Behnam,

You may want to verify that your changes to cultivar parameters did anything at all.  Did they increase or decrease LAI?  If so, then you would change ETAA slightly.  Did they change the crop cycle?   But then you would expect effects on ETAA only relatively late in the crop cycle.

Most cultivar parameters do not have a large effect on irrigation requirement, if they do not affect the crop's LAI or the length of cycle.  What are you trying to change?  What is your evidence that cultivar differences affect actual ET?

There is a parameter in CROPGRO species file called KEP (may have same in ECO file for other DSSAT crops).  KEP changes the extinction coefficient for total energy (not necessarily PAR).  BUT, I don't think cultivars vary much in that (the KEP).

Do you want to change water-use-efficiency?  First, I believe the variation in WUE among cultivars is really small, so don't get carried away here.  But if you want that, then increase or decrease LFMAX (to increase DM gain, but at same rate of water loss, slightly adjusted up or down depending also on LAI).  So, a higher LFMAX, would be higher WUE and higher yield.

Again, what is your evidence that cultivar parameters should affect ETAA?

Ken Boote

________________________________________
From: DSSAT - Crop Models and Applications [[log in to unmask]] On Behalf Of Behnam [[log in to unmask]]
Sent: Monday, February 21, 2011 2:04 PM
To: [log in to unmask]
Subject: Making changes in Cultivar parameters ... no change in Actual ET              (ETAA) values

Dear DSSAT Users,
I have made several changes in cultivar parameters, but ETAA values
didn't change. Do the cultivar parameters have no effect on ETAA
values? If they don't, so, How the crop parameters can affect the
irrigation requirement?

Regards
Behnam Ababaei