284 Bacteria in Relation to Country Ldfe 



organin phosphorus of the humus. As to the rate at 

 which the phosphorus of the humus may become avail- 

 able under different soil conditions, and as to the value 

 of such phosphorus compounds as compared with mineral 

 phosphates, we know practically nothing. Certain in- 

 vestigations seem to establish a certain relation between 

 the reduced content of organic phosphorus and the de- 

 pleted fertility of the prairie soils. 



Bacterial activities and phosphate fertilizers. — Phos- 

 phate fertihzers like ground phosphate-rock (floats), 

 ground bone, superphosphates, and Thomas slag, are 

 likewise affected by the activities of soil bacteria. It is 

 well known that floats may be made more effective and 

 more available by being composted with barnyard 

 manure. In the light of the foregoing remarks, it is not 

 difficult to understand why this should be so. The 

 barnyard manure with its vast numbers of bacteria, its 

 organic matter undergoing decay, and its large amounts 

 of carbon dioxid, must of necessity hasten the solution 

 of the insoluble phosphate. Similarly, in the case of 

 green-manures, particularly those rich in nitrogen, the 

 use of floats may yield profitable returns. Conditions 

 favorable for the rapid increase of bacteria and of bac- 

 terial products are thus created and, therefore, also for 

 the comparatively rapid conversion of the insoluble 

 phosphoric acid into available forms. 



From the standpoint of soil fertility, in its more 

 permanent relations, this matter is of very considerable 

 economic significance. If, by the proper supply of organic 

 materials and the proper encouragement of bacterial 

 activities largerreturns can be secured from the untreated 



