First Name: | Bruce |
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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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