CROP FAILURES 181 



equivalent; that is to say, if a crop of clover that would yield two 

 tons of hay were plowed under, the soil would be enriched by about 

 eighty poimds of nitrogen per acre. 



When the clover is cut for hay and sold off the farm, the field 

 growing the crop is not enriched. If at the start the soil were very 

 rich the nitrogen content would even be less after the growing of 

 the clover. On the other hand, if the soil were comparatively 

 poor in available nitrogen, a gain would result. 



When the clover crop is fed on the farm, the amoimt of nitrogen 

 that may be gained is equal to the amount contained in the hay 

 minus the loss in feeding. When manure is well cared for, there 

 is a possibility of regaining about sixty per cent of the nitrogen 

 in the hay, or about twenty-four pounds for every ton of clover 

 hay fed. 



What was said of clover may apply to alfalfa except that one ton 

 of alfalfa hay contains fifty pounds of nitrogen. Information 

 concerning other kinds of legumes is meager; nevertheless, it 

 remains true that a legume can add about twice as much nitrogen 

 to the soil when it is plowed under as when it is fed and the manure 

 returned to the land. 



Certain investigations have shown that the roots of cowpeas, 

 soybeans, crimson clover^ etc., contain a very low per cent of 

 the total nitrogen. Very probably when these crops are removed 

 from the land, some nitrogen is removed from the soil. 



Clover Sod Better Than Timothy. — Under like conditions it is 

 well known that a corn crop, for example, on clover sod yields 

 much better than on a timothy sod. This is largely becau'se 

 clover roots are very rich in nitrogen, and they decompose rapidly, 

 thus causing the Uberation of a good supply of plant-food elements. 



Crop Failures Owing to Lack of Nodule Bacteria. — ^Poor 

 yields, and even absolute crop failures, are not rare experiences 

 resulting from a lack of proper nodule bacteria. Lack of ahalfa 

 nodule organisms was the cause of twenty-six per cent of the 

 alfalfa failures studied in the south half of Wisconsin in the period 

 between 1912 and 1917. It is a common mistake to think that 

 because one kind of legume grows well on a certain soil any 

 other kind of legume would necessarily thrive there. This is not 

 the case, however, since different species of legumes require quite 

 different species of nitrogen-fixing bacteria. Many farmers have 

 experienced absolute failm-e in alfalfa because they thought that 



