Wei Fang and Walter Ray Dept. of Bio-Industrial Mechatronics Engineering

1. Moisture Content Measurement of Bark and Sphagnum Moss Using ECH2O Sensor for the Production of  Phalaenopsis Wei Fang and Walter Ray Dept. of Bio-Industrial Mechatronics Engineering National Taiwan University Taipei, Taiwan, ROC IHC01832

11. Objectives • Find a sensor • Establish a water content monitoring system • Work on Sphagnum moss & bark

12. Why is it important to automatically measure water content in the media? • Skillful hand-watering personnel is not easy to find/ to train. • Hobby growers  professional growers • Increasing production area rapidly • Setting up foreign branch • Uniform quality requirement • …etc.

13. Many sensors available

14. ECH2O Soil Moisture Probes -5 • Probe Type • Dielectric constant measurement • Measurement Time • 10 ms • Resolution • 0.002 m3/m3 (0.1%) • Power • Requirements: 2.0 VDC @ 2mA to 5 VDC @7mA • Output: 10-40% of excitation voltage (250-1000 mV @ 2500 mV excitation) -10 -20 • Manufacturer: • Decagon Devices, Inc., USA

15. ( ) q = - - 0 . 000695 mV 0 . 29 .......... ...... ECH2O 20 ( ) q = - - 0 . 000936 mV 0 . 376 .......... .... ECH2O 10 Campbell, 2004 Converting eqs. provided by the manufacturer are for Soil only. @ 2500 mV excitation

16. 7 soil types tested Campbell, 2004

17. Converting equations for soil can’t applied to other growing media such as Sphagnum moss and bark. Problem

18. PC Indoor Experimental setup HID Lamp continuously on g / g Simulated greenhouse PE roof 雙層塑膠布屋頂 雙層塑膠布屋頂 RI 1203 Growth media w/ sensor (no plants) fan inlet mV ● Loadcell Data logger ●

19. Conversion from gravimetric moisture ratio to Volumetric moisture ratio g water Bulk density g media m3 water m3 media

20. Bulk Density, g/cm3

21. Experiment of Pre-submerge • Before use • Treatment 1: Submerge the barks in water overnight (current practice of most growers) • Treatment 2: No pre-submerge (suggested by the manufacturer) • When use • After filled into the pot, • Watering thoroughly • Allow for drain out • Start recording the sensor output

22. Use it directly, do not submerge the bark in the water before use.

23. Difference due to pre-submerge in Tap water w/ Orchiata bark #5 Orchiata bark #9 Orchiata bark #8 w/o

24. Small conclusions • Pre-submerge makes little difference for bark no.8 (smallest particle) • For large particle, without pre-submerge • Hold little water in the beginning • Dry out easily • Require frequent watering  If watering is conducted manually, pre-submerge will normally preferred. wash-out of add-in Dolomite

25. Difference due to pre-submerge in Tap water Orchiata bark #5 Orchiata bark #9 Orchiata bark #8

26. Converting equations derived for ECH2O-10 Note: y in g/g, x in mV; pre-submerged overnight

27. 3 sources of Sphagnum Moss were investigated Imported from New Zealand (NZ) Chile China

28. Experiment of tightness of Sphagnum Moss filled in a pot

29. Preparation • Before use • Sphagnum moss was pre-submerged in tap water overnight • When use • Pressed until feeling moist not wet (hold with both hands) • Fill the pot with moist sphagnum moss • Watering thoroughly • Allow for drain out • Start recording the sensor output

30. Difference due to tightness of NZ Sphagnum Moss filled into a pot tight loose Photos taken after the experiment

31. Difference due to tightness of Chile Sphagnum Moss filled into a pot

32. Difference due to tightness of China Sphagnum Moss filled into a pot

33. Difference due to sources of loosely filled Sphagnum Moss Sp. Moss from China has the greatest mV output due to high EC of dissolved water. When loosely filled, 3 types of moss performed quite differently. China Chile Sp. Moss from Chile has the greatest water holding capability when loosely filled.

34. NZ Chile China

35. Small conclusions • Some SOPs are required to fill the pot when using Sphagnum Moss as growth media. • Fixed amount of Moss for fixed size of pot is preferred. • Tightly filled is preferred. • Water holding capability Chile > NZ > China Sphagnum Moss

36. ECH2O-10 vs.ECH2O-5

37. Using ECH2O-10 in various EC range Chile NZ China

38. Using ECH2O-5 in various EC range Chile NZ China

39. Small conclusion • ECH2O-5 sensor is less sensitive to EC variation, that make it a better sensor compare with ECH2O-10

40. Converting equations for ECH2O-10 on Sphagnum Moss Note: y in g/g, x in mV

41. Linearequations for ECH2O-5 on Sphagnum Moss Note: y in g/g, x in mV

42. Polynomialequations for ECH2O-5 on Sphagnum Moss Note: y in g/g, x in mV

43. Conclusions • ECH2O-10 and ECH2O-5 can be used to continuously monitor the water content of media used in growing Phalaenopsis. (ECH2O-5 is EC insensitive in the range of 0~2.21 mS/cm) • Converting equations were derived for 3 sources of Sphagnum Moss and 3 sizes of Orchiata bark.

45. Thank you for your attention

47. What is Permittivity ? • The permittivity of a medium is an intensive physical quantity that describes how an electric field affects and is affected by the medium. • Permittivity can be looked at as the quality of a material that allows it to store electrical charge. A given amount of material with high permittivity can store more charge than a material with lower permittivity.

48. What is dielectric constant ? • The dielectric constantεris defined as the ratio: εr= εs / εo = εs /( 8.85 x 10-12 F/m) = εs x 1.13 x 1011 • Where εs: the static permittivity of the material in question, ε0: the vacuum permittivity. This permittivity of free space is derived from Maxwell's equations and is equals theratio D/E in vacuum, whereDis the electric flux densityandEis theelectric field intensity. • In vacuum (free space), the permittivity εs is just ε0, so the dielectric constant is unity.

49. Dielectric constant of some materials at room temperature