188 



THE ROTHAMSTED EXPERIMENTS. 



admittedly higher than was suitable for experiments with 

 different manures. Accordingly, the produce without manure, 

 with mineral manure alone, and with ammonium-salts alone, 

 was higher than that obtained under the same manurial 

 conditions in either of the other localities ; whilst the pro- 

 duce of grain with the highest manuring — that is, with the 

 mineral manure and ammonium -salts together — was com- 

 paratively low ; the crop having been over-luxuriant, with an 

 excessive proportion of straw. 



Continuous 

 cropping. 



Effect of 

 manures 

 on wheat. 



Farmyard 

 manure. 



Without 

 manure. 



Summary and General Conclusions. 



It has been shown that root-crops may be grown for many 

 years in succession on ordinary arable land, provided a 

 proper tilth be maintained, and suitable manures are applied. 

 Full crops of barley also have been grown for more than 

 40 years in succession on such land. Leguminous crops, on 

 the other hand — beans and clover, for example — entirely 

 failed when it was attempted to grow them for many years 

 in succession on ordinary arable land ; though large crops of 

 red clover have been obtained for 40 years in succession on 

 rich garden-soil. Lastly, as shown by the results relating to 

 wheat, it has been successfully grown for more than 50 

 years in succession, without manure, with farmyard manure, 

 and with various artificial manures, on ordinary, and cer- 

 tainly not rich, arable land. The unmanured and the farm- 

 yard manure plots have, respectively, been treated exactly in 

 the same way in each of the 50 years. The artificially 

 manured plots, however, as a rule, did not receive the same 

 manure from year to year during the first 8 years, 1844-51 ; 

 but, with a few special exceptions, each has been treated 

 uniformly during the 43 years, 1852-94 inclusive. Accord- 

 ingly, most of the comparisons that have been drawn refer 

 to the period of 40 years, 1852-91. 



Eeferring first to the results obtained on the farmyard 

 manure plot, the average annual produce over the 40 years 

 was 34| bushels, and over the 51 years of 33| bushels — in 

 the one case nearly 7 bushels, and in the other 5£ bushels, 

 more than the average of the United Kingdom under ordinary 

 rotation ; in both not much short of three times the average 

 produce of the United States, and more than 2\ times the 

 average of the whole of the wheat-lands of the world. 



"Without any manure whatever, the average annual pro- 

 duce was 13 bushels over the 40, and 13f bushels over the 

 51 years; in both cases more than the average of the United 

 States under ordinary cultivation, including their rich prairie 

 lands, and about the average of the whole world. 



