350 ANNUAL REPORT OF THE Off. Doc. 



limestone has been substituted for the quicklime. Limestone is a 

 combination of calcium or more commonly of calcium and mag- 

 nesium with carbon and oxygen. When the limestone is burnt its 

 carbon combines with part of the oxygen and goes off as carbon di- 

 oxide, the carbonic acid gas of the older chemistry. This combina- 

 tion constitutes nearly half the weight of the original stone, so that 

 it requires approximately two tons of limestone to carry the amount 

 of calcium and magnesium found in one ton of burnt lime; and since 

 it is impossible to grind the stone to as fine a powder as that pro- 

 duced by burning and slaking we should use at least two tons of 

 powdered stone as the equivalent of one ton of burnt lime. 



In slaking, lime absorbs about one-third its weight of water, so 

 that it requires a ton and a third of hydrated lime to carry as much 

 calcium as is found in one ton of burnt lime. 



When exposed for a long time to the air carbon dioxide is absorbed, 

 and the lime reverts to its original condition of carbonate of lime. 



Lime is not required by all soils, and when used in excess may 

 cause loss instead of gain. This is shown by the experiments at 

 Pennsylvania State College, the soil of which overlies limestone, in 

 which two tons of burnt lime applied every 4 years, in a rotation of 

 corn, oats, wheat and clover, has caused a reduction, instead of an 

 increase, in yield, except when used in connection with yard manure, 

 when the yield was somewhat greater than from the same quantity 

 of manure used in the absence of lime. 



One of the effects of lime is to cause a rapid decomj)osition of the 

 organic matter in the soil by fostering bacterial action, and when the 

 lime is not supplemented by manuring or by such use cf other fertil- 

 izing materials as will favor a larger growth of crops, and ther»^fore 

 of crop roots, the stock of organic matter mar be so depleted as to 

 reduce the yield of the land. Where ground limestone was used in- 

 stead of burnt lime, in the Pennsylvania experiments, there was a 

 small increase in yield. 



In pot tests at the Ohio Station, made on a very acid soil, the 

 yield fell off when burnt lime was applied in excess of seven tons per 

 acre, although ground limestone was used up to twenty-five tons per 

 acre without any sign of injury. 



These results show the fundamental importance of lime in the 

 maintenance of fertility, because of its great effect on the clover 

 crop ; but also show that lime cannot take the place of other fertiliz- 

 ing elements, but can only perform its full service when associated 

 with phosphorus, potassium and nitrogen, all three; no one of the 

 four can be omitted in the treatment of a soil which has been de- 

 pleted of its fertilit}^ of such exhaustive husbandry as had the one 

 under this experiment. 



It does not follow, however, that it is necessary to add lime to all 

 soils. Attention has already been called to the small effect of lime 

 on the soil overlying limestones at Pennsylvania State College. The 

 Ohio Station has a test farm in western Ohio, where the underlying 

 rocks and limestones, and where experiments with fertilizers, manure 

 and lime have been in progress for eleven years. In these experi- 

 ments, fertilizers carrying phosphorus, potassium and nitrogen are 

 producing practically the same effect that has followed the use of 

 similar fertilizers at the main station, but the increase from lime is 

 comparatively insignificant. 



