650 



SCIENCE 



[N. S. Vol. XLIV. No. 1140 



down in the rainfall, including also nitrous and 

 nitric acid, produced as described above, tend to 

 unite in the soil with the most readily attackable 

 bases in the basic silicates and with the lime of 

 the carbonate of lime before they can attack raw 

 rock phosphate effectively. 



That the acids attack the hasic silicates is 

 agreed, and this means that some of the 

 potash minerals naturally contained in the 

 soil are thus rendered soluble, and the potas- 

 sium contained in them made available to 

 higher plants. Potash minerals are important 

 and abundant constituents of all normal soils. 

 The idea conveyed by this part of the quoted 

 statement is in agreement with the published 

 results of the Illinois Experiment Station 2 and 

 was sufficiently considered by the authors of 

 Bulletin 190, as the following quotation indi- 

 cates : 



The nitrous acid produced may act upon com- 

 pounds of iron, aluminum, potassium, sodium or 

 magnesium which occur in soils or it may act upon 

 tricalcium phosphate, calcium silicate or calcium 

 carbonate, if present. 



To intimate, as Wheeler does, that the acids 

 will choose to unite first with these basic 

 silicates before attacking effectively the raw 

 rock phosphate, is not in accord with the scien- 

 tific facts, nor does it appear to be sound 

 chemical reasoning, and no mention is made 

 by "Wheeler of the acid silicates contained in 

 the soil which may react with raw rock phos- 

 phate. To establish minute acid and alkaline 

 areas in the soil is to approach the ideal for 

 both the biological and chemical factors to 

 work in unison in liberating insoluble ma- 

 terials. Ground limestone made up of vari- 

 ous degrees of fineness actually provides 

 alkaline areas, and fermentations of organic 

 residues are always developing acid areas. As 

 raw rock phosphate is dissolved by acids, 

 whether produced by bacteria or by chemical 

 means, and, as it is so placed that some of it 

 must have contact with the fermenting areas, 

 it is not difficult to understand why it be- 

 comes soluble and why it produces increased 

 crop yields, even though at many other points 

 in the soil centers of alkalinity exist. 



The tricalcium phosphate used by us is 



2 Bulletin 182, "Potassium from the Soil." 



commented upon by Dr. Wheeler as " an espe- 

 cially soluble artificial tricalcium phosphate." 

 If tricalcium phosphate was a soluble material, 

 which of course it is not, there would have 

 been no logical reason for conducting the 

 experiments. 



The " high temperature " of the experiment 

 is mentioned by Wheeler, and, although of 

 minor importance, we note from the records 

 that during the seventy-eight days from July 

 4 to September 18, 1916, there were sixty- 

 one days on which the temperature of the 

 air ranged above that of the experimental 

 laboratory. At best, temperature could only 

 influence the rate of biochemical action in 

 this experiment. 



In regard to the statements bearing on the 

 extent of this solvent action of nitrite bac- 

 teria in soils, it is necessary to quote in part 

 the last paragraph of Wheeler's letter. 



In their hope of confining the solvent action of 

 the nitrous acid as fully as possible to the raw rock 

 phosphate, Hopkins has recommended that the phos- 

 phate be turned under in intimate contact with or- 

 ganic matter, yet when one realizes the even closer 

 contact of the many soil particles with the organic 

 matter at the same time, it will be obviously im- 

 possible for the nitrous acid to attack wholly or 

 even chiefly the raw rock phosphate. 



In the table below taken from Illinois Bul- 

 letin 190 are presented the amounts of phos- 

 phorus, calcium, and nitrogen required by 

 standard crops, and the amounts of phosphorus 

 and calcium which would be made soluble if 

 all the nitrogen required for the crop should 

 be oxidized to nitrate and should act upon 

 pure rock phosphate. 



The figures show that there is possible of 

 solution from this biochemical process about 

 7 times as much phosphorus as corn, wheat, 

 or oats require, and 9 times as much as 

 timothy requires. Greater differences occur 

 in the calcium figures, there being possible of 

 solution 14 times that required for corn, 18 

 times that required for wheat, 12 times that 

 required for oats, and 8 times that required 

 for timothy. 



Nowhere in Dr. Wheeler's letter has he 

 pointed out that the nitrous acid furnishes 



