CLOVERS AND OTHER LEGUMES 255 



phorus. Moreover, in practically all parts of the United 

 States which are given over chiefly to grain and stock 

 farming, the supply of phosphorus in the soil is being 

 gradually reduced. 



Just as clovers will not succeed in an acid soil, so they 

 will not thrive in a soil deficient in phosphorus. When 

 any given farm or agricultural section has reached the 

 stage at which phosphorus is lacking in the soil the suc- 

 cessful growing of clovers has because of this fact become 

 impossible until this element of plant food is restored in 

 some form to the soil whether as barnyard manure or 

 commercial fertilizers. 



190. How a Lack of Humus affects Clovers. — Con- 

 trary to the popular belief, legumes, and particularly 

 clovers, with the exception of sweet clover, are not crops for 

 soils lacking in organic matter. It is a difficult task to 

 get clover established on such soils ; and good farmers 

 often tell us to add manure or otherwise increase the 

 humus content of the ground before sowing clover or 

 alfalfa. 



A motto which might well be painted on the grain 

 drill is, " Legumes are to be used on this farm to main- 

 tain fertility, not as a remedy for abused or ill-treated 

 soil." 



191. How Absence of Friendly Bacteria affects the 

 Clovers. — The cardinal virtue of the legumes is that 

 they leave more nitrogen in the soil than they find. This 

 they can not do, however, unless the necessary friendly 

 bacteria make their homes in the root nodules as explained 

 in Section 180. 



Unless the soil already contains the particular kind 

 of bacteria needed by a given legume, the bacteria must 



