oct.8,i92i Relation of Sulphates to Plant Growth and Composition 109 



the cultures receiving nitrate fertilizer the addition of sulphate sulphur 

 apparently caused increased growth or had just the opposite efifect. 

 If the concentration of the sulphates was great enough to produce a 

 toxic effect, the sodium nitrate may have counteracted this action. 



The wjiter has observed just the opposite effect with clover seedlings 

 growing on agar agar-mineral salt nutritive media. One gm. of sodium 

 nitrate per liter had a noticeably toxic effect, while the same concentra- 

 tion of sodium sulphate produced no noticeably injurious effect. In the 

 cultures containing both the same concentration of sodium nitrate and 

 sodium sulphate there was an improvement in growth over the former 

 sodium-nitrate cultures. 



Application of nitrates produced very good 5delds on a comparative 

 low sulphur assimilation by the plants. The question naturally arises 

 whether the rape does not absorb sulphur, if present, far in excess of that 

 required for carrying on the synthesis of its organic compounds. This 

 appears so noticeable in comparing the figures in Table V. Of course 

 it is realized that the optimum concentration of nutrients for plant 

 nutrition has always been a problem. The acetic acid-insoluble nitrogen 

 is higher in the rape grown on the soil receiving nitrate fertilizer only, 

 compared with that in the rape which received both nitrate and sulphate 

 fertilizer. There seems to be a tendency of the sulphates to decrease 

 this form of nitrogen. Sulphate application increased the organic 

 sulphur and total sulphur content of the rape, while at the same time the 

 presence of these sulphate compounds retarded growth where no nitrates 

 were added. The extremely high sulphate content is very obvious in 

 these samples of rape. This may account for the high ash content. The 

 percentage of ash in the samples of rape varies considerably, depending 

 upon the fertilizer treatment and magnitude of growth. Such a variation 

 did not occur with the clover. 



SUMMARY 



Sodium sulphate and calcium sulphate had a beneficial effect on 

 nodule development and nitrogen assimilation of the red clover grown 

 on previously sterilized soil. On a similar series which was artificially 

 inoculated with Bacillus radicicola at the time of seeding, sulphates 

 caused no increase in nodule development. 



When a soil of high sulphur content was used, the nitrogen content in 

 clover of the third and fourth crops was lower on the control pots than 

 where either sulphur, calcium sulphate, or sodium sulphate was applied. 

 As sulphate sulphur was present in all plants, the low nitrogen content 

 could not be explained by a cessation in protein synthesis due to the 

 absence of sulphates. 



This again shows the relation of sulphates to nitrogen assimilation and 

 the favorable influence of sulphates on the legume bacteria or on some 

 other agency controlling nitrogen assimilation. 



