124 



DISCOVERY 



felt as to supplies of nitrogen for fertilisers in the 

 future. 



The phosphatic fertilisers have an equally interesting 

 history. Their value was predicted by Theodore de 

 Saussure 120 years ago. During the first half of the 

 nineteenth century the need was exclusively supplied 

 by bones ground and added to the fields and pastures 

 of England. When the demand became greater than 

 the supplies from kitchens and butchers' shops of this 

 country, there were large imports from abroad. It 

 was said — and in view of the sources of supply it might 

 be difficult to refute the tale — that the Continental 

 battlefields were worked over to provide bones for the 

 English market, and in one of Liebig's characteristic 

 outbursts he anathematises England for her in- 

 satiable greed in hanging like a vampire round the 

 neck of Europe, sucking the life-blood from the 

 living and not sparing even the bones of the dead. 

 It was Lawes' first experiment at Rothamsted that 

 did away with the necessity for finding new sources 

 of bones. 



Geologists in the early forties had found large deposits 

 of calcium phosphate in Spain and elsewhere on the 

 Continent, and in the Eastern Counties of this country ; 

 in 1843 Lawes showed that while these had little, if 

 any, direct fertilising value, they became immediately 

 effective if treated with sulphuric acid. In the chemical 

 terminology of the day the product was called super- 

 phosphate of lime — a name which it still retains. This 

 is now made in enormous quantities, the production 

 exceeding 10,000,000 tons per annum. 



Many years later — in 1884 — it was shown that the 

 slag obtained in the basic Bessemer converter had 

 high fertiliser value, and right up to 1914, and indeed 

 to some extent even yet, this slag was used with great 

 effect on the grasslands of the country. But with the 

 suppression of the Bessemer converter by the open 

 hearth there has come a change in the nature and 

 properties of the slag, necessitating careful technical 

 experiments to find how the new material can best 

 be used in agriculture. 



It has been stated above that Lawes found the raw 

 mineral phosphate to be ineffective as fertiliser. Further 

 work has shown that this is largely a matter of fineness 

 of grinding. With the highly efficient mills now avail- 

 able mineral phosphates can be ground so finely that 

 some at any rate have high fertiliser value under 

 certain conditions. In the Aberdeen district it has 

 been shown that some of the mineral phosphates may 

 be almost as effective as superphosphate. It does not 

 appear that ground phosphates would generally prove 

 as useful as superphosphate or basic slag, but there 

 is evidence that^in some conditions they are almost as 

 good, and in many conditions they would find a useful 

 place in the fertiliser scheme. 



World Supplies of Phosphates 



At present fears of phosphate exhaustion are remote. 

 There are great deposits controlled by France in North 

 Africa where the limits of the beds are not yet known ; 

 there are also large deposits in the United States. 

 But, curiouslv enough, the deposits are very local ; 

 the far-flung British Empire contains none of import- 

 ance so far as is known, beyond a few islands, the most 

 familiar of which is Nauru. The African and LTnited 

 States deposits are being dra\N-n upon to the extent of 

 6,000,000 tons per annum, and one wonders what will 

 happen when the pressure of scarcity begins to be felt, 

 as it inevitably must be. One could picture mankind 

 struggling against phosphatic scarcity, suffering physical 

 disease and mental deterioration as supplies diminished 

 and became less and less able to solve the problem as 

 the need became more and more urgent, till the final 

 degradation and collapse of civilisation. But history 

 shows that things never turn out as badly as might be 

 feared, and we may be sure that some way will be 

 found to overcome the difficulty. 



Space does not permit more than a brief reference 

 to the potassic fertilisers : these came exclusively from 

 Germany before the war, but in part from Alsace now. 



We must, however, turn to the work the agricultural 

 investigator is called upon to do in connection with 

 these various fertilisers. The general fact that fer- 

 tilisers increase crop yields needs much modification 

 when one descends to particulars. Weather condi- 

 tions profoundly affect the response of crops to artificial 

 fertilisers. One and the same fertiliser mixture which 

 in one season gives results fully equal to, or even 

 surpassing, those of farmyard manure, may on the same 

 farm, and even in the same field, prove a failure in 

 another season. The effect of soil is equally sharply 

 marked. 



Statisticians have during recent years been evolving 

 methods for dealing with cases where several factors 

 vary simultaneously. These methods have been applied 

 by Mr. R. A. Fisher to the Rothamsted field data. 

 He has been able to trace certain statistical regu- 

 larities which foreshadow the possibility of important 

 developments. Up to the present four factors causing 

 variation have been disentangled and expressed 

 quantitatively : they are slow changes in the field — 

 such as changes in the amount of weeds, etc., deterior- 

 ation of soil, weather changes, such as rainfall, etc. 



The statistical studies, combined with the results 

 obtained by the soil and plant investigators, open up 

 the possibility of predicting crop yields when weather 

 and soil conditions are knowTi ; not indeed with 

 absolute certainty, but with a specified degree of 

 probability. Once this could be done, it would be 

 possible to draw up tables showing the expectancj' of 



