446 
Journal of Agricultural Research 
Vol. Y, No. 10 
of the data given in Table III with those secured at the beginning of the 
experiment (Table I) can be made, for on October 15 the moisture in the 
first foot of every plot except H was within the' limit of variation, where 
by preliminary tests the effects due to water can be appreciated by our 
means of measurement. Therefore, disregarding water as a factor, it is 
apparent that cowpeas possibly have a tendency to maintain the friability 
of either plowed or unplowed land. The data also show that the plot G, 
plowed and artificially shaded, was almost as compact as the adjoining 
plowed plot (H) which was not shaded. This may be interpreted either 
that the shade was inefficient or that the loosening of the soil is due to 
some other factor. From the conclusions of Wollny 1 on this point and 
from the experimental data to be presented below it seems probable that 
this preservation of soil structure is due to increased bacterial activity, 
resulting in the formation of humus. This was actually demonstrated 
by Wollny. 
The nitrate analysis of the plots at the close of the experiment, together 
with the bacterial count and the nitrifying and ammonifying efficiency, 
is given in Table VI. 
Table: VI.— Nitrate analysis, bacterial count, and nitrifying and ammonifying efficiency 
of soil on October J5, IQI2 
Item. 
Depth. 
Plot D 
(unplowed; 
clean). 
Plot E 
(unplowed; 
cowpeas). 
Plot F 
(plowed; 
cowpeas). 
Plot G 
(plowed; 
shaded). 
Plot H 
(plowed; 
clean). 
First foot... 
16.93 
9.76 
17- 833 
5. 06 
40. 91 
Nitrate as NO s 
Second foot 
5. 88 
4.42 
7. 08 
n. 55 
IO - 3 ° 
...p. p. m.. 
' Third foot.. 
6. 31 
9. 18 
4. 08 
18. 42 
10. 20 
.Fourth foot 
4. 42 
3 * 73 
4.48 
4.72 
7- 69 
Number of bac¬ 
teria per 
gram of soil. 
First foot. . 
8,481, 000 
29,985,000 
17, 929, OOO 
9 > 344 , 400 
7, 720, OOO 
Ammonifyi n g 
efficiency.« 
.do. 
197. 19 
166. 20 
177 * 50 
163. 80 
167. 20 
Nitrifying effi¬ 
ciency. 
73 - 5 ° 
1 
65. 40 
99-25 
124. 25 
! 
-s- 50 
a The determination of ammonia in the ammonifying-efJiciency studies was made by the distillation 
and titration method. 
The amounts of nitric nitrogen in the soil in the fall, as shown by the 
data of Table VI, reveal the fact that all plots are going into winter with 
more available nitrogen in the soil than they contained in the early 
spring, as shown in Table II. It is also seen that cultivated plots, either 
cropped or uncropped, are richer in nitric nitrogen at the end of the 
season than are the plots not plowed. The low nitrate content of the 
first foot of the plot artificially shaded can not be explained. Lastly, 
the results check with previous investigations in the fact that under even 
a legume treatment there exists less nitrate in the soil in the fall than 
1 Wollny, Ewald. Op. cit. 
