WHEAT 29 



Use of Dung. 



Three plots were selected in 1905 to illustrate the effects of dun<r 

 applied occasionally, either alone or in combination with artificial 

 manures. The quantities applied per acre are as follows : — 



Plot 19. 14 tons Dung 1905, and every fourth year. 

 Unmanured intervening years. 



Plot 20. 14 tons Dung 1905, and every fourth year. 



n cwt. Nitrate of Soda ^ ^ intervenino- 



200 lb. Superphosphate - ^'^'''^> intervening 



100 lb. Sulphate of Potash ) ^^^^ ' 



Plot 13.* 14 tons Dung 1905, and every fourth year. 



6 cwt. Fish Guano 1907, and every fourth year.f 



BROADBALK FIELD 



Wheat 



The experiments on the continuous growth of wheat were begun in 

 the Broadbalk field in 1843, but for the first eight years the manuring was 

 of a varied description, so that only three of the plots have received the 

 same treatment during the whole period of seventy years. The plots as 

 seen to-day began in 1852, since which time the few changes in manuring 

 have been matters of detail and not of principle. 



The chief difficulty experienced in growing wheat continuously is 

 that of keeping the land clean ; not only does the crop occupy the 

 ground for the greater part of the year, and so leave little opportunity 

 for cleaning operations, but the weeds whose habit of growth is favoured 

 by the crop tend to accumulate from year to year. Thus in spite of 

 repeated hand-hoeings, some weeds, like the "Black Bent" grass, 

 Alopectiriis agrestls, are kept under with the greatest difficulty. 



On Plot 3 wheat has been grown without manure every year since 

 1843, for four years previously no manure had been applied to the field, 

 so that the present crop is the seventy-fourth without manure. After a 

 drop in production during the first few years, the yield has been 

 practically constant for the last fifty years, fluctuating only with the 

 season, and showing no immediate prospect of declining. The average 

 crop over this period has amounted to about 12i bushels per acre, 

 approximately equal to the average yield, taking the whole world over. 



Effect of Nitrogenous Manures. 



Plots 6, 7, and 8 should be compared with Plot 5, since all receive the 

 same mineral manures, but different amounts of nitrogen as ammonium - 

 salts. 



Plot 5, which receives the minerals but no nitrogen, grows very little 

 more than the continuously unmanured plot ; its average over the whole 

 period is only 14-5 bushels, as against 12-6 without manure of any descrip- 



* The southern half of Plot 13 received a dressing of 2000 lb. of ground lime in 1907. 

 t The fish guano was applied in 1910 instead of 1911. 



