UNITED STATES DEPARTMENT OF AGRICULTURE 
DEPARTMENT BULLETIN No. 1377 
,D.C. 
March, 1926 
A STUDY OF THE VALUE OF CROP ROTATION IN RELATION TO 
SOIL PRODUCTIVITY 
By Wilbert W. Weir, Associate Soil Technologist, Bureau of Soils 
CONTENTS 
Page 
Introduction 1 
Primary objects of study 3 
Method of study - 3 
Experiments selected for study. .. .. 5 
Discussion of evaluation methods 5 
First method, involving assumptions.. 6 
Second method 7 
Third method -- 8 
Effects of crop rotation and of the use of fertili- 
zers on crop yields 10 
Rothamsted experiments with wheat and 
barley... - 10 
Experimental data... 11 
Rotation and the use of fertilizers con- 
joined - 13 
Diagrammatic summary of Rotham- 
sted results _. . 16 
Columbia experiments with wheat, corn 
and oats 18 
Experimental data 19 
Rotation and fertilization practiced 
independently 23 
Rotation and the use of fertilizers con- 
joined 25 
Wooster experiments with wheat, corn and 
oats 29 
Experimental data — 29 
Page 
Effects of crop rotation and of the use of fertili- 
zers on crop yields— Continued. 
Wooster experiments with wheat, corn and 
oats— Continued. 
Results when rotation and fertilization 
are practiced independently 35 
Results when crop rotation and the use 
of fertilizers are conjoined ___ 36 
Germantown experiments with tobacco... 38 
Urbana experiments with corn 39 
Florence experiments with cotton 41 
Rotation and fertilizer efficiencies as affected by 
soil reaction 44 
Summary of relative values of crop rotation and 
of conjoint effects of rotation and the use of 
fertilizers 54 
Value of crop rotation and of the use of fertili- 
zers in maintaining and increasing soil pro- 
ductivity 57 
Maintaining soil productivity 57 
Increasing soil productivity 59 
Effect of soil reaction on rotation and use 
of fertilizers 60 
General discussion 60 
General summary and conclusions 65 
Literature cited 68 
INTRODUCTION 
The maintenance of soil productivity depends largely on those fac- 
tors which are commonly referred to as farm practices, notably cul- 
tivation of the soil, crop rotation, the use of fertilizers and agricultural 
lime, land drainage, and irrigation. Taking into consideration all 
kinds of soils and the more or less established systems of agriculture, 
three of these farm practices assume outstanding prominence: (1) 
Cultivation; (2) rotation of crops; and (3) the use of fertilizers. 
Cultivation of the soil includes the preparation of a suitable seed 
bed and any subsequent stirring of the soil to kill weeds or to con- 
serve soil moisture. The preparation of the seed bed, a practice 
which has come down to us from times immemorial, is universally 
recognized as a necessary first step in the production of farm crops 
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