32 RESULTS WITH WHEAT 



the same manures. This method has great advantages when 

 the crop in question is not one which deteriorates by constant 

 cultivation on the same land. By repeating the experiments 

 through many seasons trustworthy average results are obtained. 

 Any tendency to accumulation or exhaustion of fertility attend- 

 ing the use of different manures is also made apparent. 



The wheat experiments in Broadbalk field commenced in 

 1843, the first harvest being in the following summer. Most 

 of the plots in this field have an area of six-tenths of an acre. 



Manures applied. One plot has from the commence- 

 ment been entirely unmanured ; another has had fourteen 

 tons of farmyard manure ploughed in every autumn ; a third 

 has received every year, except the first, a dressing of am- 

 monia salts without any other manure. The remaining plots 

 received in the earlier years various experimental manures, 

 but in 1852 a constant system of manuring was commenced, 

 and has been maintained with few exceptions ever since. 

 We shall select as most suitable for our present discussion 

 the results obtained on certain plots during forty years, 

 1852-91 ; these results will be found in Table V., page 33. 



The superphosphate and alkali salts applied each year to 

 plots 5, 6, 7, 8, have consisted of 3^ cwts. of bone-ash super- 

 phosphate, 200 Ibs. of sulphate of potash, 100 Ibs. of sul- 

 phate of soda, and 100 Ibs. of sulphate of magnesia per acre. 

 These manures have been uniformly applied in the autumn, 

 before drilling the wheat. 



The ammonia salts supplied throughout the experiments 

 have been a mixture of equal parts sulphate and chloride. At 

 the commencement of the experiments, 400 Ibs. of mixed 

 ammonia salts were estimated to supply 100 Ibs. of ammonia. 

 The quality of the commercial salts has however gradually 

 improved, and during recent years the 400 Ibs. of ammonia salts 

 must have supplied no Ibs. of ammonia. We shall have to 

 take this varying quality of the ammonia salts into account in 

 calculating the return obtained from the quantity of ammonia 

 applied. The time of applying the ammonia salts to the land 

 has varied during the course of the experiments ; the influence of 

 this factor on the produce obtained will be discussed later (p. 41). 



