308 THE SMALL GRAINS 



334. Sources of lime. Aside from gypsum and the 

 lime phosphates, there are three forms of lime most 

 commonly applied as soil amendments quick or burned 

 lime, hydrated or slaked lime, and limestone. For all pur- 

 poses except the neutralizing effect upon sodium carbonate 

 by gypsum, any of these forms may be used. However, 

 quicklime, being very caustic, should not be applied where 

 there is little humus or on light sandy soils, as it quickly 

 exhausts the humus. On the other hand, it may be 

 preferable to the limestone form where there is great 

 soil acidity and much organic matter. In the experi- 

 ments at the Maryland Experiment Station, it was found 

 that shellmarl, very abundant in Maryland, gave better 

 results in crop yields than any other of many forms of 

 lime used. As magnesium carbonate will neutralize more 

 soil acidity than the same weight of calcium carbonate, and 

 as magnesium is an essential plant-food, it would seem 

 desirable, where convenient, to use dolomite or magnesium 

 limestone, but it should not be applied in excessive quan- 

 tities. Ground limestone should not be made too fine, 

 as it will then be used too rapidly and much of it wasted 

 through leaching. An 8-mesh or 10-mesh sieve (64 or 

 100 holes to the square inch) is probably fine enough for 

 economic screening, while nothing coarser than a 4-mesh 

 sieve should be used. 



335. Applications of lime may be made at such times as 

 other farm work and weather permit, but are probably 

 better done after plowing, the lime being harrowed in. 

 Ground limestone or lime carbonate should be applied 

 first at the rate of about 4 tons to the acre, and, for per- 

 manent maintenance, 2 tons every 4 years thereafter. 

 In strength, 100 pounds of lime carbonate equals about 

 56 pounds of quicklime or 74 pounds of freshly slaked 



