93 Steenbjerg: Microelements from a Practical Point of View 



for the different fertilizing values of the copper minerals, if the 

 minerals are added in increasing amounts at the same degree of 

 fineness, seems to be the varying copper content which causes a 

 very different "copper surface." So there are three factors of 

 importance when the value of copper minerals as fertilizers has 

 to be evaluated: 



J) The degree of fineness 



2) The "copper surface" 



3) The price per kg of copper 



These three factors may be combined in many different ways 

 in order to give the cheapest copper effect. 



•(D 



V Copper pyrite I 

 + Bornite I 

 X " n 

 (D) Malachite I 

 " 1 



0.02 0,06 0,10 



Textfigure \5.—Ahscissa: Relative copper surface.— Ordinafe: Increase 

 in dry matter yield. 



Finally a few words about chemical analyses of plants for 

 microelements and the use of these analyses as indicators of defi- 

 ciencies of microelements. 



The relationship between the percentage of a plant nutrient 

 in the dry matter and the amount added to the soil of the plant 

 nutrient in question is expressed by a curve which first falls and 

 then rises as the content of the plant nutrient increases in the 



