Mar. i, 1921 Relation of Calcium Content to Soil Reaction 



865 



The total acidity in the soil was mentioned in a preceding paragraph 

 as the total quantity of hydrogen ions which may be produced when 

 the equilibrium is continually shifted by the introduction of hydroxyl ions. 

 On such a basis it is possible to calculate the amount of lime required 

 to satisfy this acidity as measured by the electrometric titration. It was 

 also shown in a preceding paragraph that 1 cc. of N/25 calcium hydroxid 

 used in titrating 10 gm. of soil is equivalent to 400 pounds of calcium 

 carbonate per acre. Table IV has been prepared by using this factor 

 and the titration figures from Table II. In the last column of Table 

 IV are given the figures of the lime requirement of these soils as deter- 

 mined by the Hopkins method. It is at once seen that there is no close 

 agreement in the figures obtained by the two methods. This does not 

 necessarily argue for the greater practical value of the figures obtained 

 by the electrometric method nor against the Hopkins method. Similar 

 disagreements can be found if other well-known acidity methods are 

 compared. The figures presented in Table III make it appear that 

 some of the calcium hydroxid is taken up by colloidal clay. Just how 

 much this amounts to is not known, nor the manner. This forms part 

 of an investigation now going on at this laboratory. 



Methods do not show any agreement as to the amount of calcium car- 

 bonate that should be added to an acid soil. Hopkins (7) states that 10 

 tons of limestone per acre on some soils is not too large a quantity. 

 The figures in Table IV show that the amounts of lime required to change 

 from a more acid reaction than denoted by P H 7 to neutral, or P H 7, is 

 not in general larger than the figures obtained by the Hopkins method, 

 though there is no agreement between individual samples. The amounts 

 required to change from the initial reaction to that denoted by P H 8.3 

 are not far from the amounts recommended for use on acid soils, and 

 the amounts required to bring the reaction to P H 10 are in all cases 

 less than 10 tons per acre. 



Table IV. — Electrometric measurements in equivalents of CaC0 3 per acre in o to 7 inches 

 of the surf ace soil in comparison with amount of CaC0 3 required by the Hopkins method 



GROUP I, SOILS WHOSE ALKALINITY WAS ABOVE PH 8.3 



Soil 

 No. 



County. 



Soil type. 



Pounds 

 per acre 

 of CaC03 

 required 



by the 

 Hopkins 

 method. 



1 169 

 1227 

 1043 

 1297 

 1 199 

 1119 

 1206 



Reno 



Greenwood . . 



Russell 



Montgomery 



Jewell 



Finney 



Jewell 



Reno 



Pratt loamy fine sand 



Crawford clay 



Benton loam 



Oswego silt loam 



Laurel very fine sandy loam . 



Dune sand 



Lincoln silty clay loam 



Kirkland clay 



Alkali. 

 ' Alkali'. 



a It is assumed that i cc. of iV'25 Ca(OH)2 is equivalent to 400 pounds CaC03 per acre. 



