All,

Dr Sehgal has made a good point re yield trends and access to
technology. Also, much of the data from long-term trials in the
rice-wheat region suggests a plateauing of wheat yields and possibly
decline in rice. Dr's Pathik, Aggarwal & Ladha (amongst others) have
also performed some detailed analyses of yield trends, and potential
yields through simulation in the rice-wheat region of south Asia. Some
of this information is in press or actually published. They may wish to
share this information.

Peter Grace

Vinay Sehgal wrote:

> Dear Roger
>
> I have some experience of modelling yields of major
> crops in India (sub-tropical & Tropical) using trend
> and statistical methods.
>
> The yields trends of two major viz. Wheat & Rice over
> last 30 years have shown a very significant rising
> trend at NAtional, State and District levels.
>
> This trend is showing plateau in crop regions which
> are technologically advance in last 7-10 years. Rather
> there are reports of stagnation of yields and in some
> cases (e.g. Wheat in Ludhiana Punjab)showing a falling
> trend.
> But in regions of India where techological saturation
> has not yet reached (esp. low latitudes and rainfed)
> the yields are showing a definitive rising trend since
> last 15-20 years. In many a cases this rise is even
> exponential.
>
> Your contention may be right that the climate chnage
> and environmnetal degradation may be reversing the
> technology trend but our observation is that the
> improvement in techology is masking the negative
> impacts of climate change and ecosystem degradation.
>
> Dr V.K. Sehgal
> Crop Inventory & Modelling Division
> Space Applications Centre (ISRO)
> Ambawadi Vistar P.O.
> Ahmedabad - 380 015
> Ph. +91-79-6774001
>
> --- Roger Rivero <[log in to unmask]> wrote:
> > Dear friends:
> >
> > In published literature about yield forecasting in
> > middle (temperate) latitudes it has become a
> > tradition (so it seems to me) to decompose yields
> > time series in a linear or nonlinear mean trend plus
> > a random perturbation that alternates in sign about
> > this mean trend.
> >
> > The mean trend is almost always an upward one and
> > have been related to the steady progress in
> > technology (cultivars, management, etc.) while the
> > random perturbation have usually been assigned to
> > climate variability. This random component have been
> > the subject of forecasts methods based in
> > statistics, longe range weather forecasting,
> > biophysical models or whatever.
> >
> > Though I don´t have enough data to make any
> > assertion about it, I would like to know if any of
> > you have been able to documentate such an upward
> > trend in (actual) yields for low (tropical)
> > latitudes.
> >
> > It seems to me that a trend in yield could be not
> > only the result of technological development but of
> > other factors as climate change. But what could be
> > worse, an upward trend may not be present in lower
> > latitudes because of a negative impact of climate
> > change and unsustainable land management leading to
> > progressive degradation of agricultural ecosystems
> > in spite of technological improvements as
> > irrigation, more productive cultivars and
> > fertilizers.
> >
> > I would like to know if some of you have been able
> > to documentate these trends in lower (tropical)
> > latitudes.
> >
> > Roger E. Rivero Vega
>
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