15 



2001bs. of ammonium salts per acre, and the dressings were in- 

 creased up to 8001bs. per acre. It was then found that the effect (»f 

 the last 2001bs. of fertiliser, i.e., of the increase from 600 to SOOlbs. 

 was very small and unprofitable, while the first 2001bs. had proved 

 distinctly useful. This is in accordance with the Law of Diminish- 

 ing- Returns. It was assumed, therefore, that the law held for 

 Hght as well as for heavy dressings of manure and a deduction was 

 made for which the evidence was rather slender, that a small 

 dressing of manure gave the largest rate of profit, while further 

 dressings gave a relatively smaller return. 



Recent work, however, has disturbed this view. 2001bs. per 

 acre of ammonium salts is too large a unit for modern practice, 

 hence more interest attaches to the effect of the smaller than to the 

 larger dressings. Examination of the Broadbalk results shows 

 that the largest return is given, not by the first dressing, but by the 

 second. 



The conditions of an experimental field are not quite those of 

 practice, and accordingly a new experiment has been started to see 

 if under ordinary conditions of farming the highest rate of profit is 

 given by good rather than by small dressings of fertilisers. The 

 results of the first year (1920) suggest that this may be so. 



INCRKASH IN \VHK.\T CROP, 1920, FROM SPRING DRESSINGS OF 

 SULPHATE OF AMMONIA AND SUPERPHOSPHATE (p. 79). 



While the single dressing (lOOlbs. sulphate of ammonia per 

 acre) gave no appreciable increase in grain, and only a few cwts. of 

 additional straw, the double dressing gave increases of no less than 

 7 bushels of grain and 12 cwts. of straw. Late application of the 

 double dressing, however, was risky, giving an unhealthy straw 

 liable to lodge and prone to disease. 



If funds allow, the experiment will be developed on a much 

 fuller scale : it certainly is of great importance in fertiliser practice. 



INVESTIGATIONS ON ARTIFICIAL FERTILISERS. 



The artificial fertiliser position has been profoundly modified 

 by the War, and extensive factories now manufacture nitrogenous 

 fertilisers from the air. Of these nitrate of lime, nitrate and 

 muriate of ammonia, and nitrolim have been or are under investi- 

 gation at Rothamsted. 



A further importafit source of organic nitrogenous manure is 

 sewage. The total amount of nitrogen contained in the sewage 

 of the United Kingdom is estimated at 230,000 tons per annum, 

 which is equivalent to 1,150,000 tons of sulphate of ammonia — 



