Abstract
A study was conducted during April 2007 to May 2009 to examine the ozone status, its effects on crops and to mitigate ozone losses in Bangladesh Agricultural University Campus, Mymensingh. Ozone concentrations were measured at 4 weeks interval using passive samplers. The first pair of passive samplers were exposed April'07 and continued 5 times till December'07. Experimental result showed that ozone concentrations were recorded as 16.75 - 34.75 ppb. Two pair of passive samplers were exposed during January and April 2008 where the ozone concentrations were within 19.75 - 34.75 ppb. In 2009 the passive samplers were exposed upto 4 times (January-April) and found that ozone concentrations varied from 17.25 to 36.25 ppb. The variations of ozone concentrations in the month of January of 2008 and 2009 were between 17.25 - 19.75 ppb. The ozone concentrations in the month of April of 2007 2008 and 2009 ranged from 29 to 36.25 ppb. There was also a good positive correlation between the ozone concentration with temperatures and total sunshine hour. The same application ensured negative correlations with the RH values. Ozone biomonitoring study used O₃ sensitive (NC-S) and O₃ resistant (NC-R) white clover genotypes and worked on the principle that the difference in plant foliar injury as well as the biomass ratio between the O₃ sensitive and O₃ resistant clover genotypes can be directly related to the prevalent O₃ concentrations during the exposure period. The experiment was conducted in two growing seasons starting from April 2007 to January 2009. Virus-free clover cuttings 7-10 cm long, with 3- 4 leaf nodes were planted in 11 pots in glasshouse and 15 l volume white pots with 30 cm diameter. The injury assessments were made on the same day per week. The experimental results revealed that the ozone-resistant clover genotype NC-R had on average a higher biomass as compared to the biomass of the ozone-sensitive clover genotype NC-S at all harvests. Accordingly, the biomass ratio NC-S/NC-R genotype was between 0.50 and 0.69, and 0.75 and 0.87 in the first and second experiment respectively. However, the difference in the average biomass per pot between the two genotypes was only significant at harvest 2ⁿᵈ, 3ʳᵈ and 4ᵗʰ of the 2007 and harvest 2ⁿᵈ and 3ʳᵈ of the 2007/08 growing period. The medium foliar injury class of the NC-S plants varied slightly during the growing periods with the peak damage being reported for the 2ⁿᵈ harvest during the 2007 and the 2ⁿᵈ and 4ᵗʰ harvest during the 2007/08 experiment. The median injury score never exceeded injury score class 1. The NC-R plants never expressed ozone-induced foliar injury. Chemical protectant study using ethylenediurea (EDU) was also carried out with local crop varieties such as potato, mungbean and Indian spinach. Fifty percent of the plants were treated with EDU solution freshly prepared in deionized water. An EDU-concentration of 300 ppm was applied to spinach, whereas mungbean and potato required a concentration of 400 ppm EDU. The EDU application was repeated every 10 days up to the maturity of reproductive parts with an increasing amount of solution after every second treatment. Control plants (approx. 20) were treated with the similar amount of deionized water. The weekly injury symptoms were assessed on the same day per week. EDU treated potato plants showed better growth and yield attributes than that of potato plant cultivated without EDU. During the potato growing period the ozone concentrations was comparatively lower (16.75 ppb in December 227), so only 2 plants showed medium injuries. Mungbean plant cultivated with EDU produced highest plant height, no. of branch/plant, no. of leaves/plant, no. of pod/plant and dry wt./plant. Mungbean plant cultivated without EDU showed lower plant attributes. Visual ozone injury on mungbean plant was also observed with 20% of plants (cultivated without EDU) suffering from ozone injury. Indian spinach plant grown with EDU also produced higher growth attributes such as plant height, no. of branch/plant, no. of leaves/plant, leaf length and leaf breath. The fresh weight and total dry matter (TDM) were also higher in Indian spinach plant grown with EDU than that of crop grown without EDU. Forty percent of the plants showed visual ozone injury and 2 plants produced medium level of injury. Plant cultivated with EDU showed no injuries on leaves which enhance the fresh leaves of Indian spinach. However, it may be concluded that the prevailing O₃ concentrations at the experimental site led to a decrease of crops biomass.