ao July, 191 2.] Influetice of Certain Soil Constituents^ &^c. 399 



somewhat after the manner of hot lime, which is strongly alkaline. After 

 -a longer period (Table IV.) apparently it had all become converted into the 

 neutral carbonate, and it then exercised, a fine effect somewhat resembling 

 mild lime. Excess of magnesium carbonate may be harmful to crop plants, 

 but apparently this eftect will nut be exercised through its influence on 

 nitrification. 



SuperpJiosphatc has ap[)reciably increased the nitrification of added 

 ammonia as compared to the soil receiving no application (No. i), and on 

 referring to the chemical analysis of the soil, it is seen to be very poor 

 in phosphoric acid (-032 per cent.). The result is interesting as showing 

 that phosphates may help to nourish the nitrifying organisms as well as 

 the crop. Still the nitrate production is very far behind that of .several 

 other materials which have been considered. Where it is not required to 

 nourish the organisms, superphosphate being acid will probably do hann. 

 This particular subject has been investigated by Dr. Fraps in America.* 

 Working with ten different soils, he found that phosphatic acid decreased 

 the nitrate supply from 100 tO' 70 on the average of five soils, and in- 

 creased it from 100 to 196 on the average of the five others. 



Ferric Hydrate (No. 10) has been distinctly favorable to nitrification, 

 although it was slow, and the effect was chiefly noticeable at the later 

 date. Some recent inve.stigations at Rothamsted, by Ashby, indicate a 

 similar beneficial effect of iron rust (ferric hydrate) on nitrification, f The.se 

 experiments were conducted in water cultures, and it is Interesting to con- 

 firm the result here under .soil conditions. Red and chocolate soils con- 

 tain most ferric hydrate, and this may contribute to their fertility. 



Comiuoii Salt had a bad, eftect all round, and the larger application 

 {\ per cent.) Avas worse than the smaller (| per cent.). Crops fail on 

 salt or alkali soils, and no doubt the effect is produced in part by the 

 influence of this constituent in checking nitrification. 



Citric Acid (Nos. 13 and 14) hindered nitrification very .seriously, and 

 the heavier application had a bad effect on the nitrate production through- 

 'Out. It is noticeable with these sour soils that the nitrate production in 

 the controls was reduced in an exceptional degree. These controls received 

 no ammoniacal manure. Looking to the bad effect of acidity, and com- 

 paring it with the effect of mild lime, the advantage of liming sour land 

 and neutralizing its acid becomes manifest. 



Starch and. Sugar in the aerated bottles (Nos. 15 and 16) did not help 

 nitrification at the first (Table III.), but they destroyed the nitrates already 

 present — denitrification. This may happen at times after ploughing in 

 green or fresh stable manure, especially on stiff' wet soils. At the close of 

 the experiments, the soils" showed no trace of either starch or sugar by 

 chemical tests. These had apparently rotted away, and the sugar would 

 rot fastest. If that were so. then the sugar bottle would soonest be able 

 to re-start nitrification, and at the close indeed it contained considerably 

 more than the other. 



The sugar bottle kept sealed (No. 17) never showed nitrates anywhere, 

 and one may conclude that working and tillage to admit air will stimulate 

 -nitrification. This will be particularly useful when green or stable 

 manure has been applied .some time before. 



While conducting these experiments, an interesting point arose as to 

 the probable effect of dry storage of .soil upon the vigour of the nitrifying 

 -organisms contained in it. Four bottles were set up with a special soil, 



* Bui. Texas Airic. Exp. St. 159 (1908), pp. 15, 16. 

 t Joiii-. Ajrlc. Sci., Vol. II. (1907-8), pp. 52 et. seg. 



