EFFICIENCY OF FERTILIZERS 361 



and by producing phosphate of lime, renders the phos- 

 phoric acid more available for the plant. 



230. Organic matter. The ways in which organic 

 matter contributes to economy in the use of fertilizers 

 are: (1) By improving the soil structure. (2) By con- 

 serving moisture. (3) By producing through decompo- 

 sition carbon dioxide which, dissolved in water, is a 

 weak but continuously acting solvent of the mineral 

 fertilizers; also by forming organic acids that act in a 

 similar way. (4) It furnishes a source of food and energy 

 for bacteria, which aid in rendering soluble the absorbed 

 fertilizing constituents. 



It is particularly in rendering available to plants the 

 more difficultly soluble phosphate fertilizers that organic 

 matter directly aids in making fertilizers more effective. 



Farm manure is undoubtedly the best all-round ferti- 

 lizer to be had. In addition to adding organic matter and 

 certain mineral plant-food materials, it introduces into 

 the soil, and furnishes a favorable medium for the growth 

 of large numbers of bacteria that are of great value in 

 rendering available the plant nutrients contained in soils. 



The use of raw or untreated phosphates to replace 

 superphosphates in soil manuring has received much 

 attention in Germany and to some extent in this country 

 in recent years. Raw phosphates, being much more 

 difficultly soluble than the superphosphates, do not, 

 under most conditions of the soil, give as marked 

 returns. On the other hand, the raw phosphate has the 

 advantage of being very much cheaper, and of not con- 

 taining sulfuric acid. The extent to which raw phosphates 

 will become available in the soil depends largely on the 



