Assessing effects of ambient ozone on injury and yield of bean with ethylenediurea (EDU): three years of plant monitoring at four sites in The Netherlands.

EDU (ethylenediurea) and non-EDU-treated bean plants (Phaseolus vulgaris L. cv. Lit) were exposed to ambient air at four rural sites in The Netherlands during the growing seasons of 1994 through 1996 to investigate the responses to ambient ozone. Ozone-induced foliar injury was observed each year and differences in injury between sites depended on year. On average, injury amounted to 27% in 1994, to 8% in 1995 and to 1% in 1996. Injury increased with increasing ozone exposure (AOT40) and the estimated AOT40 value corresponding with 5% injury was circa 3650 nl l(-1) h ozone. The highest ozone levels accumulated at each site for five consecutive days before injury exceeded the proposed short-term critical level for injury development. EDU reduced injury and its protective effect was positively related to the injury intensity in non-EDU-treated plants. Yield of green marketable pods (intermediate harvest) and mature pods (final harvest) was generally reduced in non-EDU-treated plants compared to EDU-treated plants and differences in yield reduction between harvests varied between years. The yield of mature pods was reduced in 1994 and 1996 while the yield of green pods was reduced in 1995 by ozone only. Since yield reduction was not correlated with AOT40. the EDU method was not valid to determine an ozone exposure-yield reponse relationship for bean.