INPUT AS RELATED TO OUTPUT 
17 
Net Relations of Three Input Factors to Yield of Potatoes 
INCREASE 
IN YIELD 
BUSHELS 
30 
20 
I 
ADJUSTED 
TOTAL YIELD 
BUSHELS 
5 10 15 20 
VALUE IN DOLLARS OF MANURE AND FERTILIZER APPLIED 
125 
120 
60 
65 
ADJUSTED 
TOTAL YIELD 
BUSHELS 
150 
140 
7.0 75 80 
DEPTH OF PLOWING IN INCHES 
85 
90 
130 
120 
NO 
100 
^ 
^^ | 
y 
/ $*\ 
10 
12 14 16 
SEED P-kANT-CO^RER. ACRE IN- BUSHELS, 
Fig. 6. — Diminishing returns from the use of fertilizer and manure are evident. An 
optimum depth of plowing- is well defined. Planting sufficient seed is essential to good 
yields. Each of these relations shows up more clearly now that the effects of other 
causal factors have been eliminated by the partial correlation method 
96698°— 24 3 
