LIMING THE SOIL 367 



199. Form of lime to apply. — The experimental data 

 regarding the relative effectiveness of the different forms of 

 lime are not only meagre but also somewhat contradictory. 

 In practice it is best to assume that the effectiveness of the 

 lime depends on the amount of magnesium and calcium car- 

 ried and is influenced to a much less degree by the particular 

 combinations in which these bases may occur. For example, 

 one and a half tons of medium to finely ground limestone 

 carrying 50 per cent, of calcium oxide should be as effective 

 as one ton of burned lime analyzing 75 per cent, calcium oxide. 

 While there is a difference in the rapidity with which the 

 various forms react, there seems to be but little difference be- 

 tween them over the period of a rotation when they are ap- 

 plied in chemical equivalent amounts. 



Accepting this relationship as a practical working basis, 

 four factors must be considered in deciding what form of 

 agricultural lime to apply. These factors are as follows: 

 (1) chemical equivalents, determined by chemical combina- 

 tion and purity; (2) cost a ton, freight on board; (3) freight; 

 and (4) cost of haul and application to the land. 



It is evident that, if the various forms of lime are equally 

 effective in chemical equivalent quantities, once these amounts 

 are determined the question becomes a problem in arithmetic. 1 

 The importance of the factors above listed can best be shown 

 by working out an actual case. 2 



^aO x 1.32 = Ca(OH) 2 MgO X 1.44 = Mg(OH) 2 



CaO X 1.78 as CaC0 8 MgO X '2.09 — MgCO, 



Ca(OH) 2 X .76 = CaO Mg(OH) 2 x .69 = MgO 



Ca(OH) 2 X 1.35 as CaCO, Mg(OH) 2 X 1.44 — MgC0 3 

 CaC0 3 X .56 = CaO MgC0 3 X .48 as MgO 



CaC0 3 X .74 = Ca(OH) 3 MgC0 3 X .69 = Mg(OH) 2 



CaO X .70 = MgO MgO X 1.39 ss CaO 



a Calcium oxide and calcium hydroxide have an advantage over ground 

 limestone in percentages of calcium carried and possibly in initial ac- 

 tivity. They are, however, more disagreeable to handle and do not 

 mix with the soil so well since they tend to lump on becoming moist. 

 Partially or wholly carbonated lumps are often found in the soil years 

 after the caustic lime has been applied. 



