FOOD FOR PLANTS 167 



trate. The different manures were applied in 

 amounts sufficient to furnish about 4 gms. of nitro- 

 gen per cylinder. Calculated on the acre basis the 

 manures were applied at the rate of about 16 tons. 



The crops were grown in regular rotation, and con- 

 sisted of the following: Corn, oats, wheat and tim- 

 othy. The oats crops were followed in each case by 

 a so-called residual crop whose function it was to 

 take up such available nitrogen compounds as were 

 not utilized by the main crops. 



Analyses were made of all of the main crops and 

 residual crops. In the case of the wheat, the grain 

 and the straw were analyzed separately. In the case 

 of the timothy, the first cutting and aftermath were 

 analyzed separately. The analytical material for the 

 ten years included, therefore, more than a thousand 

 crop samples. Records were made of the yields of 

 dry matter, of the proportions of nitrogen in the dry 

 matter of each crop, of the total nitrogen in each 

 crop, of the proportion of manure and fertilizer nitro- 

 gen recovered, and of the relative availability of the 

 several nitrogenous materials employed. In addi- 

 tion to these careful analyses were made of the soil 

 samples drawn from the several cylinders at the end 

 of each rotation. 



The results secured may be briefly summarized as 

 follows : 



1. There was a marked falling off in the yields 

 between the first and second rotation, especially in 

 the soils which had received no applications of animal 

 manure. 



2. The nitrogen compounds in liquid manure were 



