than a medium with a pH of 7. Similarly, a growing medium with apH of 5 is 10 times more acidic than one with a pH of 6.

By the law of logarithms, a growing medium with a pH of 5 is 100 (10 x 10) times moreacidic than a medium of with a pH of 7. This factor of 100 is the reason it is moredifficult to raise the pH from pH 5 to 7 than it is to raise from pH 6 to pH 7. This means


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that if 10 pounds of lime are required to raise the pH from 5 to 6, then 100 pounds arerequired to raise the pH from 5 to 7. In actual situations, other factors influence theratios to change the values.

ESSENTIAL MACRO-ELEMENTS

Nitrogen (N)

Nitrogen is very important to plant growth and is usually found in the largest amounts inthe leaves. On a dry weight basis, two to six percent of a healthy leaf is nitrogen.

Plants cannot absorb the elemental form of nitrogen (N). Primary absorption occurs asnitrate (NO3

-) while ammonium (NH4+) and amino (NH2

+) can also be absorbed. In soilbased media there are a group of bacteria present which can convert ammoniumnitrogen to nitrate nitrogen. These bacteria are not present in soilless media used bygrowers. Consequently ammonium nitrogen can quickly become toxic to roots. When

bacteria convert ammonium nitrogen to nitrate nitrogen, there is an intermediary stepinvolved. That is the formation of nitrites, which are normally very short lived radical butfairly toxic to roots. This can happen under low temperature and water loggedconditions. If you detect nitrite in your medium, you know there is water logging.

Nitrate nitrogen, while inside the roots, is converted to ammonium and to amino formsand used to make proteins and other chemicals needed by the plants. That is whyfertilizers containing nitrate nitrogen like calcium nitrate and potassium nitrate willproduce slow and steady growth. Ammonium and urea based fertilizers can producesoft and lush growth in plants.

Ammonium nitrogen can be used if plant growth is slow but it should be used when thegrowing medium temperature is above 16oC and the light is good. Use of ammoniumfertilizers should be avoided until the end of March. Where pH is alkaline, use ofammonium fertilizer is an advantage because it can help to bring down the pH. Urea isa good source of nitrogen for foliar feeding. Wherever plants are slow and need agrowth boost, urea should be applied to the leaves. Nitrogen is mobile within the plant,so it can be transported from lower to upper leaves. That is why deficiency symptomswill first appear on the lower leaves.

Measurement of nitrogen in tissue is a useful tool to manage the growth and bud set inplants, especially tree seedlings. It should be monitored on a weekly basis after week16 of the growth. Bud set in conifer species will be difficult if tissue nitrogen is over twopercent.

Phosphorus (P)

Phosphorus has several important functions. It must be available in sufficient quantitiesearly in the life of the plants to assist in cell division and differentiation. It is alsorequired for root growth and formation of buds. Both the respiratory and photosynthetic


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processes require phosphorus for high energy phosphate bonds. Most of thephosphorus is taken up in the form of the primary orthophosphate ion ( H2PO4

--).Smaller amounts of secondary orthophosphate (HPO4

--) and organic phosphoruscompounds are also absorbed.

Two facts should be remembered about phosphorus:

* If you are using phosphoric acid to neutralize the carbonates and bicarbonates inwater, do not assume that phosphorus from phosphoric acid will be available forplant use. Add an additional 40 to 80 ppm of phosphorus based on the need ofplant growth period.

* A pH of above 6.8 in the growing medium can tie up phosphorus with calcium andit may not be available to the plant. We have seen phosphorus deficiencies inplants because of pH related problems.

Because of the negative charge of orthophosphate, it is not attached to clay particlesand can easily tie up with aluminum in the growing mix. Phosphorus deficiency resultsin stunting of plants and deep green or purple leaf colour with poor root development.Phosphorus uptake is reduced at a growing medium temperature of below 12oC.Phosphorus is slightly mobile within plant tissues. Phosphorus and iron levels in planttissues act in opposition to each other. At a high level of phosphorus, an iron deficiencymay develop. Similarly, a high level of iron may cause a phosphorus deficiency.

Potassium (K)

Potassium is absorbed by plants in its ionic form (K+). It plays an important role in theregulating of the opening and closing of stomata and in water retention. It promotes thegrowth of meristematic tissue, activates some enzymatic reactions, aids in nitrogenmetabolism and the synthesis of proteins, catalyses activities of some mineral elementsand aids in carbohydrate metabolism and translocation. Potassium is found in planttissues as a soluble, inorganic salt, while nitrogen and phosphorus are converted intocomplex compounds. It is absorbed by the plants in large amounts without becomingtoxic.

Potassium is highly mobile within the plant. High potassium as compared to nitrogen isused by growers in Alberta. This is to exert an antagonistic effect on the uptake ofnitrogen so that the growth is slowed down. Nitrogen to potassium ratios can bechanged to obtain faster or slower growth. N:K ratio of 2 to 1 will result in fast,vegetative growth of plants. An equal ratio will maintain good growth while a ratio of 1to 2 will harden the growth. That is why hardening fertilizer regimes contain an N to Kratio of 1 to 2.


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Calcium (Ca)

Calcium is absorbed in the ionic form (Ca++). Most of the calcium inside the plant is inthe form of calcium pectate in the middle lamellae of the cell walls. In tree seedlings it ispart of the lignin and tannin complex as well. The calcium prevents the leaching of

mineral salts from the cells. Much of the stiffness of plants is due to calcium. Calciumis immobile and is not translocated from older to younger leaves. It's uptake from thegrowing medium is dependent on the active water transport. If plants are nottranspiring, then calcium movement will be minimal. Slow or poor development ofterminal and side bud shoots is generally related to a lack of calcium in the tissue. Incucumbers, poor development of side shoots is an indication of calcium deficiency whilein tomatoes; blossom end rot is due to poor calcium translocation. Most growers supplyenough calcium through their feeding program but it is the poor uptake which causesproblems. Make sure that the moisture deficit is in the range of 3 to 7 g/m3.

Magnesium (Mg)

Magnesium is absorbed as Mg++. It is the only mineral element contained in chlorophyll.Magnesium appears to be related to phosphorus metabolism. A number of enzymesystems require magnesium to work properly. Magnesium is mobile within the planttissues. Thus, symptoms of a lack of magnesium show up first on lower leaves. Thesymptoms could appear later, on the entire plant as yellowing of interveinal areas withveins remaining green.

Magnesium deficiencies have been noted in many crops and is likely due to the higherpotassium we use in our fertilizer programs. Foliar feeding of magnesium has givensatisfactory results.

Sulfur (S)

Sulfur is taken up from the soil in the form of sulfate ions (SO4 --). Small amounts ofsulfur may be taken in through the leaves as sulfur dioxide. Sulfur seems to be involvedin the formation of chlorophyll but it is not a component of the chlorophyll molecule.Nitrogen and sulfur deficiencies may look alike. As long as enough sulfur is suppliedfrom magnesium sulfate, its deficiency is unlikely to occur.

TRACE OR MICRO-ELEMENTS

These elements are as important as major elements but they are required in smallamounts. Their deficiency or toxicity can occur readily.

Iron (Fe)

Its deficiency has been noted in plants primarily due to alkaline pH in the growingmedium. It is taken up by the plant in the form of ferrous ions (Fe++) or complex organicsalts. Iron may also be absorbed as ferric ion (Fe+++) form. Plants may contain large


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amounts of ferric ion but still show severe iron deficiency symptoms. Thus, a tissue irontest cannot be used as a diagnostic test for confirming iron deficiency.

Iron acts with certain enzyme systems that carry on respiration. It is also required in theformation of chlorophyll. Unlike magnesium it is not a component in the chlorophyll

molecule. Iron is immobile. Thus, a deficiency of iron appears first in the youngestleaves as a chlorosis. If the deficiency is not corrected, the leaves may turn light yellowand then almost completely white. Iron chelate is commonly used by many growers intheir fertilizer programs.

Manganese (Mn)

Plants absorb manganese in the form of the manganous ion (Mn++). It is used in theactive growing parts of plants and is involved in certain enzyme systems that oxidizeother elements such as iron. An excess of manganese may cause iron deficiency.

Manganese is immobile. Thus, a deficiency appears first in the new growth.Manganese and iron deficiencies may be confused because symptoms are similar.Manganese toxicities are more common in tree seedlings. This is because of atendency to grow them at acidic pH values. The uptake of manganese is several timeshigher at pH values below 5. The damage appears as browning of needle tipsprogressively moving inwards. The entire needle may turn brown. The damage isgenerally irreversible. Toxicity has been seen in tomatoes and cucumbers wheremanganese containing fungicides like Manzate have been used.

Copper (Cu)

Plants absorb copper in the form of the cupric ion (Cu++). It is needed for the properfunction of many enzyme systems. It stabilizes chlorophyll and delays its breakdown.Thus, copper helps to increase the effective life of leaves. It is immobile, an enzymeactivator in respiration, seed formation and root growth. Organic growing media like theone used by growers can tie up copper to a considerable degree. That is why copperdeficiencies are frequently noticed in many plants. We recommend the use of relativelyhigher levels of copper in our feeding programs. A lack of copper in tree seedlings caneasily be confused with boron deficiency because symptoms are similar. Terminalshoots may die back and witches' broom symptoms appear. It is best to monitor tissuecopper levels on a regular basis. Both copper chelate and copper sulfate are suitable forplant use.

Zinc (Zn)

Zinc is an intermediately mobile nutrient. It is required to regulate consumption ofsugars essential for early growth and plant maturity. It plays an important role inphotosynthesis. Zinc deficiency is well known as small or tiny leaves disorder. Rootsabsorb the zinc ion (Zn++). Zinc is also absorbed through leaves so one has to becareful with the use of zinc based fungicides. Its deficiency has not been noticed in


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Alberta grown plants but toxicities are possible due to the high zinc content in somewater supplies. Watch for higher zinc levels when you are collecting water fromgreenhouse frame. Galvanized gutters may contribute significant amounts of zinc.

Molybdenum (Mo)

This element is required in the smallest amount of all trace elements. It appears thatmolybdenum is used in the nitrogen cycle in the formation of nitrogen compounds andthe breakdown of nitrates. The leaves lose their good green colour and become moredark blue in colour. When molybdenum is lacking in the plant, nitrates are not absorbedfrom the growing medium even if it is present in large amounts.

Chlorine (Cl)

Chlorine deficiency is not well documented in plants. Its importance has beenrecognized in plants such as tomatoes. Enough chlorides are present in our water

supplies. Too much chloride in the growing mix causes more problems than a lack ofchloride. Needle tip burning is the major symptom of chloride excess in spruce andother conifers.

Other Elements

Sodium, aluminum and silicon are found in the tissues of many plants. Sodium levelsover one percent of the dry matter should be a cause of concern. Aluminum is found inroot tissue and ties up phosphorus in large amounts. Silicon increases the cationexchange capacity of the growing medium and is used by many growers whenmanganese toxicity is suspected.

High fluoride levels, over 1 ppm, has caused problems with tip burning in spruceneedles.


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WATER STATUS AND QUALITY FOR CROP PRODUCTION

INTRODUCTION

Water is essential for plant growth. It influences plant growth in four major ways:

1. Water is the major constituent of a plant, comprising 80 to 90 percent of the freshweight.

2. Water is the "solvent" providing nutrient transport within the plant.

3. Water is a biochemical reactant in many plant processes, the most important beingphotosynthesis and respiration.

4. Water is essential for maintaining turgidity in plant cells, promoting cell elongationand plant growth.

Water is used as a coolant by the plant through the transpiration processes.

THE WATER STATUS

Although a detailed biochemical understanding of water status inside the plant is notessential, it will help to be familiar with the concepts of water content and waterpotential. Water content is what is present inside the plant at a given time. Basicallyplant water content will be determined by how much has been absorbed through roots,how much is being lost through transpiration and how much is being stored by the plantitself.

Plant water content is in a constant change during the day, when transpirational lossesthrough leaves usually exceeds the rate of water absorption through the roots. This lagbetween water uptake and water loss creates a condition of internal water stress withinthe plant. This stress is normal during daylight hours within normal limits. If the stressis allowed to reach extreme levels for extended periods, the plant growth rate declinesand eventually the plant dies.

Good growers understand this water stress concept and manage plants accordingly.The use of environmental control computers has helped growers understand themoisture deficit relationship to plant growth.

Moisture deficit is a calculation, based on temperature and air relative humidity thatgives a numerical value that is related to the amount of water loss from a crop. Toohigh or too low a level of deficit can affect the growth of the plant.

The moisture deficit is measured in many units but the most commonly used isgrams/m3 of air. Under high humidity conditions the moisture deficit is low and there is


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no need by the plant to produce more roots. Consequently there is less rootdevelopment.

Under high deficit situations the transpiration rate is high and if roots cannot meet thedemand of water then stomata start closing which slows down the photosynthesis. It is

suggested to use a deficit range of between 3 and 7 grams/m

3.

WATER POTENTIAL

Water potential of a plant is a measure of energy status of water that is usuallyexpressed in pressure units and is composed of the following:

WP = OP + PP + MP + GP

OP = Osmotic Potential - the component produced by dissolved solutes.

PP = Pressure Potential - the component produced by the inward pressure of cellwalls in plants or due to water weight or air pressure in soil.

MP = Matric potential - the component produced by the adhesive attraction of watermolecules to surfaces or adhesion and cohesion in small capillaries.

GP = Gravity Potential - the component produced by the force of gravity.Plant Water Potential (PWP) - the energy status of water within the plant. MP is smallin well watered plants. GP is negligible in small plugs and seedlings. PWP = OP + PP.

Growing Medium Water Potential (GMWP) - the energy status of water within the

growing medium. PP and GP are negligible in small containers. GMWP = MP + OP.

Plant Moisture Stress (PMS) - a way of describing plant water status.

Plant Water Potential is dynamic and changes with time as soil moisture andatmospheric demand change. On a typical sunny day in a well-irrigated growingmedium, a plant begins to transpire as soon as the sun comes up, assuming that therelative humidity is not very high. Once transpiration begins, PWP decreases until thestomata close at which point the PWP levels off. Towards sunset, the PWP begins toincrease as atmospheric demand declines and the plant replenishes its moisturecontent from the water in the growing medium.

Under high evaporative demand and a moderately dry growing medium the PWP is lowto start with because the plant is unable to completely recharge its moisture supplyovernight. PWP declines further at noon and continues in the afternoon. If this patterncontinues, over time, young seedlings can show moisture stress resulting in growthdamage.


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Growing Medium Water Potential

The potential of water in the growing medium solution is called the growing mediumwater potential (GMWP) and is composed of two parts: OP, which reflects the influenceof dissolved salts, and MP, which measures the attraction of water molecules for the

surfaces and small pores in the growing medium. The OP of the growing mediumsolution increases as the soil water content decreases due to evaporation ortranspiration. This is due to a loss of moisture and a consequent increase in salt levels.

The MP reflects the energy with which the water in the growing medium is held bymatric forces and is related to the size of pores in the growing medium. The porevolume of a growing medium is a function of particle size and arrangement and iscomposed of air and water, which change in inverse proportion to one another.

After thorough irrigation, excess water is drained out of the container by gravitationalforces, leaving the growing medium essentially saturated. This is referred to as

"container capacity". When the growing medium is watered to its container capacity theMP is very high. This means that there is little water stress and water is readilyavailable to the seedling.

As the growing medium loses water through evaporation and seedling transpiration thelarge pores drain first and are filled with air. The pores never drain completely. A thinfilm of water sticks around the growing medium particles. The thinner the water film, thelower the MP and the higher the moisture stress. This means less water is available tothe plant. The smaller pores are the last to loose their water. Eventually the watercontent will be so low that the plant is unable to obtain water as quickly as it loses it totranspiration and the plant will begin to lose turgor and wilt. The permanent wilting pointoccurs when the plant is unable to recharge its moisture reserves overnight andremains flaccid.

WATER QUALITY

Most Alberta growers have access to good quality water but some growers rely on "dugout water". When we talk about quality, it means different things to different people.This is because the quality is dependent on intended use. For irrigation purposes waterquality is determined by two factors:

1. The concentration and composition of dissolved salts.

2. The presence of suspended particles, pathogenic organisms, algae, pesticide andherbicide contamination.

Effects of salts on irrigation water quality

A salt is defined as a chemical compound that releases charged particles called ionswhen dissolved in water. For example, potassium nitrate (KNO3) releases two ions, one


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a positively charged cation (K+) and the other is negatively charged anion (NO3-). Salts

can be either beneficial or harmful depending on the characteristics of the specific ionsinvolved, as well as the total salt concentration. KNO3 is a fertilizer salt and both K

+

and NO3- are nutrient ions needed by the plant for growth. Salts such as sodium chloride (NaCl),

consist of harmful ions (Na

+

and Cl

-

) that can damage or kill plant tissue.

Water analysis generally provides the concentration of following major ions.

ION NAME CHEMICAL SYMBOL EQUIVALENT WEIGHT

CATIONS

Calcium Ca + 20

Magnesium Mg + 12

Sodium Na+ 23

Potassium K+ 39

ANIONS

Bicarbonate HCO3- 61

Carbonate CO3- 30

Chloride Cl- 36

Sulfate SO42- 48

Boron * - -

* Boron occurs in several different ionic forms in irrigation water and therefore aspecific ionic formula cannot be given.

In addition to specific ion concentrations, a water quality test should providemeasurements of Electrical Conductivity, pH and Sodium Absorption Ratios (SAR).

Electrical Conductivity

EC is a measure of total dissolved solids in water. It is reported in millimhos ormillisiemens. As EC increases, the quality of the water decreases. It is a useful tool tomonitor plant development. EC and SAR are taken into consideration to make adecision on quality. SAR reflects the relationship between sodium, calcium andmagnesium. The higher the ratio of sodium to calcium and magnesium, the higher thedanger of sodium toxicity. This is how the quality is judged:

* Water having a SAR of less than 4


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* EC of 0.8 mmhos or less is considered suitable for irrigation of crop plants undernormal conditions.

* EC between 0.81 and 2.2 mmhos. The water is considered marginal in qualitybut can be used if special management practices are followed.

* Water with an EC above 2.2 mmhos is not suitable for crop production.

Special Management Practices

1. Provide adequate drainage.2. Never allow the growing medium to dry out. A moist growing medium should be

maintained.3. Maintain air relative humidity between 70 and 80 percent.4. Analyse growing medium samples frequently.5. Follow regular leaching practices.

Sodium

Sodium is directly toxic to young seedlings. It can be taken up by the plant as asubstitute for potassium. Sodium has a serious damaging effect on growing mediumstructure. An excess of sodium ions relative to calcium and magnesium ions can causeclay particles to disperse and seal up the pores, which seriously reduces permeabilityand gas exchange. In peat based media where there are no clay particles, sodium canbe attached to the peat fibre and its concentrations can increase significantly higher inrelation to calcium and magnesium. Testing of nutrients must be done on a regularbasis. Toxicity threshold for sodium is around 50 ppm.

Bicarbonates

Bicarbonates are not toxic but levels above 100 ppm make the water very hard and maycause problems for plant growth. High bicarbonates are associated with high alkalinitythus increasing the media pH over a period of time. The precipitation of calcium and/ormagnesium carbonate can cause foliar staining which is sometimes difficult to remove.Water can be acidified to neutralize these bicarbonates in water.

Iron

Iron in its oxidized form Fe+++, has a very low solubility and can therefore easilyprecipitate as amorphous iron hydroxide which can plug irrigation lines.

Boron

Boron can be quite toxic to small plants. Its level should be carefully monitored in thegrowing medium and for plant nutrition.


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Zinc

Excessive levels of zinc have been found in water supplies where the water is collectedfrom galvanized metal. Excess zinc may cause problems with copper uptake.

pH

pH of Alberta water supplies is generally over 7 and this can cause problems in severalways. pH of water over 6.8 can cause calcium to react with phosphorus and thusprecipitate out in the solution. When you are irrigating with water of pH over 7, eventhough the medium pH is around 4, iron and manganese deficiencies are possible.Adjust pH of water to around 6.

WATER TREATMENTS

Dug Out Water

Many Alberta growers collect water from a large run-off area. The water is generally ofgood quality. In winter we have seen problems with low water levels and consequentlysucking mud with water. This can cause two problems: 1. Silt and clay may bedeposited in the growing medium and change the porosity and drainage characteristicsof the medium. 2. The fungus Pythium , can accompany this water and cause seriousdamping off problems.

In one case where the dug out was located in a clay area, a large number of suspendedparticles were delivered to the crop causing water logging. Herbicide contamination is

another potential problem. Treatments are available to remove suspended particles. Inthe case of herbicide contamination, installation of charcoal filters should be considered.

In Saskatchewan 38% of growers use well water as the source for greenhouse cropirrigation, followed by 31% from municipal sources, 26% from dugouts, and 5% fromrivers and creeks.

Hard Water from Wells

If calcium levels are over 100 ppm, then growers must use acid to neutralize carbonatesand bicarbonates. Hard water can be chemically softened but such water is not suitable

for plant growth. The quantity of acid needed to neutralize bicarbonates depends ontheir amount present in water supply. Phosphoric, nitric, sulphuric and citric acid can beused for this purpose although commercially, the first three acids are more commonlyused. Neutralizing 60 ppm or one milliequivalent of bicarbonates require 7 litres of 85%phosphoric acid, 13.8 litres of 37% nitric acid and 3 litres of sulphuric acid for 100,000litres of water. A level of 60 ppm of bicarbonates should be maintained in water to haveenough buffering capacity and maintain a pH of around 6.0.


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pH is logarithmic so it can drop very rapidly after a certain point. So don’t depend onthe calculation alone. Check the pH after the desired amount of acid has been addedand then make corrections accordingly. We have seen cases where the pH dropped toa level of 3 and grower did not realize until the damage was done.

Following table provides a summary of amounts of acid required to neutralize 60 ppm ofbicarbonates. A level of between 30-60 ppm of bicarbonates should be maintained inthe water supply.

Acid Millilitres/100 litres of water

37% Nitric acid 13.8

61% Nitric acid 8.4

75% Phosphoric acid 8.0

85% Phosphoric acid 7.0

93% Sulfuric acid 3.0

Acids are corrosive so proper care should be taken in handling them. When diluting theacid, add acid into the water not water into the acid. Wear proper clothing, gloves andsafety glasses. Calibrate pH meter frequently and obtain new buffers every year.

High Sodium Water

Some growers have no choice but have access to soft water. Such growers usereverse osmosis to make their water usable.

FERTILIZER MANAGEMENT

INTRODUCTION

All plants need sixteen elements to grow properly. These are called essential elements.Any one of these elements can become the limiting factor in the growth of plants. Thisis important to understand because many times growers get upset that a fertilizerprogram is not working. When you look closely you will find a limiting factor which mayor may not relate to fertilizer elements. For example, in a recent situation with a tomatogrower it was found that plants were not growing properly and fruit was not sizing up. Allthe fertilizer elements were being supplied in adequate amounts. It was found that thecarbon dioxide generator was not working properly and the plants were starving forcarbon. Thus, a lack of carbon became a limiting factor for these tomato plants.


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WHAT ARE THE ESSENTIAL ELEMENTS FOR PLANT GROWTH?

Carbon, hydrogen, oxygen, nitrogen, phosphorus, potassium, calcium, magnesium,sulfur, iron, manganese, copper, zinc, boron, molybdenum and chlorine are consideredto be essential for plant growth. Out of these 16 elements carbon, hydrogen and

oxygen are taken up from the air while the rest of the elements are supplied through theroots as fertilizer elements.

WHAT DO THOSE NUMBERS ON FERTILIZER BAGS MEAN?

Fertilizers are required by law to be labeled to indicate nitrogen, phosphoric acid andpotash contents. Thus the three numbers indicate the contents of nitrogen, phosphoricacid and potash. For example a fertilizer labeled as 20-20-20 would mean that itcontains:

* 20 percent nitrogen: N

* 20 percent phosphoric acid: P2O5 * 20 percent potash: K2O

Most of the time a fertilizer program calls for parts per million concentration of nitrogen,phosphorus and potassium. Thus, it is important to understand that the number 20percent is phosphoric acid, not phosphorus and similarly 20 percent potash is notpotassium. Phosphoric acid can be converted to phosphorus by multiplying by 0.43 andpotash can be converted to potassium by multiplying by 0.83. Here are a few examplesfor further clarification:

Fertilizer N:P2O5:K2O N:P:K

20-10-20 20-10-20 20-4.3-16.6

10-52-10 10-52-10 10-22.3-8.3

20-20-20 20-20-20 20-8.6-16.6

28-14-14 28-14-14 28-6.02-11.6


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WHAT ARE PARTS PER MILLION?

Parts per million is a unit of fertilizer concentration. When a fertilizer program isdesigned it is specified that it will contain so much concentration of nitrogen or otherelements in so many parts per million of water. Here are some other terms to become

familiar with parts per million (ppm):

* One pound of a substance in 100,000 gallons of water equals one ppm (Onegallon of water weighs 10 pounds).

* One percent concentration equals 10,000 ppm.* Milligrams of a substance per liter of water equals one ppm.* Grams per litre equals 1000 ppm

ANY FORMULAS TO CALCULATE PPM?

Yes! You can use different formulas to calculate ppm for your fertilizer programs. If youlike imperial units then the formula is:

* Ounces per 100 imperial gallons = ppm desiredGrade x 0.62

OR

* ppm = Ounces per 100 imperial gallons x grade x 0.62

Grade is percent fertilizer content.

For example, the formula calls for 200 ppm of nitrogen from 20-10-20 fertilizer. Usingthe above formula:

ppm desired = 200

Grade of fertilizer = 20 percent nitrogenmultiplication factor 0.62

20020 x 0.62 = 16 ounces/100 gallons of water

You can multiply 16 ounces with 20 percent nitrogen and 0.62 and get your ppm fromthere. It means that if you know the ounces per 100 gallons of water you can calculateppm concentration. You can also establish a simple rule for quick mental use.One pound or 16 ounces of a fertilizer in 100 imperial gallons of water will giveyou ppm 10 times the value of the fertilizer grade. For example one pound of 20- 10-20 fertilizer in 100 gallons of water gives you 20 x 10 ppm of nitrogen, 10 x 10ppm of phosphoric acid and 20 x 10 ppm of potash .


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If you use U.S. gallons then use a multiplication factor of 0.75 instead of 0.62 If you likemetric units to calculate parts per million of an element then use the following formula:

* ppm desired x litres of water = grams of fertilizer

grade of fertilizer x 10

OR

* grams of fertilizer x grade x 10 = ppmlitres of water

Example

I want to make a nutrient solution containing 130 ppm of nitrogen using potassiumnitrate which is 13-0-44.

- ppm desired 130 ppm of nitrogen- amount of water 100 litres- grade of fertilizer 13 percent nitrogen

Using the above formula: 130 x 100 = 100 grams13 x 10

I also have 44 percent potash with the fertilizer I used. I want to find out how muchpotash I have. Using the formula:

- grams of fertilizer x grade x 10 = ppmlitres of water

100 x 44 x 10 = 440 ppm100

We can use the same rule for quick mental calculation as we did for imperial gallons.One hundred grams of a fertilizer in 100 litres of water will give you parts per millionequal to 10 times the grade of the fertilizer.

Example

- One hundred grams of 13-0-44 in 100 liters of water will give you 130 ppm ofnitrogen and 440 of potash.

REMEMBER: 100 grams/100 liters of water is the same thing as one pound in 100gallons of water. This is because one pound weighs 450 grams and 100 gallonsequal 450 liters of water.


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SOLUBILITY OF FERTILIZERS

Solubility of fertilizers differs in cold and hot water. That can play an importantrole when you are preparing a fertilizer program in a stock tank. That is, you

have to prepare a fertilizer solution several times stronger to go through theinjector. Here are the solubilities of various fertilizers:

Solubility of Fertilizers in grams/100 mL of water

Fertilizer Formula Cold Hot

Urea 46-0-0 78.0

Ammonium nitrate 34-0-0 118.0 871.0

Ammonium sulfate 21-0-0 70.0 103.0

Calcium nitrate 15.5-0-0 102.0 376.0

Potassium nitrate 13-0-44 13.0 247.0

Potassium chloride 0-0-60 34.0 56.0

Potassium sulfate 0-0-50 12.0 24.0

Monoammonium phosphate 11-52-0 22.0 173.0

Magnesium sulfate 26.0 73.0

Borax 1.6 14.0 Copper sulfate 31.0 203.0

Manganese sulfate 105.0 111.0

Ferrous sulfate 15.0 48.0

Sodium molybdate 56.0 115.0

DIFFERENT SOURCES OF FERTILIZERS

Nitrogen

Anhydrous ammonia 80-0-0Urea 46-0-0Ammonium nitrate 34-0-0Uracil 34-0-0Ammonium sulfate 21-0-0Calcium nitrate 15.5-0-0


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Potassium nitrate 13-0-44Sodium nitrate 15-0-0

Phosphorus

Monoammonium phosphate 11-52-0Diammonium phosphate 21-63-0Monopotassium phosphate 0-53-34

Potassium

Potassium nitrate 13-0-44Potassium sulfate 0-0-50Potassium chloride 0-0-62Monopotassium phosphate 0-53-34Potassium bicarbonate 0-0-46

Potassium silicate 0-0-12

Calcium

Calcium nitrate 15.5-0-0 + 19 percent caCalcium chloride 18 percent caCalcium carbonate 38 percent caCalcium hydroxide 54 percent caDolomite lime 22 percent ca

Magnesium

Magnesium sulfate 10 percent mgMagnesium nitrate 9 percent mgDolomite lime 9 percent mg

SOURCES OF MINOR ELEMENTS

Iron

Iron sulfate Fe 21 percentIron chelate Fe 13.2 percent + 68 percent EDTAIron chelate Fe 7.0 percent + 48.6 percent DTPA

Manganese

Manganese sulfate Mn 29.5 percentManganese chelate Mn 13.0 percent + 68 percent EDTA


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Copper

Copper sulfate Cu 25 percentCopper chelate Cu 14 percent + 63 percent EDTA

Zinc

Zinc sulfate Zn 35 percentZinc chelate Zn 14 percent + 62 percent EDTA

Boron

Boric acid B 17.5 percentBorax B 15.0 percent

Molybdenum

Sodium molybdate Mo 46 percent


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PREPARING A FERTILIZER PROGRAM

Understanding the Design Principles

Plants have a vegetative phase and a reproductive growth. Vegetative meansthat it is developing leaves and roots while reproductive means it is producingflowers and fruits. Besides temperature, light and watering, fertilizers play amajor role in making a plant vegetative or reproductive. Most greenhouse plantsneed to maintain both stages of growth. Domination of either stage is notdesirable. For example, a strongly vegetative tomato or cucumber plant wouldnot yield good fruit. Fertilizers containing high nitrogen in relation to potash willcause rapid vegetative growth, assuming that temperature, water and light is notlimiting. For example 28-14-14 fertilizer is designed for rapid vegetative growth.

In a fertilizer, equal amounts of nitrogen in relation to potash is used to maintain

steady growth of plants. For example 20-20-20 or 20-10-20 is a plantmaintenance feed.Low nitrogen in relation to potash is meant for hardening a plant and also usedwhen plants are flowering and fruiting. At that time plants like cucumber, tomatoand peppers need higher potash to fill the fruits. Examples are 13-0-44, 18-11-27 or 8-12-30.

High phosphate fertilizers like 10-52-10, 9-45-15 or 10-30-10 are used for goodroot establishment in the early stages of plant development.

Remember that you have to provide other elements required for plant

growth.

Step 1

Some nutrients may be available through your water. Get an analysis of thewater to be used. High sodium water is not usable for greenhouse irrigation.Nitrogen, phosphorus and potassium are not generally in such quantities that youhave to make adjustments. Calcium, magnesium and iron are the threeelements which may be present in large quantities. Availability of calcium andmagnesium depends on pH. It is our experience that you shouldn't count on 100percent availability of calcium and magnesium from your water. Allow a factor of25 percent availability of what is contained in your water. Iron is in the form offerric ion and it may not be available to plants. If you collect water from thegreenhouse then watch the zinc level. It may be high enough that you don't needto add any extra zinc in your feeding program.

Step 2

Work out the volume of water in your irrigation system. It is easy to calculate:


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1) If you have a large tank in which you mix fertilizer then you will know how

many gallons or liters the tank is. Sometimes the tank capacity is indicated inU.S gallons.

2) If you are using an injector system then know the size of the stock tank anddilution rates. For example if you have a 200 L stock barrel and dilution rate is1 to 200, then you will multiply 200 with 200 and that will give you a volume of40,000 liters of water.

3) New irrigation systems have a very small mixing tank and water is addedbased on the demand by the irrigation area. Fertilizers are added by acomputer using electrical conductivity as a guideline. In such cases properfertilizer mixing is done in stock tanks where you choose the concentration.Once in a while the nutrient solution should be analyzed to make sure you aredelivering to the plant what you think you are.

Now we are ready to design a fertilizer program with following nutrientconcentrations at plant delivery point:

Nitrogen 200 ppm Phosphorus 40 ppmPotassium 350 ppm Calcium 150 ppmMagnesium 70 ppm Sulfur 100 ppmIron 3.0 ppm Manganese 0.8 ppmCopper 0.15 ppm Zinc 0.2 ppmBoron 0.25 ppm Molybdenum 0.12 ppm

We have a variety of fertilizer sources available to us as outlined in previoustables.

Step 3

Take all your calcium first. You need 150 ppm of calcium and the source iscalcium nitrate, 15.5-0-0 + 19 percent calcium. Using the ppm calculationformula:

ppm desired x litres of water = grams of fertilizergrade of fertilizer x 10

let us plug in the figures:

150 x 100 = 79 grams19 x 10

If you have an injector at 1:200 dilution ratio and a stock tank of 200 liters thenyour total amount of water is 40,000 liters. You can either use the figure of


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40,000 liters in the formula or multiply the 100 liters figure with 400 to get the finalamount of calcium nitrate to be used. That will equal to 31.6 kg. This amountwill be dissolved in 200 liters of stock tank.

Step 4

Find out how much nitrogen you got by using 79 grams of calcium nitrate in 100liters of water. The formula is:

grams of fertilizer x grade x 10 = ppmAmount of water in liters

79 x 15.5 x 10 = 122 ppm100

So calcium nitrate contributed 150 ppm of calcium and 122 ppm of nitrogen. Westill require 200 - 122 = 78 ppm of nitrogen.

Step 5

Get all your phosphorus from mono potassium phosphate 0-53-34. Remember53 percent is phosphate and we have to convert it to phosphorus by multiplying53 percent by 0.43 and that will equal 22.8. That is the figure we will use for ourphosphorus calculation.

Using the ppm desired formula:

40 x 100 = 17.5 grams22.8 x 10

Make adjustments for the amount present in your water.

Step 6

Calculate the amount of potassium you got from 17.5 grams of 0-53-34 in 100liters of water. Remember 34 percent is potash not potassium. Multiply 34 with0.83 to get potassium which equals 28.2.

Thus ppm of potassium = 17.5 x 28.2 x 10 = 49.3 ppm100

Step 7

Take the balance of nitrogen, that is 78 ppm, from potassium nitrate which is 13-0-44.

78 ppm x 100 litres = 60 grams


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13 x 10

How much potassium is obtained from 60 grams/100 liters of potassium nitrate13-0-44? Remember 44 percent is potash and it will be 36.5 percent potassium.

60 grams x 36.5 x 10 = 219 ppm100 liters

Total potassium from steps 6 and 7 is 268 ppm. Total required is 350 ppm.Thus we still need 82 ppm of potassium.

Step 8

Take this potassium from potassium sulfate 0-0-50 which is 41.5 percentpotassium (50 x 0.83). Using the formula:

82 ppm desired x 100 litres of water = 19.7 grams41.5 x 10

Now we have satisfied our requirements for nitrogen, phosphorus, potassium andcalcium.

Step 9

Take all your magnesium from magnesium sulfate which is 10 percent Mg.

50 ppm desired x 100 litres of water = 50 grams10 percent mg x 10

Step 10

Calculate how much sulfur you got from potassium sulfate and magnesiumsulfate. Potassium sulfate has 18 percent sulfur while magnesium sulfate has 12percent sulfur.

Sulfur from 19.7 grams of 0-0-50:

19.7 x 18 x 10 = 35.4 ppm100 litres

Sulfur from 50 grams of magnesium sulfate:

50 x 12 x 10 = 60 ppm100 liters


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Thus total sulfur is 35.4 + 60 = 95.4 ppm which is close to our 100 ppm ofrequirement.

Step 11

Iron required is 3 ppm and will use 13 percent iron chelate:

3 ppm required x 100 liters = 2.30 grams13 percent iron x 10

Step 12

We need 0.8 ppm of manganese from manganese chelate which is 13 percentmanganese.

0.8 ppm desired x 100 liters = 0.61 grams13 percent mn x 10

Step 13

We need 0.15 ppm of copper from copper chelate, which is 14 percent copper.

0.15 ppm desired x 100 liters = 0.10 grams14 percent cu x 10

Step 14

We need 0.2 ppm of zinc from zinc chelate which is 14 percent zinc.

0.2 ppm desired x 100 liters = 0.14 grams14 percent zn x 10

Step 15

We need 0.25 ppm of boron from borax, which is 15 percent boron.

0.25 ppm desired x 100 litres = 0.16 grams15 percent b x 10

Step 16

We need 0.12 ppm of molybdenum from sodium molybdate which is 46 percentmolybdenum.

0.12 ppm desired x 100 liters = 0.026 grams46 percent mo x 10


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This completes our requirements for all nutrients. You may have noticed thattrace elements are required in very small quantities and it will be difficult to weighthem. You make strong solutions called stock solutions.

MAKING STOCK SOLUTIONS FROM TRACE ELEMENTS

Let us take molybdenum for example. In the above example we only need 0.026grams of sodium molybdate in 100 liters of water. Multiply 0.026 grams with1000 which is equal to 26 grams. Multiply 100 liters of water with 1000 as wellwhich is 100,000 liters of water. Dissolve 26 grams in one liter of water which isequal to 1000 mL. Thus 1000 mL of stock solution is good for 100,000 liters ofwater. Thus 1 mL of stock solution can be added to 100 liters of water. Keep thestock solution in a dark glass bottle in a fridge. You can mix all the traceelements together and make up a stock solution. Keeping individual elementsseparate is of advantage that you can make adjustments when necessary.

PRINCIPLES OF MIXING FERTILIZERS

All fertilizers can be mixed in the diluted form. However when you are makingconcentrates then certain elements cannot be mixed together. Do not mixcalcium nitrate with any fertilizer containing phosphate and sulfate. It isbest to feed calcium nitrate separately .

pH, YOUR WATER AND FERTILIZER

What is pH?

pH is a measurement of the acidity or alkalinity (base) of a solution. Whensubstances dissolve in water they produce charged molecules called ions. Acidicwater contains extra hydrogen ions (H+) and basic water contains extra hydroxyl(OH-) ions. pH is measured on a scale of 0 to 14. Neutral water has a pH of 7.Acidic water has pH values less than 7, with 0 being the most acidic. Likewise,basic water has values greater than 7, with 14 being the most basic. A change of1 unit on a pH scale represents a 10 fold change in the pH, so that water with pHof 6 is 10 times more acidic than water with a pH of 7, and water with a pH of 5 is100 times more acidic than water with a pH of 7. That is the reason why It takeslonger time to adjust the pH of the growing medium. pH constantly changes

during the crop duration and must be monitored regularly. Also growers mustknow the optimum ranges of pH for the crops they are growing.

Why it is important?

It is important because the uptake of nutrients depends on proper pH in thegrowing medium.


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What is an optimum range?

Soilless mixes 5.5 - 6.5

Soil-based mixes 6.0 - 6.8

Rockwool 5.8 - 6.4

Nutrient solution 5.5 - 6.5

What happens if optimum ranges are not followed?

* Iron and manganese deficiencies occur at pH values above the optimumranges.* Manganese and boron toxicities are known below the optimum ranges.

Why pH changes are difficult to make?

This is because pH description is logarithmic. More hydrogen ions are required tochange the pH from 5.5 to 4.5 than from 6.5 to 5.5. The important fact tounderstand is that pH also reflects the buffering capacity of a medium. It willchange slowly.

How do you adjust the pH of a growing medium?

You add calcium carbonate lime or dolomite lime to acidic peat moss to make italkaline. Alberta peat moss has a pH between 3.5 and 6.0, therefore liming rateswill vary. This is an important point to follow. Check the pH of your peat moss

and figure out the amount of lime you need. Calcium hydroxide and potassiumbicarbonate are also used to raise the pH of a growing medium.

What about ready made mixes?

Enough lime is added to bring the growing medium to a minimum pH level.Based on your fertilizer programs pH may become acidic quickly. You have tomonitor pH on a regular basis. Plant damage has been observed because of apH below 5.

What do you do if you detect an acidic pH while the plants aregrowing?

Apply potassium bicarbonate at one gram per liter directly or through the feedingline. Do not mix it with other fertilizers.

Soak hydrated lime 100 grams in 100 liters of water. Let it sit overnight and thenuse the "lime water " to irrigate plants. Apply enough volume to thoroughly wet


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the growing medium. Many irrigations may be required. Rinse leaves afterapplication. If pH is on alkaline side then adjust the pH of the fertilizer solution toaround 5.5 or start using fertilizers with higher ammonium nitrogen.

What about fertilizers and pH?

Fertilizers containing ammonium nitrogen tend to be acidic in nature. Fertilizerswith nitrate nitrogen tends to be alkaline in nature. Let us look at a fewexamples:

The commercial fertilizer 19-0-16 has a potential acidity of 30 pounds of calciumcarbonate equivalent/ton. It contains following types of nitrogen.

- Nitrate nitrogen = 14.4 percent- Ammonium nitrogen = 4.6 percent- Urea nitrogen = 0 percent

17-6-6 has a potential acidity of 1800 pounds of calcium carbonate/ton. It hasammonium nitrogen at 17 percent.

16-4-12 has a potential alkalinity of 73 pounds of calcium carbonate/ton. It hasnitrate nitrogen, 9.97 percent, Ammonium nitrogen at 1.05 percent and ureanitrogen at 4.98 percent.13-0-44 has a potential alkalinity of 452 pounds of calcium carbonate/ton. It hasnitrate nitrogen at 13 percent.

Can I use fertilizer to change the pH of water?

Slight changes are possible but it takes two to three months before changes inthe growing medium will be noticed. You can choose acidic or alkaline fertilizersto regulate the pH in the growing mix. Avoid using fertilizers with pesticides.

If my water is alkaline, how can I bring the pH down?

Use nitric acid, sulphuric acid or phosphoric acid. Construct a pH curve of yourwater because pH may drop very quickly if too much acid is added to the water.There are guidelines available to calculate acid requirements based oncarbonate and bicarbonate amounts in water. Use proper acid head for injection.Metal heads may corrode and may inject too much acid into the system.


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Do plants change pH of the growing medium?

Yes, plants change the pH of the growing medium. Look at the pictures below:

Plants like Petunias, Bacopa, Scaveola and Calibrachoa are iron inefficientgroups of plants and if pH goes over 6.5 they will show Iron deficiency. Plantslike Geraniums and New Guinea Impatiens are iron efficient group of plants andwill show iron toxicity at pH below 5.5. Availability of trace elements like iron,manganese, copper, boron and molybdenum is up to 4 times higher when pHmoves to acidic side and lower when pH moves to alkaline side.

WHAT IS ELECTRICAL CONDUCTIVITY?

Electrical conductivity or EC is a measure of electrical current through a solution.It is measured by an EC meter and recorded as millisiemens/cm or millimhos/cm.To give you an idea about the EC of different water:

Type of water EC

Distilled water not measurable

Dug out water 0.2 - 0.5 mmhos

Edmonton water 0.4 - 0.6 mmhos

Well water 0.5 - 2.0 mmhos

Fertilizer solution 1.5 - 2.5 mmhos


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How can I monitor the EC of my crop?

Measure the EC of your fertilizer solution. Measure the EC of leachate from apot, from a styroblock, from a bedding plant tray or from a rockwool block. TheEC of leachate should not be more than the E of your fertilizer solution. Some

recommendations:

EC 0.8 mmhos/cm and below = need fertilizerEC 0.9 to 2.0 = maintain feedEC 2.0 and above = caution

A higher EC can be maintained if plants are vigorous and demand more fertilizerbut you have to keep the growing medium moist.

Can I use E.C. management to control the growth of my plants?

Yes, it is important to understand that EC is a valuable tool to control the growthof plants when water restriction is difficult due to the use of media with higherwater holding capacity especially early in the season when light is limiting. This ishow it works:

• For vegetable seedlings grown in December, January and early February,after transplanting raise the EC by using additional amounts of potassiumsulfate 0-0- 52 and feed around an EC of 4.0. The EC of the growingmedium could rise to up to 8.0 mS and in that case do some leaching withplain water. Such a high EC is not detrimental to tomato seedlings as longas there is enough water in the growing media.

• Cucumber, water melon, zucchini, mini- cucumbers seedlings can be wellcontrolled in growth with a feed EC of 3.0 mS and block EC around 4.0mS.

• Peppers can be treated like cucumber.

• Lettuce EC in seedlings should be maximum 3.0 mS.

• Bedding plants, general EC is around 2.5 mS in pots and around 2.0 mSin smaller volume plugs.

Once the seedlings are planted in the final container then EC will be managedbased on light conditions. Higher the light, lower will be the EC.

Here are couple of examples where very high EC affected the growth of crops.This grower grows spinach and lettuce for farmers market in winter with somesupplemental light in bedding plants trays. Once the harvest is completed, thegrowing medium is reused. The plants are very dark green in color and verycompact. They are not stretching.


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Notice the leach E.C. Below 3.0 millimhos is normal for winter production. Thegrower mixed the old growing medium with the new one without leaching andthat is the result.

Growers must invest in a good pH and E.C meter and monitor the crop regularlyespecially crops like petunias and geraniums.

Plant Nutrition, Water and Fertilizer Management

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