422 EXPERIMENT STATION RECOED. [Vol.36 



For the sizes investigated, evaporation was higher from the finer soil particles 

 than from the coarser when both are completely saturated. 



" Reducing the intensity of sunshine greatly reduces the rate of evaporation. 

 Slight changes in temperature have a marked effect on evaporation. A thin 

 mulch, if kept dry, is effective in reducing evaporation. Dry mulches, com- 

 posed of fine particles, seem to be less effective than if composed of coarser 

 particles. Compacting the surface of the soil increases evaporation. Dissolved 

 salts in high concentrations reduce the evaporation of moisture from soils." 



A list of 21 references to literature bearing on the subject is given. 



Keep our hillsides from washing, A. R. Whitson and T. J. Dunnewald 

 {Wisconsin Stn. Bui. 272 {1916), pp. 18, figs. 14).— This bulletin deals with the 

 extent and l)ad results of erosion on Wisconsin soils and describes preventive 

 measures applicable to conditions of the State, including tillage, alternation of 

 crops on sidohills, use of horizontal channels and terraces, protection of ravines 

 and watercourses with stones and grass roots, gradual removal of trees from 

 wooded hillsides, and the use of sidehill land for pasture. 



Protozoa, as affecting bacterial activities in the soil, S. A. Waksman 

 {Soil Sci., 2 {1916), No. 4, pp. 363-376).— Experiments conducted at the New 

 Jersey Experiment Stations on the interaction between protozoa and bacteria in 

 a clay soil and a light loam soil are reported. 



It was found that the presence of protozoa seemed to check the bacterial 

 numbers, which were found to be smaller in the soils where the protozoa were 

 present than in the corresponding soils where they were absent. The ammonify- 

 ing efficiency of the soil did not follow the changes in bacterial numbers. 



Heating the soil at 65° C. for five hours destroyed the protozoa in all instances 

 but one and greatly reduced the bacterial numbers ; but when the proper amount 

 of moisture was added and the soils were allowed to incubate for 30 days, the 

 bacterial numbers increased to almost three times those of the check. There 

 was a corresponding increase in ammonia production in the soil. 



The action for 48 hours of 4 per cent toluene, which was then allowed to 

 evaporate for 48 hours, killed the ciliates, but not the flagellates ; this treatment 

 also reduced the bacterial numbers, but they at once increased after the toluene 

 was allowed to evaporate. The action of toluene and heat was greatest upon 

 soils having a high content of organic matter, whether the protozoa were active 

 or not. 



The light loam soils kept out of doors gave higher bacterial numbers and 

 higher ammonifying efficiency than those kept under laboratory temperatures, 

 and the latter gave higher numbers and ammonifying efficiency than those kept 

 at 30°. The soils with optimum moisture content gave in the main higher 

 bacterial numbers and ammonifying eflSciency than those of higher moisture 

 content. 



Nitrification in semiarid soils, I, W. P. Kelley {U. S. Dept. Agr., Jour. Agr. 

 Research, 7 {1916), No. 10, pp. ^i7-i37).— Previous investigations on this sub- 

 ject are briefly reviewed and laboratory studies at the California citrus substa- 

 tion of the relation of the concentration of nitrogenous materials and the period 

 of incubation to the rate of nitrification are reported. 



The results of the investigations showed that the amounts of nitrate formed 

 from dried blood, bone meal, or ammonium sulphate during 4 weeks' incubation 

 varied greatly with the amount of nitrogenous materials employed. When 1 

 per cent of dried blood was used (the proportion commonly employed in con- 

 ^entional nitrification studies) the nitrifying activity was found to be feeble or 

 even negative in certain soils in which 1 per cent of bone meal and from 0.2 

 to 0.3 per cent of ammonium sulphate underwent active nitrification. When 



