CROP ROTATION" IN RELATION TO SOIL PRODUCTIVITY 
47 
These differences in the relation of crop yields to fertilizer results 
are determined by the interaction of three factors: Fertilizer, crop, 
and crop rotation. 
Whether or not a fertilizer will produce higher results on an acid 
soil when its reaction has been altered by liming depends in a large 
measure on the chemical character of the fertilizer. Experimental 
data show that (1) for most farm crops, the highest efficiency of an 
acidic fertilizer is effected on a nonacid soil or on an acid soil that has 
been limed; (2) under the same soil conditions, a basic fertilizer 
usually gives the best, or at least as good results without liming.. 
These two points are strikingly illustrated by the results obtained on 
rotation plots 24 and 29 in the long-time liming tests conducted at 
Wooster. Ohio, as shown in Table 48. 
Table 48. 
■Relation of fertilizer efficiency to change in soil reaction as affected by 
liming, Wooster, Ohio 
Average 
Average 
Increase 
Plot 
Crop 
Fertilizer composition ^^{ 
yield 
per acre 
on acid 
soil, 
yield 
per acre 
on acid 
soil, 
decrease 
in 
fertilizer 
effi- 
ciency * 
unlimed 
limed 
Acidic compound 
24 
Corn 
Ammonium sulphate, acid phos- Bushels 
phate, and muriate of potash. 
45.79 
55.35 
+3.52 
Oats 
do.. do 
51.46 
54.64 
-2.98 
Wheat 
do do 
24.41 
30.63 
+1.33 
Clover 
do Pounds 
1,986 
3,374 
+801. 00 
Timothy 
do do 
Basic compound 
2,740 
4,365 
+712. 00 
29 
Corn 
Nitrate of soda, basic slag, and Bushels 
muriate of potash. 
45.58 
51.16 
-0.13 
Oats 
do do 
50.67 
50.39 
-4.66 
Wheat 
do do 
29.35 
28.76 
-4.00 
Clover 
do Pounds 
2,823 
3,221 
-136.00 
Timothy 
do do 
3,384 
4,107 
-90.00 
1 Calculated from data given in the bulletins to which reference has been made. 
Attention is called to the behavior of the oat crop, which, under 
the conditions of the Wooster experiments, seems to favor acid condi- 
tions, and thus has not been benefited by liming. Furthermore, the 
oat plant commonly shows a preference for ammonium salts, prob- 
ably because of its ability to utilize nitrogen in ammonia form. 
Corn also exhibits the same assimilation ability (7, p. 179). 
When, in a long-continued cropping system, an alteration or change 
of the soil reaction by liming does not effect a greater fertilizer effi- 
ciency, even though the yield of a crop is larger because of the lim- 
ing, particularly when the crop shows but little or no response to a 
direct application of lime, it becomes plainly evident that crop rota- 
tion is the factor which assumes the greatest prominence in the 
maintenance of soil productivity under liming conditions. It is pos- 
sible to evaluate crop rotation under these conditions only when ex- 
perimental data present comparable vields both in rotation and in 
continuous culture. The only experimental data so far published 
that are in harmony with these conditions are those on the first 
