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Physical Characteristics of Soilless Substrates

Substrate Technology, Water and Mineral Nutrition in Protected Agriculture Workshop. Day 1 Topic 2. Physical Characteristics of Soilless Substrates. Andrew G. Ristvey Extension Specialist Commercial Horticulture. University of Maryland Extension Wye Research and Education Center

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Physical Characteristics of Soilless Substrates

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  1. Substrate Technology, Water and Mineral Nutrition in Protected Agriculture Workshop Day 1 Topic 2 Physical Characteristics of Soilless Substrates Andrew G. Ristvey Extension Specialist Commercial Horticulture University of Maryland Extension Wye Research and Education Center College of Agriculture and Natural Resources University of Maryland

  2. Smarter Substrate Management • Objectives for this topic include: • Review soilless substrate physical properties • Relate those factors to air and water availability • Evaluations for physical properties

  3. Soils vs Soilless Substrates What are the important physical differences between soils and soilless substrates? Parent materials or components Particle size Porosity Air and water availability

  4. Pinebark Perlite USDA System Particle Size Soils Soilless Substrates • Composition • Particle Size = Pore • Texture • Structure ACE / NETC 99

  5. Water %Air % Total Pore Space Soilless Substrates Physical Properties • Three Phases of Growing Media by volume Solid (matrix) – 33 to 50% Liquid (water) – 15 to 45% 45% Solid (matrix) Gas (air) – 10 to 40% Water %+Air % = Total Pore Space 15 - 45% Water 10 - 40% Air Matrix Component Porosity: determines the ratio between

  6. Pinebark Perlite Variability of Components • Peat Moss • Pine bark • Perlite • Coir • Rice Hulls • Shredded palm leaves • and other organics • Sand • Gravel • Vermiculite • Highly Variable • Physical properties • Very porous • Leach very easily • Various combinations • Plant Available Water • the % volume of water that plants can retrieve

  7. Electron micrograph of Sphagnum Peat Component Structure (Handreck & Black, 1994)

  8. Typical Substrates Utilized in Costa Rica

  9. Porosity: Air and Water Availability • Physical Properties Particle Size and Composition: Their affect on: • Air-Filled Porosity (AFP) • Water Holding Capacity (WHC) • AFP - air in the substrate after irrigation / drainage • WHC – water in the substrate after irrigation / drainage

  10. Pores • When we buy substrate---we are buying pores! • What else can affect substrate AFP and WHC? • Handling • Watering • Age • Container geometry • Potting - do not compress substrate - water the plant in

  11. water air water air Soil particles Soil particles Components Affect AFP and WHC Porosity: • Macropores Water drain through freely (< 4mm) • Mesopores  Water at CC (1 to 0.5mm) • Micropores  Water might work as “buffer” (0.5 to 0.03mm) • Ultramicropores  Water held beyond 1.5 Mpa (<0.01mm) Drzal et al. (1999)

  12. Components Affect AFP and WHC • Particle size affects WHC and AFP • Capillary action • water tension - water is attracted • to surfaces with a force large • enough to support a relatively • large mass of water against the • ‘pull' of gravity • the smaller the particle, the • more firm the hold

  13. Components Affect AFP and WHC • Physical Properties : Pore Size • Pore size affects WHC and AFP

  14. Soilless Substrates Important Attributes of Soilless Media • Recommended physical characteristic values for soilless • substrates, after irrigation and drainage are (% volume): • Air-Filled Porosity - 10 to 30% or 20 to 35% (field test) • Water Holding Capacity - 45 to 65%; • Available water content - 25 to 35%; • Unavailable water content - 25 to 35%; • Note: A substrate with many coarse particles has a large air space • and a relatively low water holding capacity.

  15. W2 – (W5 + W4) X 100 WHC = % W3 Field Test for AFP W1 = Saturated container media W2 = Drained container (several hours later) W3 = Volume of Substrate W4 = Weight of Container W5 = Weight of Dry Media Saturation W1 – W2 AFP X 100 % AFP = W4 W3 – Total Volume

  16. Substrate Technology, Water and Mineral Nutrition in Protected Agriculture Workshop Day 1 Topic 3 Substrate Management Andrew G. Ristvey Extension Specialist Commercial Horticulture University of Maryland Extension Wye Research and Education Center College of Agriculture and Natural Resources University of Maryland

  17. Smarter Substrate Management • Objectives for this topic include: • Composting and aging • Storage of substrates • Handling of substrates

  18. Composting and Aging Compostingis a biological process where complex organic material is degraded into more basic organic components at a rate faster than decomposition would occur naturally. Aerobic Composting is a thermophilic (generating heat) process Aging is not composting, because there is no heat generation

  19. Composting and Aging • The process of efficient composting requires several ingredients. • The basic recipe: • A source of organic material • Microorganisms • C:N ratio of more than 30:1 – this may mean the addition of • a nitrogen or carbon source • Proper moisture levels – 45 to 60% by weight • Oxygen • pH stabilizer, if needed

  20. Composting and Aging Composting Chemistry: The C:N Ratio

  21. Composting and Aging • The result of efficient aerobic composting is . • Generation of Heat ≈ 55 Co • C:N Ratio of between 10 and 15 : 1 • Degradation of organic material and increase Cation Exchange Capacity

  22. Composting and Aging Microorganisms

  23. Composting and Aging The Aerobic Cycle http://www.theteggroup.plc.uk/technical_library/microbiology_of_invessel_composting

  24. Cellulose Lignin Composting and Aging • Cellulose and Lignin… • Why some substrates degrade • faster than others • Cellulose is a sugar • Lignin is a more • complicated molecule • and more difficult • to degrade

  25. Composting and Aging • When it goes wrong… • Compounds like alcohols and methane are developed in anaerobic composting. • Weed and pathogens are not destroyed

  26. Adding Compost to Growing Media • Consistency – can you assure? • Well/properly composted • Water Holding capacity Pore Space? • Nutrient availability • what is in compost? • adjust your nutrient management plan?

  27. Adding Compost to Growing Media • First, analyze your compost • All macro and micro nutrients • How much should be added? • Base your addition on nutrients, WHC AFP and EC • Usually no more than 20% • Check your WHC and AFP

  28. Smarter Substrate Management • There are three lines of defense against plant diseases • To prevent pathogens from entering the production systems • Create cultural conditions that work for plant growth and against disease development • Correctly and timely treat disease problems that do arise But first… Prevention! is crucial to successful plant health management

  29. Storage of Substrates

  30. Storage of Substrates • Storage – high and dry? • Potting - do not compress substrate - water the plant into pot • What else? • Handling • Watering • Age

  31. Storage of Substrates

  32. Practical Examination for Substrates • Capillary Force practical experiment • Particle Distribution Analysis • Field Porosity and water holding capacity tests Question: Does particle size affect AFP and WHC?

  33. Substrate Re-use and handling

  34. Substrate Technology, Water and Mineral Nutrition in Protected Agriculture Workshop Day 2 Topic 4 Irrigation in Protected Environments: Checking Irrigation System Efficiency John Lea-Cox and David Ross Nursery Extension Specialist / Extension Engineer University of Maryland Extension College of Agriculture and Natural Resources University of Maryland

  35. Overhead Irrigation Systems The pros and cons of overhead irrigation systems. • Cons • Efficiency low - depending • Larger volumes needed • Higher pressures needed • Pros • Easy management • Lower labor costs • Less infrastructure

  36. Micro Irrigation Systems The pros and cons of microirrigation systems. • Cons • Greater management • Higher costs – more specialized equipment needed • Potential Higher labor costs • Pros • Higher Efficiency • Less volume needed • Lower pressures • Less waste

  37. Irrigation Audits Summary Is your irrigation system working properly? First, do an inspection & repair problems. Second, check pressures and flow rates. Third, do a test for uniform application. Decide on changes to improve system and water wisely. ACE / NETC 99

  38. Uniform Water Application? Applying water uniformly should be goal # 1, particularly for container crops Question - Where are your dry spots after irrigation? If none, do you knowingly overwater some plants to adequately water other plants? How do I check my irrigation system? ACE / NETC 99

  39. System Audit Procedure First, inspect for problems and repair them. 1. Damaged pipelines and risers 2. Damaged, clogged, worn, or broken nozzles or drip tubes. ACE / NETC 99

  40. System Audit Procedure Second, check pressure and flow rate. 1. What were the pressures and flow rates of the system when new? 2. Check pressure at pump, beginning and end of laterals, and before and after filters. 3. Check the nozzles for wear and flow rate. Check drip tubes for clogging. ACE / NETC 99

  41. Pressure Check Installed or Portable Pressure Gauges

  42. Pressure Check Filter Pump Pressure Gauge Laterals – drip or sprinkler

  43. Pressure variation in a Lateral For good design, pressure variation from one end of a lateral to the other should not exceed +/-10 percentof the average lateral design pressure. Actual variation in lateral is 20%. Average of 50 psi 45 psi 55 psi

  44. Nozzle Pressure versus Water Distribution Pattern Too High Correct Pressure Too Low Pressure affects Application Pattern Correct operating pressure is best! Pressure too high or too low causes distortion of application pattern.

  45. Nozzle Flow Rate Use a bottle or bucket to catch the water discharged from the nozzle for one minute. Measure the volume of water caught. Convert to gal/min.as in nozzle chart. Measure nozzle pressure, if possible.

  46. Nozzle Flow Rate RainBird 14DH Nozzle (new) specs for water discharge at a given pressure.

  47. Nozzle Flow Rate RainBird 14DH Note changes in gpm for changes in PSI.

  48. Nozzle Wear Check Use drill bit to check size carefully.

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