Is Hydroponics Really that Easy? Petrus Langenhoven, Ph.D. Horticulture and Hydroponics Crops Specialist January 5, 2017 1 Outline • What is Hydroponics? • Irrigation Water Chemical Quality • Container Media/Substrates … Greenhouse Irrigation Water Quality Guidelines • Nutrient Solution Management … Electrical Conductivity (EC) • Nutritional Disorders … pH • Irrigation Water Biological Quality … Alkalinity and control … Monitoring Biological Quality of Irrigation Water • Hype Around Organic Hydroponics 2 What is Hydroponics? 3 What is Hydroponics? • The word hydroponics technically means working water, stemming from the Latin words "hydro" meaning water, and "ponos" meaning labor. • Hydroponics is a subset of hydroculture and is a method of growing plants using mineral nutrient solutions, in water, without soil. • Two types of hydroponics, solution culture and medium culture. • Solution culture types (only solution for roots) … Continuous flow solution culture, Nutrient Film Technique (Dr Alan Cooper, 1960’s) … Aeroponics • Medium culture types (solid medium for roots, sub- or top irrigated, and in a container) … Ebb and Flow (or flood and drain) sub-irrigation … Run to waste (drain to waste) … Deep water culture, plant roots suspended in nutrient solution … Passive sub-irrigation, inert porous medium transports water and nutrients by capillary action. Pot sits in shallow solution or on a capillary mat saturated with nutrient solution. 4 Photos: Petrus Langenhoven 5 Main Characteristics of Various Growing Systems Source: Pardossi, A. et al., 2011. Fertigation and substrate management in closed systems 6 Open versus Closed Soilless Systems Source: Pardossi, A. et al., 2011. Fertigation and substrate management in closed systems 7 2014/15 season 100.6 kg∙m-2 = 20.6 lb∙ft-2 or 1006 ton∙ha-1 = 449 US tons∙acre-1 or 1006 ton∙ha-1 = 897,352 lbs∙acre-1 Source: http://delphy.nl/en/news/growing-under-100-led-lighting/ 8 Container Media / Substrates 9 Characteristics of an Ideal Container Substrate Generally growers select a substrate based on its availability and cost, as well as local experience Drain fraction of at least 20 – 25% is used to prevent root zone salinization • Adequate mechanical properties to guarantee plant stability • Low bulk density; bulk density lower than 900 kg∙m3 and maybe as low as 80-120 kg∙m3 (light weight) • High total porosity (70-90%), sum of macropores and micropores. Good water-holding capacity (50-65%). Available water (>30%). Air capacity (10-20%). Good aeration and drainage • High permeability to air and water. Even distribution of air and water to sustain root activity • pH of between 5.4 and 6.6 (dolomitic or calcitic limestone can be added to adjust pH) • Low soluble salts content • Chemically inert • High cation exchange capacity (CEC), capacity of substrate to hold positively charged ions; ideal level of about 6-15 meq per 100 cc • Ability to maintain the original characteristics during cultivation • Absence of pathogens and pests • Availability in standardized and uniform batches 10 Popular Container Media/Substrates Inorganic Media Organic Media Natural Synthetic Sand Foam mats (Polyurethane) Sawdust Gravel Polystyrene Foam Composted Pine Bark Rockwool “Oasis” (Plastic Foam) Wood chips Glasswool Hydrogel Sphagnum Peat moss Perlite Biostrate Felt® (Biobased Product) Coir (Coconut Peat/Fiber) Vermiculite Rice Hulls Pumice Expanded Clay Zeolite Volcanic Tuff 11 pH of Different Media | Cation Exchange Capacity CEC - Capacity to hold and exchange mineral nutrients 12 Rockwool Perlite 60% diabase (form of basalt rock, dolerite), Naturally occurring, nonrenewable, 20% limestone, and 20% coke inorganic, siliceous volcanic rock Melted at 2912°F, spun at high speed into thin fibers Grinded and popped at ±1800°F. Expands to between 4 and 20 times larger Heated with phenolic resin and wetting agent to bind them together and lower the natural Characteristics: hydrophobicity of the material. Pressed into Lightweight, sterile, white, porous aggregate slabs Finished product is a “closed cell” that does Characteristics: not absorb water. Water will adhere to Low bulk density and high porosity surface High water-holding capacity (80%) and good Usually included in mixture to improve aeration drainage or increase aeration Chemically inert with pH 6.0 to 6.5 Neutral pH of between 6.5 and 7.5 No CEC or buffering capacity Low CEC Dissolve at low pH, below 5.0 Chemically inert Reusable. Can last for up to 2 seasons 13 Vermiculite Coconut Coir It’s a mica-like, silicate mineral Coconut fiber / dust is an agricultural waste product derived from the husk of coconut fruit Contains mineral water between ore plates Alternative to peat moss and bark When heated at 1832°F, ore plates move Composted for 4 months apart into an open, accordion-like structure Characteristics: Characteristics: Can have high amounts of salts Water and air content varies according to texture Very light, high water retention and good aeration components Low bulk density More fiber – High air and low water content pH value is 7 to 7.5, and low EC More peat – a lot of water and little air Low pH can release Al into the solution Coir is hydrophilic, disburse evenly over the surface of fibers Has a permanent negative electrical charge, and therefore CEC is high Higher pH than peat moss, pH is 5 to 6 Not inert and can store lots of nutrients, high CEC High nutrient content (K, Ca and Mg) Require more Ca, S, Cu and Fe than peat moss. Greater N- Used as component of mixes and in propagation immobilization than peat moss May contain excessive levels of K, Na and Cl. Soak and rinse well before use Use for up to 2 - 3 years 14 Composted or Aged Pine Bark Sphagnum Peat Moss Used in combination with peat for Partially decomposed sphagnum moss, structure predominantly from Canada Available in different colors, indicate degree of Predominant substrate in nursery decomposition industry Light-colored peat, larger particles and limited Screened and aged (4-6weeks) decomposition. Provides excellent aeration and decompose faster than black peat Young bark decomposes more rapidly Black peat is highly decomposed, physical Bark should have little to no white properties vary greatly wood Characteristics: Low bulk density High water-holding capacity High air capacity High CEC Naturally acidic with pH value between 3.0 to 4.0 Low nutrient content, but high CEC Naturally hydrophobic when dry Shrinkage results after water evaporates from pot 15 Summary of Different Chemical and Physical Properties of Some Common Materials Used to Create Growing Media Source: Wilkinson, K.M. et al., 2014. Tropical Nursery Manual 16 Examples of Common Substrate “recipes” Growers can Formulate to Produce Greenhouse and Nursery Crops Source: Owen, W.G. and R.G. Lopez, 2015. Purdue Extension Pub. HO-255-W. Evaluating container substrates and their components 17 Nutrient Solution Management 18 Electrical Conductivity (EC), depends on how many charged particles are present in the solution. Measure of how well a solution or substrate conducts electricity Cations EC H+ Units may be confusing Na+ 1 mmho∙cm-1 NH + 1 dS∙m-1 4 K+ 1 mS·cm-1 Ca2+ 10 mS∙dm-1 Mg2+ Plus micro- 100 mS∙m-1 Anions nutrients 1000 µS∙cm-1 OH- EC reading is impacted by temperature HCO - -1 3 Temp (°F) Temp (°C) EC (mS∙cm ) Cl- 59 15 1.62 - NO3 68 20 1.80 - H2PO4 2- 77 25 2.00 SO4 86 30 2.20 19 What are the Effects of Salt Stress (high EC) on Plants? • Osmotic … Loss of osmotic gradient for water absorption … Worst case scenario: Results in wilting even though the substrate is moist … Prolonged stress may result in reduced growth (shorter internodes and smaller leaves); even without wilting • Toxic concentrations of ions … Excess absorption of sodium and chloride … Excess absorption of micronutrients such as boron, manganese, iron Excessive in Media Low Tissue Level • Carbonate and bicarbonate … High pH will impact solubility of nutrients NH4, Na, K, Ca, Mg Na, K, Ca, or Mg … Over time pH of container substrate will increase PO Zn or Fe … Precipitation of calcium and magnesium 4 • Nutrient antagonisms Ca B … Absorption of one nutrient might be limited by excess concentrations of another Cl NO3 Source: Paul Nelson 20 pH scale is logarithmic. Value will not decrease linearly when acid is added or increase linearly when basic is added • Half of all nutritional Measurements disorders can be attributed to pH- related problems • pH affects nutrient solubility • Only dissolved nutrients are taken up by roots Source: Fundamentals of EnvironmentalSource: Fundamentals The logarithmic scale of pH means that as pH increases, the H+ concentration will decrease by a power of 10. Thus at a pH of 0, H+ has a concentration of 1 M. At a pH of 7, this decreases to 0.0000001 M. At a pH of 14, there is only 0.00000000000001 M H+ 21 Optimal nutrient availability in hydroponic nutrient solution at pH range of 5.5 to 6.5 | Substrate, generally between 5.4 to 6.4 Influence of pH on the availability of essential nutrients in a soilless substrate (container media) containing sphagnum peat moss, composted bark, vermiculite and sand Problems associated with out of range substrate pH www.hydrofarm.com Source: Source: Source: Bailey, D.L., P.V. Nelson, and W.C. Fonteno. Substrate pH and Water Quality 22 Factors Affecting Root Media (substrate) pH • Acidic Media … pH less than 7 … Sphagnum peat moss, pine bark, coir, composts • Neutral Media … pH around 7 … Perlite, sand, polystyrene • Alkaline