No. 6. DEPARTMENT OF AGRICULTURE. 879 



The alfalfa shows a strange indiHereiice to the precise form in 

 which the phosphoric acid is supplied. The crop was light in every 

 case, and the phosphoric acid already present in the barren soil used, 

 seems to have sufficed for the slender product. 



STIMULATING EFFECT OF ACID PHOSPHATE IN THE EARLY STAGES 



OF GROWTH. 



A report of this work would be incomplete if it failed to take note 

 of certain facts observed in the course of the experiment which can- 

 not be shown in the diagram, where only the final results are given. 



Throughout the whole series of experiments the effect of the acid 

 rock was marked, the plants receiving it in nearly every case at 

 once taking the lead, and keeping- it to the end. The horse-beans fur- 

 nish a marked exception to this rule, the more nearly equal devel- 

 opment being perhaps due to the large amount of nutriment stored in 

 the seed. When this supply was exhausted, the phosphoric acid 

 hunger manifested itself. 



In by far the larger number of cases, especially with the clover, 

 timothy, turnips and rutabagas, the good effects of the acid rock 

 were more marked during the first few weeks of growth than ai a 

 later stage, when the roots become more fully developed, and had 

 begun to forage for themselves. This fact, also, is shown in the 

 figures of the clover and timothy. It would appear that the young 

 l)lants feed but little uj)on the insoluble phosphates, but that the 

 organic acids present in the sap of the roots exert a solvent action 

 upon the insoluble phosphates in Ihe soil, gradually converting 

 them into available forms. 



It will be noticed that in this work only the immediate effect of the 

 phosphates has been taken into consideration, no mention having 

 been made of the unused phosjjhoric acid remaining in the soil at 

 the close of the experiment. In actual field work, the good effect 

 of the ground rock would, of course, be far more lasting than that 

 of the iicid rock. 



liox experiments w^ere made at the New Hampshire Experiment 

 Station in 1S93, with winter rye, the phosphoric acid being suj)- 

 jilied by roasted Redonda, ground bone and basic slag. The re- 

 sult showed that the rye gave nearly as good returns with the 

 roasted Redonda as with the other phosphates. The result con- 

 firms the work here reported. It will be seen by reference to the 

 diagram here given that the corn, barley, oats and timothy (plants 

 closely related to rye) gave better results with the Redonda phos- 

 pliale than with the thiely giound Florida rock. 



