8 SOILS OF THE EASTERN UNITED STATES. 



IMPROVEMENT IN SOIL EFFICIENCY. 



The high value of the Marshall silt loam for the production of 

 general farm crops has practically eliminated the production of 

 special crops upon the type, so that any discussion of the limitations 

 of soil efficiency must be that of the limitations upon the production 

 of such crops as corn, wheat, oats, and hay. The high value of the 

 type for the production of corn has led, not infrequently, and par- 

 ticularly in the earlier days, to the long-continued production of 

 corn year after year upon this soil. For a long period of time prac- 

 tically no decreases in yield were observed, or where such occurred 

 their cause was coupled with climatic difficulties rather than with 

 the practice of the cropping system. Within later years, however, 

 it has been recognized by the majority of farmers in the eastern 

 portion of the central prairie States, both upon the Marshall silt 

 loam and upon other soils, that adequate crop rotation constitutes 

 one of the necessities for the maintenance of soil efficiency. In 

 consequence crop rotations have been adopted over practically all 

 the Marshall silt loam which is tilled in Indiana, Illinois, and the 

 greater part of Iowa and Missouri. The most common rotation 

 includes two or three years devoted to the production of corn, fol- 

 lowed most frequently by a single year of sowing to oats or, to a 

 limited extent, to wheat, succeeded by two or three years devoted 

 to the growing of timothy and clover, of clover alone, or to an 

 increasing extent, of alfalfa. With the adoption of such rotations 

 the yields of corn have largely been restored to their former magni- 

 tude or even increased. This fact has been noted repeatedly during 

 the progress of soil surveys over the territory described. 



In the study of the Marshall silt loam in one of the Indiana coun- 

 ties where it has been extensively mapped, a sample of this soil was 

 taken from a cultivated field which had been cropped continuously 

 to corn for seven years with an average yield of 45 bushels per acre. 

 The field had never been sown to clover nor had any fertilization of 

 any kind ever been attempted. In the test of the manurial require- 

 ments of this soil sample, various fertilizing ingredients were applied 

 to the soil singly and in different combinations. None of these 

 treatments produced any appreciable increase in the growth of the 

 plants. At the same tune the plants used as indicators and grown 

 both upon the treated and the untreated soil were of sjood size and of 

 normal condition. This would indicate that thorough cultivation, 

 the proper handling of the soil, coupled with an adequate crop rota- 

 tion, is practically the only treatment of the type required for the 

 maintenance of its efficiency. 



It has also been noted in a number of areas that the production 

 even of a single small grain crop between the periods when the fields 

 were planted to corn has had a beneficial effect upon the succeeding 



