PCC MarchApril Final Draft

NDRE and leaf chlorophyll can serve
as proxies for relative plant N status
within a field. Many factors can affect
absolute greenness or chlorophyll values,
including variety, crop injury and
environmental factors. Because of this,
it is important to remember that the
absolute values given by these devices
are only meaningful when compared to
a reference zone like the N-rich zone.
What do the Readings Mean?
Plant reflectance and transmittance
measurements are best interpreted
by expressing values measured in the
broader field relative to the N-rich reference
zones, according to the following
equation:
Relative value= (Production area value)/(N-rich
zone value)
The relative value is sometimes referred
to as a Sufficiency Index (SI) and
will usually result in a decimal value
between 0 and 1. When the SI is below
a certain threshold, it indicates that
the production area is experiencing
detectable N deficiency relative to the
N-rich zone. Table 2 shows SI ranges
for proximal and remotely-sensed data
and the associated plant N status.
When it comes to deciding on N fertilization
in California small grains, a
N fertilizer response is almost certain
when plant N status is “Highly Deficient”,
very likely when the status is
“Deficient” and uncertain when the
status is “Sufficient”. The SNQT supplements
the plant measurements with
information about the current nitrate
concentration in the root zone.
If a grower decides that a N fertilizer
application is warranted based on the
combination of plant and soil measurements,
the next step is to figure
how much N is necessary. This can be
determined using a crop growth and
N uptake model in conjunction with
yield and protein goals. As part of our
larger demonstration project, we will
be releasing an online decision support
tool in 2021 that integrates these
components and provides customized
predictions of crop response to in-season
N fertilizer.
SI Value Range
> 0.95 High
0.95 – 0.80
< 0.80
SI Category
Medium
Low
Plant N Status
Sufficient
Deficient
Highly Deficient
Table 2. Sufficiency Index (SI) values and associated plant N sufficiency status, calculated
as the production area value divided by the N-rich zone value.
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Summary
California farmers are under pressure
to increase N use efficiency and
reduce the potential for N loss to the
environment. N-rich reference zones
are a tool that can assist in these goals
while considering and managing the
risk of reduced yields. By implementing
N-rich reference zones, using a suite
of tools to monitor them during the
season and comparing results to the
broader field, a grower gets real-time
knowledge to inform N fertilizer management
in small grains. The information
gained from implementing N-rich
reference zones can help growers make
fertilizer applications when increased
yield and/or protein benefits are likely
and avoid them when they are not.
These improvements in N fertilizer
decision-making can yield better economic
and environmental outcomes in
California small grain systems.
Comments about this article? We want
to hear from you. Feel free to email us at
article@jcsmarketinginc.com
Ceres Imaging delivers
irrigation management
solutions to improve
profitability across
your operation.
Using advanced analytics
and high-resolution
aerial imagery, we can
help you:
> Detect common
irrigation issues
> Measure your
progress and ROI
> Optimize your farm-level
irrigation strategy
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March / April 2021 www.progressivecrop.com 11