1250 SOIL PHYSICS, CHKMISTKV AN']> MICKOCIOL,OGY 



which it was proposed to determine the content of assimilable phosphoric 

 acid, were filled with samples manured with potassium nitrate and magnesium 

 sulphate ; and those of the third, which were for the purpose of ascertaining 

 the content of assimilable nitrogen, contained samples manured with acid 

 potassium phosphate (KHg PO4) and sulphate of magnesia; those of the fourth 

 received a complete mineral manuring, that is to say : potassium nitrate, 

 acid potassium phosphate and magnesium sulphate ; in the vessels of the 

 fifth series the sterilised earth was put, and in those of the sixth the chlo- 

 roformed earth. 



The sterilisation of the soil was carried out in vessels ])laced in an auto- 

 clave where they were subject to sterilisation by steam for one hour at a 

 pressure of 2.5 atmospheres. 



After cooling, the specimens sterilised in this way were watered with 

 sterilised water to the optimum point of humidity. 



The chloroforming was carried out by placing the corresponding sam- 

 ples in bottles with ground stoppers and adding to each sample 50 cc. of 

 chloroform. After they had been left for three days in the bottles the sam- 

 ples were taken out, and, when the chloroform had completely evaporated, 

 were placed in the vessels. The vessels having been prepared in this way, 

 oats were sown in them, after the seeds had been previously treated with 

 an 0.2 % solution of formalin and washed with distilled water ; the seeds 

 were then germinated in an incubator. In each vessel 8 seeds were put ; 

 after germination only the four most vigorous plants were left. 



During the entire period of growth, the plants were watered with rain 

 water to the optimum of humidity, the water being supplied from below 

 by means of a special tube fitted to each vessel. The results of the experi- 

 ments as regards the fertility of the tchernoziom in the 6 series of specimens 

 studied are summarised in the accompanying table. 



This table contains no particulars as to the effects of the steriHsation 

 of the layer immediately below the arable layer (from 17.7 to 35.5 cm in 

 depth) nor of the cleared land, or the lucerne soil, because on the sterilised 

 samples of these soils the plants died in the course of their period of growth. 

 The writer partly discerns the causes of this phenomenon in the fact that 

 the sterilised soils, during the first few days, clearl3^ exhibit a low capacity 

 of water absorption, which proves that the sterilisation of the soil by means 

 of steam produces not only biological but also physico-chemical changes. 

 In order to obviate this drawback it is advised that the soil should be wa- 

 tered with distilled water to the optimum point of humidity for 6 or 7 days ; 

 if this precaution is taken the young plants suffer less. Passing on now to 

 the general considerations emerging from the figures in the table, it is seen 

 that the sterilisation of the tchernoziom brings with it a considerable in- 

 crease in the production of the total vegetable mass, and that the effect of 

 sterilisation, disregarding slight fluctuations one way or the other, is the 

 same as that produced by complete mineral manuring. 



As regards the chloroforming, it also brought about an increase in the 

 total vegetable mass produced ; its effect nevertheless was less considerable 

 as compared with sterilisation and complete mineral manuring. What 



