Hello Romulo (and others),

The questions you ask are precisely the kinds of questions we want to 
address in the special session and then look at how to coordinate future 
activities, so we can all move ahead more efficiently in our particular 
research area.  I don't want to raise expectations too highly, but our 
intention is to follow the ASA session with a larger international 
symposium to be held at CIMMYT in late 2004 or perhaps 2005.

One way of approaching your particular problem is first to determine more 
precisely what it is you want to understand from your research.

For example, Rolf Sommer examined data from a maize tillage experiment 
conducted at CIMMYT using CERES Maize, which basically does not deal with 
tillage effects.  He was able to show, however, that the yield differences 
between conventional and zero till, likely had to do with improved crop 
water status under zero till.  The conclusion there is that in some 
circumstances, even a relatively simple model can provide useful insights.

If you want to examine whether zero-till with residue retention will 
improve soil structure over time, and particularly with different crops or 
levels of inputs, you may be pushing the limits of currently available 
models.  Many models assume that properties related to structure are 
constant with management.  For example, although residues may be 
incorporated and decomposed, this processes not affect drained upper limit 
and lower limit.

There are many ongoing efforts, however, to strengthen the models in the 
area of tillage, and our hope is to get a better view of what is working, 
what needs to be studied further in the field, what applications people 
envisage, etc.

I am sure participants in the special session would appreciate hearing 
about tillage research in Brazil and any suggestions you or your 
colleagues in EMBRAPA might have on modeling tillage.

Best regards,
Jeff White






"Romulo P. Scorza Jr." <[log in to unmask]>
Sent by: DSSAT - Crop Models and Applications <[log in to unmask]>
02/28/2003 03:05 PM
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Dear all,

I got some data from a field experiment in which they tested the influence 
of different tillage practices on the physical, chemical and biological 
soil properties and also on the productivity of some crops. 
One idea came to my mind: to use a simulation model that uses as input 
data those physical, chemical and biological properties and theferore 
conclude after some simulations the implications of these different 
tillage practices. However, I have some problems:

1) Which simulation models are more suitable for this situation?

2) Which processes that I should consider (simulate) to have these soil 
properties as important parameters? 

3) Will these simulation models (or the process I am looking at) be 
sensitive to the physical, chemical and biological properties? 

Sorry for this quite broad question but I hope some of you can help me.

Kind regards,

Rômulo

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ROMULO PENNA SCORZA Jr., Ph.D.
Embrapa - CPAO
BR 163  KM 253,6 - Caixa Postal 661
CEP 79804-970 - Dourados - MS - BRAZIL 
Phone: + 55 (67) 425-5122
Fax: + 55 (67) 425-0811
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