THE SUPPLEMENT TO THE 



Tropical Agriculturist and Magazine of the C. A. 8. 



Compiled by A. M. & J. FERGUSON. 



No. 5,] MAY, 1909. [Vol. IV. 



FERTILITY AND MANURING. 



It has been usual for the agricultural student 

 to be told that the soil is the cultivator's Bank, 

 and that, in order that it may continue to be 



solvent," he must replace the drafts upon it by 

 crops he cultivates, and make good the deficit 

 by additions of manure to replace lost fertility. 

 It would appear, however, that this very simple 

 conception of the relation between manuring and 

 fertility would need some modification, inasmuch 

 as the action of fertilising agents is far more 

 complex than has hitherto been supposed. In- 

 deed, one of the most important problems of 

 modern agriculture would seem to be how most 

 intelligently to make use of manures in main- 

 taining fertility. On the one hand we have, still, 

 a number of landowners who are sceptical as to the 

 value of manures, stubbornly holding to the belief 

 that manuring "spoils''' a plant, in that a tree, if 

 once manured, will always need fertilising, and if 

 manure is withheld, its last stage will be worse 

 than the first. At the opposite pole we have the 

 high cultivator who believes in and practises heavy 

 manuring. In the last annual report of the 

 Secretary to the American Department of Agri- 

 culture we read that while the quantity of 

 manures now employed is enormous, and their 

 use extending, "a large fraction of the money 

 expended— perhaps, one-third— is wasted, and 

 brings no adequate return owing to a lack 

 of understanding of the soil's requirements." 

 This is rather a serious indictment against 

 Agricultural Chemistry, since the cultivator 

 or farmer in the West is, as a rule, entirely 

 guided by expert advice. But if there are de- 

 fects in the system of manuring adopted in such 

 an up-to-dato country as the United States of 

 America, how much more (proportionately) must 

 be the "waste" in this colony, where, in themajo- 

 rityof cases, the cultivator is a law unto himself 

 in the matter of manuring ? 



The lack of understanding, we are told, is as 

 regards the manner in which the soil feeds the 

 crop, and the influence of fertilisers upon this 

 feeding. It is commonly known that plants get 

 their food from solutions of salts which are taken 



61 



in by the roots by " osmosis " — a process of 

 diffusion. But it is not generally recognised that 

 evaporation and transpiration of water by soil 

 and plant result in an upward movement of soil 

 moisture from the subsoil, often from great 

 depths. By this means plant food (in solution) 

 is brought up from the subsoil to the soil proper 

 and there fixed. The addition of manure 

 does not merely increase the supply of plant 

 food present in it in available form, but has 

 other far-reaching effects which scientific re- 

 search is only now discovering. Infertility in a 

 soil, i.e., inability to produce good crops, has 

 D een traced in many cases, not to the absence of 

 plant food, but to the presence of compounds dele- 

 terious to plant growth. These latter are, so far as 

 has been ascertained, of organic origin, consisting 

 of decomposition products of plant tissue, and 

 excretions of germinating seeds or of the roots of 

 growing plants. Some of these substances have 

 been isolated and identified and their properties 

 determined. The "curing 'of such "sick soils" 

 is to be effected by intelligent methods of agri- 

 cultures—proper drainage, crop rotations and 

 the judicious use of fertilisers, by which means 

 the toxic bodies referred to are destroyed or 

 absorbed, and suitable conditions for cultivation 

 secured. A proper rotation of crops is useful 

 inasmuch as the excreta of one kind of plant are 

 not necessarily harmful to another, and different 

 species assist in the destruction and removal of 

 objectionable excretions. Natural manures and 

 artificial fertilisers are no less valuable, so that a 

 rational use of these substances, which not 

 merely supply plant food, but also act as soil 

 correctives, is of fundamental importance in agri- 

 cultural practice. 



There are thus new elementb to be reckoned with 

 and fresh considerations to be weighed in adop- 

 ting a system of manuring, which, as indicated 

 above, should be calculated not only to make up 

 for a deficiency of soluble plant food in the soil, 

 but also to neutralise such toxic substances as are 

 likely to have an injurious effect on cultivated 

 crops. For further enlightenment on this sub- 

 ject we must look to our local staff of scientists. 



