114 The Potato 



The comparatively higli prices received for this early crop 

 makes heavy fertilizing, often over 2000 pounds to the 

 acre, profitable. By contrast, the irrigated sections of 

 the Rocky INIountain region often have soils very rich in 

 the mineral plant-food elements. Though often low in the 

 supph' of nitrogen, this is obtained by rotating the potato 

 crop with alfalfa. This would render fertilizers of little 

 value for these conditions even if the high freight costs 

 from our present sources of supply did not put fertilizers 

 out of the question. 



Scientists are not fully agreed as to the functions of the 

 different elements in the soil used by plants. Experiments 

 have proved that several must be present or plants will 

 not grow. The common term "plant-food" is applied 

 from these experiments. Fertilizers have other actions 

 of value to plants, some well understood, and some which 

 have only been discovered and are as yet not very well 

 known. One is their favorable action on the beneficial 

 bacteria present in the soil.^ Certain fertilizers, by ren- 

 dering soil conditions more favorable for them, increase 

 indirectly the fertility of the soil as well as by their direct 

 action. Our knowledge of these bacteria is limited at 

 present in some directions, but it is certain that their 

 importance to agriculture is very great, much greater than 

 is generally known. One limit to the yield of farm crops 

 is the amount of water which is available for their use. 

 This is shown by the great gains from the practice of irri- 

 gation. Fertilizers practically increase the water supply 

 by increasing the concentration of the solution of plant- 

 foods in the soil water and so enable the plants to secure 

 more from the same amount of water in the soil.- 



1 Office of Expt. Sta., Bui. 194. 



« U. S. D. A., Bureau of Soils, Bui. 22. 



