CROP ROTATION IN RELATION TO SOIL PRODUCTIVITY 
51 
The results of the long-continued liming tests herein recorded are 
few in number and hence inadequate in forming the basis of a general 
statement or principle; yet from a study of the data as summarized 
in Tables 47, 49, and especially 50, it would seem that, under the con- 
ditions of these experiments, the liming problem, with respect to 
productivity maintenance, is primarily a clover-rotation problem, and 
that the increases in the yields of such crops as wheat, corn, and oats 
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Fig. 7.— Chart visualizing the effects of soil reaction on the effectiveness of rotation and the use 
of fertilizer, as indicated by the yields of wheat at Wooster, Ohio. The plot numbers are given 
below each bar. L indicates the plots receiving lime. The horizontal-vertical crosshatching 
in each of the last two bars in the chemical-fertilizer series indicates (a) how much greater the 
actual increase effected by conjoining rotation and the use of fertilizer is than the sum of their 
separate increases, and (6) the unallocated increase effected by the interaction of rotation and 
the use of fertilizer 
which may result when soil acidity is reduced or neutralized are due 
to indirect effects of liming. 
Ill Figures 7, 8, 9, and 10 are visualized the results of the long-time 
liming tests herein described. In each case it is shown what propor- 
tion of the yield is credited to cultivation alone, the increase m yield 
effected by combining rotation or the use of fertilizers with cultiva- 
tion, and the increase effected over cultivation by conjoining rotation 
and the use of fertilizers. 
