Hoagland 



14 — 



Plant Nutrition 



Later investigation based on the principles of base 

 exchange made clear the dominating factors. In the 

 black alkali soils the calcium held by the clay colloids 

 had been replaced to a large extent by sodium, and 



Ca HOH 

 Mg + HHCO, - 



Water and 



Neutral clay ^^^onic acid ^""^ ^'^^ 



KOH 

 Ca(HCO,), 

 Mg(HCO,), 



Removed from 



surface horizons 



by leaching 



(27) 



Ca Cft K Ca K 



Na 



Colloid 



Mg 



K Mg Ca Na Ca 



Arid reQion[ 

 Desert soils 

 Arid brown soils 

 Chestnut soils 



Ca Mg Ca K 



CaHCaMg 



Ca Na CX 



Transidnn zone 



Chcrnuzcniii 



Ca H Ca 



Humid region 

 Gray-brown-podsolic 



soils 

 Podsols 



Moisture region 



Arid (alkali soil) 



Transition (chernozem) 

 Humid (podsol) 



Percentage composition of adsorbed 

 cations 



Na 



30 



2 



Trace 



K 



15 

 7 

 3 



Mg 



20 

 14 

 10 



Ca 



35 

 73 

 20 



H 







1 



67 



Total 



100 

 100 

 100 



Textfigure 3. — To illustrate three general soil conditions 

 and the relations of replaceable basic ions in each general 

 type of soil. Note the different relative percentage of the 

 several ions, especially of sodium, calcium and hydrogen 

 ions. (From Jenny, Factors in Soil Formation, 1941. Cour- 

 tesy McGraw-Hill Co.). 



the sodium colloid has very different properties from 

 the calcium colloid, properties which may lead to dis- 

 astrous consequences for agriculture. To reclaim the 

 soil it is necessary to displace and leach away sodium 

 and to put back calcium in the colloid. The question 



