114 



Journal of Agricultural Research 



Vol. XVI, No. 4 



In the lower concentrations a given molecular quantity of potassium 

 carbonate is much more toxic to the nitrifiers than is an equivalent 

 molecular quantity of the sulphate, nitrate, or chlorid, the toxicity of the 

 compounds varying in the order named. 



In the highest concentration tested the chlorids reduce the nitrify- 

 ing powers to 35.6 per cent, the sulphate to 32.4 per cent, the nitrate to 

 2.5 per cent, the carbonate to 14.8 per cent. 



The toxicity of the potassium salts is governed largely by the elec- 

 tro-negative ion combined with the potassium and if the osmotic pres- 

 sure plays any great part it is masked by other factors. 



INFLUENCE OF CALCIUM SALTS 



The compounds used in this series were calcium chlorid, calcium 

 nitrate, calcium sulphate, and calcium carbonate. The first two were 

 added to the soil according to the usual method from a standard solution, 

 whereas the sulphate and carbonate were weighed into the soil, carefully 

 mixed, and then treated in the ordinary manner. 



A number of determinations were made in each case and compared 

 with sterile blanks, so that the results as reported in Table VI are the 

 average of four or more closely agreeing determinations. 



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

 dried blood and varying amounts and forms of calcium salts 



[The untreated soil is taken as loo per cent) 



Fraction of molecular weight in loo 

 gjn. of soil. 



Amount of 

 calcium. 



Percentage of nitric-nitrogen formed in presence of — 



Calciujn. 

 chlorid. 



Calcium 

 sulphate. 



Calcium 

 nitrate. 



. Calcium 

 carbonate. 



None 



78X10-^ 

 156X10-^ 

 3I2XIO-". 

 625X10-''. 

 lasXio-**. 



25Xi<^'. 



iXio-3. 

 2X10-^ 

 3X10-3. 



P.p. in. 



None 

 3. 12 

 6. 24 



12.35 



24. 82 



49.64 



99. 28 



198. 56 



397- 12 



794. 24 



1191.36 



100. o 



87.9 



79.0 



88.2 



84.0 



86.8 



127.4 



160.3 



167. 6 



124- 5 

 99.2 



117. I 

 "5-9 

 143-9 

 140.9 

 125. o 

 148.8 



151- 7 

 180.6 

 196.7 

 189. 2 



100. o 

 99. I 

 88.8 



92-5 

 102. I 



92. I 

 100. 8 



86.9 



46.8 

 • 0.4 

 ■ 20. 2 



100. o 

 99.4 

 97.2 

 97.2 

 85-3 

 95-9 

 97.2 

 79.0 

 82.0 

 59-2 

 59-1 



In marked counterdistinction to its action on the ammonifying 

 organisms, calcium carbonate fails to stimulate in any of the concentra- 

 tions. This, however, is not surprising, as the soil which is being used 

 in this work contains over 12 per cent of calcium carbonate, which is 

 undoubtedly abundant for the maximum activity of these organisms. 

 We do, however, find a gradual increase in toxicity as the quantity of 

 calcium carbonate added to the soil increases, so that by the time 1,191.4 

 parts of calcium in the form of the carbonate have been added the nitri- 



