38 
BULLETIN 1377, U. S. DEPARTMENT OF AGRICULTURE 
In the last two bars of each series the horizontal and vertical 
hachure may be interpreted to represent either the values for R and F 
(the increases effected by rotation when added to the use of fertilizers 
and the increases effected by the use of fertilizers when added to 
rotation) or the values of r and/ (the increases effected by rotation 
and the use of fertilizers when practiced independently of each other). 
It is to be noted that in the bar showing the yield of wheat on 
plot 11 (rotation and fertilizer) the hachure showing the values for 
rotation (R) and fertilizers (F) overlap to the extent of 4.61 bushels, 
as indicated by the horizontal-vertical crosshatching. This value 
of 4.61 bushels measures the interactive effects of rotation and the 
use of chemical fertilizer when the two practices are conjoined. The 
horizontal-vertical crosshatching also shows how much greater the 
increase effected by the conjoint action of, rotation and the use of 
fertilizer is than the sum of the increases effected by these two 
practices when acting separately. 
GERMANTOWN EXPERIMENTS WITH TOBACCO 
The experiments on tobacco at Germantown, Ohio, were begun in 
1903. Published results cover the 16-year period from 1903 to 1918, 
inclusive (12, pp. 629-634)- The rotation involved consists of 
tobacco, wheat, and clover, grown in the order named. Only 
tobacco is grown in continuous culture. The rotation plots are 
repeated, so that tobacco yields are obtained for each year. 
The Germantown plots are one-twentieth of an acre in size and 
are located on a heavy soil designated as Miami clay loam, which is 
the product of the weathering of a thick bed of glacial drift composed 
largely of the detritus of limestone rocks. Thus, originally, this 
soil was well supplied with carbonate of lime, and for this reason 
tobacco has not responded to liming. The experimental results 
selected for this study have been obtained on unhmed soil. 
The yields of tobacco which are nearest to being comparable are 
those which have been obtained on the plots indicated in Table 36. 
Table 36. — Soil treatment and yields on Germantown, Ohio, plots 
[16-year averages, 1903-1918] 
System of cropping 
Plot 
Crop 
Fertilizer materials used (per acre to 
tobacco) 
Average 
yields 
Nitrate 
of soda 
Acid 
phosphate 
Muriate 
of potash 
Manure 
per 
acre 
Continuous culture. 
I 9 
\H, 14, 17 
f 12 
Tobacco . . 
Pounds 
320 
Pounds 
320 
Pounds 
120 
Tons 
Pounds 
1,064 
875 
do 
18 
(Tobacco _. . 
240 
480 
120 
1,141 
{Wheat 
I 32 
Iciover 
(Tobacco 
10 
993 
{Wheat 
[Clover 
! 
« Same treatment on each plot. 
The data of the tobacco yields on the selected Germantown plots 
are summarized in Tables 37 and 38. 
