EXPERIMENT STATION BULLETINS. 601 



is not increased relatively by the initial treatments and also these ele- 

 ments are added in some cases. 



While in general the proper balance of mineral nutrients a soil should 

 have for good crop production is at present not known, it is conceded 

 that the nutrient element in the least available quantities in soils limits 

 plant growth. These results tend to show that the addition of a certain 

 salt not carrjdng mineral nutrients to soils may establish a better bal- 

 ance than formerly existed, while a different fertilizer salt may cause 

 a wider range from the proper ratio. The proper kind and quantity of 

 fertilizer to apply to a certain soil depends somew^hat upon the total 

 effect produced and not entirely upon the element or elements added. 

 Increased crop yields obtained from the use of fertilizers, NaNOg for 

 instance, may not be due to added N alone because this fertilizer has a 

 marked effect on the solubility of other nutrient elements. Negative re- 

 sults sometimes obtained from the use of fertilizers may be due to de- 

 pressed solubility of some important element which may be close to the 

 point of becoming a limiting factor. An effect often observed in fertilizer 

 practice is that applied chemicals give practically no results on the first 

 crop with marked increases in yield on the following crop. From the 

 data presented these effects may be explained on the basis that applied 

 fertilizers may cause changes in the soil that are immediately harmful 

 to plant growth, that is, an excess of some component combined with 

 the acid radical of the salt added, as for instance CaCL, or an organic 

 compound ; a change in soil reaction ; a depression of carbonate content ; 

 or depressing the solubility of some element thereby causing it to become 

 a limiting factor. After several months' time the soil may recuperate 

 from these changes and give the added plant food elements an opportun- 

 ity to produce beneficial effects on the crop. 



Proper fertilization of a soil, therefore, is a complicated problem. 

 When once a fertilizer i-s applied to a soil permanent changes are pro- 

 duced and an entirely different soil results. These changes should be 

 considered before a second application of fertilizer is made to the same 

 area if best results are to be obtained. The possibility of unbalancing 

 the soluble plant food content of soils by the use of one fertilizing salt, 

 as well as the need for a system of fertilization based on soil composition 

 and effects produced upon the soil by added fertilizers and natural 

 processes, is apparent from these results. Providing these factors were 

 considered in field fertilization experiments it is possible that results 

 obtained could be more fully explained and the use of fertilizers made 

 more profitable. 



