CHAPTER XII 

 FERTILIZERS AND SHADE-CROPS 



WE often hear it said that western soils 1 are inex- 

 haustible; and indeed it is true that they are fairly rich in 

 many of the elements of fertility. But we now know from 

 experience that land cropped year after year to wheat 

 becomes unprofitable, that even the second crop of pota- 

 toes is rarely satisfactory, and that all fruit association men 

 and local dealers know that small apples and pie peaches 

 are becoming more and more common. 



1 Some of our readers have no doubt seen the papers on various phases 

 of soil fertility published in recent years by the Bureau of Soils of the 

 United States Department of Agriculture. Their investigations seem to 

 show that there is no such thing as soil exhaustion, as generally under- 

 stood, but rather that there is an inexhaustible supply of all of the 

 mineral elements of plant-food in ordinary soils. They contend that 

 the decreased yields of the various crops is due to poisonous sub- 

 stances excreted by the roots of plants. Thus, according to this view, 

 any crop may soon poison the land to such an extent that proper devel- 

 opment of the plants is hindered, and decreased yields result. The 

 remedy, according to this theory, is naturally a proper rotation of crops 

 and methods of soil sanitation. The idea that the roots excrete poison- 

 ous materials is an old one, and new evidence lends support to it ; but 

 that this is accountable for all of the many cases of unsatisfactory 

 yields is difficult to believe. At any rate the writers prefer for the pres- 

 ent to adhere to the well-established theories, believing that the avail- 

 able supply of plant-food may be depleted. The presence of decaying 

 vegetable matter in the soil improves its physical condition, helps to 

 set plant-food free, and, in a measure, takes the place of crop rotation in 

 the orchard. This may best be supplied and conserved under arid con- 

 ditions by the use of shade-crops. 



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