22 MAINE AGRICULTURAL EXPERIMENT STATION. 



same time becomes largely soluble in ammonium citrate. On 

 long standing a reverse action takes place, the phosphate pass- 

 ing again to the insoluble condition. It is probable that the 

 reversion is more rapid when roasted Redonda has been applied 

 to the soil. Comparatively little of this phosphate is sold, yet 

 on account of the high percentage of phosphoric acid which 

 it carries and the ease with which it may be converted into 

 the citrate soluble condition, it would prove a valuable fertilizer 

 if it is as available to the plant as the chemical analysis would 

 seem to indicate. 



A series of experiments has been carried on at this Station to 

 determine the relative value of three forms of phosphatic mate- 

 rials to eight common crops; and also, at the same time, to deter- 

 mine the varying ability of different crops to appropriate phos- 

 phoric acid from the same source. The phosphates used were: 



i. Acidulated Florida rock. That is, a rock phosphate that 

 had been treated with sulphuric acid, a large part of its phos- 

 phate being thereby converted into the available form. This 

 sample contained 20.60 per cent total phosphoric acid, of which 

 16.90 per cent, was available (14.97 per cent, soluble, 1.93 per 

 cent, citrate soluble.) 



2. Crude, finely ground Florida rock (Floats), containing 

 32.88 per cent, total phosphoric acid, none of which was soluble, 

 with only 2.46 per cent, soluble in ammonium citrate. This 

 was obtained from the commercial ground rock by stirring it 

 with water, allowing the coarse particles to subside and then 

 pouring off the turbid water. The '''Floats'"'" were the sediments 

 deposited from these washings. 



3. A phosphate of iron and alumina (Redonda), containing 

 49.58 per cent, phosphoric acid, a large part of which, 42.77 per 

 cent, was soluble in ammonium citrate. 



The plants grown were peas, clover, turnips, ruta-bagas. bar- 

 lev, corn, potatoes and tomatoes. The experiments were con- 

 ducted in the forcing house, wooden boxes being used, each 

 containing 120 pounds of clean sand. 



Ninety-six boxes were used, twelve for each kind of plant. 

 In the first box the acid rock was used: in the second, the crude 

 rock: in the third, the phosphate of iron and alumina; in the 

 fourth, no phosphate. The next four boxes were treated in the 



