Uday:

A few notes in text below:

K. J.  Boote

At 12:36 PM 9/13/01 +0530, you wrote:
>Dear Sir,
>
>Thanks for your valuable comments. However, I have some clarification for
>your doubts
>
> > First, the DSSAT models do not respond to P or K.
>
>This may be the reason since literature also shows that Peanut crop responds
>for P & K positively. Hence the treatment with fertilizer does not predict
>higher yeild compared to the one without fertilizer.
>
> > As for N, it is possible that the non-fertilized (no N) peanut crop can
> > yield more because N-fixation is greater than when fertilized with 40 kg
>of
> > N which would inhibit nodule growth and N-fixation just long enough, so
> > that you would have poor nodulation at crtical time of pod growth.
>
>I am not sure whether all crop N requirement  can be met by fixing N through
>atmosphere. It seems some N input by way of fertilizers is necessary. The N
>appication was decided after all these calculations(considering soil N
>before sowing) and the fertlizer we applied is the regular recommonded dose
>for Peanut in our soils. Hence I may expect slightly higher values of all
>yield parameters in the teatment with N.
>
>May I get some details of N balance calculations which DSSAT does during
>simulation.
The peanut model will take up mineral N if available, based on root length
in the soil layers.  However, when N is not available, the model allows
nodules to form and assimilate to be directed to nodules to supply
N2-fixation.  We programmed it this way, to mimic what we observed for the
full-season runner peanut cultivars that we grow on our sandy southeastern
US soils.  They never show yield response to fertilizer N. Same for soybean
here. This would lead me to question the common(?) practice in India of
supplying fertilizer N as either being associated with short-season
cultivars (Spanish) or poor rhizobium presence.  It is possible that
short-season cultivars are less efficient in nodulating.  Or lastly, the N
supplied may "enhance" vegetative expansion, thus overcoming a light
capture limitation common for short season peanut.

See chapter by Godwin on N balance processes (for nonlegumes) in American
Society of Agronomy Monograph 31, Modeling Plant and Soil Systems,
ASA-CSSA-SSSA, Madison, WI.  And no, I do not have reprints.

> > Lastly, it is not good to run the model with water balance turned off, yet
> > N balance turned on.  Or was it done to specify optimum irrigation to
> > create "no water stress."
> >
>
>I compared the Pod, Bomass and  Seed yield and max leaf area under N and
>No-N treatments
>at same conditions of soil moisture. Both the treatments were irrigated at
>15% depletion of available soil moisture throughout the growth period. So
>there was no water stress under both these treatments. Hence, water balance
>was not turned off during the simulation.
>
>Thanks.
>
>Uday Khodke
>
> > Ken Boote
> >
> > At 08:18 PM 9/12/01 +0530, you wrote:
> > >Dear Members,
> > >
> > >I am using DSSAT 3.5 for peanut crop growth simulation. I have calibrated
> > >the model with one of my treatments which is without water stress and
> > >recommonded (N P K as 40:60:30) fertilizer input. The observed and
> > >simulated data for this perticular treatment are matching.
> > >
> > >I simulated another treatment keeping all the inputs same as above
>except,
> > >there was no fertilizer.
> > >
> > >I observed tnat the simualated Pod yield, total biomass and max leaf area
> > >and seed yield in case of treatment without fertilizer are higher
>compared
> > >to the treatment with fertilizer. In my opinion the treatment with
> > >fertilizer should show higher values.
> > >
> > >I will appreciate your comments on this please.
> > >
> > >Thanks.
> > >
> > >Uday