172 SYSTEMS OF PERMANENT AGRICULTURE 



applied in dolomitic limestone may produce quite as much benefit 

 for its own sake as will the element potassium on most soils where it 

 proves more or less beneficial. (The limestones in Pennsylvania 

 and in the northern parts of Ohio, Indiana, and Illinois are, as a 

 rule, more or less magnesian, containing, as an average, perhaps 30 

 per cent of magnesium carbonate and 60 per cent of calcium car- 

 bonate, with 10 per cent of impurities, which would be equivalent 

 to a purity of 95 per cent for the common limestone.) 



As an experiment, the double decomposition and leaching proved 

 a success, as is clearly shown in Series F, pot 6 being changed from 

 a sterile condition to as productive soil as any. It should be re- 

 membered that high temperatures may occur at a critical period, 

 and consequently seasonal variations are marked even in glass- 

 house cultures. Loew's ratio finds little support from these data. 



Incidentally, it may be stated that during the progress of these 

 experiments, several resistant plants have developed, w r hich 

 explains some apparent discrepancies in the yields of wheat from 

 pots near the border line of injury; and consequently the seeds 

 of these resistant plants have been used in part throughout one 

 or more series. In 1908, one half of each pot was planted with 

 ordinary (O.) wheat, and the other half with the resistant (R.) 

 strain, and, consequently, double the weights harvested are re- 

 corded for the 1908 yields. 



AMOUNT OF LIMESTONE TO APPLY 



From the information thus far secured, no fixed limits can be 

 placed upon the amounts of limestone to use as an initial applica- 

 tion to acid soils. One ton to the acre is more than enough to 

 destroy the acid commonly contained in the plowed soil, provided 

 the limestone is sufficiently fine and thoroughly mixed with the 

 soil; but, as a rule, it is less expensive to apply more limestone 

 and then to allow the mixing to go on more slowly by the neces- 

 sary processes of plowing, disking, harrowing, etc., in the regular 

 farm operations, keeping in mind also that the heavier the appli- 

 cation, the longer it will last. 



About one half of the water that falls in rain and soaks into the 

 soil is brought back to the surface from lower depths by capillary 



