June 26, 1916 



Mineral Phosphates and Plant Nutrition 



491 



crops developed to full maturity, while the clover and alfalfa were cut 

 for hay. Cowpeas and soybeans grown during the winter months were 

 cut for hay, but those planted in the spring produced a seed crop. 



Complete data on time of blooming, time of heading, number of plants, 

 number of stems, and height of plants were collected for a comparison 

 which might be of value in interpreting results, although such records 

 will be omitted from, this paper. The total weight of grain and straw, 

 together with photographs, will suffice for drawing conclusions. 



After harvesting the pot cultures, the materials were suspended in 

 cheesecloth bags from the roof of the greenhouse for a period of two 

 weeks. This was sufficient time for the product to come to a constant 

 air-dried condition. Usually two weighings at an interval of two days 

 were made as a check to insure accurate results. 



ANALYSIS 



The plants were first cut fine and then ground in a steel mill until the 

 particles would pass a sieve of 80 meshes to the inch. Next, the materials 

 were thoroughly mixed and samples taken for analytical purposes. 



The method for the determination of phosphorus was essentially the 

 Pemberton outline, with slight modifications. 



Two gm. of the sample ^ were weighed out and moistened with calcium 

 acetate. The sample was then dried in an electric oven and afterwards 

 transferred to a muffle and there remained until the product was burned 

 to a white ash. The ash was taken up with 5 c. c. of nitric acid and 

 heated on a water bath for several minutes. It was necessary to filter 

 to remove any silica present. From this point the regular procedure 

 followed in the volumetric method was observed. 



The mineral phosphates used in this investigation represent six types 

 from different sections of the United States and Canada. The total 

 phosphorus and the phosphorus soluble in citric acid are reported in 

 Table I. 



Table I. — Total phosphorus and citric-acid-soluble phosphorus in various kinds of rock 



phosphate ^ 



Kinds of phosphate. 



Tennessee brownti rock pHosphate . . . 

 Tennessee blue rock phosphate . . . . 



Utah rock phosphate 



South Carolina land rock phosphate 



Florida soft rock phosphate 



Canadian apatite 



Phosphorus. 



Total. 



12.75 

 13.40 

 13.81 



13-75 



13.98 



". 75 



Soluble in 

 citric acid. 



9.92 



10. 29 



8.66 



6.89 



IO-55 

 5-57 



1 Two gm. was satisfactory for straw and hay, but for the grain }i cm. was sufficient. 



' Four gm. of each of the miner;;! i)liosph;ites were placed in a i-liter llask aiul then 1,000 c. c. of a 0.2 per 

 cent solution of citric acid was poured on the ground rock, where it remained for 48 hours with occasional 

 shaking. Then some of the solution was filtered and 100 c. c. of the filtrate taken for analysis. 



