Mineral Nutrients 147 



in solution cultures. According to Nobbe, nutrient solu- 

 tions half this strength, on the one hand, or three times as 

 strong, on the other, failed to give the best results with a 

 majority of the plants tested. The higher concentration, 

 however, is far too weak to produce any immediately 

 recognizable osmotic disturbance. The plasmolyzing con- 

 centration of KNO 3 , for example, would be for many plants 

 10 to 15 parts per thousand. Nevertheless, from the above 

 facts, it is evident that aside from all financial considera- 

 tions in the application of fertilizers there is a definite 

 physiological limit to the application of soluble commercial 

 manures. 



Neglecting for the moment the effect of the soil upon 

 solubility, an extreme case may be taken: assume that 

 500 pounds per acre of fertilizer are applied to a loamy 

 soil, and that all of the fertilizer goes into solution. If 

 the water-holding capacity of the soil is 40 per cent and 

 the actual water-content, say, 15 per cent, there would be 

 in the upper 7 inches of soil about 315,000 pounds of water, 

 and the concentration of the KNO 3 alone would be li parts 

 per thousand. This calculation is, of course, far from 

 what would actually occur, for the soil is a strong absorp- 

 tive matrix, and by no means all of a soluble nutrient added 

 would be effective in the soil solution. Moreover, in most 

 cases, a relatively small quantity of the fertilizers added 

 remains in soluble form. 



Commercial fertilizers applied in the drill or in contact 

 with the seed may readily be present in sufficient quantity 

 to be injurious to the germinating seedling. Claudel and 

 Crochetelle 1 find that solutions of 1 to 1000 of ammonium 



1 Annales agron., 22 : 131-142, 1896. 



