The Food of our Agricultural Crops. 77 
succession. The absence of effect upon the leguminous crops 
from the application of nitrate of soda as a top-dressing is the 
more remarkable as analyses of the subsoil, where lucerne (the 
roots of which have penetrated nine feet from the surface) has 
been growing for some years, showed that considerable quantities 
of nitric acid had been removed ; while upon a soil where white 
clover had been grown, the subsoil below the reach of the roots 
was much richer in nitric acid than it was within the range of the 
roots. Comparing these results with those on the adjoining soil 
and subsoil, where wheat and fallow had been under experiment 
for many years, there appeared to have been greater production 
of nitric acid in the soil where the white clover had grown than 
where the wheat grew ; and, at the same time, the subsoil where 
the lucerne was growing was poorer in nitric acid than the subsoil 
of the white clover or of the wheat-land. In one year as much 
as 300 lb. of nitrogen per acre has been taken off in the lucerne, 
although the land has received no manure containing nitrogen 
for thirty years ; while the wheat crop alternating with fallow 
cannot collect one-tenth of that quantity. 
It would appear from these results, that during the growth 
and decay of leguminous crops considerable amounts of nitrates 
are formed and taken up by the plants, but the actual source of 
these nitrates is not yet clearly established. One-quarter of the 
adjoining field has grown continuous barley crops, nitrate of soda 
being used every year as a top-dressing ; on the other three- 
quarters of the field barley is also grown, but red clover is occa- 
sionally sown with the barley upon one of these quarters, so that 
about once in eight years each of the three quarters has grown 
red clover instead of barley. The clover is made into hay, and 
carried off, and the barley which follows the clover receives no 
manure. The general result of this is, that the barley follow- 
ing the clover is quite as good a crop as the continuous barley 
manured with the nitrate of soda ; and although the clover has 
carried away very much larger quantities of nitrogen than the 
barley, the first nine inches of the clover-soil shows by analysis 
a considerably larger amount of nitrogen than the barley-land. 
More nitrogen is carried off in the clover than in the barley, 
and more nitrogen is found in the top soil of the clover-land 
than in that of the barley ; and this fact is quite in accordance 
with the experience of practical farmers, though they draw their 
conclusions from the increase of the succeeding crop, and not 
from analysis of the soil. We have hitherto, however, been un- 
successful in our attempts to ascertain if the increase of nitrogen 
in the top soil has been obtained by the clover from the subsoil. 
Although an attempt to grow beans continuously in a field 
