170 TJniversiixj of California Publications in Agricultural Sciences [Vol. 1 



Owing to the general distribution of the efficient ammonifying 

 organisms above described in most soils, it is extremely improb- 

 able, to judge from our results, that we may look forward 

 to a protitable form of inoculation of soils with ammonifying 

 bacteria. The choice, however, of the form of nitrogenous fer- 

 tilizer for a soil, which will be most readily made available, when 

 available nitrogen is needed, may indeed be something of much 

 greater practical significance, a.s our data would appear to 

 indicate. Particularly emphatic are our results in illustrating 

 that, at least so far as pure cultures are concerned, and as also 

 partly shown by J. G. Lipman-^ and others, with mixed cultures, 

 prevalent ideas with respect to the relative availability of common 

 nitrogenous fertilizers are incorrect. Both tankage and cotton- 

 seed meal, and, in some cases, fish guano, show higher avail- 

 abilities than dried blood, which we have always been in the 

 habit of regarding as the most available of organic nitrogenous 

 fertilizers (based only on vegetation tests). 



Nor do we argue too far afield from our subject when we 

 make the remarks just preceding. We recognize fully that 

 availability as measured by ammonification does not necessarily 

 denote availability as measured by nitrification nor by assimila- 

 tion of nitrogen by plants. We cannot, however, help noting, 

 also, that a persistent preference exists among practical orchard- 

 ists in this state for tankage as against dried bood and we 

 therefore feel that, judged by other critera, similar conclusions, 

 must be drawn to those adduced from our experiments with pure 

 cultures of ammonifying bacteria. 



We have decided, however, to go much further in these experi- 

 ments and are now prosecuting more elaborate investigations on 

 nitrogen transformation not only to ammonia but also to nitrates. 

 In these studies we shall deal with the soil flora as existing in a 

 large variety of soil types freshly collected from the field for our 

 purposes. Moreover, we shall employ the raw, unsifted fertilizer 

 material just as it is used by the farmer. From these investiga- 

 tions we hope to glean much more evidence which will be of 

 great practical significance, and, like the results above described, 

 also of marked scientific interest. 



