January 28, 19 15] 



NATURE 



60- 



in the increased crop ; with an application of 200 lb. 

 there may be a waste of 25 per cent, of the nitrogen, 

 with still greater losses as the application is increased. 

 The loss is not due to mere washing out of soluble 

 materials, because it is greatest when the nitrogen is 

 applied in organic manures. Under existing condi- 

 tions, high productivity in the soil is associated with 

 a high rate of waste, and nowhere is this more 

 marked than when cultivation is carried on under 

 tiopical conditions, so that one of the chief difficulties 

 of tropical and semi-tropical agriculture is to maintain 

 the stock of humus and nitrogen in the soil. An illus- 

 tration of the waste that so often goes on in the soil 

 is furnished in the practice of the cultivators under 

 glass in England. For the growth of cucumbers and 

 tomatoes they are in the habit of making up a very 

 rich medium, half soil and half dung, but after a very 

 few crops they are no longer able to use this mixture 

 profitably, but must throw it away and renew their 

 beds, though the rejected soil is still extremely rich 

 in the elements of plant food. The recent investiga- 

 tions at Rothamsted have shown that the fertility of 

 this ■■ sick " soil can be restored by merely heating it 

 for an hour or two to a temperature approaching that 

 of boiling water, the cost of which operation is con- 

 siderably less than that of renewing the soil. In this 

 case the uselessness of the sick soil appears not to be 

 due to the destruction of the nitrogen compounds, but 

 to their retention in a condition unavailable for the 

 plant. The nitrogen compounds have to be broken down 

 to ammonia or nitrates before they can feed the plant ; 

 this process is elYected by certain groups of bacteria, 

 the numbers of which are limited in the sick soil by 

 the excessive development of another group of soil 

 organisms — protozoa, amcebse, etc., that feed upon 

 the bacteria. 



We are only just beginning to take stock of all the 

 changes in- the soil materials that are effected bv living 

 organisms, some necessary, some competitors with 

 the plant, some wasteful ; the ultimate problem is to 

 bring these processes under control in the field as well 

 as in the laboratory. The antiseptic treatment of the 

 land at large, after the fashion we can now clean up 

 soils in pots, may seem an impossible dream, but not 

 more impossible than the production of a heavily 

 yielding weedless field of wheat would have seemed to 

 primitive man. Already much may be done to set up 

 a better micro-flora and -fauna in the soil by improving 

 its physical conditions. The good effects of such pro- 

 cesses as liming and drainage are largely due to the 

 encouragement that is thereby afforded to the valuable 

 organisms. Soil inoculation with such necessary 

 bacteria as those which fix nitrogen when living in 

 the nodules on the roots of leguminous plants has 

 been widely attempted, but with very little practical 

 success. The failures have generallv been due to the 

 fact that soils from which the nodule organism is 

 absent are without it because of some chemical or 

 physical defect ; it is not sufficient merelv to seed it 

 with the organism, the soil itself must first of all be 

 brought into a state to maintain its existence. The 

 best of grass seeds would be wasted unless the land 

 on which they are sown is first made clean and fertile. 

 The amelioration of soils on their physical side, bv 

 bringing clay and silt to the sands, sand and coarse 

 particles of various kinds to the clays, will eventually 

 be taken up on a great scale, now that engineering 

 has made it possible to move earth wholesale bv 

 cheaper means than by primitive suade and cart. I 

 have seen a cold clay cairying miserable pasture con- 

 verted into good market garden land by nothing more 

 than the application of a thick la'er of town refuse 

 and ashes; on'y organisation is needed to make such 

 processes economic, even when the immediate, and 

 not the ultimate, return is reckoned. 

 NO. 2361, VOL. 94] 



From the point of view of manures we shall have 

 £0 look forward to an ultimate scarcity of nitrogenous 

 fertilisers ; the exhaustion of sodium nitrate is only a 

 question of time, the present sources of sulphate of 

 ammonia will disappear with the coal, and the water 

 power which is now giving us nitrate of lime and 

 cyanamide will then be too precious to be used in 

 making fertilisers. Even if the new process for the 

 synthesis of ammonia proved as economical as is 

 expected, we ought still to depend upon the natural 

 processes of nitrogen fixation, and make the farm 

 self-supporting as regards nitrogen at a high level of 

 production. The clover crop in the rotation usually 

 followed in England will, under present conditions, 

 gather in enough nitrogen for the growth of about 

 twenty-four bushels of wheat to the acre, an equal 

 quantity of barley, and twelve tons of turnips. How 

 can we similarly maintain production at a level of 

 40 bushels of wheat, with other crops in proportion, 

 yet without any nitrogenous fertiliser from outside? 



A more immediate problem of the same kind is 

 before the investigator; all around our great cities 

 exist great market gardening industries, which have 

 been built up by means of the cheap supplies of stable 

 manure that were to be obtained therefrom. The 

 market gardener close to London and as far afield as 

 Bedfordshire, rendered thin sands and gravels fertile 

 by using 40 tons or more of London dung everj* year, 

 but the advent of the motor-car has curtailed, and 

 will eventually put an end to, that supply, in which 

 case how is the market gardening to be carried on? 

 Nitrogen compounds and the other bare elements of 

 plant food can be bought, but humus is also necessaiy 

 to get these thin soils to yield a proper growth; what 

 needs to be worked out is the cheapest and most effec- 

 tive way of utilising leguminous green crops and the 

 other nitrogen-fixing organisms of the soil to maintain 

 the fertility of such land, keeping in view the fact 

 that it cannot be thrown out of productive cultivation 

 for any length of time. What is needed is not a field 

 experiment merely, but a discussion of a whole system 

 of cultivation on the economic as well as on the scien- 

 tific side. This suggests the general consideration 

 that economic research in agriculture is still in its 

 infancy. How often do we find close at hand two 

 farmers, both good practical men, with entirely diver- 

 gent views on the rotation to follow or the manage- 

 ment of their stock, one swearing by early maturity 

 and a forcing diet, the other by cheap if slow produc- 

 tion. The advantage of one system over the other is 

 not a inere matter of opinion and personal idiosyn- 

 crasy, it is possible to reduce it to terms of pounds, 

 shillings, and pence. The prime necessity is the appli- 

 cation to farming of a system of costs book-keeping, 

 such as prevails in a well-organised business. It is 

 possible to obtain such figures from a farm ; the 

 method is as yet perhaps too complicated for the 

 ordinary farmer to follow, but as an instrument of 

 investigation in the hands of a teacher at one of the 

 agricultural colleges it may be made to yield results 

 of great value both to the individual farmer and to 

 all those who have to take more general views of 

 agriculture. 



Returning to the purely scientific aspects of research, 

 the whole of existence is based upon the fundamental 

 process by which the green leaf utilises the energy of 

 the light falling upon it to split up the carbon dioxide 

 of the atmosphere and transform it into those funda- 

 mental carbon compounds — sugars, starches, etc., 

 which build up the substance of the plant. The 

 animal creates nothing; it is only a transformer, and 

 rather a wasteful one at that, of the compounds 

 initially built up by the plant. Now, though the leaf 

 is thus the prime creative force, it is vet a compara- 

 tively ineffective machine for dealing with the energv 



