14 



It is seen that the increased yield of nitrogen in the crops varied ex- 

 ceedingly with the same amount supplied in manure, according to the 

 condition as to supply of mineral constituents. Plot 10, with the ammo- 

 nium-salts alone, gives the smallest increased yield of nitrogen in the 

 crop ; and plots 7 and 9, with the most complete mineral manure, each 

 more than twice as much; the other plots giving intermediate amounts. 



The order of the estimated loss of nitrogen by drainage is almost the 

 converse of that of the increased yield in the crops. Plot 10, which 

 gives the least increased yield in the crop, shows the greatest loss by 

 drainage; and plots 7 and 9, which yield the greatest increase in the 

 crop, show the least loss by drainage. 



The excess in the soils (over plot 5) is obviously much more in the 

 order of the increased yield in the crops. Plot 10, with the least in the 

 increase of crop and the most in the drainage, shows the least excess in 

 the soil; whilst plots 7 and 9, with the greatest increased yield in. the 

 crop, and the least loss by drainage, show the greatest excess in the soil. 



It is clear, therefore, that whilst the excess in the soil has no direct 

 relation to the amount supplied in the manure, it has a very obvious 

 relation to the increased yield in the crop ; in other words, to the amount 

 of growth. The last column of the table brings this out more clearly. 

 Excepting in the case of plot 10, with the ammonium-salts alone, there 

 is a general uniformity in the proportion of the excess in the soil over 

 plot 5 to the increased yield in the crop over plot 5 ; and the variations, 

 such as they are, have an obvious connection with the conditions of 

 growth. Thus plots n, 12, and 14, all with a deficient supply of potash, 

 show approximately equal proportions retained in the soil for 100 of in- 

 crease in the crop. Plots 13, 7, and 9, again, all with liberal supplies of 

 potash, show higher, but approximately equal, proportions retained in 

 the surface-soil for TOO of increased yield in the crop. 



Upon the whole, it is obvious that the relative excess of nitrogen in 

 the soils of the different plots is little, if at all, due to the direct retention 

 by the soil of the nitrogen of the manure, but it is almost exclusively de- 

 pendent on the difference in amount of the residue of the crops of the 

 stubble and roots, and perhaps of weeds. 



This leads to the consideration of the actual differences in the crop 

 with equal nitrogen supply and different mineral supply. This is illus- 

 trated by the results in Table VI., which shows the effects of mineral 

 manures alone, of ammonium-salts alone, and of ammonium-salts with 

 different mineral manures. 



