164 BOTANICAL GAZETTE [MARCH 
ammonifying organisms. There are three chlorides, one nitrate, 
and one sulphate which were slightly more toxic for nitrifiers than 
for ammonifiers. In most cases the resistance of the ammonifiers 
to salts is sufficiently greater that nitrification in a soil may be 
materially decreased without seriously interfering with ammonifica- 
tion. Moreover, the toxicity of salt increases with concentration 
much more rapidly toward nitrifiers than toward ammonifiers. 
TABLE II 
MOLES OF THE VARIOUS SALTS PER 100 GM. OF SOIL REQUIRED TO RETARD 
NITRIFICATION IN SOIL IN UNIT TIME 
Chloride Nitrate Sulphate Carbonate 
COM ei 7B io 7 | sb 167% aX x07%") 685X107? 
Potassium. 5 52.52 sk. 3 ac6X10—" | 419% t0—" | I5s6X10—' | 150K I1O~" 
PION tio! | sraX10~' | reo x10" | 645K 10" 
Manganese es 312 XI0—? 25x 10-* tX 1907? 78X10—7 
We mio * | «550 X10") TSO Xo | 150K 10 
Magnesiim.: - soe. fi: 48X10-7 798X107" | 625 xX 10-7 IBXKI0=* 
* Not toxic at 3 X1o—3, highest concentration tested. 
TABLE IT 
MOLES OF THE VARIOUS SALTS PER I00 GM, OF SOIL REQUIRED TO RETARD 
AZOFICATION IN SOIL 
Chloride Sulphate Nitrate Carbonate 
RM Se axio—= 2xX10—-* ax i967 2 107% 
Potamiun. . 6.526 2X10-— 1X10-3 2X10-3 125 X10—* 
Caicttin: 3 5G oo mea 110-"" 1xXr10~-* on” 
rnonectint: 0.0). 7o. +x<167*" 1x10-" x16" TX 107 - 
MORRDADEN ee, od. 1X10-* 1xX10-3 <10-** 1x167 
eS Sarin EE ae 5xX10—” Ce aioe 5x 10~* 5xX10—* 
The order of toxicity of the anion in the case of the nitrifiers is 
nearly the reverse of that for the ammonifiers. The order for 
nitrification is CO,;>NO,>SO,>Cl, whereas the order of toxicity 
of the cation as measured in terms of nitrification becomes K >Mg 
>Fe>Mn>Ca>Na. It is evident, therefore, that both the anions 
and cations exert an influence in determining the toxicity of the 
salts. - 
Examining nitrogen fixation (12) in the same light the results 
given in table III are obtained. 
