Crop Rotation 291 
The average for the incubated samples was 39.14 parts of nitrate. 
The months of May, June and July were highest, but the first six months 
all showed a high content for the incubated samples. 
TABLE 7. 
Nitrifying Power—Difference Between Fresh and Incubated Samples. 
Series Nitrates—Parts Per Million 
Number and Plot No. and : 
Rotation 1920 Crop | Mar. Apr. May | June July Aug. | Sept. Oct. Ave. 
I, E— 1 Wheat...} 36.59 | 22.27 | 15.44 | 20.13 3.85 2.62 3.62 4.14 | 13.58 
Corn, Wheat....... ZACOTDE.-e:- 16.43 | 28.57 | 15.29 | 47.05 3.69 | 55.68 | 30.16 | 12.48 | 26.17 
II, E— isComee..- 24.74 | 24.11 | 21.87 | 47.67 | 26.65 | 14.94 | 18.27 6.27 | 23.07 
Corn, Oats, Wheat..| 2 Oats..... 26.700) 26:12 |) Lie 38 | 10.77 | 1546 7.73 | 13.99 8.30 | 15.81 
3 Wheat 16.26 | 28.38 | 15.41 | 29.30 | 13.02 | @J.87 5.39 6.22 | 14.48 
Ill, E.— 1 Unlimed..| 12.22 | 29.33 | 18.90 | 10.73 | 10.92 6.71 5.70 4 14.58 | 10.95 
Cont. Wheat....... 2 Limed...| 16.49 | 32.39 | 15.24 | 24.60 | 23.09 4.59 | 10.63 | 11.57 | 17.32 
I, W.— ANOatS ee 19.43 | 34.59 | 17.24 | 20.13 | 11.28 ete) asl 6.17 | 15.46 
Corn, Oats, Wheat) 2 Wheat 20.38 | 24.64 | 20.86 | 26.66 | 14.73 |} 7.78 | 5.50} 4.14 | 15.58 
RSIS Ec 2 ve 22 e-ese) 3 Beans....| 20.24 | 17.68 | 16.92 | 99.83 | —.03 0. 7.14 2.02 | 20.48 
4 Corm:.-. - 16.05 | 21.91 | 15.21 | 30.07 | 11.60 | 13.38 | 11.42 6:13 | 15.72 
, W— tomes... 24.68 | 15.49 | 29.31 | 50.27 | 15.48 | 79.68 Tow 8.25 | 26.98 
Corn, Wheat, Beans.| 2 Wheat 24.09 | 24.29 | 17.71 | 14.59 | 11.63 3.01 3.74 (yeaa ee ly 
3 Beans 32.99 | 32.85 | 17.37 | 34.33 | 15.11 7.88 | 20.49 | 77.5 29.81 
(Cont. Corn) 
BU aat\ Gs Se ee eee 1 Cormeen. = 12.85 | 17.59 | 48.92 | 38.03 7.75 | 25.25 9.32 2.06 | 20.22 
AvexallPlOtsins ea dctecesrs snes Ziessn|| 2osco | coal o2e80) | iae2e | lo.47 | Oral ICS | 
DISCUSSION OF TABLE 7. 
Nitrifying Power of the Various Plots as Determined by the Dif- 
ferences between the Untreated Incubated and the Fresh Samples. 
The averages for the period of the differences between the un- 
treated and fresh samples are 13.58 parts, 14.48 parts, 10.95 parts, 
17.32 parts, 15.58 parts and 13.17 parts of nitrates per million parts of 
moisture-free soil for the plots containing wheat. The lowest average 
was found for the unlimed continuous wheat plot, and the highest aver- 
age for the limed continuous wheat plot. 
The averages for the period for the corn plots were 26.17 parts, 
23.07 parts, 15.72 parts, 26.98 parts and 20.22 parts of nitrate per mil- 
lion parts of moisture-free soil. The lowest difference, 15.72 parts, was 
for the corn plot in the corn, oats, wheat, soybean rotation, Series I. W., 
which plot also showed a low average for the fresh samples. This plot 
contains a large amount of gravel when compared with the other plots. 
The averages for the oat plots were 15.81 parts and 15.46 parts of 
nitrate per million parts of moisture-free soil. 
The averages for the soybean plots were 20.48 parts and 29.81 
parts per million. 
These results in Table 8 show that the nitrifying power of the 
corn and soybean plots as measured by this test is nearly the same, 
and is much higher than the nitrifying power of the wheat and oat 
plots, which plots are about equal in nitrifying power. 
