WHEAT. 179 



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

 more in the order of the increased yield in the crops. Plot m the S0lL 

 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 con- 

 nection with the conditions of growth. Thus, plots 11, 12, 

 and 14, all with a deficient supply of potash, show approxi- 

 mately 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 100 of 

 increased yield in the crop. 



From the various results which have been adduced, it is Nitrogen 

 obvious that the relative excess of nitrogen in the soils of ™?dw 

 the different plots is little if at all due to the direct reten- 

 tion of the nitrogen of the manure ; and that it is almost ex- 

 clusively dependent on the difference in the amounts of the 

 crop-residues (of the stubble and roots, and perhaps of weeds), 

 of which there will be the more the greater the amount of 

 crop grown. 



It may be here observed that the detailed estimates, of 

 which the results given in Table 50 are a summary, do not 

 account for the whole of the nitrogen applied to the experi- 

 mental plots ; and it is believed that most, if not the whole, 

 of the unaccounted for amounts are due to loss by drainage Loss of 

 beyond that estimated from the pipe drainage. However, in linage! 1 

 the use of ammonium-salts or nitrate of soda, in smaller 

 quantities per acre than those used in the experiments, and 

 in the course of a rotation of various crops, with varying 

 character and range of roots, as in ordinary agriculture, there 

 will be less loss of nitrogen by drainage than that indicated 

 in these experiments. In the Eothamsted soil and subsoil, 

 with chalk below affording good natural drainage, or in soils 

 generally with good drainage, natural or artificial, it is not 

 probable that there is any material loss by evolution as free fjf^ n 

 nitrogen. Where, however, nitrogen is applied in large nitrogen. 



