AGRONOMY: C. B. LIPMAN 
479 
with certain qualifications soon to be indicated, is the most prominent 
of the four mentioned in connection with the nutritional problems of 
our crops. We are therefore in a position to confirm, as a result of our 
studies on truly arid soils, Stewart's^ statement with respect to the 
intensity of nitrification in them, which was based on studies of the 
more distinctly semi-arid soils of Utah. While we possess ample evi- 
dence in support of Stewart's contention in the respect noted, I feel 
constrained to state that Stewart's criticism of Hilgard's explanation on 
the humus and humus-nitrogen question as between humid and arid 
soils is unwarranted by the facts, as we hope to show in detail in our 
forthcoming publications. The qualification which needs to be made 
with reference to our assertion as to the feeble nitrifying power of arid 
soils is that this power is more distinctly relatively rather than abso- 
lutely feeble. Thus we have found that some forms of nitrogen are 
very readily nitrified by certain arid soils which are not capable of 
nitrifying other forms of nitrogen at all. For example, the nitrogen of 
steamed bone-meal or cotton-seed meal or even of sulphate of am- 
monium is efficiently transformed into nitrate by many of our soils, 
which will not only produce no nitrate in a month's incubation period 
out of dried blood or high-grade tankage, but will even cause a loss of 
nitrate from that already contained in the soil. It appears further that 
the forms of nitrogen which nitrify most readily in humid soils give the 
most unsatisfactory results in arid soils as a general rule. 
The nutritional factor contributing to the unsatisfactory growth of 
our crop plants is evidently then, in general, the soil's lack of power to 
transform enough of its own nitrogen supply or of the supply added in 
fertilizers or manures into a usable form. We must now give considera- 
tion to the theoretical aspects of the reasons underlying the condi- 
tion just mentioned. There can be but little question that the feeble 
powers of the nitrifying flora of arid soils is primarily to be attributed 
to a deficiency in the supply of readily decayed organic matter in such 
soils. Inasmuch as the organic matter serves as a source of energy 
for the microorganisms, its initial small supply in virgin soils of this 
region coupled with the readiness with which it is depleted by oxidation, 
must operate to enfeeble and perhaps destroy the nitrifying bacteria. 
When we remember how small a supply of organic matter we start with 
in our soils and further that long hot dry seasons are the best of conditions 
for its dissipation through oxidation, it is small wonder that soil manage- 
ment by methods intended for application under eastern conditions 
should so far intensify the process, by constant tillage, that the neces- 
sary energy supply for the nitrifying bacteria should soon be so low as 
