478 NATUEE AND PROPERTIES OF SOILS 



growtli cnrve.^ This formula has been questioned by several 

 investigators,^ who have shown that a number of conditions, 

 such as light, heat, and moisture, tend to disturb the applica- 

 tion of such a law. The fact that crop yield is the summation 

 of so many varying factors seems to argue in favor of no hard 

 and fast rule regarding the increased growth due to the added 

 increments of an element in the minimum. It is enough, in 

 the practical utilization of fertilizers, to remember that in 

 order to obtain the best results from fertilizers a mixture 

 should be used that is approximately balanced so far as the 

 effects of the nutrients are concerned, the crop as well as the 

 chemical constitution of the soil being considered. 



269. Fertilizer brands. — In an attempt to meet the de- 

 mands for well-balanced fertilizers suited to various crops and 

 soils, manufacturers have placed on the market a large num- 

 ber of brands of materials containing usually at least two of 

 the important nutrient elements, and nearly always the three ; 

 the former being designated as incomplete fertilizers, while 

 the latter are spoken of as complete. These various brands 

 usually have a significant name,^ which frequently implies the 

 usefulness of the material for some special crop growing on a 

 particular soil. Oftener, however, the brand name bears no 

 relation either to crop or soil. The name should always be 

 ignored in fertilizer purchase, the availability and composi- 

 tion being the important considerations. 



_£,= (a — j)k. Integrating, log (a — j) =c— kx. 



y=; total yield from any number of increments. 



s = amount of any particular fertilizer constituent utilized. 



a == maximum yield and is a constant. 



k = a constant depending on y and x, variables. 



^Pfeiffer, Th., Blanck, E., and I^lugel, M., Wasser und lAcht als Veffe- 

 tationsfaTctoren und Hire JBeBiehungen sum Gesetze vom Mmirmmi; 

 Landw. Ver. Stat., Band 76. Seite 2H-223, 1912. 



Also, Maz6, P., Becherches sue Us delations de la Flante avec les 

 Elements NutriUfs der Sol; Compt. Eend., Tome 154, pp. 1711-1714, 

 1912. 



® Potato and Corn Fertilizer, Golden Harvest, Ureka Corn Special, 

 Blood and Bone, Harvest King, Soil Builder and the like. 



