-----Original Message-----
From: DSSAT - Crop Models and Applications
[mailto:[log in to unmask]] On Behalf Of Richard Ogoshi
Sent: Thursday, 8 July 2004 2:14 PM
To: [log in to unmask]
Subject: Re: Soil evaporations and poor yield predictions

Hello Juan,
   You can increase the soil albedo (SALB in SOIL.SOL file) which will
lessen the soil temperature and soil evaporation. Please see  Ritchie,
J.T.
1998. Soil water balance and plant water stress. In G.Y. Tsuji, G.
Hoogenboom, and P.K. Thorton (eds.) Understanding Options for
Agricultural Production. Kluwer Academic Publishers, Dordrecht, The
Netherlands.
   Increasing soil albedo will be somewhat like placing straw (high
albedo) on soil.
   Hope this helps.
Sincerely,
Richard

At 04:55 PM 07/07/2004, Juan Pablo Monzon wrote:
>Hello
>
>I am having problems with the simulation of soil evaporation. I want to

>simulate a no tillage soil and I can not find a way to reduce the soil
>evaporation.  The FAO 56 paper recommends reducing the total evaporable

>water by 5% for each 10% of soil surface cover with straw, but I can
>not change this parameter in the model, the only one I can change is
>the SLU1 ( ready evaporable water). Do you have any suggestions??
>
>I also made a simulation with CROPGRO in very shallow soils and in a
>year with low precipitation and I observed that during the water stress

>the top weight of soybean modeled by the CROPGRO dropped from 3000kg.ha

>to 2100 kg.ha and them after the stress it start to grow again, and I
>do not know why this is happening. I also noticed that the harvest
>index dropped to even 5% in some situations. We have observed for our
>conditions very stable harvest index, even with low yields. The Cropgro

>simulated yield of 100-200kg.ha when the actual yields were of
>2000kg.ha. It seems that the model has problems when the water
>conditions are very poor. This was surprising because in more normal
>situations the model does a good estimation of crop yield and yield
variations (r2=,72 and RMSE= 292kg).
>
>Thank you
>
>Juan
>PhD student Argentina