III.] RESIDUES LEFT BY NITROGENOUS MANURES gj 



manures and a residue of ammonium salts. The results 

 are set out in Table XXVII., the basis of comparison 

 being a third plot, which receives both the ammonium 

 salts and the mineral salts in the same year, and a 

 fourth plot, which never receives any ammonium salts, 

 but the minerals every year. 



Table XXVII.— Residual Effect of Manures. 



ROTHAMSTED. WHEAT (1852-I902). 



Thus the residue from the ammonium salts applied 

 in the previous year only raises the yield by 0-4 bushel 

 of grain and 0-9 cwt. of straw above the yield of the 

 plot which never receives any nitrogen, whereas the 

 application of fresh ammonium salts on Plot 7 causes 

 an increase of 18 bushels of grain and 20-8 cwt. of 

 straw. On the other hand Plot 17, with the residues of 

 mineral manures applied in the previous year, only falls 

 behind Plot 7 to which they had been applied in the 

 same year, by 2-5 bushels of grain, and 3-5 cwt. of straw. 



A very similar experiment is included among the 

 Woburn plots, the only difference being that there the 

 minerals are put on every year, and that the trials are 

 also repeated with nitrate of soda. 



Table XXVIII. shows the average results for the 

 five years, 1882-86, from which it will be seen that the 

 ammonium salts left behind considerable residues which 



