IN YOUR ORCHARD
TIME TO CONSIDER
As the hustle of harvest finally recedes, late September and October provide a time to finish up a few orchard
practices and begin the process of re-developing any orchard blocks. This period also provides an opportunity to
evaluate what went well and identify areas of improvement for 2019 while the trees have leaves. An overview and
update of some of the practices are included below.
Postharvest Nitrogen
Postharvest nitrogen budgets should be evaluated.
Work at UC Davis has indicated that 15–20 percent
of the nitrogen demand occurs from harvest through
the postharvest period. This suggests that somewhere
between 20–30 pounds of nitrogen is utilized during this
period, which could be sourced from residual nitrate in
the soil or postharvest applications. A further breakdown
of the uptake curve shows that less than eight percent of
the annual need occurs after September, suggesting the
importance of timeliness in application [Figure 1].
Applications of nitrogen in the postharvest tend to be
relatively inefficient due to several factors, including
tree defoliation, leaching by early rains or long
irrigations, shorter days and lower water use. This
suggests that more nitrogen may be needed to achieve
a 20–30 pound uptake, but studies in Kern County
failed to see a response from applications greater
than 50 pounds per acre of nitrogen applied after
Nonpareil harvest (mid-August). Rates should not exceed
this amount and applications made in September and
October should be significantly reduced.
Mid-July leaf nitrogen and residual soil nitrate should
be taken into consideration when determining the
amount. Nitrogen applications to trees with adequate or
excessive mid-July leaf nitrogen levels (greater than 2.5
percent) are most likely not needed. This is supported by
research conducted by Franz Niederholzer (UCCE Yuba/
Sutter/Colusa) who has shown that
mid-September or later postharvest
nitrogen applications to trees with
mid-July leaf nitrogen at or over
2.5 percent did not improve crop
yields the following year. Trees were
followed for four years within this
study and nitrogen applied in these
situations was lost to leaching.
Postharvest Orchard Review
With the hustle of harvest slowing
down, late fall is a good time to
walk the orchard and look for any
issues that can be addressed in
the following months. Take time
to reflect on the challenges of the
season and be on the lookout for
the following:
Figure 1: Rates of nitrogen uptake vary during the year. During the postharvest period,
less than 15% of the total year’s nitrogen uptake occurs, with less than 8% occurring
after August. Reduce postharvest nitrogen rates if applications are made late in the fall.
Figure courtesy of Dr. Saiful Muhammad and Dr. Patrick Brown, UC Davis.
3 6
A L M O N D F A C T S
