B. P. I.—592. 
ORCHARD GREEN-MANURE CROPS IN CALIFORNIA. 
INTRODUCTION. 
The use of green-manure crops for the maintenance of soil fertility 
is one of the oldest of agricultural practices. In California such 
crops have been used in a limited way for a long time, yet it is only 
within recent years that their practical value has become fully recog- 
nized. The growing of these crops has attained its greatest develop- 
ment in the citrus orchards of the southern part of the State, where 
they have been longest used. 
As far back as the early nineties some of the more progressive 
orchardists were beginning to realize the necessity of some such prac- 
tice as green manuring and to this end utilized the natural growth 
of bur clover and other weeds, such as alfilaria,? brome-grasses, etc. 
The Canada field pea was the first of the legumes to be used exten- 
sively as a green-manure crop, and by 1900 it was being quite gen- 
erally grown in the citrus orchards of the southern part of the State. 
Common vetch and bur clover were also being utilized at this time. 
In many parts of California, green-manure crops have not been used 
to any extent, but not entirely without reason. That their use can 
be made much more general than at present is quite certain, and as 
their value is more fully appreciated and their adaptation to the 
various sections demonstrated their use will be proportionately 
increased. 
For a number of years the Bureau of Plant Industry has been work- 
ing to secure better crops for green manuring than the ones now used 
and to aid in the demonstration of the adaptability of the ones now 
being grown. The Agricultural Experiment Station of the Uni- 
versity of California has also done extensive work in demonstrating 
the value of various green-manure crops in that State. 
In California the work of the Bureau of Plant Industry has been 
carried on in cooperation with orchardists and farmers throughout 
the various sections and at the United States Plant Introduction 
Garden at Chico, where extensive tests have been made. This work 
has clearly indicated the superiority of certain crops over others and 
their adaptation for varying purposes and conditions. 
a Known also as alfilerilla and pin-grass. 
190 7 
