502 Journal of Agricultural Research voi. vi, no. 13 



The solutions dissolve very little of the phosphorus from the insoluble 

 phosphate. 



Brown rock phosphate and Florida soft rock phosphate gave the best 

 results vath clover, but the former was very much better suited for oats 

 than the latter. There is a slight indication that phosphates which are 

 more soluble in water are more easily assimilated by plants. 



THE INFLUENCE OF FERMENTING DEXTROSE AND CROP RESIDUES 

 ON THE AVAILABILITY OF PHOSPHORUS IN FINELY GROUND ROCK 

 PHOSPHATE 



Though the data are not conclusive, a large number of field experiments 

 conducted in America show that raw phosphate, when applied in con- 

 junction with organic matter, produces very appreciable increases in 

 crop yields. The work which follows is an effort to determine the in- 

 fluence of decaying substances on the availability of the phosphorus in 

 crude phosphate rock. Dextrose was employed because it ferments 

 rapidly under greenhouse conditions. Crop residues are also included 

 in this section, but owing to the slow growth of crops through the winter 

 months it will not be possible to do more than to make a preliminary 

 report on this phase of the problem. 



Throughout the study included in this division, the glass battery jars 

 were utilized with success and the same quantity of sand employed as 

 previously noted — namely, 4,800 gra. per pot. For all the cultures grown 

 in the dextrose section, the sand was leached with dilute hydrochloric 

 acid. 



The first series reported below was outlined primarily to secure data 

 on the value of rock phosphate alone and in conjunction with dextrose 

 for rye and clover. It will be observed that the applications of the rock 

 phosphate and the dextrose were made on the percentage basis. In 

 order to hasten fermentation, an infusion from a rich soil was a part of 

 the treatment. This series was planted on April 12, 191 3, and harvested 

 on August 19, 1 91 3. 



Since dextrose applied at the rate of 48 gm. per pot injured the rye and 

 destroyed the clover, a point of importance to decide was what quantity 

 v/ould not injure plant development, but would assist in the liberation of 

 phosphorus. With this point in mind, series 6 was planned. The 

 planting was done on June 21, 191 3, and the crop harvested on December 

 I, 1913. (See Table XI.) 



The dextrose in series 5 had no beneficial influence. If the average of 

 pots 7, 8, and 9 is compared with the results from either set of pots i, 2, 

 and 3 or pots 4, 5, and 6, it will be evident that the dextrose is harmful. 

 Clover failed to make growth where the dextrose was added, but did 

 fairly well on the pots which received rock phosphate alone. 



