18 



vision. We know that, chemically, a soil may be all that is desired, and 

 yet prove unproductive; a mechanical analysis may elucidate the cause of 

 this; or, if that too result satisfactorily, the soil may be otherwise physi- 

 cally defective, for instance, in porosity; or perhaps it may lack moisture. 

 The various chemical constituents of plant food do not comprise the whole 

 chain of contingencies upon which a soil's fertility, and still less its pro- 

 ductiveness, depends, but they do form links in that chain, and, as the 

 strength of a chain is measured by that of its weakest link, so the poten- 

 tial fertility of a soil well provided chemically may be dependent upon, 

 and therefore limited by, defects along other lines. Hence chemical 

 analysis does not test the strength of the chain, but only that of certain of 

 its links. The fact that the links thus tested prove to be sound does not 

 render the entire chain sound. A soil which yields to acid extraction a 

 large reserve stock of all plant food constituents may be deficient in other 

 respects : even if physical unfitness or alkalinity do not affect its fertility, 

 defective water supply, or unfavourable situation, or many other agencies, 

 may cause it to be unproductive,* no matter how fertile it may be. On 

 the other hand, if by chemical analysis certain links in this chain are 

 found to be defective, then, no matter how excellent the condition of the 

 remaining links, the defects must be remedied ere the chain can be fit for 

 use. 



The results of the analyses detailed in the sequel show that there are 

 many soils in the Colony which are thus weak in certain respects, and if 

 the investigations here described do no more than point out the districts 

 and areas where such weakness exists, they will have served a useful pur- 

 pose. A chemically-poor soil invariably needs working up, and such in- 

 vestigations as these can show where soils answering to that description 

 are to be found. The fact that soils rich in plant foodf are not invariably 

 fertile, or, if fertile, do not produce an adequate return, is no argument 

 against the worth of analysis. In brief, chemical analysis can designate 

 bad soils even if it does not aim at pointing out good ones; and yet even 

 this it is at times capable of doing, as the following analyses more than once 

 witness. Hilgard may here again be quoted. He says : J 



" It seems to be generally true that virgin soils showing high percentages of plant 

 food, as ascertained by extraction with strong acids (such as hydrochloric, nitric, etc.), 

 invariably prove highly productive : provided only that extreme physical characters do 

 not interfere with normal plant growth, as is sometimes the case with heavy crops or 

 very coarse sandy lands. To this rule no exception has thus far been found" 



* " Fertility and crop production are different terms. Fertility is a property inherent 

 in the soil : it is what the soil is capable of doing if it is under the best possible conditions. 

 The yield of crops, on the other hand, is not dependent upon the fertility alone. ... If 

 your seed is not properly selected, if your planting season is too early or too late, if the 

 soil is not properly cultivated, if the climatic conditions are not favourable, your crop 

 yield may be affected, but the fertility of the soil that inherent power of the soil, under 

 the best conditions, to produce a crop will not necessarily be impaired." (Whitney : 

 "Soil Fertility," 1906, pp. 5, 6. 



" The productivity of a given piece of land depends upon a large number of agencies, 

 any one of which may be the limiting factor in the crop yield. We may enumerate, for 

 example, temperature and water supply, both determined by the climate, by the natural 

 physical structure of the soil, and by modifications in its texture induced by cultivation : 

 there are, further, the aeration and the actual texture of the soil, the initial supply of 

 plant food of various kinds, and, again, the rate at which this last item is rendered 

 available to the plant by bacterial action or by purely physical agencies. All these factors 

 interact upon one another, to all of them, and not merely to the nutrient constituents does 

 Liebig's law of the minimum apply, so that any one may become the limiting factor and 

 alone determine the yield. It is of no use, for example, to increase the phosphoric acid 

 content of a soil, however deficient it may be, if the maximum crop is being grown that is 

 consistent with the water supply, or if the growth of the plant is being limited by 

 insufficient root range caused by bad texture and the lack of aeration in the soil." (A. D 

 Hall : "Recent Developments in Agricultural Science." Brit. Assn. Rep., 1906, p. 275.) 



t i.., yielding large proportions to strong hydrochloric acid. 



j Op. cit., p. 343. 



