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WINTER GREEN-MANURE CROPS. 15. 
labor is necessary. The inoculation of this crop may also be attained 
by spreading inoculated soil over the field at the time of seeding and 
’ working it in with the seed, or the seed may be inoculated with pure 
cultures of the bacteria which form nodules on the roots of this plant. 
Such cultures have been distributed by this Department for several 
years, and the results obtained from their use have been favorable in 
many cases. 
COMMERCIAL FERTILIZERS. 
In the citrus orchards of California commercial fertilizers are quite 
generally applied, while in few deciduous orchards are fertilizers used 
in any form. Where fertilizers are used they are usually applied in 
connection with a green-manure crop. 
The value of a green-manure crop is largely due to the part it plays 
in liberating plant food in the soil. In the decay of organic matter 
and the giving off of carbonic-acid gas, the action on phosphorus and 
potassium compounds is such as to make them more available as 
plant food. Vegetable acids, which are always more or less present 
with a green-manure crop, also aid in liberating plant food. Thus, 
elements present in a soil but not available as plant food may be 
made so by the use of a green manure.? 
From the facts just stated it will be readily seen that a green- 
manure crop may serve a useful purpose when used in connection 
with commercial fertilizers, especially where the various plant-food 
elements are only partially available in the soil. 
WINTER GREEN-MANURE CROPS NOW USED IN CALIFORNIA 
ORCHARDS. 
The green-manure crops now used in California, in the order of | 
their importance, are as follows: Common vetch, Canada field peas, 
bur clover, fenugreek, hairy vetch, and Indian melilot. 
Common vetch and field peas are by far the most extensively 
planted, while hairy vetch and melilot are very little used. Bur 
clover and fenugreek are used to but a limited extent, although they 
are of considerable importance. 
COMMON VETCH. 
The common or spring vetch (Vicia satwa) is the most exten- 
sively grown green-manure crop in California. It is being grown 
throughout the orchard sections wherever green-manure crops are 
being used at all (see fig. 3). It is adapted to quite varied con- 
ditions and succeeds in all sections of the State. In the coast sec- 
tions, as well as inland, it makes a good growth and does well on both 
the light and the heavy soils. | 
$e @See E. W. Hilgard, Soils, pp. 19-21, 63, 126, and 394-396. 
