630 Circular No. 7. 



quantity. It is the form in which nature has appHed Hme most largely 

 and with the results of which we are familiar. The saying that a 

 limestone soil is always a fertile soil may be too broad and indefinite, 

 but it has a large basis of truth. Note the blue-grass soils of south- 

 eastern Pennsylvania, the Valley of A^irginia and north-central Ken- 

 tucky ; also much of the wheat land of the northwest, where we have 

 observed 50 per cent of lime carbonate in layers of soil near the surface. 

 Supporting these observations are the positive results of several 

 experiment stations over a period of years. To quote only one or two, 

 Maryland found a somewhat larger yield from five years' results, 

 including 3 crops of corn and one of wheat, when 13,000 pounds shell 

 marl or 2,600 pounds of ground shell lime were used than when 1,400 

 pounds of lump lime were used. 



Average of Plots, 5 Years. 



Grain. . Straw. 



Ground lime stone 8,240 lbs. 13,750 lbs. 



Caustic lime 7,440 lbs. 12,100 lbs. 



Hunt summarizes 25 years' experience with lime in a four-year 

 rotation of corn, oats, wheat and clover at the Pennsylvania Station. 

 This shows that for the whole period, 4,000 pounds of lump lime once 

 in four years gave poorer results than 4,000 pounds ground limestone 

 every two years. 



Limestone or marl will do the work, but this fact need be no dis- 

 couragement to the lime dealer. We have shown that all forms of 

 lime come to the carbonate form in the soil. We shall next show that 

 the effect and availability of lime is determined very largely by its 

 degree of fineness and the thoroughness with which it is mixed with the 

 soil. The matter therefore resolves itself into the question of the form 

 in Zi'hich the largest amount of lime in the finest state of division can be 

 gotten on the soil. Practically, it is often more convenient to reach 

 this proper degree of fineness through burning than through grinding. 



4. Fineness of division. The finer the form of the lime the 

 greater its availability. Excluding the sulfates, we are inclined to 

 put more emphasis on the fineness than upon the combination, whether 

 oxid, hydrate or carbonate. Considering the calcium content, the first 

 cost and freight and the fineness, it is often better to use the lump or 

 hydrated or ground lime than the ground limestone or marl. We 

 usually put the matter to farmers on this basis. It is found impos- 



