It is also urged that ground mineral phosphates, undis- 

 solved, should be applied directly to the soil. But why add more 

 insoluble phosphoric acid when there is already in the soil a 

 supply for many centuries? The phosphoric acid which is 

 taken off in crops should be returned, but in a soluble, diffusible 

 form, not only to feed the growing crop, but by its catalytic 

 action to help in the diffusion and assimilation of other plant foods 

 and so hasten maturity, for time is everything in this latitude. 



Basic Slag Phosphates 



These are, no doubt, valuable in their place, but they have 

 their limitations. According to the official methods of analysis 

 in this country, slag phosphates contain no soluble phosphoric 

 acid. Therefore, when one applies them, he is only adding to 

 the sum total of phosphoric acid in the soil, of which the soil, as 

 we have seen, contains enough for centuries. Slag phosphates, 

 however, are made up of about one-fourth free lime, and are 

 valuable where the soil is acid. Probably a considerable part, 

 if not all, of the efficiency of slag phosphates is due more to the 

 free lime than to the phosphoric acid which they contain. If 

 one needs to use lime to sweeten his soil (and he frequently 

 does) and at the same time desires to apply additional phos- 

 phoric acid in an inexpensive form, we recommend a mixture 

 of 1,500 pounds of high grade superphosphate and 500 pounds 

 of agricultural lime. This will give a ton which will contain 

 as much active lime and practically as much phosphoric acid 

 as slags contain, and will cost less per ton than slags. It will also 

 have the advantage that the phosphoric acid will all be quickly 

 available and since available phosphoric acid (soluble and re- 

 verted) is absolutely essential in the growth of quick crops, the 

 application of acid phosphate and lime, applied separately or 

 combined in a mixture as suggested, will be found far more 

 efficient than basic slag phosphates, as well as less expensive. 



Potash, the Third Element 



Viewed from the standpoint of their chemical analyses, 

 potash (K2O) plays an important part in the structure of plants. 

 It is absolutely essential in the formation of the woody fibre of the 

 stalk and in the sugar and starch contained therein, and espe- 

 cially in tubers and roots like potatoes and beets. 



11 



Soluble 



and 



Diffusible 



Value 

 Chiefly 

 Due to 

 Lime 



A New 

 Mixture 



