52 FAKM GRASSES OF THE UNITED STATES 



On the Pacific Coast a species of fern {Pteris aqui- 

 lina) is the worst weed in grass-lands, particularly 

 west of the Cascade Mountains, in Washington and 

 Oregon. It is provided with rather formidable under- 

 ground stems, and is difficult to eradicate. It may be 

 held in check by cutting twice or three times a season. 

 When young and tender, sheep and goats will eat it, 

 and it may be eradicated by stocking the land heavily 

 with these animals. It does not bother much on land 

 that is plowed eight or ten inches deep once a year, 

 and hence is not very troublesome on well-cultivated 

 fields. 



MANURING GRASS-I<ANDS 



The use of fertilizers is one of the most unsatisfac- 

 tory subjedls to handle in the whole range of agricul- 

 tural science. It is now just one hundred years since 

 the first carefully planned fertilizer experiments were 

 laid out by a modern investigator. Sixty-two years 

 ago Liebig's great work was published, in which the 

 theory was announced that by analyzing the soil and 

 the crop the chemist could prescribe the fertilizers to 

 be applied in any given case. This theory was the 

 basis of the work of the agricultural chemists for half 

 a century. Innumerable fertilizer experiments have 

 been conducted with tha utmost care. The soil has 

 been analyzed times almost without number. The 

 constitution of the mineral matter removed from the 

 soil by plants has been determined to a nicety. It is 

 definitely known that chemical fertilizers frequently, 

 we may say usually, exert a decidedly favorable influ- 

 ence on growing crops. It is absolutely impossible, 

 however, to say just what fertilizers or how much of 



