Rational Principles of Manuring. 189 



phosphoric acid they take up, compared with other crops, 

 would not indicate this. Then, turning from the mineral or 

 ash-constituents to the nitrogen, an average crop of beans 

 will contain from two to three, and one of clover-hay from 

 three to four, or more, times as much nitrogen as one of 

 wheat or barley ; but land in such condition as to grow 

 a full crop of the rich-in-nitrogen beans or clover, without 

 nitrogenous manure, would not grow a full crop of wheat 

 or barley, containing so much less nitrogen, without liberal 

 nitrogenous manuring. 



It is, then, under the existing conditions of practical agri- 

 culture, certainly not necessary to supply to the land all the 

 constituents that have been removed from it, or that would 

 be contained in the crops it is wished to grow, and neither 

 more nor less of them than would be so removed. On the 

 contrary, we should supply all, or only some, and more or 

 less, according to the circumstances. 



17. Farmyard Manure alone, and with Ammonia-salts in 

 addition: Plots 2 and 1. The effects of various important 

 individual constituents of manures, and of various mixtures 

 of them, having been discussed, it now remains to interpret 

 the results obtained on the application of that complex and 

 heterogeneous mixture, farmyard manure. 



For eight years, 1856-63, plot 2 received annually farm- 

 yard manure at the rate of 14 tons per acre. Over the same 

 period, plot 1 received the same quantities of farmyard 

 manure, but with 200lb. ammonia-salts per acre per annum 

 in addition. At the end of the eight years the application 

 of farmyard manure was stopped on both plots, but the 

 ammonia-salts were still annually applied to plot 1. The 

 reason the farmyard manure was withheld was partly because 

 so large an annual application was obviously not thoroughly 

 taken up by the soil, and it was thought somewhat 

 obstructed the vegetation; and partly because calcula- 

 tion indicated how small a proportion of the constituents 

 applied was recovered in the increase of crop, and that there 



