The effects of exposure time and rate on the survival and yield of lettuce, barley and wheat

Abstract

Experiments were conducted to compare the effects of 137 Cs gamma radiation given as either 1-, 4-, 8- or 16-hr treatments at constant rates (CR) with 36-hr fallout decay simulation (FDS) or buildup and fallout decay simulation (Bu + FDS) treatments with variable exposure rates. Seedlings of lettuce were given Bu+FDS, FDS and 1-, 4-, 8- and 16-hr CR treatments. Barley and wheat seedlings were given FDS, 8- and 16-hr CR treatments. Following irradiation the lettuce plants were transplanted to the field, barley to the greenhouse and wheat to a growth chamber. The criteria of effect used were survival and yield. Young barley seedlings were given a total exposure of 1600 R at 32 different rates ranging from 60 R/hr to 4800 R/hr. The first leaf of each seedling was measured after 8 days of growth. For equal total exposures, FDS treatments were more effective than 16-hr CR treatments in reducing survival and yield of all three crops. The ratio 16-hr CR/FDS at the LD 50 was 1·43 for lettuce, 1·23 for barley and 1·37 for wheat. For yield, the FDS was more effective only at exposures above the LD 50 . Lettuce survival increased with exposure time between 1 hr and 16 hr but this was a linear increase only after 4 hr. Barley seedling height decreased as the exposure rate increased from 60 R/hr to about 1000 R/hr. Above 1000 R/hr further increases in exposure rate had no further effect on seedling height. The greater effectiveness of the high exposure rates observed in these experiments substantiate our conclusion that the increased effect of an FDS treatment compared to a 16-hr CR treatment is attributable to the high initial exposure rates of the former. Similar results for survival and yield reduction for the 8-hr CR treatment and the FDS treatment were observed. Hence, those investigators lacking the facilities to simulate fallout decay could use an 8-hr CR treatment to approximate the same effects as simulated fallout decay treatments.