120 ELEMENTS OF AGRICULTURE 



yard manure, millet grown; a gain of 10.48 grams of 

 nitrogen. 



The soil that was kept bare contained a gram more 

 nitrogen in the fall than it did in the spring. There was a 

 slight gain when millet was grown. When a gram of 

 nitrogen was added in the form of nitrate of soda, the crop 

 and soil contained 3.73 grams more nitrogen than were 

 present in the fertilizer and soil at the beginning. But, 

 when barnyard manure was used, there was a gain of 10.48 

 grams ten times as much nitrogen as was added in the 

 manure. These gains came from the air. The nitrogen 

 was fixed by organisms acting independently of legumes. 

 (Millet is not a legume.) 



Certain conditions greatly favor the activities of these 

 important organisms. The soil should be well aerated 

 and drained, and it must contain sufficient lime and humus. 

 The striking results with the barnyard manure are proba- 

 bly due to the humus that it contains, and perhaps partly 

 due to the organisms that it brings with it. This partly 

 explains why fertilizers alone cannot take the place of 

 manure. 



118. Importance of Grasses. Grasses do not have the 

 power of obtaining any nitrogen from the air, but when 

 land is left in sod there is usually a considerable gain in 

 nitrogen. A field at Rothamsted, England, was left to 

 grow up to weeds and grasses for twenty years. No legumes 

 were grown on it, but there was a gain of over forty-four 

 pounds of nitrogen per acre per year enough to much more 

 than grow a good crop each year. 1 



Every farmer knows that a field that has been in sod 

 for a few years produces much better crops when it is 



Book of the Rothamsted Experiments, by A. I). Hall, p. 139. 



