214 Journal of Agricultural Research voi. iv, N0.3 



note that the nitrifying powers of soils were always found to be far supe- 

 rior in those containing mixtures of salts favorable to barley growth. 

 There appears to be a direct relation, therefore, between the nitrate-nitro- 

 gen supply and barley growth, as pointed out by the senior writer else- 

 where (4) ; and, further, in view of our specific tests in connection with 

 the experiments under discussion and others, there seems to be a direct 

 relationship between the qualitative and quantitative salt relationships 

 in a soil and its nitrifying power. Is it not just possible, therefore, that 

 in one important respect at least antagonism between ions in soils is 

 attributable to the improved conditions brought about in the nitrate 

 supply? One important question, however, would still remain: Why 

 does a certain salt combination improve the nitrifying power of a soil ? 

 This question may perhaps be solved by methods now being employed 

 by Loeb (7, 8) and Osterhout (13), but the answer thereto still appears to 

 be very remote. 



The puzzling fact, which has been referred to above, of the difference in 

 effect of a single salt on barley in the same soil in two successive crops 

 permits some interesting theoretical considerations. It appears possible 

 that the stimulating effect noted in the first crop as proceeding from the 

 addition of the lowest quantity of every one of the salts is to be attributed 

 indirectly to a physical improvement in the heavy clay-adobe soil for 

 reasons too well known to soil scientists to need discussion here ; in other 

 words, the yield of dry matter obtained with additions of o.i per cent of 

 sodium chlorid and o.i per cent of sodium sulphate is to be regarded as 

 representing the algebraic sum of the improvement in the soil's physical 

 condition through the action of the salt and the depression in growth 

 through direct influences on the barley plant and indirectly on the soil 

 bacteria. Assuming, however, that the improvement wrought in the 

 soil's physical condition is a greater factor for crop improvement in this 

 case than the last-named effects are for the depression of plant growth, 

 one would naturally expect that the results of the interaction of the two 

 phenomena must be to produce a larger crop in salt-treated soil than is 

 produced in the untreated control soil. The next question will be, there- 

 fore, How can one account for the remarkable improvement in the yield 

 of the control soil in the second crop ? This, it appears to us, is explicable 

 on the basis of a gradual improvement in the control soil during the 

 growth of the first crop through root action and appreciable changes in 

 contraction and expansion, resulting in better crumb structure; but 

 more completely through a physical improvement of the thoroughly 

 mixed, dry control soil, which is allowed to bake in the loose condition for 

 three months or more between the two crops. The crop produced in the 

 control pots during the second season therefore has all the advantages of 

 physical soil improvement, or many of them, possessed by the salt- 

 treated soil during the first season, and in addition is free from disad- 

 vantages introduced by the salt, as explained above. On the basis of 



