PCC MarchApril Final Draft

Using N-Rich
Reference Zones to
Inform In-Season
Nitrogen Fertilization
Practices in California
Small Grains
By MICHELLE LEINFELDER-MILES | UC Cooperative Extension
NICK CLARK | UC Cooperative Extension
TAYLOR NELSEN | Department of Plant Sciences, UC Davis
TOM GETTS | UC Cooperative Extension
KONRAD MATHESIUS | UC Cooperative Extension
SARAH LIGHT | UC Cooperative Extension
GIULIANO GALDI | UC Cooperative Extension
and MARK LUNDY | Department of Plant Sciences, UC Davis
Over the last year, a team from
UCCE has been working with
California small grains growers
on practices that can improve nitrogen
(N) use efficiency. At demonstration
sites, we have implemented practices
that UC Grain Cropping Systems Specialist
Mark Lundy has been investigating
for several years, namely N-rich
reference zones, a soil nitrate quick test,
handheld reflectance devices and aerial
imagery. We demonstrate how to use
these tools to manage N fertilizers in
small grain crops across variable soil
and climatic conditions in the Sacramento
Valley, Delta, San Joaquin Valley
and Intermountain Region.
The demonstrations are funded by the
CDFA Fertilizer Research and Education
Program and a USDA-NRCS
California Conservation Innovation
Grant. Our goal is to help growers and
consultants learn and implement these
practices to guide N fertilization in
small grains, thereby increasing crop
productivity and N use efficiency while
reducing potential for N loss to the
environment.
What are “N-Rich
Reference Zones”?
Reference zones are most useful to
growers who can apply the majority of
their seasonal N budget during or after
the tillering stage of growth. Previous
work has shown that N fertilizer
applied during the season−between the
tillering and heading stages of small
grain development−results in higher
yields, higher protein and increased fertilizer
use efficiency compared to preplant
applications. The reference zone
is a relatively small area within the field
where extra N fertilizer is added at the
beginning of the season. This extra fertilizer
ensures that the reference zone
will not be N-limited from planting
until an in-season fertilizer decision is
made. When a grower is determining
whether and how much N fertilizer to
add in-season, measurements from
both the reference zone and the broader
field are compared to understand
whether the broader field is sufficient in
plant-available N.
Fertilizer N Rate and
Field Variability
Fertilizer N rate and field variability
are two important considerations when
creating N-rich reference zones. The
amount of N to apply in the N-rich
zone will depend on several factors
such as yield goal, protein goal and
when the expected in-season fertilizer
application will take place. There
should be sufficient N applied to the
reference zone at planting to ensure
that the plants in the zone are not limited
by N at the stages of growth when
the in-season fertilizer is applied. Table
1 (see page 9) gives some examples of
how much N fertilizer to apply to the
N-rich zone for a range of potential
yields.
It is important to establish the N-rich
zones in representative parts of the
field. Areas of the field that are unique
(i.e. low areas, high areas, gravel
strips, etc.) should be avoided. It is
also important that the zones capture
field variability. If certain areas have
distinct soil types or known patterns
of yield or management differences, a
grower should establish multiple zones
to account for these sources of spatial
variability if they represent large
areas in the field. Soil maps (available
from casoilresource.lawr.ucdavis.edu/
soilweb-apps/) and historical aerial
imagery can often help in identifying
field patterns and good location(s) for
reference zones.
How and When to Apply the
N-Rich Zone Fertilizer
A grower can establish N-rich zones
during the pre-plant fertilizer application.
For example, a grower may apply
50 pounds N per acre across the field
and then make another pass or two in
the zone to apply an additional 50 to
100 pounds N per acre (depending on
what the grower calculates is necessary,
as described above.) This method might
be most easily adopted by growers. We
have observed, however, that if the
fertilizer is placed too deep in the soil
profile, the N may not be readily available
to the seedling crop early in the
season because it is below the root zone.
Therefore, N-rich zones established by
this method may not provide a reliable
early-season point of comparison.
Instead, we have found that broadcasting
urea is the most effective way to
establish N-rich zones. At our demonstration
sites, we broadcasted urea after
tillage or shortly after planting, but
always ahead of a storm or irrigation
event that could incorporate the fertilizer.
Orienting the zones perpendicular
to the rows or tractor passes also helps
8 Progressive Crop Consultant March / April 2021