472 NATURE AND PROPERTIES OF SOILS 



nitrogen^ seems to have the quickest and most pronounced 

 effect, not only when present in excess of other constituents, 

 but also when moderately used. It tends primarily to encour- 

 age above ground vegetative growth and to impart to the 

 leaves a deep green color, a lack of which is usually due to 

 insufficient nitrogen. It tends in cereals to increase the 

 plumpness of the grain, and with all plants it is a regulator 

 in that it governs to a certain extent the utilization of potash 

 and phosphoric acid. Its application tends to produce succu- 

 lence, a quality particularly desirable in certain crops. In its 

 general effects it is very similar to moisture, especially when 

 supplied in excessive quantities. 



The peculiarity of nitrogen lies not only in its absolute ne- 

 cessity for plant growth, its stimulation of the vegetative 

 parts, and its close relationship to the general tone and vigor 

 of the crop, but also in the fact that it was not one of the 

 original elements of the earth's crust. During the formation 

 of the soil it slowly and gradually became present, brought 

 down by rains and fixed naturally in the soil through the 

 agency of bacterial action. Now it exists in complex nitrog- 

 enous compounds of the more or less decayed organic matter, 

 and becomes available to plants largely through bacterial 

 activity. 



It may be stated with certainty that one of the possible 

 limiting factors to crop growth is a lack of water-soluble nitro- 

 gen at critical periods in amounts necessary for normal devel- 

 opment. Since soluble nitrogen may be very readily lost 

 from the soil by leaching, the problem of proper plant nutri- 

 tion becomes a serious one. Not only must the farmer be able 

 so to regulate the addition of nitrogen in fertilizers as to obtain 

 the highest efficiency, but he must understand the control and 



*For a discussion of nitrogen in relation to crop yield, see Hunt, T. F., 

 The Importance of Nitrogen m the Growth of Flmts; Cornell Agr, 

 Es;^, Sta.3 Bui. 247, 1907. 



