THE SOIL, SOLUTION 



mineral nutrients as does the preceding 1 wheat crop. The invest- 

 igation of Lawes and Gilbert 2 on fairy rings showed that the 

 continual widening of the rings can not be satisfactorily explained 

 by the comparison of the mineral constituents in the soil within 

 and without the rings. Work at Woburn 3 on the effect of 

 grass on apple trees finds no other plausible explanation than 

 that the growing grass produces in the soil organic substances 

 detrimental to young apple trees. A number of similar cases 

 have been recorded. 



1 Mr. J. G. Smith has made a comparison between the potash and 

 phosphoric acid content of the wheat and following crop of ragweed 

 grown on a farm in Fairfax Co., Va. His unpublished results, with some 

 others found in the literature, are given in the following table : 



On the whole, ragweed seems to require and take from the soil about 

 as much mineral matter as does wheat. It is stated by some of the 

 dairy farmers near Washington, who cut the mixture of ragweed, other 

 weeds and grass following wheat, for a hay crop, that the weight of the 

 ragweed crop is generally heavier than that of the wheat crop. There- 

 fore the ragweed actually removes more mineral matter from the field 

 than does the wheat. These facts lend no support to the popular notion 

 that wheat "exhausts" the soil of its "available" mineral plant nutrients. 

 For analyses of a number of common American weeds, see Analyses of 

 the ashes of certain weeds, by Francis P. Dunnington : Ann. Chem. Jour., 

 2, 24-27 (1880). 



2 Note on the occurrence of "fairy rings," by J. H. Gilbert : Jour. 

 Linn. Soc., 15, 17-24 (1875). 



* Second, third and fifth reports of the Woburn Experimental Fruit 

 Farm, 1900, 1903, 1905. 



