118 



Journal of Agricultural Research 



Vol. XVI, No. 4 



The manganous carbonate is peculiar in that at the lower concentration 

 it is toxic, but at a concentration of 125 X io~^ mole it acts as a stimulant. 

 The chlorid is most active at 156X io~" mole, and in the next concentra- 

 tion the nitric nitrogen content of the soil is reduced to one-half-normal, 

 and at a concentration of 3X io~^ mole there is only 4.5 per cent of the 

 normal nitric nitrogen present in the soil. 



The manganous sulphate stimulates throughout a much wider range 

 of concentrations than does the chlorid, and at the highest concentration 

 tested it had reduced the nitrification to only three-fourths-normal. 



Manganous nitrate is a more pov/erful stimulant than any of the other 

 salts, and stimulates in the same concentrations as does the sulphate, 

 but it is much more toxic in the higher concentrations than are any of 

 the other salts. Although the carbonate is not a very active stimulant 

 at any of the concentrations tested, neither is it very toxic. 



influence; of iron salts 



The compounds used in this series were ferric chlorid, ferric sulphate, 

 ferric nitrate, and ferric carbonate. All except . the carbonate were 

 added to the soil in solution. The carbonate was added in the form of a 

 dry powder and carefully mixed vnth. the soil. Considerable difficulty 

 was experienced in getting duplicate determinations to agree when the 

 sulphate was applied to the soil, and the results as reported represent the 

 average of eight sets of determinations. The chlorid, nitrate, and car- 

 bonate represent the average of four closely agreeing sets of determina- 

 tions The results are given in Table IX. 



Table IX. — Percentage of nitric nitrogen formed in loo gm. of soil containing 2 gm. 

 of dried blood and varying amounts and forms of iron salts 



[The untreated soil is taken as loo per cent] 



Aniou!:t oE iron. 



None 



2-9 



5-8 



II. 6 



23-2 



46. 5 



93- o 



186.0 



372-3 



744- 6 



I, 116. 9 



Percentage of nitric-nitrogen forjned in presence of- 



Ferric 

 chlorid. 



100. O 

 103.4 



101. o 



115- 5 

 1x6. 5 

 128. 4 

 103.4 



102. 6 



78-5 

 32.6 

 10. 9 



Ferric 

 sulphate. 



100. O 

 102. O 

 94. 2 

 67. O 

 82.8 

 97.1 



97-5 



98.9 



100. o 



84-3 

 87.9 



Ferric 

 nitrate. 



100. 

 95 

 95 

 92 

 90 

 89 

 86 

 89 

 53 



Ferric 

 c-arbonate. 



100. O 

 102.5 

 104. I 

 102. 9 

 96. o 

 99.4 

 100. 7 

 105.6 

 no. 7 

 117-4 

 104. 5 



From these results it may be seen that all of the iron salts, with the 

 exception of the nitrates, increase the nitric nitrogen of the soil. The 

 maximum stimulation for the chlorid occurs when 46.5 p. p. m. of iron 



