370 University of California PubJicatioits in AgriculfuraJ Sciences [Vol. 1 



in either of tlie other sericvS, a result which is explicable since 

 nitrogen is a more important limiting factor than phosphorus, 

 and phosphorus is in turn more important as a limiting factor in 

 growth than potassium. Hence in a solution where nitrogen is 

 deficient, and potassium and phosphorus present in optimum 

 amounts, a smaller crop production results than is the case where 

 phosphoi'us is the deficient factor. A deficiency of potassium 

 does not so seriously affect the intake of other salts, with the 

 result that a better crop is produced than is the case where 

 phosphorus is the deficient factor. 



The method of analysis which it was necessary to use makes 

 the analytical values for phosphorus and magnesium rather un- 

 reliable. In series II, where phosphate was added in increasing 

 quantities from pot 1 to pot 5 in each group, the analysis of the 

 water extract shows the effect of this increment. It will be 

 noticed tliat the analytical values are all of about the same order 

 of magnitude, which may point strongly to adsorption by the 

 sand. No general conclusion as to the adsorption of phos- 

 phorus and of magnesium can be drawn for the reasons above 

 enumerated. 



In the case of potassium the method of analysis was much 

 more accurate. There is evidence in series I, groups A, B, C, 

 and D, of an increase in the amount of potassium absorbed which 

 in general seems to be related to the more vigorous growth re- 

 sulting from the increasing quantities of nitrogen as added in 

 these groups. A similar relation holds in the other two series, 

 as will be seen from the ratios between potassium added aud 

 potassium remaining, which are higher where the nitrogen is 

 added in large quantities than is the case where this element was 

 present in small quantities. The high ratios of potassium added 

 to potassium remaining after growth, therefore, usually oecui- 

 where the dry weight is highest. 



Not much can be said on the absorption of calcium. In 

 series I it is noticeable that the quantity of calcium remaining, 

 as compared in the four groups of this series, bears an inverse 

 relation to the calcium added. Less calcium is absorbed from 

 the solutions of low total concentration than from those which 

 luive a high concentration. Since the crop production was 



