T12 RECLAIMING LOST NITROGEN 
these forces more thoroughly under the control of the farmer than 
to-day. 
In making use of this means of gaining nitrogen the following 
facts must be considered. 
1. Selection of a Proper Legume.—The question of the proper 
legume to grow in any soil, for the purpose of fixing its soil nitrogen, 
is one that must be determined largely by experiment. Jn all cases 
it should be the legume that grows most luxuriantly upon soils not 
particularly well fertilized, and which, at the same time, produces 
the most abundant crop of tubercles upon its roots. These factors 
will depend upon climate, the chemical nature of the soil and the 
variety of soil bacteria. In selecting the legume the individual 
must take into consideration all the facts within his reach. Some 
species grow better in some climates than others, and certain soils 
seem to be, for some reason, better adapted for particular species, 
quite independent of the question of the presence of the proper soil 
bacteria. By the proper consideration of the facts of his experi- 
ence the farmer can, without much difficulty, determine what 
species of legume grows best in his soil. The most vigorously 
growing legume is the best. In clay soils red and yellow clover, 
lupin, seradtlla, horse beans, alfalfa, and vetches are successfully 
grown. Which of the varieties is to be selected must be deter- 
mined by the conditions of the soil and the needs of the farmer for 
the particular crop which he raises. The essential feature must 
be that the species selected should be one that will grow well in 
the soil in question, otherwise the advantage of the nitrogen fixa- 
tion will not be obtained. 
2. Insuring Presence of Proper Bacteria.—In order that the soil 
may increase its nitrogen store it is evidently necessary for tuber- 
cles to develop in large numbers on the roots of the legumes. For 
this purpose, of course, it is necessary that the proper variety of 
bacteria shall be present in the soil, otherwise no tubercles will be 
formed, or the tubercles formed will be few and small. To insure 
this result may sometimes require a little experimenting and ob- 
