436 



EVENING DISCOURSE. 

 Table I. 



The figures in column 2 are calculated from values in the Annual Report of the 

 Rothamsted Experimental Station for 1929. The percentage of nitrogen in the crops 

 was not determined — the figures given in column 3 are taken from published data of 

 food analyses. The percentage of nitrogen in crops fertilised with artificial nitrogenous 

 fertilisers are usually higher than in unfertiUsed crops, so that these figures are probably 

 somewhat low. The nitrogen efficiency of the fertilisers in column 4 is the percentage 

 of the nitrogen in the fertilisers which appears in whole or part of the crop described 

 in column 2. 



In Table II the increased yields are recalculated so as to show the increased crop 

 obtained from 1 cwt. of sulphate of ammonia in common units. 



Table II. 



If we feed grass to a cow giving 2 gallons of milk a day we find that 1 lb. of nitrogen 

 causes sufficient extra grass to grow to keep the cow alive and to give 2 gallons of 

 milk per day. Since 2 gallons of milk contain 0-8 lbs. of proteins, or 0-128 lbs. of 

 nitrogen, we have 12'8 per cent, of the nitrogen of the fertiliser appearing in the milk, 

 or the efficiency with which the fertiliser is used via grass to make milk is 12-8 per cent. 



The efficiency of meat production is lower, 1 lb. of nitrogen fertiliser only producing 

 0-05 lbs. of nitrogen in beef, or an efficiency of 5 per cent, on the fertiliser. 



Summing up these nitrogen efficiencies we have : — 



Fertiliser to grain .... 

 ,, Potatoes 



,, grass or hay . 



„ milk .... 



,, beef . . . . . „ 5 „ or lower. 



It is not surprising that grass shows a higher efficiency than other crops because 

 the roots cover the ground more completely. I think that the efficiencies on the 

 whole are very high. Compare them with the energy efficiency of a high-class 

 locomotive on the railways, which is not more than 8 per cent. 



These efficiencies are the best estimates I can get of the average results obtained 

 in this country. In good years when the rainfall and temperature are right the yields 

 are much higher — in years of drought the extra yield obtained from nitrogen fertilisers 

 is less. I have records of experiments where the nitrogen efficiency fertiliser to grass 

 was as high as 80 per cent., and others in a year of drought when this efficiency was 



