118 CHEMISTRY OF FARM PRACTICE 



terials are secured by buying them in car-load lots from 

 the manufacturer or wholesaler. The author has known 

 as great a difference as 60 per cent in cost between buying 

 in car-load lots from the wholesaler and in buying in small 

 quantities from the retailer. 



Experiments have been conducted to determine which 

 source of phosphorus is most effective for the different 

 crops on different soils, taking into account the cost of 

 the material carrying the phosphorus. The results of these 

 experiments agree that ground phosphate rock is the most 

 economical source of phosphorus on the market. It has 

 an additional advantage in that its content of phosphorus 

 is higher than that of any other commercial source, thus 

 enabling the purchaser to transport a large number of 

 pounds of phosphorus in a ton of material. Its chief 

 disadvantage lies in the fact that it is the most unavail- 

 able source of commercial plant food. 



Ground phosphate rock can be used to advantage under 

 two sets of conditions: 



(a) For sprinkling in stalls or barnyards where animal 

 manures are accumulating. This addition of ground phos- 

 phate rock should be made at intervals so that it will be- 

 come thoroughly incorporated with the manure. It is 

 advisable to add ground phosphate rock at the rate of 

 from 50 to 100 pounds for each ton of manure accumulated, 

 the quantity within these limits depending upon the total 

 amount of manure to be applied per acre. If applications 

 of more than 12 tons of manure per acre are to be made, 

 50 pounds of ground phosphate rock per ton should suffice; 

 if lighter applications of manure are to be made, 100 pounds 

 per ton would be preferable. The thorough incorporation 

 of the finely ground phosphate in the animal manure will 

 subject a large surface area of that material to the action 

 of the acids present in the manure, causing some of it to 

 be converted into the more available forms. After the 

 manure is applied to the field, the processes of nitrifica- 



