20 
Sm J. B. LAWBS AND PROFP^SSOR J. H. GILBERT ON THE 
wliicli some ammonium salts, or nitrate had, up to 1878, been applied, but which has 
received no manure since. The results given in the third line of the above Table (YIII.), 
relate, however, to a plot which has not received any nitrogenous manure from the 
commencement, but was not brought into experiment until five years later than the 
other plots. 
Here then, in a field where beans had been grown for many years, had frequently 
yielded only small crops, and sometimes failed, and the land had then been left fallow 
for several years, where the surface soil had become very poor in total nitrogen, where 
both surface and subsoil were very poor in ready formed nitric acid, and where there 
was a minimum amount of crop-residue near the surface for decomposition and 
nitrification, there were grown very large crops of red clover containing very large 
amounts of nitrogen. On a plot where a purely mineral manure, containing potash, 
had been applied for 27 years up to 1878, but no manure whatever since, 347 lbs. of 
nitrogen were gathered, almost wholly by the clover. On a jolot, on half of which 
the mineral manure only, and on tlie other half the same mineral manure with some 
ammonium salts or nitrate had been applied up to 1878, but nothing since, 330 lbs. of 
nitrogen were removed in the crops. Lastly, where on half the plot there had been 
no manure whatever for nearly 40 years, and on the other half ammonium salts or 
nitrate to 1878, but nothing since, 281 lbs. of nitrogen were yielded in the crops. 
It may be said, therefore, that about 300 lbs. of nitrogen had been gathered by the 
clover growing on a soil upon which beaus had yielded smaller and smaller crops, and, in 
fact, had eventually practically failed, and which was very poor both in total nitrogen near 
the suiTace, very poor in ready formed nitric acid to a considerable depth, and very poor 
in nitrogenous crop-residue for nitrification. If therefore the clover had taken up its 
nitrogen either wholly or mainly as nitric acid, the supply could not be due to recent 
C]‘op-residue. 
Not only was so much nitrogen removed in the crops, but the surface soil became 
deterniinably richer in nitrogen, as the following results will show. The plots are the 
same as those to which Table VII. refers ; and the determinations are those made in 
samples of surface soil collected in April, 1883, before the sowing of the barley and 
clover, and in November, 1885, after the removal of the crops. 
