10. ORCHARD GREEN-MANURE CROPS IN CALIFORNIA. 
are not irrigated, or if water is applied it is early in the summer, and 
not in the fall when it could be utilized in starting the crop. 
Winter rains must be depended upon to germinate seed sown in the 
fall, and only in the most favorable seasons are they early enough to 
allow much growth before cold weather. When the first rains come 
late, but little growth is made by fall-sown seed until the warmer 
weather of the latter part of winter or early sprmg. Thus, only in 
the most favorable years will the growth be sufficiently early to 
allow its utilization for green manure. Where water is available for 
fall irrigation the question ceases to be one of the possibility of grow- 
ing a good green-manure crop and becomes one of the returns justify- 
ing the expense. 
CONDITIONS UNDER WHICH GREEN-MANURE CROPS SHOULD NOT 
BE USED. 
There are some sections in which green-manure crops can be grown 
satisfactorily, but their utility nevertheless seems questionable. This 
is especially true in lemon orchards having a very heavy soil, and to 
a less degree in orange orchards. By a heavy soil is not meant a 
heavy loam, but an adobe or a soil approaching that texture. On 
such soils the discontinuance of cultivation which is necessitated by 
the growing of a green-manure crop allows the soil to become quite 
hard and packed, thus permitting very imperfect aeration. This is 
a most undesirable soil condition to maintain during a period of sev- 
eral months, and its injurious effects may be seen in the unthrifty 
appearance of the trees. Where this effect is very marked it is 
undoubtedly best not to use a green manure, but to use stable manure 
instead, if such is available. 
In the Porterville and Oroville citrus districts, where the soils are 
quite generally of a heavy type, the foregoing statement does not 
apply as definitely as in the southern California districts. This is 
due to seasonal differences. The trees in the two former sections 
have a more nearly dormant period of growth during the early win- 
ter than those in the latter, in which case the effect of noncultivation 
is not so marked. Where on account of heavy soils it 1s not advisable 
to grow a green-manure crop, stable manure, if available, should be 
used in lightening the soil. 
QUALITIES DESIRABLE IN A GREEN-MANURE CROP. 
No one plant possesses all the desirable qualities of an ideal green- 
manure crop. However, in the various crops used for such pur- 
poses, practically all the desirable qualities are represented, though 
varying in degree. The conditions under which a green manure is to 
be grown determine to some extent whether a certain quality is 
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