Edible Products. 



512 



[June, 1912, 



heating the soil under the conditions of 

 rice culture in Western India must be 

 regarded as only an opening of the 

 subject- But subject to revision in the 

 light of future investigation we may 

 summarize the conclusions which we 

 have so far reached as follows : — 



1. The rab process, as used in the pre- 

 paration of the seedbed for rice in 

 Western India, owos its efficiency to two 

 causes — the heating of the soil, and the 

 ash and other manurial material left on 

 the land. The actually increased re- 

 turns in the improved seedlings obtained, 

 vary very much, but normally the 

 weight of the seedlings obtained is from 

 one and a half times to twice as great as 

 without the treatment. 



2. Of this increase nearly sixty per 

 cent, is due to the effect of heating, an:l 

 the balance to the ash and other mate- 

 rials added. 



3. Taking the effect of heating alone, 

 with which the present study deals, it 

 may be said that during ordinary burn- 

 ing with eowdung rab, the temperature 

 at £ inch deep does not go beyond 110*0. 

 and at 1 inch deep not beyond 85°C, The 

 whole heating process does not last 

 longer than 1£ to 2 hours. 



4. The result of heating the soil to 75°C. 

 was only very slight at any time. 



5. At temperatures higher than this, a 

 very great increase in fertility resulted 

 up to a maximum at about 125°C. Be- 

 yond this point (at 150°O), the effect 

 appears to be less. 



0. The greatest effect is produced 

 when the heating is conducted immedi- 

 ately before the sowing of the crop. If 

 the soil is heated six weeks before the 

 rice is sown, the effect is a little less ; 

 while if conducted three months before 

 sowing, comparatively little effect is 

 obtained. 



7, This action of heating affects the 

 growth of the plants. On speed of 

 germination it has no beneficial effect, — 

 apparently sometimes slightly retarding 

 the process. This retardiug does not 

 appear to be due to the production of a 

 deleterious substance. 



8. The heating of the soils in question 

 does lead to the production of a consider- 

 ably increased supply of assimilable 

 mineral plant foods in the soil, and of 

 soluble organic matter. Very little 

 of the benefit of heating can be due to 

 this cause, because very little effect was 

 produced when growing rice plants were 

 treated with extracts of such heated soil. 



9. The heating of the soils iu question 

 also materially changes the physical 

 condition of the soil, in that a large part 

 of the viscous, sticky, " clay " substance 

 is brought into a condition in which it 

 will not remain suspended in water. 

 This effect is a very passing one, the 

 mere keeping of the air-dry soil for six 

 weeks being sufficient to materially 

 reduce it, while it has disappeared after 

 three months. 



10. The power to precipitate soil in 

 the way described under (9) is shared by 

 the oilcake which is most effective as a 

 rab substitute (safflower cake) and by no 

 other among the cakes at our disposal. 

 A material like gypsum which has a 

 similar precipitating effect gives an 

 increase iu yield of about one-quarter 

 the amount produced by heating the 

 soil. Further addition of gypsum be- 

 yond the quantity required to precipi- 

 tate the viscous matter to the extent 

 done by the heating process, gives no 

 further increase in yield. 



11. The change in the physical condi- 

 tion of the soil by the action of heat is 

 one of t he causes, though only secondary 

 cause of the beneficial effect of the rab 

 process. 



12. The heating process has the 

 effect of destroying a very large pro- 

 portion of the active aerobic life of the 

 soil, but even when kept in an air-dry 

 condition the organisms rapidly again 

 multiply, till, six weeks after the heating, 

 the serobic activity is far greater than in 

 the unheated sample. The difference dis- 

 appears on further keepiug of the soil. 



13. The fertility of the soil is not de- 

 pendent on the presence of large number 

 of soil organisms at the moment when 



