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Comment 36 for Workshop on the Proposed Rice Cultivation Offset Protocol and Updates to Existing Offset Protocols (offset-protocol-ws) - 1st Workshop.


First Name: Bruce
Last Name: Linquist
Email Address: balinquist@ucdavis.edu
Affiliation:

Subject: Rice protocol comments
Comment:
2.2 Early drain activities 
Unclear to me why 75% heading is used. Usually 50% heading is
referred to. 
Unclear how these samples are to be taken. Are you referring to a
percentage of plants or panicles? These are different. A plant
contains a number of panicles. The primary panicle usually reaches
heading before the secondary or tertiary panicles. 
Also, not sure why a sample needs to be taken so close to the
inlet. This is a very unrepresentative portion of the field. Two
problems with this (1) The inlet water is cold in many irrigation
districts and these plants will be significantly delayed relative
to the rest of the field (2) often the rice stand is very sparse so
close to the inlet because the water comes into the field at a high
volume which can uproot young seedlings. 
Depending on who is taking these samples they can pick samples to
suit their desires. Even within a relatively uniform field check,
there can be a difference in crop development of over a week. 
The protocol assumes that all rice varieties and in all years the
field can be drained at this time period. Most crops develop on a
basis of degree days (DD) so that in a cool year it takes longer to
reach a certain growth stage than in a warmer year. Very little
work has been done on looking at growth stages following heading.
Also, it is safe to assume that varieties differ in this regard. I
would suggest making the drain date based on a particular growth
stage rather than a number of days after a certain stage. In the
south, a lot of draining occurs around R7 which is approximately 3
weeks after heading but this is approximate (varies with variety
and seasonal temps). R7 is also a defined growth stage that is
relatively easy to determine in the field.

2.3 Alternate Wet and Dry Activities
The AWD procedure dictates that the soil must remain above 35%
moisture level. What is this? Is this 35% of what? This needs to be
clarified as there are many different ways to determine soil
moisture.
What research is this 35% moisture based on? I assume it is to
minimize N2O emissions. However, low N2O emissions is more likely
to be the result of good water and N management. Fields should not
be drained or allowed to dry when there is a lot of N in the soil.

How is a grower going to tell when the top 10 cm is not saturated
but remains above 35%? 
The biggest problem with this is that fields are highly variable
with some parts likely to be still flooded while other parts are
aerobic. The protocol mentions that saturated parts of the field
will not be credited but how will this be accomplished without
either a lot of walking the field or sensors? In non-zero graded
fields the fields are sloped so you will have flooded conditions at
the bottom of the field but at the top you may achieve the desired
soil moisture but only in a small uppermost part of the field. The
rest of the field is a variation between saturated and this “ideal”
point.
How will yield losses be handled?
Not clear why N2O is not accounted for in this protocol. Just about
all research in this area show higher N2O losses associated with
AWD compared to a continuous flood. The amount of N2O losses is
highly variable. With poor water and N management (result of poor
timing) N2O emissions can be extremely high. For example letting
the field dry or drain shortly after fertilizer applications can
result in high N2O emissions and denitrification losses.
Alternatively, with good management N2O emissions (while perhaps
higher) may be almost negligible. 

3.1 General Eligibility Requirements
I am curious as to why the protocol requires that rice be grown of
the same maturity. There is no indication in the literature that
crop duration affects GHG emissions. Furthermore, by doing this one
discourages growers from using shorter duration varieties which may
save water. Really there is no published data suggesting any of the
currently used US varieties differ in terms of emissions. I am
aware of some publications that are forthcoming which show varietal
differences. However, the research groups have not identified
varietal characteristics of low emitters that the DNDC could use. 

3.2 Location
I have not seen, nor am I aware, of any published research where
measured field emissions have been calibrated and validated using
the DNDC model anywhere in the US. This whole protocol is based on
the ability of the DNDC model to accurately predict emissions from
these various mitigation practices. The model needs to be peer
reviewed before this protocol goes into effect. 

Appendix A Pg 48
Recording harvest date is mentioned twice: (a-3) and (a-7)

Appendix B: Table B DNDC input parameters. 
Where do these numbers come from? These should be referenced. Some
of the data look strange to me. For example, why the difference in
Grain:Shoot:Root fractions between the various locations. Also,
should not the sum of those fractions be equal to 1.0? They are for
California but not MRD (0.78) and LGC (0.76). I also find it
strange that the optimum temperature is so different among regions
(20 vs 25). I do not believe this is supported by the literature.
In step 2 it seems that one is adjusting the model to “fit” the
data. In this case to fit the yields. This may require more or less
thermal time to achieve the best fit. By adjusting this thermal
time one is also changing the duration of the crop. Usually longer
crop duration requires a longer flood period. However, in these
cases your flood periods are fixed (farmers provide you with
those). 

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Date and Time Comment Was Submitted: 2014-03-31 15:57:34



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