EXPERIMENT STATION BULLETINS. 291 



and clover. Soil acidity may be corrected by the use of some form of 

 lime. The forms of lime generally used for agricultural purposes are 

 the following : Burned or stone lime, air-slaked lime, ground lime stone, 

 and land plaster. Burned lime is the most active form of lime and is 

 quite caustic. It is usually obtained in lumps and must first be slaked 

 before it can be applied. This is conveniently done by putting it in 

 small piles and sprinkling just enough water over it so that it will 

 break down into a fine powder, or the piles may be covered with moist 

 earth and allowed to stand until it breaks down into a powder, when 

 it may be spread with a shovel. 



When the stone lime is exposed for some time to the atmosphere, it 

 gradually takes up moisture and breaks down into a powder form, 

 when it is known as air-slaked lime. Lime can be purchased in this 

 form and it may be applied with a drill or lime spreader. An ob- 

 jectionable feature to the use of either of these two forms is their 

 causticity, which renders them disagreeable to handle. 



The ground lime stone is now being prepared in this state and can be 

 obtained at reasonable rates. This form of lime is not as active as the 

 two mentioned above, but it has the same effect upon the soil and un- 

 doubtedly is much safer to use, especially when the lime must be ap- 

 plied immediately before the seed is sown. One hundred pounds of 

 ground lime stone is equal in neutralizing power to fifty-six pounds of 

 burned lime or seventy-four pounds of air-slaked lime. 



Land plaster was formerly used to quite a large extent both in the 

 United States and Canada, but at the present time its use is very lim- 

 ited. Since the lime in land plaster is already fully saturated with the 

 acid radicle of sulphuric acid, it cannot neutralize soil acidity, and its 

 beneficial eft'ects are supposed to be due to its power of making avail- 

 able some of the insoluble potash compounds in the soil. 



Marl is another form of lime that is more or less abundant in the 

 state. It is often found underlying marshes and along shores of small 

 lakes, and when it can be gotten out at not too great an expense, it is 

 a valuable form of lime to use for agricultural purposes. The lime is 

 in the form of the carbonate, the same as the lime rock and it varies in 

 purity from 50% to G0% calcium carbonate to nearly 100%. On ac- 

 count of the large amount of water which it contains in its natural 

 condition, it is not profitable to transport it for any considerable dis- 

 tance without first drying it. 



Available Plant Food. The availability of the plant food in a soil 

 is dependent upon several factors, the most important being those 

 mentioned above. When all of these conditions have been fulfilled, it 

 may then be profitable to use commercial fertilizers. It is a self-evi- 

 dent fact that the farmer who sells the greater part of the product of 

 his farm is slowly but surely depleting the stock of plant food in the 

 soil, and it is not unreasonable to assume that under such conditions 

 the time will come sooner or later when the soil will become unproduc- 

 tive for an actual lack of available plant food. Such deficiency may be 

 supplied by commercial fertilizers. The dairyman or stockman who 

 feeds the product of his farm to his cattle and judiciously cares for the 

 manure and puts it all back on the farm, need have but little fear of de- 

 pleting the store of available plant food in the soil, because the actual 



