Not only is there general accordance in the character of the results in 

 different localities, when the averages of a number of years are taken, 

 but the non-effect of the residue from previous application of ammonium- 

 salts is as marked in the sandy soil at Woburn as in the very different 

 soil at Rothamsted, Reference to Table X. will illustrate this. Stack- 

 yard field. Woburn, received mineral manure, and ammonium-salts=:86 

 Ibs. nitrogen, for five successive years. The field was then divided, one 

 portion receiving the same manure as before, and the other the mixed 

 mineral manure, but no nitrogen. In the next year, 1883, the portion 

 which had received nitrogen in the previous year received mineral ma- 

 nures only, and conversely the other portion, which had received mineral 

 manure only in 1882, received both mineral manure and ammonium- 

 salts. It is seen that in each year, 1882 and 1883, the portion which 

 received the nitrogenous manure yielded large crops (43^ and 45^ 

 bushels) ; whereas, the portion on which mineral manures alone suc- 

 ceeded ammonium-salts and large crops, yielded very small crops 131^ 

 and 171^ bushels, respectively, against 14^ and 17^ bushels on the 

 plot where the same mineral manures were used year after year. It is 

 thus seen that there was no available and effective residue where the 

 ammonium-salts had previously been applied. It may be stated, how- 

 ever, that in 1884 there was notable effect from unexhausted residue of 

 nitrogenous manure ; the explanation probably being that there had been 

 very little rain, and consequently very little loss by drainage during the 

 winter of 1883-4. 



TABLE X. 



Wheat grown year after year on the same land. 

 Stackyard Field, Woburn. 



(1) Mixed Mineral Manure alone. (2) Mix. Min. Man. and Ammonium-Salts = 86 Ibs. N. 



Having illustrated the soil conditions necessary for the growth of 

 wheat, it will be well to call attention to one practical application of 

 these long-continued field experiments. For thirty-two years (1852-83) 

 an estimate has been made of the average produce of wheat per acre in 

 the United Kingdom, based upon the yield at Rothamsted on the un- 

 manured, the farm-yard manured, and three of the artificially manured 

 plots taken as one. From this the total yield of the country has been 

 calculated ; to this the imports have been added, and the quantity re- 

 quired for seed deducted, the final figure showing the total amount 

 available for consumption, and from this the consumption per head of 

 the population has been reckoned. It may be said at once that these 

 results proved to be very near the truth. But the point of interest to a 

 wheat-growing and wheat-exporting country like America is, the evi- 

 dence which the results afford as to the constantly increasing require- 

 ments of a largely importing country like Great Britain. 



