Very well done, bugbuster!!!
 
At 04:30 PM 5/7/99 -0400, you wrote:
>Dear DSSAT colleagues,
>
>This is about a possible bug with DSSAT models.  The default initial soil
>NO3 and NH4 in DSSAT is 0.1 ppm per layer (IPSLIN).  The user may override
>this value in the experiment file (FILEX).  If the user enters a value of <
>0.1 ppm for the top few layers, then something unusual happens:  The top
>layers have 0.01 ppm NO3 or NH4, deeper layers have 0.1 ppm (the default).
>
>This is only a minor problem.  A bigger problem is that NO3 and NH4 needs
>to be at least 0.5 ppm for the N uptake and transformation routines
>(NUPTAK, NTRANS) to work.  In those routines the minimum allowed soil
>concentration is 0.25-0.50 ppm.  If the user initialized the model with
>less than 0.5 ppm, then these equations give negative values and bad things
>happen:
>
>Subroutine NUPTAK:
>RNH4U(L) = RFAC*SMDFR*FNH4*(NH4(L)-0.5)*DLAYR(L)
>
>Subroutine NTRANS:
>B2      = (NH4(L)-0.5)/FAC(L)
>
>I came across this problem when I simulated a sequence of several years of
>unfertilized corn.  My temporary fix was to add these lines to the input
>program, at the end of IPSLIN:
>
>do i = 1, nlayr                                                      !AG
>   iNO3(i) = max (0.5, iNO3(i))                                      !AG
>   iNH4(i) = max (0.5, iNH4(i))                                      !AG
>enddo                                                                !AG
>
>Aris Gerakis
>
>
>
>
>
>
>
>
>Dept. of Crop and Soil Sciences                 Voice: (517) 353 8537
>Plant  and  Soil Sciences Bldg.                 F a x: (517) 353 8538
>Michigan    State    University
>East Lansing,   MI 48824 - 1325
>E-mail: [log in to unmask]
>http://nowlin.css.msu.edu/aris/
 
 
Jon I. Lizaso
Dep. Agricultural & Biosystems Engineering
124 Davidson Hall
Iowa State University    515 294 7350 (Voice)
Ames IA 50011            515 294 2552 (Fax)