i 9 i 4 ] Guy West Wilson 207 



Schreiner and Lathrop 2 have conducted extensive studies on the 

 chemistry of steam-heated soils and their relation to plant growth. 

 They autoclaved the soil samples at a temperature of 135 C, and 

 under a pressure of 30 pounds, for a period of three hours. As a 

 result of this treatment they note increased amount of soluble mat- 

 ter in the soil extract and retarded plant growth, both of which are 

 to be expected under the circumstances. All the materials found in 

 unheated soils were present in the heated samples except nucleic 

 acid which was broken down and united with some of the protein 

 substances to form new compounds. The effect on plant growth is 

 explained by the fact that while beneficial elements are present they 

 are overbalanced by harmful compounds. Upon the balance of 

 these elements, then, depends the results upon plant growth. ' This 

 balance is influenced by cultural treatment, fertilizers, liming, crop 

 growth, or crop rotation, etc., as well as by steaming." 



Articles have also appeared, from time to time, upon the effect 

 of soil sterilization as practiced commercially. This is accomplished 

 by forcing steam into the soil in situ. While the nominal tempera- 

 ture to which the soil is subjected by this treatment is quite high, 

 there are great difficulties in the way of securing an even distribu- 

 tion of the steam in the soil-mass. The results are a very uneven 

 sterilization, the after effects of which are quite different from those 

 obtained by other methods where the penetration is subject to less 

 fluctuation. In this type of sterilization the prime object is to rid 

 the soil of the nematodes, insect pests, injurious fungi and bacteria 

 which may have accumulated in it. From this standpoint the method 

 of soil treatment is satisfactory in so far as it reduces the ravages 

 of these pests on the subsequent crop. 



A summary of our knowledge along these lines has recently been 

 published by Stone, 3 who noted acceleration in the growth of lettuce 

 and cantaloupes on steam-heated soil, when it was rich in organic 

 matter, while the results were bad on poor soil. The gross effect 

 of such treatment on plant growth is apparently analogous to that 

 following subjection of the soil content of the plot to a more evenly 



2 Schreiner, O. S., and Lathrop, E. C. : The chemistry of steam-heated soils, 

 U. S. Dept. Agric, Soils Bull., 89: 1-37; 1912. 



3 Stone, G. E. : The present status of soil sterilization, Ann. Rep., Mass. Agr. 

 Expt. Sta., 24: 121-125 (pi. 1, 2) ; 1912. 



