December, 1910.] 



521 



Scientific Agriculture, 



The second and third classes of bac- 

 teria 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 ni ero- 

 genous food. Of these nitrogen-fixing 

 bacteria, one is that which grows in the 

 root-tubercles of Leguminosae,and which 

 causes their special value for enriching 

 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 condi- 

 tions 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 nitro- 

 gen-fixing soil organisms diminish to a 

 minimum ; and the soil loses more nitro- 

 gen by waste and drainage than it gains 

 from the air. 



In this case also, therefore, burning off 

 the stubble is bound ultimately to pro- 

 duce a diminution in the amount of 

 nitrogen added to the soil by these 

 nitrogen-fixing soil organisms, since it 

 decreases the supply of carbohydrate 

 material on which they live. Steam 

 sterilisation by destroying the small 

 animal organisms which eat these 

 bacteria along with others might tem- 

 porarily increase their activity, but 

 such treatment is not of course practic- 

 able on a large scale. When steam 

 sterilisation is used by horticulturists 

 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 suffi- 

 cient to cause 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 com- 

 paratively 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 pro- 

 vides precisely those conditions which 

 66 



aid in the spieadof 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 produc- 

 ing 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 in 

 his own part, and which might, when 

 properly husbanded, have lasted him his 

 whole lifetime. 



The use of fire to clear the ground in 

 preparation for cultivation is common 

 among all savage races who practice a 

 more or less rudimentary kind of agri- 

 culture, 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 " rub- 

 blish" 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. Pre- 

 cisely the same thing applies on a large 

 scale, and to an even greater extent, to 

 agriculture. 



URINE-EARTH AS MANURE. 



(From the Central Agricultural 

 Committee, Madras, Circular No, 25.) 

 The following circular showing the 

 value of urine as manure is published 

 for general information. It is based 

 upon an article contributed by Mr. D. 

 (Jlouston, m.a., B.sc, Deputy Director 

 of Agriculture, Central Provinces, to 

 the " Agricultural Journal of India," for 

 July, 1910 :— 



2. It is a well-known fact that manure 

 is a most important factor in agricul- 

 tural economy and it is equally well- 

 known that, in this Presidency, the 

 cultivator is seriously handicapped by 

 the increasing difficulty of obtaining an 

 adequate supply of manure. Even the 

 limited supply that is available consists 

 generally of the ash of cattle-dung 

 mixed with house sweepings. This is 

 not a valuable manure as its nitrogen 

 content is low, 97 per cent, of it being 

 lost in the process of burning the cattle 

 dung for purposes of fuel. The result is 

 that, in large areas, the soil becomes 

 exhausted and the ryots are unable to 

 raise profitable crops. 



