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AQUAPONICS PLANT NUTRITION

Plant Nutrition Hydroponics Aquaponics Uses minerals that are water soluble and ready to be taken up by plant roots Scientific research has provided information on what minerals in what quantities are needed Aquaponics Nutrients available are related to fish Size Number Quantity of food Precise analysis requires a lab report

Plant Nutrition Nitrogen Phosphorous Calcium Potassium Sulfur MACRO Nutrients Micro nutrients Nitrogen Phosphorous Calcium Potassium Sulfur Magnesium Iron Manganese Boron Zinc Copper Molybdenum

Ph and nutrient availability to plants pH – concentration of hydrogen ions 0.0 to 14.0 Less than 7.0 acidic 7.0 neutral Greater than 7.0 basic Important to plant growth Very low pH <4.5 or high pH >9.0 can severely damage plant roots pH level changes directly affects availability of nutrients Majority of nutrients available at pH range 6.0-7.5 Extremely low levels cause some micronutrients (manganese) to be released at toxic levels New, popular grow mediums like perlite, LECA, and rockwool have neutral pH

Concentration of elements Aquaponics – built in fertilizer No precisely mixed formula Supports a variety of vegetables but lacks specific nutrients needed for some fruiting plants

Concentration of elements Average Concentration for Healthy Plant Growth (PPM) Nitrogen (N) (nitrate form) 70-300 Nitrogen (N) (ammonium form) 0-31 Potassium (K) 200-400 Phosphorous (P) 30-90 Calcium (Ca) 150-400 Sulfur (S) 60-330 Magnesium (Mg) 25-75 Iron (Fe) 0.5-5.0 Boron (B) 0.1-1.0 Manganese (Mn) Zinc (Zn) 0.02-0.2 Molybdenum (Mo) 0.01-0.1 Copper (Cu) Carbon (C) Oxygen (O) Hydrogen (H) Are supplied by Water (H2O) And Carbon Dioxide Gas (CO2)

Plant uses of Individual elements Each element has a specific function in plant growth

Nitrogen (n) Component of proteins Essential part of protoplasm Occur as stored foods in plant cells Part of chlorophyll Part of amino acids Part of alkaloids Part of some plant hormones

Sulfur (s) Forms part of protein molecule 0.5-1.5% of this element makes up a plant protein Essential for the action of certain enzymes and coenzymes

Phosphorous (P) Component of some plant proteins (phospholipids, sugar phosphates, nucleic acids, ATP and NADP) Highest percentages of phosphorous occurs in the parts of plant that are growing rapidly

Potassium (K) Accumulates in tissues that are growing rapidly Migrates from older tissues to growing portions Ex: during maturing of crop will move from leaves to fruit

Calcium (CA) All ordinary green plants need calcium One of the constituents of the middle lamella of the cell wall in the form of calcium pectate Affects the permeability of cytoplasmic membranes and the hydration of colloids Found in combination with organic acids in the plant

Magnesium (mg) Constituent of chlorophyll Occupies central position in the molecule Only compound of plants that contain magnesium as stable component Enzyme reactions – mostly those involving transfer of phosphate are activated by magnesium ions

IRON (FE) Number of essential compounds in plants contain iron The site on some electron carriers where electrons are absorbed and then given off during electron transport Role in energy conversion reactions of photosynthesis and transpiration

Boron (b) Exact function in plant metabolism is unclear Plays a role in carbohydrate breakdown Boron deficiency – stunted roots and shoot elongation, lack of flowering, darkening of tissues and growth abnormalities

Zinc (zn) Essential to normal development of a variety of plants Large quantities are toxic

Manganese (mn) Activator of several enzymes of aerobic respiration Deficiency sign is chlorosis Leaf taking on a mottled appearance

Copper (cu) Constituent of certain enzyme systems Ascorbic acid oxidize Cytochrome oxidase Found in plastocyanin – part of the electron transport chain in photosynthesis

Molybdenum (mo) Important in enzyme systems involved in nitrogen fixation and nitrate reduction Plants with deficiency can absorb nitrate ions but are unable to use this form of nitrogen

Deficiencies and excesses Aquaponic crops respond quickly to nutrient deficiencies/toxicities due to no soil buffer Discoloration of foliage Deficiencies are more common than toxicities Potassium Potassium hydroxide Calcium Calcium hydroxide Iron Chelated iron Can add to system in minute quantities with no harm to the fish Plant growth suffers; fruit set might not occur

Nutrient concentration testing Measuring conductivity Electrical conductivity (EC) is a measure of the ability of nutrient salts in a solution to conduct electrical current Helps a hydroponic grower to know the concentration of their fertilizer solution Varies with the concentration of nutrients in the solution as well as the chemical composition of nutrient solution. Higher EC = higher concentration of nutrient salts TDS (total dissolved solids) is also a measurement of the concentration of nutrients

Nutrient concentration testing EC readings in aquaponics can provide a guide to changes in nutrient concentration Reading lower than those in hydroponics Nutrients in aquaponics are continually generating so a lower concentration is required Organic nature of nutrients results in lower concentration of salts and lower EC reading Area needs more study Generally measured at 77°F – raise in temperature will cause a higher reading of EC even though no nutrients have been added; lower temperature will have a lower reading Always measure at a consistent 77°F or purchase a temperature compensated meter

Advanced nutrient testing Neither EC or TDS meter indicate precisely what nutrients make up a solution More complete kits are available for this purpose Many commercial growers test on a regular basis to ensure proper balance of nutrients for optimum plant production Regular leaf analysis is an excellent tool for determining health of plants Dried, crushed, and analyzed Determine exact nutrient content Commercial labs offer more precise results Sometime only way to determine what is wrong with plant since symptoms of deficiencies may be similar

Reference Nelson, R. L. Aquaponic Food Production Raising Fish and Plants for Food and Profit. 2008. Nelson and Pade, Inc. Montello, WI. Pgs. 125-132. With contributions from John S. Pade