430 



UTILIZATION OF MINERAL SALTS 



eral, however, it has been found that most species of plants, under a given 

 set of climatic conditions, grow^ almost equally well over a considerable range 

 of variations in the mineral salt complex of a solution culture, a sand culture, 

 or a soil. 



In 19 1 5 Shive pointed out that the six principal elements — nitrogen, sulfur, 

 phosphorus, calcium, potassium, magnesium — could be supplied by a solution 

 containing only three salts. He proposed a "three salt" solution containing the 



Fig. 96. Symptoms of mineral element deficiencies as shown by tobacco plants. The 

 deficient elements are: (i) nitrogen, (2) phosphorus, (3) potassium, (4) calcium, (5) 

 magnesium, (7) boron, (8) sulfur, (9) manganese, (10) iron. All of the elements 

 were present in (6). Photograph, U. S. Department of Agriculture. 



salts Ca(N03)2, KH2PO4, and MgS04 to which was added a trace of iron 

 salt. Shive's solution has been a popular one ever since its introduction and 

 these three salts have been used in various proportions and concentrations. 

 However, most present-day investigators use a "four-salt" solution to provide 

 these six elements. Shive and Robbins (1938) suggest a solution made up 

 with the following volume molar concentrations: KH2PO4 0.0023 M, 

 Ca(N03)2-4H20 0.0045 M, MgS04 ■ 7 H.O 0.0023 M, and (NH4)2- 

 SO4 0.0007 M. Minute quantities of iron (as FCSO4 • 7H2O), boron (as 



