920 



SCIENCE 



[N. S. Vol. XLIV. No. 1148 



some writers for the purpose of making it appear 

 that the same reaction will take place in the soil 

 in connection with raw rock phosphate to essen- 

 tially the same extent. This, however, is not true, 

 as will be explained. 



All agricultural soils contain the bases soda, 

 lime, potash and magnesia combined as silicates. 

 Often these silicates are highly basic or, in other 

 words, the proportion of base to the silica is so 

 great that pure water will dissolve appreciable 

 quantities of the bases. Furthermore, if soils have 

 been limed heavily, especially with coarse lime- 

 stone such as has been recommended by Dr. Hop- 

 kins, they are likely to contain in addition some 

 carbonate of lime. The organic acids and the car- 

 bonic acid produced in the decomposition of veg- 

 etable matter or brought down in the rainfall, in- 

 cluding 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. In 

 other words, when nitrous acid is produced in a 

 soil which has been properly limed and has, there- 

 fore, been rendered sufficiently basic for the best 

 production of agricultural plants, it is incredible 

 that all or most of it will react upon raw rock 

 phosphate in the soil to the extent that it did in the 

 water cultures used by Hopkins and Whiting in 

 which there was nothing but phosphate which it 

 could attack. 



In this connection let me cite Lyon, Fippin and 

 Buckman who, in their recent book on soils, say: 



"It has been found, for instance, that calcium 

 carbonate decreases the availability of raw rock 

 phosphate and bone meal. ' ' 



This action of the calcium carbonate is similar 

 to the action of the highly basic silicates, and it 

 corresponds to the action of the ammonia in stall 

 manure when it is stored under the best condi- 

 tions for its preservation, for the ammonia com- 

 bines with the acid so readily as to interfere seri- 

 ously with its solvent action on raw rock phos- 

 phate. In fact, it was probably because of this 

 that Hartwell and Pember in Rhode Island and 

 Hart and his coworkers in Wisconsin failed to 

 demonstrate that composting manure and raw rock 

 phosphate made the latter soluble or highly avail- 

 able to plants. 



In this connection note what Director Thorne, of 

 the Ohio Agricultural Experiment Station, says: 



"Where we have used floats as a reenforcement 

 of manure on this farm alongside of acid phos- 

 phate, the acid phosphate has given us a slightly 

 larger net gain in the average of the 18 years' 



work, and a decidedly larger gain during the last 

 half of this period — a result the opposite of what 

 we expected when we started the experiment. The 

 floats and the acid phosphate being used in the 

 same quantity, or 40 pounds per ton of manure, we 

 expected that the larger accumulation of phos- 

 phorus in the soil due to the floats would finally 

 result in the floats exceeding the acid phosphates in 

 total and net gain, but this has not happened. ' ' 



If there were such a tremendous solvent effect 

 of raw rock phosphate in the soil as some writers 

 would make us believe after they have read and 

 commented upon this bulletin, it is surprising that 

 the Tennessee Agricultural Experiment Station 

 should report as it does on raw rock phosphate, for 

 Professor Mooers says: 



"In reply to your recent inquiry will say that 

 we have not published anything recently with re- 

 gard to the comparative values of acid phosphate 

 and rock phosphate, but we have conducted ex- 

 periments with these two materials on various 

 types of soil in different parts of the state for the 

 past ten years. The results of our experimental 

 work do not allow us to recommend raw rock phos- 

 phate for general use. In fact, we discourage its 

 use anywhere in the state and recommend acid 

 phosphate as the most profitable of all phosphates. 

 In some of our experimental work the raw rock 

 has given profitable returns, but in no instance 

 clearly equal to acid phosphate. In all of the ex- 

 periments the two materials have been used in ap- 

 proximately equal money values and in connection 

 with green manuring, which is supposed by some 

 to increase appreciably the availability of rock 

 phosphate. 



"In some of our experiments conducted on soils 

 especially poor in phosphoric acid the returns 

 from the rock phosphate have been very meager 

 and not at all comparable with those from acid 

 phosphate. For .us to give the preference to rock 

 phosphate would be to ignore all of our experi- 

 mental data. I may add that when the land is 

 limed the acid phosphate shows considerably 

 greater superiority over the rock phosphate than 

 where unlimed. " 



The work of Hopkins and Whiting was done on 

 an especially soluble, artificial triealeium phos- 

 phate, in a solution in a glass vessel kept at a 

 high temperature where the acid could attack noth- 

 ing but the phosphate, whereas the farmer has to 

 deal with a soil containing far more readily de- 

 composable silicates and carbonates, substances 

 upon which the acid can react to a very large ex- 

 tent before it has a chance to attack the less sol- 

 uble raw phosphate rock. 



