j 4 COLORADO EXPERIMENT STATION 
While it is no doubt true that humus does aid in improving the 
physical condition of the soil, it is probable that most of the beneficial 
effect, such as giving fibre, and tilth as well as increasing the water 
holding capacity, is due in a much larger degree to the partially de¬ 
cayed organic matter. 
By leguminous plants is meant the family which includes the 
beans, peas, clovers, alfalfa and vetches. These are the only plants 
of importance so far as now known which have the power of taking 
nitrogen from the air and converting it into combinations which other 
plants can use. Thus they actually add plant food to the soil and 
nitrogen is the most expensive element to supply in commercial form 
as well as the most difficult to keep, since it is readilly dissipated in 
gaseous form. The manner in which such plants take nitrogen from 
the air was a mystery for a long time. It was finally determined that 
a certain species of bacterium lives on the roots of vigorous legumes 
where the swollen regions or tubercles are formed. This low form 
of plant life is able to take the free nitrogen from the air and change 
it into forms which plants can use. Consequently legumes can be 
grown on land from which nitrogen has been exhausted. 
It was also found that leguminous plants do not thrive in soil 
where the accompanying bacteria are absent. This led to the making 
of pure cultures of the bacteria which are now supplied in commercial 
form. These cultures after being diluted and sufficient multiplication of 
bacteria has taken place, are sprinkled over the land, or better still, 
seeds are soaked in the culture material just before planting. 
Such cultures have not been the success that was anticipated but 
in the meantime a mass of overdrawn articles on the subject has been 
printed in magazines and papers. The result has been that many 
farmers have been lead to believe that by simply applying the cultures 
to their land wonderful benefit would result to any and all crops. The 
truth is, these cultures have no direct effect on any plants other than 
the legumes. And moreover, should one wish to secure such material 
he must designate the particular crop he intends to grow. Cultures 
from clover bacteria would not be expected to have any effect on beans 
or alfalfa. It would be idle to apply these cultures to land which is 
already producing good crops of any of these plants. 
What crops shall be grown for shade crops and how shall they 
be handled? This is a difficult question to answer as the practice is 
new and but little has been learned as yet about the subject. The 
system of cover crops as advocated in the East will not apply for var¬ 
ious reasons. We can not plant in the fall and expect to get much 
growth to plow under in the spring because of the short seasons. Then 
it might not be advisable to irrigate at the particular time the seed 
should be sown as would probably need to be done to insure the germi¬ 
nation of the seed. We have also found that fall plowing is better 
suited to our conditions than spring, particularly if a crop or manure 
is to be turned under. If a mass of vegetable matter is plowed under 
in the spring the ground is apt to remain so porous that difficulty 
