74 



tion in each instance; similar effects were produced by 

 heating to still higher temperatures." 



Working with soils from the Pennsylvania plots, 

 Given (6) found at the end of 7 days, that the acid soil 

 from plot 32 had produced the greatest amount of am- 

 monia from dried blood. This result was confirmed by 

 repeated experiments. Further studies showed the 

 soil from plot 32 incapable of supporting more than a 

 very feeble nitrification. 



White (23) has shown b}^ laboratory studies on the 

 acid soils from the Pennsylvania plots that nitrification 

 of organic substances proceeds at a very slow rate, and 

 that ammonium sulphate is not at all nitritied. 



Both Greaves (5) and Brown (2) have shown that 

 ammonification may proceed after the addition of 

 considerable amounts of manganese salts to soils; 

 but Brown's work indicates that the nitrifying organ- 

 isms are rather sensitive to manganese compounds. In 

 view of the fact that soluble manganese has been found 

 in the soil from Pennsylvania; and manganese, alumi- 

 num, and iron in the Hawaiian soils, it seems probable 

 that these compounds in solution may be responsible, 

 in a large measure, for the reduced, or inhibited, nitri- 

 fication in these soils. This view is not necessarily in 

 conflict with the observations that nitrification does 

 take place in acid field soils carrying a large amount of 

 such elements in solution. In times of drought, the 

 writer has often noted that there was a large accumu- 

 lation at the surface of the salts contained in soils. At 

 times, nearly the entire nitrate and soluble manganese 

 content of our plot soil has been found in the top inch 

 of soil. To substantiate this view the following is 

 given. In November, 1917, the surface soil from about 

 5 square feet was scraped from one plot, to a depth of 

 about one-half inch. A water extract of this soil con- 

 tained 200 p. p. m. of manganese, and 1200 p. p. m. of 

 nitrates. Another sample taken from this area, after 

 the first had been removed, gave an extract with 10 

 p. p. m. of manganese, and 225 p. p. in. nitrates. Pea 

 cultures grown in these extracts produced .064 and .091 

 grams of roots, and .164 and .314 grams of tops, re- 

 spectively. 



White presents data showing that similar conditions 

 may obtain in the soil studied by him. During these 

 periods of dry weather, when the salts are largely con- 

 centrated at the surface, nitrification may proceed in 

 the deeper layers of the soil; again, with the coming 



