Hi DSSAT list members
It might be worth mentioning that sugarcane yield decline has been
recognized as a real phenomenon in Australia and to a lesser extent
South Africa (that I am aware of) and that considerable resources have
been allocated to determine the causes and identify remedies.
Abraham Singels
SASEX
South Africa

>>> [log in to unmask] 09 May 2002 04:45:19 >>>
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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