Dec. 4, 1916 
Nitrification in Semiarid Soils 
421 
nous materials or other abnormal conditions were employed. In such 
cases the results by the reduction method were frequently much higher 
than by the colorimetric method. Further reference will be made to 
this point later. It is recognized that the colorimetric method is not 
accurate where high concentrations of nitrate occur, but the results are 
believed to be sufficiently accurate for the purposes of this paper. 
EXPERIMENTAL WORK 
The soil used was for the most part drawn from the fertilizer plots 1 
referred to above. This soil has been derived from the disintegration 
of monzonite and is a light, sandy loam, very low in organic matter and 
nitrogen. It is underlain with a deep subsoil similar in nature to the 
surface soil. A composite sample composed of about 20 borings was 
obtained from each plot sampled and also from the virgin soil 2 near by. 
The samples were taken to a depth of 6 inches with a King soil tube and 
were then immediately brought to the laboratory and spread out on clean 
paper to dry. After becoming air-dry and being thoroughly mixed, 
duplicate portions of 150 gm. were mixed in tumblers with 1.5 gm. of dried 
blood, and the moisture content made up to 15 per cent with distilled 
water, after which the samples were incubated at 25 0 to 28° C. 
In order to ascertain the formation of ammonia, 50-gm. portions were 
withdrawn at the end of 7 and 28 days, and the ammonia determined by 
distilling with an excess of magnesium oxid, and at the end of 28 days 
the nitric nitrogen was determined. The average of closely agreeing 
duplicates is recorded in Table I. 
Tabu$ I .—Ammonificaiion and nitrification of I per cent dried bfood (in parts per 
million) 
Soil. 
Ammonia nitrogen. 
Nitric nitrogen. 
After 7 
days. 
After 28 
days. 
Original 
soil. 
Gain in 28 
days. 
Virgin. 
584 
38s 
I. 2 
5 - 5 
Control plot. 
503 
400 
2. I 
2. 5 
Manured plot. 
497 
287 
8.4 
241. 6 
The* foregoing data show that active ammonification took place in the 
soil from each plot studied and that a relatively high concentration of 
ammonia still occurred at the end of 28 days. The lesser amount of 
ammonia found in each case at the end of 28 days was probably due 
in part to the loss of ammonia by volatilization. Strong odors of ammonia 
were detected, especially in the tumblers containing the virgin soil and 
1 It is not deemed necessary at this point to discuss in detail the different treatments that have been 
applied in the field experiments. A more complete discussion will be presented in a subsequent paper. ' 
2 The term "virgin soil’' as used in this paper signifies uncultivated soil still bearing native vegetation. 
