CROP ROTATION AND IRRIGATION 113 



other crops gave a poorer yield on land that had been continu- 

 ously sown in wheat. "Land which produced three crops of 

 wheat and one cultivated crop in a period of four years, gave 

 almost as much wheat and more profitable returns than did the 

 land which produced four crops of wheat in succession. ' ' 1 Ex- 

 periments have been made in the continual culture of wheat on 

 a certain piece of ground, there being no fertilizing of any 

 kind, as, for example, the "experimental acre" in Kansas. This 

 trial was begun in 1880, and by 1896 the yield was falling off. 

 Permanent spots of diminished fertility had then appeared. 

 Though they may have been due in part to surface-washing, 

 partial exhausting was undoubtedly a factor. 2 



Historic experiments in growing wheat continuously without 

 fertilizing have been carried on in England for over 50 years. 

 "The yield has fallen to about 12 or 13 bushels to the acre, 

 but for the past 20 years there has been little or no difference 

 in the yield, except slight fluctuations due to seasonal condi- 

 tions. So far as is known, the soil will produce 12 or 13 

 bushels to the acre annually for hundreds of years. " 



The Crop Rotations of the United States now generally 

 practiced in some typical counties of states leading or promi- 

 nent in their geographical divisions, are given below: 



Pennsylvania. Corn, wheat two years, grass two years (York, 

 Franklin, etc.). Corn, oats, wheat, grass three years (Chester, 

 Westmoreland) . 



Minnesota. Wheat two years, oats, wheat, flax (Marshall). 

 Corn, wheat two years, oats (Lac qui Parle). Corn, wheat two 

 years, grass two years (Ottertail, Todd, etc.). 



Washington. Wheat, rest (Adams). 



California. Wheat, rest (Solano, San Joaquin, etc.). 



Maryland. Corn, wheat two years, grass two years (Mont- 

 gomery, Frederick, Talbot, etc.). The rotation on dairy and stock 

 farms includes wheat for only one year. 



Oklahoma. Wheat without rotation (Grant, Garfield, Kingfisher, 

 etc.). Wheat, corn, (Dewey). Wheat three years, oats (Kay). 



No crop, nor even any one class of crops, such as the cereals, 

 should be continuously grown on a soil that will produce a 

 variety of crops. On ordinary soils, cereal crops should be 

 rotated every two to four years with a leguminous crop, such 

 as clover or alfalfa. The North Dakota experiment station 

 finds that wheat should have a good place in the rotation be- 

 cause it is a particular crop, and that the average yield of 



1 N. D. Bui. 48, p. 735: Bui. 39, p. 458. 



2 Kan. Bui. 59 (1896), p. 90. 



3 Indus. Com., 10:clxxxviii, 



