14 



EXPERIMENT STATION. 



[Jan. 



the experiments began. Supposing the substances applied and 

 the crops removed to have been of average composition, the 

 income and outgo of plant food elements per acre has been as 

 shown in the following table : — 



Plant Food Elements ai)plied and removed, per Acre. 



This comparison, which must represent the facts with sub- 

 stantial accuracy, shows that the soil has received rather more 

 than double the application of phosphoric acid and potash re- 

 moved, and since scientific investigations have shown that under 

 ordinary conditions there is but little waste of these elements 

 from soils by leaching, the condition of the soil of this field 

 in so far as regards these elements, must evidently be much 

 better now than when the experiments began. 



On the other hand, it will be noted that the crops have car- 

 ried away substantially two and one-half times as much nitrogen 

 as has been applied to the field. It might be supposed, there- 

 fore, that this soil must now be highly exhausted of this element, 

 but, in view of the large crops which it is now producing, it 

 does not seem probable that this is the case ; and in. considering 

 this matter it must be remembered that during the past twelve 

 years a mixed hay crop, which has always contained a large 

 proportion of clover, has alternated with corn in periods of 

 two years for each. It is a well-known fact that when soils are 

 highly enriched in j^hosphates and potash in available forms, 

 and at the same time prevented from becoming acid by suitable 

 applications of lime, the conditions are i^eculiarly favorable 

 for the assimilation of atmospheric nitrogen by clovers and 

 other legumes. The clover in this field has, without doubt, 

 assimilated large quantities of atmospheric nitrogen. It is in- 

 deed true that the clover crops have not been plowed nnder ; 

 they have been harvested and made into hay; but a largo 

 amount of nitroo'en oric'inallv taken from the air must have 

 remained in the roots and stul)bl(^, and wo must conclude that 



