720 EXPERIMENT STATION KECOBD. 



It was fouud that, as a rule, nitriflcatloii was uot very active in untilled soils. 

 Amuioniflcatiou was much more active than nitrification in such soils. The 

 inactivity of nitrification in the uucullivatc'd soils was uot due to acidity or lack 

 of organisms, but largely to deficient aeration. Tillage improved the aeration 

 and thus stimulated nitrification as well as ammonification. Sterilization by 

 heat did uot promote nitrification but increased the production of ammonia. 

 Partial sterilization stimulated ammonification for a short time, usually about 

 two weeks, after which there was a decline in ammonification. Nitrification 

 was temporarily inhibited by partial sterilization, but later recovered its activ- 

 ity, lielnoculation of the partially sterilized soil with untreated .soil stimulated 

 nitrification without checking ammonification. Partial sterilization caused .-i 

 permanent increase in available nitrogen (nitrates and ammonia) in certain soils 

 and a temporary increase in others. 



Calcium carbonate produced considerable stimulation of ammonification of 

 dried blood and soy-bean meal in certain soils; in others it had little effect iu 

 this respect. Magnesium carbonate, on the other hand, produced marked stimu- 

 lation In the majority of cases. Dolomitic and calcareous lime.stones produced 

 much the same effects as calcium carbonate. 



Calcium carbonate stimulated nitrification in certain soils and was without 

 effect in others. Magnesium carbonate was toxic to nitrification in the majority 

 of cases. Nitrification was as active in the manganiferous and titaniferous soils 

 as in the others studied, but magnesium carbonate was especially toxic to nitri- 

 fication iu these soils, this effect being more marked iu the case of soy-bean meal 

 than iu the case of dried blood. Dolomitic and calcareous limestones and cal- 

 cium carbonate produced similar effects as regards nitrification. 



The results regarding the effect of the lime-magnesia ratio on ammonification 

 and nitrification were inconclusive. 



In general, the exijeriments emphasize the importance of maintaining the best 

 aeration possible In Hawaiian soils. 



The lime-niag'nesia ratio. — I, The effects of calcium and magnesium car- 

 bonates on ammonification. II, The effects of calcium, and mag'nesiuni car- 

 bonates on nitrification, "W. P. Kelley {Centhl. Bakt. [etc.], 2. Abt., 42 (1914), 

 Xos. n-lS, pp. 5W-526; 21-22, pp. 577-^82).— The experimental results con- 

 tained in these two articles are reported for the most part in the above. The 

 general conclusion is reached that the Hme-magnesia ratio is not of great impor- 

 tance to the ammonifying and nitrifying flora of the soil. The concentration of 

 magnesium in solution and its relations to the concentration of the other constit- 

 uents are of more importance. 



The influence of arsenic upon the nitrog'en-fixing' powers of the soil, J. E. 

 Greaves and II. P. Anderson {Centhl. Bukt. [etc], 2. Abt., 42 {1914), No. 

 10-L'i. pp. 244-254. fig. 1). — In continuation of previotis studies on the influence 

 of arsenic compounds on the soil flora (E. S. R., 30, pp. 423. 424) the authors 

 found that arsenic when applied to a soil in the form of lead arsenate, sodium 

 arsenate, arsenic trisulphid, or zinc arsenite, stimulates the nitrogen-fixing 

 powers of the soil, this effect being greatest with lead arsenate and least with 

 zinc arsenite. Paris green did not stimulate in any of the concentrations tested 

 :ind became ver5' toxic at a concentration of 120 parts per million. Sodium 

 arsenate became toxic at a concentration of 40 parts per million and at 250 

 parts per million nitrogen fixation was entirely stopped. Lead arsenate was 

 not toxic even at a coucentration of 400 parts iier million, and the toxicity of 

 arsenic trisulphid and zinc arsenite was very small at this coucentration. 



" The stimulation noted ... is uot due to any inherent peculiarity of the soil 

 used, for soils which vary greatly in physical and chemical properties had their 

 nitrogen-fixing powers greatly increased when arsenic was applied to them. 



