62 



CONTROL SERIES No. 54 



Series III. Growth Secured with Double the Optimum Amount of Phosphoric Acid. 



Conclusions. 



Bearing in mind the undesirability of tlrawing conclusions from one season's 

 work, it does not seem out of place to indicate briefly the outstanding observations. 



1. In most instances, in both Series I and Series II, the availability based 

 ujjon i>hosplioric acitl recovery was higher than that based upon yield of dry 

 matter. 



2. In Series I, where the minimum ration of ])hosphoric acid was used (about 

 200 pounds of iihosphoric acid per acre), only one of the phosphate carriers, 

 Ammo-Phos (13-46), gave dry matter yields equaling 16% Superphosphate, al- 

 though three others — ^Precipitated Bone (imported). Triple Superphosphate, and 

 Ober Residue A — gave availability between 91 and 98+ on the basis of dry matter 

 yield. On the basis of phosphoric acid recovery, six carriers exceeded Super- 

 phosphate. In the order of greatest recovery they are: Triple Superphosphate, 

 Ober Residue A, Ammo-Phos (13-46), Ammoniated Sujierphosphate, Fused 

 Phosphate and Potash, and Basic Slag Phosphate {l(}%). Three other carriers 

 — High Grade Residue By-Product, Available Phosphate, and Precipitated Bone 

 (imported) — gave averages above 90. The recovery of a greater proportion of 

 phosphoric acid, accompanied by a very much smaller yield of dry matter, in 

 these six phosphates as compared with 16% Sujieriihosphate, is a fact rather 

 difficult to explain. It does not seem that it could be due to a deficiency of the 

 rarer elements of plant food, as care was taken to supply many of these in the basic 

 fertilizer ration. 



The raw mineral products — Colloidal Phosjihate and Finely Ground RocJ: 

 Phosphate did not show, in this series, any average gain in dry matter yield over 

 the no-phosphate pots. Based on recovery of phosphoric acid, they showed 

 availability amounting to one-fourth that of Superphosphate. 



Ober Residue B, as might be expected, gave a relatively low yield of dry matter 

 as well as phosphoric acid recovered, yet the average availability was better than 

 one-half the standard set by the Superphosphate, indicating that the phosphoric 

 acid left in the residue and ordinarily classed as insoluble phosphoric acid, has in 

 reality considerable plant food value. 



In case of the other products the tabulated results are self-exi)lanatory, and 

 show an average relative availability varying from 58 to 98 based on dry matter 

 yield, and from 64 to 95 based on recovery- of phosphoric acid, as compared with 

 Superphosphate at 100. 



