1917] AGRICULTURE IN WAR-TIME. 221 
The top dressing of impoverished meadows early in the season has also 
been found a profitable practice. 
These then constitute some of the more important features respecting 
manure in our propaganda. 
CLOVER, ALFALFA AND THE LEGUMES GENERALLY. 
Though the fact that the growth of clover increased the yields of 
succeeding crops has been known since the days of the Ancients, the 
explanation of the fact awaited the discovery of Hellriegel and Wilfarth 
in 1886. These scientists showed that the leguminosae have the power 
to appropriate the free nitrogen of the air that is in the interstices of the 
soil, through the activity of certain bacteria that reside in nodules or 
tubercles on their roots. Their presence is an example of useful symbio- 
-sis. These bacteria pass on the elaborated nitrogen to their host for 
the development of root and stem and leaf. The immense value of a 
leguminous crop in the rotation must be at once obvious. The legumes 
alone of all our crops, leave the soil richer rather than poorer for their 
growth. Even when the crops are cut and used as fodder—and very 
rich fodder they make by reason of their high nitrogen content—the soil 
will be richer for their growth, because of the nitrogen in their root 
system. Experiments have shown that by the growth and turning under 
of clover, alfalfa and other legumes from 50 to 150 lbs. of nitrogen can be 
added to the soil per acre. And this enrichment is not in nitrogen only; 
it is in humus-forming material and in the mineral plant food therein 
held and which is set free for crop use as the organic matter further 
decomposes. Alfalfa with its heavy and deep root system stands first 
among the legumes in this nitrogen appropriation; red clover comes next. 
The manurial value of these leguminous crops is easily observable for 
three or four years, that is, throughout the whole rotation and, at a 
conservative estimate may be said to be equal to that of an application 
of five to ten tons of farm manure per acre. This fact has been estab- 
lished by repeated experiments. All grain crops in the rotation should 
be sown with clover or a mixture of grass seed with clover or alfalfa, 
for this method not only furnishes an abundant yield in the following 
season of highly nutritious fodder but manures and improves the land 
in a way and at a cost not possible by any other means. 
It sometimes happens that the soil does not possess the nitrogen- 
fixing bacteria. In such cases, made known by the absence of nodules 
on the roots of the crop, inoculation must be resorted to. This is more 
especially necessary with alfalfa. Cultures for this inoculation may be 
obtained from the botanical laboratories of the Experimental Farm, or 
