86 THE ESSENTIALS OF AGRICULTURE 



Keeping the land covered with a crop during the fall, winter, 

 and spring months is a very practical method of checking erosion, 

 as well as of preventing the loss of plant food from leaching. 

 Crimson clover, rye, winter wheat, winter oats, and barley are 

 crops used for this purpose. 



94. Crop rotation. A small grain crop, such as oats or wheat, 

 or a grass crop, such as timothy or blue grass, is less exhaustive 

 to the soil than a cultivated crop, like corn. Consequently, 

 cultivated crops should be alternated with small grain and grass 

 crops. It is also important to include in the rotation a legume 

 crop, such as clover, alfalfa, cowpeas, or field peas, because of 

 the ability of legumes to fix nitrogen from the air. This policy 

 may not always be feasible ; but it suggests the first great 

 principle of maintaining fertility, that of crop rotation. 



The following is a table showing the effect of different crop 

 rotations upon soil fertility, as measured by the soil's ability to 

 produce corn : 



EXPERIMENTS IN CROP ROTATION 



YIELD OF CORN AT END 

 I. 1 ROTATION OF PERIOD 



Corn, continuously 28 years 22 bushels per acre 



Corn, oats, 28 years 36 bushels per acre 



Corn, oats, clover, 28 years 59 bushels per acre 



Pasture, 18 years; corn, oats, clover, 



10 years 7j; bushels per acre 



II.2 



Corn, continuously 1 7 years 1 1.8 bushels per acre 



Corn, wheat, clover, 17 years 50.7 bushels per acre 



Corn, oats, wheat, clover, and timothy, 1 7 



years 54.7 bushels per acre 



Corn, oats, wheat, clover, and timothy 



manured, i 7 years 77.8 bushels per acre 



It should be borne in mind that these results were obtained 

 with all crops, even the cornstalks, removed from the land. 



1 Illinois Experiment Station, Circular 95. 



2 Missouri Experiment Station. Results not yet published. 



