382 NATURE AND PROPERTIES OF SOILS 



conraged, soil bacteria will be stimulated, and more nutrients 

 will become available for crop use. Such stimulation, how- 

 ever, will soon wane, and if nothing is returned to the land, 

 productivity must ultimately drop back to even a lower level 

 than before the lime was applied. 



Lime is, to a great extent, a soil amendment and as it in- 

 creases crop growth, the draft on the soil becomes larger. 

 Greater effort is necessary, therefore, in order to maintain 

 the fertility of the land when lime is used than when such ap- 

 plications are not made. Farm manure, crop residues and 

 green-manures should be utilized to the fullest extent and 

 when these are insufficient to keep up the potash and phos- 

 phoric acid of the soil, commercial fertilizing materials must 

 be resorted to. Lime improperly used exhausts the soil, but 

 when properly and rationally applied it becomes one of the 

 important factors in the maintenanoe of a more or less con- 

 tinuous productivity. 



It is interesting in this connection to consider certain fig- 

 ures from the Ohio Experiment Station.^ Maize, oats, wheat 

 and clover and timothy were grown in a five-year rotation 

 on both limed and unlimed plats fertilized in various ways. 

 The results of table LXXXVII (page 383) are averages for a 

 period of twelve years. 



It is immediately evident that the effectiveness of the lime 

 was increased by the use of both fertilizers and farm manure. 

 Conversely, the returns from the fertilizers and the manure 

 were markedly influenced by the lime. The lime increased 

 the effectiveness of the acid phosphate 20 per cent. The in- 

 creases with the acid phosphate plus potassium chloride and 

 with the complete fertilizers were 22 and 10 per cent., re- 

 spectively. Lime increased the returns of farm manure only 

 4 per cent., indicating that manure itself may function as a 



^ Thome, 0. E., The Maintenance of Soil FerUUty, lAimng the Land; 

 Ohio Agr. Exp. Sta., Bui. 279, 1914. 



