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DUL higher than SAT when adjusted for SOM #153
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Nice use of embedded code in markdown! I need to learn this trick. The regressions equations from Gupta and Larson 1979 did not include SAT, but I agree this is a problem. How about we limit DUL to (SAT-0.10). We should then similarly limit LL to no more than (DUL-0.10) since it can continue to be modified. |
@palderman |
Here are the lines of code: (why don't they show up as embedded code?) |
@chporter, I think it doesn't show up embedded because it's not from this repo (it's from your fork). I'd prefer a solution that is more conceptually coherent. It seems to me that the reason we are adjusting Before I get into my ideas for
I can get the first one (Water Resources) and I think the coefficients match. Assuming that's the right reference, I'm a bit bothered by our implementation. There is only one equation given in that article:
This does not match what we have in the code. For example, using the coefficients provided in Table 1 of that article, the equation for -0.10 bars would be:
What we have now is: dssat-csm-os/Soil/SoilUtilities/SOILDYN.for Lines 1207 to 1208 in 0ea6a91
First, I'm not sure about the validity of applying regression coefficients to the marginal change in the predictors. It seems to me that the logic is that we first assume:
Then we assume
which leaves us with:
I'm uneasy about that reasoning, but maybe it's okay.
Edit: I question the nomenclature, but dssat-csm-os/Soil/SoilUtilities/SOILDYN.for Line 1203 in 0ea6a91
I have some thoughts about how to handle |
@chporter, what do you think of adjusting I realize that -0.04 is not the same as 0, but it's probably better than assuming that Note that I also adjusted bulk density according to the equations in SOILDYN.for: The inflection point in both plots at just below ΔSOM = 3 is due to the fact that we limit the ΔBD: dssat-csm-os/Soil/SoilUtilities/SOILDYN.for Lines 1181 to 1182 in 0ea6a91
but ΔSOM continues to increase. |
@palderman Yes, I agree now that we should probably be adjusting SAT with the other soil water capacity variables. I think your method makes sense and is better than our current method of leaving SAT unmodified. The inflection point is bothersome and the limits that cause it are arbitrary. I'm open to suggestions for improving these. The reference I used is the first one you listed: "Estimating soil water retention..." by Gupta and Larson, 1979. Thanks for digging into this. |
The existing code allows DUL to increase above SAT when DUL is adjusted for SOM. Although DUL and LL are adjusted, there is no concomitant adjustment for SAT:
dssat-csm-os/Soil/SoilUtilities/SOILDYN.for
Lines 1203 to 1215 in 37d00a5
As a result, DUL_SOM can be higher than SAT under some conditions. I think we have a couple of options:
As it is, if DUL does become higher than SAT and SW happens to be equal to SAT then we can get floating point exceptions in OXLAYER (and possibly other places?):
dssat-csm-os/Soil/Inorganic_N/OXLAYER.for
Lines 201 to 203 in 37d00a5
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