112 CONSERVATION AND IMPROVEMENT OF SOIL 



Ashes, if made from hard wood and well stored to prevent 

 leaching, contain, besides about four per cent of potash, a good 

 supply of lime. This may be calculated at the rate of about thirty- 

 three per cent of calcium carbonate, or 600 to 700 pounds to the 

 ton. Marl is found in many parts of America in deposits accessible 

 for agricultural purposes. It is rich in lime of a form well suited 

 for agricultural purposes. The richness of the particular deposit 

 should be determined, as the compositions vary widely. It may 

 sometimes be found to contain ninety per cent of calcium 

 carbonate. 



Action of Different Kinds. The most active forms of lime in 

 the soil are the quick lime or calcium oxide, and the hydrate. 

 Carbonated lime in the form of ground limestone acts more slowly. 

 The former burn out the humus from soils more rapidly than pul- 



I 786 LBS. 300O LBS. 



GROUND ROCK HARD WOOD 



OR ASHES 

 OYSTER SHPLL 



FIG. 79. Equivalents in the different forms of lime when applied to .soil. 



verized limestone. They are more effective in causing the decay 

 of organic matter and the unlocking of plant food from the soil. 

 Their effects upon the soil are not so permanent. Pulverized lime- 

 stone acts slowly in the unlocking of plant food and in causing 

 the decay of organic matter and humus. Its effect upon the soil 

 lasts for several years. The lasting effects are determined some- 

 what by the fineness of the powder. The finest forms are used up 

 more quickly because they are more rapid in their action. Coarser 

 forms act slower and last longer. 



Just what form of lime to apply to the soil depends upon several 

 soil conditions, besides the question of which is most available 

 for purchase. If a heavy supply of organic matter has been plowed 

 under and a rapidly growing crop, such as cabbage or other truck 

 crop, is to occupy the field immediately, quick lime, or calcium 



