0141731 



Chaney 1980). Typical phytotoxic criteria for total soil zinc 

 were reported by various authors as 250 to 500 ppm (Kitagishi and 

 Yamane 1981, Chapman 1960, El-Bassam and Tietjen 1977, Linzon 

 1978, Kabata-Pendias 1979, Kloke 1979, Melsted 1973, Chaney et al . 

 1978) . The suggested 500 ppm hazard level for the Helena Valley 

 is also the level suggested by Chaney et al . (1978) and has been 

 selected because it best fit data from the reviewed literature 

 (Table 42) . 



The tolerable total soil zinc concentration (200 ppm) is 

 based on the observation that reductions in yields of most 

 species, with the exception of soybeans, were generally low at 

 concentrations less than 200 ppm while levels greater than 200 ppm 

 were shown to result in yield reductions for many crops. Vegeta- 

 tive yields for two of the specific crops of interest for the 

 Helena Valley, barley and wheat, were reported to be decreased by 

 16 percent and 18 percent at total soil zinc concentrations of 200 

 ppm and 300 ppm respectively (Boawn and Rasmussen 1971). Mitchell 

 et al . (1978) noted reductions in wheat grain yields of 3 to 14 

 percent in the 100 to 180 ppm total soil zinc range and 12 to 29 

 percent at 340 ppm total soil zinc. No data were found in the 

 reviewed literature relating alfalfa yields and total soil zinc 

 levels below 200 ppm. 



3.4.2.2 Extractable soil zinc 



The 60 ppm phytotoxic extractable soil zinc hazard level has 

 been selected utilizing data reported by Boawn (1971), Boawn and 

 Rasmussen (1971) and Walsh et al . (1972) (Table 43). Boawn (1971) 

 reported normal yields for 12 leafy vegetables at a DTPA extract- 

 able soil zinc concentration of 55 ppm. Boawn and Rasmussen 



(1971) noted a 16 percent reduction in the vegetative yield of 

 barley at 88 ppm DTPA extractable soil zinc and Walsh et al . 



(1972) reported a 66 percent yield reduction of snap bean pods at 

 47 ppm DTPA extractable soil zinc. The 5 ppm DTPA extractable 

 soil zinc tolerable level is based on the observations of Boawn 

 and Rasmussen (1971) who noted no yield reductions for a number of 



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