120 EXPEKIMENT STATION EECORD. 



" The addition of a quantity of nitrogen as ammonium sulpliate greater tlian 

 170 parts per million to each 100 gm. of soil sample showed an inhibiting 

 action on the nitrifying organisms." 



The formation and decomposition of humus as well as its action on 

 nitrogen assimilation, F. Lohnis and PI. H. Green {Centbl. Bald, [etc.], 2. 

 AM., 40 (1914), No. 1-8, pp. 52-60; ads. in Chem. ZentU., 191},, I, No. 12, pp. 

 1212, 1213). — Experiments are reported in which stable manure, green manure, 

 straw, peat, and sugar were mixed with sand in the proportion of 1 : 10 and 

 allowed to undergo humification for 4i months both with and without access 

 of air. 



The process was most rapid with stable manure, somewhat slower with green 

 manure, and slowest with straw. The sugar yielded almost no humus and the 

 peat underwent a slight oxidation. Partial aeration was most favorable to 

 humification. With full aeration a considerable part of the nitrogen of stable 

 manure and green manure was nitrified. At the same time, in the case of 

 green manure there was a large loss of free ammonia. 



Substances obtained from the humified materials by treatment with soda 

 solution and hydrochloric acid were mixed with soil and allowed to undergo 

 nitrification for five weeks. In this way characteristic differences were ob- 

 served. The largest amount of nitrate was obtained from the green manure 

 humus, but practically identical results were obtained with humus derived 

 from stable manure subjected to aeration. On the other hand, humus derived 

 from stable manure without aeration yielded much less nitrate. The nitrogen 

 compounds of peat humus were nitrified to a very slight extent. The straw 

 humus interfered with the nitrification process in the same manner as unde- 

 composed straw. 



The fixation of nitrogen by Azotobacter in mannite solution was appreciably 

 promoted by the addition of small amounts of humus (0.2 per cent). The stable 

 manure humus was especially favorable to such fixation. The other forms of 

 humus gave very nearly the same results, not only among themselves but as 

 compared with soil extract rich in iron. The favorable effect on nitrogen fixa- 

 tion appeared to be due more to an improvement of the nutrient medium in 

 chemical properties than to increased adsorption of oxygen and nitrogen. In 

 the latter direction the experiments showed no pronounced differences. 



The effect of copper, zinc, iron, and lead salts on ammonification and 

 nitrifi-cation in soils, C. B. Lipman and P. S. Bukgess {Univ. Cal. Pubs., Agr. 

 8ci., 1 (1914), No. 6, pp. 127-139). — Experiments carried out by the direct soil 

 culture method, described in a previous article (E. S. R., 26, p. 322), led to 

 the conclusion that " copper, zinc, iron, and lead exercise toxic effects on the 

 ammonifying flora of a sandy soil from southern California in all concentra- 

 tions, ranging from 50 to 2,500 parts per million of their sulphates ; such toxicity 

 is relatively small, however, and is more marked at concentrations below 0.1 

 per cent than above it, in most cases; the metals named exercise no stimulating 

 effect on the ammonifying flora at any concentration. Copper, zinc, iron, and 

 lead exercise marked stimulating effects on the nitrifying flora of the same 

 soil and frequently more than double the normal nitrate yield ; the same metals 

 may in very small concentrations exercise toxic effects on the nitrifying flora 

 or no effect at all, but they are markedly stimulating at much higher concen- 

 trations; with the one exception of lead sulphate, the metals named showed 

 very marked stimulation for nitrification even at 0.15 per cent, the highest con- 

 centration employed ... A brief discussion is given of possible causes for the 

 effects of the metallic salts under consideration on the soil flora." 



