Plant nutrition, water and fertilizer management

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

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

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

Contact Information: Dr Mohyuddin Mirza

Phone: 780-463-0652, email: drmirzagreen@gmail.com , www.agga.ca

MANAGEMENT IN GREENHOUSE GROWN

CROPS

Fundamental Aspects of Plant Nutrition

Any Formulas to Calculate PPM? 16

Solubilities of Fertilizers 18

Different Sources of Fertilizers 19

Preparing 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

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 This means that the presence of a particular element in a plant tissue does not indicate that the element is essential for growth For example silicon, chromium and cobalt have been 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 remaining seven elements in the above list are micro-nutrients They are required in small amounts 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 the growing medium to make simple foods by the process of photosynthesis These substances are needed to make amino acids, proteins and protoplasm Other elements are 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 corrected through foliar feeding

Absorption through roots is the major route of nutrient uptake If the root system is damaged 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 interaction between root respiration and soil water Inorganic salts applied as fertilizers are broken apart by a chemical process called dissociation

At any time, both molecules and separate ions of the salt are present A molecule consists of two or more ions For example, potassium chloride (KCl) supplied as a fertilizer is dissociated in the soil solution into potassium (K+) and chloride (Cl-) ions

Ions with positive (+) charges are called cations Ions with negative (-) charges are called 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 ionic exchange

Cation-Exchange Capacity

The actual process of nutrient uptake by plants is controlled by the cation-exchange

capacity (CEC) of the growing medium This action is associated with the clay particles

of 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 the combination of hydrogen from the soil water and the carbon dioxide resulting from root respiration These hydrogen ions, which have a positive charge, exchange their positions in the soil solution for positively charged cations held on the surface of the clay particles These cations are then absorbed by the roots

The cations are calcium, potassium, magnesium, sodium, and ammonium ions The roots 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 calcium because 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 remain

in solution unless absorbed by the plant or lost through leaching If leaching is not adequate, anions can build up in the soil solutions and cause an increase in the electrical conductivity of the root zone medium The practical implications are that nitrates are easy to leach with over watering and thus deficiency in plants can occur rather quickly

pH Effect on Nutrient Absorption

Uptake of nutrients is strongly affected by the pH of the growing medium Our experience is that the pH of the growing mix should be between 5.5 and 6.5 Below that value the uptake of manganese, iron and boron increases considerable and can cause tip burning and toxicity problems Enough dolomite lime should be added to raise the

pH to around 5.5 Dolomite lime can be replaced with potassium bicarbonate because calcium is supplied through calcium nitrate and magnesium through magnesium sulfate

Many growers have reported difficulties with pH adjustments while plant seedlings are being grown It takes a long time to change pH from a lower to a higher value or vice versa Since the pH scale is based on logarithms, a growing medium with a pH of 6 is

10 times more acidic than a medium with a pH of 7 Similarly, a growing medium with a

pH 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 more acidic than a medium of with a pH of 7 This factor of 100 is the reason it is more difficult to raise the pH from pH 5 to 7 than it is to raise from pH 6 to pH 7 This means

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

Nitrate nitrogen, while inside the roots, is converted to ammonium and to amino forms and used to make proteins and other chemicals needed by the plants That is why fertilizers containing nitrate nitrogen like calcium nitrate and potassium nitrate will produce slow and steady growth Ammonium and urea based fertilizers can produce soft and lush growth in plants

Ammonium nitrogen can be used if plant growth is slow but it should be used when the growing medium temperature is above 16oC and the light is good Use of ammonium fertilizers should be avoided until the end of March Where pH is alkaline, use of ammonium fertilizer is an advantage because it can help to bring down the pH Urea is

a good source of nitrogen for foliar feeding Wherever plants are slow and need a growth 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 symptoms will first appear on the lower leaves

Measurement of nitrogen in tissue is a useful tool to manage the growth and bud set in plants, especially tree seedlings It should be monitored on a weekly basis after week

16 of the growth Bud set in conifer species will be difficult if tissue nitrogen is over two percent

Phosphorus (P)

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

processes require phosphorus for high energy phosphate bonds Most of the phosphorus is taken up in the form of the primary orthophosphate ion ( H2PO4 ) Smaller amounts of secondary orthophosphate (HPO4 ) and organic phosphorus compounds are also absorbed

Two facts should be remembered about phosphorus:

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

* A pH of above 6.8 in the growing medium can tie up phosphorus with calcium and

it may not be available to the plant We have seen phosphorus deficiencies in plants because of pH related problems

Because of the negative charge of orthophosphate, it is not attached to clay particles and can easily tie up with aluminum in the growing mix Phosphorus deficiency results

in 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 plant tissues act in opposition to each other At a high level of phosphorus, an iron deficiency may 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 the regulating of the opening and closing of stomata and in water retention It promotes the growth of meristematic tissue, activates some enzymatic reactions, aids in nitrogen metabolism and the synthesis of proteins, catalyses activities of some mineral elements and aids in carbohydrate metabolism and translocation Potassium is found in plant tissues as a soluble, inorganic salt, while nitrogen and phosphorus are converted into complex compounds It is absorbed by the plants in large amounts without becoming toxic

Potassium is highly mobile within the plant High potassium as compared to nitrogen is used by growers in Alberta This is to exert an antagonistic effect on the uptake of nitrogen so that the growth is slowed down Nitrogen to potassium ratios can be changed 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 1

to 2 will harden the growth That is why hardening fertilizer regimes contain an N to K ratio of 1 to 2

Calcium (Ca)

Calcium is absorbed in the ionic form (Ca++) Most of the calcium inside the plant is in the form of calcium pectate in the middle lamellae of the cell walls In tree seedlings it is part 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 Calcium

is immobile and is not translocated from older to younger leaves It's uptake from the growing medium is dependent on the active water transport If plants are not transpiring, then calcium movement will be minimal Slow or poor development of terminal and side bud shoots is generally related to a lack of calcium in the tissue In cucumbers, poor development of side shoots is an indication of calcium deficiency while

in tomatoes; blossom end rot is due to poor calcium translocation Most growers supply enough calcium through their feeding program but it is the poor uptake which causes problems 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 enzyme systems require magnesium to work properly Magnesium is mobile within the plant tissues Thus, symptoms of a lack of magnesium show up first on lower leaves The symptoms could appear later, on the entire plant as yellowing of interveinal areas with veins remaining green

Magnesium deficiencies have been noted in many crops and is likely due to the higher potassium we use in our fertilizer programs Foliar feeding of magnesium has given satisfactory results

amounts of ferric ion but still show severe iron deficiency symptoms Thus, a tissue iron test 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 the formation 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 youngest leaves as a chlorosis If the deficiency is not corrected, the leaves may turn light yellow and then almost completely white Iron chelate is commonly used by many growers in their fertilizer programs

Manganese (Mn)

Plants absorb manganese in the form of the manganous ion (Mn++) It is used in the active growing parts of plants and is involved in certain enzyme systems that oxidize other 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 a tendency to grow them at acidic pH values The uptake of manganese is several times higher at pH values below 5 The damage appears as browning of needle tips progressively moving inwards The entire needle may turn brown The damage is generally irreversible Toxicity has been seen in tomatoes and cucumbers where manganese 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 proper function 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 enzyme activator in respiration, seed formation and root growth Organic growing media like the one used by growers can tie up copper to a considerable degree That is why copper deficiencies are frequently noticed in many plants We recommend the use of relatively higher levels of copper in our feeding programs A lack of copper in tree seedlings can easily be confused with boron deficiency because symptoms are similar Terminal shoots may die back and witches' broom symptoms appear It is best to monitor tissue copper levels on a regular basis Both copper chelate and copper sulfate are suitable for plant use

Zinc (Zn)

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

Alberta grown plants but toxicities are possible due to the high zinc content in some water supplies Watch for higher zinc levels when you are collecting water from greenhouse 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 that molybdenum is used in the nitrogen cycle in the formation of nitrogen compounds and the breakdown of nitrates The leaves lose their good green colour and become more dark blue in colour When molybdenum is lacking in the plant, nitrates are not absorbed from the growing medium even if it is present in large amounts

Chlorine (Cl)

Chlorine deficiency is not well documented in plants Its importance has been recognized 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 of chloride Needle tip burning is the major symptom of chloride excess in spruce and other conifers

Other Elements

Sodium, aluminum and silicon are found in the tissues of many plants Sodium levels over one percent of the dry matter should be a cause of concern Aluminum is found in root tissue and ties up phosphorus in large amounts Silicon increases the cation exchange capacity of the growing medium and is used by many growers when manganese toxicity is suspected

High fluoride levels, over 1 ppm, has caused problems with tip burning in spruce needles

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 fresh weight

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

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

4 Water is essential for maintaining turgidity in plant cells, promoting cell elongation and 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 not essential, it will help to be familiar with the concepts of water content and water potential Water content is what is present inside the plant at a given time Basically plant 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 plant itself

Plant water content is in a constant change during the day, when transpirational losses through leaves usually exceeds the rate of water absorption through the roots This lag between water uptake and water loss creates a condition of internal water stress within the plant This stress is normal during daylight hours within normal limits If the stress

is allowed to reach extreme levels for extended periods, the plant growth rate declines and 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 the moisture deficit relationship to plant growth

Moisture deficit is a calculation, based on temperature and air relative humidity that gives a numerical value that is related to the amount of water loss from a crop Too high 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 is grams/m3 of air Under high humidity conditions the moisture deficit is low and there is

no need by the plant to produce more roots Consequently there is less root development

Under high deficit situations the transpiration rate is high and if roots cannot meet the demand 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/m3

OP = Osmotic Potential - the component produced by dissolved solutes

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

MP = Matric potential - the component produced by the adhesive attraction of water molecules 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 small

in 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 and atmospheric demand change On a typical sunny day in a well-irrigated growing medium, a plant begins to transpire as soon as the sun comes up, assuming that the relative humidity is not very high Once transpiration begins, PWP decreases until the stomata close at which point the PWP levels off Towards sunset, the PWP begins to increase as atmospheric demand declines and the plant replenishes its moisture content from the water in the growing medium

Under high evaporative demand and a moderately dry growing medium the PWP is low

to start with because the plant is unable to completely recharge its moisture supply overnight PWP declines further at noon and continues in the afternoon If this pattern continues, over time, young seedlings can show moisture stress resulting in growth damage

Growing Medium Water Potential

The potential of water in the growing medium solution is called the growing medium water potential (GMWP) and is composed of two parts: OP, which reflects the influence

of 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 medium solution increases as the soil water content decreases due to evaporation or transpiration 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 by matric forces and is related to the size of pores in the growing medium The pore volume of a growing medium is a function of particle size and arrangement and is composed of air and water, which change in inverse proportion to one another

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

"container capacity" When the growing medium is watered to its container capacity the

MP is very high This means that there is little water stress and water is readily available to the seedling

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

WATER QUALITY

Most Alberta growers have access to good quality water but some growers rely on "dug out 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 water quality is determined by two factors:

1 The concentration and composition of dissolved salts

2 The presence of suspended particles, pathogenic organisms, algae, pesticide and herbicide contamination

Effects of salts on irrigation water quality

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

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 ions involved, 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

* Water having a SAR of less than 4

* EC of 0.8 mmhos or less is considered suitable for irrigation of crop plants under normal conditions

* EC between 0.81 and 2.2 mmhos The water is considered marginal in quality but 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 a substitute for potassium Sodium has a serious damaging effect on growing medium structure An excess of sodium ions relative to calcium and magnesium ions can cause clay particles to disperse and seal up the pores, which seriously reduces permeability and gas exchange In peat based media where there are no clay particles, sodium can

be attached to the peat fibre and its concentrations can increase significantly higher in relation to calcium and magnesium Testing of nutrients must be done on a regular basis Toxicity threshold for sodium is around 50 ppm

Bicarbonates

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

WATER TREATMENTS

Dug Out Water

Many Alberta growers collect water from a large run-off area The water is generally of good quality In winter we have seen problems with low water levels and consequently sucking mud with water This can cause two problems: 1 Silt and clay may be deposited in the growing medium and change the porosity and drainage characteristics

of the medium 2 The fungus Pythium, can accompany this water and cause serious

damping off problems

In one case where the dug out was located in a clay area, a large number of suspended particles were delivered to the crop causing water logging Herbicide contamination is another potential problem Treatments are available to remove suspended particles In the case of herbicide contamination, installation of charcoal filters should be considered

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

Hard Water from Wells

If calcium levels are over 100 ppm, then growers must use acid to neutralize carbonates and 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 on their amount present in water supply Phosphoric, nitric, sulphuric and citric acid can be used for this purpose although commercially, the first three acids are more commonly used 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 100,000 litres of water A level of 60 ppm of bicarbonates should be maintained in water to have enough buffering capacity and maintain a pH of around 6.0

pH is logarithmic so it can drop very rapidly after a certain point So don’t depend on the calculation alone Check the pH after the desired amount of acid has been added and then make corrections accordingly We have seen cases where the pH dropped to

a 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 of bicarbonates A level of between 30-60 ppm of bicarbonates should be maintained in the water supply

Acid Millilitres/100 litres of water

High Sodium Water

Some growers have no choice but have access to soft water Such growers use reverse osmosis to make their water usable