Cover Crops and Moisture. 185 
II. It improves the chemical conditions of the soil: 
Catches and holds some of the leaching ni- 
trates; 
Adds humus; 
Renders plant-foods available; 
Appropriates nitrogen, if it is leguminous. 
As a rule, crops grown for cover alone should 
be sown not earlier than midsummer. The most 
thorough tillage can then be given early in the sea- 
son, and the benefits of the cover can be secured 
for the early fall and winter. It is generally advis- 
able to grow a crop which answers for both a cover 
and green manure, although it is easily possible to 
make the soil too nitrogenous for some fruits by 
the extravagant use of such fertilizers. It will also 
be observed, from the above enumeration of the bene- 
fits arising from cover crops, that crops which are 
killed by the winter may still be exceedingly use- 
ful. The reader must also be reminded, in passing, 
that much of the value of the cover crop depends 
upon its being plowed under very early in spring, 
as explained in the last chapter. 
There is much confusion in the popular mind 
concerning the relation of cover: crops to moisture. 
Some contend that any crop which shades the ground 
will keep the surface moist and conserve moisture, 
whilst others, knowing that all plants exhale water, 
consider that any crop tends to make the land dry. 
Both these opinions are partly correct. A crop 
which occupies the soil the entire season, and which 
does not allow of cultivation, will make the land 
