February, 1910.] 



129 



Scientific Agriculture. 



similar rearrangement of the organisms 

 of the soil and a similar increase in its 

 fertility, though not so great a degree. 



We are now in a position to sum up 

 the changes which take place in soil 

 when it is subjected to one of these so- 

 called "sterilisation " processes : — 



(1.) Seeds of weeds, mosses, liverworts, 

 &c, are killed. Fungi and their spores 

 are also destroyed. It is found, how- 

 ever, at Rothamsted that the soil is 

 very susceptible to reiofectiou when it 

 is afterwards exposed in pots. Occasion- 

 ally it becomes covered with moulds, 

 and the usual green algae rapidly cover 

 the surface with a mat. 



(2.) The texture of heavy soils is 

 distinctly improved. 



(3.) The heating gives rise to sub- 

 stances, of which ammonia is probably 

 the chief, harmful to germination. This 

 harmful effect will be less marked if 

 the soil is stored for a time after the 

 heating. 



(4.) All organisms of an order higher 

 than bacteria are killed off; the soil, 

 for example, is rendered clean of eel- 

 worms, at the same time certain 

 organisms which normally limit the 

 number of bacteria in the soil are des- 

 troyed. 



(5.) Thus provided with a clear field, 

 the ammonia-producing bacteria increase 

 rapidly, and there is a correspondingly 

 greater production of plant food from 

 the soil and manure, followed by an 

 increase of crop. Certain groups of 

 bacteria are killed off, e.g., those which 

 convert ammonia into nitrates ; hence 

 plants which only take in their nitrogen 

 as nitrates do not show increased growth 

 on the sterilised soil ; only those plants 

 (actually the majority) which can utilise 

 indifferently ammonia or nitrates are 

 benefited. Even in their case it is pos- 

 sible to see that they are feeding upon 

 ammonia and not upon the nitrates 

 they obtain from normal soil, e.g., the 

 cereals are shorter in the straw than 

 would be expected from the richness 

 in nitrogen. Nor is it always possible 

 to reinoculate the soil with the nitrifi- 

 cation organisms, heat-sterlisation seem- 

 ing to produce some substance which 

 inhibits the nitrification bacteria. 



Space does not permit of a discussion 

 of the results of greenhouse practice 

 with sterilised soils in the light of these 

 conclusions, but they will be found to 

 illuminate much that has been obscure 

 and contradictory iu the reports. At 

 any rate, it is clear that it is impossible 

 to lay down the law beforehand as to 

 whether " sterilisation " of soil will or 

 will not be beneficial in a particular 



17 



case. Experiment alone can show which 

 of the numerous factors will be involv- 

 ed, Similarly, though a number of 

 applications to practice suggest them- 

 selves, it would be unwise to discuss 

 them until more experimental work is 

 forthcoming. 



THE EFFECT OF GRASS ON TREES. 



By Spencer Pickering. 



(From the Gardeners' Chronicle, Vol. 

 XL VI., No. 1199, December, 1909.) 

 The effect of grass on trees is pro- 

 bably intimately connected with that 

 fundamental question in agriculture to 

 which no comprehensive answer has 

 yet been obtained, namely, the fertility 

 of the soil. The casual observer may 

 dismiss the subject by stating that it 

 is simply due to the grass robbing the 

 tree of its nourishment or its moisture, 

 but such a statement can only be based 

 on ignorance of the facts, and of all 

 the work which has been done in the 

 matter. The subject has been under in- 

 vestigation at the Woburn Experimen- 

 tal Fruit Farm for the last 16 years , 

 one report (the third) dealing with it 

 was published in 1903, and it is hoped 

 that another will be issued before very 

 long. 



Although no final solution of the 

 problem has yet been obtained, consider- 

 able progress has been made in the 

 matter, and various possible explan- 

 ations have been definitely negatived. 

 Foremost amongst these is the theory 

 that the action is due to the grass 

 absorbing all the food and water from 

 the soil. The original experiments are, 

 perhaps, the most striking, though not 

 the most precise, on this point. A large 

 number of apple tretss were planted in 

 rows, 11 feet apart, in 1904 ; the ground 

 in one row was kept tilled, and that 

 in the other row laid down to grass ; 

 the grass, when cut, is left to rot on 

 the ground, and the same amount of 

 manure is given to both rows of trees. 

 Those in the tilled soils are now such 

 large trees that half of them have had to 

 be removed, their spread being some 

 15 to 18 feet ; those in grass did not 

 grow at all for several years, and only 

 began to make growth when their roots 

 extended beyond the grassed area ; they 

 are still miserable specimens of trees, 

 about one-sixth the size of the others, 

 and the crops borne by them have only 

 been about one-tenth of that of their 

 neighbours. Yet the grassed soil is 

 actually richer than the tilled soil. In 

 the fifteen years it has had removed from 



