CROP ROTATION IN RELATION TO SOIL PRODUCTIVITY 29 
Columbia, Mo., illustrating the following results: The average yields 
that have been obtained from cultivation alone ; the increase effected 
by conjoining crop rotation or the use of fertilizers with cultivation ; 
and the total increases effected, over cultivation alone, by combin- 
ing rotation and the use of fertilizers. 
In each of the bars in which are shown the additive effects of 
combining rotation and the use of fertilizer, the diagonal hachure 
at the top represents the value of the use of fertilizer (F), and the 
diagonal hachure below the unhachured space represents the value 
of rotation (R). The unhachured portion represents the value of 
the interactive effects of rotation and the use of fertilizer when one 
practice is conjoined with the other; or it may show in each case 
how much less is the actual gain due to -the conjoint effects of rota- 
tion and fertilizers than the sum of the increases effected by rota- 
tion and fertilization when practiced independently of each other, 
that is, the value of r plus the value of/. It can not be determined 
just how much of the unallocated portion of the gain should be 
credited to R and F, in the one case, or how much should be sub- 
tracted from the values of r and /, in the second case. 
WOOSTER EXPERIMENTS WITH WHEAT, CORN, AND OATS 
The fertility experiments at Wooster (13) were begun in 1893. 
Here a 5-year rotation consisting of corn, oats, wheat, clover, and 
timothy is under test; and the various plots are repeated five times 
so as to give the yields of all the crops each year. Thus in these 
experiments an average yield of corn, for example, in rotation for 
a period of successive years represents the same seasonal effects as 
the corresponding average yield of corn grown in continuous culture 
for the same years. The published results herein considered cover 
the 25-year period from 1894 to 1918, inclusive. 
Both the rotation and continuous-culture tests at Wooster are 
located on a silt loam of the Wooster series. The surface soil has 
a yellowish-brown color and a mealy structure and is underlain by 
a brownish-yellow, friable stratum having a silt loam texture. The 
soil had been subjected to exhaustive cropping prior to 1893; and 
in reaction, it is acid. 
In rotation, corn, oats, wheat, clover, and timothy are grown on 
five tracts of land, each of which is divided into 30 one-tenth-acre 
plots. In continuous culture, corn, oats, and wheat are grown on 
three tracts, each consisting of 10 one-tenth-acre plots. In all cases 
two fertilized plots, as Nos. 2 and 3, He between two check plots, as 
Nos. 1 and 4. Four of the plots in continuous culture receive no 
treatment and six are fertilized, four with complete chemical ferti- 
lizers and two with farm manure. 
EXPERIMENTAL DATA 
In Table 28 are given the data on the fertilizers used on all the 
plots in continuous culture and on similarly fertilized plots in rota- 
tion. The last column of the table shows, for comparison, the aver- 
age yield on each plot indicated for the 25-year period. 
It is to be observed that, on the basis of the quantity of chemical 
fertilizers applied per acre, the most comparable yields for corn and 
oats are to be obtained by averaging the yields on plots 2 and 3 in 
