28 EXPEKIMENT STATION RECORD. 



the higher plants, but have more frequently an indirect effect on plants by 

 furnishing conditions favorable to organisms which supply them with nitrogen 

 compounds and render phosphoric acid soluble. 



The purpose and interpretation of fertilizer experiments, G. N. Coffey 

 {Jour. Amer. Soc. Agron., 5 {1914), No. 4, pp. 222-230, fig. 1). — The principal 

 points emphasized in this article are (1) the need of greater uniformity in 

 the methods of fertilizer experimentation in order that the results secured 

 may be more nearly comparable; (2) the advisability of determining the rela- 

 tive need of a soil, and of different soils, for the different fertilizing elements; 

 (3) the reliability of the results secured from the use of the elements alone 

 for this puii^ose; (4) the suggesting of a line along which it maj^ be possible 

 to work out a satisfactory plan for obtaining this information; and (5) the 

 proposing of a method by means of which it may be possible to interpret the 

 results of fertilizer experiments in a way most easily understood by the farmer. 



The plan proposed would involve simple uniform tests of the three fer- 

 tilizing constituents separately on all important soil types and from data so 

 obtained calculating the most profitable fertilizer combinations to use. Such a 

 method, based on tests of single fertilizer constituents at Wooster and Strongs- 

 ville, Ohio, is applied in this article to experiments made at the two places 

 named and at the Pennsylvania Station. The method of calculation is stated 



as follows: ~^~r~ ==X where A =amount of nitrogen (or potash) applied; 



/A'^=inerease from nitrogen (or IK from potash) ; /P=increase from phos- 

 phorus'; CP=cost of phosphorus; C2V^=cost of nitrogen (or CK cost of potash) ; 

 and X=relative proportion for most profitable returns. 



" The first part of the formula is predicated upon the theory that the relative 

 need of a soil for the elements is proportional to the increases produced by 

 these elements ; the second upon the theory that the amount of these elements 

 used should be varied in proi)ortion to their cost. While these theories may not 

 hold absolutely true, they probably represent as near an approach to a general 

 statement as can be made at the present time." 



On the plans of fertilizer experiments, P. L. Gile {Jour. Amer. Soc. Agron., 

 6" {1914), Ao. 1< pp- 36-41, fig- !)■ — The application of the law of minimum as 

 enunciated by Liebig and modified by ^litscherlich to field experiments is dis- 

 cussed, and it is pointed out that while tlie plain principles w'hich common sense 

 jind the experience of investigators show should govern in the planning and 

 execution of fertilizer tests are universally recognized they are not always 

 followed. There are various considerations which make it probable that the 

 increased growth of crops resulting from an increase of the element in mini- 

 mum is repi'esented by a curve as Mitscherlich holds and not a straight line as 

 Liebig's definition of the law of minimum indicates. This is in accord with 

 Hall's application of the law of diminishing returns to fertilizer experiments and 

 with the excess (Luxus) consumption by plants of a fertilizer added in 

 increasing amounts. 



"With the variable conditions that field experiments are subject to. it is 

 doubtful if the increased growth caused by fertilizers will often follow exactly 

 the theoretical rate. For this reason it seems that a plan of a fertilizer test 

 somewhat as follows would give resiilts which are more accurate than many 

 of the present plans for such experiments and yet afford conclusions that are 

 not dependent on theoretical considerations. 



" In a test of the availability of different forms of nitrogen, for instance, 

 all the plats shoifid receive phosphoric acid and potash in considerable excess. 

 The standard, or most available form of nitrogen, as nitrate of soda, 

 should be applied in several quantities, say at the rate of 20, 30, 40, 60, and 90 



