SOILS AND FERTILIZERS 427 



stituents (potash and phosphoric acid) in which it is somewhat 

 deficient. Caustic lime has been found effective in destroying the 

 denitrifying power of manure, above referred to, but there are cer- 

 tain serious objections to its use. It is well known that it has a 

 tendency to drive off ammonia from organic matter such as manure. 

 However, if the lime is applied to the fresh manure, the danger of 

 loss from the escape of ammonia has been found to be very small. 

 It is only after fermentation has commenced in the manure that the 

 danger of loss on application of lime becomes serious. It has been 

 suggested that it might be safe and economical to mix caustic lime 

 or marl with the manure to destroy its denitrifying power and to 

 cover the heap with earth to prevent the escape of ammonia. A 

 second objection to lime is that it tends to convert the available 

 nitrogen of manure into insoluble and less available forms, but this 

 tendency is, in a measure, compensated for by the fact that, in ad- 

 dition to destroying the denitrifying organism, as already explained, 

 the lime promotes nitrification, or the formation of nitrates, when 

 the manure is applied to the soil. Lime should not be used in con- 

 nection with superphosphate, because it renders the phosphoric 

 acid which the latter contains insoluble and destroys the effective- 

 ness of the superphosphate as a preservative. 



Bisulphid of carbon almost entirely destroys the denitrifying 

 organism, but its use in practice is not recommended because of its 

 expensiveness. Sulphuric acid has proved very effective, not only 

 preserving the fertilizing constituents but increasing the availabil- 

 ity of the nitrogen, but its general use can hardly be recommended. 



One point which has been clearly brought out by recent inves- 

 tigation is that the addition of straw may very decidedly reduce 

 the fertilizing value of manure, the injurious effect being greater 

 the larger the amount of straw used. This is explained by the fact 

 that straw contains organisms which convert the available nitrogen 

 in manures and in the soil into forms which the plant can not util- 

 ize. The excessive use of straw as litter under animals should there- 

 fore be carefully avoided if the most effective manure is desired. 



A small amount of gypsum (land plaster) sprinkled on the 

 moist dung or urine is commonly used as a means of fixing the am- 

 monia. Kainit and acid phosphate (superphosphate) have also 

 been recommended as preservatives of manure, but recent experi- 

 ments indicate that none of these substances is of much value for 

 preventing loss of nitrogen, which is the main object of the use of 

 preservatives. In fact, the investigators who have given the most 

 attention to the subject of the preservation of manure are generally 

 disposed to attach much more importance to the proper use of ab- 

 sorbents and to keeping the manure heap compact and uniformly 

 moist than to the use of preservatives. If kainit and acid phosphate 

 are used they will increase the value of the manure by adding potash 

 and phosphoric acid. If applied in the stall they should be cov- 

 ered with litter so that they do not come in contact with the feet 

 of the animals. 



