Anwar,

Overestimation with zero N fertilization should be mostly attributed to how 
well the the soil organic matter model functions.  The other possibility is 
that the crop has too much root length density (and depth) and/or allows 
too much N uptake.

What soil organic matter option did you use (the newly-added Century option 
or the former Godwin Papran option)?  I have found the DSSAT-CENTURY option 
to overestimate N mineralization for one maize experiment here in Florida, 
but that is just one small test.

Let's request feedback from DSSAT developers who may have tested the N 
mineralization of the new DSSAT-CENTURY organic matter mineralization 
option?  Arjan?  Walter?  Bill? Tony? U. Singh?  What do you think?

Thanks,
Ken Boote


At 07:07 PM 1/7/04 +0900, you wrote:
>Dear Modeller
>
>Happy New Year!
>I have been trying to simulate wheat yield by new DSSAT-4 in four
>different soils of Japan. The variety is a Japanese cultivar. Actually I
>like to see N responses; so I have 4 nitrogen levels (i.e. 0, 80, 160 &
>240 kg N/ha application). The data set of 160 N kg/ha treatment of one
>soil was used to determine the Genetic Coefficients.
>
>the simulated values for phenology, grain yield, biomass, grain N,
>aerial biomass N and straw N were mostly within 20% or near predicted
>values in fertilized plots (i.e. 80, 160 & 240 kg N/ha) of three soils.
>However, in 0 N plots (no N application), simulated values for grain
>yield and biomass is overestimated though the simulated values for
>phenology, grain N, aerial biomass N and straw N were mostly within 20%
>or near predicted values. Can anyone give some reasons please for
>overestimation of grain yield and biomass in 0 N plots.
>
>Thanks in advance.
>
>Anwar
>
>
>
>Dr M. R. Anwar
>Department of Soils & Fertilizers
>National Agricultural Research Center (NARC),
>3-1-1 Kannon-dai, Tsukuba,
>Ibaraki 305-8666, JAPAN
>Telephone: Work: + 81 ­ 298-388827, Home: + 81 ­ 298-588007
>Fax: + 81 ­ 298-388837 (work), E-mail: [log in to unmask]