FERTILIZERS 103 



the land the toxic substances excreted by one kind have time 

 to escape or become neutralized before the same crop is again 

 grown there. In some cases, however, the excretions from one 

 set of plants seem harmful to others. The butternut tree has 

 been found antagonistic to the shrubby cinquefoil that some- 

 times, infests the pastures in New England and elsewhere, 



Photograph by the University of Illinois 



FIG. 84. Wheat crop averaging 21.5 bushels to the acre 



This wheat was grown on land adjoining that shown in preceding figure. In ad- 

 dition to lime and legumes the soil has had an application of phosphorus 



while a similar antagonism seems to exist between grass and 

 certain fruit and shade trees. Additions of various substances 

 to the soil seem to neutralize these poisonous excretions of 

 plants and enable them to continue in vigorous growth. Some 

 contend that this is the only value to be derived from fertiliz- 

 ers. Whatever the reason for adding fertilizers, the fact re- 

 mains that good crops cannot long be produced without them. 

 Nor will an excess of one needed element compensate for the 



