ECONOMIC USE OF FORAGES IN LIVESTOCK PRODUCTION 13 
Tasie 6.—lorage and grain production combinations and substitution 
rates, Marshall silt-loam soils * 
Production combinations per acre Average quantity of 
grain replaced per 
pound of forage 
Proportion of total 
feed production that 
is forage (percent) 
Forage Grain (pounds) added (pounds) 
Pounds 3 nee 
Sek eta 2501) ao ff 
DO te Ce 1, 690 10. 6 
\ a7 { 
AO RG sidsos. 1eN 2, 045 16. 4 
\ oe { 
G00 er we 2,313 20. 6 
\ Le p) { 
S000! OY oust te. . 2, 496 24.3 
\ 45048 { 
OOO ca! Gace cae 2,592 27.8 
\ a isis { 
1900 HTS OF OV Sat 2, 603 31.6 
print alge 
1400 od (sf drrapravy 2, 528 35.6 
80 { 
Go0ee ee 2, 367 40. 3 
\ 1, 25 { 
1800s. 10 _. sons 2,119 45. 9 
\ 1. 66 { 
POON ke a 1, 786 52. 8 
} 2. 09 { 
phoggewolol dl ta 1, 367 6. 7 
2, 
PAGO aha Rt. ine dios 862 oe | 73. 6 
1 Based on data from Seventh Annual Report (7). Forage and grain com- 
binations are derived from the regression equation X,=1249.8+ 2.4169X,— 
0.00107428X,?, where X, refers to pounds of grain and X, refers to pounds of 
forage per acre. 
grain than a similar increase when the proportion of forage in the 
rotation is already high; that is, forage substitutes for grain at an 
increasing rate. 
Forage-grain substitution relationship for rotations on Marshall 
silt-loam soil are shown in table 6. These substitution rates were 
estimated on the basis of rotation experiments on the Page County, 
Iowa, experimental farm (7). Columns 1 and 2 show the quantities 
of grain and forage produced as various proportions of an acre of 
land in a rotation are devoted to grain and forage. They reflect the 
major effects of the rotation on yields after it has been in effect for 
several years. Column 3 of the table shows the average reduction in 
production of grain with each pound of increase in production of 
forage. The negative substitution rates in the upper portion of the 
column denote a complementary relationship between forage and 
erain—each increase in production of forage is accompanied by an 
increase in production of grain. Increases in production of forage 
*While the rotation results give only a few forage-grain combinations, addi- 
tional combinations were derived by varying the acreage devoted to various 
rotations. 
