30 CALIFORNIA AGRICULTURAL ExTENsioN Service [Cro 42
also supply considerable organic matter. The leguminous plants
mentioned, however, not only supply humus but increase the nitrogen
content of the soil, both of which are of value. Cover crops are usually
planted in the fall, some about the middle of September in order to
have the plants established before cold weather. In many sections
when planted so early it is necessary to make provision for irrigation
to start the cover crop. Melilotus indica is broadcasted at the rate of
20 to 25 pounds to the acre. If bur clover (Medicago hispida) is
growing wild and contains nodules on the roots, then artificial inocula-
tion for Melilotus may not be necessary. Unless the soil is already
inoculated with the proper bacteria, artificial inoculation of the soil
may be advisable with some legumes.
Commercial Fertilizers—The fertilizer element to which the peach
is most likely to respond is nitrogen, since it, more than most fruit
trees, requires a soil rich in available nitrogen. However, in Cali-
fornia, there are many soils that seem to have enough nitrogen for
the best yield of peach trees. Moreover, under some conditions, nitro-
gen may reduce the size of peaches as a result of the inerease in set,
and reduce the color because of the shade from the increased foliage.
With adequate water, and vigorous trees, excessive amounts of nitrogen
may delay ripening several days. It is considered satisfactory to
apply the fertilizers just before the spring plowing. The tree is in
greatest need of nitrogen at this time. Nitrogen in the form of
ammonium sulfate may be applied at the rate of one-half pound per
tree for young orchards, up to as much as four or five pounds per
tree, for mature orchards. Generally peach trees show little or no
response from applications of either phosphorus or potassium.
Frost Protection.>—As the flower buds open they become more
susceptible to low temperature. The blossoms are more tender the
longer they have been open, and the young fruits are more tender than
the newly opened flowers. The young fruits apparently become increas-
ingly subject to frost until they are about one-half inch in diameter.
It is usually the seed that is killed, the other part of the fruit requir-
ing a lower temperature to kill it.
It is possible to protect the blossoms and young fruit against frost
injury by means of orchard heating. The cost of heating is con-
siderable and the use of heaters for peaches would generally be so
infrequent that their purchase would rarely be warranted. Initial
cost of equipment for heating with ‘‘lard pail’’ heaters is about $60
per acre and the annual overhead cost, to be prepared to heat, is about
"12 Schoonover, W. R. and R. W. Hodgson. Orchard heating in California. Cali-
fornia Agr. Exp. Sta. Bul. 398:1-69. 1925. t
