NITROGEN ACCUMULATED IN CLOVER CROPS 147

Now even this latter amount corresponds to what would be
considered a fair, though not a large crop, when clover is grown
in rotation once only in four or eight years or more ; so that the
produce in the earlier years on this rich garden soil was very
unusually heavy. Indeed the average annual produce over the
whole period of fifty years — namely, 5794 lb., or more than 2|
tons of hay — would be a good yield for the crop grown only
occasionally in the ordinary course of agriculture.
But it is when we look at the figures in the last column of
the table, which show the estimated amounts of nitrogen in the
crops, that the importance and significance of these results
obtained on rich garden soil are fully recognised ; and this is
especially the case when they are compared with those
obtained on ordinary arable land.
Thus the amount of nitrogen in fair crops of wheat, barley,
or oats, would be 40-60 lb. per acre, of beans about 100 lb., of
meadow hay about 50 lb., and of clover grown in rotation, from
100 to 150 lb. ; but on this rich garden soil the produce of
clover has in one year contained more than 400 lb. of nitrogen,
and the average over the first ten years was 247 lb. The
average over the whole period of fifty years is 140 lb., or about
as much as a fair but not large crop grown occasionally under
the ordinary conditions of agriculture.
