CROP ROTATION IN RELATION TO SOIL PRODUCTIVITY 
13 
This greater effect, however, has little or no meaning from the point 
of view of practical farming, since these fertilizer applications are so 
at variance with modern fertilizer practices. Even an annual acre 
application similar to that made on plot 6 may be regarded as exces- 
sive; if not excessive, certainly uneconomical. 
The value of rotation in maintaining the barley yields is greater 
than that of 392 pounds of superphosphate, in continuous culture, or of 
a mixture of chemicals containing 392 pounds of superphosphate and 
200 pounds of sulphate of potash. In comparing plots 4-A, Hoos field, 
and No. 6, Broadbalk field, it appears that this particular fertilizer 
treatment is much more effective on barley than on wheat. 
Of the different fertilizer treatments indicated in Table 2, only 
two can be considered in further study: No. 6 on the Broadbalk 
field and 4-A on the Hoos field, since the treatments on these plots 
come nearest to being comparable with those on the fertilized plot 
2-C,Agdell field. 
ROTATION AND THE USE OF FERTILIZERS CONJOINED 
In order to compare the effects of rotation and the use of fertilizer 
when practiced independently of each other with their effects when 
these practices are conjoined, it is necessary that the same kind and 
quantity of fertilizer be used per acre on a crop in rotation as when it 
is grown in continuous culture. On the rotation plots on the Agdell 
field, plot No. 2 in series C receives the same kind of fertilizer salts 
as plots No. 6 on the Broadbalk field and 4-A on the Hoos field. The 
quantity applied per acre in each case, however, is not the same for 
the rotation period. Nevertheless, these are the best comparisons 
possible on the Rothamsted fields. 
In Table 3 are shown the kinds and quantities of fertilizer materials 
that are applied on the three plots under consideration. 
Table 3. — Fertilizers applied on three plots at Rothamsted 
Crop 
Pounds of fertilizer salts applied per acre 
Total 
per acre 
Field and plot No. 
Ammon- 
ium t 
salts 
Super- 
phos- 
phate 
Sulphate 
of 
potash 
Sodium 
sulphate 
Magne- 
sium 
sulphate 
for each 
rotation 
period 
(pounds) 
Agdell 2-C 
Rutabagas 
Barley 
200 
392 
500 
100 
200 
Legumes , 
} 1, 392 
Wheat 
Hoos 4-A— 
Barley 2 .. 
200 
200 
392 
392 
200 
200 
ioo 
100 
ioo 
100 
3 968 
Broadbalk 6 
Wheat * . 
3,968 
1 Equal parts of ammonium sulphate and ammonium chloride. 
1 Continuous culture, fertilizers applied annually. 
It is to be observed that nearly three times as much fertilizer is 
used per acre on the plots in continuous culture per rotation period 
as on the plot in rotation. Furthermore, on the Agdell field no 
direct application of fertilizer is made to either wheat or barley in 
the rotation. Barley thus receives the residual effects of the ferti- 
lizer one year after its application in the rotation, and wheat receives 
these effects three years after. These points must be kept in mind 
when the following results are considered. 
