Juan,

The SLU1 is just stage 1 evaporation.  Stage 2 evaporation which can be
considerable, depends on the depth of water you have in your top layer,
which should always start at 5 cm, then 10 cm.  Maybe, define the second
and third layers as 5 cm each to limit evaporation.

Check your runoff (graph it).  With very high clay content, you may be
losing too much water to runoff, especially if your soil is a cracking clay
which has good infiltration when cracked (which the curve number system
does not know how to handle).

On the other hand, the default DSSAT methods for calculating water-holding
capacity typically under-estimate the true water-holding capacity of soils
with any substantial clay content.  Default is always near 13% volumetric,
but our experience with many soils, shows that water holding capacity can
be easily be 15-17% for such soils.

Lastly, the model is configured (code problem) to have (too slow) soil
water release with high clay content soils.  This is my opinion, but the
code has not been fixed yet.

Good luck,
Ken Boote
At 01:40 AM 7/6/04 -0700, you wrote:
>Hello
>I am trying to simulate no tillage soybean with the Cropgro, and I can not
>lower the soil evaporation. Even if I change the SLU1 to 0.0 the model
>still simulate a very high soil evaporation. And in very shallow soils
>(<40cm) the yield are 100-200kg when the observed yields are 2000kg, and I
>think that if I can transformed that soil evaporation into crop
>transpiration the yields will improve. When I test the Cropgro with
>shallow soils in dry year the model simulated very low yields, but I do
>not have any problem in more normal year or more depth soils. I appreciate
>any collaboration.
>Juan from Argentina