Scientific A griculturc. 



[DECEMKER, 1010. 



give the best chance of the mutual pro- 

 vision of many of the materials that are 

 required in the raising of the different 

 products. 



The mention of the most obvious 

 general means toward the conservation 

 of the resources that are contained in 

 the soil has been left until the last. It is 

 sufficiently self-evident that this means 

 is included in education. Much has been 

 done in the past to elucidate the best 

 methods in connection with this, and 

 the investigation can be said to have 

 passed the experimental stage. It now 

 rem uns to extend the practical appli- 

 cation of its results, so that, with the 

 spiead of agricultural knowledge, there 

 will be brought about a greater respect 

 tor the soil as a producer, and a better- 

 appreciation of the inter-dependence of 

 the factors that limit production 



All the different phases of agricuitural 

 production, in a given community, react 

 on one another, and the state of the 

 general efficiency does much to regulate 

 the extent to which the fertility of the 

 soil is maintained. The prosperity of 

 such a community, therefore, depends on 

 the value of its inhabitants as agricul- 

 tural workers, so that, if this is to be 

 maintained or increased, there must be 

 a wide recognition of the necessity for 

 general effort towards improvement. 



THE INFLUENCE OF STUBBLE 

 BURNING ON THE FERTILITY 

 OF THE SOIL. 



By Alfred J. Ewart, d.sc, ph.d., p.l.s. 



(From the Journal of Agriculture, 

 Victoria, Vol. VIII., Pt. 10, 

 October, 1910.) 



The statement is frequently made that 

 burning off the stubble after a grain 

 crop improves the fertility of soil and 

 favours the growth of the succeeding 

 crop. This effect is generally ascribed 

 to the alkaline ashes left behind after 

 burning, but since these ashes are no 

 greater in amount than what is returned 

 to the soil when the stubble is ploughed 

 in, the only difference could lie in the 

 tact of their being immediately avail- 

 able for absorption by the plant, in- 

 stead of being slowly set free as the 

 stubble decomposed in the soil. 



The experience of others has Jed them 

 to deny either that stubble burning does 

 improve the fertility of the soil, or That 

 if theve is any effect, it can be due to 

 the ames of the crop. Mr. Herbert 

 (Journal of Agriculture of South Aus- 

 tralia, 1910, p, 791) compared the effects 



of scattering ashes over oue plot and 

 burning rubbish on auother. The ex- 

 periment, though a very crude on a, 

 showed in favour of the latter plot. In 

 the same Journal, p. 967, the explan- 

 ation is suggested that where stubble 

 burning exercises a beneficial effect on 

 the succeeding crop, this may be due to 

 the effect of the partial sterilisation of 

 the soil by heat. Recent investigations 

 have shown that steaming soil, or heat- 

 ing it to 180° Fahrenheit, temporarily 

 destroys the minute animal organisms 

 which feed upon the nitrate-producing 

 and nitrogen-fixing organisms in the 

 soil. As the result, the bacteria increase 

 in numbers and make more nitrogen 

 available for the use of the crop. 



As against this explanation, we have 

 the fact that burning of stubble only 

 heats the immediate surface of the soil 

 and does not appreciably affect the 

 temperature of the deeper layers below 

 the surface inch or two. Even in burn- 

 ing off dense scrub, it is surprising to 

 how small an extent the soil below the 

 surface layers becomes heated. It is 

 only when thick roots smoulder away 

 underground, or when the soil contains 

 so much peat or humus as to burn itself, 

 that it becomes strongly heated to any 

 depth. The explanation, therefore, 

 though ingenious, cannot be regarded 

 as definitely established without further 

 proof. 



It should be remembered that three 

 classes of bacteria, which render nitro- 

 gen available for the use of the plant, 

 exist in the soil. The first group, which 

 we may generally term Nitrate bacteria, 

 are concerned in converting the organic 

 nitrogen of the humus in the soil (which 

 ordinary plants cannot use), into ni- 

 trates, chiefly of Calcium and Potassium, 

 which they can freely absorb. This 

 action can only go on when alkaline or 

 alkaline earth bases are present such as 

 Calcium, Potassium, Magnesium, &c. 

 The addition of such -substances in the 

 form of ashes, even if the amount was 

 slight, might temporarily increase the 

 production of nitrates, particularly in 

 acid soils. At the same time, this means 

 that more humus is oxidised and the 

 nitrogen capital of the soil reduced. 

 Further, it is only where the soil con- 

 tains nitrogenous humus, that any such 

 action is possible. Hence, stubble burn- 

 ing not only decreases the amount of 

 humus returned to the soil, but also 

 accelerates the exhaustion of that al- 

 ready present in it. Owing _ to their 

 high mean temperature, the oxidation of 

 humu« is already sufficiently rapid in 

 naos-t Victorian soils, 



