a30 



E 



ing the level of pollution in 

 the greenhouse, then gas 

 samples should be collected 

 and sent to commercial or 1 

 academic laboratories — 



at 



equipped with a gas chro- 

 matograph for further deter- 

 mination. On the other lS:o 

 hand, when color change is ^ 

 not detected, it indicates '" 



that either there is no ethyl- 

 ene in the greenhouse or if 

 ethylene exists, its concen- 

 tration is < 0.1 ppm. At 900 

 this level, some ethylene 

 sensitive plants will be af- 

 fected whereas those less _'™' 

 sensitive would not display g«oo 

 symptoms. If a grower de- ~^o\ 

 tects subtle changes in g 

 plants that suggest possible 5 

 ethylene existence in the S300 

 greenhouse, then it would ,„„ 

 be advisable to send gas 

 samples to an analytical 

 laboratory for analysis. ° 



It is best to check for 

 ethylene pollution in the 

 morning before the vents 

 are open and after the fur- 

 nace has been running for an entire 

 night. As soon as the vents are 

 opened, the ethylene gas dissipates 

 quickly and it is unlikely that a 

 grower will detect the existence of 

 the pollutant. Collect the gas 

 samples from the end opposite to 

 the entry point through which some 

 of the ethylene has already escaped. 

 The color changes in the detector 

 tube occur as soon as sufficient air 

 (400 ml for the low-range tubes) 

 has been pulled through the tubes 

 and readings can be taken immedi- 

 ately. With time, the blue color (the 

 reaction of the fillers inside the de- 

 tector tubes and the ethylene mol- 

 ecules) will fade, therefore, stressing 

 the importance of reading the tubes 

 immediately. The fading of the 

 color is temperature dependent and 

 storing the tubes in a cooler (refrig- 

 erator) will slow down the process. 



C2H4 concn. (ppm) 



Figure 2. Determination 

 of ethylene concentrations 

 ranging from 0.2 ppm to 

 50 ppm (A) or from 50 

 ppm to 800 ppm (B) by 

 1 ml of gas injected into 

 a Shimadzu gas chromato- 

 graph fitted with a flame 

 ionization detector or by 

 drawing 400 ml of gas 

 through a GASTEC^"^ gas 

 detecting device fitted with 

 a low-range ethylene detec- 

 tor tube. Data are means 

 + standard deviations of 

 readings contributed by 

 twelve participants tn a 

 blank study. Standard de- 

 viations smaller than the 

 symbols are not displayed. 



200 300 400 500 600 700 



C2H4 Concentration (ppm) 



As previously stated, it is advisable 

 that growers check for ethylene pol- 

 lution in the greenhouse each year 

 when first firing up the heater (ide- 

 ally when the house is vacant) and 

 periodically throughout the winter. 

 Given that many greenhouses in the 

 New England area consist of many 

 small houses, each equipped with 

 their own furnace, it would be a 

 worthwhile investment for a grower 

 to purchase an ethylene detecting de- 

 vice. I suggest that checking for the 

 existence of ethylene in the green- 

 houses should be part of the regular 

 cultural practices, just like checking 

 for pH and conductivity during the 

 growing season. By regularly moni- 

 toring for ethylene in the green- 

 house, a grower will detect small 

 leaks in the furnace before it be- 

 comes a serious problem and destroys 

 the entire crop. 



Acknowledgment: I wish to express 

 my sincere gratitude to New Hamp- 

 shire Growers' Association for partially 

 funding this project and to all of the 

 participants of this project in the De- 

 partment of Plant and Soil Sciences 

 at the University of Massachusetts. 



Disclaimer: Use of trade names in 

 this publication does not imply en- 

 dorsement of products or criticism of 

 those not mentioned. There are other 

 gas detecting devices sold commercially 

 under a different brand name but 

 they appear to work similarly. 



TOTTER 2003 



23 



