GRAIN CROPS 213 



quantity will be withstood fairly well. Loughridge (19) 

 found it to do well in the presence of 740 parts per million 

 of sodium carbonate. Although Dymond and Houston (4) 

 state that barley was growing on soil having been flooded 

 by sea water and containing 16,000 to 20,000 parts per 

 million of salt in the upper six inches of soil, it is probable 

 that the plant roots were not feeding in the zone contain- 

 ing the salts. It withstands black alkali better than 

 wheat. The highest sodium chloride content of soil 

 that barley has been observed to tolerate unaffected was 

 640 parts per million in a California soil (19) which also 

 contained other salts. Traphagen (29) places 10,000 

 parts per million of sulphates as the danger limit for 

 barley where two-thirds of this was sodium sulphate. 

 Barley should be more important as an alkali land crop, 

 Oats are generally considered to be intermediate between 

 wheat and barley in alkali resistance. Kearney's obser- 

 vations (17) indicate wheat and oats to be about equal 

 in this respect, but most others show oats to be the more 

 tolerant, especially of sodium carbonate and sodium 

 chloride. The author (6) found 5000 to 10,000 parts per 

 million of total salts in the upper foot and 6000 to 8000 

 parts per million for the average of the top four feet in 

 soils producing a medium crop of oats. Others indicate 

 much less than this to have caused serious trouble. A 

 very wide difference is noted for the effect of sodium car- 

 bonate, but it appears that from 600 to 700 parts per mil- 

 lion of this salt is as much as is safely withstood. No 

 figures are available for the tolerance of oats to sodium 

 chloride alone or where this salt composes the main alkali, 

 but where much carbonate is present 700 to 1400 is more 

 than the crop can withstand safely. Traphagen (29) 

 places the limit for sulphates the same for oats as for 

 wheat and barley. 



