2o8 Studies of Plant Growth in Heated Soil [Jan. 



distributed heat at a lower temperature. The effects of tillage are 

 also to be taken into account as possibly causing a more equal dis- 

 tribution of the elements after steam sterilization. Stone expresses 

 the opinion that the acceleration which he and others have noticed 

 in the case of steam-sterilized soils in market gardening districts is 

 due rather to the chemical changes within the soil than to any modi- 

 fication of its flora or fauna. 



Lodge and Smith 4 have studied the effects of steam heat on soils 

 in relation to the growth of bacteria as well as green plants. They 

 used soil sterilized for 45 minutes under a pressure of 15 pounds of 

 steam at a temperature of 125 ° C. Percolates of these soils were 

 sown with Bacillus sttbtilis. Their experiments showed that where 

 the soils were rich in organic matter steam heat increased subsequent 

 bacterial growth, while in soils deficient in organic matter such 

 growth was retarded. They report similar results with green 

 plants, and emphasize the fact that in the soil used protozoans were 

 not present to an appreciable extent. 



Various attempts have been made to explain the observed effects 

 of soil-heating upon subsequent plant growth. Russel and Hutch- 

 inson 5 attribute the changes observed by them to the destruction of 

 the soil-inhabiting protozoa and the consequent greater activity of 

 the soil bacteria. Lyon and Bizzell hold, on the other hand, that 

 the results are due entirely to the chemical changes in the soil itself. 

 Bolley 7 concludes that the most important factor is the destruction 

 of the fungi and bacteria which are present in the soil and which 

 might produce disease in the crops grown. Seaver and Clark con- 

 sider " that the whole question of the effects of heating soils is a 

 very complex one and one in which the experimenter's interpreta- 

 tion of results depends upon his training and point of view; whether 

 it be bacteriological, chemical or phytopathological. It is very 



4 Lodge, C. A., and Smith. R. G. : Influence of soil decoctions from steri- 

 lized soils upon bacterial growth. Ann. Rep., Mass. Agr. Expt. Sta., 24: 126- 

 134; 1912. 



5 Russel and Hutchinson: The effect of partial sterilization of soils on the 

 production of plant food, Jour. Agr. Sci., 3: 111-114; 1909. 



6 Lyon, T. L., and Bizzell, J. A. : Effect of steam sterilization on the water- 

 soluble matter in soils, Bull. Cornell Agr. Expt. Sta., 275 ; 1910. 



7 Bolley, H. L. : Interpretation of results in experimentation on cereal crop- 

 ping methods after soil sterilization, Science, 33: 229-234; 1912. 



