706 Ground Mineral Phosphates as Manures. [Nov., 



GROUND MINERAL PHOSPHATES 



AS MANURES. 



D. A. Gilchrist, 

 Professor of Agriculture, Armstrong College, 

 Newcastle-upon-Tyne. 



Dr. Aitken's Experiments in Scotland, 1879-1889. — Trials 



of ground mineral phosphates were made for many years at the 

 Pumpherston Agricultural Experimental Station of the High- 

 land and Agricultural Society of Scotland, by the late Dr. 

 Aitken, Chemist to the Society. The results are now of 

 special interest when ground mineral phosphates are again 

 being offered to farmers in considerable quantity. Dr. Aitken 

 conducted trials for seven years previous to 1886, and found 

 these ground mineral phosphates very erratic in their action. 

 He concluded* that their utility varied with the softness of the 

 mineral, and with the fineness of grinding. The phosphates 

 which produced the best results were Carolina land phosphaie, 

 Belgian phosphate, and Aruba phosphate, but these were also 

 the finest ground. He reported that they produced better 

 results in wet than in dry seasons, and that they acted best 

 on land rich in organic matter. He also found that phosphatic 

 guano and precipitated phosphate acted better than ground 

 mineral phosphates, but that bone ash did not act so well. He 

 concluded that superphosphate was the most reliable kind of 

 phosphate for general use, but that with a more thorough 

 system of grinding the dissolving of phosphates might be 

 dispensed with. 



In the following year Dr. Aitken recorded! most valuable 

 results on the value of mineral phosphates of different degrees 

 of fineness. In 1886 he conducted at Pumpherston trials of basic 

 slag containing 40 per cent, phosphates (then a new manure), 

 and the following ground mineral phosphates : — Curacao, 87 per 

 cent, phosphates; Canadian, 59 per cent, phosphates; Carolina, 

 57 per cent, phosphates; and Belgian, 40 per cent, phosphates; 

 and also of superphosphate, 28 per cent, soluble phosphates. 

 The crop was turnips and the plots were one-twentieth of an 

 acre in area. In all cases the plots received (per acre) 100 lb. 

 of sulphate of ammonia and 60 lb. of sulphate of potash (50 

 per cent, potash). He found, although all the ground mineral 



* Transactions of! t lie Highland and Agricultural Society, 1X8>>, p. 351. 

 t t)o. do. * , 1887, p. 245.' 



