Plant nutrition, water and fertilizer management

PLANT NUTRITION AND FERTILIZER MANAGEMENT IN GREENHOUSE GROWN CROPS 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 CONTENTS Fundamental Aspects of Plant Nutrition Introduction Absorption of Nutrients Essential Macro-Elements Trace or Micro-Elements Water Status and Quality for Crop Production Introduction Water Status Water Potential Water Quality 10 Water Treatments 13 Fertilizer Management Introduction 14 What are the Essential Elements for Plant Growth? What these Numbers on Fertilizer Bags Mean? What are Parts Per Million? 15 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 Principles of Mixing Fertilizers 27 pH, Your Water and Fertilizer? 27 What is Electrical Conductivity 29 Sample Fertilizer Programs………30 27 14 15 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 is 10 times more acidic than a medium with a pH of Similarly, a growing medium with a pH of is 10 times more acidic than one with a pH of By the law of logarithms, a growing medium with a pH of is 100 (10 x 10) times more acidic than a medium of with a pH of This factor of 100 is the reason it is more difficult to raise the pH from pH to than it is to raise from pH to pH This means that if 10 pounds of lime are required to raise the pH from to 6, then 100 pounds are required to raise the pH from to In actual situations, other factors influence the ratios to change the values ESSENTIAL MACRO-ELEMENTS Nitrogen (N) Nitrogen is very important to plant growth and is usually found in the largest amounts in the 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 as nitrate (NO3-) while ammonium (NH4+) and amino (NH2+) can also be absorbed In soil based media there are a group of bacteria present which can convert ammonium nitrogen to nitrate nitrogen These bacteria are not present in soilless media used by growers Consequently ammonium nitrogen can quickly become toxic to roots When bacteria convert ammonium nitrogen to nitrate nitrogen, there is an intermediary step involved That is the formation of nitrites, which are normally very short lived radical but fairly toxic to roots This can happen under low temperature and water logged conditions 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 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, 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 to will result in fast, vegetative growth of plants An equal ratio will maintain good growth while a ratio of to will harden the growth That is why hardening fertilizer regimes contain an N to K ratio of to 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 to 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 Sulfur (S) Sulfur is taken up from the soil in the form of sulfate ions (SO4 ) Small amounts of sulfur may be taken in through the leaves as sulfur dioxide Sulfur seems to be involved in 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 supplied from 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 small amounts Their deficiency or toxicity can occur readily Iron (Fe) Its deficiency has been noted in plants primarily due to alkaline pH in the growing medium It is taken up by the plant in the form of ferrous ions (Fe++) or complex organic salts Iron may also be absorbed as ferric ion (Fe+++) form Plants may contain large 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 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 ppm, has caused problems with tip burning in spruce needles 10 WATER STATUS AND QUALITY FOR CROP PRODUCTION INTRODUCTION Water is essential for plant growth It influences plant growth in four major ways: Water is the major constituent of a plant, comprising 80 to 90 percent of the fresh weight Water is the "solvent" providing nutrient transport within the plant Water is a biochemical reactant in many plant processes, the most important being photosynthesis and respiration 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 10 19 If you use U.S gallons then use a multiplication factor of 0.75 instead of 0.62 If you like metric 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 * grams of fertilizer x grade x 10 = ppm litres of water OR Example I want to make a nutrient solution containing 130 ppm of nitrogen using potassium nitrate 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 grams 13 x 10 I also have 44 percent potash with the fertilizer I used I want to find out how much potash I have Using the formula: - grams of fertilizer x grade x 10 = ppm litres of water 100 x 44 x 10 = 440 ppm 100 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 million equal 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 of nitrogen and 440 of potash REMEMBER: 100 grams/100 liters of water is the same thing as one pound in 100 gallons of water This is because one pound weighs 450 grams and 100 gallons equal 450 liters of water 19 20 SOLUBILITY OF FERTILIZERS Solubility of fertilizers differs in cold and hot water That can play an important role 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 the injector 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 26.0 73.0 1.6 14.0 31.0 203.0 105.0 111.0 Ferrous sulfate 15.0 48.0 Sodium molybdate 56.0 115.0 Magnesium sulfate Borax Copper sulfate Manganese sulfate DIFFERENT SOURCES OF FERTILIZERS Nitrogen Anhydrous ammonia Urea Ammonium nitrate Uracil Ammonium sulfate Calcium nitrate 20 80-0-0 46-0-0 34-0-0 34-0-0 21-0-0 15.5-0-0 21 Potassium nitrate Sodium nitrate 13-0-44 15-0-0 Phosphorus Monoammonium phosphate Diammonium phosphate Monopotassium phosphate 11-52-0 21-63-0 0-53-34 Potassium Potassium nitrate Potassium sulfate Potassium chloride Monopotassium phosphate Potassium bicarbonate Potassium silicate 13-0-44 0-0-50 0-0-62 0-53-34 0-0-46 0-0-12 Calcium Calcium nitrate Calcium chloride Calcium carbonate Calcium hydroxide Dolomite lime 15.5-0-0 + 19 percent ca 18 percent ca 38 percent ca 54 percent ca 22 percent ca Magnesium Magnesium sulfate Magnesium nitrate Dolomite lime 10 percent mg percent mg percent mg SOURCES OF MINOR ELEMENTS Iron Iron sulfate Iron chelate Iron chelate Fe 21 percent Fe 13.2 percent + 68 percent EDTA Fe 7.0 percent + 48.6 percent DTPA Manganese Manganese sulfate Manganese chelate 21 Mn 29.5 percent Mn 13.0 percent + 68 percent EDTA 22 Copper Copper sulfate Copper chelate Cu 25 percent Cu 14 percent + 63 percent EDTA Zinc Zinc sulfate Zinc chelate Zn 35 percent Zn 14 percent + 62 percent EDTA Boron Boric acid Borax B 17.5 percent B 15.0 percent Molybdenum Sodium molybdate 22 Mo 46 percent 23 PREPARING A FERTILIZER PROGRAM Understanding the Design Principles Plants have a vegetative phase and a reproductive growth Vegetative means that it is developing leaves and roots while reproductive means it is producing flowers and fruits Besides temperature, light and watering, fertilizers play a major role in making a plant vegetative or reproductive Most greenhouse plants need to maintain both stages of growth Domination of either stage is not desirable For example, a strongly vegetative tomato or cucumber plant would not yield good fruit Fertilizers containing high nitrogen in relation to potash will cause rapid vegetative growth, assuming that temperature, water and light is not limiting 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 plant maintenance feed Low nitrogen in relation to potash is meant for hardening a plant and also used when plants are flowering and fruiting At that time plants like cucumber, tomato and peppers need higher potash to fill the fruits Examples are 13-0-44, 18-1127 or 8-12-30 High phosphate fertilizers like 10-52-10, 9-45-15 or 10-30-10 are used for good root establishment in the early stages of plant development Remember that you have to provide other elements required for plant growth Step Some nutrients may be available through your water Get an analysis of the water to be used High sodium water is not usable for greenhouse irrigation Nitrogen, phosphorus and potassium are not generally in such quantities that you have to make adjustments Calcium, magnesium and iron are the three elements which may be present in large quantities Availability of calcium and magnesium depends on pH It is our experience that you shouldn't count on 100 percent availability of calcium and magnesium from your water Allow a factor of 25 percent availability of what is contained in your water Iron is in the form of ferric ion and it may not be available to plants If you collect water from the greenhouse then watch the zinc level It may be high enough that you don't need to add any extra zinc in your feeding program Step Work out the volume of water in your irrigation system It is easy to calculate: 23 24 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 in U.S gallons 2) If you are using an injector system then know the size of the stock tank and dilution rates For example if you have a 200 L stock barrel and dilution rate is to 200, then you will multiply 200 with 200 and that will give you a volume of 40,000 liters of water 3) New irrigation systems have a very small mixing tank and water is added based on the demand by the irrigation area Fertilizers are added by a computer using electrical conductivity as a guideline In such cases proper fertilizer 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 are delivering to the plant what you think you are Now we are ready to design a fertilizer program with following nutrient concentrations at plant delivery point: Nitrogen Potassium Magnesium Iron Copper Boron 200 350 70 3.0 0.15 0.25 ppm ppm ppm ppm ppm ppm Phosphorus Calcium Sulfur Manganese Zinc Molybdenum 40 ppm 150 ppm 100 ppm 0.8 ppm 0.2 ppm 0.12 ppm We have a variety of fertilizer sources available to us as outlined in previous tables Step Take all your calcium first You need 150 ppm of calcium and the source is calcium nitrate, 15.5-0-0 + 19 percent calcium Using the ppm calculation formula: ppm desired x litres of water = grams of fertilizer grade of fertilizer x 10 let us plug in the figures: 150 x 100 = 79 grams 19 x 10 If you have an injector at 1:200 dilution ratio and a stock tank of 200 liters then your total amount of water is 40,000 liters You can either use the figure of 24 25 40,000 liters in the formula or multiply the 100 liters figure with 400 to get the final amount of calcium nitrate to be used That will equal to 31.6 kg This amount will be dissolved in 200 liters of stock tank Step Find out how much nitrogen you got by using 79 grams of calcium nitrate in 100 liters of water The formula is: grams of fertilizer x grade x 10 = ppm Amount of water in liters 79 x 15.5 x 10 = 122 ppm 100 So calcium nitrate contributed 150 ppm of calcium and 122 ppm of nitrogen We still require 200 - 122 = 78 ppm of nitrogen Step Get all your phosphorus from mono potassium phosphate 0-53-34 Remember 53 percent is phosphate and we have to convert it to phosphorus by multiplying 53 percent by 0.43 and that will equal 22.8 That is the figure we will use for our phosphorus calculation Using the ppm desired formula: 40 x 100 = 17.5 grams 22.8 x 10 Make adjustments for the amount present in your water Step Calculate the amount of potassium you got from 17.5 grams of 0-53-34 in 100 liters of water Remember 34 percent is potash not potassium Multiply 34 with 0.83 to get potassium which equals 28.2 Thus ppm of potassium = 17.5 x 28.2 x 10 = 49.3 ppm 100 Step Take the balance of nitrogen, that is 78 ppm, from potassium nitrate which is 130-44 78 ppm x 100 litres = 60 grams 25 26 13 x 10 How much potassium is obtained from 60 grams/100 liters of potassium nitrate 13-0-44? Remember 44 percent is potash and it will be 36.5 percent potassium 60 grams x 36.5 x 10 = 219 ppm 100 liters Total potassium from steps and is 268 ppm Total required is 350 ppm Thus we still need 82 ppm of potassium Step Take this potassium from potassium sulfate 0-0-50 which is 41.5 percent potassium (50 x 0.83) Using the formula: 82 ppm desired x 100 litres of water = 19.7 grams 41.5 x 10 Now we have satisfied our requirements for nitrogen, phosphorus, potassium and calcium Step Take all your magnesium from magnesium sulfate which is 10 percent Mg 50 ppm desired x 100 litres of water = 50 grams 10 percent mg x 10 Step 10 Calculate how much sulfur you got from potassium sulfate and magnesium sulfate Potassium sulfate has 18 percent sulfur while magnesium sulfate has 12 percent sulfur Sulfur from 19.7 grams of 0-0-50: 19.7 x 18 x 10 = 35.4 ppm 100 litres Sulfur from 50 grams of magnesium sulfate: 50 x 12 x 10 = 60 ppm 100 liters 26 27 Thus total sulfur is 35.4 + 60 = 95.4 ppm which is close to our 100 ppm of requirement Step 11 Iron required is ppm and will use 13 percent iron chelate: ppm required x 100 liters = 2.30 grams 13 percent iron x 10 Step 12 We need 0.8 ppm of manganese from manganese chelate which is 13 percent manganese 0.8 ppm desired x 100 liters = 0.61 grams 13 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 grams 14 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 grams 14 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 grams 15 percent b x 10 Step 16 We need 0.12 ppm of molybdenum from sodium molybdate which is 46 percent molybdenum 0.12 ppm desired x 100 liters = 0.026 grams 46 percent mo x 10 27 28 This completes our requirements for all nutrients You may have noticed that trace elements are required in very small quantities and it will be difficult to weigh them 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 0.026 grams of sodium molybdate in 100 liters of water Multiply 0.026 grams with 1000 which is equal to 26 grams Multiply 100 liters of water with 1000 as well which is 100,000 liters of water Dissolve 26 grams in one liter of water which is equal to 1000 mL Thus 1000 mL of stock solution is good for 100,000 liters of water Thus mL of stock solution can be added to 100 liters of water Keep the stock solution in a dark glass bottle in a fridge You can mix all the trace elements together and make up a stock solution Keeping individual elements separate 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 making concentrates then certain elements cannot be mixed together Do not mix calcium nitrate with any fertilizer containing phosphate and sulfate It is best 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 When substances dissolve in water they produce charged molecules called ions Acidic water contains extra hydrogen ions (H+) and basic water contains extra hydroxyl (OH-) ions pH is measured on a scale of to 14 Neutral water has a pH of Acidic water has pH values less than 7, with being the most acidic Likewise, basic water has values greater than 7, with 14 being the most basic A change of unit on a pH scale represents a 10 fold change in the pH, so that water with pH of is 10 times more acidic than water with a pH of 7, and water with a pH of is 100 times more acidic than water with a pH of That is the reason why It takes longer time to adjust the pH of the growing medium pH constantly changes during the crop duration and must be monitored regularly Also growers must know 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 the growing medium 28 29 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 optimum ranges * 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 to change the pH from 5.5 to 4.5 than from 6.5 to 5.5 The important fact to understand is that pH also reflects the buffering capacity of a medium It will change slowly How you adjust the pH of a growing medium? You add calcium carbonate lime or dolomite lime to acidic peat moss to make it alkaline Alberta peat moss has a pH between 3.5 and 6.0, therefore liming rates will 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 potassium bicarbonate 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 to monitor pH on a regular basis Plant damage has been observed because of a pH below What you if you detect an acidic pH while the plants are growing? Apply potassium bicarbonate at one gram per liter directly or through the feeding line Do not mix it with other fertilizers Soak hydrated lime 100 grams in 100 liters of water Let it sit overnight and then use the "lime water " to irrigate plants Apply enough volume to thoroughly wet 29 30 the growing medium Many irrigations may be required Rinse leaves after application If pH is on alkaline side then adjust the pH of the fertilizer solution to around 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 Fertilizers with nitrate nitrogen tends to be alkaline in nature Let us look at a few examples: The commercial fertilizer 19-0-16 has a potential acidity of 30 pounds of calcium carbonate equivalent/ton It contains following types of nitrogen - Nitrate nitrogen = 14.4 percent - Ammonium nitrogen = 4.6 percent - Urea nitrogen = percent 17-6-6 has a potential acidity of 1800 pounds of calcium carbonate/ton It has ammonium nitrogen at 17 percent 16-4-12 has a potential alkalinity of 73 pounds of calcium carbonate/ton It has nitrate nitrogen, 9.97 percent, Ammonium nitrogen at 1.05 percent and urea nitrogen at 4.98 percent 13-0-44 has a potential alkalinity of 452 pounds of calcium carbonate/ton It has nitrate 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 in the growing medium will be noticed You can choose acidic or alkaline fertilizers to 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 your water because pH may drop very quickly if too much acid is added to the water There are guidelines available to calculate acid requirements based on carbonate and bicarbonate amounts in water Use proper acid head for injection Metal heads may corrode and may inject too much acid into the system 30 31 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 inefficient groups of plants and if pH goes over 6.5 they will show Iron deficiency Plants like Geraniums and New Guinea Impatiens are iron efficient group of plants and will show iron toxicity at pH below 5.5 Availability of trace elements like iron, manganese, copper, boron and molybdenum is up to times higher when pH moves 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 31 32 How can I monitor the EC of my crop? Measure the EC of your fertilizer solution Measure the EC of leachate from a pot, from a styroblock, from a bedding plant tray or from a rockwool block The EC of leachate should not be more than the E of your fertilizer solution Some recommendations: EC 0.8 mmhos/cm and below EC 0.9 to 2.0 EC 2.0 and above = need fertilizer = maintain feed = caution A higher EC can be maintained if plants are vigorous and demand more fertilizer but 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 growth of plants when water restriction is difficult due to the use of media with higher water holding capacity especially early in the season when light is limiting This is how it works: • • • • • For vegetable seedlings grown in December, January and early February, after transplanting raise the EC by using additional amounts of potassium sulfate 0-0- 52 and feed around an EC of 4.0 The EC of the growing medium could rise to up to 8.0 mS and in that case some leaching with plain water Such a high EC is not detrimental to tomato seedlings as long as there is enough water in the growing media Cucumber, water melon, zucchini, mini- cucumbers seedlings can be well controlled in growth with a feed EC of 3.0 mS and block EC around 4.0 mS 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 mS in smaller volume plugs Once the seedlings are planted in the final container then EC will be managed based 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 some supplemental light in bedding plants trays Once the harvest is completed, the growing medium is reused The plants are very dark green in color and very compact They are not stretching 32 33 Notice the leach E.C Below 3.0 millimhos is normal for winter production The grower mixed the old growing medium with the new one without leaching and that is the result Growers must invest in a good pH and E.C meter and monitor the crop regularly especially crops like petunias and geraniums 33 ... 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. .. 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. .. needles 10 WATER STATUS AND QUALITY FOR CROP PRODUCTION INTRODUCTION Water is essential for plant growth It influences plant growth in four major ways: Water is the major constituent of a plant,