No. 4.] KEEPING UP FERTILITY. 105 



the cost. A pound of soluble phosphoric acid in super- 

 phosphates costs til)out six and one-half cents. A pound 

 of acid almost entirely in insoluble form, as in South 

 Carolina rock, can be bouiiht for about three cents. If 

 required for immediate use by the plant, the farmer must 

 pay the hio:her price ; but if he can buy and apply in advance 

 of present need, he may effect a saving by buying the 

 cheaper form. Nature will in the course of a few years 

 render it available. 



Dr. Goessmann's special phosphoric acid experiments are 

 of interest in this connection. Without going into details, I 

 may say that his plan is to apply equal money's worth of 

 phosphoric acid in different materials to plats of land liber- 

 ally supplied with nitrogen and potash. The materials 

 selected have been dissolved bone-black, South Carolina 

 phos})hate, Florida rock phosphate, INIona guano and phos- 

 phatic slag. According to the system followed, two or three 

 pounds of phosphoric acid in the cheaper natural phosphates 

 have been applied for every one pound in the bone-black. 

 This experiment began in 1890, the crop being potatoes. 

 The dissolved bone-))lack gave the largest crop, but was 

 followed closely by the South Carolina phosphate and the 

 phospliatic slag. In 1891 the crop was winter wheat. The 

 South Carolina phosphate, Mona guano and the slag each 

 gave a larger yield of grain than the bone-black, but the lat- 

 ter gave considerably more straw than either. In 1892 the 

 crop was serradella. The plats in the order of their yield, 

 beginning with the largest, were : phosphatic slag, Mona 

 guano. South Carolina phosphiite, dissolved bone-black and 

 Florida phosphate. The last-named, however, received no 

 phosphate the previous year. That plat the first year re- 

 ceived apatite, but the second year it was not possible to get 

 any apatite, and therefore no phosphate was applied. In 

 1893, the crop being corn, the order of yield of graiii was : 

 Mona guano, South Carolina phosphate, dissolved l^one- 

 black, phosphatic slag and Florida phosphate. Both the 

 slag and the Florida phosphate stood relatively much higher 

 in yield of stover. During the past year the field has been 

 in barley without the further application of phosphates, and 

 the order of yield has been : phosphatic slag, Mona guano, 



