[SHUTT] NITROGEN-ENRICHMENT OF SOILS 115 
matter how rich the soil might have been in its virgin state. 
It is necessary, therefore, to be constantly replenishing the 
store of organic nitrogen if fertility is to be maintained. This 
can be accomplished through the application of farm manures or 
the growth of a leguminous crop. The legumes as is now well known 
are very rich in nitrogen, obtained in part at least from the atmosphere, 
and these facts make this class of plants extremely valuable as manurial 
agents. To determine their relative value as soil enrichers seven of the 
more important leguminous crops (clovers, common red, mammoth red 
and crimson, alfalfa, hairy vetch, soya bean and English horse bean) 
were grown and analysed, the weight and nitrogen-content of stem and 
leaves and of the roots, per acre, being determined. The clovers and 
alfalfa were found to be the most valuable, chiefly by reason of larger 
root system in which might be stored from one-third to one-half the 
total amount of nitrogen in the crop. From 100 to 150 lbs. per acre 
may by this means be added to the soil if the crop is ploughed under, 
an amount of nitrogen equivalent to that furnished by an application 
of 10 tons of ordinary barnyard manure. 
To determine by direct examination of the soil the amount of 
nitrogen which might become part and parcel of the soil through the 
growth of clover, and which would subsequently be available for crop 
use, a plot of extremely poor soil was seeded with clover. No nitrogen 
was supplied, but phosphoric acid and potash were furnished in suitable 
forms. The increase in nitrogen due to the ploughing under of two 
crops was found to be 175 lbs. per acre, very satisfactory evidence of the 
manurial value of clover. 
Evidence was brought forward as to the increase of productiveness 
of the soils through the growth of clover, as shown by crop yields of 
wheat, barley, oats, corn and potatoes. The beneficial influence was 
markedly observable on the third crop following the turning under of 
the clover. An illustration may suffice: In series I consisting of two 
adjacent plots of similar soil, upon one of which clover was sown and 
turned under in the autumn, corn was planted. The following season 
the two plots were seeded to oats and in the third year of experiment 
they carried a crop of sugar beets. The yield in fodder corn on the plot 
that had grown clover exceeded that of its neighbor by 8 tons 480 lbs. 
per acre. Similarly the increased yield in oats was 23 bushels 18 lbs. 
and of the sugar beets in the third year after the clover had been turned 
under, 13 tons 1,400 lbs. 
