lo Oct.. 1910.] Tltc lufiitcucc of Stubble Burning. 647 



The .second and third classes of bacteria bring the nitrogen of the air, 

 which is useless to the ordinary plant, into combinations which are, or 

 become, available for the plant's use as nitrogenous food. Of these 

 nitrogen-fixing bacteria, one is that which grows in the root-tubercles of 

 Legumii/oscc and which gives to these plants their special value for enrich- 

 ing the soil with nitrogen. The third group, of which the best known 

 is perhaps the form called Azotobacter, grows free in the soil and is in 

 part responsible for the maintenance or increase of the nitrogen content 

 in virgin soils. The nitrogen-fixing bacteria, which grow free in the soil, 

 can, however, only flourish when they are supplied with carbohydrates 

 such as are provided under natural conditions by the slow decomposition 

 of the plant-remains returned to the soil. If the soil is cropped and, still 

 more, if the stubble is burnt, the supply of humus soon becomes so small 

 that these nitrogen-fixing soil organisms diminish to a minimum and the 

 soil loses more nitrogen by waste and drainage, than it gains from the air. 



In this case also, therefore, burning off the stubble is bound ultimately 

 to produce a diminution in the amount of nitrogen added to the soil by 

 these nitrogen-fixing soil organisms, since it decreases the supply of carbo- 

 hydrate material on which they live. Steam sterilization by destroying 

 the small animal organisms which eat these bacteria along with others, 

 might temporarily increase their activity, but such treatment is not of course 

 practicable on a large scale. When steam sterilization is used by horti- 

 culturalists for destroying weed seeds in manure and potting soil, it appears 

 to cause an increase of nitrogen available for the plant's use and this may 

 be sufiicient to cau.se excessive leafy growth. Apparently, this is the 

 result of an increase in the bacteria which produce nitrates from humus, 

 and not in the nitrogen-fixing bacteria. Hence, the action will be best 

 shown where large quantities of humus are present, as in stable manure 

 or rich garden soil. Here, a little waste of humus is a comparatively 

 small matter, whereas on an agricultural scale, maintenance of the humus 

 content of the .soil is one of the most important factors in preserving 

 its fertility. 



The burning of the stubble destroys a few weed seeds but. at the same 

 time, the warmth and the resulting ash favour the germination of any 

 hard seeds present in the soil and also provides precisely those con 

 ditions which aid in the spread of fire weeds, some of which easily become 

 troublesome. It makes the impoverishment of virgin soils cropped without 

 manuring take place more rapidly than would otherwise be the case, and 

 it does this without producing any commensurate increase in the crop to 

 compensate for the loss of the capital stored in the soil in the form of 

 nitrogenous plant- food while it was in a virgin condition. It is the act 

 of a spendthrift to burn away in a year or two the capital which was 

 accumulated for him by nature without any effort on his own part, and 

 which might, when properly husbanded, have lasted him his whole life- 

 time. 



The use of fire to clear the ground in preparation for cultivation is 

 common among all savage races who practise a more or less rudimentary 

 kind of agriculture, but with the .scientific advance of agriculture fire 

 plays less and less part in its daily doings. Even in a garden, the less 

 the amount of ' ' rubbish ' ' that is burnt, instead of being rotted wherever 

 sufficiently soft and free from weed seeds, the less the amount of manure 

 that will need to be carted in to keep up its fertility. Preci.sely the same 

 thing applies on a large scale, and to an even greater extent, to Agri- 

 culture. 



z 2 



