The Relations of Lime to Soil Improvemext. 629 



seem to result in the more rapid destruction of humus than less soluble 

 forms. It must therefore be used in less amounts, in order not to 

 injure crop growth during the early period of its contact. Sandy soil 

 will stand less of this form than clay. In' soils low in humus, prob- 

 ably 1,200 pounds is a fair limit for sand and 1J/2 or 2 tons for heavy 

 clay. Those soils rich in organic matter will stand a larger amount 

 without injury. 



(b.) Basic slag is a readily available form of lime and of phos- 

 phate, without any inherent objectionable qualities. Its use is a mat- 

 ter of expense. The same point applies to ashes. 



(c.) In the case of all hydrates of lime it must be remembered 

 that they come ultimately to the carbonate form. The soil atmosphere 

 and moisture, especially where much humus is present, are several 

 hundred times as rich in carbon dioxid as the outside air. \\'hile lime 

 in large lumps " air slakes " relatively slowly, when in the fine pow- 

 der in which it should be incorporated in the soil, the change is rapid. 

 We know of no determinations of the rate of this change in the soil 

 and do not see how it can be accurately determined in normal soil ; 

 but there is much reason to believe that the reversion would be com- 

 plete in a few weeks at most. 



The availability of lime, whether as oxid, hydrate or carbonate, is 

 determined ultimately by the availability of the carbonate. 



(d.) The solubility of lime carbonate in pure water is about one 

 part to 30 thousand. But this does not at all measure its availability 

 in the soil. Lime carbonate is over 30 times as soluble in carbonated 

 water as in pure water, and the soil solution is a carbonated water. 

 The development of caves is due to this formation of the more soluble 

 bi-carbonate where carbon dioxid is present. Thus: 



Again, the availability of the lime is influenced by the organic 

 acids and by the numerous other mineral substances always in solution 

 in the soil water. There is abundant reason for the availability of 

 pure lime carbonate, which may be applied as ground lime rock or 

 marl. There is the further fact to be remembered that no injury 

 need be expected to follow the use of ground rock or marl in any 



