66 BULLETIN 1377, U. S. DEPARTMENT OF AGRICULTURE 
Under the conditions of the 16-year tests on tobacco at German- 
town, Ohio, crop rotation is from 12.5 per cent to 28.3 per cent as 
effective as the use of chemical fertilizer and about 33 per cent as 
effective as the use of a 10-ton application of manure. When rota- 
tion and the use of fertilizer are combined, their effects are some- 
what less than fully additive (pp. 38-39). 
Under the conditions of the experiments on brown silt loam at 
Urbana, 111., results for 14 years show that crop rotation without 
fertilizer is 302.2 per cent as efficient as the combined use of manure, 
phosphate, and lime without rotation in effecting increases in the 
yield of corn (over check plot in continuous culture). When rota- 
tion is added to the use of fertilizers, the increase effected is 113.4 
per cent greater than when the use of fertilizers is added to rota- 
tion. When rotation and the use of fertilizers are conjoined their 
combined effects in increasing the yield of corn are more than fully 
additive (pp. 39-41). 
The 6-year results on cotton at Florence, S. C, show that rotation 
without fertilizers is 60.6 per cent as effective as the use of chemical 
fertilizer without rotation. When one practice is conjoined with the 
other, rotation is only about 25 per cent as effective as the use of 
fertilizer in effecting increases in yield. Under the conditions of 
these experiments the combined effects of rotation and fertilizer are 
less than fully additive (pp. 41-44). 
The nature of the liming tests at Wooster, Ohio, and at Florence, 
S. C, made it possible to study the effect of soil reaction on the effects 
of crop rotation and the use of fertilizers in effecting increases in the 
yields of wheat. Indian corn, and oats (Wooster), and of cotton 
(South Carolina). These experiments show that an alteration or 
change in the soil reaction as effected by liming has increased the 
absolute and relative values for rotation when conjoined with the 
use of fertilizers — the average increase in the relative values over 
unlimed conditions being 23 per cent. This increase in the relative 
value for rotation due to liming is reflected in the increased additive 
effects when, on limed soils, rotation and the use of fertilizers are 
conjoined (pp. 44-54). 
If these long-time tests are typical of results showing the effects of 
liming, it would seem that the liming problem is primarily a clover- 
rotation problem (pp. 51-54). 
Summary of foregoing results : 
(1) Including all crops and all soils considered, crop rotation is 
practically 75 per cent as efficient as the use of fertilizer in effecting 
increases in crop yields. 
(2) In general, crop rotation is nearly 90 per cent as efficient as 
the use of fertilizer in effecting increases in the yields of wheat, corn, 
and oats. 
(3) Excluding such crops as clover, timothy, and cowpeas, the 
average relative effectiveness of rotation is practically 20 per cent 
higher on soils whose reactions have been altered or changed by 
liming, than on acid soils. 
(4) Except in case of barley at Rothamsted, the conjoint effects of 
rotation and the use of fertilizers on crop yields are additive— being 
often more than fully additive (pp. 55-56). 
When rotation evaluations are based on the maintenance yields or 
the average yields obtained at the beginning of the experiments accord- 
